Towards highly selective detection using metal nanoparticles: A case of silver triangular nanoplates and chlorine

Author’s Accepted Manuscript TOWARDS HIGHLY SELECTIVE DETECTION USING METAL NANOPARTICLES: A CASE OF SILVER TRIANGULAR NANOPLATES AND CHLORINE Vladimir V. Apyari, Marina O. Gorbunova, Anastasiya V. Shevchenko, Aleksei A. Furletov, Pavel A. Volkov, Alexey V. Garshev, Stanislava G. Dmitrienko, Yury A. Zolotov

PII: DOI: Reference:

www.elsevier.com/locate/talanta

S0039-9140(17)30885-8 http://dx.doi.org/10.1016/j.talanta.2017.08.056 TAL17852

To appear in: Talanta Received date: 10 July 2017 Revised date: 12 August 2017 Accepted date: 16 August 2017 Cite this article as: Vladimir V. Apyari, Marina O. Gorbunova, Anastasiya V. Shevchenko, Aleksei A. Furletov, Pavel A. Volkov, Alexey V. Garshev, Stanislava G. Dmitrienko and Yury A. Zolotov, TOWARDS HIGHLY SELECTIVE DETECTION USING METAL NANOPARTICLES: A CASE OF SILVER TRIANGULAR NANOPLATES AND CHLORINE, Talanta, http://dx.doi.org/10.1016/j.talanta.2017.08.056 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 galley proof before it is published in its final citable 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.

TOWARDS HIGHLY SELECTIVE DETECTION USING METAL NANOPARTICLES: A CASE OF SILVER TRIANGULAR NANOPLATES AND CHLORINE Vladimir V. Apyaria,*, Marina O. Gorbunovab,c, Anastasiya V. Shevchenkob, Aleksei A. Furletova, Pavel A. Volkovd, Alexey V. Garsheva,e, Stanislava G. Dmitrienkoa, Yury A. Zolotova a

Department of Chemistry, Lomonosov Moscow State University, Leninskie gory, 1/3, 119991

Moscow, Russia b

Southern Federal University, Department of Chemistry, Zorge st., 7, 344090 Rostov-on-Don,

Russia c

Rostov State Medical University of the Ministry of Healthcare of Russian Federation,

Pharmaceutical Faculty, Nakhichevansky lane, 29, 344022 Rostov-on-Don, Russia d

Scientific-Research Institute of Chemical Reagents and Special Purity Chemicals, Bogorodsky

Val st., 3, 107076 Moscow, Russia e

Department of Materials Science, Lomonosov Moscow State University, Leninskie gory, 1/73,

119991 Moscow, Russia

Abstract The article describes a novel approach towards improving selectivity of volatile compounds detection using metal nanoparticles. It is based on combination of sensitive optical detection using convenient nanoparticle-modified paper test strips and dynamic gas extraction improving selectivity to volatile compounds. A simple and inexpensive setup allowing for realization of this combination is described. Analytical prospects of the approach are shown by the example of chlorine determination in highly salted aqueous solutions using silver triangular nanoplates and digital colorimetry. The limit of detection is equal to 0.03 mg L-1 and the determination range is 0.1–2 mg L-1. This determination can be successfully carried out in solutions containing at least 2∙105 greater molar amounts of Na+, K+, Zn2+, Cl–, SO42–, and H2PO4– with no sample pretreatment. The approach seems to be compatible with different types of nanoparticles with respect to detection of various analytes, thus having good opportunities for further development.

Keywords: selective detection, dynamic gas extraction, metal nanoparticles, silver triangular nanoplates, chlorine, digital colorimetry

*

Corresponding author: e-mail: [email protected]

1

1. Introduction Metal nanoparticles, especially gold and silver, have found various applications in analytical chemistry. A huge lot of these applications is based on development of surface plasmon resonance optical sensors with nanoparticles both in a colloid solution and attached to solid supports [1–5]. Currently many nanoparticle based optical sensing systems have been developed [6–10]. Their significant advantages are high sensitivity, ease of the analytical response detection, tunability of the optical and analytical parameters. At the same time, there are some limitations constricting selectivity as well as other valuable properties of such systems. One of the main problems is aggregative instability of nanoparticles at high ionic strength. It is conditioned by decreasing zeta-potential which provides electrostatic stabilization of nanoparticles [11–14]. This problem can be partially eliminated by attaching nanoparticles to solid supports, thus making solid-based micro/nanosensors. However, in general, the number of matrix materials for these micro/nanosensors is very limited and the preparation procedures are sophisticated. Therefore, procedures for simple surface modification of sensor matrices are of interest [15]. Another problem, which sometimes requires quite sophisticated modification of nanoparticles increasing their cost, is strong interference when analyzing complex matrices. A good way to solve these problems would be spatial separation of nanoparticles from the interfering ions and compounds, with preserving their sensing ability. Herein, we report on a novel approach towards improving selectivity of metal nanoparticles with respect to volatile compounds detection. It is based on combination of optical detection using convenient nanoparticle-modified paper test strips and dynamic gas extraction. Nanoparticles provide sensitivity of the method whereas simultaneous dynamic gas extraction ensures their isolation form severe matrix affects. Analytical prospects of the approach are shown by the example of chlorine determination. This disinfectant is one of the most frequently used for treatment of water due to its capability to destroy the outer surfaces of bacteria and viruses. According to recommendations, 2 to 3 mg L-1 of chlorine should be added into water to get an effective disinfection and acceptable residual concentration; the suggested concentration for free chlorine in a well-maintained swimming pool is 1.5 to 2 mg L-1 [16]. Currently, a number of simple test kits for detection of chlorine is available [17]. However, the task of sensitive and selective determination of this analyte still remains actual, that can be proved by a significant number of research papers regarding this problem published in

recent

years.

The

electrochemical

[16,

18–22],

luminescent

[23–25]

and

spectrophotometric/colorimetric [26–32] methods have been proposed for determination of free chlorine in waters. 2

To demonstrate application of the proposed approach to the case of chlorine determination, in this paper, silver triangular nanoplates (AgTNPs) were chosen as the nanoreagent. There is evidence that AgTNPs are most subjected to action of some oxidants, e.g. hydrogen peroxide [33]. They possess an intense absorption in the long-wave spectral region which can be strongly affected by state of the particles and their morphology [34]. These effects have been applied for development of various analytical methods [27, 35–37]. Among them, an assay for chlorine can be also found [27]. To sum up, the aim of this work is to develop a novel approach towards the highly selective detection using metal nanoparticles, based on combination of optical detection and dynamic gas extraction, which is demonstrated by the example of chlorine determination in highly salted aqueous solutions using AgTNPs.

2. Materials and methods 2.1. Reagents and instruments The following reagents were used in the study: silver nitrate, sodium citrate, polyvinylpyrrolidone, hydrogen peroxide, sodium borohydride, sulfuric acid, hydrochloric acid, potassium permanganate. All the reagents were at least of analytical grade. Working solutions of the substances were prepared by dissolving their weighed portions or aliquots and dilution in deionized water obtained using Millipore Simplicity water purification system (Merk Millipore). For preparation of paper test strips modified with AgTNPs, the paper Whatman Grade 113 (Whatman International Ltd) was used. Chlorine stock solution was prepared by bubbling gaseous chlorine obtained by a reaction of hydrochloric acid with potassium permanganate through water. The concentration of chlorine was established by iodometric titration. Working standard chlorine solutions were prepared by dilution of the stock solution immediately before use. Absorption spectra of solutions were recorded by SF-103 spectrophotometer (Akvilon, Russia), diffuse reflectance measurements were carried out using Eye-One Pro minispectrophotometer (X-Rite) [38, 39] on a white base. The measured diffuse reflectance coefficient values (R) were recalculated in terms of the Kubelka–Munk function by the formula F = (1-R)2/(2R). Paper strips were scanned using Canon CanoScan LiDE 210 (Canon) on a white background with the resolution of 300 ppi. The scanned images were processed in Adobe Photoshop 7.0 graphical editor in the RGB mode by averaging RGB color coordinates of individual pixels within the round test zone. TEM-images were recorded using transmission electron microscope Libra 200 (Zeiss, Germany) at the accelerating voltage of 200 kV, the limit of information in bright field 3

transmission microscopy registration mode is better than 0.1 nm. Dispersions of the AgTNPs samples in hexane/heptane were deposited onto copper grid support with a formvar film covered by amorphous carbon Formvar®/Carbon Reinforced Copper Grids 3440C-MB (SPI, USA). Scanning electron microscopic studies of paper test strips microstructure were carried out using scanning electron microscope Jeol JSM 7100 F (Jeol, Japan) at the accelerating voltage of 10 kV. Recording SEM images was performed with a detector of back reflected electrons at the low vacuum operation mode. Dynamic gas extraction was processed using a setup represented in Fig. 1. It included a glass vessel for analyzed solution (1) closed with a rubber stopper (2), a test strips holder (3) with a test strip grasped (4), an air microcompressor (5) connected via a polymer hose (6) with a glass bubbler (7) sealed in the vessel.

2.2. Preparation of AgTNPs Synthesis of AgTNPs was performed as described [40] with minor modifications. Glassware used in the synthesis was pre-washed with freshly prepared "aqua regia", thoroughly rinsed with distilled water and air-dried. A 0.5 mL portion of 0.01 M silver nitrate aqueous solution was diluted with 4.1 mL of deionized water. Then 2.3 mL of 1% sodium citrate aqueous solution, 0.6 mL of 20 g L-1 polyvinylpyrrolidone aqueous solution and 1.2 mL of 3% hydrogen peroxide aqueous solution were successively added under vigorous stirring. Then 1.0 mL of a freshly prepared 0.1 M sodium borohydride aqueous solution was dropwisely added to the solution under stirring. Mixture got pale yellow-green color, which half an hour later abruptly changed to intense emerald-green and then to blue-violet. The stirring was stopped. The asprepared AgTNPs colloidal solution was stored at room temperature. The final concentration of AgTNPs in the solution was 56 μg mL-1 (0.52 mmol L-1 in terms of silver atoms), which was calculated based on the introduced silver amount assuming quantitative yield of the product.

2.3. Preparation of paper test strips modified with AgTNPs Deposition of AgTNPs onto the paper was performed as follows. A 1.5 mL portion of two times diluted AgTNPs solution was placed into a Petri dish. A paper disk of Whatman Grade 113 was placed to cover the solution portion. This was accompanied by rapid and quite uniform distribution of the solution across the paper. Then the Petri dish was placed on an electric hot plate and dried in air at ~ 80 °C. The operation was repeated until the desired content of AgTNPs on the paper was achieved. The modified paper was cut into test strips and fitted inside the test strips holder. The content of AgTNPs on paper was calculated based on the added total amount of AgTNPs solution. 4

2.4. Procedure A standard solution of chlorine or an analyzed sample of 100 mL was placed into the glass vessel of the dynamic gas extraction setup. A 2 mL portion of concentrated sulfuric acid was added to the solution. The vessel was firmly closed with the stopper with attached test strips holder containing the AgTNPs modified test strip. The air microcompressor was turned on and the air was bubbled through the solution with the volume velocity of 2.8 L min-1 during 20 min. Then the test strip was withdrawn and scanned. The saved image file was analyzed in terms of R,G,B-color coordinates.

3. Results and discussion 3.1. Principle of the approach A principle that underlies the proposed approach to improving selectivity of metal nanoparticles with respect to volatile compounds is based on spatial separation of the nanoparticles from interfering ions and other non-volatile compounds by air barrier. The proposed approach is based on gas separation without using membrane. This concept is associated to the principle of membraneless gas separation developed by Phansi et al. [41]. In fact, it can be assumed as a gaseous membrane between an analyzed solution and a nanoparticle containing sensing material. It should be stressed that the approach proposed in this article is applicable only to analytes able to penetrate this gaseous membrane, that is volatile compounds. The dynamic regime of the setup operation enables simultaneous detection of analytes by the sensing layer and easy control of sensitivity by changing the operation time. In case of chlorine, the air stream extracts gaseous chlorine from the acidified solution under analyzing and carries it to the paper modified with AgTNPs. The reaction of chlorine with immobilized AgTNPs results in their oxidation and appearing a white spot on the test strip. The decrease of the color intensity can be correlated with the concentration of chlorine in the solution.

3.2. Characterization of AgTNPs and paper modified with AgTNPs Spectrophotometric measurements revealed that synthesized in this study AgTNPs have an intense absorption band associated with the surface plasmon resonance with the maximum at 610 nm (Fig. 2a). A TEM study was done to estimate parameters of AgTNPs. An example of the TEM image is shown in Fig. 2b. According to the evaluation of the TEM images, it was found that the AgTNPs edge length is 50 nm (standard deviation = 12 nm), whereas their thickness is 5

3.6 nm (standard deviation = 0.8 nm). The AgTNPs colloidal aqueous solution is stable and retains their spectral characteristics practically unaltered for at least 1 month. For preparing paper modified with AgTNPs we proposed an impregnation method [42]. Its advantages are simplicity, ease of AgTNPs amount control on paper, rapidity of a procedure, which is a result of prompt AgTNPs solution distribution over paper and quick water evaporation at 80 °C. It is important that the AgTNPs spectral characteristics are preserved during described above modification. Like AgTNP colloids, the modified papers are stable for at least 1 month. As it can be seen from Fig. 2c, a diffuse reflectance spectrum of the modified paper contains an absorption band similar to the solution. SEM image of the modified paper reveals Ag nanoparticles distributed on the surface of paper fibers (Fig. 2d). Availability of AgTNPs on the fiber surface and preserving their optical properties are significant features allowing application the resulting test strips for rapid optical detection.

3.3. Interaction of paper modified with AgTNPs with chlorine Interaction of AgTNPs on paper with chlorine was performed using dynamic gas extraction setup described above. In this study, paper test strips modified with 3 different amounts of AgTNPs (0.09; 0.18 and 0.27 mg g-1) were used. The concentration of chlorine in solution was varied from 0 to 2 mg L-1. It was shown that this interaction results in discoloration of the paper due to oxidation of AgTNPs. Results of electron probe microanalysis show that a zone of chlorine passing through the paper contains 3 times greater chlorine amount (0.16 mmol g-1) compared to a zone that had no contact with chlorine gas (0.05 mmol g-1). The increase in chlorine content reaches ~ 0.11 mmol g-1, which is 40 times greater than amount of AgTNPs in terms of silver. This indicates intense absorption of chlorine by paper during the dynamic gas extraction. Discoloration of AgTNPs-modified paper can be monitored by scanning the papers and calculating corresponding RGB color coordinates using common image processing software. This process leads to increasing all the three color coordinates as represented in Fig. 3. It was found that dependence of RGB color coordinates on the concentration of chlorine can be adequately described by first order exponential equation similar to one proposed in our previous works [43]: y  y0  Ae c t , where y is R, G or B color coordinate, c is the concentration of an analyte, y0, A and t – regression parameters. According to [43] a criterion for choosing the most sensitive color coordinate for analytical applications is maximum of A/t ratio. In case of chlorine, A/t ratios were 290, 260 and 165 for R, G and B color coordinates, respectively. This indicates that the most sensitive color coordinate is R. This coordinate was used as an analytical response in all further experiments. 6

An important parameter affecting sensitivity of chloride detection and determination range is amount of AgTNPs on the paper. It was demonstrated that when the amount of AgNPs on the paper is decreased, the A/t ratio is also linearly decreased (Fig. 4), which makes sensitivity worse and determination range narrow. Extrapolation of this linear dependence to xaxis results in the AgTNPs amount of about 0.06 mg g-1, which can be considered as the lower limit of AgTNPs amount making detection of chlorine by the proposed method possible. Table 1 summarizes some analytical features of the method with test strips containing different amounts of AgTNPs. Limit of detection (LOD) values were calculated as 3s0/(A/t), where s0 – standard deviation of R color coordinate for the blank. Based on these findings, the AgTNPs amount of 0.27 mg g-1 was chosen for selectivity study.

3.4. Selectivity study According to the proposed approach, non-volatile compounds, which don’t produce gaseous substances in acidic medium, shouldn’t affect AgTNPs on the paper. This was confirmed by study of colorimetric response of AgTNPs modified paper regarding 1 M solutions of some common salts: NaCl, ZnSO4, KH2PO4, Sr(NO3)2, (NH4)2C2O4, (NH4)2Cr2O7, BaCl2, and MnCl2. The results are represented in Fig. 5. They indicate that at least of 1 M concentration of Na+, K+, Sr2+, Ba2+, Mn2+, Zn2+, H2PO4–, SO42–, C2O42–, Cr2O72– and at least of 2 M concentration of NH4+, Cl–, NO3– produce insignificant effects, which are lower or comparable with the triple standard deviation of the blank, whereas Cl2 at the concentration of 4.2 μM produces a remarkable signal. An important fact to be noted is the absence of remarkable effect of such a strong oxidant as Cr2O72– (data point 4 in Fig. 5), which would affect AgTNPs while direct contacting. Another observation that can be derived from Fig. 5 is the increased response for the data points 5 and 6. Probable reason for this consists in two times higher concentration of Cl – in these solutions, which produce small amounts of HCl in the acidic medium, affecting AgNPs. To demonstrate possibility of chlorine determination in highly salted solutions by the proposed method, the determination of 0.3 mg L-1 chlorine was carried out in a solution containing 1 M NaCl, ZnSO4, and KH2PO4, which is more than 2∙105 times greater molar excess compared to the concentration of Cl2. The choice of these salts was made as they mostly contain common inorganic ions that abundantly present in various samples (except for Zn2+). The results (Table 2) indicate that the accuracy and precision of such a determination are adequate in spite of the high concentrations of salts. Comparison of the proposed method with other methods described in literature (Table 3) shows that it possesses an intermediate position regarding sensitivity and determination range, whereas its selectivity is superior compared to the reported in literature data. This proves good 7

prospects of the proposed approach based on dynamic gas extraction towards solving a problem of highly selective detection using metal nanoparticles.

4. Conclusion Prospects of combining nanoparticle-based optical detection with dynamic gas extraction towards solving a problem of highly selective detection using metal nanoparticles have been shown by the example of chlorine determination using silver triangular nanoplates. This approach is promising for determination of volatile compounds. It has been demonstrated that applied to chlorine, the proposed method allows for its determination in the presence of about 2∙105 molar excess of common ions, which makes it possible to analyze highly salted solutions with no any sample pretreatment. This method can be easily hyphenated with modern measuring techniques, such as digital colorimetry; it is effective, simple to perform and cheap.

Acknowledgements This work was supported by the Russian Foundation for Basic Research [grant number 15-33-70002 mol_a_mos].

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Table 1. Some analytical features of the method LOD, mg L-1

Amount of AgTNPs,

Determination

RSD, %

mg g-1

range, mg L-1

0.09

0.8–2

0.3

23

0.18

0.3–2

0.1

18

0.27

0.1–2

0.03

8

(for 0.3 mg L-1 Cl2)

Table 2. Determination of chlorine in 1 M solution of NaCl, ZnSO4, and KH2PO4 (P = 0.95, n = 3) Added Cl2, mg L-1

Found Cl2 ± tP,f∙s/√n,

Relative standard

Lower limit of

mg L-1

deviation, %

tolerance (mol/mol)

0

< LOD

–

–

0.3

0.35 ± 0.06

8

2∙105

12

Table 3. Comparison of the proposed method with other methods for determination of chlorine described in literature Method

LOD, μM

Determination

Tolerance

range, μM

limit

Reference

Most common commercially available test kits

1.0–2.4*

0–42 to 0–141

–

[17]

Voltammetry (Polymelamine-modified screen

5.5

10–7000

–

[18]

28

28–2800

–

[19]

0.044

9.9–215.2

~1

[20]

Voltammetry (Prussian Blue electrode)

0.11

0.35–42

~1

[21]

Electrical resistivity measurement (paper-

7.0

7–700 and

103

[22]

printed carbon electrode) Linear sweep voltammetry with inkjet printed silver electrodes Cyclic voltammetry (Polydopamine@electrochemically reduced graphene oxide-modified electrode)

based electrochemical sensor)

700–7000

Fluorimetry (Luminescent ZnO quantum dots)

0.041

0.05–0.7

~1

[23]

Fluorimetry (Amino-functionalized metal-

0.04

0.05–15

10

[24]

0.5

0.5–30 and 30– –

organic frameworks nanoplates-based energy transfer probe) Chemiluminescence (Poly(luminol)-based sensor) This study

[25]

110 0.42

1.4–28

* Calculated by us as 1/3 of the declared lower measurement increment

13

2∙105

–

14

Fig. 1. Setup for processing dynamic gas extraction: 1 – glass vessel for analyzed solution; 2 – rubber stopper; 3 – test strips holder; 4 – test strip; 5 – air microcompressor, 6 – polymer hose; 7 – glass bubbler (7).

a

b

A 0.45 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00 400

500

600

700 l, nm

c

d

F 0.6

0.5

0.4

0.3

0.2

0.1

0 400

500

600

700 l, nm

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Fig. 2. Absorption spectrum of AgTNPs in water colloid solution (a) and their TEM image (b) (the insert is ED pattern); diffuse reflectance spectrum of paper modified with AgTNPs (c) and its SEM image (d). cAgTNPs = 11 μg mL-1 (a, b) and 0.27 mg g-1 (c, d).

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y 250 240 230

B

BG R G R

220 210 200 190 180 170 0

0,5

1

1,5

c(Cl2), m g L

2

2,5

-1

Fig. 3. Dependence of the RGB color coordinates for paper modified with AgTNPs on the concentration of chlorine in the analyzed solution (the inserts are images of corresponding samples). cAgTNPs = 0.27 mg g-1.

A/t 350 y = 1424.8x - 90.569 R² = 0.9971

300 250 200 150 100 50 0 0

0.1 0.2 Amount of AgTNPs, mg g-1

0.3

Fig. 4. Dependence of A/t ratio on the amount of AgTNPs on the paper. Color coordinate – R.

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DR 45

4.2 μM Cl2

40 35 30 25 20

1 M salts solutions 15 10

3s0 level

5 0 1

2

3

4

5

6

7

Fig. 5. Increase of R color coordinate of AgTNPs modified paper with respect to the presence of 1 M salts compared to 4.2 μM Cl2 in the analyzed solution. 1-NaCl, ZnSO4, KH2PO4, 2Sr(NO3)2, 3-(NH4)2C2O4, 4-(NH4)2Cr2O7, 5-BaCl2, and 6-MnCl2. The horizontal line shows the level of triple standard deviation of the blank.

Highlights A novel approach improving selectivity of detection using nanoparticles is proposed

It combines optical detection using nanoparticle and dynamic gas extraction

Chlorine is detected in highly salted solutions using AgTNPs and digital colorimetry

Determination can be carried out at 2∙105 greater molar amounts of some ions

Approach seems to be compatible with different types of nanoparticles and analytes

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Graphical abstract

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