High-sensitivity Stokes spectropolarimetry on cyanobacteria

•Measurement of Mueller matrix scattering coefficients from 640 nm to 750 nm.•Linear and circular scattering from Synechococcus and Chroococcidiopsis.•Geometry and chlorophyll absorption cause spectrally dependent circular scattering.•Homochirality is not detectable in this direct scattering experiment.

We investigate the spectral signatures arising from the optical properties of chlorophyll in linear and circularly polarised scattered light from cyanobacteria. We include Stokes scattering coefficient measurements on two cyanobacteria species, Chroococcidiopsis and Synechococcus to a fractional polarisation of ±0.0001 across visible wavelengths. We find that the largest circularly polarised optical signatures from our cyanobacteria samples can be described by optical scattering from spheroidal objects with internal reflections and absorption and, importantly, light scattering from chiral processes is not identifiable in our narrow band light scattering data. We believe previous light scattering measurements attributing chirality effects to cyanobacteria may have been dominated by internal scattering processes.