Oxidized Porous Silicon Nanostructures Enabling Electrokinetic Transport for Enhanced DNA Detection

Nanostructured porous silicon (PSi) is a promising material for the label-free detection of biomolecules, but it currently suffers from limited applicability due to poor sensitivity, typically in micromolar range. This work presents the design, operation concept, and characterization of a novel microfluidic device and assay that integrates an oxidized PSi optical biosensor with electrokinetic focusing for a highly sensitive label-free detection of nucleic acids. Under proper oxidation conditions, the delicate nanostructure of PSi can be preserved, while providing sufficient dielectric insulation for application of high voltages. This enables the use of signal enhancement techniques, which are based on electric fields. Here, the DNA target molecules are focused using an electric field within a finite and confined zone, and this highly concentrated analyte is delivered to an on-chip PSi Fabry-Pérot optical transducer, prefunctionalized with capture probes. Using reflective interferometric Fourier transform spectroscopy real-time monitoring, a 1000-fold improvement in limit of detection is demonstrated compared to a standard assay, using the same biosensor. Thus, a measured limit of detection of 1 × 10^-9 m is achieved without compromising specificity. The concepts presented herein can be readily applied to other ionic targets, paving way for the development of other highly sensitive chemical and biochemical assays. 1000-fold sensitivity enhancement of porous Si (PSi) biosensors for nucleic acid detection is achieved by a novel label-free assay that interfaces PSi Fabry-Pérot interferometry with isotachophoresis. The presented concepts can be readily applied to other ionic targets, paving way for the development of other highly sensitive chemical and biochemical assays.