A novel amperometric catechol biosensor based on α-Fe₂O₃ nanocrystals-modified carbon paste electrode

Figures & data

Figure 1. XRD pattern of crystalline α-Fe₂O₃ NCs prepared by sol-gel method.

Figure 2. FT-IR spectra of laccase solution (a), and laccase immobilized α-Fe₂O₃NCs-CPE (b) showing formation of nanobiocomposite.

Figure 3. (a) CVs of α-Fe₂O₃ NC-modified CPE and BCPE in 10 mM of Fe(CN)₆^3−/4− solution measured at a scan rate of 50 mV s⁻¹; (b) Electrochemical impedance spectra of α-Fe₂O₃NCs–CPE in 10 mM of Fe(CN)₆^3−/4− at a polarization potential of 0.2 V in a frequency range of 1–10⁶ Hz. Inset shows corresponding spectra of BCPE.

Figure 4. CVs of BCPE, α-Fe₂O₃NCs–CPE, and Lac-α-Fe₂O₃NCs–CPE in presence of 0.2-M pH 7 PBS solution in presence and absence of 1-mM catechol at a scan rate of 50 mV s⁻¹.

Figure 5. The plot of the peak current vs. the square root of the scan rate for α-Fe₂O₃ NCs–CPE (inset: CVs at different scan rates) in 0.2-M pH 7 PBS solution containing 1 mM of catechol.

Figure 6. Schematic representation of laccase-catalyzed oxidation of catechol with its subsequent electrochemical reduction on the α-Fe₂O₃ NC-modified CPE.

Figure 7. Effect of solution pH (a) applied potential (b) and temperature (c) on the steady-state current response of Lac-α-Fe₂O₃NCs–CPE in 0.2-M pH 7 PBS solution containing catechol.

Figure 8. (a) Chronoamperometric responses of Lac-α-Fe₂O₃NCs–CPE on successive addition of different concentrations and volumes of catechol solutions into pH 7, 0.2 M of PBS solution at an applied potential of 0.3 V; (b) Calibration curve with nonlinear fitting for Lac-α-Fe₂O₃NCs–CPE response. Inset: Calibration curve with linear fitting.

Table 1. A comparison of biosensing properties of various laccase-based catechol biosensors.

Electrode description	Substrate	Detection limit (μM)	Linearity (μM)	Ref.
Laccase/carbon fibres	Catechol	NR	1–90	Freire et al. (2001)
Lac/AP-rGOs/Chit/GCE	Catechol	7	15–700	Zhou et al. (2013)
MB-MCM-41/PVA/lac	Catechol	0.331	4–87.98	Xu et al. (2009)
Laccase/CNTs − CS/GCE	Catechol	0.66	1.2–30	Liu et al. (2006)
PDA-Lac-NiCNFs/MGCE	Catechol	0.69	1–9100	Li et al. (2014)
Lac-α-Fe2O3NC-CPE	Catechol	4.28	8–800	This study

Figure 9. Relative responses of the biosensor for different phenolic compounds including catechol, 2-chlorophenol, 2-nitrophenol, guaiacol, and catechin. A total of 100 μM of the phenol in pH-7 PBS solution is used in all cases.

Table 2. Determination of catechol in real water samples.

Sample	Cadded (μM)	Cfound (μM)	Recovery (%)
Tap water	100	101.3	101.3
Textile industry effluent 1	100	97.3	97.3
Textile industry effluent 2	100	98	98

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