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 indirectdetectionof bacteria via their lysate. The developed sensor is based on poroussilicon membranes, which are known for their many attractive opticaland physical properties. Unlike traditional porous silicon biosensors,the selectivity of the bioassay presented in this work does not relyon bio-probes attached to the sensor surface; the selectivity is addedto the analyte itself, by the addition of lytic enzymes that targetonly the desired bacteria. The resulting bacterial lysate is thenable to penetrate into the porous silicon membrane and affects itsoptical properties, while intact bacteria accumulate on top of thesensor. The porous silicon sensors, fabricated using standard microfabricationtechniques, are coated with TiO2 layers using atomic layerdeposition. These layers serve as passivation but also enhance theoptical properties. The performance of the TiO2-coatedbiosensor is tested for the detection of Bacillus cereus, using the bacteriophage-encoded PlyB221 endolysin as the lyticagent. The sensitivity of the biosensor is much improved comparedto previous works, reaching 10(3) CFU/mL, with a total assaytime of 1 h 30 min. The selectivity and versatility of the detectionplatform are also demonstrated, as is the detection of B. cereus in a complex analyte.