The Label-Free SoPRanoTM Gold Nano-Rod assay depends on absorbance shifts that are induced by protein binding due to localized surface plasmon resonance (LSPR). A protein is coupled to a gold rod and if interaction of the coupled protein with another protein occurs, a red shift of the absorbance maximum can be detected that is derived from a change in the local refractive index.
The method requires acquisition of absorbance spectra which is provided by all spectrometer-based microplate readers by BMG LABTECH. They were able to detect the slight differences in absorbance of human serum albumin coupled gold-nano-rods and the hSA-rods bound by anti-hSA antibodies. The assay allowed for detection of different concentrations of the antibody and for kinetic measurements revealing binding constants.
In contrast to other LSPR-based systems, SoPRanoTM requires no specialized and costly instrumentation. Instead, a microplate reader acquires the absorbance spectrum which is done by a spectrometer-based BMG LABTECH instrument in less than a second.