Abstract: A compact sensor for detecting the presence of biological or chemical species includes a microdisk laser and a wavelength shift detector. The microdisk laser is coated with a biological or chemical recognition element, which binds preferentially with a target analyte. Because the recognition element and the target analyte adhere to the sidewall surface of the microdisk laser, they increase the effective diameter of the laser, which shifts the output wavelength by a detectable amount. The presence of a wavelength shift indicates the presence of the target analyte, and the magnitude of the wavelength shift corresponds to the mass load of the target analyte on the sidewall surface of the microdisk laser.