Silicon Rich Silicon Nitride Microchannels to Determine Fluid Composition by Near Infrared Absorbance

The aim of multiparameter microfluidic sensors is to determine multiple physical and chemical properties of liquids and gases at a microscale on a same chip platform. Silicon-rich silicon nitride (SiRN) microfluidic channels fabricated with MEMS surface channel technology (SCT) are currently used in multiparameter sensors to detect physical parameters like mass flow rate, density, and pressure with high sensitivity. However, the current platform has limited information on sensing chemical parameters like fluid composition for mixtures of more than two different fluids when using traditional physical methods. The growing interest in integrating optics to microfluidic devices for such measurements has led to an attempt to integrate optics in the current multiparameter sensing platform. Here, we demonstrate absorbance measurements using the Beer-Lambert law for four different methanol in water mixtures in a microfluidic device fabricated with SiRN microchannels using coupled multimode optical fibers. We compare the measured transmission spectral response with the theoretical response of methanol-water mixtures. The absorbance measurements show the feasibility of integrating optical methods at near infrared wavelengths in the state-of-the-art multiparameter flow sensor technology platform.