We report a direct one-pot approach, employing tetrakis(hydroxymethyl)phosphonium chloride (THPC) and 11-mercaptoundecanoic acid (11-MUA) as combined reducing/capping agents, for the rapid preparation of fluorescent gold nanoclusters (AuNCs) from HAuCl4 in aqueous solution at room temperature. The as-prepared AuNCs exhibit a fluorescence emission at 535 nm, a quantum yield of 1.8% and average diameters of 2.0 ± 0.5 nm. The resultant MUA/THPC–AuNCs have been exploited, for the first time, for the highly sensitive and selective detection of silver ions (Ag+) in aqueous solution when using EDTA as a masking agent for Hg2+. The fluorescence intensity quenches linearly within the range of 25 nM to 3 μM with high sensitivity (LOD = 9 nM, S/N = 3) and this sensing system has been applied for environmental water sample analysis.

We report a one-pot approach to prepare fluorescent gold nanoclusters (AuNCs) from HAuCl4 by simply using 11-mercaptoundecanoic acid (11-MUA) as a reducing and capping agent, in an aqueous solution of NaOH at room temperature. The as-prepared water-soluble AuNCs with average diameters of 1.8 ± 0.4 nm exhibit a unique fluorescence excitation at 285 nm, a maximum emission at 608 nm, and a quantum yield of 2.4%. We find that the fluorescence of 11-MUA-AuNCs can be quenched by several metal ions but selectively by Cr3+ ions when using EDTA as the masking agents for other metal ions. This phenomenon is further exploited as a “turn-off” fluorescent sensor for sensitive and selective detection of Cr3+ ions. Upon the quantitative addition of Cr3+ in the presence of EDTA, the fluorescence intensity quenches linearly within the range of 25 nM to 10 μM with high sensitivity (LOD = 26 nM, S/N = 3). Furthermore, the 11-MUA-AuNCs could be used to detect Cr6+ indirectly by using ascorbic acid to reduce Cr6+ into Cr3+ in aqueous solution.

In situ probing protein–particle interactions and activities of proteins on colloidal nanoparticle (NP) surfaces is a long-standing key challenge in understanding the nanobio interfaces and virtually important for a variety of biological and biomedical applications. The interactions of NPs with proteins, for instance, are known to form NP bioconjugates or protein coronas; protein surface immobilization and molecular layer-by-layer deposition techniques are widely used, but a clear understanding of the confinement effect on protein activity by molecular coating, at the monolayer level, remains poorly understood. We explore here a novel approach, using colloidal plasmonic nanocomplexes coated with glucose oxidase (GOx) as self-sensing nanoprobes for in situ optical probing of surface-confined enzymatic activity, which is at least 1–2 orders of magnitude more sensitive than standard colorimetric assays for detecting GOx activity. We found that enzymatic activity of monolayer-confined GOx on colloidal NPs was significantly enhanced as compared with free GOx (also proved by conformational changes from circular dichroism studies), with a low apparent Michaelis–Menten constant Km of ∼0.115 mM and high turnover kcat/Km of ∼8394 M–1·s–1; compared with the “anchored-type” suspending GOx, the outmost polyelectrolyte monolayer-protected “sandwiched-type” GOx exhibits significantly improved enzymatic activities toward higher temperatures and wider pH range. This finding is of fundamental important and instructive for safe use of such nanomaterials for bioapplications.

As a simple and flexible 2D platform, the water–air interface is envisioned as an environmentally-friendly approach to prepare ultrathin free-standing nanomembranes (FNMs) of monolayered nanoparticles of interest via interfacial self-assembly. However, attempts so far have been rather rare due to the lack of efficient methods. In this article, we report on a facile and general strategy for fabrication of a family of noble metal-based FNMs by a simple and reagentless interfacial self-assembly tactics to prepare functional (plasmonic or catalytic) FNMs, such as Au, Ag, Pd, Pt-FNMs and their bimetallic hybrids, Ag/Au-FNMs and Pd/Pt-FNMs. The organic solvent-free process, varying somewhat from metal to metal only in precursors, reducing agents and dosage of reagents used, is found to be a general phenomenon and ligand-independent (irrespective of the monolayer quality of the resulting FNMs), allowing the growth of high-quality noble metal-based FNMs with well-defined nanoparticulate and monolayer morphology as large as several square centimeters. Heat treatment (boiling) is performed to accelerate the formation of FNMs within 15 min. More significantly, the as-prepared plasmonic Au-FNMs acting as a SERS substrate show a superior activity; whereas the resulting catalytic Pd-FNMs, except for their excellent ethanol electrooxidation performance, exhibit higher electrocatalytic activity for formic acid oxidation than commercial catalysts.

This paper describes a simple and facile method for the synthesis of Ag/Au bimetallic hollow and porous nanoshells (HPNSs) with controllable porosity, using polycrystalline Ag nanoparticles as starting templates. The optical and catalytic properties of the HPNSs can be easily tuned by using hydrogen peroxide as a mild etchant to controllably dissolve Ag atoms from the precursor Ag/Au bimetallic hollow nanoshells (NSs). The surface plasmon bands of the HPNSs can be easily tuned from the visible to the near infrared (NIR) region. As a model reaction to evaluate the catalytic activity of the HPNSs, we chose the reduction of p-nitrophenol by NaBH4 to afford p-aminophenol. The porous NSs exhibit higher catalytic activity than non-porous NSs even though the latter have higher Au/Ag ratios than the former. Although the composition (Au/Ag ratio) may have some effect, the morphology (porosity) of the HPNSs plays the most important role in the catalysis. The as-synthesized plasmonic HPNSs, due to their facile aqueous-phase preparation, tunable optical properties (in the visible and NIR windows), and unique porous hollow structures, have promising potential applications in various fields ranging from biosensing, nanomedicine (drug/gene delivery, cancer theranostics, etc.), to catalysis and solar cells. Open image in new window

We report a direct one-pot approach, employing tetrakis(hydroxymethyl)phosphonium chloride (THPC) and 11-mercaptoundecanoic acid (11-MUA) as combined reducing/capping agents, for the rapid preparation of fluorescent gold nanoclusters (AuNCs) from HAuCl4 in aqueous solution at room temperature. The as-prepared AuNCs exhibit a fluorescence emission at 535 nm, a quantum yield of 1.8% and average diameters of 2.0 ± 0.5 nm. The resultant MUA/THPC–AuNCs have been exploited, for the first time, for the highly sensitive and selective detection of silver ions (Ag+) in aqueous solution when using EDTA as a masking agent for Hg2+. The fluorescence intensity quenches linearly within the range of 25 nM to 3 μM with high sensitivity (LOD = 9 nM, S/N = 3) and this sensing system has been applied for environmental water sample analysis.

We report a one-pot approach to prepare fluorescent gold nanoclusters (AuNCs) from HAuCl4 by simply using 11-mercaptoundecanoic acid (11-MUA) as a reducing and capping agent, in an aqueous solution of NaOH at room temperature. The as-prepared water-soluble AuNCs with average diameters of 1.8 ± 0.4 nm exhibit a unique fluorescence excitation at 285 nm, a maximum emission at 608 nm, and a quantum yield of 2.4%. We find that the fluorescence of 11-MUA-AuNCs can be quenched by several metal ions but selectively by Cr3+ ions when using EDTA as the masking agents for other metal ions. This phenomenon is further exploited as a “turn-off” fluorescent sensor for sensitive and selective detection of Cr3+ ions. Upon the quantitative addition of Cr3+ in the presence of EDTA, the fluorescence intensity quenches linearly within the range of 25 nM to 10 μM with high sensitivity (LOD = 26 nM, S/N = 3). Furthermore, the 11-MUA-AuNCs could be used to detect Cr6+ indirectly by using ascorbic acid to reduce Cr6+ into Cr3+ in aqueous solution.