Dual-angle light scattering spectroscopy for calibration-free measurements of scatterer suspensions

It can be difficult to employ optical techniques for analyzing biological structures smaller than or comparable to the wavelength of light, such as extracellular vesicles or some types of bacteria. Biological light scattering spectroscopy (LSS), developed to address this problem, has been successfully used for characterizing tissue on cellular and subcellular scales. At the same time, calibration with a reference sample of known optical properties can complicate LSS measurements. In this Letter, we present dual-angle LSS (daLSS), which is designed for calibration-free measurements of scatterer suspensions. It employs measurements of a sample at two distinct angles, which then allows system effects to be removed entirely. Not only does daLSS simplify and speed up the measurement procedure, but it also makes spectra more reproducible, an important feature for diagnostic techniques. We validated the technique by accurately reconstructing the sizes of polystyrene microspheres with diameters less than 100 nm and then demonstrated that not only are the daLSS spectra of several common bacteria strains easily distinguishable but they are also highly reproducible.