Novel application of electrochemical bipolar exfoliated graphene for highly sensitive disposable label-free cancer biomarker aptasensors

Abstract

Label-free aptasensors can be a promising point-of-care biosensor for detecting various cancer diseases due to their selectivity, sensitivity, and lower cost of production and operation. In this study, a highly sensitive aptasensor based on gold-covered polyethylene terephthalate electrodes (PET/Au) decorated with bipolar exfoliated graphene is proposed as a possible contender for disposable label-free aptasensor applications. Bipolar electrochemical exfoliation enables simultaneous exfoliation, reduction, and deposition of graphene nanosheets on prospective electrodes. Our comparative study confirms that the bipolar exfoliated graphene deposited on the negative feeding electrode (i.e., reduced graphene oxide) possesses better electrochemical properties for aptasensing. The optimized aptasensor based on bipolar exfoliated graphene deposited on PET/Au electrodes exhibits a highly sensitive response of 4.07 μA log c ^-1 (unit of c, pM) which is linear in the range of 0.0007-20 nM, and has a low limit of detection of 0.65 pM (S/N = 3). The aptasensor establishes highly selective performance with a stability of 91.2% after 6 days. This study demonstrates that bipolar electrochemistry is a simple yet efficient technique that could provide high-quality graphene for biosensing applications. Considering its simplicity and efficiency, the BPE technique promises the development of feasible and affordable lab-on-chip and point-of-care cancer diagnosis technologies.

Fig. 1. Schematic illustration of a (a) bipolar exfoliation cell, (b) development of PET/Au/rGO_Apt PDGF-BB aptasensors, (c) target incubation, and a (d) three-electrode electrochemical cell with a Ag/AgCl reference electrode, Pt wire counter electrode, and PET/Au/rGO_Apt in 5 mL aqueous electrolytes of 0.1 M PBS/5 mM K₃Fe(CN)₆/0.05–1 M KCl.

Fig. 2. (a) SEM images of BPE-rGO deposited on the negative feeding electrode. (b) TEM image (SAED patterns in the inset, yellow circles are associated with 〈11̄00〉 planes and green circles are associated with 〈21̄10〉 planes). (c) HRTEM image of BPE-rGO.

Fig. 3. FTIR spectra of SS/GO, SS/rGO, SS/GO_Apt, and SS/rGO_Apt electrodes.

Fig. 4. (a) CV (40 mV s⁻¹) plots of bare SS and BPE-graphene deposited on SS electrodes before and after aptamer immobilization. (b) The areal capacitance calculated from CV plots. (c) The CV plots of the SS/rGO electrode at different scan rates in the range of 10–100 mV s⁻¹. (d) Calibration curves of reduction and oxidation peak currents versus the square root of scan rates. (e) The DPV plots of BPE-based aptasensors based on graphene deposited on the negative feeding electrode at various development stages and the sensing responses of the aptasensors to 100 pM PDGF-BB. (f) The DPV plots of BPE-based aptasensors based on graphene deposited on positive feeding electrodes at various development stages and the responses of the aptasensors to 100 pM PDGF-BB.

Fig. 5. (a) Peak currents obtained from DPV curves measured in response to 100 pM PDGF-BB for defining the optimum reaction times. (b) Peak currents obtained from DPV curves in response to 100 pM PDGF-BB for analyzing the effect of pH on the peak current. (c) Peak currents obtained from DPV curves measured in response to 100 pM PDGF-BB for studying the effect of incubation temperature. (d) Peak currents obtained from DPV curves measured in response to 100 pM PDGF-BB for studying the effect of KCl concentration on the peak current. (e) DPV response of the SS/rGO_Apt electrode to PDGF-BB ranging from 0–10 nM. (f) Obtained calibration curve of peak currents measured from DPV responses.

Fig. 6. (a) SEM image of BPE-graphene deposited on the PET/Au negative feeding electrode. (b) The DPV plots of PET/Au-based aptasensors based on graphene deposited on the negative feeding electrode at various development stages and the response of the aptasensor to 100 pM PDGF-BB. (c) Peak currents obtained from DPV curves measured in response to 100 pM PDGF-BB for studying the effect of aptamer concentration. (d) DPV curves of the PET/Au/rGO_Apt electrode response to PDGF-BB ranging from 0–20 nM. (e) Calibration curve for peak currents measured from DPV curves. (f) DPV peak current measured in response of PET/Au/rGO_Apt electrodes to 10 nM PDGF-AA, 1 μg mL⁻¹ bovine serum albumin (BSA), 10 nM PDGF-AB, and 100 pM PDGF-BB.