Solid-state electronic devices based on biomolecules as current carrying elements have numerous applications from diagnostics to therapeutics. Casein micelle based solid-state device through metal-protein-metal electrical junctions designed for elucidating protein-drug interaction as well as proof-of-concept theranostics are the highlights of this proposed work. This biocompatible electronic platform has multifunctionality, transducing interactions between protein-drug and drug-analyte into electrical signals providing a sophisticated interface between nanoelectronics and biological information processing systems. Casein's pH-responsive behavior and its interaction with the drug cysteamine were realized through current–voltage (I-V) technique, using this multifunctional biosensing platform. Moreover, successful elucidation of interaction between the drug cysteamine and analyte cysteine on an electronic platform, led to the realization of proof-of-concept theranostics. Further, investigation of the piezoelectric response of casein-BT film renders prospects in self-powered application; demonstrated by means of piezoelectric nanogenerator (PNG). The developed sensing platform opens up possibilities to investigate the potential interactions and application in theranostics before commensing clinical trials. © 2019 Elsevier B.V.