Paper immobilized BSA-decorated gold nanoclusters for single-step optical sensing of glucose and cholesterol without cross-reactivity

Minimally invasive methods for detecting glucose, cholesterol and hydrogen peroxide are crucial for monitoring the nutritional and health status of humans and animals. The peroxidase mimetic activity by nanozymes is one of the versatile methods for detecting glucose, cholesterol, hydrogen peroxide, and other biomolecules. However, the strict requirement of acidic pH limits their sensing and interfacing ability with natural enzymes. The present study developed bovine serum albumin (BSA) coated gold nanoclusters (AuNC) immobilized on paper fabric to enable single-step visual detection of glucose, cholesterol and hydrogen peroxide in complex biological fluids like serum and milk. The BSA-AuNC suspension and immobilized paper fabric synergistically interface with the natural oxidative enzymes, glucose oxidase or cholesterol oxidase, at physiological pH. The concomitant loss in the fluorescent intensity of BSA-AuNC-loaded paper fabric exposed to the generated hydrogen peroxide (glucose/glucose oxidase or cholesterol/cholesterol oxidase) was directly proportional to the concentration of glucose or cholesterol. These reactions enabled simple visual detection as well as quantification of hydrogen peroxide, glucose and cholesterol using Image-J software and common smartphone-based mobile applications. The detection ability of BSA-AuNC-embedded paper fabric is specific and remains unaltered in the presence of similar oxidase enzymes or similar substrate analogues. With these unique features, the BSA-AuNC embedded paper fabric stands out as a prominent analytical device with enormous potential as a simple, user-friendly detection tool for monitoring biomolecules that are important to health, nutrition, and environmental safeguarding.