Signal enhancement of surface plasmon resonance immunoassay using enzyme precipitation-functionalized gold nanoparticles: A femto molar level measurement of anti-glutamic acid decarboxylase antibody

Cuong Cao, Sang Jun Sim

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83 Citations (Scopus)


Colloidal gold nanoparticles (AuNPs) and precipitation of an insoluble product formed by HRP-biocatalyzed oxidation of 3,3′-diaminobenzidine (DAB) in the presence of H2O2 were used to enhance the signal obtained from the surface plasmon resonance (SPR) biosensor. The AuNPs were synthesized and functionalized with HS-OEG3-COOH by self assembling technique. Thereafter, the HS-OEG3-COOH functionalized nanoparticles were covalently conjugated with horseradish peroxidase (HRP) and anti IgG antibody to form an enzyme-immunogold complex. Characterizations were performed by several methods: UV-vis absorption, DLS, HR-TEM and FT-IR. The Au-anti IgG-HRP complex has been applied in enhancement of SPR immunoassay using a sensor chip constructed by 1:9 molar ratio of HS-OEG6-COOH and HS-OEG3-OH for detection of anti-GAD antibody. As a result, AuNPs showed their enhancement as being consistent with other previous studies while the enzyme precipitation using DAB substrate was applied for the first time and greatly amplified the SPR detection. The limit of detection was found as low as 0.03 ng/ml of anti-GAD antibody (or 200 fM) which is much higher than that of previous reports. This study indicates another way to enhance SPR measurement, and it is generally applicable to other SPR-based immunoassays.

Original languageEnglish
Pages (from-to)1874-1880
Number of pages7
JournalBiosensors and Bioelectronics
Issue number9-10
Publication statusPublished - 2007 Apr 15
Externally publishedYes



  • Anti-GAD antibody
  • Enhancement
  • Enzyme precipitation
  • Gold nanoparticles
  • Oligo(ethylene glycol)
  • Surface plasmon resonance

ASJC Scopus subject areas

  • Biotechnology
  • Analytical Chemistry
  • Electrochemistry

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