Luminescence catalyst immunoassay of β2-microglobulin with haemin as a chemically amplifiable label

Luminescence biosensors

A novel optical biosensor for homogeneous immunoassay has been developed on the basis of the finding that electrochemical luminescence of pyrene-labelled antigen is extremely inhibited by immunochemical complexation. Electrochemical luminescence homogeneous immunoassay for human serum albumin (HSA), as a model analyte, was performed with a platinum plate electrode which was located in the vicinity of an optical fibre tip. HSA was determined in the concentration range of 3-25 X 10(-6) mol/l. To improve electrochemical luminescence measurement an optical fibre electrode has been developed by fabricating a transparent platinum film on the top of an optical fibre. The minimum detectable limit of luminol was 10(-11) mol/l with the optical fibre electrode. Luminol was applied as a label for homogeneous immunoassay.

Pulse immunoassay for human immunoglobulin G using antibody bound latex beads

Pulse immunoassay was applied in the immunoassay of human immunoglobulin G (H-IgG). Antibodies to H-IgG were covalently immobilized on the surface of latex beads (1 microM). Immunoreaction of the antibody bound latex beads (Ab-L) and H-IgG was performed using electric pulses. Agglutination rate (AR), defined by the following equation, was used to estimate the immunoreaction rate (formula; see text) where Nn is the total number of beads forming n bead agglutinations. Each Nn was determined by analyzing photographs of the samples. When 140 microliter of Ab-L suspension (0.7%) containing H-IgG (6.7 X 10(-6) g ml-1) was reacted using electric pulses (peak height 2 kV cm-1, pulse width 20 microseconds, pulse frequency 8 kHz), AR increased sharply and reached 50% after 10 min. In contrast, when the same sample was reacted without electric pulses, AR increased very slowly and only reached 20% after 20 min. Therefore, the immunoreaction of H-IgG and Ab-L can be carried out more rapidly by applying electric pulses.