Towards a flexible electrochemical biosensor fabricated from biocompatible Bombyx mori silk

In modern days, there is an increasing relevance of and demand for flexible and biocompatible sensors for in-vivo and epidermal applications. One promising strategy is the implementation of biological (natural) polymers, which offer new opportunities for flexible biosensor devices due to their high biocompatibility and adjustable biodegradability. As a proof-of-concept experiment, a biosensor was fabricated by combining thin- (for Pt working- and counter electrode) and thick-film (for Ag/AgCl quasi-reference electrode) technologies: The biosensor consists of a fully bio-based and biodegradable fibroin substrate derived from silk fibroin of the silkworm Bombyx mori combined with immobilized enzyme glucose oxidase. The flexible glucose biosensor is encapsulated by a biocompatible silicon rubber which is certificated for a safe use onto human skin. Characterization of the sensor set-up is exemplarily demonstrated by glucose measurements in buffer and Ringer's solution, while the stability of the quasi-reference electrode has been investigated versus a commercial Ag/AgCl reference electrode. Repeated bending studies validated the mechanical properties of the electrode structures. The cross-sensitivity of the biosensor against ascorbic acid, noradrenaline and adrenaline was investigated, too. Additionally, biocompatibility and degradation tests of the silk fibroin with and without thin-film platinum electrodes were carried out.