Understanding the rules of life is one of the most important scientific endeavours and has revolutionised both biology and biotechnology. Remarkable advances in observation techniques allow us to investigate a broad range of complex and dynamic biological processes in which living systems could exploit quantum behaviour to enhance and regulate biological functions. Recent evidence suggests that these non-trivial quantum mechanical effects may play a crucial role in maintaining the non-equilibrium state of biomolecular systems. Quantum biology is the study of such quantum aspects of living systems. In this review, we summarise the latest progress in quantum biology, including the areas of enzyme-catalysed reactions, photosynthesis, spin-dependent reactions, DNA, fluorescent proteins, and ion channels. Many of these results are expected to be fundamental building blocks towards understanding the rules of life.

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We present a laser scanning multiphoton endomicroscope with no distal optics or mechanical components that incorporates a polarization-maintaining (PM) multicore optical fibre to deliver, focus and scan ultrashort pulsed radiation for two-photon excited fluorescence imaging. We show theoretically that the use of a PM multicore fibre in our experimental configuration enhances the fluorescence excitation intensity achieved in the focal spot compared to a non-PM optical fibre with the same geometry and confirm this by computer simulations based on numerical wavefront propagation. In our experimental system a spatial light modulator (SLM) is utilised to programme the phase of the light input to each of the cores of the endoscope fibre such that the radiation emerging from the distal end of the fibre interferes to provide the focused scanning excitation beam. We demonstrate that the SLM can enable dynamic phase correction of path-length variations across the multicore optical fibre whilst the fibre is perturbed with an update rate of 100 Hz.Index Terms-Adaptive optics, multiphoton endomicroscope, polarization-maintaining multicore optical fibre, and wavefront shaping.

Fluorescent proteins (FPs) have revolutionized cell biology by allowing genetic tagging of specific proteins inside living cells. In conjunction with Fö rster's resonance energy transfer (FRET) measurements, FP-tagged proteins can be used to study protein-protein interactions and estimate distances between tagged proteins. FRET is mediated by weak Coulombic dipole-dipole coupling of donor and acceptor fluorophores that behave independently, with energy hopping discretely and incoherently between fluorophores. Stronger dipole-dipole coupling can mediate excitonic coupling in which excitation energy is distributed near instantaneously between coherently interacting excited states that behave as a single quantum entity. The interpretation of FP energy transfer measurements to estimate separation often assumes that donors and acceptors are very weakly coupled and therefore use a FRET mechanism. This assumption is considered reasonable as close fluorophore proximity, typically associated with strong excitonic coupling, is limited by the FP b-barrel structure. Furthermore, physiological temperatures promote rapid vibrational dephasing associated with a rapid decoherence of fluorophore-excited states. Recently, FP dephasing times that are 50 times slower than traditional organic fluorophores have been measured, raising the possibility that evolution has shaped FPs to allow stronger than expected coupling under physiological conditions. In this study, we test if excitonic coupling between FPs is possible at physiological temperatures. FRET and excitonic coupling can be distinguished by monitoring spectral changes associated with fluorophore dimerization. The weak coupling mediating FRET should not cause a change in fluorophore absorption, whereas strong excitonic coupling causes Davydov splitting. Circular dichroism spectroscopy revealed Davydov splitting when the yellow FP Venus A206 dimerizes, and a novel approach combining photon antibunching and fluorescence correlation spectroscopy was used to confirm that the two fluorophores in a Venus A206 homodimer behave as a single-photon emitter. We conclude that excitonic coupling between Venus A206 fluorophores is possible at physiological temperatures.