Osaka Prefecture University

Real-Time Evaluation of Bacterial Viability Using Gold Nanoparticles

LastUpDate: April 05, 2018

Dr.Hiroshi SHIIGI, Dr.Tsutomu NAGAOKA and other members of their research group in Department of Applied Chemistry, Osaka Prefecture University, successfully demonstrated a simple and real-time evaluation of bacterial viability based on chemical interactions between gold nanoparticles (Au NPs) (*1) and substances secreted by bacteria. This colorimetric procedure makes it possible to evaluate the bacterial viability with naked eyes and is potentially applicable in various fields such as the medical, pharmaceutical, agricultural, and food-related industries for the purpose of hygiene management and quality control.  

Main Point of Research

Figure. Color change of the suspension on a ratio of live/dead bacteria.picture

Figure. Color change of the suspension on a ratio of live/dead bacteria.

The color of Au NPs dispersion depends on its dispersion state, which is reddish for dispersed state and bluish for aggregated one. As the

proportions of dead bacteria increased, the color immediately changed and shifted from red, through purple, to blue. The bacterial viability could be accurately determined by the absorbance at a specific wavelength. The proposed method enables us to visually evaluate the viability of various bacteria regardless of gram positive, gram negative(*2) and fungus species.

Overview of Research

Bacterial viability is one of the important parameters contributing to various aspects of research related to hygiene management, antibacterial agents, and the effective use of beneficial bacteria. Therefore, it is necessary to develop a simple method to check for bacterial viability that can be performed anywhere without complicated skills and large-scale equipment, to prevent bacterial contamination or evaluate their activities. In this work, we found that the color of the bacterial suspension depended on the dispersion state of Au NPs based on chemical interactions between molecular-modified on the surface of Au NPs and substances secreted by bacteria.

The color of the bacterial suspension varies from red, the original color of Au NPs in the dispersed state, then purple to blue corresponding to bacterial viability. Although the viability was accurately determined by the absorbance at a specific wavelength, this real-time assessment could be easily recognized with the naked eye.

This method is useful not only for the bacterial viability estimation in various applications but also for evaluating the biological functions of bacteria focusing on their secretions of which deoxyribonucleic acids from dead bacteria or extracellular polysaccharide from live bacteria.

This research results were published in the March 1st, 2018 issue of the Analytical Chemistry, an online journal of American Chemical Society, and titled: “Real-Time Evaluation of Bacterial Viability Using Gold Nanoparticles”


*1 Gold nanoparticles

It is also called gold colloid. Since it exhibits red color in the dispersed state, it has been utilized by many craftsmen for stained-glass arts in Medieval Europe. In recent years, it is also used as a label in test strip for influenza and pregnancy.

*2 Gram-positive bacteria, Gram-negative bacteria

By Gram staining test, Gram-positive bacteria become purple while Gram-negative bacteria are somehow reddish. These behaviors in staining are caused by the differences in the structure of their cell walls. The Gram-positive bacteria are covered with thick peptidoglycan layer, while the surface of Gram-negative bacteria are covered with lipopolysaccharide.

Research Grant

This work was financially supported by the Ministry of Agriculture, Forestry, and Fisheries through a Science and Technology Research Promotion Program for the agriculture, forestry, fisheries, and food industries, Japan Society for the Promotion of Science (JSPS) through a Grant-in-Aid for Scientific Research (B) (KAKENHI 16H04137) and a Grant-in-Aid for Challenging Exploratory Research (KAKENHI 26620072), a Grant-in-Aid for JSPS Research Fellowship (16J07230).


Graduate School of Engineering

Dr. Hiroshi SHIIGI

E-mail shii[at] *Please change [at] to @.