Microfluidics has variety of applications for chemical analyses and biomedical diagnoses.One of the challenges faced by microfluidics lies in the difficulty of detecting very dilute concentration of analytes (e.g., pathogen in saliva) with ultrasmall volumes in microchannels.The poor detection sensitivity results from the extremely small quantities of analytes that are injected onto the separation column and the very short (10-100 μm) optical detection path lengths.In chemical or biochemical analyses such as the detection of drug molecules in biological fluids, the drug and its metabolites are usually at much lower concentration than prepared in a laboratory.