ELECTROPOLYMERIZATION continued
Table 1 – Determination of UA concentration in human urine samples using MIP-MGCE (µmol L–1 Sample (urine) Sample 1 Sample 2 Sample 3
Detected content 0.86 1.12 1.48
In contrast, for nMIP-MGCE, almost no peak cur- rent was observed (curve f in Figure 2b), which may be attributed to the fact that the nMIP film was polymerized in the absence of UA; therefore no cavities with binding sites were obtained. The results indicated that nMIP-MGCE was unable to recognize UA.
Performance of the imprinted sensor
Selectivity of the MIP-MGCE The selectivity of MIP-MGCE to UA was evalu- ated by testing its linear sweep voltammetry (LSV) responses in the presence of some pos- sible interfering substances (structures shown in Figure 3). The selectivity of the imprinted electrode to UA was evaluated by calculating the anodic peak current ratio (Is and I0
/I0 are the anodic peak current of K3
), where Is [Fe(CN)6
]
in the presence and absence of interfering substances. A tenfold excess of caffeine (CA), theophylline (TP), adenine (AD), xanthine
Added content 1.00 1.00 1.00
Found content 1.80 2.16 2.53
(XA), hypoxanthine (HXA), dopamine (DA), and ascorbic acid (AA) over UA caused a minimal change in peak current: The peak current ratio varied only slightly, from 0.90 to 1.05. These results indicate that MIP-MGCE showed higher recognition selectivity for UA.
Calibration graph and detection limit A linear relationship between the anodic peak current and UA concentration was obtained covering the concentration range from 2.0 × 10–7
to 2.0 × 10–5 M; the linear regression equa-
tion is Δi (μA) = 0.0644 +1.2632 C (μM) (current data obtained from Figure 4), with a correlation coefficient of 0.9997. The detection limit is cal- culated to be 8 × 10–8 blank signals.
M based on the 3σ of the
Reproducibility and stability of MIP-MGCE The reproducibility of the measurements was evaluated by measuring the LSV responses of K3
[Fe(CN)6] in the presence of 2.0 × 10–6 M
uric acid at the same MIP-MGCE. The relative standard deviation (RSD) for seven successive determinations is about 3.5%. The response of the imprinted electrode decreased to 94% after storing for one week, and 90% of the original responses were retained after two weeks.
Figure 4 – LSV curves of MIP-MGCE in 1.0 mmol/L [Fe(CN)6
]3– after incubation in
different concentrations of UA (from bot- tom to top): 0, 0.2, 0.4, 0.8, 2, 4, 8, and 20 μM. Supporting electrolyte: N2
. -saturated PBS (0.05
M, pH 7.0) containing 0.1 M KCl. Scan rate: 50 mV sec–1
Determination of UA in human urine samples All of the samples were diluted 200 times with 0.05 M phosphate-buffered saline (PBS, pH 7.0) in order to fit into the linear range of UA deter- mination. To verify the efficacy of the proposed method, the samples were spiked with UA solu- tion, and the amount of UA was then determined. The results are shown in Table 1.
Conclusion In this study, an MIP-MGCE formed by the cyclic
voltammetric electro-polymerization of an oPD film on MGCE was successfully fabricated. The proposed low-cost chemical sensor can
AMERICAN LABORATORY • 28 • SEPTEMBER 2013
, n = 3)
Recovery (%) 94
104 105
RSD (%) (n = 3) 3.2 3.6 2.5
potentially be applied to measurements of UA in physiological samples.
References 1. Dutt, V.V.; Mottola, H.A. Determination of
uric acid at the microgram level by a kinetic procedure based on a pseudo-induction period. Anal. Chem. 1974, 46, 1777. 2. Yamanaka, H.; Togashi, R. et al. Optimal range of serum urate concentrations to minimize risk of gouty attacks during anti- hyperuricemic treatment. In: Purine and Pyrimidine Metabolism in Man Ix. Plenum Press: New York, NY, 1998, pp 13.
3. Zen, J.M.; Kumar, A.S. et al. Recent updates of chemically modified electrodes in ana- lytical chemistry. Electroanalysis 2003, 15, 1073.
4. Po-Yen Chen, Vittal, R. et al. A novel molecu- larly imprinted polymer thin film as biosen- sor for uric acid. Talanta 2010, 80, 1145.
5. Wang, X.; Wu, M. et al. Simultaneous elec- trochemical determination of ascorbic acid, dopamine and uric acid using a pal- ladium nanoparticle/graphene/chitosan modified electrode. J. Electroanal. Chem. 2013, 695, 10.
6. Zhang, Z.H.; Luo L.J. et al. A polypyrrole- imprinted electrochemical sensor based on nano-SnO2
/multiwalled carbon nano-
tubes film modified carbon electrode for the determination of oleanolic acid. Electro- analysis 2011, 23, 2446.
Dr. Peng is a Senior Researcher, Department of Chemistry, Quanzhou Normal University, Bincheng Rd. 28, Quanzhou 362000, Fujian, PR China; tel.: +86 595 2291 9531; fax: +86 595 2291 9530; e-mail:
youyuanpeng@hotmail.com. The author is grateful for the financial support pro- vided by the Science Foundation of Quanzhou, Fujian Province (grant no. 2012Z112).
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