Soft, flexible, and conductive composite polycaprolactone/molybdenum films: A new type of reliable electrode materials for fully biodegradable electrochemical biosensors

Use of fully biodegradable materials for temporary electrical sensing devices has become an attractive approach in healthcare monitoring to enable the elimination of surgical risks associated with the removal of implantable sensors and mitigate the environmental hazards caused by the increasing accumulation of electronic waste. However, the construction of fully biodegradable electronic sensors poses significant challenges in terms of materials selection and design considerations, especially in biochemical sensing where direct contact between the sensing element and aqueous analyte solution is required for detection. In such a sensing configuration, conductive films made of pure biodegradable metals dissolve rapidly and interfere with the measured signals. We present a new formulation of highly conductive, soft, and flexible composite polymer films suitable for biodegradable electrodes in electrochemical biosensors. The films are fabricated using conventional printing techniques from inks and pastes comprising polycaprolactone, molybdenum microparticles, and a biodegradable surfactant employed to ensure good microparticle dispersion and favorable mechanical properties. Obtained films exhibit excellent electrical conductivity (~1000 S/m) and stable impedance profile in a broad frequency range (10⁻¹–10⁴ Hz), which makes them particularly suitable for electrodes in impedimetric sensing. Under physiological conditions in vitro, the composite polymer films degrade in a controlled manner via gradual molybdenum corrosion and polycaprolactone hydrolysis. During the first weeks of degradation, composite films almost completely retain their geometry, electrical conductivity, and mechanical properties, which indicates great potential for reliable monitoring applications. To demonstrate the practical application of polycaprolactone/molybdenum composite films, we employ them as electrodes in fully biodegradable impedimetric sensors for amylase detection based on measuring the degradation of thin glycogen (polysaccharide) coatings. The innovative formulation of electrically conductive polycaprolactone/molybdenum films shows promising properties that can unlock the possibility of constructing fully biodegradable electrochemical biosensors for the point-of-care testing and monitoring of diverse relevant analytes in healthcare.