Apparatus and method of assay in utilizing attenuated total reflection

An assay apparatus utilizing attenuated total reflection comprising:

• a sensor unit, said sensor unit including a transparent dielectric medium and a thin film, having a first surface and a sensing surface reverse thereto, said first surface overlying on said dielectric medium to constitute a thin film/dielectric interface, said sensing surface causing reaction of sample fluid;
• an optical assay unit for applying illuminating light to said interface through said dielectric medium in such a form as to satisfy a total reflection condition and for deriving information of reaction of said sample fluid by detecting said illuminating light reflected by said interface;
• a fluid processor for preparing said sample fluid at a density by mixing with diluent fluid;
• an evaluator, responsive to an evaluating assay in using said sample fluid prepared by said fluid processor, for comparing measured data output by said optical assay unit with a reference parameter stored in a data storage, in order to evaluate suitability of said measured data for analysis;
• and
• a density determiner, responsive if said evaluator estimates lack of said suitability, for determining a succeeding density of said sample fluid to be used in a succeeding evaluating assay according to said measured data with said estimated lack of said suitability;
• wherein said fluid processor prepares said sample fluid at said succeeding density determined by said density determiner, for said succeeding evaluating assay according to said succeeding density of said sample fluid.