Novel Electrochemical Aptasensors Based on Bipolar Exfoliated Graphene for Label-Free Detection of Cancer Biomarkers
Authors: Forouzanfar Shahrzad , Khakpour Iman , Alam Fahmida , Pala Nezih , Wang Chunlei 
Published: July 2021

Early detection of cancer can noticeably increase the survival chance of many cancer patients. Quantifying cancer biomarkers detectable from blood is an efficient way for early detection of cancer diseases. Among various discovered cancer biomarkers, platelet-derived growth factor-BB (PDGF-BB) is an essential biomarker for early detection of cancer and monitoring cancer patients. This biomarker plays a vital role in developing and lymphatic metastasis of solid malignant tumors such as brain, lung, breast, and liver; which enlightens the importance of developing point-of-care (POC) biosensors for the detection of PDGF-BB. In recent years, the application of synthetic DNA or RNA-based bio-recognizers (i.e., aptamers) in cancer biomarker sensor development has been vastly investigated. Electrochemical label-free aptamer-based biosensors (also known as aptasensors) are highly suitable for POC. In this study, the application of bipolar exfoliated (BPE) graphene for developing PDGF-BB label-free aptasensors is investigated. Graphene as a single, two-dimensional layer of carbon atoms has very interesting features suitable for biosensor applications. The common graphene synthesis methods require complicated and costly processes and excessive use of harsh chemicals, as well as complex subsequent deposition procedures. In this study, a single setup has been used for exfoliation, reduction, and deposition of graphene nanosheets on a conductive electrode based on the principle of bipolar electrochemistry of graphite in deionized water. We investigated the properties of aptasensors based on graphene oxide (GO) deposited on a positive electrode feeding electrode and reduced-GO (rGO) deposited on a negative electrode feeding electrode. The PDGF-BB affinity aptamers were covalently immobilized by binding amino-tag terminated aptamers and carboxyl groups of GO and rGO surfaces. In this study, Fourier-transform infrared spectroscopy (FTIR) was used to study the surface characteristics of synthesized graphene and developed aptasensors. The scanning electron microscopy (SEM) was used to study the morphology of the bipolar exfoliated GO and rGO. The SEM study demonstrated that the rGO has a porous vertically aligned structure with pore sizes of around 100 nm, while GO has bulky flattened plates with random cracks. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used for characterizing the BPE graphene-based aptasensors in different stages of development and their sensing performances. The turn-off sensing strategy was implemented by measuring the peak-currents from DPV plots. The optimized aptasensor based on rGO showed a wide linear range of 0.75 pM-10 nM, high sensitivity of 7.83 A Logc-1 (unit of c, pM), and a low detection limit of 0.53 pM. However, the optimized aptasensor based on GO reached to its saturation point around 150 pM. This study demonstrated that bipolar electrochemistry is a simple yet efficient technique that could provide high-quality graphene for biosensing applications. Considering the BPE technique's simplicity and efficiency, this technique is highly promising for developing feasible and affordable lab-on-chip and point-of-care cancer diagnosis technologies.