A novel nutrient sensor using liquid core waveguide technique is reported, implementing Teflon AF 1601S coated microchannels. Straight PDMS microchannels replicated from a master were coated with Teflon AF 1601S and sealed with a Teflon AF 1601S coated Pyrex 7740 wafer. It formed a liquid core waveguide with a low index of refraction channel in which a high index aqueous solution was flowed. Light generated by a fiber-coupled tungsten halogen lamp propagated by total internal reflection to the end of the channel where the light was detected using a CCD array spectrometer. There is a dramatic difference between channels with and without a Teflon coating. The absorbance response of this sensor varies linearly with concentration. This innovative technique provides a potentially low-cost and high efficient approach to fill the inspection technology gap between in-situ and laboratory analyses. It is believed that the novel process is expected to give an impact to the aqueous inspection and to create a highly value-added technology in optical test, measurement industry.