Buffers overall stabilize the antigen or antibody used to coat an ELISA microwell plate, optimizing absorption and interaction with the detection antibody. Substrates must be highly sensitive and are used to increase the rate of reaction (optimal density) in an assay and measured using a precision micro-titer absorbance plate reader, such as a spectrophotometer. Diluent additives are used in ELISAs to equalize any differences between the sample matrices (serum, plasma, urine, etc.) and the calibrator control used to generate a standard curve. Diluents are used when performing an assay to dilute samples and increase signal-to-noise ratios.