A gold nanoparticle/cellulose nanofiber composite film for tattoo-type biosensors

Thin-film technology is important for the development of wearable devices. Layers of metals, such as chromium and nickel, can be formed on a substrate using conventional deposition techniques, including sputtering and vapor deposition. However, stability and biocompatibility issues have limited their application in wearable devices. This includes the deterioration of electrical conductivity due to corrosion and the development of metal allergies. Furthermore, thin films are prone to cracking and peeling in response to shape changes owing to their lack of flexibility. To address these issues, we utilized cellulose nanofibers (CNFs), which exhibit light weight, high strength, and excellent flexibility, and gold nanoparticles (AuNPs), which are chemically stable and biocompatible, to fabricate a new conductive composite film. Because AuNPs and CNFs spontaneously combine in a mixed solution, the AuNP/CNF film was easily formed by filtration. The AuNP/CNF film electrode demonstrated almost the same electrode properties as a gold plate, exhibiting a typical current response (peak separation = 73 mV) in K₃[Fe(CN)₆] solution. The enzyme-modified electrode, with glucose oxidase immobilized on the AuNP/CNF film, showed good concentration dependence (detection limit: 0.010 mM) in the glucose concentration range of 0.010-20 mM. The Michaelis-Menten constant was estimated to be 5.2 ± 0.2 mM. The AuNP/CNF film exhibited excellent conductivity and flexibility, allowing real-time monitoring of electrical current response when attached to the skin, suggesting its potential as a flexible sensor electrode for wearable devices and smart textiles.