We report on the first detailed use of broadband cavity enhanced absorption spectroscopy (BBCEAS) as a detection system for immunoassay. A vertical R ≥ 0.99 optical cavity was integrated with a motorised XY stage, which functioned as a receptacle for 96 well microtiter plates. The custom built cavity enhanced microplate reader was used to make measurements on a commercially available osteocalcin sandwich ELISA kit. A 30 fold increase in path length was obtained with a minimum detectable change in the absorption coefficient, αmin(t), of 5.3 × 10-5 cm-1 Hz-1/2. This corresponded to a 39 fold increase in the sensitivity of measurement when directly compared to measurements in a conventional microplate reader. Separate measurements of a standard STREP-HRP colorimetric reaction in microtiter plates of differing optical quality produced an increase in sensitivity of up to 115 fold compared to a conventional microplate reader. The sensitivity of the developed setup compared favorably with previous liquid-phase cavity enhanced studies and approaches the sensitivity of typical fluorometric ELISAs. It could benefit any biochemical test which uses single pass absorption as a detection method, through either the label free detection of biologically important molecules at lower concentrations or the reduction in the amount of expensive biochemicals needed for a particular test, leading to cheaper tests.
Bajuszova, Z., Ali, Z., Scott, S., Seetohul, L. N., & Islam, M. (2016). Cavity Enhanced Immunoassay Measurements in Microtiter Plates using BBCEAS. Analytical Chemistry, 88(10), 5264-5270. https://doi.org/10.1021/acs.analchem.6b00375