A device for determination of analytes has optical material with a deposit on a surface thereof. The deposit includes an analyte-reactive reagent and a particulate material for enhancing reflectance of a light beam emitted through the optical material into the analyte-reactive reagent. The enhanced reflectance provides a return of light through the optical material at a level which is not only analytically useful, but involves sufficient returned light intensity so as to enable markedly improved sensitivity and accuracy in analytical determinations. A suitable particulate material is one of hollow spherical particles. Moreover, the particulate material may be selected for a property such as a neutralizing charge that suppresses the membrane-disruptive effects of certain types of optical materials and hemolytic reagents on blood cells such as erythrocytes.