Gold nanoparticles-based fluorescence resonance energy transfer for competitive immunoassay of biomolecules

A novel platform for competitive immunoassay of biomolecules was designed based on fluorescence resonance energy transfer (FRET) between fluorescein isothiocyanate (FITC) and gold nanoparticles (AuNPs). The antigen was first labeled with FITC, and the FITC labeled antigen was then reacted with AuNPs functionalized with a relative antibody to obtain the nanometer-sized sensor. The FRET between FITC and AuNPs led to the fluorescent quenching of FITC. Upon the recognition of the target antigen, the FICT labeled antigen was released from the AuNPs surface because of competitive immunoreaction, the distance between the FITC and AuNPs increased, and the interaction between FITC and AuNPs became weaker, which significantly hindered the FRET and, thus, increased the fluorescence of FITC. The change in fluorescence intensity produced a novel method for detection of the target. By using immunoglobulin M (IgM) as a model analyte, the competitive immunoassay had a limit of detection of 42 pM. The present method was applied for the determination of IgM in human serum with satisfactory results. The proposed method exhibits several advantages such as high quenching efficiency and sensitivity, and good specificity toward target versus other analogues. Moreover, this strategy could be conveniently extended for the detection of other biomolecules by using the corresponding antigens and respective antibodies.