S. Safaripour, L. Moncada, T. Hutter
University of Texas at Austin,
United States
Keywords: Optofluidics, microplastics, UV-Vis spectroscopy, fiber optics
Summary:
Water contamination with microplastics is a growing global issue that threatens human health. Detecting these particles, typically ranging from 1 μm to 5 mm in size, is essential for ensuring the safety of drinking water. Current detection techniques often rely on complex, high-cost laboratory procedures that can be time-consuming. In this project, we present a simple optofluidic chip designed to quantify microplastic particles within a sample and estimate their relative sizes. The chip is fabricated using rapid, low-cost methods that do not require access to cleanroom facilities and consists of a three-inlet microchannel with optical fibers integrated perpendicular to the channel direction, on the same horizontal plane (x–y plane). The three inlets allow the sample and the microplastics to be hydrodynamically focused at the center of the channel, guiding it precisely between the optical fibers. The chip’s microchannels were created by laser engraving an acrylic sheet to a depth of 245 µm, and two 125 µm-diameter multimode fibers were integrated perpendicular to the channel and connected to a UV-Vis spectrometer for data collection. The chip was tested using orange polyethylene microspheres with sizes ranging from 106 µm to 125 µm. Results showed that each time a bead passed through the light path, the intensity of the light detected by the spectrometer decreased. This drop in intensity indicates the presence of a bead and reflects how much light was blocked by it. The collected were then compared to a video recording of the beads flowing through the channel to confirm that the dips in the spectrum occurred at the same time as the beads passed. Based on this, the number of particles was counted, which was then used to estimate their concentration in the sample. Furthermore, analyzing the magnitude of the intensity drop along with the width of each drop, calculated using full width at half maximum (FWHM), gives us the information about how much light was obstructed and the duration of each particle’s passage. These two parameters, and their distribution, can help estimate the sizes of particles present in the sample. The significance of this project lies in introducing a low-cost, user-friendly device capable of detecting microplastic particles in water without relying on professional laboratory methods. The device is compatible with different types of optical fibers and its dimensions can be adjusted based on the sample and the expected size range of microplastics. This flexibility also gives us the opportunity to integrate multiple fibers along the channel, allowing simultaneous detection and measurement using fibers of various core diameters.