Separation-free cholesterol detection using an enzyme-doped hydrogel opto-microfluidic hybrid chip via colorimetry and light extinction spectroscopy.

Cholesterol levels serve as a critical biomarker for the diagnosis of cardiovascular diseases. However, conventional detection methods are often time-consuming and reliant on specialized laboratory equipment. In this study, we present a novel microfluidic lab-on-a-chip platform designed for the rapid and accurate detection of cholesterol, employing an enzyme-doped agarose hydrogel combined with colorimetric analysis. The chip incorporates sensing zones of varying lengths (4 mm, 5 mm, and 6 mm), enabling multiple optical measurements from a single sample. By integrating optical absorbance with RGB imaging, the system achieves high sensitivity and specificity, with a detection limit as low as 0.0065 mM and a sensitivity of 0.411 absorbance/mM. The chip design features microlenses and optical fibers to enhance light transmission and promote smooth fluid flow. Requiring only 10 μL of sample, the platform is both minimally invasive and highly efficient. Validation experiments using serum and whole blood samples demonstrate excellent recovery rates (95.8 %-110.6 %) and high precision (relative standard deviation, RSD <3.54 %). This portable, cost-effective device offers a reliable solution for routine cholesterol monitoring and early cardiovascular risk assessment.