Measuring Single Bacterial Viability in Optical Traps with a Power Sweeping Technique

Area of Science:

• Microbiology
• Biophysics
• Analytical Chemistry

Background:

• Accurate bacterial viability assessment is critical for public health, food safety, and environmental monitoring.
• Existing methods like agar plating and dye assays are time-consuming, complex, and can be cytotoxic.

Purpose of the Study:

• To develop a novel, rapid, label-free bacterial viability assay.
• To utilize optical tweezers and a power sweeping strategy for single-cell analysis.

Main Methods:

• Developed a bacterial viability assay using optical tweezers with a power sweeping strategy.
• Defined the mobility restriction coefficient (MRC) based on bacterial nanomotion under varying laser powers.
• Validated the assay using live and dead *Escherichia coli* and *Photobacterium phosphoreum*.

Main Results:

• Established a strong correlation between bacterial viability and the mobility restriction coefficient (MRC).
• Demonstrated real-time, long-term viability characterization of individual *P. phosphoreum* cells.
• Proposed a 'spinning-induced stabilization' mechanism to explain observed mobility changes in inactivated bacteria.

Conclusions:

• The developed optical tweezers assay is a reliable, label-free method for single-cell bacterial viability assessment.
• This assay shows significant potential for applications in antibiotic susceptibility testing, drug screening, and rapid diagnostics.