Enhanced Fluorescence-Based Detection of Vibrio Cells Over Nanoporous Silica Substrate

The food and waterborne pathogens threaten the human health through porous borders that require immediate detection in real time. The present work reports the development of a nanoporous silica-based platform for the rapid detection of Vibrio cells. The nanoporous thin film has been developed over silicon substrate utilizing PMSSQ (polymethylsilsesquioxane, (CH₃SiO_1.5)_n) and PPG (polypropylene glycol, CH((CH₃)CH₂O)_n) combination in PGMEA (propylene glycol methyl ether acetate) solvent as provided earlier by Gangopadhyay et al. (Nanotechnology 20, 2009 [1]). The PPG acts as a porogen and evaporates on heat treatment giving a porous structure and assembles the PMSSQ nanoparticles. The films were characterized through FTIR, EDAX, and SEM microscopy, and it was found out that the functional groups like OH, CH₃, Si–CH₃, Si–O, and Si–O–Si were present abundantly in the porous structure, which can be further modified for its application in biology. An aliquot of 2.5 µl Vibrio cell solution was immobilized (over nanoporous silica film) to study its fluorescence intensity under an epifluorescence microscope. Vibrio (Vibrio harveyi (ATCC^® 700106^™)) cells possess self-fluorescing effects with bleaching characteristics. The fluorescence images (with the progression of time) are acquired and processed through Image J (courtesy NIH), and relative fluorescence of the cells are calculated as a function of time. A 1.7 times increase in the overall fluorescence intensity level is recorded in the presence of the porous silica layer as compared to uncoated silicon substrate showing immobilization capabilities of these films.