A grating-coupled porous silicon (PSi) waveguide with an integrated polydimethylsiloxane (PDMS) flow cell is demonstrated as a platform for near real-time detection of chemical and biological molecules. This sensor platform not only allows for quantification of molecular binding events, but also provides a means to improve understanding of diffusion and binding mechanisms in constricted nanoscale geometries. Molecular binding events in the waveguide are monitored by angle-resolved reflectance measurements. Diffusion coefficients and adsorption and desorption rate constants of different sized chemical linkers and nucleic acid molecules are determined based on the rate of change of the measured resonance angle. Experimental results show that the diffusion coefficient in PSi is smaller than that in free solutions, and the PSi morphology slows the molecular adsorption rate constant by a factor of 10(2)-10(4) compared to that of flat surface interactions. Calculations based on simplified mass balance equations and COMSOL simulations give good agreement with experimental data.
Keywords: (050.2770) Gratings; (130.2790) Guided waves; (130.6010) Sensors.