Introduction of magneto-fluorescence fluctuation microspectroscopy for investigating quantum effects in biology

Abstract Magnetic field effects on radical pairs in chemical systems are generally well understood and have been successfully investigated with various spectroscopic techniques. However, understanding radical pairs and their quantum nature in biological systems is still in its infancy, which is due to the limitation of high-sensitivity instrumentation. Another reason for this lack of understanding is due to the complexity of biochemical reactions and minute magnetic field-induced changes on radical pair reactions (as low as or lower than a percent). The system design presented here is a new optical system to capture the quantum mechanical nature of biology with a high signal-to-noise ratio. Our magneto-fluorescence fluctuation microspectroscopic approach has the capability of measuring magnetic field effects as low as 0.2% on fluorescence signals near the single-photon level with single-photon avalanche diodes, and is demonstrated by magnetic field effects on 23 molecules. An additional detection system in the form of an EMCCD camera offers spatially resolved magnetic field effects with a novel post hoc digital lock-in amplifier for phase-sensitive camera detection. The aforementioned attributes are demonstrated with radical pair photochemical reactions on model biological systems. The instrument uncovers the importance of photodegradation on protein–flavin interactions via magnetic field effects, which will prove paramount when searching for similar quantum effects in biological locales.