Improvement of Surface-Enhanced Raman Scattering Method for Single Bacterial Cell Analysis

Area of Science:

• Analytical Chemistry
• Biophysics
• Materials Science

Background:

• Surface-enhanced Raman scattering (SERS) offers label-free, single-cell bacterial analysis.
• Limited reproducibility currently hinders the widespread application of SERS in microbiology.

Purpose of the Study:

• To develop a sensitive and reproducible SERS method for analyzing individual bacterial cells.
• To optimize silver nanoparticle (AgNP) synthesis and deposition techniques for enhanced SERS signals.

Main Methods:

• Optimized AgNP synthesis via fast dropwise addition of AgNO3, yielding smaller (45 ± 4 nm) and stable nanoparticles.
• Employed orthogonal experiments to optimize SERS enhancement factors, including centrifugation, AgNP preparation, concentration, ionic strength, and cell density.
• Investigated SERS signal origin, identifying the cell envelope as the primary source.

Main Results:

• Achieved significantly improved SERS signals using centrifugation compared to simple mixing of cells and AgNPs.
• Demonstrated sensitive and reproducible SERS spectra from single *Escherichia coli* cells.
• Verified the method's feasibility for detecting 13C isotope incorporation (up to 25%) and discriminating bacterial species.

Conclusions:

• The optimized AgNP preparation and deposition method significantly enhances SERS sensitivity and reproducibility for single bacterial cell analysis.
• This improved SERS technique is valuable for bacterial isotope detection and species differentiation.
• The study provides a robust methodology for advancing SERS applications in microbiology.