Modified pencil graphite electrode as a low-cost glucose sensor

Abstract

A manganese oxides mediator was electrodeposited onto a low-cost pencil graphite electrode (PE) from an easily available and affordable potassium permanganate precursor. The modified manganese oxides coated PE (MnOxides/PE) was previously utilized as a hydrogen peroxide sensor according to its electrocatalytic activity for hydrogen peroxide oxidation in an ammonium buffer (pH 9.0) medium. The amperometric detection of hydrogen peroxide is possible at +0.50 V vs Ag/AgCl instead of +0.80 V vs Ag/AgCl using an unmodified PE. Further modification of the MnOxides/PE with glucose oxidase immobilization converted the modified PE into a glucose sensor by hydrogen peroxide detection in a phosphate buffer (pH 7.4) at the same operating potential. The linear concentration range of glucose detection by the batch technique was 0.056–1.41 mM, with a sensitivity of 2.19 μA mM−1. A detection limit of 18.3 μM and a percentage RSD of 5.0% were obtained from five different sensors. Through the flow injection analysis technique, a low-cost open-flow cell containing a volume of 1.4 mL was fabricated from a plastic vial and a micropipette tip. Using the injection volume of 200 μL and flow rate of 1 mL min−1, the linear concentration range of glucose detection was determined to be 0.56–5.55 mM, with the sensitivity of 0.72 μA mM−1, the detection limit of 0.29 mM, the response time of 20 s, and sample throughput of 34 samples per hour. The application of the proposed sensor to detect glucose in sport and energy drink samples showed good precision, with the percentage RSD of 0.7–5.6% (n = 3) and a recovery percentage of 97–103%.