Dung Q. Nguyen, Kengo Ishiki, Dr. Hiroshi Shiigi and other members of their research group in Department of Applied Chemistry, Osaka Prefecture University, developed a new method for identifying the target bacteria using an organic-inorganic nanostructure adsorbed onto the indium-tin-oxide (ITO) electrode. Using such raspberry-like nanostructure: we called nanoraspberry(*1) as an electrochemical label, this method enabled to detect the target bacteria from just a single cell.

The main point of research

Graphical abstract
Schematic of a voltammetric immunoassay for Escherichia coli O157:H7 by using a nanocomposite consisting of gold nanoparticles and polyaniline on an ITO electrode

Establishing an electrochemical label, the bacterial detection can;

• Be highly-sensitive identifying a single cell adsorbed onto the ITO electrode.
• Be possible to quantify target cells adsorbed onto the ITO electrode, wide ranging from a single cell to 10⁶ cells.
• Be possible to determine the target cell specifically even in the presence of other bacteria.
• Be as fast as an hour based on the electrochemical response of the nanostructure spontaneously bound to target cells.
• Be simple and low-cost process.
• Be compatible with a portable electrochemical device.

Overview of research

The raspberry-like nanostructure comprises of highly dense gold nanoparticles (AuNPs) (*2) and polyaniline (PANI) (*3), a conductive polymer is potentially quite attractive as a cell label. Taking advantage of the unique characteristics, we developed a new method for bacterial detection.

A drop of bacterial cell suspension was added to the ITO electrode and allowed to dry. The electrode with adsorbed cells was then immerged in the nanostructure dispersion. While observing current response and a good correlation between current density and number of cells on the ITO electrode, the specific bacterial detection was obtained through the current response for a single cell regardless of the presence of other unwanted cells. This method can also be feasible with a portable electrochemical device(*4) to analyze the levels of pathogenic bacteria in multiple samples under any circumstances to reduce undesirable bacteria as to manage the quality of food, medicine and healthcare products contributing to achieve greater public health.

These research results were published in an online journal of Microchimica Acta, and titled: “Single cell immunodetection of Escherichia coli O157:H7 on an indium-tin-oxide electrode by using an electrochemical label with an organic-inorganic nanostructure”

• Microchimica Acta (“Springer” Web site)

• Full text of press release (Japanese language)（676KB）

Glossaries

*1 Nanoraspberry

When aurates are reduced using aniline, the gold nanoparticles (AuNPs) and polyaniline are synthesized. In 2006, we succeeded to develop positively-charged AuNPs of which the raspberry-like aggregation was on a nanoorder level. (Chem. Commun., 2006,4288-4290)

*2 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.

*3 Polyaniline

Polyaniline (PANI) is a conductive polymer discovered by Dr. A. G. MacDiarmid and Dr. A. J. Heeger who received the Nobel Prize in Chemistry with Dr. H. Shirakawa (Emeritus Professor, Tsukuba University). Polyaniline possesses an electrical conductivity depending on its redox state and doping level.

*4 Electrochemical device

Electrochemical sensors are devices that give information about the composition of a system in real time by coupling a chemically selective layer (the recognition element) to an electrical transducer. Most of continuous glucose monitoring for diabetes adopt this type of sensors.

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 (25020A), and by Japan Society for the Promotion of Science (JSPS) through a Grant-in-Aid for Scientific Research (B) (KAKENHI 25288039, 16H04137)