An apparatus is provided for sensing an analyte in a fluid. The apparatus includes a fluid collecting device configured to collect the fluid containing the analyte; a fluid input in fluid communication with the fluid collecting device configured to input the fluid containing the analyte into the fluid collecting device, an analyte interactant in fluid communication with the fluid collecting device, wherein the analyte interactant, when contacted by the analyte, reacts to cause a first change in thermal energy within the fluid collecting device; a modulator that causes a second change in thermal energy; a thermal sensing device comprising at least one pyroelectric device thermally coupled to the fluid collecting device to generate a first signal in response to at least one of the first change in thermal energy and the second change in thermal energy; a control device operatively coupled to the thermal sensing device and the modulator that generates a second signal, wherein the second signal comprises information useful in characterizing the analyte. A related method also is disclosed.