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Microfluidics is a rapidly growing field as it allows high resolution and sensitive detection using minimal amounts of material, ideal for developing point of care and lab on chip devices. The capabilities of microfluidics could be greatly enhanced if sensors can be integrated. The motivation of our work is to develop a technology platform which allows integrating several types of optical sensor within microfluidics. Using femtosecond laser technology, we can realize both channels and optical waveguides in the same material which can be used as building blocks for realizing sensors. Here we used Fused Silica (2.5 cm x 0.75 cm x 500 µm), an inert material which is transparent deep into the UV-spectrum while allowing femtosecond laser processing followed by chemical etching, to develop a compact transparent microfluidic chip platform. We demonstrated the capability by integrating a channel (measuring 1 cm x 500 μm x 300 μm) to perform a dynamic light scattering technique, where the fluid is illuminated and the resulting scattering intensity fluctuations are analyzed to detect the diffusion coefficient and hydrodynamic radius of particles in solution undergoing Brownian motion. To validate this technique, a water solution containing 0.01% polystyrene particles with a diameter of 200 nanometers was pumped through the microfluidic chip. We subjected the solution to 2 seconds of continuous wave laser illumination at three distinct wavelengths: 638 nm, 1307 nm, and 1550 nm. The resulting scattered light was captured by a fiber-coupled optical detector and subsequently amplified. Our findings demonstrate that the particle size can be accurately determined from the scattered light vector, with a maximum deviation of 5%, by fitting an autocorrelation function and extracting the hydrodynamic radius. This research holds significant implications for the development of new optofluidic techniques in biomedical applications.
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