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Wednesday, 11 December 2019

A novel device to “see” bacterial contaminants

Researchers of the ICN2 Nanobioelectronics and Biosensors group, led by ICREA Prof. Arben Merkoçi, have developed a novel sensor to detect bacterial contamination in water or food samples that combines the high sensitivity of electrochemical sensors with the simplicity of a visual read-out.

Monitoring of bacterial contamination in food and water is a procedure of the highest importance to guarantee public health. Accurate examinations can be carried out through specific laboratory tests, which provide precision and reliability, but often require long procedures and expensive equipment. In many cases, though, the possibility to perform tests quickly and in the point of care, that is, in the place where the sample is collected, represents an important asset. Electrochemical sensors have been developed for this kind of applications, since they can offer high sensitivity and specificity.

The ICN2 Nanobioelectronics and Biosensors group, led by ICREA Prof. Arben Merkoçi, has developed a smart chip that pushes this technology a step forward by combining the advantages of electrochemical sensors with the convenience of a simple visual read-out. This electrochromic device changes color according to its oxidation state, which is generated by an electric potential applied to its electrode, and its interaction with bacteria.

As explained in a paper recently published on Analytical Chemistry, these devices are based on polyaniline (PANI) -- which is an electrochromic material that is able to provide a fast response and a wide range of color variations -- and indium tin oxide electrodes. Antibodies are immobilized on the surface of the electrode, so that they can create bonds with the bacteria when in contact with a contaminated sample. The presence of such bonds and their variable concentration affect the response of the device, which, as a consequence, changes color.

This new sensor has been tested for Escherichia Coli (E.Coli) contamination, following the indications of agencies such as the United States Food and Drug Administration. As there exist many different bacteria and testing samples for each of them is impossible, the E.Coli has been chosen as a generic indicator for the overall bacterial contamination of fresh products and water. However, the device can be tailored for other specific bacteria by simply changing the antibody fixed to the electrode.

The PANI-based electrochromic sensor has proved to work by providing reliable information about E.Coli contamination after an incubation time of one hour at room temperature. It means that the result of a point-of-care analysis could be obtained in 60 minutes on average. Further studies could be devoted to improving the limit of detection of the sensor, which is the lowest quantity of contaminant that can be identified, and to shortening the incubation time.

The easy read-out, which allows detecting the presence of bacterial contaminants by the naked eye, its fast response and portability, as well as its high sensitivity and specificity, make this novel electrochromic sensor an optimal tool for environmental and food contamination monitoring.

 

Reference article:

Smart Chip for Visual Detection of Bacteria Using the Electrochromic Properties of Polyaniline, Saba Ranjbar, Mohammad Amin Farahmand Nejad, Claudio Parolo, Saeed Shahrokhian, and Arben Merkoçi, Anal. Chem. 2019, 91, 23, 14960-14966. DOI: 10.1021/acs.analchem.9b03407