Resonance scattering detection of trace microalbumin using immunonanogold probe as the catalyst of Fehling reagent–glucose reaction

A novel and sensitive resonance scattering (RS) spectral immunoassay for the determination of microalbumin (Malb) was developed, based on the catalytic effect of immunonanogold (ING) probe on Fehling reagent–glucose reaction, and resonance scattering effect of Cu2O particles. Nanogold particles in size of 10 nm were used to label goat anti-human microalbumin (GMalb) to obtain an ING probe (AuGMalb) for Malb. The probe produced unspecific aggregation in pH 5.0 citric acid–Na2HPO4 buffer solutions. Upon addition of Malb, the dispersed ING complex formed. The ING complex in supernatant was obtained by centrifuging and was used as catalyst for the reaction between Fehling reagent and glucose to form the Cu2O particles to amplify the resonance scattering signal at 610 nm. With addition of Malb, the ING complex in the supernatant increased and the RS intensity at 610 nm (I610 nm) enhanced linearly. The enhanced intensity ΔI610 nm was proportional to the Malb concentration in the range of 0.014–0.43 ng ml−1, with a detection limit of 7.2 pg ml−1. The proposed method was applied to detect Malb in human urine sample with satisfactory results.