Changes in total light scattering and absorption caused by changes in particle conformation

reversible changes in light transmission and scattering by cells and large subcellular particles (e.g. mitochondria and chloroplasts) have been widely observed. Such optical changes are presumably caused by subtle changes in particle conformation: changes in particle volume with no change in dry weight, and changes in internal structure. Mie's and van de Hulst's equations for homogeneous spheres are used to determine how total scattering and absorption by suspensions change when the particles swell or shrink by taking up or extruding water. It is found that if particle volume increases by 1% with no change in dry weight, log 10 (1/transmission) can decrease by as much as 2 3% or increase by as much as 2% depending on the initial particle parameters and wavelength. It is found that true absorption, the capture of energy, can increase by as much as 2 3% if particle volume increases 1%. A new method is proposed for determining the effects of internal particle structure on observable light fluxes. The method is used to predict the effects of some changes in internal particle structure on total scattering, as determined from transmission measurements, and on whole particle scattering, as determined by measurements of small angle scattering. It is found that when a particle becomes less homogeneous, large angle scattering should increase and small angle scattering should decrease. The net effect is to either increase or decrease suspension transmission depending on initial particle size and wavelength.