Glassy carbon electrodes sequentially modified by cysteamine-capped gold nanoparticles and poly(amidoamine) dendrimers generation 4.5 for detecting uric acid in human serum without ascorbic acid interference

doi:10.1016/j.aca.2013.12.025

Analytica Chimica Acta

Volume 812, 17 February 2014, Pages 18-25

https://doi.org/10.1016/j.aca.2013.12.025 Get rights and content

Highlights

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We constructed a modified electrode for detecting uric acid contained in human serum.
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Electrochemical detection of uric acid was comparable with the enzymatic method.
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Interference of ascorbic acid was not observed.

Abstract

Glassy carbon electrodes (GCE) were sequentially modified by cysteamine-capped gold nanoparticles (AuNp@cysteamine) and PAMAM dendrimers generation 4.5 bearing 128-COOH peripheral groups (GCE/AuNp@cysteamine/PAMAM), in order to explore their capabilities as electrochemical detectors of uric acid (UA) in human serum samples at pH 2. The results showed that concentrations of UA detected by cyclic voltammetry with GCE/AuNp@cysteamine/PAMAM were comparable (deviation <±10%; limits of detection (LOD) and quantification (LOQ) were 1.7 × 10⁻⁴ and 5.8 × 10⁻⁴ mg dL⁻¹, respectively) to those concentrations obtained using the uricase-based enzymatic-colorimetric method. It was also observed that the presence of dendrimers in the GCE/AuNp@cysteamine/PAMAM system minimizes ascorbic acid (AA) interference during UA oxidation, thus improving the electrocatalytic activity of the gold nanoparticles.

Graphical abstract

Introduction

Determination of uric acid (UA, Scheme 1A) in human serum acquired a new relevance in the last decade since several cases of hyperuricemia have been associated with hypertension, obesity, diabetes, [1] and preeclampsia [2], [3], [4]. UA (pK_a1 = 5.4, pK_a2 = 9.8 [4]) has been oxidized in pH 4 aqueous medium at ∼0.52 V vs. AgǀAgCl on glassy carbon electrodes (GCE) with slow electron transfer kinetics [5]. To overcome this limitation, GCE must be electro-activated in order to modify their surfaces with carboxyl groups [6], [7], poly(vinyl alcohol) [8], poly(Evans blue) [5], OH- and COOH-terminated carbon nanotubes or graphitic oxide [9], [10], [11], [12], [13], among others functionalities. The primary result of these processes is that the anodic currents associated with Reaction 1a [9] are promoted because UA molecules were preconcentrated on the glassy carbon surfaces.

The deposition of gold nanoparticles (AuNp) on properly pretreated GCE to get UA preconcentration capabilities [13], [14], [15] resulted in electrocatalytic activity that significantly improved its sensitivity in determining UA in urine and/or human serum. Nevertheless, the electrochemical response of UA contained in human serum is typically interfered by simultaneous oxidation of ascorbic acid (AA, Scheme 1B) (pK_a = 4.10 [16]) following Reaction 1b [17]. Therefore, differential pulse voltammetry (DPV) has traditionally been used to differentiate the electrochemical responses of UA and AA [5], [6], [7], [8], [10], [13], [14], [15]. However, this situation creates an opportunity to determine whether working electrodes, modified by multifunctionalized materials (which have a soft but well-organized molecular architecture) would favor the preconcentration and oxidation of UA over AA.

Poly(amidoamine) (PAMAM) dendrimers are unimolecular micelles that have been used for coating electrodes in order to endow the naked substrate with new physico-chemical properties [18]. Electrodes which have been modified in this way with dendritic materials have been employed to detect organohalogenated molecules [19], aggregate prussiates [20], [21], [22] and Ni(II)-tetraaza macrocycles [23], and promote the formation of supramolecular complexes based on β-cyclodextrin and ferrocenyl groups [24]. It was also reported that PAMAM dendrimers show remarkable capabilities to bind gold nanoparticles [25].

In this study, GCE were sequentially modified by cysteamine-capped gold nanoparticles (AuNp@cysteamine, Fig. 1a) and PAMAM dendrimers generation 4.5 bearing 128-COOH peripheral groups (Fig. 1b) in order to improve the electrochemical detection of UA in the presence of AA (as the main electroactive interference), both contained in random human serum samples diagnosed with hyper- or hypouricemia. According to published reports [26], [27], COOH-terminated PAMAM dendrimers were chosen since carboxylic groups avoid non-specific adsorption of serum proteins on modified electrodes.

Section snippets

Materials

Na₂HPO₄ anhydrous (99.1%), KH₂PO₄ (99.3%), H₂SO₄ (98.3%wt.), HCl (36.5–38%wt.), NaBH₄ (98%), and MeOH (HPLC grade) were purchased from J.T. Baker, while Ru(NH₃)₆Cl₃ (99.0%) and HAuCl₄·H₂O (99.9985%-Au) were obtained from Strem Chemicals. Cysteamine hydrochloride (HSCH₂CH₂NH₂·HCl, ≥98%), N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDC, 98%), PAMAM dendrimer generation-4.5 (5%wt. in MeOH), l-ascorbic acid (99%), and uric acid (≥99%) were acquired from Sigma–Aldrich. Random human

Modification of GCE with AuNp@cysteamine

Fig. 4A shows the CV response obtained for AuNp@cysteamine-modified GCE immersed in aqueous 0.5 M H₂SO₄. This figure shows broad anodic peaks between 0.8 and 1.2 V, which were associated to the electro-formation of AuO through the consecutive Reactions (2) and (3). Similarly, broad cathodic peaks were observed between 0.7 and 0.4 V due to the reverse sense of the same reactions [34].

Since the charge (Q_AuO) required to grow a AuO monolayer on polycrystalline gold was reported to be 200 μC cm⁻² [34],

Conclusions

Electrochemical detection of UA was successfully carried out in human serum samples using GCE that were sequentially modified by gold nanoparticles and dendritic micelles to appropriately combine their electrocatalytic and preconcentration properties, respectively. Electrocatalytic oxidation of UA carried out by gold nanoparticles were found to be enhanced at diluted UA concentrations by interfacial preconcentration of UA promoted by the presence of dendritic materials. Electroanalysis of human

Acknowledgments

The authors would like to thank CONACyT and FOMIX QUERETARO-CONACYT for financial support (Grants 106000 and QRO-2010-C01-145394, respectively). A.S.R.S. thanks CIDETEQ for the support of the Undergraduate Scholarship Program. J.A.B.A. thanks CONACyT for the support of the Postgraduate Scholarship Program. The authors also thank César A. Alvarez-Casillas (Research Program of CIDETEQ for Undergraduates) for all the technical support offered to help carry out electrodeposition of gold on glassy

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View full text

Glassy carbon electrodes sequentially modified by cysteamine-capped gold nanoparticles and poly(amidoamine) dendrimers generation 4.5 for detecting uric acid in human serum without ascorbic acid interference

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Materials

Modification of GCE with AuNp@cysteamine

Conclusions

Acknowledgments

Bioelectrochemistry

Colloids and Surfaces B

Sensors and Actuators B

Sensors and Actuators B

Sensors and Actuators B

Sensors and Actuators B

Electrochemistry Communications

Journal of Electroanalytical Chemistry

Electrochimica Acta

Analytica Chimica Acta

Electrochemistry Communications

Biomaterials

Coordination Chemistry Reviews

Colloids and Surfaces A

Bioelectrochemistry

Electrochimica Acta

Journal of Electroanalytical Chemistry

Analytical Biochemistry

Journal of Molecular Structure: THEOCHEM

Journal of Molecular Structure

Cleveland Clinic Journal of Medicine

Placenta

Hypertension