A hand-held photometer for quantitative dot-immunobinding assays.

A simple multichannel transmission photometer is presented. This instrument is designed to give a quantitative result from dot-immunobinding assays. The optoelectronic components of the system (yellow GaP light-emitting diode and CdS photoresistor) have been selected to match the absorbance maximum of the product generated by the peroxidase-catalyzed oxidation of 4-chloro-1-naphthol. The standard deviation of duplicate measures is lower than 0.5% on a single channel and lower than 1.5% on different channels. The photometer is able to read linearly the absorbance of samples up to a value of A585 = 3.0. As an application example, the photometer was used to read the results of the titration of sera of Leishmania-infected dogs on Leishmania donovani antigens.