Sensitivity enhancement of differential splitter-based transduction for photonic microcantilever arrays

Low-cost optical cavity based sensor with a large dynamic range

We have proposed an optical cavity based biosensor using a differential detection method for point-of-care diagnostics. For experimental demonstration of the proposed device using a two-laser system through refractive index measurements, an optical cavity structure is designed, fabricated, and measured. The differential value calculated with intensities of two different wavelengths has a larger responsivity with respect to the refractive index change as compared with the intesity of an individual wavelength. However, the repeatability test shows that the two-laser system has a tight fabrication tolerance due to its small dynamic range. In this paper, we introduce a three-laser system for an optical cavity sensor with a chained differential detection method and present the experimental measurement results showing a large dynamic range and large fabrication tolerance. The measured dynamic range of this system is more than three times greater than that of the two-laser system. The repeatability test using the three-laser system demonstrates a larger fabrication tolerance as a result of the increased dynamic range.

Transient deflection response in microcantilever array integrated with polydimethylsiloxane (PDMS) microfluidics

We report the integration of a nanomechanical sensor consisting of 16 silicon microcantilevers with polydimethylsiloxane (PDMS) microfluidics. For microcantilevers positioned near the bottom of a microfluidic flow channel, a transient differential analyte concentration for the top versus bottom surface of each microcantilever is created when an analyte-bearing fluid is introduced into the flow channel (which is initially filled with a non-analyte containing solution). We use this effect to characterize a bare (nonfunctionalized) microcantilever array in which the microcantilevers are simultaneously read out with our recently developed high sensitivity in-plane photonic transduction method. We first examine the case of non-specific binding of bovine serum albumin (BSA) to silicon. The average maximum transient microcantilever deflection in the array is -1.6 nm, which corresponds to a differential surface stress of only -0.23 mN m(-1). This is in excellent agreement with the maximum differential surface stress calculated based on a modified rate equation in conjunction with finite element simulation. Following BSA adsorption, buffer solutions with different pH are introduced to further study microcantilever array transient response. Deflections of 20-100 nm are observed (2-14 mN m(-1) differential surface stress). At a flow rate of 5 μL min(-1), the average measured temporal width (FWHM) of the transient response is 5.3 s for BSA non-specific binding and 0.74 s for pH changes.