Dark-Field Microscopic Detection of Bacteria using Bacteriophage-Immobilized SiO₂@AuNP Core-Shell Nanoparticles

To replace molecular biological and immunological methods, biosensors have recently been developed for the rapid and sensitive detection of bacteria. Among a wide variety of biological materials, bacteriophages have received increasing attention as promising alternatives to antibodies in biosensor applications. Thus, we herein present a rapid and highly selective detection method for pathogenic bacteria, which combines dark-field light scattering imaging with a plasmonic biosensor system. The plasmonic biosensor system employs bacteriophages as the biorecognition element and the aggregation-induced light scattering signal of gold nanoparticle-assembled silica nanospheres as a signal transducer. Using Staphylococcus aureus strain SA27 as a model analyte, we demonstrated that the plasmonic biosensor system detects S. aureus in the presence of excess Escherichia coli in a highly selective manner. After the sample and the S. aureus phage S13′-conjugated plasmon scattering probe were mixed, S. aureus detection was completed within 15-20 min with a detection limit of 8 × 10⁴ colony forming units per milliliter.