Coupled Turbidity and Spectroscopy Problems: A Simple Algorithm for Volumetric Analysis of Optically Thin or Dilute,...

Area of Science:

• Analytical Chemistry
• Microbiology
• Biophysics

Background:

• Bacterial culture analysis often requires invasive sampling or lacks real-time chemical insights.
• Complex media present challenges for accurate, simultaneous physical and chemical characterization.
• Existing methods struggle with simultaneous monitoring of organism number and medium composition in situ.

Purpose of the Study:

• To introduce and validate binary spectronephelometry (BSN) for real-time, noninvasive analysis of bacterial cultures.
• To demonstrate the simultaneous monitoring of organism number density and fluid medium chemistry.
• To assess BSN's applicability in complex media with unassigned Raman spectra.

Main Methods:

• Irradiating bacterial cultures in fluid media with a near-infrared laser within a cuvette.
• Collecting backscattered light, including Rayleigh-Mie scattering and inelastic emissions (Raman, fluorescence).
• Calibrating BSN against optical density at 600 nm (OD600) for organism number density.

Main Results:

• BSN successfully monitored organism number density and provided a measure of medium chemical makeup for *Escherichia coli*, *Pseudomonas aeruginosa*, and *Shewanella oneidensis*.
• The approach remained effective despite changing turbidity and medium chemistry.
• Total inelastically emitted light correlated with the chemical state of complex media like lysogeny broth (LB).

Conclusions:

• Binary spectronephelometry offers a noninvasive, simultaneous, and continuous method for analyzing bacterial cultures in real-time.
• BSN is valuable for characterizing both organism population and the chemical environment, even in complex biological media.
• This technique holds potential for diverse applications in basic and applied research involving bacterial cultures.