Effect of etching time on optical response of calmodulin-functionalized porous silicon calcium detector

Porous silicon (PSi) gained a lot of significance lately as a biosensor due to its significantly high absorption capacity, easily modulable porosity, and its biocompatibility. In this work, the etching time dependence of the optical response of PSi-based calmodulin (CaM) surface-functionalized calcium detector is studied. PSi was fabricated on P-type silicon wafers by electrochemical etching process. Increase in electrochemical etching time significantly increases the porosity of the PSi substrate. Thus, the optical response of the PSi-based calcium detector is observed to be remarkably affected by the change in etching time. Studies were performed on both nano (structure size ranging from 6 to 19 nm) and macro (pore size ranging from 6 to 1.5 µm) PSi. Optical parameters such as reflectance, scattering, and absorptance of the PSi-based optical detector were analyzed and notable changes were recorded for changing etching time in both nano- and macro-PSi samples. This study helps to drastically improve the sensitivity of PSi-based optical calcium detector, and the concept may be incorporated in the designing of calcium or other ionic and chemical sensors with improved selectivity and sensitivity. Thus, the study is useful in the fabrication of PSi-based calcium sensors with optimized etching time so that highly sensitive and precise calcium detection can be possible using it. Graphical Abstract