A simple, one-pot, "green" synthetic route, based on the "biomineralization" capability of a common commercially available protein, bovine serum albumin (BSA), has been developed for the preparation of highly stable Au nanocrystals (NCs) with red emission and high quantum yield.

A simple label-free method for the detection of Hg(2+) ions with high selectivity and sensitivity has been developed by using fluorescent Au NCs in aqueous media. The sensing mechanism was based on the high-affinity metallophilic Hg(2+)-Au(+) interactions, which effectively quenched the fluorescence of Au NCs.

Here, we report a general and facile method for effective layer-by-layer exfoliation of transition metal dichalcogenides (TMDs) and graphite in water by using protein, bovine serum albumin (BSA) to produce single-layer nanosheets, which cannot be achieved using other commonly used bio- and synthetic polymers. Besides serving as an effective exfoliating agent, BSA can also function as a strong stabilizing agent against reaggregation of single-layer nanosheets for greatly improving their biocompatibility in biomedical applications. With significantly increased surface area, single-layer MoS2 nanosheets also exhibit a much higher binding capacity to pesticides and a much larger specific capacitance. The protein exfoliation process is carefully investigated with various control experiments and density functional theory simulations. It is interesting to find that the nonpolar groups of protein can firmly bind to TMD layers or graphene to expose polar groups in water, facilitating the effective exfoliation of single-layer nanosheets in aqueous solution. The present work will enable to optimize the fabrication of various 2D materials at high yield and large scale, and bring more opportunities to investigate the unique properties of 2D materials and exploit their novel applications.

This paper reports a simple and scalable method for the synthesis of highly fluorescent Ag, Au, Pt, and Cu nanoclusters (NCs) based on a mild etching environment made possible by phase transfer via electrostatic interactions. Using Ag as a model metal, a simple and fast (total synthesis time < 3 h) phase transfer cycle (aqueous → organic (2 h incubation) → aqueous) has been developed to process originally polydisperse, nonfluorescent, and unstable Ag NCs into monodisperse, highly fluorescent, and extremely stable Ag NCs in the same phase (aqueous) and protected by the same thiol ligand. The synthetic protocol was successfully extended to fabricate highly fluorescent Ag NCs protected by custom-designed peptides with desired functionalities (e.g., carboxyl, hydroxyl, and amine). The facile synthetic method developed in this study should largely contribute to the practical applications of this new class of fluorescence probes.

Quantum dots (QDs) are of great interest to biological applications such as fluorescent biosensors and biolabels. Our study describes a synthesis of glutathione-capped CdTe QDs in aqueous solution that is cost-efficient and convenient compared to the conventional organometallic approaches. The fluorescence of the as-prepared glutathione-capped CdTe QDs was tunable from 500 to 650 nm. Without any postpreparation treatment, the glutathione-capped CdTe QDs achieved quantum yields (QYs) as high as 45 %, comparable to, or even better than, QDs derived from organometallic routes. With an overall size as small as 4 nm, they could gain access to cellular targets and stain fine features such as the cell nucleolus. These QDs were successfully conjugated with biotin for immunostaining and with F3 peptide for delivery to live cells, demonstrating their potentially broad application as biolabels.Fluorescent semiconductor nanoparticles or QDs have been extensively investigated in the past decade, and have been widely used as biolabels in imaging and biodetection.[1] Fluorescence imaging can greatly benefit from the use of QDs, which show brighter fluorescence, less photobleaching, and multiple colors with a single excitation. For biolabeling applications, QDs are commonly capped with trioctylphosphine oxide (TOPO) through organometallic synthesis, followed by phospholipid, [2] silica, [3] or polymer [4] coating to impart watersolubility and biocompatibility. With the multilayer coating, the final size of the QD biolabels would typically be 12-20 nm, which might be too bulky to gain access to cells for in vitro and in vivo imaging. In addition, the large dimensions would dramatically lower the labeling efficiency on specific target sites within the cells. Compared to conventionally used organic dyes, the size of QDs presented a major drawback as it limited the range of applications in biolabeling. To overcome this obstacle, water-soluble QDs with only one layer of capping ligand on the surface have been developed by ligand exchange with thiols [5] or phosphine [6] on TOPO-capped QDs.Both the ligand-addition and ligand-exchange methods were complicated, and even the high-quality QDs derived from organometallic methods have exhibited reductions in QY from 65-85 % in the organic phase to 35-50 % in aqueous solution.[7]Alternatively, thiol-capped QDs could be prepared directly in aqueous solution with thiols as stabilizers, but low QYs of 1-10 % were typically obtained.[8] Although their QYs could be significantly improved by a variety of after-treatments, such as photochemical etching, [8] size-selective precipitation, [9] and long-term illumination, [10] these QDs have a tendency to agglomerate during such treatments. Glutathione is a thiol-containing oligopeptide found in most organisms, and it plays an important role in the detoxification of heavy metals in plant cells. The physiological mechanism of detoxification involves the binding of heavy-metal nanoclusters by glutathione and the formation of a phytochelatin shell, cat...

Fluorescent semiconductor nanocrystals or quantum dots (QDs) are of great interest to many applications such as photonic devices and bio-labeling. We have developed an aqueous synthesis for glutathione (GSH)-capped ZnSe and Zn 1-x Cd x Se alloyed QDs, the fluorescence emissions of which are tunable between 360 and 500 nm. They show high quantum yields (QYs) of up to 50 %, with narrow bandwidths of 19-32 nm. The GSH-capped Zn 1-x Cd x Se QDs are highly water-soluble and biocompatible, allowing for blue fluorescent labeling in biological imaging applications. The facile synthesis of glutathione-capped ZnSe and Zn 1-x Cd x Se QDs presented is simple and cost-effective compared to the conventional organometallic approaches. It represents the first direct synthesis of blue fluorescent QDs in aqueous solution. The approach can be easily scaled up for the commercial production of alloyed nanocrystals of various compositions.QDs have attracted significant attention for applications in photonics, lasers, and biological imaging.[1] The fascinating optical properties of QDs are dependent on their size, shape, and composition. Developing new synthesis for QDs with controlled structure and properties has been an important research area in nanotechnology. While most QDs were prepared through an organometallic route, water-based synthesis with thiols as capping ligands has been developed as an interesting alternative.[2] Although aqueous synthesis is simple, reproducible, and less energy intensive, broad emissions and low QYs have made these thiol-capped QDs less promising for biological applications compared to their trioctylphosphine oxide (TOPO)-capped counterparts. Recently, CdTe QDs prepared with GSH as the capping ligand provided QYs of up to 62 % and tunable fluorescence emissions between 500 and 680 nm, [3] which were comparable with QDs prepared by the organometallic route. GSH has been used by plant cells to detoxify soils contaminated by heavy metals. GSH-capped CdTe QDs were found to be more biocompatible than other water-soluble QDs. [3a, 3c] These recent studies demonstrated that GSH was superior to other thiols as a capping ligand for CdTe QDs. QDs with different fluorescence colors are usually prepared by tuning the nanocrystallite size. However, CdTe QDs emitting blue fluorescence are extremely small in crystallite size (< 2 nm) and highly unstable. GSH-capped CdSe QDs have been synthesized by Baumle et al. [4] and Zheng and Ying.[5]However, the fluorescence emissions were only tunable in a very narrow range (500-530 nm), with maximum QYs of ∼ 16 %. GSH-capped ZnTe and CdS QDs prepared in aqueous solution have also shown very weak blue fluorescence or broad trap emission.[5]A different strategy for tuning the fluorescence color of QDs without changing the crystallite size has been achieved with core/shell composites [6] and alloyed nanocrystals. [7] For example, Zhong et al. have prepared Zn x Cd 1-x Se alloyed nanocrystals through the incorporation of Zn into CdSe nanocrystals by an organometallic route. [7a...

Highly emissive and air-stable AgInS2-ZnS quantum dots (ZAIS QDs) with quantum yields of up to 20% have been successfully synthesized directly in aqueous media in the presence of polyacrylic acid (PAA) and mercaptoacetic acid (MAA) as stabilizing and reactivity-controlling agents. The as-prepared water-dispersible ZAIS QDs are around 3 nm in size, possess the tetragonal chalcopyrite crystal structure, and exhibit long fluorescence lifetimes (>100 ns). In addition, these ZAIS QDs are found to exhibit excellent optical and colloidal stability in physiologically relevant pH values as well as very low cytotoxicity, which render them particularly suitable for biological applications. Their potential use in biological labelling of baculoviral vectors is demonstrated.

In this article, the very recent progress of various functional inorganic nanomaterials is reviewed including their unique properties, surface functionalization strategies, and applications in biosensing and imaging-guided therapeutics. The proper surface functionalization renders them with stability, biocompatibility and functionality in physiological environments, and further enables their targeted use in bioapplications after bioconjugation via selective and specific recognition. The surface-functionalized nanoprobes using the most actively studied nanoparticles (i.e., gold nanoparticles, quantum dots, upconversion nanoparticles, and magnetic nanoparticles) make them an excellent platform for a wide range of bioapplications. With more efforts in recent years, they have been widely developed as labeling probes to detect various biological species such as proteins, nucleic acids and ions, and extensively employed as imaging probes to guide therapeutics such as drug/gene delivery and photothermal/photodynamic therapy.