Portable optical biosensor for point-of-care monitoring of salivary glucose using a paper-based microfluidic strip

The manuscript describes a technique for fabrication and validation of a standalone handheld optical biosensor designed for non-invasive monitoring of glucose through saliva. In this cost-effective process, a 3D-printed glucose test strip was filled with sieving paste comprising of cellulose, polyethylene glycol (PEG), polyvinyl alcohol (PVA) and glycerol, onto which, glucose oxidase-peroxidase (GOD-POD) enzymes and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) chromogenic dye were co-immobilized. The enzymatic reaction produced H₂O₂ as by-product with which the ABTS reacted, leading to colour change on the detection zone of the strip which was detected by the developed glucometer. The in-house developed meter included an optically isolated section in its structure for inserting the strip to prevent interference from the ambient light conditions. The biosensor exhibited a broad detection range of 28–204 mg/dL of glucose concentration, with a sensitivity of 26.89 count/mg/dL and a limit of detection (LOD) at 28 mg/dL, within a response time of 120 s. The device along with strips was validated with clinical samples, comparing salivary glucose levels (SGL) to blood glucose levels (BGL) using a commercial glucometer i.e., Accu-Chek Active. Student's t-test on clinical data yielded p-values of 0.018, 0.01, 0.008, and 0.003 in fasting and post-prandial samples of non-diabetic and diabetic patients respectively, which represents a significant correlation. The device also passed Clarke's error grid analysis and is hence considered medically acceptable. The low-cost and simple-to-use saliva-based glucometer should be ideally suited for mass screening of diabetes as well as day-to-day health check-ups in a non-invasive and painless manner.