A “lab on a chip” includes an optofluidic sensor and components to analyze signals from the optofluidic sensor. The optofluidic sensor includes a substrate, a channel at least partially defined by a portion of a layer of first material on the substrate, input and output fluid reservoirs in fluid communication with the channel, at least a first radiation source coupled to the substrate adapted to generate radiation in a direction toward the channel, and at least one photodiode positioned adjacent and below the channel.