Different size biomolecules anchoring on porous silicon surface: fluorescence and reflectivity pores infiltration comparative studies

The performance of porous silicon optical based biosensors strongly depends on material nanomorphology, on biomolecules distribution inside the pores and on the ability to link sensing species to the pore walls. In this paper we studied the immobilization of biomolecules with different size, such as antibody anti aflatoxin (anti Aflatox Ab, ∼150 KDa), malate dehydrogenase (MDH, ∼36KDa) and metallothionein (MT, ∼6KDa) at different concentrations on mesoporous silicon samples (∼15 nm pores diameter). Fluorescence measurements using FITC‐ labeled biomolecules and refractive index analysis based on reflectivity spectra have been employed together to detect the amount of proteins bound to the surface and to evaluate their diffusion inside the pores. Here we suggest that these two techniques should be used together to have a better understanding of what happens at the porous silicon surface. In fact, when pores dimensions are not perfectly tuned to the protein size a higher fluorescence signal doesn't often correspond to a higher biomolecules distribution inside the pores. When a too much higher concentration of biomolecule is anchored on the surface, steric crowd effects and repulsive interactions probably take over and hinder pores infiltration, inducing a small or absent shift in the fringe pattern even if a higher fluorescence signal is registered. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)