Porous Silicon Based Protocol for the Rapid and Real-Time Monitoring of Biorecognition Between Human IgG and Protein A Using Functionalized Superparamagnetic Beads

Optical interferometer biosensors based on porous silicon (PSi) are being studied for chemical and biological sensor applications. In particular, single PSi is a promising sensing platform for biomolecules and based on monitoring changes in the optical thickness
$(2nL)$
from Fabry–Pérot fringes due to magnetic particle-labels covering PSi surfaces. These methods offer a fast, and one-step method for immunoassaying by combining nano-sized superparamagnetic beads (SPBs) with interferometer PSi platforms. Furthermore, SPBs covered with biomolecules have a higher reflective index than the biomolecules alone, which results in larger shifts of the optical thickness
$(2nL)$
by the penetration of SPBs inside pore walls of PSi. In this work, we immobilized protein A onto macropore PSi and used optical reflection to detect human IgG immobilized onto nano-sized SPBs by measuring changes of optical thickness
$(2nL)$
. Furthermore, the optical thickness
$(2nL)$
was proportional to mass of the biomolecules, thus the
$\Delta 2nL$
corresponded to the mass fraction of active IgG with SPBs inside PSi pores. Therefore, we quantified the changes of optical thickness
$(2nL)$
to enable the detection of SPBs functionalized human IgG based on protein-A modified macropore sized PSi platform.