| Label-free optical biosensors are widely used for the detection of pathogens due to their low-cost, real-time detection and high sensitivity. A Mach-Zehnder Interferometer (MZI) based biosensor has been developed for the detection of gram-positive bacteria, Listeria monocytogenes. An extensive theoretical analysis of MZI configurations was performed to determine the critical dimensions for a high sensitivity monomodal waveguide. These MZI waveguides, with nanometer size ridge structure, were fabricated using standard micro/nanofabrication techniques. Using the fabricated MZI waveguides, an efficient optical immunoassay technique for the detection of Listeria was demonstrated. The MZI biosensor was able to detect Listeria at concentrations close to 105 cfu/ml, which is lower than the infection dose for human beings. SEM analysis and light intensity measurements showed the biosensor is highly selective to Listeria over other microbial species. Finally, a calibration scheme of the MZI biosensor was developed to determine an unknown concentration of Listeria in a given sample. |
