Abstract: Aspects relate to an integrated and compact attenuated total internal reflection (ATR) spectral sensing device. The spectral sensing device includes a substrate, a spectrometer, and a detector. The substrate includes an ATR element, a microfluidic channel, and a channel interface at a boundary between the ATR element and the microfluidic channel formed therein. The ATR element is configured to receive input light and to direct the input light to the channel interface for total internal reflection of the input light at the channel interface. An evanescent wave produced by a sample contained within the microfluidic channel based on the total internal reflection of the input light attenuates the light output from the ATR element and the resulting output light may be analyzed using the spectrometer and the detector.