Nano- Gold Fluorescent Probes For The Study And Application In Biological Macromolecules

The new type of fluorescent nanoprobe with its special quantum size effects and small dimension effects exhibits many different optical characteristics compared to the homogeneous single-molecule or large object, and thus has attracted great attention in the applied research field on analytical chemistry. Currently, Metal and semiconductor nanoparticles are a topic of considerable interest in chemistry, biology, and materials sciences. This broad and interdisciplinary interest arises not only from their novel sizedependent electronic and optical properties but also from their dimensional similarities with biological molecules such as nucleic acids and proteins. In addition, they exhibit special physical and chemical properties which possess the quantum size effects, dielectric confinement effects, surface effects, macroscopic quantum tunneling effect and so on. So the quantum dots with these special optical characteristics applied in the fluorescent biological analytical applications have become a wide research focus. Compared to conventional organic dyes, QDs possess many advantages, such asnarrower emission spectra, tunable maximum emission wavelength with changeable sizes and compositions, photostability, high brightness, long fluorescence lifetime and biocompatibility, which have been successfully used as fluorescent probe or sensor in the imaging of biological samples and cells. Recently, photoluminescent QDs has become a new hotspot and they are widely used in chemistry, biology, and medical sciences for biomolecular recognition. With the rapid development of nano-biotechnology, inorganic nanoparticles widely applied in the FRET studies with unique spectral characteristics and photochemical stability. Following recent advances in the growing field of nanotechnology, nanomaterials can be designed as exquisitely sensitive chemical and biological sensors. At the present, bioconjugated gold nanoparticles (Au NPs) and quantum dots have been demonstrated as quenchers and fluorescent donors, respectively, for photoluminescence quenching. Concerns have been raised, however, regarding the toxicity of quantum dots; several studies have suggested that the cytotoxicity of quantum dots might be mediated by their release of Cd2+. Thus, there is a demand for the development of nontoxic photoluminescent NPs to replace potentially toxic quantum dots in bioassays. In contrast to semiconductor quantum dots(QDs), photoluminescent Au QDs are highly attractive for biolabeling and bioimaging applications because of their ultrafine size and nontoxicity.When used in living cells, biocompatibility and nuclease stability are the key properties for therapeutic and diagnostic applications. Therefore, some fluorescent probes base on organic dyes or semiconductor QDs to detect target RNA and protein are rarely used for live cell experiments. Hence, the design of elegant new assembled nanobiosensors for realizing the analysis and determination of bioactive molecules in vivo or in vitro has become a great challenge to the scientific workers.Based on the merits of Au nanodots with good optical characteristics and biocompatibility, we newly assembled two fluorescent probe for the direct determination of bioactive moleclues in biological systems.First, we studied a novel MBs based on the fluorescence resonance energy transfer (FRET) which used photoluminescent Au nanodots (11-MUA-LAuND) as fluorescencet donors and 3 nm spherical Au NPs as quencher. Because 11-MUA-LAuND photolumenescence at the wavelengths (λemmax) was centered at 510~520 nm, which overlaps to a great extent with the surface plasmon resonance (SPR) band of the 3 nm AuNPs, we chose them for use as donors. Specifically, the novel MBs resist enzymatic degradation and photobleach, exhibit good biocompatibility, and are sensitive to detect target RNA in cells.Second, a new nanocomplex Au nanodots–peptide–Au NPs (11-MUA-LAuND–DEVD–Au NPs) was assembled, and thus detected caspase-3 expression specificity in apoptosis. In our study, AuNPs are chosen as quencher mainly based on several unusual properties, such as high quenching efficiencies, better cellular uptake ability and extraordinary intracellular stability. In the absence of caspase-3, the fluorophore is effectively quenched, but when they meet the specific caspase-3, the amide bonds in peptides were cleaved by intracellular caspase-3, and restoring fluorescence of the Au nanodots. The novel probes are sensitive to detect caspase-3 in apoptosis.