Self-Supported Bragg Stacked Microcavities for DNA Sensing

Porous silicon (PSi) layers are prepared on the single-crystal silicon surface by electrochemical etching, and PSi membranes (PSiMs) are fabricated by separating the PSi layers from the single-crystal silicon substrate using high-current pulses. PSiMs have better adsorption and response time than nonseparated PSi layers, making them more suitable for sensing applications. PSi microcavity (PSM) structures are widely used for the detection of biomolecules in biosensors because of their high transmission resonance peaks with narrow full-width at half-maximum (FWHM) in the reflection spectra. However, when compared to PSiMs, the permeability of the PSM on the silicon substrate is low, resulting in a significant reduction in its detection sensitivity. In this study, an efficient self-supported Bragg stacked microcavity (SBSM) structure was prepared for the detection of DNA biomolecules by combining the advantages of PSM and PSiMs. The redshift of the reflectance spectra obtained in the concentration range of 0.1–
$0.5 ~\mu \text{M}$
shows a good linear relationship, with a detection limit of 2.2 nM. The detection sensitivity is improved by more than a factor of ten when compared to the PSM structure on the silicon substrate. The novel device allows DNA biomolecules to enter the porous layers more easily, especially the defective layer, thus improving its detection sensitivity.