The researchers, from Zhejiang Normal University in China and Sweden’s Umeå University, said that a better understanding of the growth process of microorganisms could reduce food waste and prevent people from being sickened by food poisoning.
Using a technique referred to as tuneable diode laser absorption spectroscopy (TDLAS), the team was able to develop an easy-to-use instrument to assess bacterial growth of various types of samples under a variety of conditions.
TDLAS is by far the most common laser-based absorption technique for quantitative assessments of species within a gas phase. It can be used to measure the concentration of specific gaseous species—including carbon monoxide, CO2, water and methane—within gaseous mixtures by using absorption spectrometry based on tuneable diode lasers.
“One major advantage TDLAS offers is its ability to achieve very low detection limits, on the order of parts per billion,” said Jie Shao, lead author.
“Apart from concentration, it’s also possible to determine other properties of the gas under observation—temperature, pressure, velocity and mass flux.”
The group’s basic setup simply involved a tuneable diode laser as the light source, beam shaping optics, the sample, receiving optics and one or more detectors.
“The emission wavelength of the laser was tuned over a characteristic absorption line transition of the species within the gas being assessed,” said Associate Professor Shao.
“This caused a reduction of the measured signal intensity, which we could use to determine the gas concentration.”
When the wavelength was rapidly tuned across the transition in a specific manner, it could be combined with wavelength modulation, which gave the TDLAS technique an enhanced sensitivity, known as WM-TDLAS.
By applying the technique to transparent containers of organic substances like food items or medical samples, bacterial growth could be quickly evaluated.
“Although we anticipated that the WM-TDLAS technique would be suitable for assessing bacterial growth, we didn’t expect this level of accuracy,” Prof. Shao noted.
“In contrast with conventional and more invasive techniques that require contact with the tested items, the WM-TDLAS method is truly noninvasive, making it ideal for monitoring the status of food and medical supplies, or as a tool to determine under which environmental conditions bacterial growth is expected to be severe. It can provide real-time analysis.”
The researchers now plan to enhance the technique to allow for assessments of microbial growth in a wider variety of samples, expanding beyond food items and medical supplies.
Source: Applied Optics
doi: 10.1364/AO.55.002339
“Wavelength-modulated tuneable diode-laser absorption spectrometry for real-time monitoring of microbial growth.”
Authors: Jie Shao, Jindong Xiang, Ove Axner and Chaofu Ying.