Integration of promising technologies that can enhance sensitivity, selectivity, and throughput into micro total analysis systems (μTAS) are important in making them useful in precise screening of reaction byproducts in analytical chemistry, cellular biology and pharmaceutical industries. But unfortunately so far a method to precisely determine molecular signatures of reagents is missing in μTAS. We have developed a technique whereby molecular signatures of 50 pL of liquid reagents confined within a bimetallic microchannel cantilever can be obtained. This is achieved using wavelength dependent mechanical bending of the cantilever under infrared (IR) radiation. This technique also allows simultaneous physical characterization of the liquid reagent using variations in resonance frequency. It is useful in lab-on-a-chip devices and has a myriad of applications in drug screening, bioreactor monitoring, and petrochemical analysis.