A rapid and sensitive immunoresonance scattering spectral assay for microalbumin

BACKGROUND: Microalbuminuria (MAU) is the earliest clinical finding for renal disease and a risk factor for hypertensive cardiovascular disease. Several methods, including enzyme-linked immunosorbent assay (ELISA), radioimmunoassay (RIA), immunoturbidimetry (IT), immunonephelometry (IN), chemiluminescence immunoassay (CLIA), fluorescence immunoassay (FIA) and time-resolved fluorescence (TRF) have been applied for detection of MAU. However, the resonance scattering (RS) spectral assay, based on the immunoreaction and its resonance scattering effect, has not been reported. METHOD: In the presence of 75 mg/l polyethylene glycol (PEG), the immunoreaction of microalbumin (Malb) and its goat anti-human Malb antibody took place specifically in pH 4.4 buffer solution and aggregated to form immunocomplex particles that exhibit a strongest resonance scattering peak at 488 nm, and it was used to assay of Malb. RESULTS: The RS intensity at 488 nm (DeltaI) was proportional to the Malb concentration (C) in the range of 0.03-0.96 mg/l, the regression equation was DeltaI=116.0C-2.1, the detection limit was 0.02 mg/l. Urine samples from 20 healthy subjects were assayed by this assay. The results were in agreement with those obtained with IT. CONCLUSION: This assay has been applied to detection of Malb in real samples, with simplicity, rapidity, high sensitivity and good selectivity.