In addition to requiring large equipment and a reliable power supply, drug testing involves the handling of reagents that require specialized knowledge. In Japan, drug testing is conducted by sending samples to forensic science research institutes or specialized laboratories for analysis. However, such facilities can only process a limited number of samples. A drug-detection device that can be safely operated at the scene of criminal investigations by non-specialist investigators will facilitate on-site primary screening (*1), thereby reducing the burden on laboratories and hastening criminal investigations. Therefore, a method for the safe analysis of drug toxicants through the application of the "electrical" contact-free wireless power transfer (*2) technique was developed by Associate Professor Takahashi and his team.

The wireless power transfer system is highly portable and safe. However, a novel approach was required to conduct chemical analysis owing to the complex alternating current running through the system. A mechanism capable of detecting target substances using light instead of electric current was devised to quantitatively measure the amount of target drugs. The system comprises a substance that emits light in a solution on reacting with the drugs. Electric current was incorporated on the negative side of the alternating current by a diode, and a voltage was applied to cancel it. Drug detection was conducted by placing a sample, such as urine, in a container containing electrodes and turning on the power of the wireless power transfer device. This system can be easily operated by investigators in the field.

A device was developed for the detection of methamphetamine (a stimulant drug component) (*3) in this study. Notably, this device can also be used for the detection of other drugs by adjusting its electrodes. The range of its applications can be expanded by increasing the number of drugs that can detected and modifying the shape of the device. Furthermore, by leveraging the features of the wireless power transfer technique, it will facilitate authorities to detect the presence of drugs in locations with limited access to electric power, such as sewer pipes. The basic principles of the technology must be established, and the theoretical considerations must be enriched to incorporate its use in the field of forensic science. We aim to continue research in this field in the future.