If you can record spectra, the absorbance at 800nm is the indication of the presence of scattering. You can take that value as a wavelength independent background. (crude correction). You can assume a 1/Lambda^4 dependence. (Still rather wrong). If you are rich, their are special spectrometers for scattering samples. (With the PMT close to the cuvette. You can use a microscope with a large numerical aperture together with a fiber spectrometer to build a micro spectrograph. But you will be limited to the 400nm-700nm wavelength region.

Robert Bernard Pansu, thanks for answering. The release was measured separately for each component, either as Se NPs loaded with the enzyme asparaginase or as total absorbance.