Parallel optical read-out of micromechanical pillars applied to prostate specific membrane antigen detection

Micro and nanomechanical sensors represent a promising tool for biochemical detection because of their extreme sensitivity, fast response and low cost. Micro-pillars, in particular, are columnar resonators that can be easily arranged in dense arrays, offering a significant reduction of the analyte volume, the parallelization of the detection method and thus an increasing of measurements reliability. Moreover, through a proper functionalization, they offer a promising platform for proteins label-free detection. Here we describe the implementation of a read-out approach that allows the simultaneous measurement of tens of pillars in parallel and its application to the detection of a tumor marker, the Prostate Specific Membrane Antigen (PSMA). Pillars have been functionalized with an homogenous monolayer of antibody against PSMA (D2B, Kd<10-9M) and PSMA has been detected in a range of concentrations between 300pM and 100nM, in buffer and in diluted bovine serum; the minimum detectable concentration in buffer was around 1nM and the Kd of the system was 18nM. The acquisition of the signal from up to 40 sensors in parallel enabled the application of statistical data analysis and thus overcame the variability of single measures obtaining a significant response for small antigen amounts. As a first application, the combination of a PSMA specific antibody with the parallel approach was shown to be effective in the 1nM to 6nM range which is the window of PSMA concentration with clinical interest.