Microbiological total viable count detection based on tunable diode laser wavelength-modulation spectroscopy

Total viable counts (TVC) are vitally critical to health management, and the quantitative testing of TVC is an essential part of the microbiological testing process. This work demonstrates the rapid and accurate measurement of microbiological TVC using a wavelength-modulated tunable diode laser based on absorption spectroscopy (WM-TDLAS). To detect CO2 in sealed culture bottles, a tunable distributed feedback (DFB) laser with a central wavelength of 2004 nm was employed as the light source. Experiments with Salmonella show that the technique can generate effective second harmonic signals, allowing the detection limit to be 71.8 ppm. Simultaneously, the optimal parameters for measuring the growth curve of Salmonella at various concentrations were determined to establish the standard curve used to calculate the TVC. When compared to the conventional method ISO 4833:2013, the new detection method illustrates good correlation (R2 = 0.98), and the results can be obtained within the detection range of 1-8 log10(CFU/mL) in 4-12 h, saving at least 36 h. Thus, it was shown that WM-TDLAS is a user-friendly, non-invasive technique that allows rapid and accurate assessment of TVC.