Complete microsystem using SOI photodiode for DNA concentration measurement

In this paper, we describe a complete microsystem allowing the measurement of DNA concentration based on ultraviolet (UV) absorption. The system includes an ultraviolet light-emitting diode (LED) as light source and a silicon-on-insulator (SOI) lateral PIN diode as photodetector. After demonstrating the feasibility of the system with a quartz container, measurements are performed on DNA samples in PCR tubes by direct trans-mittance. The measurement of the sample in the tubes implies no waste neither manipulation of the samples. We study the impact of variation of the different parameters of the system, i.e. the wavelength of the LED, the light power reaching the samples and the bias of the photosensor. We are able to measure responses for DNA concentrations in the range from 400 ng/μL to 4 pg/μL and correlate bacteria concentrations to the induced photocurrent of the diode from 6.10¹¹ spores/mL to 6.10⁷ spores/mL. The system features a present precision of current measurements of 2%. In the optimal case, a limit of detection (LOD) of 0.02 ng/μL has been estimated.