Geiger Mode Single Photon Counting: A Laboratory Experiment Exploring Delayed Fluorescence in Plants

The time-resolved detection of very low intensity light emission has become an essential capability in many areas of science including molecular biology, fluorimetry, DNA sequencing, virus detection, nanoparticle research, and optical materials development. Among the most basic techniques for the detection of rapidly fluctuating low-intensity light is photon counting. Despite its extensive applications in the physical and biological sciences and engineering, photon counting techniques have traditionally been left out of undergraduate curricula due to the prohibitive cost of the equipment and the complexity of its operation. However, the recent development of the low-cost silicon photomultiplier device, a solid-state single photon avalanche diode detector, has enabled the availability of easy-to-operate, low voltage, advanced timing performance, and highly sensitive photon counting systems well within the budget of undergraduate teaching laboratories. In this contribution, we provide a strategy to introduce undergraduate interdisciplinary chemistry and physics students to silicon-photomultiplier-based photon counting through the interesting phenomenon of delayed fluorescence from photosystem II in plants. This experiment is perhaps best suited for an upper-level undergraduate laboratory and should stimulate the interest of students across a wide variety of disciplines, from physical chemistry to molecular biophysics to photonics instrumental analysis.