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Hemolysis is the rupture of the red blood cells (RBCs) with consequent release of hemoglobin to the blood plasma. To detect hemolysis, the red blood cells have to be separated from the blood plasma. Current clinical methods require centrifugation steps for cell/plasma separation, which is time consuming and not suitable for integration into Point-of-Care (PoC) devices. The lack of a fast and reliable PoC hemolysis detection is a central cause of hemolysis being the largest source of unsuitable samples received in clinical laboratories worldwide. Here, we present an optofluidic approach to address this issue. To measure the free hemoglobin in plasma of whole blood, evanescent waveguide absorption is accomplished in wavelength range of 400-430 nm, where hemoglobin has the strongest absorption. For separation of the RBCs, nano-filters are imprinted on top of the waveguide, enabling local blocking of RBCs from the evanescent field region. By this means, our sensor is able to accomplish hemolysis detection on whole blood without any need of sample preparation such as centrifugation. Various nano-imprint techniques are employed to define the gratings couplers (368 nm pitch) and nano-filters(400 nm pitch). The sensor is fabricated on a flexible polymer membrane, enabling easy integration. The nano-imprint fabrication used here allows easy up-scaling for industrial adaption. Furthermore, we use gratings couplers to disperse the guided broadband light and accomplish spectral analysis with a linear camera, which enables highly compact optical setup. We tested the hemolysis sensor integrated in a modified commercial PoC blood gas analyzer. Whole blood and plasma with different free hemoglobin concentrations are tested, proving the filtering ability of the sensor. Detecting interference from other blood proteins such as bilirubin is successfully demonstrated by spectral analysis algorithm. Long-term tests for more than a month further show its high repeatability, specificity, and reliability. We envision large potential in improving PoC blood diagnostic quality by our sensor as well as further applications in optical detection in turbid media.
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