Development of biological delayed luminescence irradiation source system

Abstract: The analysis and application of biological delayed luminescence is a hotspot in many interdisciplinary areas. However, the irradiation source of biological delayed luminescence has not been thoroughly investigated. In order to solve some problems of the current biological delayed-luminescence detection system, including the poor repeatability and reliability caused by the delay error of the external excitation light source and the superimposed interference of natural light, a biological delayed-luminescence irradiation source system is presented in this paper. This irradiation source system mainly consists of a constant temperature irradiation chamber, a tricolor RGB-LED matrix irradiation light source, an electronic shutter isolator, and a control circuit. The irradiation source system is assembled with the BPCL Series weak luminescence meter. The proposed system has technical improvements in three aspects related to the external excitation light source. 1) It features multiple automation selections in irradiation frequency, irradiation intensity, and programmable irradiation timing. Under the control of the MCS-51 single-chip microcomputer, 16 light spectra with varying chrominance can be selected in the range of 410-625 nm, with LED driving current adjustable from 16-40 mA for different brightness, and the irradiation time is adjustable within the range of 0-999 s. 2) It features fast switching of the electronic shutter in lighting and detection process in the same channel of a darkroom. When the light source is on, the shutter is closed automatically. During measurement, the shutter is opened automatically when the light source is off. It therefore reduces the superimposed interference with natural light and the delay error. 3) Because of the temperature sensitivity of the biological delayed luminescence, a temperature sampling circuit called the 'single integral type A/D converter' with a simple structure is designed based on the working principle of the 'double integral type A/D converter'. Combining with the MCU, this temperature-sampling circuit works as a temperature controller, which can maintain a constant temperature in the sample chamber. After using this irradiation source system, the results of the background noise and stability testing showed that the noise deviation in average photon counting was less than 4.5 cps (counts per second). The relative error in five repetitive tests was 0.7%, achieving a high repeatability of the delayed luminescence curves. The test results of the delayed luminescence in germinating corn further showed that the R2 of the delayed luminescence curves fitting was greater than 0.99. Good reliability and repeatability can be achieved in this system.