Photosensing Resolution of Wireless Communication Chip in Inhomogeneous RF-Magnetic Field

We have developed a wireless biosensing system for bioluminescence measurements that includes a sensor chip with a volume of 2.5 ×2.5 ×0.5 mm3 and a read/write (R/W) coil. This sensor chip monolithically integrates a photosensor for detecting bioluminescence, a control circuit, and a coil for communication. In order to operate the sensor chip in a sample solution, we employed an RF magnetic field for the transmission of data and electric power between the chip and the R/W unit. The magnitude of the field around the chip changes significantly with the positional relationship between the sensor chip and the R/W coil. Therefore, evaluating the stability of the sensor chip operation, especially the resolution of signal processing, is important. In our system, a resolution of ±30 µV was achieved in an inhomogeneous field ranging from 160 to 379 A/m. We also quantified the adenosine triphosphate (ATP) by measuring bioluminescence to demonstrate the stability of the sensing operation. Although the RF magnetic field fluctuated in the reaction cell where the sensor chip was located, an almost linear relationship between the ATP amount and the sensor response was obtained.