Chemiluminescence reactions enhanced by silver nanoparticles and silver alloy nanoparticles: Applications in analytical chemistry

Accepted Manuscript Title: Chemiluminescence reactions enhanced by silver nanoparticles and silver alloy nanoparticles: applications in analytical chemistry Author: Mortaza Iranifam PII: DOI: Reference:

S0165-9936(16)30090-5 http://dx.doi.org/doi: 10.1016/j.trac.2016.05.018 TRAC 14761

To appear in:

Trends in Analytical Chemistry

Please cite this article as: Mortaza Iranifam, Chemiluminescence reactions enhanced by silver nanoparticles and silver alloy nanoparticles: applications in analytical chemistry, Trends in Analytical Chemistry (2016), http://dx.doi.org/doi: 10.1016/j.trac.2016.05.018. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Chemiluminescence reactions enhanced by silver nanoparticles and silver alloy nanoparticles: applications in analytical chemistry Mortaza Iranifam * * Tel.: +98 9144075996; Fax: +98 41 37276060. E-mail address: [email protected] and [email protected]. Department of Chemistry, Faculty of Science, University of Maragheh, P.O. Box: 55181-83111, Maragheh, Iran

Highlights     

AgNPs and Ag alloy NPs–enhanced chemiluminescence (CL) systems were discussed. AgNPs and Ag alloy NPs improved the analytical performance of the CL methods. AgNPs and Ag alloy NPs as catalysts, reductants and energy acceptors in CL systems. Silver nano–sized islands can intensify CL reactions through the plasmonic effect. AgNPs and luminol–functionalized AgNPs were used as labels in CL immunoassays.

Abstract Silver nanoparticles (AgNPs) and silver alloy nanoparticles (Ag alloy NPs) are capable of amplifying the intensity of chemiluminescence (CL) reactions by different ways such as participating in phenomenon of surface plasmon resonance and cooperating as catalysts, reductants and even energy acceptors. Because of these properties, AgNPs and Ag alloy NPs have played important roles in improvement of analytical performance of CL–based techniques; consequently, leading to further extension of analytical applications of these techniques. In this paper, the literature on AgNPs and Ag alloy NPs–enhanced CL systems and their analytical applications were

Page 1 of 65

reviewed. In addition, the analytical figures of merits of the AgNPs– and Ag alloy NPs–enhanced CL methods were tabulated and some of them were compared with those of other methods, especially CL methods which were used uncatalyzed CL reaction or catalyzed by nanomaterials rather than AgNPs and Ag alloy NPs.

Keywords Chemiluminescence; Silver nanoparticles; Silver alloy nanoparticles; Catalysts; Reductants; Surface plasmon resonance

Contents: 1. Introduction 2. AgNPs surface plasmons-amplified CL reactions 3. AgNPs and Ag alloy NPs as catalysts of CL reactions 3.1. AgNPsand Ag alloy NPscatalyzed luminol CL reactions 3.1.1. LuminolH2O2 CL reaction 3.1.2. LuminolK3Fe(CN)6 CL reaction 3.1.3. LuminolAgNO3 CL reaction 3.1.4. LuminolKIO4 CL reaction 3.1.5. LuminolKMnO4 CL reaction 3.2. AgNPsand Ag alloy NPscatalyzed KMnO4 CL reactions 3.3. AgNPsand Ag alloy NPscatalyzed peroxyoxalate chemiluminescence (PO-CL) reactions 3.4. AgNPscatalyzed K3Fe(CN)6 CL reactions 3.5. AgNPs– and Ag alloy NPs–catalyzed Ce(IV) CL reactions

4. AgNPs as energy acceptor in CL reactions 2 Page 2 of 65

5. AgNPs as reductant in CL reactions 6. Conclusions and future prospects 7. Acknowledgments

8. References

Abbreviation

AgNPs, Silver nanoparticles; AR, Amplex red; BSA, Bovine serum albumin; 2CEES, 2-Chloroethyl ethyl sulfide; CHL, Chloramphenicol; CL, Chemiluminescence; Cu NCs, Copper nanoclusters; Cu(OH)2/CuO NWs, Copper hydroxide/copper oxide nanowires; CRET, Chemiluminescence resonance energy transfer; DIP, Dipyridamole; F, Fluorophore; HRP, Horseradish peroxidase; HRP-avidin, Horseradish peroxidase-streptavidin; GFAP, Glial fibrillary acidic protein; GFLX, Gatifloxacin; GO, Graphene oxide; GOD, Glucose oxidase; GSH, Glutathione; IL, IAA, Indoleacetic acid; Ion liquid; LOD, Limit of detection; Lum-AgNPs, Luminol– functionalized silver nanoparticles; 2-ME, 2-Methoxyestradiol; MEC, Metalenhanced chemiluminescence; MF, Moxifloxacin; 6-MP, 6-Mercaptopurine; MTMEC, Microwave triggered metal enhanced chemiluminescence; NAC, N-Acetyl-Lcysteine; NFLX, Norfloxacin; ODI, 1,1`-Oxalyldiimidazole; Rh6G, Rhodamine 6G;ROS, Reactive oxygen species; μ-PADs, Microfluidic paper-based analytical devices; PO-CL, Peroxyoxalate chemiluminescence; SPCC, Surface plasmon-coupled chemiluminescence; SPR, Surface plasmon resonance; SIFs, Silver nano-sized islands; TCPO, Bis-(2,4,6,- trichlorophenyl)oxalate;

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1. Introduction Silver nanoparticles (AgNPs) are nano-sized particles of silver that can be synthesized in different shapes (Fig.1) such as hexagonal nanoplates [1], nanowires [2], pentagonal nanorods [3], decahedral NPs [4], bipyramids [5], nanocubes [6], nanoflowers [7] and nanospheres [8]. Place of Figure 1 AgNPs are demonstrating unique optical properties associated with the surface plasmon resonance (SPR) besides to distinctive catalytic, electrocatalytic and antibacterial activities that are shape- and size-dependent [9-11]. Generally, the antibacterial activity of bulk silver provides by silver ions released from the surface of this noble metal [12]. Compared with bulk silver, AgNPs are cost-effective with a controllable release rate of silver ions [13]. Indeed, AgNPs can penetrate into the bacterial cell membrane and thereby, disrupting its biological activity; consequently, leading to death of the bacterial [10]. As another property, NPs of noble metals including Au, Cu and Ag show a strong UV-vis extinction band that cannot be seen in the spectrum of the bulk metal [9, 14]. Of all metals, the molar extinction coefficient of AgNPs is larger than that of AuNPs and CuNPs [9]. It should be 4 Page 4 of 65

stated that extinction coefficient is sum of the absorption and the scattering coefficients [15]. This phenomenon is result of collective oscillation of the conduction electrons of AgNPs due to their interaction with a light beam at specific wavelengths [9, 14]. Indeed, the collective oscillation of the conduction electrons, referred to as SPR, is induced by alternating electric field of light beam whose frequency is similar to that of the electrons oscillation [9, 14, 15]. The wavelength and intensity of the extinction spectrum peak(s), so-called SPR peak(s), of AgNPs are dependent on the shape and size of AgNPs, the surrounding medium of AgNPs, distance between AgNPs, adsorbed species on the surface and their dielectric properties

[16-18].

Moreover,

when

the

wavelength

of

emission

of

chemiluminescence (CL) reaction and the SPR peak(s) are overlapped, the energy of the excited chemiluminescent species is transferred to surface plasmons in AgNPs [15]. As a consequence, the light emission with similar spectral characteristics to the chemiluminescent species is enhanced. It is termed a plasmon-based luminescent enhancement [15]. This phenomenon was first reported in silver island films deposited onto a glass microscope slide [19]. Catalytic and electrocatalytic activities are other promising properties of AgNPs that stem from their high surface-tovolume ratio and high surface energy, increasing activity of their surface atoms [20]. In general, CL is the emission of light during chemical reactions [21, 22]. To light emission, the CL reaction must release enough energy to form product(s) in electronically excited state. For instance, for emission with wavelengths in the range of 400–750 nm, the exothermic chemical reaction should release energy about 40– 70 kcal.mol-1 [23, 24]. In general, the CL methods can be classified into two general types: (a) direct methods, where oxidation of analyte leads to generate emitting species, and (b) indirect methods, where analyte presents enhancing or inhibitory 5 Page 5 of 65

effects on the CL reactions [25]. In the CL systems, the luminol, peroxy-oxalate derivatives, acridinium ester, and tris(2,2`-bipyridyl)Ru(II) (Ru(bpy)32+) are often used luminescence reagents. Among the ultra-weak CL systems, the peroxide, including H2O2, ONOO-, HCO4-and HSO5-, induced ultra-weak CL reactions are widely used in the analytical chemistry [26]. In comparison with absorption spectrophotometry and photoluminescence spectroscopy, no external light source and even monochromator are required in CL detection instruments, thus it is described as a dark-field technique [27]. Lack of external light source in CL detection systems endows CL-based analytical techniques with some merits including avoiding scattering phenomenon and, consequently, reducing background signal, removing the possible fluctuation problem of the external light source, eliminating interferences resulted from a non-selective excitation species and implementing these techniques without using monochromator to resolve the excitation wavelengths and scatter. All advantages thereof lead to improving limit of detection (LOD) and simplifying of instrumentation [27, 28]. Other advantages of CL-based analytical techniques are wide linear dynamic range, ease of operation and high sensitivity. In the light of these merits, CL-based techniques are welldeserved recognition among scientists and have found a plethora applications in various scientific arenas as diverse as food [29], clinical [30], pharmaceutical [31, 32], forensic [33, 34] and environmental analysis [35, 36]. However, relatively low intensity of light elicited form some CL reactions appears as a problem in further development of sensitive CL-based analytical methods [37]. To circumvent this problem, various nanomaterials such as CuO [38, 39], Fe3O4 [40], carbon [41], Se [42], CdS [43, 44], CdTe [45], Au [46], Pt [47] and Ag [48] NPs were used as enhancers in CL reactions. Among these NPs, AgNPs, AuNPs and Au/Ag alloy NPs 6 Page 6 of 65

are those of most widely used NPs for CL reactions amplifying. Interestingly, AgNPs presented a higher catalytic activity than Au and Pt NPs towards wellknown luminol–H2O2 CL reaction [49]. This superiority was attributed to the fact that redox potential of Ag is lower than that of Au and Pt. Therefore, H2O2 can oxidize AgNPs easier than AuNPs and PtNPs and consequently produce larger amount of hydroxyl radicals [48]. Besides luminol–H2O2 CL reaction, the AgNPs presented catalytic activity towards other CL reactions such as luminol–KMnO4 [50], luminol–K3Fe(CN)6 [51], Br––KMnO4 [52], Ce(IV)–Na2SO3 [53] and bis (2,4,6-tricholorophenyl) oxalate (TCPO)–H2O2 [54], among others. Ag alloy NPs are also capable of catalyzing different CL reactions such as luminol–H2O2 [55, 56], TCPO–Amplex red (AR)–H2O2 [57] CL reactions. Moreover, in the lucigenin [58] and luminol [59, 60] CL reactions, AgNPs acted as reductants. The capability of AgNPs and Ag alloy NPs in enhancing CL reactions and subsequently improving sensitivity of CL-based analytical methods has attracted keen attention of researchers. Therefore, this review presents a comprehensive overview of the findings of published studies in this topic. 2. AgNPs surface plasmons-amplified CL reactions In 2006, Geddes et al. [19, 61] demonstrated that the intensity of light eliciting from CL reactions can be amplified through the transferring of the energy of excited chemiluminescent species to metal surface plasmons that are the free electrons in metals which collectively oscillate at frequencies similar to the light [15]. The surface plasmons emit light with spectral properties similar to that emit from the chemiluminescent species, besides to the uncoupled free space emission. This phenomenon,

named

metal-enhanced

chemiluminescence

(MEC),

was

first

7 Page 7 of 65

demonstrated by using silver nano-sized islands (SIFs) or particles deposited onto a glass microscope slide [19]. Place of Figure 2 A typical experimental geometry designed to MEC studies is shown in Fig. 2A. In this experiment, a small aliquot of CL reagents including either H2O2-9,10diphenylanthracene for blue emission or 9,10-bis(phenylethynyl)-anthracene for green emission were positioned between two SIFs-deposited glass microscope slides. The CL spectra for blue and green CL reactions from the silvered and unsilvered parts of the glass microscope slide are presented in Fig. 2B and 2C. As can be seen in Fig. 2B and C, in contrast to unsilvered part of the glass, the CL emission was visible on the silvered part of the glass and CL intensity was about 4 and 10 times higher than the unsilvered part of the glass for blue and green CL reactions, respectively. Further studies revealed that AgNPs had no or negligible catalytic activity towards the CL reactions and MEC was only the reason of this enhancement [15, 19]. Latter, Geddes’s research group [62] found that the exposure of CL reagents placed on SIFs to low-power microwaves led to an increase in the rate and intensity of CL reaction. The phenomenon, which was named microwave triggered metal enhanced chemiluminescence (MT-MEC), was ascribed to the preferential microwave heating of SIFs and, consequently, heating of those CL reagents which were in the vicinity of the SIFs [62]. The MT-MEC strategy was able to localize CL reaction in the vicinity of the silvered surfaces, reducing unwanted emission from the distal solution. Furthermore, it was shown that MT-MEC approach has “on demand” nature, where the CL reaction can be forced to completion when desired, by exploiting microwave heating [63]. In addition, the same research team found that low-power microwaves could accelerate the avidin binding to biotinylated bovine serum albumin (BSA). For 8 Page 8 of 65

instance, the degree of binding for 30-s microwave heating was similar to that for 30min incubation at room temperature [64]. By benefiting the accelerating effect of lowpower microwaves on the biotin-avidin binding reaction as well as accelerating and increasing effects on the MEC, Geddes’s research team [63] developed a MT-MEC method for detection of biotinylated bovine serum albumin (BSA) at femtomoles in less than 2 min. In this strategy, biotinylated BSA was incubated on a glass microscope slide. The half of slide was coated with SIFs. As a control sample, half of the glass microscope slide was left blank. As a result of incubation, a monolayer of biotinylated BSA covered surface of both SIFs and glass substrates. By adding horseradish peroxidase-streptavidin (HRP-avidin), biotinylated BSA-HRP-avidin complexes which are bound to the surfaces SIFs or glass were formed. The total photon emitted form CL reaction of HRP-acridan-H2O2 for a defined time interval was related to concentration of BSA [63]. In 2007, Geddes’s research team [65] observed that the energy from chemically induced electronic excited states species can be transferred to surface plasmons on a thin silver film with thickness of 47 nm. The observed

phenomenon,

which

was

called

surface

plasmon-coupled

chemiluminescence (SPCC), revealed that surface plasmons on silver thin film can be excited by energy of chemically excited chemiluminescent species, resulting that directional and p-polarized emission with similar spectral characteristics of chemiluminescent species which emitted light from the back of silver thin film [65]. The SPCC phenomenon indicated that isotropic chemiluminescent emission can be converted to highly directional and p-polarized emission. This phenomenon made it possible to much sufficient collection of photons elicited from CL reactions and, consequently, potentially improves sensitivity of CL-based analytical methods [15]. Besides thin film of silver, the effect of thin (1 nm thick) films of Au, Cu and Ni, 9 Page 9 of 65

deposited on glass slide, for the enhancing of CL reaction of HRPluminolH2O2 reaction in a bioassay was investigated [66]. The principle of bioassay was based on the interactions between avidin-conjugated HRP and a monolayer of biotinylated poly(ethylene-glycol)-amine (BEA). In comparison with glass slide without plasmonic metal thin films, it was found that the intensity of CL emission was enhanced on silver thin films (~2.0-fold), gold (~2.7- fold), nickel (~2.2-fold) and copper (~2.5-fold) thin films. These enhancing effects of the metallic thin films on the CL reaction was lower than that of SIFs (~3.7-fold) because surface of SIFs was rough and enzymes could be more easily adsorbed on roughened surfaces [66]. Finally, the applicability of SIFs in commercially available bioassays methods for glial fibrillary acidic protein (GFAP) was demonstrated. To this aim a standard CL immunoassay for GFAP was implemented on SIFs. The SIFs- assisted standard CL immunoassay method was able to detect GFAP at concentration as low as 10 ng mL-1 [66]. 3. AgNPs and Ag alloy NPs as catalysts of CL reactions AgNPs can catalyze (i.e. speed up) CL the reactions. In general, catalysts are substances that are not consumed in the reaction, but they can increase the rate of reaction by reducing the activation energy. In the AgNPscatalyzed CL reactions, the energy of CL reaction is released in the form of photons within a shorter timewindow, providing higher CL intensity. 3.1. AgNPs and Ag alloy NPscatalyzed luminol CL reactions Since

Albrecht

first

described

CL

property

of

luminol

(5-amino-2,3-

dihydrophthalazine- 1,4-dione) in 1928, the analytical application of luminol CL reactions have been widely addressed and research into them have blossomed [31]. In general, the CL reaction of luminol is conducted by oxidation of luminol with a strong 10 Page 10 of 65

oxidizing reagent such as H2O2, K3Fe(CN)6, KMnO4, and KIO4 in the presence of a catalyst in aqueous solution. The redox reaction gives an 3-aminophthalate ion in an excited state, emitting blue light (λmax= 425 nm) when relaxing to the ground state [31]. The quantum yield of the luminol CL reaction is about 0.01 in aqueous alkaline solution [67]. In the following of this review paper, the luminol CL reactions catalyzed by AgNPs and Ag alloy NPs are discussed. In addition, the analytical parameters of the analytical methods based on AgNPs and Ag alloy NPscatalyzed luminol CL reactions were summarized in table 1.

3.1.1. LuminolH2O2 CL reaction The CL reaction of luminol-H2O2 is the well-known CL reaction, which has found many applications. In 2007, Chen et al. [68] found that the luminol–H2O2 CL system can be catalyzed by AgNPs. The study of the effect of size of AgNPs on their catalytic activity revealed that the smaller size of AgNPs, the higher intensity of luminol–H2O2 CL reaction. Indeed, this observation stems from the fact that the smaller AgNPs featured higher surface area ratio and higher electron density in catalytic centre and therefore presented higher catalytic activity. AgNPs could transfer electrons to H2O2, generating and stabilizing OH• radicals. These radicals were able to react with luminol anion and OH2−, producing luminol and superoxide radical anions whose reaction with each other led to light emission [68]. In 2008, Guo et al. [49] compared the catalytic activity of AgNPs with AuNPs and PtNPs towards luminol–H2O2 CL reaction. They found that AgNPs are superior to AuNPs and PtNPs in increasing the intensity of luminol–H2O2 CL reaction. Later, the potential analytical application of AgNPs–luminol–H2O2 CL reaction was investigated by studying the effect of various 11 Page 11 of 65

species, whose measurements in real samples were of importance, on the CL system. In this context, it was found that nitrofurans [69] and citalopram [70] were able to increase the intensity of AgNPs–luminol–H2O2 CL reaction. However, N-Acetyl-Lcysteine (NAC) [71] could quench this CL reaction. Based on these findings, sensitive methods were developed for determination of nitrofurans [69], citalopram [70] and NAC [71]. Qi et al.[72] made a comparison between the efficiency of the catalytic activity of dispersed AgNPs and that of aggregated AgNPs towards luminol–H2O2 CL reaction. They found that aggregation phenomenon could size-dependently affect the efficiency of the catalytic activity of AgNPs and, consequently, the intensity of AgNPs-luminol-H2O2 CL system (Fig. 3) [72]. Place of Figure 3 As can be seen from Fig. 3, the aggregation of the 7 nm AgNPs increased catalytic activity of AgNPs. The aggregation of the 15 nm AgNPs led to decrease catalytic activity of these NPs. But, the aggregation did not show significant effect on the catalytic activity of AgNPs with size of 55 nm. For the case of 7 nm AgNPs, the enhancing effect of aggregated AgNPs on the CL system was attributed to the increase of electron density in conduction bands of AgNPs which in turn increased the electron transfer ability of AgNPs and thus increased their catalytic activity. In contrary to 7 nm AgNPs, in the case of 15 nm AgNPs, the aggregation led to decrease of specific surface area and electron density of conduction bands of AgNPs and, consequently, decrease of catalytic activity of 15 nm AgNPs in the aggregated form compared to dispersed form. For 55 nm AgNPs, a very weak CL emission was detected either before or after aggregation of AgNPs (Fig. 3), due to possessing a large band gap energy, resulting in a large energy of activation that was required for electron transfer [72]. Benefiting from the fact that anilines were able to aggregate 12 Page 12 of 65

AgNPs and alter the intensity of light emanated from 7 nm and 15 nm AgNPs– luminol–H2O2 CL systems, these CL systems were employed for development of an analytical method for measurement of anilines at nanomolar levels [72]. Coupling AgNPs–luminol–H2O2 CL reaction with the microfluidic paper-based analytical devices (μ-PADs) was another innovative idea which was investigated for further expanding of the analytical application of this CL reaction. In general, the μPADs are made of paper with hydrophilic/hydrophobic micro-channel networks on it which is coupled with analytical detection tools [73]. Those are capable of fluid handling and analytical determinations. In comparison with other microfluidic analytical devices made of glass, polymer and silicon, the μPADs are cheap and simple. Moreover, those do not need clean room facilities and external pump [73]. Moreover, due the fact that the paper is thin, lightweight, biocompatible, porous and flammable, the μPADs can be easily stored, transported, used for biological samples with ability of separation of suspended solids and disposed of by incineration [74, 75]. μPADs, which use only a few microliter volumes of samples, could be fabricated by using two-dimensional (2D) or three-dimensional (3D) techniques to transport fluids horizontally (in the 2D μPADs) or both horizontally and vertically (in the 3D μPADs) [73]. Innovatively, Ge et al. [76] combined AgNPs–luminol–H2O2 CL reaction with 3D µPADs and, thereby, developed 3D μPADs CL immunodevice for simultaneous detection of four cancer markers in whole blood samples in a single analytical run. Furthermore, the total time of immunoassay performed by this 3D μPADs CL immunodevice

(16

min)

was

shorter

than

that

of

3D

μPADs

electrochemiluminescence (ECL) immunodevice (about 1 h) developed by Ge et al. [77] and was approximately comparable with that of 2D μPADs ECL immunodevice (about 7-10 min) developed by Wang et al. [78] for multiplexed determination of four 13 Page 13 of 65

cancer biomarkers. Most recently, Liu et al. [79] developed a sensitive method for determination of ofloxacin (OFLX) by integrating of luminol–H2O2–AgNPs CL reaction coupled with a wax-printed paper-based analytical device (PAD). In addition to possessing general merits of PADs, the linear range and limit of detection (LOD) of the luminol–H2O2–AgNPs CL system [79] were, respectively, wider and lower than those of luminol–H2O2–AuNPs CL system [80]. In other interesting research work, He et al. [81] decorated the surface of graphene oxide (GO) nanosheets with both luminol molecules and AgNPs by reduction of Ag+ ions, which are electrostatically attached on the surface of GO, with luminol molecules and, consequently, produced GO-AgNPs nano-composites. These nano-composites featured good CL emission during reaction with H2O2. Moreover, GO-AgNPs nano-composites–H2O2 CL system was used for determination of glutathione (GSH) based on the enhancing effect of GSH on the CL system. The proposed method possessed high specificity towards GSH and was able to discriminate GSH from its structural analogues such as cysteine, tyrosine, homocysteine and ascorbic acid. This high specificity was similar to those specificity results obtained by Ce(IV)–quinine CL for GSH detection [82]. However, it should be mentioned that the LOD of Ce(IV)–quinine CL system (5 nmol L-1) for GSH [82] was lower than that of the GO-AgNPs nano-composites–H2O2 CL system (25 µmol L-1). Compared to other CL methods developed for GSH analysis, the LOD of the GO-AgNPs nano-composites–H2O2 CL system was higher than those of luminol–H2O2 (3 nmol L-1) [83] and AuNPs – luminol–H2O2 (11 nmol L-1) [84] CL systems, but the specificity of the AgNPs nano-composites–H2O2 CL system towards GSH seemed to be better than those of luminol–H2O2 [83] and AuNPs – luminol– H2O2 [84] CL systems.

14 Page 14 of 65

It has been found that Au/Ag alloy NPs were capable of enhancing the intensity of luminol–H2O2 CL reaction strongly [55, 56]. It was ascribed to ability of Au/Ag alloy NPs in accelerating of H2O2 decomposition to generate ROS [55]. In Au/Ag alloy NPs, the catalytic properties of both AuNPs and AgNPs appeared. Indeed, Au/Ag alloy NPs like AuNPs can efficiently catalyze enzymatic reactions without degradation of enzyme [85] and similar to AgNPs, Au/Ag alloy NPs show the stronger catalytic activity than AuNPs towards CL reactions [86]. Good biocompatibility is another feature of Au/Ag alloy NPs. In the light of above properties, Au/Ag alloy NPs and dendritic Au–Ag bimetallic NPs have been exploited for developing of sensitive CL-based glucose analysis approaches [86-88]. In this line, Chaichi et al.[86, 87] synthesized Au/Ag chitosan-induced Au/Ag alloy NPs with average diameter of ~12 nm and employed them for catalyzing of Cu2+–luminol–H2O2 [86] and coumarin derivatives–luminol–H2O2 [87] CL systems. As noted earlier, besides catalyzing the luminol CL reaction, Au/Ag alloy NPs were capable of catalyzing the enzymatic reaction of glucose oxidase (GOD) with glucose and consequently, generation of H2O2. The catalytic properties of these NPs towards both enzymatic and CL reactions were benefited for developing of two glucose analysis systems in real serum and urine samples [86, 87]. In the coumarin derivatives– luminol–H2O2

CL system [87], the chitosan played the role of reducing and

stabilizing agent for the synthesis of Au/Ag alloy NPs and a platform for all of effective species including luminol radical, superoxide anion radical, coumarin derivatives and Au/Ag alloy NPs on the CL reaction and electron-transfer occurring on it [87]. It is also worthy to mention that the coumarin derivatives acted as acceptors of the chemiluminescence resonance energy transfer (CRET) phenomenon with the CL of luminol as donor. It was found that the intensity of CL emission was directly 15 Page 15 of 65

dependent on the extent of interaction between coumarin derivatives and chitosan. Indeed, chitosan could increase the CL emission by the increasing rigidity of system [87]. In the Cu2+–luminol–H2O2 CL system, the glucose biosensor was designed by covalent immobilization of GOD in glutaraldehyde-functionalized glass cell. Then, chitosan-induced Au/Ag alloy NPs dispersed in ion liquid (IL) were prepared and affixed on it. The chitosan molecules used as both the reductant and stabilizer in the NPs synthesis and as a coupling agent Au/Ag alloy NPs and GOD [86]. The IL was used for improving stability of biosensor as 90% of initial response of biosensor was attainable after 2 months storage at pH 7.0. In addition, IL along with Cu2+ were able to enhance the rate of enzymatic and CL reactions, and decrease the optimum pH of the CL reaction to 7.5 [86]. Most recently, Yu et al. [88] synthesized dendritic Au–Ag bimetallic NPs via reduction of chloroauric acid with luminol in the presence of AgNPs seeds. The binding of luminol molecules onto surface of dendritic Au–Ag bimetallic NPs endowed theses NPs with CL property. Moreover, the as-prepared Au– Ag bimetallic NPs were exploited for CL determination of glucose (Fig. 4). To this determination, the as-prepared Au–Ag bimetallic NPs reacted with H2O2 produced by reaction of GOD with glucose, yielding a CL emission in the presence of HRP. The CL intensity was linearly proportional to glucose concentration in the range of 1 µmol L-1 – 1 mmol L-1 [88]. Place of Figure 4 In the term of analytical performance, Au/Ag alloy NPs– and Au–Ag bimetallic NPs – sensitized CL systems [86-88] were superior to Au NPs - sensitized CL system [85]. Li et al. [55] demonstrated that some organic compounds with –SH, –NH2, or –OH groups were able to quench the Au/Ag alloy NPs–luminol–H2O2–CL system because of their interaction with surface of Au/Ag alloy NPs and also active oxygen 16 Page 16 of 65

intermediates. Interestingly, the inhibitory effect of these compounds on the CL reaction was directly proportional to their concentrations. To explore the potential analytical applications of luminol–H2O2–Au/Ag alloy NPs CL system, calibration graphs for twelve selected compounds that have –SH, –NH2, or –OH groups such as amino acids, pyrogallic acid and hydroquinone were plotted and their corresponding LODs were calculated. The results presented high potential of Au/Ag alloy NPs– luminol–H2O2 CL system for exploitation as a versatile analytical tool. However, the study of interferences and applicability of the CL method for determination of these compounds in real samples remained unevaluated in this report. Later, in 2013, the same principle was used by Chaichi et al. [56] for development of a CL method for determination of anticancer drug flutamide on the basis of inhibiting the intensity of the Au/Ag alloy NPs–luminol–H2O2–Au/Ag alloy NPs CL system. LOD of the proposed CL system (1.2  10-8 mol L-1) is almost equal to that of square wave cathodic adsorptive stripping voltammetry method (1.55  10-8 mol L-1) [89] for determination of flutamide, reported in 2015. Moreover, the comparison of the Au/Ag alloy NPs –catalyzed CL method with other previously reported methods developed for flutamide analysis indicates that LOD of the CL method was about one order of magnitude lower than LODs of spectrophotometry methods (4.3  10-7 mol L-1 [90] and 4.7  10-7 mol L-1[91]) and that differential pulse voltammetry method (1.8  10-7 mol L-1) [92]. Recently, CL reagent–functionalized noble metal NPs have attracted attention from researchers. It is due to the fact that in the CL reagent–functionalized noble metal NPs, thousands molecules of CL reagent attached on the surface of a single functionalized nanoparticle, providing remarkable light enhancement [93]. In 2011, He et al. [93] developed a one-pot approach for synthesizing luminol–functionalized 17 Page 17 of 65

silver NPs (Lum-AgNPs). In the proposed method Lum-AgNPs were synthesised through the reduction of silver nitrate by luminol, on which luminol molecules were coated on the surface of Lum-AgNPs by Ag−N covalent interaction [93, 94]. The reaction of Lum-AgNPs with H2O2 yielded CL emission whose intensity and rate was higher

and

slower,

respectively,

than

that

of

both

luminol−H2O2

and

AgNPs−luminol−H2O2 CL systems (Fig. 5) [95]. In addition, the eliciting light from Lum–AgNPs–H2O2 was more intense than that from luminol–functionalized AuNPs– H2O2 at similar reaction conditions [93]. Place of Figure 5 For the Lum–AgNPs–H2O2 CL system, it was found that various pesticides [95], amino acids [94] and proteins [96] were capable of changing light emitting parameters including maximum light intensity (Imax), the time to emerge CL emissions (Ta), and the time to attain the CL maximum peak value (Tp ) (Fig. 5) with different degrees, providing distinct response patterns as “fingerprints” to each analyte [94-96]. However, this behaviour was not observed in the luminol–H2O2 and AgNPs–luminol– H2O2 CL systems. More importantly, Imax, Tp and Ta could be acquired by only a single experiment [94-96]. Based on these findings and by using classical principal component analysis CL sensing methods for the discrimination of pesticides [95], amino acids [94] and proteins [96] were developed. In another work by same research group, Lum-AgNPs were exploited for the labelling of chloramphenicol (CHL) and by which a competitive CL immunoassay for selective measurement of CHL in honey and milk samples was proposed [97]. The LOD of the proposed competitive CL immunoassay (7.6 ng mL-1) was comparable with previously reported competitive CL immunoassay for CHL by employing horseradish peroxidase (HRP) as a label (3.23

18 Page 18 of 65

ng mL-1) [98]. However, Lum-AgNPs labelling method was more simple and faster than HRP labelling method which was accomplished by multi-step reactions [97, 98]. 3.1.2. LuminolK3Fe(CN)6 CL reaction Potassium ferricyanide (K3Fe(CN)6) is amongst other oxidising reagent whose reaction with luminol in alkaline medium leads to light emission. In the CL reaction, Fe(CN)63- oxidised luminol molecules to produced luminol radicals (L•-) and Fe(CN)64-. Then, in the presence of dissolved oxygen molecules and Fe(CN)64-, the L•were further oxidised to hydroxy hydroperoxide anions (LOO-), whose decomposition gave the excited-state 3-amino-phthalate (AP2-), yielding the CL emission [99]. It was found that AgNPs were capable of enhancing the luminol– K3Fe(CN)6 CL reaction, due to the oxidation of luminol radical on the surfaces of AgNPs became easier [99, 100]. As can be found from the comparison of the kinetic curve of AgNPs–luminol– K3Fe(CN)6 CL system (Fig. 6) [100] with that of AgNPs–luminol–H2O2 (Fig. 3) [72], the enhancing effect of AgNPs on the luminol– K3Fe(CN)6 CL system is lower than those on luminol–H2O2. Place of Figure 6 By exploiting inhibitory effects of 2-methoxyestradiol (2-ME) [100] and gemifloxacin mesylate [51] and enhancing effect of cefditoren pivoxil [101] on the AgNPs– luminol–K3Fe(CN) CL system, sensitive CL methods were developed for determination of these compounds in the pharmaceuticals and biological fluids. In the case of 2-ME, LOD of CL method based on AgNPs–luminol– K3Fe(CN)6 system (5.0  10-10 mol L-1) [100] was lower than that of achieved by CL method based on luminol–KMnO4–CdTe quantum dots system (1.0  10-9 mol L-1) [102]. Besides good selectivity and sensitivity, the CL methods developed for determinations of

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gemifloxacin [51] and cefditoren pivoxil [101] featured wide linear ranges as much as five and six orders of magnitudes, respectively. 3.1.3. Luminol-AgNO3 CL reaction Ag+ with E0 (Ag+/Ag)= +0.799 V is stronger oxidising reagent than K3Fe(CN)6 with E0 (K3Fe(CN)6 / K4Fe(CN)6) = +0.355V. Thus, it can be expected that, similar to K3Fe(CN)6, Ag+ can be used as an oxidant in CL luminol reaction, however the reaction between AgNO3 and luminol provides no strong light emission. It is due to reason that the direct reduction of Ag+ to Ag0 is too slow in the absence of nuclei. However, it was reported that in the presence of AgNPs, Ag+ ions were capable of oxidising luminol molecules and, consequently, were reduced to Ag0 [103, 104]. As shown in Fig. 7, the mechanism of the AgNPs–luminol–AgNO3 CL system involved a one-electron oxidation of luminol by Ag+ to luminol radicals in the presence of AgNPs. Then luminol radicals reacted with the dissolved oxygen to generate the excited state of 3-aminophthalate, yielding light emission (λmax=425 nm) [103]. Place of Figure 7 Liu et al. [103] investigated the effect of the size of AgNPs on their catalytic activity towards luminol–AgNO3 CL system. In this line, they examined the effect of AgNPs in different diameters of 5, 16, 22, and 40 nm on the CL system and found that the smaller size of AgNPs, the higher intensity of AgNPs–luminol–AgNO3 CL reaction. This size-dependent catalytic behaviour of AgNPs towards luminol–AgNO3 system [103] was in agreement with those behaviour observed from AgNPs towards luminol–H2O2 system [68]. Moreover, the catalytic activity of AgNPs (~16 nm) on luminol–AgNO3 CL reaction was compared with that of AuNPs (~16 nm) [103]. It was indicated that AgNPs catalysed luminol–AgNO3 CL reaction much better than AuNPs. It was attributed to the reason that the reduction of Ag+ on the surface of 20 Page 20 of 65

AgNPs was easier than that of AuNPs [103]. Since, the intensity of AgNPs–luminol– AgNO3 CL reaction was proportional to the concentration of AgNPs, these NPs was used for labelling goat anti-human IgG and by which a CL immunoassay for human IgG was proposed [103]. The analytical applicability of AgNPs–luminol–AgNO3 CL reaction was further demonstrated by Li et al. [104]. In this line, the effect of 25 organic compounds and 18 amino acids on the AgNPs–luminol–AgNO3 CL reaction were studied. The results revealed that the most of those compounds were able to alter (inhibiting or enhancing) the CL, except four of them including L-Valine, LMethionine, p-Nitroaniline and p-(Aminomethyl)benzoic acid that showed no effect on the CL system. On the basis of inhibitory and enhancing of these compounds, a CL method was proposed for determination of six selected compounds including gallic acid,

tannic

acid,

pyrogallic

acid,

hydroquinone,

pyrocatechol

and

p-t-

butylpyrocatechol [104]. Most recently, in 2015, Maddah et al. [105] employed AgNPs–luminol–AgNO3 CL reaction for developing a sensitive CL method for measurement of 2-chloroethyl ethyl sulfide (2-CEES). It was based on the inhibition of the CL reaction by sulphur-containing molecules of 2-CEES, which was due to their high affinity to AgNPs. The CL method with LOD = 6  10-6 ng mL-1 (0.048  10-12 mol L-1) was more sensitive than electrochemical method with LOD= 1.69 × 10−6 mol L-1 [106] and spectrophotometry method with LOD= 6.7 µg mL1

[107] proposed for determination of 2-CEES. It is interesting to mention that J.-M.

Lin research`s group [108-110] developed sensitive CL methods for determination of silver (I) ions. 3.1.4. Luminol–KIO4 CL reaction In general, luminol–KIO4 CL reaction involves the oxidation of luminol by O2•− generated by the reaction of KIO4 with dissolved oxygen in alkaline solution [111]. It 21 Page 21 of 65

was found that AgNPs could enhance the intensity of luminol–KIO4 CL reaction by a factor of five [112]. Moreover, Li et al. [113] reported that this enhancing effect can be much more increased in the presence of Co2+. In this context, stabilizing oxygen radicals [112] and the catalyzing the reactions of KIO4–O2 [113] and luminol-oxygen radicals [112] were suggested to be possible reasons of the enhancing effect of AgNPs on the luminol–KIO4 CL reaction [112, 113]. Li et al. [113] investigated the effect of different sizes of AgNPs in diameters of 5, 16, 22, and 40 nm on the CL system in the presence of Co2+ and reported that the most intense CL signal observed for 22 nm AgNPs. These results were different with those behaviour observed from AgNPs on the luminol–H2O2 [68] and luminol–AgNO3 [103] CL reactions, where the smaller size of AgNPs, the higher intensity of CL system. The reason for these difference in results was remained unclear in the literature [113]. Also, the effects of 25 organic compounds and 17 amino acids on the AgNPs–luminol–KIO4–Co2+ CL system were studied [113]. The results indicated that most of those compounds amongst L-Valine and p-Nitroaniline had a strong inhibitory effect and others presented an enhancing effect [113]. As noted earlier, L-Valine and p-Nitroaniline were among of those compounds that had no effect on the AgNPs–luminol–AgNO3 CL system [104]. The potential of the AgNPs–luminol–KIO4–Co2+ CL system for analytical applications was demonstrated by exploiting the CL system for measurement of seven compounds out of those, whose effect on the CL system were studied (Table 1) [113]. Fenoterol and orciprenaline were two other compounds whose ability for enhancing of luminolKIO4 and AgNPs–luminol–KIO4 CL systems was found by Li et al. [112]. On the basis of this finding, CL methods for determination of these two compounds in the tablets were established. It was shown that LOD of the CL method based on AgNPsluminol-KIO4 system was about 10 times lower than that of the CL method based on 22 Page 22 of 65

luminol-KIO4 system, attesting the significant role of AgNPs in the improving the analytical performance of the CL methods [112]. 3.1.5. Luminol–KMnO4 CL reaction In 2011, it was found that AgNPs were capable of enhancing the CL intensity of luminol-KMnO4, by a factor of 5 [50, 114]. This extent of amplification induced by AgNPs was comparable with that of observed from CuO nanosheets (increase by a factor of about 7) [115], CdTe quantum dots (increase by a factor of about 5) [102] and copper nanoclusters (Cu NCs) (increase by a factor of 2-3) [116] on the luminolKMnO4 CL reaction. The mechanism of AgNPs–catalyzed luminol–KMnO4 CL reaction was express as follow: the decomposition of MnO4- to MnO42- in alkaline medium generated reactive oxygen species (ROS) such as •OH and O2−• whose reaction with luminol led to CL emission [50, 117]. The enhancing effect of AgNPs on the luminol–KMnO4 CL reaction could be ascribed to catalytic activity of AgNPs towards both ROS formation [50] and luminol–ROS [112] reactions. Based on enhancing effect of lisinopril [50] and inhibitory effect of bisphenol A [114] on the AgNPs–luminol–KMnO4 CL system, CL methods for the determination these compounds were developed [50, 114]. The enhancing effect of lisinopril was attributed to the adsorption of lisinopril on the surface of AgNPs causing the decrease of the oxidation potential of AgNPs [50] and the inhibitory effect of bisphenol A was ascribed to the consumption of KMnO4 by bisphenol A [114]. In the case of bisphenol A, LOD of CL method based on AgNPs–luminol–KMnO4 (1.0  10-9 g L-1 or 4.3  10-12 mol L-1) [114] was lower than that of CL method based on Cu NCs–luminol– KMnO4 (1.2  10-10 mol L-1)[116]. 3.2. AgNPs– and Ag alloy NPs–catalyzed KMnO4 CL reactions

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KMnO4 is one of the most common oxidants used in CL reactions in which the oxidation of a substrate by KMnO4 led to red light emission [118, 119]. Adcock et al. [120] have proposed that the red light emission in many CL reactions with KMnO4 in acidic solution is because of the 4T1 → 6A1 transition of manganese (II). The application of KMnO4 as a CL reagent was well-reviewed [121]. In 2013, Amjadi et al. [52] found that AgNPs could enhance a weak CL emission arising from oxidation of Br− with KMnO4 in sulfuric acid medium. It was ascribed to catalysis of redox reaction of Br−–KMnO4 by AgNPs [52]. Noteworthy, it was known that halide ions (X–) have inhibition effect on the AgNPs–catalyzed CL reaction by formation of AgX shell on the surface of AgNPs [49]. However, such effect was not seen from Br− towards the AgNPs in the AgNPs–KMnO4–Br− CL system because the concentration of Br− was so high that AgBr2− complex ions were produced rather than AgBr and thus the deposition of AgBr layer on the surface of AgNPs and, subsequently, decreasing of catalytic activity of AgNPs were prevented [52]. In addition, the effect of shape and size on the catalytic of AgNPs toward CL system was studied by using triangular and spherical AgNPs with diameters of 4 and 18 nm. The results exhibited that the larger spherical AgNPs (18 nm), the higher enhancing effect. This behaviour was in contrary to behaviour that observed from AgNPs in the luminol–H2O2 CL system [68]. It was due to reason that the smaller AgNPs featured higher surface area and surface energy, and thus they were oxidized easier than larger AgNPs and, consequently, presented lower catalytic efficiency on the CL system [52]. The analytical feasibility of AgNPs–KMnO4–Br− CL system was demonstrated by measurement of captopril based on the fact that this compound as a thiol-containing compound could attenuate the AgNPs–KMnO4–Br− CL system by binding onto the surface of AgNPs through the sulfur atoms. The analytical parameters of AgNPs– 24 Page 24 of 65

KMnO4–Br− CL system (Table 2) including dynamic linear range and LOD was better than that of CL method established based on triangular AuNPs–catalyzed luminol reaction [122]. However, both AgNPs– and AuNPs–catalyzed systems featured a very good selectivity [52, 122]. Perhaps it is interesting to mention that the reaction of relatively high concentrations of captopril with oxidants including H2O2 [123] and Ce(IV) [124] led to CL emission. Later, in 2015, Wabaidur et al. [125, 126] reported that AgNPs were capable of enhancing the intensity of the CL reaction of calceinKMnO4 in alkaline medium. The light emitters were excited calcein molecules which were generated through the energy transferring of calcein–KMnO4 reaction to unreacted calcein molecules [125]. It was also reported that AgNPs–calcein–KMnO4 CL system could be further enhanced by addition of fluoroquinolone antibiotics including gatifloxacin (GFLX) [125] and moxifloxacin (MF)[126] into the CL system. Based on this phenomenon, CL methods were developed for determination of these antibiotics (Table 2) [125, 126]. Au/Ag alloy NPs could catalyze the KMnO4– HCHO CL system such that in the presence of these NPs the intensity of the CL system increased by factor of about 7 [127]. Innovatively, the catalytic property of theses NPs was compared with AuNPs and AgNPs in the KMnO4 – HCHO CL system. It was found that the catalytic effect of Au/Ag alloy NPs was stronger than those of AuNPs and AgNPs, intensifying the KMnO4 – HCHO CL system by factors of about 3 and 2, respectively [127]. Moreover, on the basis of the attenuating effect of melamine on this CL system, due to interaction of melamine with Au/Ag alloy NPs catalysts, a method was proposed for measurement of melamine [127]. Comparison of the Au/Ag alloy NPs–catalyzed KMnO4–HCHO CL system [127] with those of other CL methods for melamine determination revealed that this CL system was superior to luminol–H2O2 [128] and luminol–K3Fe(CN)6 CL systems [129]. The CL system were 25 Page 25 of 65

comparable with luminol-myoglobin CL system [130] and finally inferior to AuNPs catalyzed TCPO – H2O2 – fluorescein CL system [131]. It should be mentioned that AuNPs– catalyzed TCPO–H2O2–fluorescein CL system featured wide linear dynamic range (six orders of magnitude) and very low LOD (3 10-13 mol L-1, 0.038 pg mL-1) [131]. Table 2 demonstrates the analytical applications of the AgNPs– and Ag alloy NPs–catalyzed KMnO4 CL reactions, including details of CL procedures and relevant analytical figures of merit.

3.3. AgNPs– and Ag alloy NPs–catalyzed peroxyoxalate chemiluminescence (POCL) reactions Peroxyoxalate chemiluminescence (PO-CL) reaction occurs through the oxidation of an aryl oxalate ester such as bis-(2,4,6,- trichlorophenyl)oxalate (TCPO) and 1,1`oxalyldiimidazole (ODI) with H2O2 in the presence of a fluorophore (F) such as safranin O [48] and dipyridamole (DIP) [54]. In the PO-CL system, the production of redox reaction of TCPO-H2O2 is high-energy 1, 2-dioxetanedione forming a charge complex with the F. The F gives one electron to the 1, 2-dioxetanedione. This electron is returned back to the F and convert F to an excited state (F*). The F* returns to the ground state, yielding CL emission. AgNPs are capable of enhancing the TCPO CL reaction by accelerating production of 1,2-dioxetanedione [48, 54]. The mechanism of TCPO–H2O2–AgNPs–DIP CL reaction is shown in Fig. 8. Unlike luminol, TCPO is insoluble in water and thus its stock solutions are prepared by dissolving the solid TCPO in organic solvents such as acetonitrile, ethyl acetate [24, 48, 54]. Place of Figure 8 Based on AgNPs–catalyzed TCPO–H2O2 CL reaction, CL methods for determination of pharmaceuticals including DIP [54] and 6-mercaptopurine (6-MP) [48] were 26 Page 26 of 65

developed (Table 2). In these methods, DIP and 6-MP acted as F and quencher, respectively [48, 54]. In the case of DIP, the comparison of analytical figures of merits of AgNPs–catalyzed [54] and uncatalyzed [132] TCPO–H2O2 CL systems revealed that application of AgNPs as a catalyser could decrease LOD of the CL system about one order of magnitude. In the case of 6-MP, LOD of AgNPs–catalyzed TCPO–H2O2 CL system (1.6  10-7 mol L-1) was higher than that of AuNPs–catalyzed luminol – H2O2 (1.1 × 10−9 mol L-1) [84]. Compared to TCPO, the light emanating from ODI – H2O2 CL reaction is faster and stronger [133, 134]. Choi et al. [135] has mentioned the potential of AgNPs in enhancing ODI–H2O2 CL reaction. However, a research work dealing with mechanistic study and/or analytical application of AgNPs–catalyzed ODI –H2O2 CL reaction was not found in the literature. It is worthy to mention that ODI is produced by the reaction TCPO with imidazole [133]. In 2013, Chaichi et al. [57] showed that Au/Ag alloy NPs were capable of catalyzing the TCPO–Amplex red (AR)–H2O2 weak CL system. The enhancing effect of Au/Ag alloy NPs on the PO–CL reaction was attributed to ability of these NPs to catalyze H2O2 decomposition and also adsorption of AR molecules on the surface of Au/Ag alloy NPs such that the rigidity and, consequently, CL intensity of AR molecules were increased [57]. Moreover, it was revealed that vitamin C could quench the CL emission via scavenging reactive oxygen species and preventing formation of the 1,2dioxetanedione. On this basis, a CL method was developed for determination of vitamin C (Table 2). However, the linear range (0.082–82.7 µg mL-1) and LOD (0.012 µg mL-1) of Au/Ag alloy NPs-catalyzed PO-CL method were interferer to the linear range (0.0176–176 ng mL-1) and LOD (0.0035 ng mL-1) of AuNPs - catalyzed luminol CL method [136] developed for determination of vitamin C. 3.4. AgNPs–catalyzed K3Fe(CN)6 CL reactions 27 Page 27 of 65

Han et al. [137] reported that the reaction between K3Fe(CN)6 and fluorescein brought about no detectable CL emission. However, they indicated that addition of AgNPs in the alkaline solution containing K3Fe(CN)6 and fluorescein led to strong CL emission with λmax at 520 nm. The mechanism of CL reaction was expressed as follows: the energy released from AgNPs–catalyzed redox reaction of K3Fe(CN)6 with a portion of fluorescein molecules was transferred to other unreacted fluorescein molecules and thereby fluorescein molecules were changed to excited molecules, whose return to the ground state led to the emission of light [137]. Moreover, it was reported that catechol could attenuate the AgNPs–K3Fe(CN)6–fluorescein CL system. Based on these findings, a CL method was developed for measurement of catechol in environment waters [137]. In term of analytical performance (Table 2), the dynamic linear range of the AgNPs–catalyzed K3Fe(CN)6–fluorescein CL system (0.1–10 μmol L-1) [137] was approximately similar with that of uncatalyzed K3Fe(CN)6–luminol CL system (0.09– 9 μmol L-1) developed for determination of catechol [138]. But, the LOD of AgNPs– catalyzed CL system (5 nmol L-1) [137] was better than that of uncatalyzed CL system (90 nmol L-1) [138]. Han et al. [139] reported that AgNPs could catalyze the K3Fe(CN)6–rhodamine 6G (Rh6G)–nitrazepam CL system. In this CL reaction, the light emitter was Rh6G molecules which released their energy as a light after accepting energy of excited oxidized nitrazepam ((nitrazepam*)ox), generated by reaction of nitrazepam with K3Fe(CN)6. Indeed, AgNPs catalyzed the redox reaction of K3Fe(CN)6–nitrazepam. Furthermore, nitrazepam* and Rh6G were absorbed on the surface of AgNPs. Thus, distance between nitrazepam* and Rh6G was shorten and energy transfer became easier [139]. The AgNPs–K3Fe(CN)6–Rh6G- nitrazepam CL system was used for determination of nitrazepam in Coca-Cola beverage, urine and plasma. The interesting advantages of the proposed method were wide dynamic linear 28 Page 28 of 65

range (four orders of magnitude) (Table 2) and its applicability for complex samples without need for separation step, among others [139]. 3.5. AgNPs– and Ag alloy NPs–catalyzed Ce(IV) CL reactions AgNPs are capable of intensifying the CL emission originating from redox reaction of Ce(IV) with some reducing compounds including ruthenium (II) complexes [140, 141] and Na2SO3 [53] and Na2S2O4 [142]. In this chemistry, it was demonstrated that citrate-capped AgNPs–catalyzed Ru(bpy)32+–Ce(IV) CL reaction could be used for determination of citrate ions (Table 2) [140]. The LOD of AgNPs - catalyzed Ru(bpy)32+–Ce(IV) CL system (4  10-9 mol L-1) was better than that of CL methods developed for the determination of citrate ions based on uncatalyzed Ru(bpy)32+– Ce(IV) CL system [143, 144]. Generally, the CL reaction involved the oxidation of both Ru(bpy)32+ and citrate with Ce(IV) to generate Ru(bpy)33+ and intermediate radicals, respectively. The further oxidation of the intermediate radicals by Ru(bpy)33+ produced Ru(bpy)32+ in an electronically excited state that emitted light at λmax=610 nm [144]. The enhancing effect of citrate-capped AgNPs was ascribed to electrostatic interactions between the negatively charged citrate-capped AgNPs and the positively charged ruthenium complexes in such way that the ligand π–π* energy gap was reduced and the quantum efficiency of the CL reaction was improved [140]. Oxidation of Ru(1,10-phenanthroline)32+ (Ru(phen)32+) with Ce(IV) led to CL emission [141]. Liu et al. [141] found that AgNPs could enhance CL emission of Ru(phen)32+–Ce(IV) system, strongly. Benefiting this finding, they developed a CL approach for determination of indoleacetic acid (IAA) based on inhibitory effect of IAA on the AgNPs–Ru(phen)32+–Ce(IV) CL system (Table 2) [141]. Yu et al. [53] used AgNPs–enhanced Ce(IV)–Na2SO3 CL system for determination of norfloxacin (NFLX) in eyedrops. In this system, SO32- was oxidised to SO2 in electronically 29 Page 29 of 65

excided state (SO2*) by Ce(IV). By addition of mixture of terbium3+ (Tb3+) and NFLX to the Ce(IV)–Na2SO3 CL system, the energy of SO2* is transferred to Tb3+ (light emitter) through NFLX. Indeed, SO2* and Tb3+–NFLX chelate were adsorbed onto the surface of AgNPs in such a way that distance between them was shortened and, thus, the energy transfer became easier (Fig. 9). Place of Figure 9 The LOD of AgNPs–catalyzed Ce(IV)–Na2SO3 CL system (2.0  10-9 mol L-1) (Table 2) was lower than those of uncatalyzed Ce(IV)–Na2SO3 (3.0  10-8 mol L-1[145]) and also Ce(IV)–Na2S2O4 CL systems (1.8  10-8 mol L-1 [146] and 6.9  10-9 mol L-1 [147]) developed for determination of NFLX. In a conceptually and experimentally similar fashion, Kamruzzaman et al. [142] developed a CL approach for determination of naproxen (NAP) by using AgNPs–Ce(IV)–Na2S2O4–Eu(III)–NAP CL system (Table 2). The catalytic activity of Au/Ag alloy NPs towards Rh6G–Ce(IV) CL system was reported by Li et al. [148] in 2009. In this system, Ce(IV) was reduced to Ce(III) the excited-state form (Ce(III)*) through the oxidation of Au/Ag alloy NPs and Rh6G in a sulfuric acid medium. Then, the energy of the produced Ce(III) was transferred to Rh6G and also its oxidized form, yielding light emission [148]. Furthermore, the effect of 22 organics and 17 amino acids on the Au/Ag alloy NPs– Rh6G–Ce(IV) CL system was studied, which made it possible to develop a CL method for measurement of 15 out them. Interestingly, those compounds that have – NH2 and –OH groups, –COOH and –OH groups, or two –OH groups in benzene ring structures led to enhance the intensity of CL system. In contrary, ethyl naphthol, which has –OH group bound to the naphthyl group, gave inhibitory effect on the CL system [148]. 4. AgNPs as energy acceptor in CL reactions 30 Page 30 of 65

Yu et al. [149] reported the enhancing effect of silver nanoclusters (AgNCs) on the Ce(IV)–Na2SO3 CL system. In this system, Ce(IV) oxidized Na2SO3 to SO2 in electronically excited state (SO2*). Then, the energy of SO2* was transfer to AgNCs, emitting light at ~550 nm. Indeed, the quantum efficiency of AgNCs was higher than that of SO2.Therfore, the intensity of light emission of AgNCs was stronger than that of SO2. The enhancing effect of AgNCs on the Ce(IV)–Na2SO3 CL system [149] is higher than that of AgNPs on the Ce(IV)–Na2SO3–Tb3+–NFLX CL system [53]. Moreover, it was found that cysteine was able to quench the AgNCs–Ce(IV)–Na2SO3 CL system. Indeed, cysteine was adsorbed onto the surface of AgNCs and prevented energy transfer between AgNCs and SO2*. As a consequent, the CL emission was decreased in the presence of cysteine [149]. It should be mentioned that cysteine showed enhancing effect on the AgNPs–luminol–AgNO3 [104], Au/Ag alloy NPs– Ce(IV)–Rh6G [148] and AgNPs–lucigenin [58], copper hydroxide/copper oxide nanowires (Cu(OH)2/CuO NWs)–luminol–H2O2 [150] CL systems. The mechanism of this enhancing effect has been discussed elsewhere [58, 104, 148, 150]. Taking advantage of inhibitory effect of cysteine, a CL method was developed for determination of cysteine [149]. The analytical performance of AgNCs–enhanced CL method was approximately similar to that of Au/Ag alloy NPs–Ce(IV)–rhodamine 6G (Table 2) [148] CL system and inferior to that of copper hydroxide/copper oxide nanowires

(Cu(OH)2/CuO

NWs)–enhanced

luminol–H2O2

CL

system

for

determination of cysteine [150]. 5. AgNPs as reductant in CL reactions Nucleophiles can decrease the redox potential of AgNPs, remarkably. Therefore, in the presence of nucleophiles, these NPs can be used as reductants in CL reactions. In this context, it was reported that AgNPs in the presence of nucleophiles including 31 Page 31 of 65

iodide ion, thiourea, mercaptoacetic acid, mercaptopropionic acid and cysteine were able to reduce lucigenin and generate CL emission in alkaline medium [58]. The CL mechanism involved the reduction of lucigenin (Luc2+•2NO3-) to Luc•+ by AgNPsnucleophile system. Then, Luc•+ reacted with the dissolved oxygen to produce the O2•−, whose reaction with Luc•+ led to CL emission [58]. Similar chemical reactivity from Au and Pt NPs towards lucigenin was observed. However, the CL intensities of AuNPs- nucleophile- lucigenin and PtNPs-nucleophile- lucigenin systems were lower than that of AgNPs-nucleophile- lucigenin system because the activities of Au and Pt were less than Ag [58]. In addition to lucigenin, the reaction of luminol with Ag NPs in the presence of Cu(II) and nucleophiles such as Cl−, I− and thiosulfate [59] and amino acids including histidine, lysine and arginine [60] provided CL emission. The mechanism governing CL reaction was that AgNPs in the presence of nucleophiles could reduce Cu(II) to Cu(I) complex, reacting with the dissolved oxygen to produce superoxide anion, whose reaction with luminol yielded CL emission [59, 60]. Furthermore, the effect of monodentate nucleophile and the related multidentate nucleophile imidazole on the AgNPs-luminol CL system was studied. It was found that the CL intensity of multidentate nucleophile (histidine) was higher than that of monodentate nucleophile (imidazole) because the interaction of multidentate nucleophile with AgNPs was more intense than that of monodentate nucleophile [60]. 8. Conclusions and future prospects Ability of AgNPs and Ag alloy NPs in increasing the intensity of CL reactions has served as the impetus for using these NPs in solving the problem of low quantum efficiency of some CL reactions. As discussed in this review paper, the enhancement effect of AgNPs and Ag alloy NPs stems mainly from plasmonic, catalytic, reducing and energy accepting properties of theses NPs. However, the catalytic effect of 32 Page 32 of 65

AgNPs and Ag alloy NPs on the CL systems were more investigated than plasmonic, reducing and energy accepting effects. In addition, luminol, peroxyoxalate, KMnO4, K3Fe(CN)6 and Ce(IV) benefitting these ,



catalyzed luminol CL systems were the most used

system in the analytical chemistry. The comparison of analytical figures of merits of AgNPs– and Ag alloy NPs–enhanced CL methods with uncatalyzed CL methods revealed that merging these NPs with CL system could usually improve the analytical performance of the CL methods. Moreover, AgNPs along with luminol– functionalized AgNPs could be used as labels in CL immunoassays. Because of these advantages, AgNPs– and Ag alloy NPs–enhanced CL system have received keen attention of researchers and have been successfully employed in CL methods. Concerning AgNPs– and Ag alloy NPs–enhanced CL methods, the author believes that the possible future researches may mainly focus on application of AgNPs and Ag alloy NPs for enhancing new CL reactions and CL determination of new analytes rather than those have been investigated. Furthermore, developing AgNPs and Ag alloy NPs–enhanced CL immunoassay systems, functionalization of theses NPs with other CL reagents rather than luminol and synthesis of new chemiluminescent nanocomposites by participating of AgNPs and Ag alloy NPs are other interesting topics for further investigation. Finally, it is thought that the role of shape in the catalytic activity of AgNPs along with their potential applications is worthwhile for further investigation. 9. Acknowledgments Mortaza Iranifam makes a point of his sincere thanks to the University of Maragheh for the financial support backing this project. References 33 Page 33 of 65

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Figure captions Fig.1. SEM images of AgNPs in the shapes of (A) hexagonal nanoplates (Figure reproduced with permission from [1]), (B) nanowires (Figure adapted with permission from [2]), (C) pentagonal nanorods (Adapted with permission from [3], © (2009) American Chemical Society), (D) decahedral NPs (Adapted with permission from [4], © (2008) American Chemical Society), (E) bipyramids (Adapted with permission from [5], © (2006) American Chemical Society), (F) nanocubes (Figure adapted with permission from [6]), (G) nanoflowers (Adapted with permission from [7], © (2011) American Chemical Society), (H) nanospheres (Adapted with permission from [8], © (2010) American Chemical Society). Fig. 2 (A) Schematic depiction of the experimental geometry for metal-enhanced chemiluminescence (MEC) studies. Chemiluminescence spectra of (B) blue and (C) green chemiluminescence dyes on glass and SIFs. The insets show the photographs of the actual glass microscope slide with SIFs and the chemiluminescence dyes placed in between two silvered glass microscope slides. The enhanced chemiluminescence emission can clearly be seen from silvered portion of the slide. SIFs-silver island films (Figure reproduced with permission from [15]). Fig. 3. The kinetic curve of luminol–H2O2 mixed with AgNPs. Conditions: luminol: 5  10-5 mol L-1; H2O2: 5  10-3 mol L-1. Blank: H2O (Figure reproduced with permission from [72]). Fig. 4. Schematic illustration of the enzyme linked CL assay for detection of dglucose based on dendritic Au–Ag bimetallic NPs (Figure reproduced with permission from [88]). Fig. 5. CL kinetic curve when 3 mM 0.5 mL of H2O2 (pH 7.4) was injected to 0.1 mL lumiol−AgNPs aqueous solution (blue line) and 0.1 mL 10 μM luminol aqueous solution in the absence (red line) and presence (black line) of AgNPs prepared by citrate reduction method, respectively. The inset shows the magnification of black line (Reprinted with permission from [96], © (2014) American Chemical Society). Fig. 6. The kinetic curve of CL reaction. Conditions: luminol, 1.010-5 mol L-1 (0.1 mol L-1 NaOH); K3Fe(CN)6, 3.010-5 mol L-1; AgNPs, 2.510-9 mol L-1; 2-ME, 5.010-8 mol L-1. (1), luminol + K3Fe(CN)6; (2),(1)+AgNPs; (3),(2)+2-ME (Figure reproduced with permission from [100]). Fig. 7. the mechanism of the luminol–AgNO3–AgNPs CL system (Figure reproduced with permission from [103]). 44 Page 44 of 65

Fig. 8. Possible mechanism of TCPO–H2O2–AgNPs–dipyridamole CL reaction (Figure reproduced with permission from [54]). Fig. 9. Schematic illustration of possible mechanism of AgNPs enhanced Tb3+–NFLX Ce(IV) –Na2SO3 CL system

45 Page 45 of 65

Table 1. AgNPs- and Ag alloy NPs-catalyzed luminol CL systems Analyte

AFP, CA 153, CA 199, and CEA

Bisphenol A (BPA)

Cefditoren pivoxil

Chloramphenicol (CHL)

Average diameter of AgNPs or Ag alloy NPs (nm) 20

17±1.0

N.R.

25

CL reaction

Linear range (LOD)

Real sample

AgNPs–luminol– H2O2

2.5–110 ng mL–1, 1.0–100, and 0.5–150 U mL–1 and 0.1– 130 ng mL–1 (1.0 ng mL–1, 0.4, and 0.06 U mL–1 and 0.02 ng mL–1)

Whole blood

AgNPs – luminol – KMnO4

1.0×10−8 − 5.0×10−5 g L−1 (1×10−9 g L−1)

AgNPs –luminol–K3Fe(CN)6

0.001–5000 ng mL-1 (0.5 pg mL-1)

Tap water, river water, barrelled drinking water Table, urine and serum

AgNPs–luminol– H2O2

1.0 × 10−8–1.0 × 10−6 g mL−1 (7.6 × 10−9 g mL−1)

Milk and honey

Comments

Ref.

A 3D origami-based CL immunodevice, [76] printed on sheets of paper via waxprinting, was developed to perform a multiplexed CL immunoassay. AgNPsluminol was synthesized by reducing Ag+ with luminol. Common metal ions, anions, and [114] organic species do not interfere with BPA determination. A sequential injection analysis (SIA) [101] with CL detection based on the enhacing effect of analyte on the Ag NPs – luminol – potassium ferricyanide system was developed. A competitive immunoassay for [97] determination of CHL using the luminol functionalized AgNPs as nanoprobe was developed

Page 46 of 65

Table 1. (Continued) Analyte

CL reaction

Linear range (LOD)

Real sample

Comments

Ref.

AgNPs–luminol– AgNO3

0.0001–1 ng mL–1 (6  10–6 ng mL–1)

River water sample

The analyte inhibited the CL reaction.

[105]

20±2.5

AgNPs–luminol– H2O2

40–2500 ng mL−1 (3.78 ng mL−1)

Tablet and human plasma

Fenoterol and orciprenaline

20

AgNPs–luminol– KIO4

0.6 - 10 ng mL−1 (0.1 ng mL−1) and 0.4 -10 ng mL−1 (0.1 ng mL−1)

Tablets

Furacilin furantoin furazolidone and furaltadone

20

AgNPs–luminol– H2O2

2.0  10–6 – 1.0  10–4, 2.0  10–7 – 1.0  10–4, 1.0  10–7 –1.0  10–4, 4.0  10–7 – 1.0 10–4 gmL–1, respectively (8  10–7 , 8  10–8, 4  10–8 and 2  10–7 gmL–1)

Feeds and pharmaceutical samples

CL reaction

Linear range (LOD)

Real sample

2-Chloroethyl ethyl sulfide (2CEES) Citalopram

Average diameter of AgNPs or Ag alloy NPs (nm) 5

The method was based on the [70] enhancing effect of analyte on the of the luminol–H2O2–AgNPs CL system The analytes enhanced the CL intensity [112] by increasing the number of active oxygen intermediates. The analyte enhanced the Ag NPs – [69] luminol – H2O2 CL reaction. The most important interferences were from Fe3+ and uricacid

Table 1. (Continued) Analyte

Average diameter of AgNPs

Comments

Ref.

47 Page 47 of 65

Gallic acid, Tannic acid, Pyrogallic acid, Hydroquinone, Pyrocatechol and p-tButylpyrocatechol

or Ag alloy NPs (nm) 35.0 ± 2

Gemifloxacin N.R.

Glucose

12

AgNPs–luminol– AgNO3

AgNPs –luminol–K3Fe(CN)6

Au/Ag alloy NPs – Luminol–H2O2– Cu2+/ion liquid

8.0  10–10 – 1.0  10–7 g mL–1 (5.0  10–10 g mL–1) 8.0  10–10 – 2.0  10–7 g mL–1 (5.0  10–10 g mL–1) 5.0  10–10 – 4.0  10–7 g mL–1 (2.0  10–10 g mL–1) 1.0  10–10 – 2.0  10–8 g mL–1 (1.0  10–10 g mL–1) 4.0  10–11 – 1.0  10–8 g mL–1 (2.0  10–11 g mL–1) 6.0  10–11 – 5.0  10–8 g mL–1 (2.0  10–11 g mL–1) 0.01-1000 ng mL-1 (0.002 ng mL-1)

Table, urine and serum

1.0  10–6 – 7.5  10–3 mol L–1 (1.0  10–6 mol L–1)

Human serum and urine

N.R.

Cationic, anionic and non-ionic [104] surfactants did not show a significant influence on the CL reaction.

A sequential injection analysis (SIA) with CL detection based on the inhibitory effect of analyte on the Ag NPs – luminol – potassium ferricyanide system was developed. The optimum pH of CL reaction was 7.5. The biosensor was stable up to analyze 570 samples during 4 months of operation.

[51]

[86]

Table 1. (Continued)

48 Page 48 of 65

Analyte

Glucose

Average diameter of AgNPs or Ag alloy NPs (nm) 12±2

CL reaction

Linear range (LOD)

Real sample

Comments

Ref.

Chitosan-Induced Au/Ag alloy NPs – luminol–H2O2– coumarin derivatives Dendritic Au-Ag bimetallic NPs – luminol–H2O2–HRP

1.5 × 10−6 – 5.0 × 10−3 mol L−1 (7.5 × 10−7 mol L−1)

Human serum and urine

Coumarin derivatives and luminol were enerrgy acceptor and energy donor of the CRET process, respectively.

[87]

Glucose

60

1.0 × 10−6 – 1.0 × 10−3 mol L−1 (4.0 × 10−7 mol L−1)

N.R.

Glutathione

22

AgNPs–luminol–H2O2

30 – 1000 µmol L–1 (25 µmolL–1)

N.R.

Human IgG

5

AgNPs–luminol– AgNO3

10-100 ng mL–1 (3 ng mL–1)

N.R.

Isoniazid

70

AgNPs–luminol–H2O2

10–1000 ng mL−1 (2.7 ng mL−1)

Tablets

Dendritic Au–Ag bimetallic NPs were [88] synthesised by a seed-assisted approach. The method could be developed for other reactions involving the generation of H2O2. AgNPs were uniformly dispersed on the [81] surface of GO nanosheets. Luminol molecules were also decorated on the surface of the nano-composites. AgNPs was used to label goat [103 antihuman IgG (secondary antibody). ] A sandwich CL immunoassay for human was developed. AgNPs catalyze the reduction of [151 dissolved O2 to H2O2 by isoniazid in ] addition to the decomposition of H2O2.

Table 1. (Continued)

49 Page 49 of 65

Analyte

L-tyrosine, L- cysteine, L-glycine, L-proline, L-histidine, dopamine, pyrogallic acid, epinephrine, tannic acid, hydroquinone, pyrocatechol and

Average diameter of AgNPs or Ag alloy NPs (nm) 29.5±2

CL reaction

Linear range (LOD)

Au/Ag alloy NPs – luminol–H2O2

2.010-6–2.010-9 g mL−1 (1.510-9 g mL−1), 2.010-6–1.010-9 g mL−1 (1.010-9g mL−1), 2.510-6–5.010-9 g mL−1 (3.510-9 g mL−1), 2.010-6–2.510-9 g mL−1 (9.510-10 g mL−1), 1.510-6–2.510-9 g mL−1 (1.510-9 g mL−1), 1.010-6–8.010-10 g mL−1 (6.510-10 g mL−1), 1.010-6–3.010-9 g mL−1 (1.810-9 g mL−1), 2.010-6–1.010-9 g mL−1 (7.110-10 g mL−1), 2.010-6–8.010-10 gmL−1 (5.010-10 g mL−1), 4.010-7–2.010-9 g mL−1 (2.110-9 g mL−1), 1.010-6–1.010-9 gmL−1 (8.510-10 g mL−1) and 2.010-6–2.010-9 g mL−1 (1.810-9g mL−1)

p-tbutylpyrocatechol,

Real sample

N.R.

Comments

Ref.

Analytes qunched the CL [55] reaction by interacting with Au/Ag alloy NPs.

Table 1. (Continued) Analyte

Average diameter of AgNPs or Ag alloy NPs

CL reaction

Linear range (LOD)

Real sample

Comments

Ref.

50 Page 50 of 65

(nm) Lisinopril

10–20

AgNPs – luminol – KMnO4

0.1 mg L−1 − 20.0 mg L−1 (0.027 mg L−1)

2-Methoxyestradiol

10±2

AgNPs –luminol–K3Fe(CN)6

5.0  10-9 – 1.0  10-7 mol L-1 (5.0  10-10 mol L-1)

N-Acetyl-Lcysteine

20±2

AgNPs–luminol– H2O2

0.034–0.98 μg mL–1 (0.010 μg mL–1)

Ofloxacin

15±5

AgNPs–luminol– H2O2

1.0 × 10−9 – 1.0 × 10−6 g mL−1 (3.0 × 10−10 g mL−1)

Eyedrop

Phenylamine, pPhenylenediamine, oPhenylenediamine, mPhenylenediamine

7 and 15

AgNPs–luminol– H2O2

2 × 10−9 – 2 × 10−6, 2 × 10−9 – 6 × 10−6, 3 × 10−9 – 1 × 10−6 and 3 × 10−9 – 8 × 10−7 g mL−1 (6.2 × 10−10, 2.6 × 10−10, 1.2 × 10−9 and 1.6 × 10−9 g mL−1)

N.R.

Ca2+, Zn2+, and Ni2+ led to a positive [50] interference on the signal, whereas ascorbic acid, uric acid, Mg2+, Cu2+, and Fe2+ produced a negative effect. Human serum The analyte had inhibitoy effect on the [100] and injections CL system. The method showed very good precision (RSD=0.75%). Pharmaceutical The analyte inhibited the Ag NPs – [71] tablets luminol – H2O2 CL reaction. Tablet and urine

A wax-printed paper-based analytical device along with AgNPs catalyzed luminol CL system for the determination of ofloxacin was presented. The analyte were able to induce the aggregation of AgNPs. Compared to dispersed AgNPs, Aggregation led to CL increase for 7 nm, decline for 15 nm and no change for 55 nm.

[79]

[72]

Table 1. (Continued)

51 Page 51 of 65

Analyte

Pyrocatechol, L-dopamine, L-ascorbic acid, hydroquinone, resorcinol, pyrogallic acid and L-cysteine

Average diameter of AgNPs or Ag alloy NPs (nm) 22

CL reaction

Linear range (LOD)

Real sample

AgNPs–luminol– KIO4

3 × 10−10 - 1 × 10−8 g mL−1 (N.R.), 9 × 10−11 - 5 × 10−8 g mL−1 (N.R.), 6 × 10−11 - 2.5 × 10−7 g mL−1 (N.R.), 6 × 10−11 - 2.5 × 10−8 g mL−1 (N.R.), 6 × 10−11 - 2.5 × 10−8 g mL−1 (N.R.), 1 × 10−10 - 1 × 10−5 g mL−1 (N.R.) and 5 × 10−8 - 1 × 10−5 g mL−1 (N.R.)

Synthesized samples for pyrogallic acid

Comments

Ref.

AgNPs could strongly enhance the CL [113] of the luminol-KIO4 system in the presence of Co2+.

52 Page 52 of 65

Table 2. AgNPs- and Ag alloy NPs-catalyzed CL reaction Analyte

Captopril

Average diameter of AgNPs or Au/Ag alloy NPs (nm) 18

CL reaction

Linear range (LOD)

Real sample

AgNPs–KMnO4– bromide

3.0  10−10 − 1.0 10−7 mol L−1 (0.12 nmol L−1)

Tablet, urine and serum

Catechol

50 ± 5

AgNPs– K3Fe(CN)6– fluorescein

Cysteine

N.R.

AgNCs–Ce(IV) – Na2SO3

Dipyridamole (DIP)

~ 20

AgNPs–TCPO– DIP–H2O2

Flutamide

14±2

Gatifloxacin (GFLX)

13

Au/Ag alloy NPs–luminol– H2O2 AgNPs – calcein – KMnO4

0.1  10-6 – 10.0  10-6 mol L-1 (5.0  10-9 mol L-1)

5.0  10-9 - 1.0  10-6 mol L-1 (2.5  10-9 mol L-1) 1.0–1000 ng mL-1 (0.9 ng mL-1)

5.0  10−7–1.0  10−4 mol L−1 (1.210−8 mol L−1) 8.9  10-9 – 4.0  10-6 mol L−1 (2.6  10-9 mol L−1)

Comments

Ref.

NaBH4 and trisodium citrate were used as [52] reducing agent and stabilizer in the AgNPs synthesis process. Tap water and By addition of of K3Fe(CN)6 solution into [137] lake water the mixture solution of fluorescein and AgNPs, a strong CL reaction was emerged immediately and the maximum CL intensity was obtained in 0.5 s. N.R. Glutathione (GSH), as like to cysteine has [149] a thiol group, did not has interference on the CL system. Tablet The optimum pH for CL reaction was 8. [54] The most important interferences were from CO32–, Pb2+ and sucrose. λmax of CL spectrum was 485 nm. Fluorophore was DIP. Human serum Box–Behnken experimental design was [56] and urine used for investigation and validation of the CL measurement parameter Pharmaceutical The synthesis of NPs was mainly based [125] formulations on the aqueous and gaseous phase and urine reaction between the AgNO3 solution and the NH3 gas.

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Table 2. (Continued) Analyte

L-cystine L-methionine, L-phenylalanine, L-dopamine, L-epinephrine, L-ascorbic acid, pyrogallic acid, 2,4dihydroxybenzoi c acid, p-aminobenzoic acid, o-aminobenzoic acid, phenol, p-aminophenol, hydroquinone, resorcinol, p-tbutylpyrocatecho l

Average diameter of AgNPs or Au/Ag alloy NPs (nm) 30

CL reaction

Au/Ag alloy NPs rhodamine 6G Ce(IV)

Linear range (LOD)

Real sample

5.0 × 10-9 -2.0 × 10-6 g mL-1 (2.7 × 10-9 g mL-1), N.R. 8.0 × 10-9 - 2.0 × 10-6 g mL-1 (4.1 × 10-9 g mL-1), 1.0 × 10-8 - 2.5 × 10-6 g mL-1 (8.2 × 10-9 g mL-1), 2.5 × 10-9 - 1.5× 10-6 g mL-1 (8.9 × 10-10 g mL-1), 2.5 × 10-9 -1.5× 10-6 g mL-1 (9.5 × 10-10 g mL-1), 2.0 × 10-6 - 4.0 × 10-9 g mL-1 (1.9 × 10-9 g mL-1), 3.0 × 10-9 - 1.0 × 10-6 g mL-1 (1.2 × 10-9 g mL-1), 1.0 × 10-9 - 2.0× 10-6 g mL-1 (6.8 × 10-10 g mL-1), 2.0 × 10-6 - 1.2 × 10-8 g mL-1 (7.4 × 10-9 g mL-1), 6.8 × 10-7 - 5.0 × 10-9 g mL-1 (2.1 × 10-9 g mL-1), 1.0 × 10-6 - 3.4 × 10-9 g mL-1 (1.6 × 10-9 g mL-1), 2.0 × 10-6 - 7.5 × 10-9 g mL-1 (3.9 × 10-9 g mL-1), 2.0 × 10-6 - 5.0× 10-9 g mL-1 (2.3 × 10-9 g mL-1), 1.0 × 10-6 - 8.0 × 10-9g mL-1 (4.5 × 10-9 g mL-1) and 1.0 × 10-6 - 5.0 × 10-9 g mL-1 (3.8 × 10-9 g mL-1)

Comments

Ref.

The CL system has a wide application [148] for the determination of such compounds. The light emitter was excited rhodamine 6G. The all calibration graphs were log-log.

54 Page 54 of 65

Table 2. (Continued) Analyte

Indoleacetic acid (IAA)

Average diameter of AgNPs or Au/Ag alloy NPs (nm) 20 ± 2.5

Linear range (LOD)

CL reaction

Real sample

Comments

Ref.

Ru(phen)32+–Ce(IV)–IAA

1.0 × 10-8 – 6.0 × 10-7 g mL-1 (9.0×10-9 g mL-1)

Synthetic samples

The most important interferences were from Mg2+, Fe3+ and Mn2+. The CL reaction occurred in the acidic solution of H2SO4.

[141]

The tolerable concentration ratios for interferences (relative error <5%) were 1000 for Na+, K+, Cl-, NO3-, SO42-,500for PO4 3-, 200 for Zn2+, Cu2+, Mg2+, Vitamins B1, B2 and 100 for Ca2+, Ethanol, Oxalate and Glucose. The synthesis of NPs was mainly based on the aqueous and gaseous phase reaction between the AgNO3 solution and the NH3 gas. Urea could be tolerated up to 10fold. The CL reaction emits orange-red light (λmax = ~580 nm). Fluorophore was Safranin O.

[127]

Melamine

10.5±1

Au/Ag alloy NPs KMnO4 - HCHO

0.01 – 35 ng mL−1 (8 pg mL−1)

Powdered milk

Moxifloxacin (MF)

14

AgNPs–calcein–KMnO4

6.0  10-8 − 2.5  10-6 mol L−1 (5.6 10-9 mol L−1)

Tablet and urine

6Mercaptopurine (6-MP)

18.23

5.5  10-7 − 5.5  10-5 mol L-1 (1.6  10-7 mol L-1)

Tablet

AgNPs–TCPO– safranin O–H2O2

[126]

[48]

55 Page 55 of 65

Table 2. (Continued) Analyte

Naproxen (NAP)

Average diameter of AgNPs or Au/Ag alloy NPs (nm) 15±2

CL reaction

Linear range (LOD)

Real sample

Comments

Ref.

AgNPs–Eu3+–naproxen– Ce(IV)– Na2S2O4

1–420 ng mL−1 (0.11 ng mL−1)

Tablets

Different inorganic acids including HCl, HNO3, H3PO4 and H2SO4 were added to the Ce(IV) solution to investigate the effect of each acid on the CL signal. H2SO4 led to strongest and most stable CL signal. The CL reaction occurred in 1.0 mol L-1 NaOH solution. The most important interferences were from phenylanaline and creatine. λmax of CL spectrum was 550 nm. More energy was transferred to Tb3+ once the complex of NFLXTb3+ formed, and AgNPs help to the process of energy transfer. For complex samples, separation procedures may be needed.

[142]

Nitrazepam

14 ± 2

AgNPs–K3Fe(CN)6– rhodamine 6G–nitrazepam

1.0  10-9 – 10.0  10-6 mol L-1 (0.1  10-9 mol L-1)

Coca-Cola beverage, urine and plasma

Norfloxacin (NFLX)

18 ± 2.5

AgNPs–Tb3+–norfloxacin– Ce(IV)– Na2S2O4

1.0 × 10-8 – 5.0 × 10-5 mol L-1 (2.0 × 10-9 mol L-1)

Eyedrops

[139]

[53]

Table 2. (Continued)

56 Page 56 of 65

Analyte

Sodium citrate

Vitamin C

Average diameter of AgNPs (nm) 19

12.0±2.0

CL reaction

Linear range (LOD)

Real sample

Ru(bpy)32+–Ce(IV)–Citrate

N.R. (4  10-9 mol L-1)

N.R.

0.082–82.7 µg mL-1 (0.012 µg mL-1)

Au/Ag alloy NPs - TCPO Tablet – Amplex red – H2O2 ampoule

Comments

Ref.

Solutions of glycine, proline and [140] tartaric acid that contained silver nitrate led to CL emission from Ru(bpy)32+- Ce(IV) system. and Optimization of effective [57] parameters in CL intensity was carried out by using the Box– Behnken design.

57 Page 57 of 65

Fig. 1

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Fig 2

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Fig. 3

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Fig. 4

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Fig. 5

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Fig. 6

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Fig. 7

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Fig. 8

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