Nippon Paint Introduces Real-time Evaluation System for Antibacterial Coatings

A research team led by Haruhiro Miyamae of Nippon Paint Co., Ltd., in collaboration with Assistant Professor Noriko Nakamura and Associate Professor Seiichi Ohta from the University of Tokyo's Graduate School of Engineering, has developed a real-time evaluation system to visualize the antibacterial effects of coatings.

Continuous Observation of Bacterial Proliferation

In this study, the research team successfully monitored bacterial growth on coating surfaces spanning several square centimeters in real time. This was achieved using E. coli expressing green fluorescent protein (Note 1) and a fluorescence observation device. This method enables the analysis of time-dependent changes in bacterial distribution on coatings, a capability not possible with conventional ISO-standard methods (Note 2).

Fluorescence images captured during the study were transformed into multiple quantitative indices, allowing for a systematic evaluation of factors such as coating size and culture medium volume. These analyses helped optimize evaluation conditions. Under these refined conditions, the antibacterial effects of coatings designed for infection prevention (Note 3) were successfully demonstrated.

This breakthrough enables more precise assessments of antibacterial coatings, supporting their wider adoption. It is expected to contribute significantly to future infection prevention efforts.

Shortcomings of Traditional Assessment Methods

The application of antibacterial and antiviral coatings on high-touch surfaces, such as those in medical facilities and public transportation, has proven effective in preventing the spread of infectious diseases, including COVID-19. Traditionally, the performance of these coatings has been evaluated using ISO-standard methods, which involve washing bacteria from the coating into a culture medium and then re-culturing them on agar plates for assessment.

However, this method does not capture real-time bacterial activity or provide spatial distribution data. Additionally, research has shown that factors such as bacterial density on the coating can significantly impact evaluation results. Despite this, systematic efforts to optimize these factors have been limited, resulting in suboptimal testing conditions.

As a result, there is a growing need for an advanced evaluation system that not only delivers more precise assessments of antibacterial coatings but also visually demonstrates their effectiveness to consumers, encouraging wider adoption.

Use of E. coli Expressing Green Fluorescent Protein

The research team successfully visualized the real-time spatial distribution of bacteria growing on coatings using E. coli expressing green fluorescent protein. This was achieved through fluorescence images captured with a custom-built observation device equipped with an LED light source, optical filter, and digital camera.

Traditional fluorescence microscopy was limited to analyzing bacterial distribution on extremely small areas, only a few square micrometers in size. Additionally, it was restricted to transparent coatings that allowed excitation light to pass through. In contrast, the research team’s specialized device enabled continuous spatial distribution analysis over several square centimeters, even on opaque coatings.

Fluorescence images were converted into quantitative indices, including the average brightness of fluorescent proteins, brightness distribution along a central axis of the coating, and brightness variability across the entire surface. These indices were systematically used to assess how factors such as coating size and culture medium volume influenced evaluation outcomes.

With optimized observation conditions, the team achieved real-time visualization of bacterial proliferation inhibition on antibacterial coatings. These coatings, previously assessed under ISO standards, demonstrated strong antibacterial effects, further validating their performance.

Paving Way for Practical Valuations Using Pathogenic Bacteria

This method can be applied to a wide range of bacterial species expressing fluorescent proteins, enabling future practical evaluations using pathogenic bacteria. By adopting this approach, researchers can more accurately assess the performance of antibacterial coatings and visualize their effects in real time.

The widespread implementation of this technology is expected to accelerate the adoption of antibacterial coatings, contributing to improved infection prevention efforts.

This research was conducted as part of the social collaboration program Creation of Innovative Coating Technologies. Established through an industry-academia partnership between the University of Tokyo and Nippon Paint Holdings, the program is set to run for five years, from October 1, 2020, to September 30, 2025.

Sources: Nippon Paint