A very low-cost pulse-amplitude modulated chlorophyll fluorometer

Abstract

The quantum yield of photosystem II (ϕPSII) is an important metric to determine a plant’s light use efficiency and to detect plant stresses. Commercial instruments that measure ϕPSII exist, but their cost may prevent widespread adoption. We present the design and realization of a chlorophyll fluorometer capable of measuring ϕPSII that uses a minimal set of optical components and relies on low-cost electronics with total component costs below USD 300. A consumer grade 405 nm laser diode obviates the need for optical elements in the excitation path, and an avalanche photodiode ensures high sensitivity. In addition, an emission filter and a collimating lens are needed. We demonstrate sensor linearity and actinic light immunity with fluorescence reference standards, and we compare our device to a commercial instrument to assess accuracy: With three plant species (Spathiphyllum, Heuchera, and Hosta) and under actinic light variations from zero to 450 μmolm−2s−1, reported ϕPSII from both instruments correlated with R2=0.87. Implications of our design choices, their costs, and alternatives are discussed.