This thesis reports the successful design, fabrication and testing of an optical MEMS sensor for the detection of the toxic phenol, catechol. Catechol's presence in food and drinking water posses a health concern due to its harmful effects on cell respiration. By-products of catechol oxidation have demonstrated increased absorbance changes in a chitosan film in the UV and near UV range. Our reported sensor utilizes patterned SU-8 waveguides and a microfluidic channel to deliver catechol samples to an electrodeposited chitosan film for absorbance measurements at 472 nm. Concentrations as low as 1 mM catechol are detected while control experiments including ascorbic acid display no measurable response. By using optical detection methods, our device does not suffer from many of the problems which plague conventional electrochemical based sensors.