An Amperometric Biosensor for Xanthine Determination Prepared from Xanthine Oxidase Immobilized in Polypyrrole Film

Figures & data

Figure 1 The effect of oxygen passage time upon the sensitivity of biosensor to 1.5 × 10⁻⁴ M xanthine in 0.025 M phosphate buffer (pH 7.4) at 25°C. (a): without the passage of oxygen (b): 5 minutes of oxygen passage, (c): 10 minutes of oxygen passage, (d): 20 minutes of oxygen passage.

Figure 2 The response time of xanthine biosensor at 25°C. Xanthine concentration: (a) 1.0 × 10⁻⁵ M, (b) 5.0 × 10⁻⁵ M, (c) 1.0 × 10⁻⁴ M in 0.025 M phosphate buffer (pH 7.4).

Figure 3 The effect of solution pH on the response to 5.0 × 10⁻⁵ M xanthine in 0.025 M phosphate buffer solution at 25°C. The operating potential is +0.7 V vs SCE.

Figure 4 The effect of temperature upon the sensitivity of biosensor against xanthine (0.025 M pH 7.4 phosphate buffer).

Figure 5 The effect of the phosphate concentration upon the sensitivity of the biosensor against xanthine (pH 7.4 phosphate buffer, 25°C).

Figure 6 The effect of enzyme concentration upon the sensitivity of biosensor against xanthine (0.025 M phosphate buffer, 25°C).

Figure 7 The effect of xanthine concentration upon the amperometric response of the biosensor (0.025 M pH 7.4 phosphate buffer, 25°C).

Figure 8 The calibration curve of xanthine biosensor (0,025 M, pH 7.4 phosphate buffer, 25°C).

Figure 9 Storage stabilization of the biosensor (0.025 M, pH 7.4 phosphate buffer, 25°C).

Table 1. The properties and the optimum working conditions of the biosensor

Parameters	Optimum conditions and characteristic
Response time	25 seconds, t95 = 3–4 minutes
Temperature	25°C
pH	7.4
Phosphate concentration	0.025 M
Enzyme amount	1,02 Unit
Working range	1.0 × 10^−5 − 4.0 × 10^−4 M
Detection limit	1.0 × 10^−6 M
Reproducibility	The relative standard deviation is 6.0% after 15 measurements and the standard deviation computed from the slopes of calibration curves is 1.4%.
Storage stabilization	The electrode maintains 95% of the initial amperometric response after 10 days and 35% at the end of the 45th day.
Km and Vmax for Xanthine oxidase enzyme	1.33 mM, 2.75 µA/minute

Table 2. The properties of xanthine biosensors literature

Carrier	Mediator	Response time	Temperature (°C)	pH	Phosphate concentration	Enzyme amount, KM	Working range	Detection limit	Reproducibility	Storage stabilization	Reference
Carbon paste	Cobalt phytalocyanin in matrix and ferricyanide in solution	30 s	–	8.0–9.0	0.05 M	%11 m/m milk cream, 7 mM	1.0 × 10^−3 − 1.5 × 10^−2 M	–	The relative standard deviation for 8 measurements is 10.3%	The amperometric response after 60 days is 60%	Kilinc et al., [1998]
Glassy carbon	Copper hegzachloro platinate	t95 = 15 s	37	7.4	0.025 M	7.01 Unit/mL, 1.11 mM	6.0 × 10^−7 − 2.0 × 10^−4 M	1.0 × 10^−7 M	The relative standard deviation for 10 measurements is 3.0%	The amperometric response after a week is 70%	Pei and Li, [2000]
Poly-(8-pyrrol-1-lactobionamido octane) and Poly-(12-Pyrrole-1-yldodecyl)	–	2 s	–	7.4	–	5 Unit	1.0 × 10^−7 − 1.0 × 10^−5 M	–	–	The amperometric response after 5 days is 100%	Llaudet et al., [2003]
Poly-(Mercapto-p-benzoquinone)	–	t95 = 60 s	30	7.3	0.06 M	0.5 U/mg, 0.04 mM	1.0 × 10^−6 − 8.0 × 10^−5 M	–	–	The amperometric response after 8 days is 30%	Arai et al., [1996]
Polypyrrole	Ferrocene	25 s, t95 = 3–4 min	25	7.4	0.025 M	1.02 Unit, 1.33 mM	1.0 × 10^−5 − 4.0 × 10^−4 M	1.0 × 10^−6 M	The relative standard deviation for 15 measurements is 6.0%	The amperometric response after 10 days is 95%, after 45 days is 35%	Our study

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