Microfluidic biochip platform sensitized by AgNPs for SERS based rapid detection of uric acid

Herein, a novel microfluidic-biochip enabled with surface enhanced Raman spectroscopy (SERS) as a readout has been demonstrated for uric acid (UA) detection as point-of care (POC) device. Three different biochip designs (D1, D2 and D3) containing pillars in a microchannel with different bending ratios were conceived and optimized for various mixing parameters using a multiphysics simulation tool. The microchannel, integrated with pillars, provide pressure perturbation, sharp corners, and variation in bending ratio improves phase shift and mixing index. Subsequently the microfluidic-biochips were fabricated by a combination of photo-and soft-lithography, and bonding strength between two Polydimethylsiloxane substrates were found stable up to a flow rate of 1.8 ml min(-1). Further to realize SERS activity in the microfluidic-biochip, cubic shape silver nanoparticles (AgNPs), with an average size similar to 68 nm, were synthesized using poly-ol method. The SERS activity was optimized by simultaneously flowing AgNPs and crystal violet (CV) dye of 10(-6)M, with double inlet in the reservoir and highest sensitivity was achieved in the D3 biochip. Further, D3 biochip was employed for detection of extended concentrations of CV and UA. The enhancement factor limit of detection and relative standard deviation was found to be 2 x 10(7), 8.9 x 10(-11) and 2.7% respectively for CV and 3.1 x 10(3), 3.2 x 10(-7) and 2.9% respectively for UA. Interference of UA with lactic acid has been tested and device was able to detect signature peaks of both biomarkers up to 50 x 10(-9) M concentration. Thus, the developed microfluidic-biochip device has potential to be used in a POC setting for onsite detection of biomarkers.