Weak Adsorption-Induced Surface Stress for Streptavidin Binding to Biotin Tethered to Silicon Microcantilever Arrays

We investigate the performance and limitations of silicon microcantilever arrays as biosensors in which receptor molecules are directly tethered to the native oxide without an intermediate metal adhesion layer such as gold. We use our recently developed in-plane photonic microcantilever (PMCL) readout method to simultaneously measure deflection of individual microcantilevers in a 16-PMCL array integrated with polydimethylsiloxane microfluidics. We demonstrate label-free biosensing of streptavidin using biotin that has been immobilized to only the top side of a subset of PMCLs within the array. The maximum surface stress that we measure is rather small (6 mN/m) for relatively high streptavidin concentration (4.7
$\mu{\rm M}$
). We attribute this result to lack of a metal adhesion layer, which eliminates strong surface stress generation from change in metal electronic charge density upon uptake of streptavidin by surface-bound biotin.