Disclosed herein are devices and systems for detecting microbial activity. A device (100) for detecting microbial contamination comprises a light source (20) that is configured to be optically coupled to an optical element (10), the optical element comprising a waveguide (2) and a diffraction grating (4), that together support a plurality of guided mode resonances at selected wavelengths of light from the light source. The device also comprises a condensing wall (40) having a condensing surface (50) on which liquid in gas (vapour) can condense, wherein the condensing surface is shaped, or engineered, to support flow of condensed liquids under gravity towards a collecting point (55) where the liquid can pool (6) around the optical element. The device further comprises a detector (30) configured to detect a property of a resonant guided mode of the plurality of resonant guided modes thereby to detect the presence or absence of microbes in the liquid that pools around the optical element.

The invention relates to a gas sensor for detecting one or a plurality of volatile compounds in a gas, the sensor comprising: a signal transducer comprising a layer comprising nanopores wherein the gas has access to the nanopores in said layer, a heating or cooling element, with adjustable temperature settings, for heating or cooling said layer comprising said nanopores, means for access of said gas to said layer comprising said nanopores, an electronic circuit, monitoring a time-dependent and a temperature-dependent signal generated by the signal transducer upon adsorption or release of a compound from the nanopores in said layer.