A colorimetric paper-based analytical device for glucose detection using a ferric-based peroxidase nanozyme

Abstract

Herein, we propose a paper-based colorimetric biosensor as an analytical device for glucose sensing (g-PAD), which is fabricated via a two-step process consisting of the inkjet printing of a barrier of carbon onto a filter paper to form a working zone for the g-PAD and the immobilization of reagents, including ferric hydroxide/nitrogen-doped graphene quantum dots (FN-GQDs) as a peroxidase nanozyme, 3,3′,5,5′-tetramethylbenzidine (TMB) as a cosubstrate color indicator and glucose oxidase (GOx) as a capture probe, onto the working zone of the g-PAD by drop-casting. Glucose sensing is conducted by adding a drop of an analyte sample onto the working zone. In this proposed g-PAD, the GOx will oxidise glucose into gluconic acid and hydrogen peroxide (H₂O₂), and then, the FN-GQDs, as a peroxidase nanozyme, will catalyse the reaction of H₂O₂ and TMB, which will convert the reduced TMB state (TMB_red) to the oxidized TMB state (TMB_ox), appearing as a color change from colorless to blue in the working zone. The blue intensity reflects the concentration of glucose in the sample, which can be recognized directly by the naked eye or by measuring the gray intensity (GI). The developed g-PAD biosensor can detect glucose in a linear range from 0.025 mM to 0.5 mM, with a limit of detection of 18.75 µM. This developed g-PAD has been tested for glucose monitoring in human blood plasma samples with high accuracy.