Abstract: This invention provides a method for detecting an analyte in a sample using electromagnetic radiation comprising: (i) providing a labelled reagent, the labelled reagent having a binding site which is capable of binding the analyte or an analogue of the analyte and a label, wherein the label is capable of absorbing the electromagnetic radiation to generate energy by non-radiative decay; (ii) providing a device having a radiation source adapted to generate a series of pulses of electromagnetic radiation, a transducer having a pyroelectric or piezoelectric element and electrodes, which is capable of transducing energy generated by non-radiative decay into an electrical signal, a detector which is capable of detecting the electrical signal, a controller for controlling the source of electromagnetic radiation and the detector, wherein the device has a first and second chamber, the first chamber containing a first reagent proximal to the transducer, wherein the first reagent is capable of binding to the analyte suc