Protein Fibril-Templated Biomimetic Synthesis of Highly Fluorescent Gold Nanoclusters and Their Applications in Cysteine Sensing.
ABSTRACT: Biomimetic synthesis of multifunctional fluorescent gold nanoclusters (Au NCs) is of great demand because of their ever-increasing applications. In this study, we have used self-assembled bovine serum albumin (BSA) amyloid-like nanofibers as the bioinspired scaffold for the synthesis of Au NCs. The amyloid fibril stabilized gold nanocluster (Fib-Au NC) has been found to have appreciable enhancement of fluorescence emission and a large 25 nm red shift in its emission maxima when compared to its monomeric protein counterpart (BSA-Au NC). The underlying mechanism accountable for the fluorescence behavior and its spectral shift has been thoroughly investigated by a combined use of spectroscopic and microscopic techniques. We have subsequently demonstrated the use of Fib-Au NCs for cysteine (Cys) sensing both in vitro and inside live cells. Additionally, cellular uptake and postpermeation effect of Fib-Au NCs have also been ascertained by detailed flow cytometry analysis, viability assay, and real-time apoptotic gene expression profiling.
Project description:In this paper, we have synthesized BSA protected gold nanoclusters (BSA Au nanocluster) and studied the effect of quencher, protein denaturant, pH and temperature on the fluorescence properties of the tryptophan molecule of the BSA Au nanocluster and native BSA. We have also studied their effect on the peak emission of BSA Au nanoclusters (650 nm). The phtophysical characterization of a newly developed fluorophore in different environments is absolutely necessary to futher develop their biomedical and analytical applications. It was observed from our experiments that the tryptophan in BSA Au nanoclusters is better shielded from the polar environment. Tryptophan in native BSA showed a red shift in its peak emission wavelength position. Tryptophan is a highly polarity sensitive dye and a minimal change in its microenvironment can be easily observed in its photophysical properties.
Project description:The efficiency of the glutathione monolayer-protected gold nanocluster (NC) Au(25) (1.2 nm metal core diameter (d)) in quenching the emission of dyes intercalated into DNA is compared to that of 2 and 4 nm gold nanoparticles (NPs). In all cases, the DNA/dye moieties and the gold particles are not covalently attached but rather form non-covalent ground state complexes. Under these conditions, steady-state measurements reveal that the quenching efficiency of Au(25) is a factor of 10 lower than that of plasmonic 4 nm gold NPs but comparable to that of 2 nm particles which do not show a distinct plasmon band. Nonetheless, significant emission quenching is observed even at very low (nM) concentrations of Au(25). The quenching efficiency of the 4 nm NPs is significantly higher for dyes emitting near the wavelength of the plasmon peak whereas that of the 2 nm gold NPs is well described by the nano-surface energy transfer (NSET) model proposed by the Strouse group (J. Am. Chem. Soc. 127, 3115 2005). Interestingly, for Au(25) the maximum quenching efficiency occurs for dyes emitting in the same wavelength range as that of the 2 and 4 nm NPs (490-560 nm), where it shows no discrete absorption features, rather than for wavelengths coincident with its HOMO-LUMO, intra-band or inter-band transitions. The fluorescence quenching properties of Au(25) NCs are therefore found to be distinct from those of larger NCs and NPs but do not appear to conform to theoretical predictions advanced thus far.
Project description:Automatic upgrade: attachment of gold nanoparticles (NPs) onto upconversion nanocrystals (NCs) results in plasmonic interactions that lead to a significant enhancement of upconversion emission of more than 2.5. Conversely, formation of a gold shell greatly suppresses the NC emission because of considerable scattering of excitation irradiation (see picture; a=NC before seed attachment; b, c=NC with attached Au NPs; c=NC with Au shell; scale bar=50 nm).
Project description:Screening of illicit drugs for new psychoactive substances-namely cathinone-at crime scenes is in high demand. A dual-emission bovine serum albumin-stabilized gold nanoclusters probe was synthesized and used for quantitation and screening of 4-chloromethcathinone and cathinone analogues in an aqueous solution. The photoluminescent (PL) color of the bovine serum albumin-stabilized Au nanoclusters (BSA-Au NCs) probe solution changed from red to dark blue during the identification of cathinone drugs when excited using a portable ultraviolet light-emitting diodes lamp (365 nm). This probe solution allows the PL color-changing point and limit of detection down to 10.0 and 0.14 mM, respectively, for 4-chloromethcathinone. The phenomenon of PL color-changing of BSA-Au NCs was attributed to its PL band at 650 nm, quenching through an electron transfer mechanism. The probe solution was highly specific to cathinone drugs, over other popular illicit drugs, including heroin, cocaine, ketamine, and methamphetamine. The practicality of this BSA-Au NCs probe was assessed by using it to screen illicit drugs seized by law enforcement officers. All 20 actual cases from street and smuggling samples were validated using this BSA-Au NCs probe solution and then confirmed using gas chromatography-mass spectrometry. The results reveal this BSA-Au NCs probe solution is practical for screening cathinone drugs at crime scenes.
Project description:Herein, we introduce a new facile method of luminescent gold nanocluster (Au NC) synthesis on the surface of bacteria for detection, counting, and strain differentiation. The limit of detection was 740 ± 14 colony-forming unit (CFU)/mL for the Gram-negative and was 634 ± 16 CFU/mL for the Gram-positive bacteria. Brief treatment with lysozyme could differentiate the Gram strains based on their luminescence intensities. The current method could also detect bacterial contaminants from water sources and kanamycin-resistant strains rapidly. This quick synthesis of Au NCs on a bacterial template attributes an easy and rapid method for enumeration and detection of bacterial contaminants and kanamycin-resistant strains.
Project description:The atomic-structure characterization of alloy nanoclusters (NCs) remains challenging but is crucial in order to understand the synergism and develop new applications based upon the distinct properties of alloy NCs. Herein, we report the synthesis and X-ray crystal structure of the Pt1Ag28(S-Adm)18(PPh3)4 nanocluster with a tetrahedral shape. Pt1Ag28 was synthesized by reacting Pt1Ag24(SPhMe2)18 simultaneously with Adm-SH (1-adamantanethiol) and PPh3 ligands. A tetrahedral structure is found in the metal framework of Pt1Ag28 NC and an overall surface shell (Ag16S18P4), as well as discrete Ag4S6P1 motifs. The Pt1Ag12 kernel adopts a face-centered cubic (FCC) arrangement, which is observed for the first time in alloy nanoclusters in contrast to the commonly observed icosahedral structure of homogold and homosilver NCs. The Pt1Ag28 nanocluster exhibits largely enhanced photoluminescence (quantum yield QY = 4.9%, emission centered at ?672 nm), whereas the starting material (Pt1Ag24 NC) is only weakly luminescent (QY = 0.1%). Insights into the nearly 50-fold enhancement of luminescence were obtained via the analysis of electronic dynamics. This study demonstrates the atomic-level tailoring of the alloy nanocluster properties by controlling the structure.
Project description:In a previous work, gold nanoclusters (Au NCs) are found to inactivate RNA virus, but the effect of surface modification of Au NCs on its proliferation is still largely unknown. Here, the effect of surface modification of Au NCs on the proliferation of pseudorabies virus (PRV) by synthesizing two types of gold clusters with different surface modification, histidine stabilized Au NCs (His-Au NCs) and mercaptoethane sulfonate and histidine stabilized Au NCs (MES-Au NCs), is investigated. His-Au NCs rather than MES-Au NCs could strongly inhibit the proliferation of PRV, as indicated by the results of plaque assay, confocal microscopic analysis, Western blot assay, and quantitative real-time polymerase chain reaction (PCR) assay. Further study reveals that His-Au NCs perform the function via blockage of the viral replication process rather than the processes of attachment, penetration, or release. Additionally, His-Au NCs are found to be mainly localized to nucleus, while MES-Au NCs are strictly distributed in cytoplasm, which may explain why His-Au NCs can suppress the proliferation of PRV, but not MES-Au NCs. These results demonstrate that surface modification plays a key role in the antiviral effects of Au NCs and a potential antiviral agent can be developed by changing the Au NC surface modification.
Project description:Glutathione (GSH)-coated gold nanoclusters (Au NCs) were synthesized in aqueous acidic medium. On deprotonation of the carboxyl groups of the GSH molecules under alkaline condition, the anionic ends react with the added cationic surfactant molecules to convert the Au NCs hydrophobic, resulting in loss of fluorescence due to apparent insolubility in water. The fluorescence is revived by adding cyclodextrins (CDs) that encapsulate the protruding hydrophobic tails of the surfactant molecules surrounding the GSH-coated Au NCs. While addition of ?-CD showed maximum revival of the Au NC fluorescence, that by adding ?-CD was lesser. Interestingly, on adding ?-CD, there was no increase in fluorescence of Au NCs at all. The size of CDs varies as ?- > ?- > ?-. It appears that the cavity size of the CD-hosts controls the fluorescence from the Au NCs abruptly, and the reason behind that was found to be formation of suprastructures, the shapes of which varied from spherical to cubic. The work shows the production of Au NC-grafted CD suprastructures that develop fluorescence on-off composites on the basis of their overall shapes.
Project description:Gold nanocages (Au NCs), as drug carriers, have been widely applied for cancer diagnosis and photothermal therapy (PTT). Transmembrane transporting efficacy of Au NCs is the fundamental and important issue for their use in PTT. Herein, we used a force tracing technique based on atomic force microscopy to track the dynamic transmembrane process of Au NCs at the single-particle level in real time. Meanwhile, we measured and compared the dynamic parameters of Au NCs with sizes of 50 and 100 nm usually used as nanodrug carriers of PTT. It is concluded that the 50 nm Au NC transmembrane transporting needs smaller force and shorter duration with a much faster speed. However, both the 50 and 100 nm Au NC transmembrane transporting depends on the caveolin-mediated endocytosis, clathrin-mediated endocytosis, and macropinocytosis, which was also confirmed by confocal fluorescence imaging. This report will provide a potential technique for screening nanodrug carriers from the perspective of transmembrane transporting efficacy.
Project description:Biomimetic synthesis has become a promising green pathway to prepare nanomaterials. In this study, bovine serum albumin (BSA)-conjugated gold nanoclusters/nanoparticles were successfully synthesized in water at room temperature by a protein-directed, solution-phase, green synthetic method. The synthesized BSA-Au nanocomplexes have fluorescence emission (588 nm) of gold nanoclusters and surface plasmon resonance of gold nanoparticles. The BSA-Au nanocomplexes display non-cytotoxicity and excellent biocompatibility on MGC803 gastric cancer cells. After conjugation of folic acid molecules, the obtained BSA-Au nanocomplexes showed highly selective targeting for MGC803 cells and dual-modality dark-field and fluorescence imaging.