Phycobiliproteins
are a class of light-harvesting fluorescent proteins
existing in cyanobacteria and microalgae, which harvest light and
convert it into electricity. Owing to recent demands on environmental-friendly
and renewable apparatuses, phycobiliproteins have attracted substantial
interest in bioenergy and sustainable devices. However, converting
energy from biological materials remains challenging to date. Herein,
we report a novel scheme to enhance biological light-harvesting through
light–matter interactions at the biointerface of whispering-gallery
modes (WGMs), where phycobiliproteins were employed as the active
gain material. By exploiting microdroplets as a carrier for light-harvesting
biomaterials, strong local electric field enhancement and photon confinement
at the cavity interface resulted in significantly enhanced bio-photoelectricity.
A threshold-like behavior was discovered in photocurrent enhancement
and the WGM modulated fluorescence. Systematic studies of biologically
produced photoelectricity and optical mode resonance were carried
out to illustrate the impact of the cavity quality factor, structural
geometry, and refractive indices. Finally, a biomimetic system was
investigated by exploiting cascade energy transfer in phycobiliprotein
assembly composed of three light-harvesting proteins. The key findings
not only highlight the critical role of optical cavity in light-harvesting
but also offer deep insights into light energy coupling in biomaterials.