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A group of researchers from the Graduate School of Engineering at Nagoya University, the Institute for Materials Chemistry and Engineering at Kyushu University, and The Institute of Scientific and Industrial Research at Osaka University, developed a portable ionic current sensor (Robust-ICS) for detecting sub- to several-micron scale particles, such as bacteria.

As ionic current sensing methods used for Robust-ICS have a function of size detection according to the proportional relationship between the volume of the sample and the signal amplitude, this method is expected as a promising measurement technique for efficient measurement of substances in various fields. However, commercially available ionic current sensing devices are not suitable for on-site measurements of bioaerosols because of the inherent limitations on their robustness and portability.

Thus, this group focused on a technique to suppress background current. Their technique to suppress background current has enhanced the amplitude of current signals, which are generated through the application of high voltage, eliminating the effect of current noise in detecting small particles. This made the measurement systems robust, leading to the fabrication of a portable ionic current sensor with a thin and lightweight electromagnetic shield.

Robust-ICS, a portable ionic current sensing device with a bridge circuit, has a height of 18 cm, a depth of 21 cm, a width of 35 cm, and a weight of less than 4kg. The device operates outdoors and in extreme environments (a temperature of 4 °C and humidity of 20% ~ a temperature of 40 °C and humidity of 100%) and is durable and sturdy. It is capable of correctly measuring particles of 500 nm~1,000 nm in diameter. The distribution of diameters of Staphylococcus aureus (S. aureus) measured by Robust-ICS corresponded to that obtained by a scanning electron microscope (SEM) with a high degree of accuracy. It is also possible to measure particles in a large electromagnetic noise environment, such as in laboratories and outdoors.

In this study, using a technique for suppressing background current using a bridge circuit from μA to under 10 pA, this group developed a current measurement technique in which tolerance against environmental effects is far higher than that of conventional ionic current sensing devices. This group has established a fundamental technique of next-generation ionic current sensors for detecting microorganisms.

Optimization of Robust-ICS for commercialization will allow for easy on-site detection of various particles in the environment. This will lead to the development of measurement sensors as safety measures against environmental contamination in food factories, pharmaceutical factories, hospitals, and vehicles, as well as security measures to prevent infection in poultry farms and airports. This group’s technique will lead to the development of environmental measurement devices capable of measuring microorganisms present in bioaerosol.


Ionic current sensing methods are useful tools for detecting sub- to several-micron scale particles such as bacteria. However, conventional commercially available ionic current sensing devices are not suitable for on-site measurement use because of inherent limitations on their robustness. Here, we proposed a portable robust ionic current sensor (Robust-ICS) using a bridge circuit that offers a high signal-to-noise (S/N) ratio by suppressing background current. Because the Robust-ICS can tolerate increased noise in current sensing, a simple, lightweight electromagnetic shield can be used and measurements under large electromagnetic noise conditions can be made. The weight of the device was lowered below 4 kg and outdoor particle detection measurements were completed successfully. Accuracy of size detection of Staphylococcus aureus (S. aureus) was equivalent to that obtained by SEM imaging.


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To learn more about this research, please view the full research report entitled "Robust Ionic Current Sensor for Bacterial Cell Size Detection" at this page of ACS Sensors.

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