This technology accurately measures viable bacteria in food within one hour, as opposed to two days, regardless of bacterial species. (Image: Hiroshi Shiigi, Osaka Metropolitan University)

A research group led by Professor Hiroshi Shiigi at the Graduate School of Engineering, Osaka Metropolitan University, has developed a technology that can rapidly and accurately determine the number of viable bacteria in food products electrochemically, using tetrazolium salt (MTT), a water-soluble molecule.

One of the most important assessment indicators for ensuring that food is free from contamination is the number of viable bacteria. However, conventional measurement methods take up to two days to yield results, and these results are only available after the food has been shipped from the factory — leading to potentially fatal consequences. Therefore, it is imperative to have a testing method that speeds up the process of identifying bacterial contamination before shipment.

The researchers have succeeded in drastically reducing the inspection time from two days to about one hour, regardless of the bacterial species.

“With this method, we can quickly measure the number of viable bacteria, allowing us to confirm the safety of food products before they leave the factory and to prevent food poisoning,” said Shiigi. “This method does not require complicated operations or expensive equipment. Therefore, we will continue to optimize the measurement conditions and expect to see the development of a portable sensor in line with the development of research aimed at practical applications.”

Here is an exclusive Tech Briefs interview — edited for length and clarity — with Shiigi.

Tech Briefs: I’m sure there were too many to count, but what was the biggest technical challenge you faced while developing this antimicrobial nanotechnology?

Shiigi: We have developed a technology to rapidly measure bacterial activity. The greatest difficulty in developing such technology is that bacteria are living things. Although it is possible to roughly equalize the number of viable bacteria in a suspension, the activity and viability will change while measuring many sample solutions. Therefore, we had no choice but to develop technology to stop time or to quickly measure bacterial activity. Although both are dream-like developments, we chose the latter.

Tech Briefs: Can you explain in simple terms how it works?

Shiigi: When a voltage is applied to a dye molecule called a tetrazolium salt, an electric current is generated due to a reduction reaction on the electrode. This dye is soluble and has excellent cell membrane permeability. When the dye enters living cells, it is converted into an insoluble form as a result of intracellular metabolism and deposited inside the cell. Therefore, when this dye is added to a bacterial suspension, the number of dye molecules in the solvent decreases proportionally to the number of live cells, and thus the current response decreases proportionally to the number of live cells. Based on this principle, it is possible to estimate the number of live bacteria in a suspension prepared from a food sample by focusing on the current response.

Tech Briefs: You’re quoted as saying, “We will continue to optimize the measurement conditions and expect to see the development of a portable sensor in line with the development of research aimed at practical applications.” How is that coming along?

Shiigi: Currently, we are continuing basic research with the aim of developing portable sensors.

Tech Briefs: What’s the next step? Do you have any plans for further research?

Shiigi: We are considering several plans for practical use. One of them is the development of inexpensive devices that are expected to become popular. This development is expected to be used in a variety of fields including medicine, pharmaceuticals, and the environment, but the most promising field is food safety. Food safety is a global issue, and many things in our lives, such as farms, food factories, and restaurants, are related to food, so this development is expected to be useful in a variety of food-related scenes.

We also spend a lot of time discussing food safety with domestic and international researchers and companies. Their helpful inputs reveal the most effective product form for the devices this development brings. We hope to publish the final form of this device as soon as possible. To that end, we would like to find the right partners and work together to implement some plans individually.

Tech Briefs: Is there anything else you’d like to add?

Shiigi: If the common ultimate goal for researchers and developers is to publish papers or obtain research funding, model answers exist for each field. However, since laboratory development is not a school exam and homework, there are no model answers. Development is a human act, involving knowledge, experience, passion, dreams, and sometimes disappointments and compromises. In that sense, development may be similar to music.

The group that plays the music called “development” can be enjoyed just by playing. Furthermore, when the performance is released to the public, those who were exposed to it and sympathized with it will be able to enjoy it. As a first step, researchers and developers should start by dreaming and having fun.