An improved amperometric sarcosine biosensor based on graphene nanoribbon/chitosan nanocomposite for detection of prostate cancer

Abstract

We describe herein an improved amperometric biosensor for detection of sarcosine, a potential biomarker for prostate cancer. The biosensor is based on covalent immobilization of sarcosine oxidase (SOx) onto nanocomposite of chitosan (CHIT) and graphene nanoribbons (GNRs) electrodeposited onto Au electrode. The GNRs were studied by transmission electron microscopy and UV spectroscopy. The working electrode (SOx/CHIT/GNRs/AuE) exhibited maximum current at a potential of 0.1V against Ag/AgCl, generated from electrochemical oxidation of H2O2, from sarcosine by immobilized SOx. The biosensor showed optimum response i.e. current (mA) within 2s at pH 7.3 and 35 ​°C. There was a linearity between current (mA) and sarcosine concentration in a wider range 0.001–100 ​μM with a minimum detection limit of 0.001 ​μM and a high sensitivity of 277.5 ​μA/μM/cm. Analytical recoveries of added sarcosine in sera were 97.35%, within and between-batch coefficients of variation were 1.08% and 1.40% respectively. A good correlation (R2 ​= ​0.99) was obtained between sera sarcosine values, as measured by the standard immuno kit method and present biosensor. The biosensor measured sarcosine levels in sera of prostate cancer patients, which was significantly higher than in apparently healthy persons. The enzyme electrode lost 20% of its initial activity during 180days, when stored dry at 4°C.