Indirect Detection of Bacteria on Optically Enhanced Porous Silicon Membrane-Based Biosensors Using Selective Lytic Enzymes

In this work, we developed a biosensor for the indirect detection of bacteria via their lysate. The developed sensor is based on porous silicon membranes, which are known for their many attractive optical and physical properties. Unlike traditional porous silicon biosensors, the selectivity of the bioassay presented in this work does not rely on bio-probes attached to the sensor surface; the selectivity is added to the analyte itself, by the addition of lytic enzymes that target only the desired bacteria. The resulting bacterial lysate is then able to penetrate into the porous silicon membrane and affects its optical properties, while intact bacteria accumulate on top of the sensor. The porous silicon sensors, fabricated using standard microfabrication techniques, are coated with TiO₂ layers using atomic layer deposition. These layers serve as passivation but also enhance the optical properties. The performance of the TiO₂-coated biosensor is tested for the detection of Bacillus cereus, using the bacteriophage-encoded PlyB221 endolysin as the lytic agent. The sensitivity of the biosensor is much improved compared to previous works, reaching 10³ CFU/mL, with a total assay time of 1 h 30 min. The selectivity and versatility of the detection platform are also demonstrated, as is the detection of B. cereus in a complex analyte.