The biosensor comprises a modular biorecognition element and a modular flexible arm element. The biorecognition element and the flexible arm element are each labeled with a signaling element. The flexible arm contains an analog of an analyte of interest that binds with the biorecognition element, bringing the two signaling elements in close proximity, which establishes a baseline fluorescence resonance energy transfer (FRET). When an analyte of interest is provided to the biosensor, the analyte will displace the analyte analog, and with it, the signaling module of the modular flexible arm, causing a measurable change in the FRET signal in a analyte concentration dependent manner. The modularity of different portions of the biosensor allows functional flexibility. The biosensor-operates without additional development reagents, requiring only the presence of analyte or target for function.