| Gold Nanoparticles (AuNPs) are some of the most extensively studied nanomaterials and have demonstrated exciting applications in catalysis, biomedicine and analytical science due to their intriguing electronic, optical, and chemical properties. This thesis explores rationally designed multifunctional AuNPs and further demonstrates their novel applications as signal transducer and/or amplifier in bio/chemical detections including SPRi-based immunoassay and colorimetric detection of heavy metal ions. The main contents are as follows:(1) Sensitive immunoassay of multiple mycotoxins by AuNP-enhanced surface plasm on resonance imaging. Detection of multiple toxic mycotoxins is of importance for food safety. Surface plasmon resonance imaging (SPRi) is an advanced tool for multiplexed immunoassay but suffers from limited sensitivity. Particularly this bottleneck is fetal for mycotoxin detection as small molecular mycotoxin only possesses one epitope for an insensitive competitive immunoassay rather than sandwich-based immunoassay. In this regard, this thesis developed an AuNP-enhanced SPRi chip to sensitively detect multiple mycotoxins. After competitive binding of monoclonal antibodies on the antigens-immobilized SPRi chip, secondary antibody-conjugated AuNPs were employed to bind with the captured monoclonal antibodies for SPRi signal amplification. Highly specific and sensitive detection was achieved for three typical mycotoxins including Aflatoxin B1 (AFB1), Ochratoxin A (OTA) and Zearalenone (ZEN) with low detection limits of 8,30 and 15 pg mL-1 and dynamic ranges covering three orders of magnitude.(2) Dual signal amplification based on on-chip atom transfer radical polymerization from AuNPs for sensitive SPRi immunoassay of tumor marker. To further address the sensitivity limitation of SPRi for practical immunoassay applications, a dual signal amplification strategy was developed by using multifunctional AuNPs, which were modified by an initiator of atom transfer radical polymerization (ATRP) and a recognition antibody. After the target marker was captured by the SPRi sensing surface, the recognition antibody directed the specific binding of functional AuNPs onto the sensing surface to form immunocomplexes for first signal amplification, and the initiator allowed for on-chip ATRP of 2-hydroxyethyl methacrylate (HEMA) from the AuNPs to further enhance the SPRi signal. Low detection limit of 1.0 ng mL-1 and broad dynamic range covering two orders of magnitude were achieved for detection of a model tumor marker, a-fetoprotein (AFP) in 10% human serum with this dual signal amplification strategy.(3) Colorimetric naked-eye detection of mercury (II) (Hg2+) based on 2, 2’-bipyridyl-induced linear aggregation of gold nanoparticles. Heavy metal ion Hg2+ is a highly toxic pollution. Simple and reliable on-site detection of Hg2+has raised considerable concern for environmental protection and human health but current methods necessitate sophisticated instruments and/or tedious procedures. In this thesis a simple, reliable and instrument-free colorimetric method for Hg2+detection was developed based on inhibition effect of Hg2+on 2,2’-Bipyridyl (Bipy) induced aggregation of AuNPs. Bipy is found to be capable of triggering the linear aggregation of citrate-capped monodisperse AuNPs with a controllable manner and generate visible color change; in the presence of Hg2+, the aggregation is efficiently decelerated/inhibited due to the formation of Au-Hg alloy layer on AuNP surface, allowing for naked-eye quantification of Hg2+in a dynamic range from 0.2 to 2.0 uM. The detection limit is as low as 38 nM if coupled to a simple UV-Vis spectrometer. The method shows excellent selectivity towards Hg2+and good reliability in various practical samples with different pH values or ionic strengths, thus holding great promise for rapid and on-site detection of Hg2+. |
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