- Email: [email protected]
Sensitive detection of dopamine and quinone drugs based on the quenching of the fluorescence of carbon dots
Sci. Bull. DOI 10.1007/s11434-016-1172-1
www.scibull.com www.springer.com/scp
Article
Chemistry
Sensitive detection of dopamine and quinone drugs based on the quenching of the fluorescence of carbon dots Xiangling Ren • Jiejie Ge • Xianwei Meng • Xiaozhong Qiu • Jun Ren • Fangqiong Tang
Received: 8 July 2016 / Revised: 12 August 2016 / Accepted: 31 August 2016 Ó Science China Press and Springer-Verlag Berlin Heidelberg 2016
Abstract In this work, we demonstrated that the quinone structure can quench the fluorescence of the carbon dots (CDs). The sensitive determination of dopamine (DA) was studied primarily based on this principle. DA would be transformed into DA quinone under alkaline conditions, which resulted in fluorescence quenching of the CDs. A good linear range from 5 nmol/L to 0.4 mmol/L was obtained and the detection limit was 1 nmol/L. Moreover, the quenching effect of quinone structure on the fluorescence of CDs was confirmed by Fourier transform infrared spectra, time-correlated single-photon counting and X-ray photoelectron spectroscopy. Remarkably, CDs were firstly applied to detect the quinone drugs quantitatively which contained typical quinone structure based on the quenching mechanism. More than this, the sensing platform was demonstrated to provide credible selectivity and satisfactory stability in human serum solution with good liner
Xiangling Ren and Jiejie Ge contributed equally to this work.
Electronic supplementary material The online version of this article (doi:10.1007/s11434-016-1172-1) contains supplementary material, which is available to authorized users. X. Ren J. Ge X. Meng (&) J. Ren F. Tang Laboratory of Controllable Preparation and Application of Nanomaterials, Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China e-mail: [email protected] J. Ge X. Qiu (&) Department of Anatomy, Guangdong Provincial Key Laboratory of Construction and Detection in Tissue Engineering, Southern Medical University, Guangzhou 510515, China e-mail: [email protected]
range. Hence, our practical application and mechanism have showed great potential for diagnostic purposes. Keywords Carbon dots Quinone structure Detection Dopamine Quinone drugs
1 Introduction The dopamine (DA) is a significant catecholamine neurotransmitter which plays an important role in the operation of the renal, hormonal, cardiovascular systems and central nervous especially [1, 2]. Abnormal DA concentrations in the brain may result in serious diseases [3] such as Parkinsonism [4], where DA levels are reduced, and schizophrenia [5], which can be related to excess DA activity. Actually, precise DA determination was becoming more and more necessary in many cases. Many different methods have been developed to detect DA, including electrochemistry [6], electrophoresis, colorimetry and high performance liquid chromatography (HPLC) analysis [7]. An amperometric nanobiosensor containing graphene oxide (GO) and gold nanoparticles was developed by Mir et al. [8] to observe dopamine released from living cells. Saylor et al. [9] reported a method for the separation and detection of analytes in the dopamine metabolic pathway was developed using microchip electrophoresis with electrochemical detection. However, electrophoretic and colorimetric methods were limited by the low sensitivity or the low selectivity [10]. HPLC and electrochemical methods need expensive equipment or complicated procedures. Thus, a facile, fast, low cost, selective and sensitive method for the detection of DA is rather essential.
123
Sci. Bull.
Recently, the fluorescent detection has attracted many attentions of researchers for its advantages, such as facile operation, low cost, real-time, rapid and good reproducibility [11]. The new classes of fluorescent carbon dots (CDs) [12], as a promising alternative to toxic metal-based QDs, have received excellent research interest due to their huge availability, high stability against photobleaching and blinking, remarkable chemical stability, eco-friendly and good for biological applications [13]. CDs were designed to detect metal ions, glutathione, nitrite, phosphate, a-fetoprotein and glucose, etc. Unfortunately, some of these detecting process needed to be assisted by medium due to small amounts of sensitive substance directly quench the fluorescence of CDs. Our previous article [13] has reported using CDs to detect acetylcholinesterase (AChE) based on adding Fe2? as a medium. The CDs which was prepared by Cui et al. [14] need be labeled on the oligonucleotide to detect Hg2?. This would make the detection system more complex. Therefore, searching more substances, which are sensitive to the fluorescence of CDs, and further studying its mechanism are highly desired. Recently, there were reports that the fluorescence of CDs were quenched by some analytes directly. Baruah et al. [15] prepared the carbon dots sizes of 0.8 nm from tea and found the carbon dots were quenched in the presence of dopamine and ascorbic acid, the minimum detectable limits were determined to be 33 and 98 lmol/L for dopamine and ascorbic acid, respectively. Ni et al. [16] found that the fluorescence of the CDs was quenched by hydroquinone (H2Q) directly and built a novel biosensor based on CDs for sensitive detection of H2Q with a detection limit down to 0.1 lmol/L. However, the detection limits in their reports were relatively high and their possible quenching mechanism was not deep enough. Herein, we found that the quinone structure quickly and sensitively effected on the fluorescence of CDs. The fluorescence of CDs were quenched when DA was transformed into DA quinone under alkaline condition. A good detection linear range for DA was achieved with a low detection limit of 1 nmol/L. This system is very convenient, simple and rapid, because it avoids the complex process of the CDs’ modification or immobilization. Moreover, the CDs were firstly used to response to quinone drugs based on the principle, such as mitoxantrone (MTZ) and doxorubicin (DOX). Under optimum condition, the fluorescence of CDs versus MTZ or DOX concentration showed a good linear response. The biosensor showed good selectivity and the DA and DOX assays were also successfully realized in human serum solution with satisfactory results. Therefore, this work was not only put forward broader application of CDs in detection of biological molecules, but also provide a new perspective on the foundations of the theory for the following further bio-application.
123
2 Materials and methods 2.1 Materials All the reagents for the synthesis of CDs were used as received throughout the work. Reactants citric acid and ethylenediamine were purchased from commercial supplier (Sigma-Aldrich). Metal ion aqueous solutions (Ag?, Na?, K?, Cu2?, Mg2?, Ca2?, Zn2?, Pb2? and Al3?) were prepared from their nitrate salts. Anion sodium solution (Cl-, S2-, COOH-, NO2-, NO3-, CO32-, Br- and SO32-) and all the metal salts have been obtained from Xilong Chemical Co. and were used without further purification. Buffer solutions were prepared using Na2CO3 and NaHCO3, proper amount of aqueous NaOH and HCl under adjustment by a pH meter. 2.2 Synthesis of CDs CDs were prepared by hydrothermal method with citric acid as the carbon source, and ethylenediamine as the coreactant according to the previous method [17]. Briefly, 1.10 g citric acid and 335 lL ethylenediamine was dissolved in 10 mL deionized water. Then the mixture was transferred to a hydrothermal synthesis reactor and heated at 200 °C for 5 h. After the reaction, the reactors were cooled down to room temperature by water. 2.3 Fluorescence quenching of CDs by DA Firstly, CDs (5 lL) was mixed with 0.05 mmol/L DA in 2 mL buffer solution (pH 7.00, 8.00, 9.16, 10.83) of four different pH value and the fluorescent spectra of the mixture at room temperature were recorded under 350 nm excitation over 10 min. Then, CDs were quenched by certain amounts of DA (0, 0.000001, 0.0001, 0.001, 0.005, 0.02, 0.05, 0.08, 0.1, 0.2, 0.3, 0.4 mmol/L) in optimal pH condition. The mixtures were equilibrated at room temperature for 15 min before the fluorescence spectra measurements were recorded. 2.4 Fluorescence quenching of CDs by pbenzoquinone In a typical test, 5 lL CDs was diluted into 2 mL buffer solution (pH 7.00) containing 0.1 mmol/L p-benzoquinone (pBQ) and the fluorescent spectra of the reaction system were measured over time. After that, a series concentration of pBQ (0, 0.025, 0.05, 0.1, 0.15, 0.25, 0.4, 0.5 mmol/L) was mixed with certain CDs and quenching trend was recorded with an excitation wavelength of 350 nm. The mixtures were equilibrated at room temperature for 1 min
Sci. Bull.
before the fluorescence spectra measurements were recorded. 2.5 Fluorescence quenching of CDs by MTZ and DOX The two typical antineoplastic drugs, MTZ and DOX, which have quinone structure like benzoquinone were picked up to quench the fluorescence of CDs at different levels. The experiment method was same as the detection of pBQ above. MTZ and DOX (diluted by aqueous solution) of different concentrations (0, 5, 10, 25, 40, 50, 75, 100, 150, 200 lg/mL) and (0, 0.4, 0.5, 1, 2.5, 5, 10, 15, 25, 40, 50, 60, 75, 100 lg/mL) were added into each of the CDs solutions, respectively. The fluorescence spectra were recorded with an excitation wavelength of 350 nm. The mixtures were equilibrated at room temperature for 5 min before the fluorescence spectra measurements were recorded.
measurements were placed in a 10 mm optical path length quartz fluorescence cuvette. Fluorescence decay time measurement was performed on a Horiba Jobin–Yvon Fluorolog-3-TCSPC spectrophotometer. Fourier transform infrared (FT-IR) spectra were determined on a Thermo Scientific Nicoled iS 50 in the region 4,000–400 cm-1. The X-ray photoelectron spectroscopy (XPS) measurements were performed on an ESCALAB-MKII 250 photoelectron spectrometer with Al Ka as the X-ray source for excitation. 2.9 Data statistics The calibration curve result was accepted according to the relative fluorescence intensity, that is, I/I0, in which I and I0 are the maximum emission intensities of the mixture in the presence and absence of quinone structure, respectively. Data are presented as mean ± SE (standard error) of three independent experiments.
2.6 Anti-interference of detection To investigate the selectivity of CDs towards quinone structure, the fluorescence response to other relevant metal ions including 50 lmol/L metal ion aqueous solutions (Ag?, Na?, K?, Cu2?, Mg2?, Ca2?, Zn2?, Pb2? and Al3?) which were prepared from their nitrate salts and 500 lmol/L anions sodium solution (Cl-, S2-, COOH-, NO2-, NO3-, CO32-, Br- and SO32-) were tested and the fluorescence spectra were recorded. 2.7 Detection in serum solution The fluorescent spectra of CDs in human serum solution were tested through following proposal. A 50 lL human serum was diluted 2 mL buffer solution containing 5 lL CDs and different concentrations of DA or DOX. A series of concentrations DA (0, 0.05, 0.1, 0.2, 0.3, 0.4 mmol/L) were added to the serum solution (pH 9.16) and the change trend of fluorescent spectra was collected by fluorescence spectrophotometer with an excitation wavelength of 350 nm. Similarly, various amounts of DOX (0, 20, 30, 40, 50, 60 lg/mL) were dissolved in aqueous solution containing human serum and the fluorescent spectra change trend was collected under an excitation wavelength of 350 nm. 2.8 Instrumentation Fluorescence measurements were carried out on a Cary Eclipse fluorescence spectrophotometer (Varian Inc.). The emission spectra of CDs were recorded upon excitation at 350 nm. The exciting slit and the emission slit were 5 and 5 nm, respectively. The samples for the fluorescence
3 Results and discussion 3.1 DA detection using CDs as fluorescent probes To study the effect of pH on the detection system of CDs towards DA, CDs were used to response to 0.05 mmol/L DA over time in the solution of different pH values (pH 7.00, 8.00, 9.16, 10.83). As shown in the Fig. 1a, the fluorescent intensity hold constant when the pH values were 7.00 and 8.00. There was an empirical evidence that a typical time-dependent fluorescence quenching of CDs was displayed in the solution of pH 9.16 and 10.83, and that the fluorescent intensity at 420 nm decreased by more than 15 % (pH 9.16) and more than 40 % (pH 10.83) within 10 min. The results suggested that DA quenched the fluorescence of CDs under alkaline conditions. Considering the poly-dopamine was usually formed when DA was under high pH value [18, 19], the lower pH value (pH 9.16) was preferred. The detection range was investigated at pH 9.16 which was showed in the Fig. 1b. The results clearly exhibited the influence of increasing DA concentrations (0–0.4 mmol/L) on the fluorescence intensity of CDs at 440 nm, and the intensity decreased by 60 % within 5 min via the addition of 0.2 mmol/L DA. The values were formed a good liner relationship between the range of 5 nmol/L–0.4 mmol/L (R2 = 0.99) showed in the Fig. 1c with a detection limit of 1 nmol/L after experimental conditions were optimized. Such situation was also observed by several other papers [20]. As can be observed from Table 1, the CDs showed advantageous linear range and detection limit towards the sensitive determination of DA.
123
Sci. Bull.
Fig. 1 (Color online) a Fluorescent changes of CDs in the solution containing 0.05 mmol/L DA under different pH conditions. b The dosedependent of DA on the fluorescent intensity of CDs. c The corresponding change of fluorescence intensity of CDs solution versus the concentration of DA. d DA was oxidized to DA quinone under the alkaline buffer solution Table 1 The detection limits and linear ranges of different materials and methods for the determination of DA Materials
Techniques
Linear range
AuNPs/Trp-GR
DVP
0.5–411 lmol/L
56 nmol/L
[21]
PCHAGCE
DVP
1–40 lmol/L
149 nmol/L
[22]
rGO/AgNT
SERS
2.5–500 lmol/L
1.2 lmol/L
[23]
BSA-AuNCs
Fluo
10 nmol/L–1 lmol/L
10 nmol/L
[2]
AuNPs
Color
33 nmol/L–3.33 mmol/L
33 nmol/L
[24]
CDs
Fluo
5 nmol/L–0.4 mmol/L
1 nmol/L
This paper
3.2 Detection of quinone structure The mechanism of the DA detection system using CDs was further investigated. As shown in the inset of Fig. 1c, it was observed that DA in the alkaline solution would display deeper brown with the increasing of the concentration of DA. It was suggested that DA had a reaction in alkaline condition and the product affected the fluorescence of CDs. As previously reported, DA was easily oxidized to quinone by ambient O2 in basic solutions [3, 25]. Therefore, we suspected that the brown material mentioned above was DA quinone, and the structural changing process was showed in the Fig. 1d. In the detection system, the fluorescent intensity of CDs
123
LOD
Reference
decreased over time in the existence of increasing DA quinone. Quinone structure exists widely in the organism and it is known that naturally occurring quinones play an essential role in electron transport in bacterial reaction center and mitochondria [26, 27]. Therefore, it is important to understand the influence of quinone structure on the fluorescence of CDs. The following experiment was designed using pBQ, which was the simplest quinone molecule, to study and verify the quenching fluorescence of CDs by the quinone structure. Firstly, influence of incubation time on the CDs-pBQ system was studied. When pBQ was added to the CDs solution, the fluorescent intensities of CDs decreased at once and remained constant (Fig. S1 online). Therefore, the pBQ directly
Sci. Bull.
Fig. 2 (Color online) a The fluorescent spectra of CDs response to different concentrations of PBQ. b Two linear range-ships between the concentrations of pBQ with the fluorescent intensity of CDs
Fig. 3 a TCSPC of CDs and CDs ? pBQ (375 nm excitation, delay time at 420 nm emission); b FT-IR of CDs before and after the effect of pBQ; XPS high resolution scan of the N 1s region of CDs (c) and CDs with pBQ (d); XPS high resolution scan of the O 1s region of CDs (e) and CDs with pBQ (f)
influenced the fluorescence of CDs. As shown in Fig. 2, the fluorescent intensity of CDs decreased gradually with the increasing concentrations of pBQ in aqueous solution, and a good linear relationships were obtained between the fluorescent intensity and the concentration of pBQ over the range of 0–2.5 mmol/L (R2 = 0.98). The results showed the quinone structure really had a special effect on the fluorescence of CDs.
3.3 Possible mechanism of the quenching To get further insight into the PL quenching mechanism, TCSPC was used to study the radiation behavior of CDs in the presence and absence of pBQ, as shown in the Fig. 3a. The decay time of CDs was 13.47 ns and has three lifetime components of 1.05 ns (*2.4 %), 15.99 ns (*70.7 %) and 7.98 ns (*26.9 %). After coordination with pBQ, the
123
Sci. Bull.
CDs/pBQ decay time decreased to 11.02 ns. Moreover, the fast decay component increased sharply: 13.16 ns (*77.3 %), 4.3 ns (*19.3 %) and 0.35 ns (*3.4 %). The significantly reduced lifetime indicated an ultrafast CDs/ pBQ electron-transfer process and led to dynamic quenching. The FT-IR absorption peaks of CDs with function of pBQ before and after were also characterized which showed in Fig. 3b. The results exhibited several characteristic bands on CDs: stretching vibrations of C–OH at 3,430 cm-1, asymmetric stretching vibrations of C–NH–C at 1,125 cm-1, bending vibrations of N–H at 1,565 cm-1, the vibrational absorption band of C=O at 1,642–1,697 cm-1, the absorption peaks at 1,508 and 1,400 cm-1 were assigned to the stretching vibrations of the C=C and O=C–O vibrations, respectively. The existence of strong absorption bands of O–H, COO- and N–H suggested that there were plenty of amine and carboxylic groups on the surface of CDs. The surface properties of CDs together with pBQ were also investigated, in which characteristic absorption bands of O=C–O, C=C, N–H groups had obvious variation. It was illustrated that the surface groups of CDs had been effected by the pBQ. XPS is a sensitive tool to analyze the atomic composition of the surface nanometre of a sample [28]. So it was also used to further analyze the chemical constitution of the CDs when the pBQ was presence and absence. As shown in Fig. S2 (online), the results displayed the CDs contained three major elements carbon (C 1s), nitrogen (N 1s) and oxygen (O 1s) with a relative proportion of 59.18 %, 10.23 % and 30.59 %, respectively. When the pBQ was presence, the relative proportion became 52.08 %, 10.64 % and 37.28 %. Here it was found the proportion of O 1s was increased obviously. The C 1s spectrum of CDs was deconvoluted into three peaks (Fig. S3a online) at 284.7, 286.2 and 288.5 eV, indicating the presence of various types of carbon bonds: C–C, C–O and C=O. The C 1s spectrum of CDs with pBQ (Fig. S3b online) also had these three peaks, and the peaks of C–O and C=O bonds increased compared with the peak of C–C bond. The N 1s spectrum of CDs was deconvoluted into two peaks (Fig. 3c) indicating the presence of two types of nitrogen bonds: C–N–C (400.4 eV) and N–H (402.0 eV). Interestingly, when the pBQ was existence the peak of N 1s spectrum (Fig. 3d) at N–H (401.6 eV) was increased significantly. It was indicated that the state of N–H groups on the surface of CDs have changed. The high-resolution O 1s spectrum of CDs (Fig. 3e) showed two peaks detected at 531.8 and 532.9 eV, which were attributed to C=O and C– OH/C–O–C groups, respectively [29]. And the peak of C=O group (located at 531.5 eV) decreased obviously after the pBQ was introduced (Fig. 3f). So the results of FT-IR and XPS spectra showed that the pBQ influenced the N–H
123
Scheme 1 (Color online) CDs was quenched by quinone structure
and C=O groups on the surface of CDs and led to the dynamic quenching. As shown in the Scheme 1, the quinone structure adsorbed onto the surface of CDs, and had interaction with N–H and C=O groups of CDs to quench the fluorescence of CDs. Hence, the principle was applied to realize the detection for the substance containing quinone structure. 3.4 Quinone drugs detection Due to the unique properties of quinone, which plays an important role in life activities, it already has been concerned widely by biologists, chemists and other universal in the field of science [30]. Recently, with the development of pharmacology, the quinone drugs attracted more and more attention [31], which have function of hemostasis, antibacterial, purgation and dieresis [32]. Moreover, it was found that the quinone drugs inhibit obviously the proliferation of tumor cells in vitro and the growth of tumor cells in vivo [33]. Quinone drugs, such as MTZ and DOX, have gotten more and more attention and rapid development [34]. Therefore, it became more necessary to develop new methods of quantitative analysis for the drugs both in vivo and in vitro. It was known that the HPLC was used commonly to analyze drugs content [35]. However, the HPLC need high cost and complicated procedures. There are few researchers focusing on the convenient fluorescent method for analysis of medicine. Based on the above fluorescence detection of quinine structure using CDs as shown in the Scheme 1, the MTZ and DOX were detected sensitively by decreasing the fluorescent intensity of CDs. An empirical
Sci. Bull.
Fig. 4 (Color online) The fluorescent spectra of CDs detection of MTZ (a) and liner ship between them (b). The fluorescent spectra of CDs detection of DOX (c) and liner ship between them and color changes in the experiment and a series concentration of DOX mixed with CDs under UV-light (365 nm) in the inset (d)
evidence was shown in Fig. 4a, which displayed a typical dose-dependent fluorescence quenching of CDs in the presence of MTZ (0–200 lg/mL) and a good liner relationship (0–50 lg/mL) (Fig. 4b) was formed just like detection of pBQ. DOX was another anti-cancer drug containing quinone structure. According the above theory, quinone structure influenced the surface groups of CDs, different levels of DOX also quenched the fluorescent intensity of CDs. As shown in the Fig. 4c, the detect range was investigated from 0 to 100 lg/mL and have a good linear range (0.5–25 lg/mL) with a low detection limit (Fig. 4d). Interestingly, it was also important to point out that DOX displayed its fluorescent characteristic spectrum at 590 nm always, and the fluorescence intensity would be enhanced with the increase of the DOX concentration. A series concentration of DOX mixed with equal CDs under UV-light (365 nm) was showed in the inset of Fig. 4d. The fluorescence of CDs at 440 nm was quenched with the concentration of DOX increased and the fluorescence of DOX at 590 nm was increased. Actually, a fluorescence ratio probe was formed through the two fluorescence spectra of DOX and CDs, and that the concentration of DOX was analyzed more precisely.
The results showed that CDs not only detected DA but also were qualitative of the quinone drugs like DOX and MTZ. It was believed that the experiment provided a practical fluorescence method for subsequent drug dosing and monitoring, which was helpful for clinical treatment. 3.5 Selectivity of detection To verify the selectivity of the as-prepared CDs, the influences of representative metallic ions and ionic strength on their fluorescent intensity have been measured. As shown in Fig. S4 (online), the fluorescent changes of CDs with 50 lmol/L of different metal ions (Fig. S4a online) was little and present only a slight quenching effect in solutions at a high ionic strength of 500 lmol/L sodium salt (Fig. S4b online). 3.6 Detecting in human serum solution The probe CDs was used to detecting DA and DOX in the human serum solution. As shown in the Fig. S5 (online), the CDs could be quenched successfully by DA in the
123
Sci. Bull.
human serum solution and good liner (Fig. S5a, b online) was formed. Similarly, the DOX was detected by CDs with a good liner in serum solution, which was showed in the Fig. S5c, d (online). The results verified the CDs could be used successfully to analyze DA and quinone drugs in human serum solution due to their properties of good stability, eco-friendly and anti-interference. Therefore, their remarkable advantages support potential future application on biomolecule fast analysis.
4 Conclusions In summary, we have successfully introduced a convenient optical method for the detection of DA based on quenching the fluorescent intensity of CDs. The detection mechanism has been discovered that the fluorescence quenching of CDs was caused by quinine structure. And through a series of characterization, the reason for quenching was analyzed that due to the interaction of quinine structure on C=O and N–H groups of CDs. The DOX and MTZ, which containing typical quinone structure, were quantitatively recognized according to the mechanism. The proposed method was successfully applied to the determination of DA and DOX in serum solution. Therefore, it was believed that this theory and practice would build a strong foundation for further biological applications. Acknowledgments This work was supported by the National Natural Science Foundation of China (61178035, 61571426, 61671435, 81671845, 81630053, 51428301, and 31572343), the National High Technology R&D Program of China (2015BAI23H01) and Beijing Natural Science Foundation (4161003). Conflict of interest The authors declare that they have no conflict of interest.
References 1. Tang L, Li S, Han F et al (2015) SERS-active Au@Ag nanorod dimers for ultrasensitive dopamine detection. Biosens Bioelectron 71:7–12 2. Tao Y, Lin Y, Ren J et al (2013) A dual fluorometric and colorimetric sensor for dopamine based on BSA-stabilized Au nanoclusters. Biosens Bioelectron 42:41–46 3. Bisaglia M, Filograna R, Beltramini M et al (2014) Are dopamine derivatives implicated in the pathogenesis of Parkinson’s disease? Ageing Res Rev 13:107–114 4. Dawson TM, Dawson VL (2003) Molecular pathways of neurodegeneration in Parkinson’s disease. Science 302:819–822 5. Kang J, Zhuo L, Lu X et al (2004) Electrochemical behavior of dopamine at a quercetin-SAM-modified gold electrode and analytical application. J Solid State Electrochem 9:114–120 6. Jiang YL, Wang BX, Meng FD et al (2015) Microwave-assisted preparation of N-doped carbon dots as a biosensor for electrochemical dopamine detection. J Colloid Interface Sci 452:199–202
123
7. Maaswinkel H, Puppala D, Mason B et al (2004) In vivo microdialysis and HPLC detection of retinal dopamine release in zebrafish. Invest Ophthalmol Vis Sci 45:625 8. Mir TA, Akhtar MH, Gurudatt NG et al (2015) An amperometric nanobiosensor for the selective detection of K?-induced dopamine released from living cells. Biosens Bioelectron 68:421–428 9. Saylor RA, Reid EA, Lunte SM (2015) Microchip electrophoresis with electrochemical detection for the determination of analytes in the dopamine metabolic pathway. Electrophoresis 36: 1912–1919 10. Salamon J, Sathishkumar Y, Ramachandran K et al (2015) Onepot synthesis of magnetite nanorods/graphene composites and its catalytic activity toward electrochemical detection of dopamine. Biosens Bioelectron 64:269–276 11. Li LH, Shi W, Wang Z et al (2015) Sensitive fluorescence probe with long analytical wavelengths for gamma-glutamyl transpeptidase detection in human serum and living cells. Anal Chem 87:8353–8359 12. Mehta VN, Jha S, Singhal RK et al (2014) Preparation of multicolor emitting carbon dots for HeLa cell imaging. New J Chem 38:6152–6160 13. Ren X, Wei J, Ren J et al (2015) A sensitive biosensor for the fluorescence detection of the acetylcholinesterase reaction system based on carbon dots. Colloids Surf B 125:90–95 14. Cui X, Zhu L, Wu J et al (2015) A fluorescent biosensor based on carbon dots-labeled oligodeoxyribonucleotide and graphene oxide for mercury(II) detection. Biosens Bioelectron 63:506–512 15. Baruah U, Gogoi N, Konwar A et al (2014) Carbon dot based sensing of dopamine and ascorbic acid. J Nanopart 2014:178518 16. Ni P, Dai H, Li Z et al (2015) Carbon dots based fluorescent sensor for sensitive determination of hydroquinone. Talanta 144:258–262 17. Zhu S, Meng Q, Wang L et al (2013) Highly photoluminescent carbon dots for multicolor patterning, sensors, and bioimaging. Angew Chem Int Ed 52:3953–3957 18. Ho CC, Ding SJ (2013) The pH-controlled nanoparticles size of polydopamine for anti-cancer drug delivery. J Mater Sci Mater Med 24:2381–2390 19. Postma A, Yan Y, Wang Y et al (2009) Self-polymerization of dopamine as a versatile and robust technique to prepare polymer capsules. Chem Mater 21:3042–3044 20. Hu M, Tian J, Lu HT et al (2010) H2O2-sensitive quantum dots for the label-free detection of glucose. Talanta 82:997–1002 21. Lian Q, Luo A, An Z et al (2015) Au nanoparticles on tryptophan-functionalized graphene for sensitive detection of dopamine. Appl Surface Sci 349:184–189 22. Li XB, Rahman MM, Xu GR et al (2015) Highly sensitive and selective detection of dopamine at poly(chromotrope 2B)-modified glassy carbon electrode in the presence of uric acid and ascorbic acid. Electrochim Acta 173:440–447 23. Luo YH, Ma L, Zhang XH et al (2015) SERS detection of dopamine using label-free acridine red as molecular probe in reduced graphene oxide/silver nanotriangle sol substrate. Nanoscale Res Lett 10:230–239 24. Chen ZB, Zhang CM, Zhou TH et al (2015) Gold nanoparticle based colorimetric probe for dopamine detection based on the interaction between dopamine and melamine. Microchim Acta 182:1003–1008 25. Liu Q, Wang NY, Caro J et al (2013) Bio-inspired polydopamine: a versatile and powerful platform for covalent synthesis of molecular sieve membranes. J Am Chem Soc 135:17679–17682 26. Gautam BPS, Srivastava M, Prasad RL et al (2014) Synthesis, characterization and quantum chemical investigation of molecular structure and vibrational spectra of 2,5-dichloro-3,6-bis(methylamino)1,4-benzoquinone. Spectrochim Acta A 129:241–254
Sci. Bull. 27. Stokes SE, Winn LM (2014) NF-kB signaling is increased in HD3 cells following exposure to 1,4-benzoquinone: role of reactive oxygen species and p38-MAPK. Toxicol Sci 137:303–310 28. Shi Y, Pan Y, Zhang H et al (2014) A dual-mode nanosensor based on carbon quantum dots and gold nanoparticles for discriminative detection of glutathione in human plasma. Biosens Bioelectron 56:39–45 29. Song L, Cui Y, Zhang C et al (2016) Microwave-assisted facile synthesis of yellow fluorescent carbon dots from o-phenylenediamine for cell imaging and sensitive detection of Fe3? and H2O2. RSC Adv 6:17704–17712 30. Morales P, Blasco-Benito S, Andradas C et al (2015) Selective, nontoxic CB2 cannabinoid o-quinone with in vivo activity against triple-negative breast cancer. J Med Chem 58: 2256–2264 31. Aguilo JI, Iturralde M, Monleon I et al (2012) Cytotoxicity of quinone drugs on highly proliferative human leukemia T cells:
32.
33.
34.
35.
reactive oxygen species generation and inactive shortened SOD1 isoform implications. Chem Biol Interact 198:18–28 Simamura E, Shimada H, Ishigaki Y et al (2008) Bioreductive activation of quinone antitumor drugs by mitochondrial voltagedependent anion channel 1. Anat Sci Int 83:261–266 Celli CM, Tran N, Knox R et al (2006) NRH: quinone oxidoreductase 2 (NQO2) catalyzes metabolic activation of quinones and anti-tumor drugs. Biochem Pharmacol 72:366–376 Van Boxtel W, Bulten BF, Mavinkurve-Groothuis AMC et al (2015) New biomarkers for early detection of cardiotoxicity after treatment with docetaxel, doxorubicin and cyclophosphamide. Biomarkers 20:143–148 Itoh N, Santa T, Kato M (2015) Rapid evaluation of the quantity of drugs encapsulated within nanoparticles by high-performance liquid chromatography in a monolithic silica column. Anal Bioanal Chem 407:6429–6434
123
www.scibull.com www.springer.com/scp
Article
Chemistry
Sensitive detection of dopamine and quinone drugs based on the quenching of the fluorescence of carbon dots Xiangling Ren • Jiejie Ge • Xianwei Meng • Xiaozhong Qiu • Jun Ren • Fangqiong Tang
Received: 8 July 2016 / Revised: 12 August 2016 / Accepted: 31 August 2016 Ó Science China Press and Springer-Verlag Berlin Heidelberg 2016
Abstract In this work, we demonstrated that the quinone structure can quench the fluorescence of the carbon dots (CDs). The sensitive determination of dopamine (DA) was studied primarily based on this principle. DA would be transformed into DA quinone under alkaline conditions, which resulted in fluorescence quenching of the CDs. A good linear range from 5 nmol/L to 0.4 mmol/L was obtained and the detection limit was 1 nmol/L. Moreover, the quenching effect of quinone structure on the fluorescence of CDs was confirmed by Fourier transform infrared spectra, time-correlated single-photon counting and X-ray photoelectron spectroscopy. Remarkably, CDs were firstly applied to detect the quinone drugs quantitatively which contained typical quinone structure based on the quenching mechanism. More than this, the sensing platform was demonstrated to provide credible selectivity and satisfactory stability in human serum solution with good liner
Xiangling Ren and Jiejie Ge contributed equally to this work.
Electronic supplementary material The online version of this article (doi:10.1007/s11434-016-1172-1) contains supplementary material, which is available to authorized users. X. Ren J. Ge X. Meng (&) J. Ren F. Tang Laboratory of Controllable Preparation and Application of Nanomaterials, Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China e-mail: [email protected] J. Ge X. Qiu (&) Department of Anatomy, Guangdong Provincial Key Laboratory of Construction and Detection in Tissue Engineering, Southern Medical University, Guangzhou 510515, China e-mail: [email protected]
range. Hence, our practical application and mechanism have showed great potential for diagnostic purposes. Keywords Carbon dots Quinone structure Detection Dopamine Quinone drugs
1 Introduction The dopamine (DA) is a significant catecholamine neurotransmitter which plays an important role in the operation of the renal, hormonal, cardiovascular systems and central nervous especially [1, 2]. Abnormal DA concentrations in the brain may result in serious diseases [3] such as Parkinsonism [4], where DA levels are reduced, and schizophrenia [5], which can be related to excess DA activity. Actually, precise DA determination was becoming more and more necessary in many cases. Many different methods have been developed to detect DA, including electrochemistry [6], electrophoresis, colorimetry and high performance liquid chromatography (HPLC) analysis [7]. An amperometric nanobiosensor containing graphene oxide (GO) and gold nanoparticles was developed by Mir et al. [8] to observe dopamine released from living cells. Saylor et al. [9] reported a method for the separation and detection of analytes in the dopamine metabolic pathway was developed using microchip electrophoresis with electrochemical detection. However, electrophoretic and colorimetric methods were limited by the low sensitivity or the low selectivity [10]. HPLC and electrochemical methods need expensive equipment or complicated procedures. Thus, a facile, fast, low cost, selective and sensitive method for the detection of DA is rather essential.
123
Sci. Bull.
Recently, the fluorescent detection has attracted many attentions of researchers for its advantages, such as facile operation, low cost, real-time, rapid and good reproducibility [11]. The new classes of fluorescent carbon dots (CDs) [12], as a promising alternative to toxic metal-based QDs, have received excellent research interest due to their huge availability, high stability against photobleaching and blinking, remarkable chemical stability, eco-friendly and good for biological applications [13]. CDs were designed to detect metal ions, glutathione, nitrite, phosphate, a-fetoprotein and glucose, etc. Unfortunately, some of these detecting process needed to be assisted by medium due to small amounts of sensitive substance directly quench the fluorescence of CDs. Our previous article [13] has reported using CDs to detect acetylcholinesterase (AChE) based on adding Fe2? as a medium. The CDs which was prepared by Cui et al. [14] need be labeled on the oligonucleotide to detect Hg2?. This would make the detection system more complex. Therefore, searching more substances, which are sensitive to the fluorescence of CDs, and further studying its mechanism are highly desired. Recently, there were reports that the fluorescence of CDs were quenched by some analytes directly. Baruah et al. [15] prepared the carbon dots sizes of 0.8 nm from tea and found the carbon dots were quenched in the presence of dopamine and ascorbic acid, the minimum detectable limits were determined to be 33 and 98 lmol/L for dopamine and ascorbic acid, respectively. Ni et al. [16] found that the fluorescence of the CDs was quenched by hydroquinone (H2Q) directly and built a novel biosensor based on CDs for sensitive detection of H2Q with a detection limit down to 0.1 lmol/L. However, the detection limits in their reports were relatively high and their possible quenching mechanism was not deep enough. Herein, we found that the quinone structure quickly and sensitively effected on the fluorescence of CDs. The fluorescence of CDs were quenched when DA was transformed into DA quinone under alkaline condition. A good detection linear range for DA was achieved with a low detection limit of 1 nmol/L. This system is very convenient, simple and rapid, because it avoids the complex process of the CDs’ modification or immobilization. Moreover, the CDs were firstly used to response to quinone drugs based on the principle, such as mitoxantrone (MTZ) and doxorubicin (DOX). Under optimum condition, the fluorescence of CDs versus MTZ or DOX concentration showed a good linear response. The biosensor showed good selectivity and the DA and DOX assays were also successfully realized in human serum solution with satisfactory results. Therefore, this work was not only put forward broader application of CDs in detection of biological molecules, but also provide a new perspective on the foundations of the theory for the following further bio-application.
123
2 Materials and methods 2.1 Materials All the reagents for the synthesis of CDs were used as received throughout the work. Reactants citric acid and ethylenediamine were purchased from commercial supplier (Sigma-Aldrich). Metal ion aqueous solutions (Ag?, Na?, K?, Cu2?, Mg2?, Ca2?, Zn2?, Pb2? and Al3?) were prepared from their nitrate salts. Anion sodium solution (Cl-, S2-, COOH-, NO2-, NO3-, CO32-, Br- and SO32-) and all the metal salts have been obtained from Xilong Chemical Co. and were used without further purification. Buffer solutions were prepared using Na2CO3 and NaHCO3, proper amount of aqueous NaOH and HCl under adjustment by a pH meter. 2.2 Synthesis of CDs CDs were prepared by hydrothermal method with citric acid as the carbon source, and ethylenediamine as the coreactant according to the previous method [17]. Briefly, 1.10 g citric acid and 335 lL ethylenediamine was dissolved in 10 mL deionized water. Then the mixture was transferred to a hydrothermal synthesis reactor and heated at 200 °C for 5 h. After the reaction, the reactors were cooled down to room temperature by water. 2.3 Fluorescence quenching of CDs by DA Firstly, CDs (5 lL) was mixed with 0.05 mmol/L DA in 2 mL buffer solution (pH 7.00, 8.00, 9.16, 10.83) of four different pH value and the fluorescent spectra of the mixture at room temperature were recorded under 350 nm excitation over 10 min. Then, CDs were quenched by certain amounts of DA (0, 0.000001, 0.0001, 0.001, 0.005, 0.02, 0.05, 0.08, 0.1, 0.2, 0.3, 0.4 mmol/L) in optimal pH condition. The mixtures were equilibrated at room temperature for 15 min before the fluorescence spectra measurements were recorded. 2.4 Fluorescence quenching of CDs by pbenzoquinone In a typical test, 5 lL CDs was diluted into 2 mL buffer solution (pH 7.00) containing 0.1 mmol/L p-benzoquinone (pBQ) and the fluorescent spectra of the reaction system were measured over time. After that, a series concentration of pBQ (0, 0.025, 0.05, 0.1, 0.15, 0.25, 0.4, 0.5 mmol/L) was mixed with certain CDs and quenching trend was recorded with an excitation wavelength of 350 nm. The mixtures were equilibrated at room temperature for 1 min
Sci. Bull.
before the fluorescence spectra measurements were recorded. 2.5 Fluorescence quenching of CDs by MTZ and DOX The two typical antineoplastic drugs, MTZ and DOX, which have quinone structure like benzoquinone were picked up to quench the fluorescence of CDs at different levels. The experiment method was same as the detection of pBQ above. MTZ and DOX (diluted by aqueous solution) of different concentrations (0, 5, 10, 25, 40, 50, 75, 100, 150, 200 lg/mL) and (0, 0.4, 0.5, 1, 2.5, 5, 10, 15, 25, 40, 50, 60, 75, 100 lg/mL) were added into each of the CDs solutions, respectively. The fluorescence spectra were recorded with an excitation wavelength of 350 nm. The mixtures were equilibrated at room temperature for 5 min before the fluorescence spectra measurements were recorded.
measurements were placed in a 10 mm optical path length quartz fluorescence cuvette. Fluorescence decay time measurement was performed on a Horiba Jobin–Yvon Fluorolog-3-TCSPC spectrophotometer. Fourier transform infrared (FT-IR) spectra were determined on a Thermo Scientific Nicoled iS 50 in the region 4,000–400 cm-1. The X-ray photoelectron spectroscopy (XPS) measurements were performed on an ESCALAB-MKII 250 photoelectron spectrometer with Al Ka as the X-ray source for excitation. 2.9 Data statistics The calibration curve result was accepted according to the relative fluorescence intensity, that is, I/I0, in which I and I0 are the maximum emission intensities of the mixture in the presence and absence of quinone structure, respectively. Data are presented as mean ± SE (standard error) of three independent experiments.
2.6 Anti-interference of detection To investigate the selectivity of CDs towards quinone structure, the fluorescence response to other relevant metal ions including 50 lmol/L metal ion aqueous solutions (Ag?, Na?, K?, Cu2?, Mg2?, Ca2?, Zn2?, Pb2? and Al3?) which were prepared from their nitrate salts and 500 lmol/L anions sodium solution (Cl-, S2-, COOH-, NO2-, NO3-, CO32-, Br- and SO32-) were tested and the fluorescence spectra were recorded. 2.7 Detection in serum solution The fluorescent spectra of CDs in human serum solution were tested through following proposal. A 50 lL human serum was diluted 2 mL buffer solution containing 5 lL CDs and different concentrations of DA or DOX. A series of concentrations DA (0, 0.05, 0.1, 0.2, 0.3, 0.4 mmol/L) were added to the serum solution (pH 9.16) and the change trend of fluorescent spectra was collected by fluorescence spectrophotometer with an excitation wavelength of 350 nm. Similarly, various amounts of DOX (0, 20, 30, 40, 50, 60 lg/mL) were dissolved in aqueous solution containing human serum and the fluorescent spectra change trend was collected under an excitation wavelength of 350 nm. 2.8 Instrumentation Fluorescence measurements were carried out on a Cary Eclipse fluorescence spectrophotometer (Varian Inc.). The emission spectra of CDs were recorded upon excitation at 350 nm. The exciting slit and the emission slit were 5 and 5 nm, respectively. The samples for the fluorescence
3 Results and discussion 3.1 DA detection using CDs as fluorescent probes To study the effect of pH on the detection system of CDs towards DA, CDs were used to response to 0.05 mmol/L DA over time in the solution of different pH values (pH 7.00, 8.00, 9.16, 10.83). As shown in the Fig. 1a, the fluorescent intensity hold constant when the pH values were 7.00 and 8.00. There was an empirical evidence that a typical time-dependent fluorescence quenching of CDs was displayed in the solution of pH 9.16 and 10.83, and that the fluorescent intensity at 420 nm decreased by more than 15 % (pH 9.16) and more than 40 % (pH 10.83) within 10 min. The results suggested that DA quenched the fluorescence of CDs under alkaline conditions. Considering the poly-dopamine was usually formed when DA was under high pH value [18, 19], the lower pH value (pH 9.16) was preferred. The detection range was investigated at pH 9.16 which was showed in the Fig. 1b. The results clearly exhibited the influence of increasing DA concentrations (0–0.4 mmol/L) on the fluorescence intensity of CDs at 440 nm, and the intensity decreased by 60 % within 5 min via the addition of 0.2 mmol/L DA. The values were formed a good liner relationship between the range of 5 nmol/L–0.4 mmol/L (R2 = 0.99) showed in the Fig. 1c with a detection limit of 1 nmol/L after experimental conditions were optimized. Such situation was also observed by several other papers [20]. As can be observed from Table 1, the CDs showed advantageous linear range and detection limit towards the sensitive determination of DA.
123
Sci. Bull.
Fig. 1 (Color online) a Fluorescent changes of CDs in the solution containing 0.05 mmol/L DA under different pH conditions. b The dosedependent of DA on the fluorescent intensity of CDs. c The corresponding change of fluorescence intensity of CDs solution versus the concentration of DA. d DA was oxidized to DA quinone under the alkaline buffer solution Table 1 The detection limits and linear ranges of different materials and methods for the determination of DA Materials
Techniques
Linear range
AuNPs/Trp-GR
DVP
0.5–411 lmol/L
56 nmol/L
[21]
PCHAGCE
DVP
1–40 lmol/L
149 nmol/L
[22]
rGO/AgNT
SERS
2.5–500 lmol/L
1.2 lmol/L
[23]
BSA-AuNCs
Fluo
10 nmol/L–1 lmol/L
10 nmol/L
[2]
AuNPs
Color
33 nmol/L–3.33 mmol/L
33 nmol/L
[24]
CDs
Fluo
5 nmol/L–0.4 mmol/L
1 nmol/L
This paper
3.2 Detection of quinone structure The mechanism of the DA detection system using CDs was further investigated. As shown in the inset of Fig. 1c, it was observed that DA in the alkaline solution would display deeper brown with the increasing of the concentration of DA. It was suggested that DA had a reaction in alkaline condition and the product affected the fluorescence of CDs. As previously reported, DA was easily oxidized to quinone by ambient O2 in basic solutions [3, 25]. Therefore, we suspected that the brown material mentioned above was DA quinone, and the structural changing process was showed in the Fig. 1d. In the detection system, the fluorescent intensity of CDs
123
LOD
Reference
decreased over time in the existence of increasing DA quinone. Quinone structure exists widely in the organism and it is known that naturally occurring quinones play an essential role in electron transport in bacterial reaction center and mitochondria [26, 27]. Therefore, it is important to understand the influence of quinone structure on the fluorescence of CDs. The following experiment was designed using pBQ, which was the simplest quinone molecule, to study and verify the quenching fluorescence of CDs by the quinone structure. Firstly, influence of incubation time on the CDs-pBQ system was studied. When pBQ was added to the CDs solution, the fluorescent intensities of CDs decreased at once and remained constant (Fig. S1 online). Therefore, the pBQ directly
Sci. Bull.
Fig. 2 (Color online) a The fluorescent spectra of CDs response to different concentrations of PBQ. b Two linear range-ships between the concentrations of pBQ with the fluorescent intensity of CDs
Fig. 3 a TCSPC of CDs and CDs ? pBQ (375 nm excitation, delay time at 420 nm emission); b FT-IR of CDs before and after the effect of pBQ; XPS high resolution scan of the N 1s region of CDs (c) and CDs with pBQ (d); XPS high resolution scan of the O 1s region of CDs (e) and CDs with pBQ (f)
influenced the fluorescence of CDs. As shown in Fig. 2, the fluorescent intensity of CDs decreased gradually with the increasing concentrations of pBQ in aqueous solution, and a good linear relationships were obtained between the fluorescent intensity and the concentration of pBQ over the range of 0–2.5 mmol/L (R2 = 0.98). The results showed the quinone structure really had a special effect on the fluorescence of CDs.
3.3 Possible mechanism of the quenching To get further insight into the PL quenching mechanism, TCSPC was used to study the radiation behavior of CDs in the presence and absence of pBQ, as shown in the Fig. 3a. The decay time of CDs was 13.47 ns and has three lifetime components of 1.05 ns (*2.4 %), 15.99 ns (*70.7 %) and 7.98 ns (*26.9 %). After coordination with pBQ, the
123
Sci. Bull.
CDs/pBQ decay time decreased to 11.02 ns. Moreover, the fast decay component increased sharply: 13.16 ns (*77.3 %), 4.3 ns (*19.3 %) and 0.35 ns (*3.4 %). The significantly reduced lifetime indicated an ultrafast CDs/ pBQ electron-transfer process and led to dynamic quenching. The FT-IR absorption peaks of CDs with function of pBQ before and after were also characterized which showed in Fig. 3b. The results exhibited several characteristic bands on CDs: stretching vibrations of C–OH at 3,430 cm-1, asymmetric stretching vibrations of C–NH–C at 1,125 cm-1, bending vibrations of N–H at 1,565 cm-1, the vibrational absorption band of C=O at 1,642–1,697 cm-1, the absorption peaks at 1,508 and 1,400 cm-1 were assigned to the stretching vibrations of the C=C and O=C–O vibrations, respectively. The existence of strong absorption bands of O–H, COO- and N–H suggested that there were plenty of amine and carboxylic groups on the surface of CDs. The surface properties of CDs together with pBQ were also investigated, in which characteristic absorption bands of O=C–O, C=C, N–H groups had obvious variation. It was illustrated that the surface groups of CDs had been effected by the pBQ. XPS is a sensitive tool to analyze the atomic composition of the surface nanometre of a sample [28]. So it was also used to further analyze the chemical constitution of the CDs when the pBQ was presence and absence. As shown in Fig. S2 (online), the results displayed the CDs contained three major elements carbon (C 1s), nitrogen (N 1s) and oxygen (O 1s) with a relative proportion of 59.18 %, 10.23 % and 30.59 %, respectively. When the pBQ was presence, the relative proportion became 52.08 %, 10.64 % and 37.28 %. Here it was found the proportion of O 1s was increased obviously. The C 1s spectrum of CDs was deconvoluted into three peaks (Fig. S3a online) at 284.7, 286.2 and 288.5 eV, indicating the presence of various types of carbon bonds: C–C, C–O and C=O. The C 1s spectrum of CDs with pBQ (Fig. S3b online) also had these three peaks, and the peaks of C–O and C=O bonds increased compared with the peak of C–C bond. The N 1s spectrum of CDs was deconvoluted into two peaks (Fig. 3c) indicating the presence of two types of nitrogen bonds: C–N–C (400.4 eV) and N–H (402.0 eV). Interestingly, when the pBQ was existence the peak of N 1s spectrum (Fig. 3d) at N–H (401.6 eV) was increased significantly. It was indicated that the state of N–H groups on the surface of CDs have changed. The high-resolution O 1s spectrum of CDs (Fig. 3e) showed two peaks detected at 531.8 and 532.9 eV, which were attributed to C=O and C– OH/C–O–C groups, respectively [29]. And the peak of C=O group (located at 531.5 eV) decreased obviously after the pBQ was introduced (Fig. 3f). So the results of FT-IR and XPS spectra showed that the pBQ influenced the N–H
123
Scheme 1 (Color online) CDs was quenched by quinone structure
and C=O groups on the surface of CDs and led to the dynamic quenching. As shown in the Scheme 1, the quinone structure adsorbed onto the surface of CDs, and had interaction with N–H and C=O groups of CDs to quench the fluorescence of CDs. Hence, the principle was applied to realize the detection for the substance containing quinone structure. 3.4 Quinone drugs detection Due to the unique properties of quinone, which plays an important role in life activities, it already has been concerned widely by biologists, chemists and other universal in the field of science [30]. Recently, with the development of pharmacology, the quinone drugs attracted more and more attention [31], which have function of hemostasis, antibacterial, purgation and dieresis [32]. Moreover, it was found that the quinone drugs inhibit obviously the proliferation of tumor cells in vitro and the growth of tumor cells in vivo [33]. Quinone drugs, such as MTZ and DOX, have gotten more and more attention and rapid development [34]. Therefore, it became more necessary to develop new methods of quantitative analysis for the drugs both in vivo and in vitro. It was known that the HPLC was used commonly to analyze drugs content [35]. However, the HPLC need high cost and complicated procedures. There are few researchers focusing on the convenient fluorescent method for analysis of medicine. Based on the above fluorescence detection of quinine structure using CDs as shown in the Scheme 1, the MTZ and DOX were detected sensitively by decreasing the fluorescent intensity of CDs. An empirical
Sci. Bull.
Fig. 4 (Color online) The fluorescent spectra of CDs detection of MTZ (a) and liner ship between them (b). The fluorescent spectra of CDs detection of DOX (c) and liner ship between them and color changes in the experiment and a series concentration of DOX mixed with CDs under UV-light (365 nm) in the inset (d)
evidence was shown in Fig. 4a, which displayed a typical dose-dependent fluorescence quenching of CDs in the presence of MTZ (0–200 lg/mL) and a good liner relationship (0–50 lg/mL) (Fig. 4b) was formed just like detection of pBQ. DOX was another anti-cancer drug containing quinone structure. According the above theory, quinone structure influenced the surface groups of CDs, different levels of DOX also quenched the fluorescent intensity of CDs. As shown in the Fig. 4c, the detect range was investigated from 0 to 100 lg/mL and have a good linear range (0.5–25 lg/mL) with a low detection limit (Fig. 4d). Interestingly, it was also important to point out that DOX displayed its fluorescent characteristic spectrum at 590 nm always, and the fluorescence intensity would be enhanced with the increase of the DOX concentration. A series concentration of DOX mixed with equal CDs under UV-light (365 nm) was showed in the inset of Fig. 4d. The fluorescence of CDs at 440 nm was quenched with the concentration of DOX increased and the fluorescence of DOX at 590 nm was increased. Actually, a fluorescence ratio probe was formed through the two fluorescence spectra of DOX and CDs, and that the concentration of DOX was analyzed more precisely.
The results showed that CDs not only detected DA but also were qualitative of the quinone drugs like DOX and MTZ. It was believed that the experiment provided a practical fluorescence method for subsequent drug dosing and monitoring, which was helpful for clinical treatment. 3.5 Selectivity of detection To verify the selectivity of the as-prepared CDs, the influences of representative metallic ions and ionic strength on their fluorescent intensity have been measured. As shown in Fig. S4 (online), the fluorescent changes of CDs with 50 lmol/L of different metal ions (Fig. S4a online) was little and present only a slight quenching effect in solutions at a high ionic strength of 500 lmol/L sodium salt (Fig. S4b online). 3.6 Detecting in human serum solution The probe CDs was used to detecting DA and DOX in the human serum solution. As shown in the Fig. S5 (online), the CDs could be quenched successfully by DA in the
123
Sci. Bull.
human serum solution and good liner (Fig. S5a, b online) was formed. Similarly, the DOX was detected by CDs with a good liner in serum solution, which was showed in the Fig. S5c, d (online). The results verified the CDs could be used successfully to analyze DA and quinone drugs in human serum solution due to their properties of good stability, eco-friendly and anti-interference. Therefore, their remarkable advantages support potential future application on biomolecule fast analysis.
4 Conclusions In summary, we have successfully introduced a convenient optical method for the detection of DA based on quenching the fluorescent intensity of CDs. The detection mechanism has been discovered that the fluorescence quenching of CDs was caused by quinine structure. And through a series of characterization, the reason for quenching was analyzed that due to the interaction of quinine structure on C=O and N–H groups of CDs. The DOX and MTZ, which containing typical quinone structure, were quantitatively recognized according to the mechanism. The proposed method was successfully applied to the determination of DA and DOX in serum solution. Therefore, it was believed that this theory and practice would build a strong foundation for further biological applications. Acknowledgments This work was supported by the National Natural Science Foundation of China (61178035, 61571426, 61671435, 81671845, 81630053, 51428301, and 31572343), the National High Technology R&D Program of China (2015BAI23H01) and Beijing Natural Science Foundation (4161003). Conflict of interest The authors declare that they have no conflict of interest.
References 1. Tang L, Li S, Han F et al (2015) SERS-active Au@Ag nanorod dimers for ultrasensitive dopamine detection. Biosens Bioelectron 71:7–12 2. Tao Y, Lin Y, Ren J et al (2013) A dual fluorometric and colorimetric sensor for dopamine based on BSA-stabilized Au nanoclusters. Biosens Bioelectron 42:41–46 3. Bisaglia M, Filograna R, Beltramini M et al (2014) Are dopamine derivatives implicated in the pathogenesis of Parkinson’s disease? Ageing Res Rev 13:107–114 4. Dawson TM, Dawson VL (2003) Molecular pathways of neurodegeneration in Parkinson’s disease. Science 302:819–822 5. Kang J, Zhuo L, Lu X et al (2004) Electrochemical behavior of dopamine at a quercetin-SAM-modified gold electrode and analytical application. J Solid State Electrochem 9:114–120 6. Jiang YL, Wang BX, Meng FD et al (2015) Microwave-assisted preparation of N-doped carbon dots as a biosensor for electrochemical dopamine detection. J Colloid Interface Sci 452:199–202
123
7. Maaswinkel H, Puppala D, Mason B et al (2004) In vivo microdialysis and HPLC detection of retinal dopamine release in zebrafish. Invest Ophthalmol Vis Sci 45:625 8. Mir TA, Akhtar MH, Gurudatt NG et al (2015) An amperometric nanobiosensor for the selective detection of K?-induced dopamine released from living cells. Biosens Bioelectron 68:421–428 9. Saylor RA, Reid EA, Lunte SM (2015) Microchip electrophoresis with electrochemical detection for the determination of analytes in the dopamine metabolic pathway. Electrophoresis 36: 1912–1919 10. Salamon J, Sathishkumar Y, Ramachandran K et al (2015) Onepot synthesis of magnetite nanorods/graphene composites and its catalytic activity toward electrochemical detection of dopamine. Biosens Bioelectron 64:269–276 11. Li LH, Shi W, Wang Z et al (2015) Sensitive fluorescence probe with long analytical wavelengths for gamma-glutamyl transpeptidase detection in human serum and living cells. Anal Chem 87:8353–8359 12. Mehta VN, Jha S, Singhal RK et al (2014) Preparation of multicolor emitting carbon dots for HeLa cell imaging. New J Chem 38:6152–6160 13. Ren X, Wei J, Ren J et al (2015) A sensitive biosensor for the fluorescence detection of the acetylcholinesterase reaction system based on carbon dots. Colloids Surf B 125:90–95 14. Cui X, Zhu L, Wu J et al (2015) A fluorescent biosensor based on carbon dots-labeled oligodeoxyribonucleotide and graphene oxide for mercury(II) detection. Biosens Bioelectron 63:506–512 15. Baruah U, Gogoi N, Konwar A et al (2014) Carbon dot based sensing of dopamine and ascorbic acid. J Nanopart 2014:178518 16. Ni P, Dai H, Li Z et al (2015) Carbon dots based fluorescent sensor for sensitive determination of hydroquinone. Talanta 144:258–262 17. Zhu S, Meng Q, Wang L et al (2013) Highly photoluminescent carbon dots for multicolor patterning, sensors, and bioimaging. Angew Chem Int Ed 52:3953–3957 18. Ho CC, Ding SJ (2013) The pH-controlled nanoparticles size of polydopamine for anti-cancer drug delivery. J Mater Sci Mater Med 24:2381–2390 19. Postma A, Yan Y, Wang Y et al (2009) Self-polymerization of dopamine as a versatile and robust technique to prepare polymer capsules. Chem Mater 21:3042–3044 20. Hu M, Tian J, Lu HT et al (2010) H2O2-sensitive quantum dots for the label-free detection of glucose. Talanta 82:997–1002 21. Lian Q, Luo A, An Z et al (2015) Au nanoparticles on tryptophan-functionalized graphene for sensitive detection of dopamine. Appl Surface Sci 349:184–189 22. Li XB, Rahman MM, Xu GR et al (2015) Highly sensitive and selective detection of dopamine at poly(chromotrope 2B)-modified glassy carbon electrode in the presence of uric acid and ascorbic acid. Electrochim Acta 173:440–447 23. Luo YH, Ma L, Zhang XH et al (2015) SERS detection of dopamine using label-free acridine red as molecular probe in reduced graphene oxide/silver nanotriangle sol substrate. Nanoscale Res Lett 10:230–239 24. Chen ZB, Zhang CM, Zhou TH et al (2015) Gold nanoparticle based colorimetric probe for dopamine detection based on the interaction between dopamine and melamine. Microchim Acta 182:1003–1008 25. Liu Q, Wang NY, Caro J et al (2013) Bio-inspired polydopamine: a versatile and powerful platform for covalent synthesis of molecular sieve membranes. J Am Chem Soc 135:17679–17682 26. Gautam BPS, Srivastava M, Prasad RL et al (2014) Synthesis, characterization and quantum chemical investigation of molecular structure and vibrational spectra of 2,5-dichloro-3,6-bis(methylamino)1,4-benzoquinone. Spectrochim Acta A 129:241–254
Sci. Bull. 27. Stokes SE, Winn LM (2014) NF-kB signaling is increased in HD3 cells following exposure to 1,4-benzoquinone: role of reactive oxygen species and p38-MAPK. Toxicol Sci 137:303–310 28. Shi Y, Pan Y, Zhang H et al (2014) A dual-mode nanosensor based on carbon quantum dots and gold nanoparticles for discriminative detection of glutathione in human plasma. Biosens Bioelectron 56:39–45 29. Song L, Cui Y, Zhang C et al (2016) Microwave-assisted facile synthesis of yellow fluorescent carbon dots from o-phenylenediamine for cell imaging and sensitive detection of Fe3? and H2O2. RSC Adv 6:17704–17712 30. Morales P, Blasco-Benito S, Andradas C et al (2015) Selective, nontoxic CB2 cannabinoid o-quinone with in vivo activity against triple-negative breast cancer. J Med Chem 58: 2256–2264 31. Aguilo JI, Iturralde M, Monleon I et al (2012) Cytotoxicity of quinone drugs on highly proliferative human leukemia T cells:
32.
33.
34.
35.
reactive oxygen species generation and inactive shortened SOD1 isoform implications. Chem Biol Interact 198:18–28 Simamura E, Shimada H, Ishigaki Y et al (2008) Bioreductive activation of quinone antitumor drugs by mitochondrial voltagedependent anion channel 1. Anat Sci Int 83:261–266 Celli CM, Tran N, Knox R et al (2006) NRH: quinone oxidoreductase 2 (NQO2) catalyzes metabolic activation of quinones and anti-tumor drugs. Biochem Pharmacol 72:366–376 Van Boxtel W, Bulten BF, Mavinkurve-Groothuis AMC et al (2015) New biomarkers for early detection of cardiotoxicity after treatment with docetaxel, doxorubicin and cyclophosphamide. Biomarkers 20:143–148 Itoh N, Santa T, Kato M (2015) Rapid evaluation of the quantity of drugs encapsulated within nanoparticles by high-performance liquid chromatography in a monolithic silica column. Anal Bioanal Chem 407:6429–6434
123