The invention generally relates to methods, reagents and devices for determining a concentration of an analyte in a sample. Provided is a proteinaceous sensor molecule for detecting an analyte of interest (A), comprising a signal generating moiety tethered to a synthetic regulatory molecule capable of modulating signal generation by intramolecular binding, wherein (i) the synthetic regulatory molecule comprises a primary ligand (L1) capable of intramolecular binding to a primary partner (BP1) on the sensor molecule; wherein (ii) the sensor molecule comprises a secondary ligand (L2) capable of binding to a secondary binding partner (BP2) which is A or a binding partner thereof; and wherein (iii) binding of L1 and L2 to their respective binding partners is mutually exclusive, such that binding of BP2 to L2 influences binding of L1 to BP1, resulting in a conformational change within the sensor molecule such that the generated signal is modulated.