complete mixing of the solutions after fluid was delivered to the detection reservoirs 420 reflectance optics was used to measure the reflected radiation at an off specular diffuse angle at two wavelengths 430 nm absorbing for the expected reaction product pnp and 630 nm as there is no absorbance from reaction product pnp at 630 nm this wavelength can be used to correct for optical imperfections in the platform stray scattering or unintended air bubbles in the optically transparent chamber the optical system also advantageously contained a beam splitter that sent a fraction of the incident light to a reference photodiode two detectors used in this optics system were the assay detector which measured diffusely reflected light and the reference detector which measured a fraction of the incident light measurements at each detector were made when both the 430 nm and 630 nm light sources were active as well as when they were u201c dark u201d or off the measured voltages were thus v d 1 measurement at absorbing wavelength u03bb 1 430 nm in assay detector v d 2 measurement at non absorbing wavelength in u03bb 2 660 nm assay detector v r 1 measurement in reference detector at absorbing wavelength u03bb 1 430 nm v r 2 measurement in reference detector at non absorbing wavelength u03bb 2 660 nm k v d 1 v d d v r 1 v r d v d 2 v d d v r 2 v r d.