The researchers have developed an external force-assisted near-field illumination biosensor (EFA-NI biosensor) that can detect small amounts of bio-substances, including viruses, in contaminant containing samples such as secondary treated sewage water. Highly sensitive measurement without removal of contaminants from the samples has been achieved by attaching magnetic beads and fine particles that scatter light to the bio-substances.

Basic principles of the EFA-NI biosensor (left) and the required number of steps compared with that of the conventional method (right)

Magnetic beads and fine particles (polystyrene beads) that scatter light are attached to a target bio-substance, and “moving light spots” are made with external magnetic force and near-field illumination for detection. It is possible to detect bio-substances without removing contaminants using the new “movement” distinction method that was not present in the conventional method.

There are many challenges to be met when detecting only a few virus particles, such as the fact that the clean environment of a laboratory is necessary, sensitivity is insufficient to detect, or sufficient sensitivity cannot be achieved or complex operational procedures need to be followed with environmental water samples because contaminants can interfere with highly sensitive detection.

In the future, with the goal of preventing infection by highly infectious viruses, the researchers will improve detection sensitivity by an order of magnitude. Also, they will try to improve performance such as making it quantitative. The researchers aim to put this to practical use as a sensor system capable of detecting trace substances in a wide range of fields, such as blood bio-markers and pollutants in the environment.