Porous silicon interferometers for high-sensitivity label-free detection of biomolecules

Porous silicon (PSi) is a promising nanostructured material for label-free interferometric biosensing, though it currently suffers of restricted “real” applications in medical diagnostics. This is usually ascribed to PSi interferometer limited sensitivity due to mass-limited diffusion of (bio)molecules inside its nanopores. Here we report on a high-sensitivity label-free interferometric technique (i.e. Interferogram Average over Wavelength, IAW, reflectance spectroscopy) for, though not limited to, PSi interferometers. The IAW reflectance spectroscopy is based on the calculation of spectral interferograms obtained by subtraction of reflectance spectra acquired after interaction of target biomolecules with the PSi interferometer inner surface, from a reference reflection spectrum acquired in buffer before injection of target molecules. The IAW reflectance spectroscopy was set up studying nonpecific adsorption of Bovine Serum Albumin (BSA) onto oxidized PSi interferometers and then validated through the development of an aptasensor using PSi interferometers for the specific detection of Tumor Necrosis Factor a (TNFa, a sepsis biomarker). In both the cases we demonstrated that sub-nanomolar detection limits (DLs) can be achieved, which are 4 orders of magnitude lower than DLs achieved using Fast Fourier Transform (FFT) reflectance spectroscopy (usually in the micromolar range), in direct label-free operation. These results open exciting perspectives for point of care (POC) analysis based on PSi interferometers, for which increasingly lower detection limits are required.