Fast protein detection using absorption properties of gold nanoparticles

Abstract

In this study we describe the use of gold nanoparticles as a fast detection system for the sensitive analysis of proteins. The immunological method allows for protein analysis at the nanogram level, as required for clinical diagnosis. Initially a test protein is used for the development of the assay. The system is subsequently adopted for alpha-fetoprotein, which is a relevant tumor marker. This work demonstrates that antibody functionalized gold nanoparticles can be used for the detection of proteins by forming gold nanoparticle aggregates. The influence of the size of the gold nanoparticles on the sensitivity of the assay is investigated in the range from 20–60 nm particles; the larger particles show here the highest relative changes. The formation of antigen–gold nanoparticle aggregates is detected by an increase in hydrodynamic diameter by dynamic light scattering (DLS). UV/Vis spectroscopy also allows assay monitoring by quantifying the red shift of the plasmon resonance wavelength. Alpha-fetoprotein can be analysed in the concentration range of 0.1–0.4 μg ml⁻¹. The influence of pH, ionic strength and ratio of sample to Au-NP solution is studied. With this method, the protein AFP can be rapidly detected as demanded for clinical diagnosis.