Label-Free Electrochemical Aptasensor Based on the Vertically-Aligned Mesoporous Silica Films for Determination of Aflatoxin B1

Abstract

Herein we report a highly specific electrochemical aptasenseor for AFB1 determination based on AFB1-controlled diffusion of redox probe (Ru(NH₃)₆³⁺) through nanochannels of AFB1-specific aptamer functionalized VMSF. A high density of silanol groups on the inner surface confers VMSF with cationic permselectivity, enabling electrostatic preconcentration of Ru(NH₃)₆³⁺ and producing amplified electrochemical signals. Upon the addition of AFB1, the specific interaction between the aptamer and AFB1 occurs and generates steric hindrance effect on the access of Ru(NH₃)₆³⁺, finally resulting in the reduced electrochemical responses and allowing the quantitative determination of AFB1. The proposed electrochemical aptasensor shows excellent detection performance in the range of 3 pg/mL to 3 μg/mL with a low detection limit of 2.3 pg/mL for AFB1 detection. Practical analysis of AFB1 in peanut and corn samples is also accomplished with satisfactory results by our fabricated electrochemical aptasensor.

Keywords: aflatoxin B1; electrochemical aptasensor; vertically aligned mesoporous silica films.

Figure 1

Illustration of preparation process of BSA/Apt/O-VMSF/ITO electrochemical aptasensor and AFB1 assay. (a) Bare ITO electrode. (b) Binary assembly consisting of SM and VMSF on the ITO glass. (c) GOPTS bearing epoxy groups functionalized VMSF/ITO. (d) Removal of SM. (e) Modification of AFB1-specific aptamer and blockage of non-specific binding sites using BSA. (f) Detection of AFB1 with the help of Ru(NH₃)₆³⁺ in the bulk solution.

Figure 2

Photographs of Autolab electrochemical workstation (a) and detection device built for AFB1 measurement. (b) Cross-sectional view SEM image, (c) top-view, (d) cross-sectional view, and (e) TEM images of VMSF. (f) Enrichment factor (ratio of anodic peak currents at the VMSF/ITO and bare ITO) of anodic peak current obtained from the VMSF/ITO electrode relative to that of bare ITO in these two probe solutions.

Figure 2

Photographs of Autolab electrochemical workstation (a) and detection device built for AFB1 measurement. (b) Cross-sectional view SEM image, (c) top-view, (d) cross-sectional view, and (e) TEM images of VMSF. (f) Enrichment factor (ratio of anodic peak currents at the VMSF/ITO and bare ITO) of anodic peak current obtained from the VMSF/ITO electrode relative to that of bare ITO in these two probe solutions.

Figure 3

CV curves (a) and EIS plots (b) of VMSF/ITO, O-VMSF/ITO, Apt/O-VMSF/ITO, BSA/Apt/O-VMSF/ITO, and AFB1/BSA/Apt/O-VMSF/ITO electrodes obtained in 0.1 M KCl containing 2.5 mM Fe(CN)₆^3−/4−. The inset in (b) is an equivalent circuit, including solution resistance (R_s), two-layer capacitance (C_dl), Warburg impedance (Z_w), and R_ct. (c) XPS profiles of O-VMSF/ITO and Apt/O-VMSF/ITO electrodes. Insets show the diffraction peaks of the N and P elements.

Figure 4

(a) Anodic peak currents of Ru(NH₃)₆³⁺ with different concentrations at the bare ITO and VMSF/ITO electrodes (bar graphs) and enrichment factors for Ru(NH₃)₆³⁺ by VMSF/ITO (point plot). (b) Anodic peak currents (bar graphs) and current variation ratio (point plot) obtained at the BSA/Apt/O-VMSF/ITO electrodes before and after incubation with 300 ng/mL AFB1 in PBS solution containing different concentrations of Ru(NH₃)₆³⁺. Optimization of incubation time for aptamer (c) and AFB1 (d). Error bars represent the standard deviation of the results measured in three parallel experiments.

Figure 5

(a) DPV curves of BSA/Apt/O-VMSF/ITO aptasensor in presence of different concentrations of AFB1 (3 pg/mL–3 μg/mL). (b) Corresponding calibration curve.

Figure 6

(a) Selectivity of aptamer sensor. Concentrations of AFB1 and other interfering species were 300 ng/mL and 3 μg/mL, respectively. Error bars represent test results from three experiments. (b) DPV signals of three different aptamers (corresponding to CRP, PSA, and CEA) before and after incubation with 300 ng/mL AFB1 in PBS solution containing 10 μM Ru(NH₃)₆³⁺. (c) Reproducibility of the aptamer sensor. Current signals were selected from seven electrodes in different batches after incubation with 300 ng/mL of AFB1. Error bars represent the standard deviations of three measurements for each electrode. (d) Stability of the BSA/Apt/O-VMSF/ITO sensor. Seven electrodes prepared in the same batch were placed at 4 °C for different days to detect the current signal of 300 ng/mL AFB1. Error bars represent the standard deviations of the results measured in three parallel experiments.

Figure 7

(a) DPV signal values of BSA/Apt/O-VMSF/ITO electrodes after incubation with 300 ng/mL AFB1 with or without 1 mg/mL of different interfering species. Error bars represent measurement errors from three experiments. (b) Photographs of peanut and corn kernels before and after culturing in humid and sultry environment for 7 days.