Detection and fingerprinting of pathogens: Mid-IR biosensor using amorphous chalcogenide films

Multilayered Ge-based chalcogenide waveguides were fabricated on Si substrates by thermal evaporation. Channel waveguides were written in the core layer by inducing photoinduced changes in the refractive index by exposure to bandgap light. Very thin (∼20 nm) Au islands were deposited on the top of the core layer for biological functionalization. FT-IR spectroscopy confirmed that the coating of the films with gold did not have a significant effect on the propagation and penetration of IR evanescent waves through the film. Self assembled monolayers (SAM) were formed on the gold islands via thiol chemistry for biological attachment. Antibody (human IgG, anti-E. coli O157:H7, and anti-Salmonella) complexes were formed on the Au islands via the SAMs. The films functionalized with anti-E. coli O157:H7 and anti-Salmonella antibodies were used to detect E. coli O157:H7 and S. enteriditis through label-free IR fingerprinting. Highly selective detection of bacterial targets was achieved at both the species (E. coli vs. S. enteriditis) and strain level (E. coli O157:H7 vs. E. coli K12). This mid infrared approach demonstrates the use of chalcogenides for biosensor.