The proliferation and existence of microorganisms in the environment have gained special attention to the safety and security of human life. Detection and characterization of microbes have significant functions when the safety and security of First Responders, government personnel, and civilians, in general, are at risk. Raman Scattering (RS) is a powerful tool for rapidly and accurately identifying, detecting, and characterizing microorganisms. This technique is non-invasive, fast, and impervious to water interference. One of its applications that has gained great improvement is Surface-Enhanced Raman Scattering (SERS), which has the added advantage of detecting microorganisms at trace levels. An excellent source of nanomaterials for the development of a SERS substrate is gold nanorods. We report on a simple, fast, and reproducible method for preparing SERS active substrates for detecting microorganisms at trace levels. In addition to SERS, Quantum Cascade lasers (QCL) were used in one of the most popular applications, Surface Enhanced Infrared Absorption Spectroscopy (SEIRA), for microorganism characterization and quantification. The SERS and SEIRA active substrates and nanomaterials were characterized by UV-Vis, Nano-Plus™, SEM, RS, and QCL at the grazing angle of incidence of measurements. Synthesis and characterization of gold nanorods (AuNR) were successfully achieved, rendering nanostructures of 30.5 - 85.9 nm. For SERS and SEIRA substrates, we used a Stainless-Steel (SS) substrates (10 x 10 mm) coated with gold AuNR using a Chemical Printer (ChemCal™) for detecting Staphylococcus aureus (Sa), Staphylococcus epidermidis (Se), and Micrococcus luteus (Ml). A mixture of these microorganisms will be characterized to further asses their complex interactions. A mathematical method to discriminate and identify the microorganisms based on their SERS spectra was developed. Statistical tools such as Principal Component Analysis (PCA) and Partial Least Squares Analysis (PLS) will be used to complement our chemical analysis, enhancing the accuracy of microbial identification.

José A. Centeno-Ortiz

Appearances