Miniaturized, portable sensing systems for medical and environmental diagnostics and monitoring are an excellent application area for microresonator sensors. Polymer microresonators are attractive components for chip scale integrated sensing because they can be integrated in a planar format using standard semiconductor manufacturing technologies. Vertically coupled microresonators, where the waveguides lie below or above the microresonator, can be fabricated using standard photolithography, enabling low cost integrated sensor systems. Microresonators can be surface customized for discrimination in, for example, chemical sensing applications, or the surface can be functionalized for biological sensing applications. To create chip scale integrated sensing systems, microresonators can be integrated with planar optical system components, such as polymer waveguides and thin film photodetectors, onto silicon using heterogeneous integration. Heterogeneous integration can also be used to integrate optical sources with sensors onto host substrates such as silicon.