Fluoroimmunoassay for Antigen based on Fluorescence Quenching between Quantum Dots and Gold Nanoparticles Peng Huang, Kan Wang, Omar Pandoli, Xueqing Zhang, Feng Gao*, Jun Shao, Xiaogang You, Rong He, Hua Song, Daxiang Cui* Department of Bio-Nano Science and Engineering, National Key Laboratory of Nano/Micro Fabrication Technology, Key Laboratory for Thin Film and Microfabrication of Ministry of Education, Institute of Micro-Nano Science and Technology, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai, China 200240 ABSTRACT A unique, sensitive, and highly specific fluoroimmunoassay system for antigen detection using gold and quantum dot nanoparticles has been developed. The assay is based on the fluorescence quenching of quantum dots caused by gold nanoparticles coated with antibody. To demonstrate its analytical capabilities, the CdTe quantum dots were coated with anti-HBsAg monoclonal antibodies (QDs-MAb1) and gold nanoparticles coated with another anti-HBsAg monoclonal antibodies (GNPs-MAb2) which specifically bound with HBsAg could sandwich the HBsAg captured by the immunoreactions. The sandwich-type immunocomplex was formed and the fluorescence intensity of quantum dots was measured. The results showed that the fluorescence intensity of quantum dots at 570 nm was negative linear proportional to the HBsAg concentration logarithm, and the limit of detection of the HBsAg was 0.928 ng/mL. This new system can be extended to detect target molecules with matched antibodies and has broad potential applications in immunoassay and disease diagnosis. Keywords: quantum dots, gold nanoparticles, fluorescence quenching, immunoassay 1. INTRODUCTION The properties and applications of semiconductor nanocrystals stand amongst the most exciting research fields in chemistry, physics and biology.[1-4] Semiconductor nanocrystals or quantum dots (QDs) exhibit interesting size-tunable optical properties due to the confinement of their electronic wave functions.[5] QDs have great advantages over traditional fluorescent dyes such as stronger luminescence, better photo stability against bleaching and physical environments such as pH and temperature, and optical tenability. These properties have been used in immunoassays, molecular imaging, and in vivo biological labels.[6,7] Optically quenched QDs have recently gained considerable interest. Several groups have demonstrated optical quenching of QDs. For example, Hak-Sung Kim et al.[8] reported that Au nanoparticles can quench QD luminescence at the single-molecule level. Clapp et al.[9] investigated FRET phenomena in QD–protein–dye conjugates by accurately controlling the donor–acceptor separation distance to a range smaller than 100Å. Medintz et al.[10] conjugated a-cyclodextrin-QSY9 dark quencher in a MBP saccharide binding site and resulted in FRET quenching of QD photoluminescence (PL). A QD–biomolecule assembly constructed using these methods may facilitate development of a novel class of hybrid sensing materials. Gold nanoparticles(GNPs) have been subject to intensive investigations because of unique properties and potential applications. For example, GNPs have been used in therapy of biomolecule detection, nonviral vectors for DNA delivery and intracellular gene regulation, DNA-programmable nanoparticle crystallization and supports for enzymes.[11-12] However, despite a number of bioanalytical applications of nanoparticles, to the best of our knowledge, there have been few attempts employing the PL quenching of QDs by GNPs for studying an immunoassay in aqueous solutions. In our previous work, we developed a fluoroimmunoassay for antigen based on fluorescence quenching signal of fluorescent dye caused by GNPs[13]. Herein we reported a novel immunoassay based on the modulation in PL efficiency between QDs and GNPs in the presence of the HBsAg which sandwiched the interactions between QD- and GNPs- conjugated biomolecules. The antigen HBsAg was chose to prove the novel immunoassay method as a typical example. * gaofeng@sjtu.edu.cn; dxcui@sjtu.edu.cn; Tel/Fax: +86 21 34206886; bne.sjtu.edu.cn Optics in Health Care and Biomedical Optics IV, edited by Qingming Luo, Ying Gu, Xingde Li, Proc. of SPIE Vol. 7845, 784514 · © 2010 SPIE · CCC code: 1605-7422/10/$18 · doi: 10.1117/12.870360 Proc. of SPIE Vol. 7845 784514-1 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 09/22/2014 Terms of Use: http://spiedl.org/terms