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Phenylboronic acid and dopamine as probe set for electrochemical detection of saccharides
Chinese Chemical Letters 24 (2013) 291–294
Contents lists available at SciVerse ScienceDirect
Chinese Chemical Letters journal homepage: www.elsevier.com/locate/cclet
Original article
Phenylboronic acid and dopamine as probe set for electrochemical detection of saccharides Jian Li *, Ya-Qin Sun, Yin-Mao Wei, Jian-Bin Zheng Institute of Analytical Science/Shaanxi Key Laboratory of Electroanalytical Chemistry, Northwest University, Xi’an 710069, China
A R T I C L E I N F O
A B S T R A C T
Article history: Received 6 December 2012 Received in revised form 5 January 2013 Accepted 18 January 2013 Available online 15 March 2013
A novel electrochemical approach for detection of saccharides via indicator displacement assay was presented. In this system, 2-fluorophenylboronic acid and dopamine (DA) were performed as probe set. The electrochemical properties of DA and the binding to 2-fluorophenylboronic acid in phosphate buffer at different pH values were investigated by cyclic voltammetry. After addition of fructose to the solution, a competition for the binding 2-fluorophenylboronic acid occurred that led to the release of the DA. The regenerate oxidation current of DA increased with increasing fructose concentration. Under optimized experimental conditions, the peak current was linearly related to fructose concentration in the range of 0.3–5.0 mmol/L with a detection limit of 0.1 mmol/L. In addition, the interaction between 2fluorophenylboronic acid and other cis-diol compounds such as glucose, galactose and mannose was investigated. ß 2013 Jian Li. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Electrochemistry Saccharides Dopamine Phenylboronic acid Indicator displacement assay
1. Introduction Considerable research has been focused on the detection of saccharides for such as clinical diagnoses, biochemical analyses and industrial process control [1]. Although some considerable progress regarding enzyme-modified electrodes have been made, some disadvantages, such as rigorous operating conditions, chemical instability and high cost still remain. Therefore, many non-enzymatic biosensors have been advocated [2,3]. It would be an alternative way to continuously monitor saccharides based on specific recognition of boronic acid derivatives to saccharides molecules. Phenylboronic acid (PBA) and its derivatives, ever since the discovery of their ability to rapidly form cyclic esters with cis 1,2- or 1,3-diols in aqueous media [4], have been extensively explored to develop various optical [5–7] and electrochemical [8,9] saccharide receptors. PBA is not electroactive, so it must be modified with redox active moieties for electrochemical sensing [10]. PBA-modified electrodes, as reagentless electrochemical sensors, have been successfully used to detect saccharides through potentiometric and voltammetric responses [11,12]. An indicator displacement assay has been reported for the detection of saccharides [13,14]. With these systems, analyte binding led to indicator displacement from the binding cavity,
* Corresponding author. E-mail address: [email protected] (J. Li).
which in turn yielded a signal modulation [13]. The advantage of this method is that the indicator is not covalently attached to receptor, and it is possible to change indicators at will. For example, PBA combined with Alizarin Red S (ARS) as a probe set had been used in optical saccharides sensors [7]. Schumacher had further investigated the recognition of saccharides using ARS as an electrochemical indicator. Upon addition of fructose, competition for the binding PBA occurred that led to the release of the ARS. The regenerated peak current of ARS was dependent on the added fructose concentration from 10 mmol/L to 50 mmol/L at the potential of 0.54 V or +0.42 V (vs. Ag/AgCl), respectively [15]. In the present study, a novel electrochemical approach for detection of saccharides applying the ensemble of 2-fluorophenylboronic acid and dopamine as the probe set was developed. There are three advantages of DA as an electrochemical indicator: (i) DA is sensitively detected by electrochemical methods, (ii) the affinity of 2-fluorophenylboronic acid for DA is lower than that of PBA–ARS, which benefits displacement of saccharides, and (iii) DA has relatively lower redox potential at around +0.20 V (vs. Ag/ AgCl), which makes the sensor resistant to interference from electroactive species. 2. Experimental Dopamine hydrochloride (DA, 98%) was purchased from Aladdin Chemistry Co., Ltd. 2-Fluorophenylboronic acid was obtained from Adamas Reagent Co., Ltd. (98%). D-Glucose, D-galactose, D-mannose
1001-8417/$ – see front matter ß 2013 Jian Li. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. http://dx.doi.org/10.1016/j.cclet.2013.01.051
[(Fig._1)TD$IG]
[(Fig._2)TD$IG]
J. Li et al. / Chinese Chemical Letters 24 (2013) 291–294
292
Fig. 1. Cyclic voltammograms recorded in PBS of 2.0 mmol/L DA with different 2fluorophenylboronic acid concentrations of (a) 0.0 mmol/L, (b) 0.5 mmol/L, (c) 1.0 mmol/L, (d) 1.5 mmol/L, and (e) 2.0 mmol/L. Scan rate: 100 mV/s.
and D-fructose were obtained from Xi’an Wolsen Bio-technology Co., Ltd. (99%, Xi’an, China). Nafion was obtained from Aldrich. The 0.1 mol/L phosphate buffered saline (PBS) was used as the supporting electrolyte and prepared from Na2HPO4 and KH2PO4. All other reagents were analytical reagent grade and double distilled water was used in experiments. Electrochemical experiments were recorded using a three electrode system controlled by CHI 660 electrochemical workstation (Shanghai Chenhua Instrument Co., Ltd., China), with a glassy carbon electrode (GCE, Ø = 3 mm) as a working electrode, an Ag/AgCl (3 mol/L KCl) reference electrode and a platinum counter electrode. 3. Results and discussion The redox behavior of DA in 0.1 mol/L PBS at pH 7.4 was investigated by cyclic voltammetry between 0.3 V and +0.8 V on the GCE. A pair of quasi-reversible redox peaks at +0.17 (P1) and 0.0 V (P2) corresponding to the electrochemical oxidation of dopamine and reduction of dopaminequinone was recorded (Fig. 1a). DA is oxidized to dopaminequinone, and the intramolecular cyclization of dopaminequinone leads to polymerization on the electrode surface [16], so the oxidation peak (P1) is significantly larger than the reduction peak (P2). After addition of 2fluorophenylboronic acid, a new pair of redox peaks (P3 and P4) was recorded at around +0.6 V (Fig. 1b–e), which was attributed to the formation of 2-fluorophenyl-boronic ester (Scheme 1). With 2fluorophenylboronic acid concentration increased, the peaks P1 emerged the positive shift and P2 emerged the negative shift decreased, whereas the peaks P3 and P4 increased (Fig. 1b–e). It is known that certain diols and boronic acids react together to form boronate esters, to an extent dependent upon the pH value of the solution [6]. In this section, the effect of pH value on the electrochemical behavior of the indicator displacement assay was investigated. The binding constant of the fructose boronate ester is lower than that of other saccharides already mentioned, so the fructose serviced as a typical analyte [8]. There was a pair of quasireversible redox peaks (P1 and P2) in the absence and presence of 2fluorophenylboronic acid in PBS (pH 5.3) of the given concentration DA (Fig. 2A). When fructose was added into the solution, there was almost no change in cyclic voltammograms. The results were attributed to the formation of 2-fluorophenylboronate ester which
Fig. 2. Cyclic voltammograms recorded in PBS of 2.0 mmol/L DA and 2.0 mmol/L 2fluorophenylboronic acid (solid line), containing 1.0 mmol/L fructose (dash line) with different pH values of (A) 5.3, (B) 7.4, and (C) 9.2. Scan rate: 100 mV/s.
was restrained in the acidic condition. To demonstrate the eligibility of the displacement assay, the study was also performed at pH 7.4 and 9.2 (Fig. 2B and C). After addition of 2-fluorophenylboronic acid, a new pair of redox peaks (P3 and P4) was recorded at around +0.6 V. When fructose was added, the currents of P3 and P4 decreased and the currents of P1 and P2 increased again due to the release of DA from 2-fluorophenylboronate ester and formation of the fructose boronate ester (Scheme 2). The increased response reached maximum at pH 9.2 because the formation of 2-fluorophenylboronate ester is optimal in basic aqueous media (Fig. 2C). However, the pH 7.4 was selected for further study because it more accurately reflects the environment in detecting saccharides. The indicator displacement assay for detection of fructose was performed by cyclic voltammetry. The current of peak P1 and P2 increased when different concentrations of fructose were added into PBS (pH 7.4) containing 0.1 mmol/L DA and 0.5 mmol/L
[(Schem_1)TD$FIG] OH
HO
O
B H2N
OH HO
F
H2N
OH H3O+
B
O F
Scheme 1. Schematic formation of cyclic phenylboronate ester via dopamine binding 2-fluorophenylboronic acid.
[(Schem_2)TD$FIG]
J. Li et al. / Chinese Chemical Letters 24 (2013) 291–294
OH
O H2 N
O
OH
O
OH
B
293
OH
B F
OH
O
saccharide
F
H2 N
OH
Scheme 2. Schematic representation of displacement assay for saccharides using dopamine as indicator.
2-fluorophenylboronic acid (Fig. 3). Because the oxidation product of DA leads to polymerization on the electrode and thus a gradual loss of the electrode activity [16], the peak P2 did not follow the concentration of fructose. The peak P4 showed no strict concentration dependence. Although the plot of the current change against the concentration of fructose showed a similar behavior for P1 and P3, the reproducibility of P1 was better. Given the above, the oxidation peaks P1 was used as analytical relevant signal to obtain the information. In order to investigate the effect of optimal concentration of the probe set on the displacement assay, a cyclic voltammetric experiment was carried out in a solution of 0.1 mmol/L DA containing 2-fluorophenylboronic acid from 0.1 to 0.9 mmol/L. The maximum current response was found when 0.5 mmol/L 2fluorophenylboronic acid was added in the presence of 1.0 mmol/L fructose (Fig. 4). Under optimized experimental conditions, the peak current was linearly related to fructose concentration in the range of 0.3–5.0 mmol/L with a detection limit of 0.1 mmol/L (Fig. 5d). This observation suggested that the positive impact on displacement by saccharides, ever since the binding constant of DA-PBA is comparatively smaller than that of ARS–PBA, resulting in more sensitive detection of fructose compared with previous report [15].
In addition, other saccharides already mentioned were also studied. All electrochemical measurements were performed as described earlier. Fig. 5a–c showed the currents of oxidation peaks P1 vs. the concentration of saccharides. The sensitivity of the approach was dependent on the saccharides with increasing binding constants following the order fructose > galactose mannose > glucose, as was identical with previous literature [6]. The amount of DA displacement is governed by the binding constant between 2fluorophenylboronic acid and different kinds of saccharides. The selectivity of the proposed electrochemical approach is not perfect in the mixture system. The linear range of the electrode is 0.5– 20.0 mmol/L for galactose and 0.5–30.0 mmol/L for mannose and 1.0–10.0 mmol/L for glucose (Fig. 6), which was comparable and even better than previously reported PBA based saccharides sensors [8,11,12,15,17], the results were listed in Table 1.
[(Fig._5)TD$IG]
[(Fig._3)TD$IG]
Fig. 5. The dependence of P1 current on the added concentration of saccharides including (a) glucose, (b) mannose, (c) galactose and (d) fructose, respectively.
Table 1 Comparison of detection range of PBA-based saccharides sensors. Sensor system Fig. 3. Cyclic voltammograms recorded in PBS of 0.1 mmol/L DA and 0.5 mmol/L 2fluorophenylboronic acid with different fructose concentrations of (a) 0.0 mmol/L, (b) 1.0 mmol/L, (c) 2.0 mmol/L, (d) 5.0 mmol/L, and (e) 10.0 mmol/L. Scan rate: 100 mV/s.
[(Fig._4)TD$IG]
Saccharides
Differential pulse voltammetry D-Fructose TIFAQ-PBA Potentiometry PABA
D-Glucose D-Fructose
Voltammetry MPBA
D-Fructose D-Mannose D-Glucose
DTBA-PBA
D-Fructose D-Mannose D-Glucose
Au-ATP-BA
D-Fructose D-Mannose D-Glucose
ARS–PBA DA-PBA Fig. 4. The calibration curve of the oxidation peaks P1 current vs. the different concentration of 2-fluorophenylboronic acid (0.1–0.9 mmol/L) in PBS (pH 7.4), with the presence of 0.1 mmol/L DA and 1.0 mmol/L fructose. Scan rate: 100 mV/s.
D-Fructose D-Fructose D-Galactose D-Mannose D-Glucose
Detection range (mmol/L) 1–200
Reference
[8]
3.4–40.8 3.4–40.8
[11]
3–100 10–300 30–300 0.3–30 3–300 3–300 0.1–100 0.1–100 0.1–50 10–50 0.3–5.0 0.5–20.0 0.5–30.0 1.0–10.0
[12]
[17]
[15] Present study
[(Fig._6)TD$IG]
J. Li et al. / Chinese Chemical Letters 24 (2013) 291–294
294
Fig. 6. The linear range curve of saccharides including (A) glucose, (B) mannose, (C) galactose and (D) fructose, respectively.
4. Conclusion In the present study, a novel electrochemical approach for the detection of saccharides based on 2-fluorophenylboronic acid and DA as the probe set was successfully developed. This approach showed salient features such as better sensitivity, simple operation and cost-effectiveness. It was promising for fabrication of nonenzymatic sensors for saccharides. Further investigations should be undertaken to screen the electrochemical indicator to enhance the sensitivity and develop a disposable sensor, which should be cheap, easily operated and of good quality. Acknowledgments This work was supported by the National Natural Science Foundation of China (No. 21075098), and Scientific Research Plan Projects of Shaanxi Provincial Department of Education (No. 09JK756). References [1] A. Heller, B. Feldman, Electrochemical glucose sensors and their applications in diabetes management, Chem. Rev. 108 (2008) 2482–2505. [2] Z.J. Luo, T.T. Han, L.L. Qu, X.Y. Wu, A ultrasensitive nonenzymatic glucose sensor based on Cu2O polyhedrons modified Cu electrode, Chin. Chem. Lett. 23 (2012) 953–956. [3] Y.Y. Song, D. Zhang, W. Gao, X.H. Xia, Nonenzymatic glucose detection by using a three-dimensionally ordered, macroporous platinum template, Chem. Eur. J. 17 (2005) 2177–2182.
[4] T.D. James, K.R.A.S. Sandanayake, S. Shinkai, Saccharide sensing with molecular receptors based on boronic acid, Angew. Chem. Int. Ed. Engl. 35 (1996) 1910– 1922. [5] G. Springsteen, B. Wang, Alizarin Red S as a general optical reporter for studying the binding of boronic acids with carbohydrates, Chem. Commun. (2001) 1608– 1609. [6] G. Springsteen, B. Wang, A detailed examination of boronic acid–diol complexation, Tetrahedron 58 (2002) 5291–5300. [7] J. Tan, H.F. Wang, X.P. Yan, Discrimination of saccharides with a fluorescent molecular imprinting sensor array based on phenylboronic acid functionalized mesoporous silica, Anal. Chem. 81 (2009) 5273–5280. [8] M. Shao, Y.M. Zhao, Phenylboronic acid-functionalized TTFAQ: modular synthesis and electrochemical recognition for saccharides, Tetrahedron Lett. 51 (2010) 2508–2511. [9] S.Q. Liu, B. Miller, A.C. Chen, Phenylboronic acid self-assembled layer on glassy carbon electrode for recognition of glycoprotein peroxidase, Electrochem. Commun. 7 (2005) 1232–1236. [10] S. Arimori, S. Ushiroda, L.M. Peter, et al., A modular electrochemical sensor for saccharides, Chem. Commun. (2002) 2368–2369. [11] E. Shoji, M.S. Freund, Potentiometric saccharide detection based on the pKa changes of poly(aniline boronic acid), J. Am. Chem. Soc. 124 (2002) 12486–12493. [12] S. Takahashi, J. Anzai, Phenylboronic acid monolayer-modified electrodes sensitive to sugars, Langmuir 21 (2005) 5102–5107. [13] S.L. Wiskur, H. Ait-Haddou, J.J. Lavigne, E.V. Anslyn, Teaching old indicators new tricks, Acc. Chem. Res. 34 (2001) 963–972. [14] B.T. Nguyen, E.V. Anslyn, Indicator-displacement assays, Coord. Chem. Rev. 250 (2006) 3118–3127. [15] S. Schumacher, T. Nagel, F.W. Scheller, N. Gajovic-Eichelmann, Alizarin Red S as an electrochemical indicator for saccharide recognition, Electrochim. Acta 56 (2011) 6607–6611. [16] Y.L. Li, M.L. Liu, C.H. Xiang, Q.J. Xie, S.Z. Yao, Electrochemical quartz crystal microbalance study on growth and property of the polymer deposit at gold electrodes during oxidation of dopamine in aqueous solutions, Thin Solid Films 497 (2006) 270–278. [17] Y.Q. Zhao, H.Q. Luo, N.B. Li, Electrochemical characterization of in situ functionalized gold p-aminothiophenol self-assembled monolayer with 4-formylphenylboronic acid for recognition of sugars, Sens. Actuators B 137 (2009) 722–726.
Contents lists available at SciVerse ScienceDirect
Chinese Chemical Letters journal homepage: www.elsevier.com/locate/cclet
Original article
Phenylboronic acid and dopamine as probe set for electrochemical detection of saccharides Jian Li *, Ya-Qin Sun, Yin-Mao Wei, Jian-Bin Zheng Institute of Analytical Science/Shaanxi Key Laboratory of Electroanalytical Chemistry, Northwest University, Xi’an 710069, China
A R T I C L E I N F O
A B S T R A C T
Article history: Received 6 December 2012 Received in revised form 5 January 2013 Accepted 18 January 2013 Available online 15 March 2013
A novel electrochemical approach for detection of saccharides via indicator displacement assay was presented. In this system, 2-fluorophenylboronic acid and dopamine (DA) were performed as probe set. The electrochemical properties of DA and the binding to 2-fluorophenylboronic acid in phosphate buffer at different pH values were investigated by cyclic voltammetry. After addition of fructose to the solution, a competition for the binding 2-fluorophenylboronic acid occurred that led to the release of the DA. The regenerate oxidation current of DA increased with increasing fructose concentration. Under optimized experimental conditions, the peak current was linearly related to fructose concentration in the range of 0.3–5.0 mmol/L with a detection limit of 0.1 mmol/L. In addition, the interaction between 2fluorophenylboronic acid and other cis-diol compounds such as glucose, galactose and mannose was investigated. ß 2013 Jian Li. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Electrochemistry Saccharides Dopamine Phenylboronic acid Indicator displacement assay
1. Introduction Considerable research has been focused on the detection of saccharides for such as clinical diagnoses, biochemical analyses and industrial process control [1]. Although some considerable progress regarding enzyme-modified electrodes have been made, some disadvantages, such as rigorous operating conditions, chemical instability and high cost still remain. Therefore, many non-enzymatic biosensors have been advocated [2,3]. It would be an alternative way to continuously monitor saccharides based on specific recognition of boronic acid derivatives to saccharides molecules. Phenylboronic acid (PBA) and its derivatives, ever since the discovery of their ability to rapidly form cyclic esters with cis 1,2- or 1,3-diols in aqueous media [4], have been extensively explored to develop various optical [5–7] and electrochemical [8,9] saccharide receptors. PBA is not electroactive, so it must be modified with redox active moieties for electrochemical sensing [10]. PBA-modified electrodes, as reagentless electrochemical sensors, have been successfully used to detect saccharides through potentiometric and voltammetric responses [11,12]. An indicator displacement assay has been reported for the detection of saccharides [13,14]. With these systems, analyte binding led to indicator displacement from the binding cavity,
* Corresponding author. E-mail address: [email protected] (J. Li).
which in turn yielded a signal modulation [13]. The advantage of this method is that the indicator is not covalently attached to receptor, and it is possible to change indicators at will. For example, PBA combined with Alizarin Red S (ARS) as a probe set had been used in optical saccharides sensors [7]. Schumacher had further investigated the recognition of saccharides using ARS as an electrochemical indicator. Upon addition of fructose, competition for the binding PBA occurred that led to the release of the ARS. The regenerated peak current of ARS was dependent on the added fructose concentration from 10 mmol/L to 50 mmol/L at the potential of 0.54 V or +0.42 V (vs. Ag/AgCl), respectively [15]. In the present study, a novel electrochemical approach for detection of saccharides applying the ensemble of 2-fluorophenylboronic acid and dopamine as the probe set was developed. There are three advantages of DA as an electrochemical indicator: (i) DA is sensitively detected by electrochemical methods, (ii) the affinity of 2-fluorophenylboronic acid for DA is lower than that of PBA–ARS, which benefits displacement of saccharides, and (iii) DA has relatively lower redox potential at around +0.20 V (vs. Ag/ AgCl), which makes the sensor resistant to interference from electroactive species. 2. Experimental Dopamine hydrochloride (DA, 98%) was purchased from Aladdin Chemistry Co., Ltd. 2-Fluorophenylboronic acid was obtained from Adamas Reagent Co., Ltd. (98%). D-Glucose, D-galactose, D-mannose
1001-8417/$ – see front matter ß 2013 Jian Li. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. http://dx.doi.org/10.1016/j.cclet.2013.01.051
[(Fig._1)TD$IG]
[(Fig._2)TD$IG]
J. Li et al. / Chinese Chemical Letters 24 (2013) 291–294
292
Fig. 1. Cyclic voltammograms recorded in PBS of 2.0 mmol/L DA with different 2fluorophenylboronic acid concentrations of (a) 0.0 mmol/L, (b) 0.5 mmol/L, (c) 1.0 mmol/L, (d) 1.5 mmol/L, and (e) 2.0 mmol/L. Scan rate: 100 mV/s.
and D-fructose were obtained from Xi’an Wolsen Bio-technology Co., Ltd. (99%, Xi’an, China). Nafion was obtained from Aldrich. The 0.1 mol/L phosphate buffered saline (PBS) was used as the supporting electrolyte and prepared from Na2HPO4 and KH2PO4. All other reagents were analytical reagent grade and double distilled water was used in experiments. Electrochemical experiments were recorded using a three electrode system controlled by CHI 660 electrochemical workstation (Shanghai Chenhua Instrument Co., Ltd., China), with a glassy carbon electrode (GCE, Ø = 3 mm) as a working electrode, an Ag/AgCl (3 mol/L KCl) reference electrode and a platinum counter electrode. 3. Results and discussion The redox behavior of DA in 0.1 mol/L PBS at pH 7.4 was investigated by cyclic voltammetry between 0.3 V and +0.8 V on the GCE. A pair of quasi-reversible redox peaks at +0.17 (P1) and 0.0 V (P2) corresponding to the electrochemical oxidation of dopamine and reduction of dopaminequinone was recorded (Fig. 1a). DA is oxidized to dopaminequinone, and the intramolecular cyclization of dopaminequinone leads to polymerization on the electrode surface [16], so the oxidation peak (P1) is significantly larger than the reduction peak (P2). After addition of 2fluorophenylboronic acid, a new pair of redox peaks (P3 and P4) was recorded at around +0.6 V (Fig. 1b–e), which was attributed to the formation of 2-fluorophenyl-boronic ester (Scheme 1). With 2fluorophenylboronic acid concentration increased, the peaks P1 emerged the positive shift and P2 emerged the negative shift decreased, whereas the peaks P3 and P4 increased (Fig. 1b–e). It is known that certain diols and boronic acids react together to form boronate esters, to an extent dependent upon the pH value of the solution [6]. In this section, the effect of pH value on the electrochemical behavior of the indicator displacement assay was investigated. The binding constant of the fructose boronate ester is lower than that of other saccharides already mentioned, so the fructose serviced as a typical analyte [8]. There was a pair of quasireversible redox peaks (P1 and P2) in the absence and presence of 2fluorophenylboronic acid in PBS (pH 5.3) of the given concentration DA (Fig. 2A). When fructose was added into the solution, there was almost no change in cyclic voltammograms. The results were attributed to the formation of 2-fluorophenylboronate ester which
Fig. 2. Cyclic voltammograms recorded in PBS of 2.0 mmol/L DA and 2.0 mmol/L 2fluorophenylboronic acid (solid line), containing 1.0 mmol/L fructose (dash line) with different pH values of (A) 5.3, (B) 7.4, and (C) 9.2. Scan rate: 100 mV/s.
was restrained in the acidic condition. To demonstrate the eligibility of the displacement assay, the study was also performed at pH 7.4 and 9.2 (Fig. 2B and C). After addition of 2-fluorophenylboronic acid, a new pair of redox peaks (P3 and P4) was recorded at around +0.6 V. When fructose was added, the currents of P3 and P4 decreased and the currents of P1 and P2 increased again due to the release of DA from 2-fluorophenylboronate ester and formation of the fructose boronate ester (Scheme 2). The increased response reached maximum at pH 9.2 because the formation of 2-fluorophenylboronate ester is optimal in basic aqueous media (Fig. 2C). However, the pH 7.4 was selected for further study because it more accurately reflects the environment in detecting saccharides. The indicator displacement assay for detection of fructose was performed by cyclic voltammetry. The current of peak P1 and P2 increased when different concentrations of fructose were added into PBS (pH 7.4) containing 0.1 mmol/L DA and 0.5 mmol/L
[(Schem_1)TD$FIG] OH
HO
O
B H2N
OH HO
F
H2N
OH H3O+
B
O F
Scheme 1. Schematic formation of cyclic phenylboronate ester via dopamine binding 2-fluorophenylboronic acid.
[(Schem_2)TD$FIG]
J. Li et al. / Chinese Chemical Letters 24 (2013) 291–294
OH
O H2 N
O
OH
O
OH
B
293
OH
B F
OH
O
saccharide
F
H2 N
OH
Scheme 2. Schematic representation of displacement assay for saccharides using dopamine as indicator.
2-fluorophenylboronic acid (Fig. 3). Because the oxidation product of DA leads to polymerization on the electrode and thus a gradual loss of the electrode activity [16], the peak P2 did not follow the concentration of fructose. The peak P4 showed no strict concentration dependence. Although the plot of the current change against the concentration of fructose showed a similar behavior for P1 and P3, the reproducibility of P1 was better. Given the above, the oxidation peaks P1 was used as analytical relevant signal to obtain the information. In order to investigate the effect of optimal concentration of the probe set on the displacement assay, a cyclic voltammetric experiment was carried out in a solution of 0.1 mmol/L DA containing 2-fluorophenylboronic acid from 0.1 to 0.9 mmol/L. The maximum current response was found when 0.5 mmol/L 2fluorophenylboronic acid was added in the presence of 1.0 mmol/L fructose (Fig. 4). Under optimized experimental conditions, the peak current was linearly related to fructose concentration in the range of 0.3–5.0 mmol/L with a detection limit of 0.1 mmol/L (Fig. 5d). This observation suggested that the positive impact on displacement by saccharides, ever since the binding constant of DA-PBA is comparatively smaller than that of ARS–PBA, resulting in more sensitive detection of fructose compared with previous report [15].
In addition, other saccharides already mentioned were also studied. All electrochemical measurements were performed as described earlier. Fig. 5a–c showed the currents of oxidation peaks P1 vs. the concentration of saccharides. The sensitivity of the approach was dependent on the saccharides with increasing binding constants following the order fructose > galactose mannose > glucose, as was identical with previous literature [6]. The amount of DA displacement is governed by the binding constant between 2fluorophenylboronic acid and different kinds of saccharides. The selectivity of the proposed electrochemical approach is not perfect in the mixture system. The linear range of the electrode is 0.5– 20.0 mmol/L for galactose and 0.5–30.0 mmol/L for mannose and 1.0–10.0 mmol/L for glucose (Fig. 6), which was comparable and even better than previously reported PBA based saccharides sensors [8,11,12,15,17], the results were listed in Table 1.
[(Fig._5)TD$IG]
[(Fig._3)TD$IG]
Fig. 5. The dependence of P1 current on the added concentration of saccharides including (a) glucose, (b) mannose, (c) galactose and (d) fructose, respectively.
Table 1 Comparison of detection range of PBA-based saccharides sensors. Sensor system Fig. 3. Cyclic voltammograms recorded in PBS of 0.1 mmol/L DA and 0.5 mmol/L 2fluorophenylboronic acid with different fructose concentrations of (a) 0.0 mmol/L, (b) 1.0 mmol/L, (c) 2.0 mmol/L, (d) 5.0 mmol/L, and (e) 10.0 mmol/L. Scan rate: 100 mV/s.
[(Fig._4)TD$IG]
Saccharides
Differential pulse voltammetry D-Fructose TIFAQ-PBA Potentiometry PABA
D-Glucose D-Fructose
Voltammetry MPBA
D-Fructose D-Mannose D-Glucose
DTBA-PBA
D-Fructose D-Mannose D-Glucose
Au-ATP-BA
D-Fructose D-Mannose D-Glucose
ARS–PBA DA-PBA Fig. 4. The calibration curve of the oxidation peaks P1 current vs. the different concentration of 2-fluorophenylboronic acid (0.1–0.9 mmol/L) in PBS (pH 7.4), with the presence of 0.1 mmol/L DA and 1.0 mmol/L fructose. Scan rate: 100 mV/s.
D-Fructose D-Fructose D-Galactose D-Mannose D-Glucose
Detection range (mmol/L) 1–200
Reference
[8]
3.4–40.8 3.4–40.8
[11]
3–100 10–300 30–300 0.3–30 3–300 3–300 0.1–100 0.1–100 0.1–50 10–50 0.3–5.0 0.5–20.0 0.5–30.0 1.0–10.0
[12]
[17]
[15] Present study
[(Fig._6)TD$IG]
J. Li et al. / Chinese Chemical Letters 24 (2013) 291–294
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Fig. 6. The linear range curve of saccharides including (A) glucose, (B) mannose, (C) galactose and (D) fructose, respectively.
4. Conclusion In the present study, a novel electrochemical approach for the detection of saccharides based on 2-fluorophenylboronic acid and DA as the probe set was successfully developed. This approach showed salient features such as better sensitivity, simple operation and cost-effectiveness. It was promising for fabrication of nonenzymatic sensors for saccharides. Further investigations should be undertaken to screen the electrochemical indicator to enhance the sensitivity and develop a disposable sensor, which should be cheap, easily operated and of good quality. Acknowledgments This work was supported by the National Natural Science Foundation of China (No. 21075098), and Scientific Research Plan Projects of Shaanxi Provincial Department of Education (No. 09JK756). References [1] A. Heller, B. Feldman, Electrochemical glucose sensors and their applications in diabetes management, Chem. Rev. 108 (2008) 2482–2505. [2] Z.J. Luo, T.T. Han, L.L. Qu, X.Y. Wu, A ultrasensitive nonenzymatic glucose sensor based on Cu2O polyhedrons modified Cu electrode, Chin. Chem. Lett. 23 (2012) 953–956. [3] Y.Y. Song, D. Zhang, W. Gao, X.H. Xia, Nonenzymatic glucose detection by using a three-dimensionally ordered, macroporous platinum template, Chem. Eur. J. 17 (2005) 2177–2182.
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