Preparation of High‐Performance Water‐Soluble Quantum Dots for Biorecognition through Fluorescence Resonance Energy Transfer

An improved method for the synthesis of high‐performance and water‐soluble quantum dots (QDs) involving the encapsulation of mercaptosuccinic acid coated QDs (MSA‐QDs) with poly(diallyldimethylammonium chloride) (PDDA) followed by their direct photoactivation with fluorescent radiation near 295 K to yield PDDA‐coated QDs (PDDA‐QDs) has been demonstrated. The quantum yield (QY) of the PDDA‐QDs was significantly improved from 0.6 (QY of MSA‐QDs) to 48 %. By using this synthetic strategy, highly photoluminescent PDDA‐QDs of varied size were readily prepared. The surface properties of PDDA‐QDs and MSA‐QDs were extensively characterized. The highly luminescent and positively charged PDDA‐QDs serve as a useful and convenient tool for protein adsorption. With a Δ⁵‐3‐ketosteroid isomerase adsorbed PDDA‐QD complex, the biorecognition of steroids was demonstrated through the application of fluorescent resonance energy transfer.     

Selenium‐Doped Carbon Quantum Dots for Free‐Radical Scavenging

Heteroatom doping is an effective way to adjust the fluorescent properties of carbon quantum dots. However, selenium‐doped carbon dots have rarely been reported, even though selenium has unique chemical properties such as redox‐responsive properties owing to its special electronegativity. Herein, a facile and high‐output strategy to fabricate selenium‐doped carbon quantum dots (Se‐CQDs) with green fluorescence (quantum yield 7.6 %) is developed through the hydrothermal treatment of selenocystine under mild conditions. Selenium heteroatoms endow the Se‐CQDs with redox‐dependent reversible fluorescence. Furthermore, free radicals such as ^.OH can be effectively scavenged by the Se‐CQDs. Once Se‐CQDs are internalized into cells, harmful high levels of reactive oxygen species (ROS) in the cells are decreased. This property makes the Se‐CQDs capable of protecting biosystems from oxidative stress.     

Room‐Temperature Solution‐Processed PbS Quantum Dot Solar Cells

Colloidal quantum dots (CQDs) are attractive absorber materials for high‐efficiency photovoltaics because of their facile solution processing, bandgap tunability due to quantum confinement effect, and multi‐exciton generation. To date, all published performance records for PbS CQDs solar cells have been based on the conventional hot‐injection synthesis method. This method usually requires relatively strict conditions such as high temperature and the utility of expensive source material (pyrophoric bis(trimethylsilyl) sulfide (TMS‐S)), limiting the potential for large‐scale and low‐cost synthesis of PbS CQDs. Here we report a facile room‐temperature synthetic method to produce high‐quality PbS CQDs through inexpensive ionic source materials including Pb(NO₃)₂ and Na₂S in the presence of triethanolamine (TEA) as the stabilizing ligand. The PbS CQDs were successfully prepared with an average particle size of about 5 nm. Solar cells based on the as‐synthesized PbS CQDs show a preliminary power conversion efficiency of 1.82%. This room‐temperature and low‐cost synthesis of PbS CQDs will further benefit the development of solution‐processed CQD solar cells.     

One‐Pot Green Synthesis of Nitrogen‐Doped Carbon Quantum Dots for Cell Nucleus Labeling and Copper(II) Detection

The doping of nitrogen into carbon quantum dots is vitally important for improved fluorescence performance. However, the synthesis of nitrogen‐doped carbon quantum dots (N‐CQDs) is usually conducted under strong acid and high temperature, which results in environmental pollution and energy consumption. Herein, the N‐CQDs were prepared by a mild one‐pot hydrothermal process. The hydrothermal reaction temperature was adjusted to control the particle size, nitrogen/carbon atomic ratio, and quantum yield. The products were water soluble with a narrow particle size distribution and good dispersion stability over a wide pH range. The N‐CQDs could penetrate into the HeLa cell nucleus without any further functionalization. Moreover, the fluorescence of N‐CQDs could be selectively quenched by Cu²⁺, which suggested applications for the detection of Cu²⁺ in human plasma.     

Visible‐Light Photocatalytic Hydrogen Production Activity of ZnIn2S4 Microspheres Using Carbon Quantum Dots and Platinum as Dual Co‐catalysts

ZnIn₂S₄ microspheres (ZIS MSs) were for the first time decorated with carbon quantum dots (CQDs) and platinum nanoparticles (NPs) as dual co‐catalysts of for photocatalytic H₂ production. The ZIS MSs co‐loaded with CQDs and Pt exhibited a high photocatalytic H₂ production rate of 1032.2 μmol h^?1 g^?1 with an apparent quantum efficiency of 2.2 % (420 nm) in triethanolamine aqueous solution under visible‐light irradiation, which was much higher than the respective photocatalytic rates of pure ZIS, Pt loaded ZIS, and CQDs‐decorated ZIS. Such a great enhancement was attributed to the integrative effect of good crystallization, enhanced light absorption, high electrical conductivity of CQDs, and the vectorial electron transfer from ZIS to CQDs and Pt NPs (ZIS→CQDs→Pt).     

An Efficient Templating Approach for the Synthesis of Redispersible Size‐Controllable Carbon Quantum Dots from Graphitic Polymeric Micelles

Access to high‐quality, easily dispersible carbon quantum dots (CQDs) is essential in order to fully exploit their desirable properties. Copolymers based on N‐acryloyl‐D ‐glucosamine and acrylic acid prepared by reversible addition–fragmentation chain transfer (RAFT) polymerization are self‐assembled into micelle‐like nanoreactors. After a facile graphitization process (170 °C, atmospheric pressure), each micellar template is transformed into a CQD through a 1:1 copy process. These high‐quality CQDs (quantum yield=22 %) with tunable sizes (2–5 nm) are decorated by carboxylic acid moieties and can be spontaneously redispersed in water and polar organic solvents. This preparation method renders the mass production of multifunctional CQDs possible. To demonstrate the versatility of this approach, CQDs hybridized TiO₂ nanoparticles with enhanced photocatalytic activity under visible‐light have been prepared.     

Kilogram-scale synthesis of carbon quantum dots for hydrogen evolution,sensing and bioimaging

A facile, low-cost, green, kilogram-scale synthesis of high quality CQDs were synthesized. The throughput of CQDs is 1.4975 kg in one pot and the as-prepared CQDs have a highly crystalline hexagonal structure with remarkable solubility, stability, and biocompatibility. It showed outstanding electrocatalytic activity, Fe³⁺ sensitivity and good biocompatibility.     

Kilogram-scale synthesis of carbon quantum dots for hydrogen evolution,sensing and bioimaging

The development of large-scale synthetic methods for high quality carbon quantum dots (CQDs) is fundamental to their applications. However, the macroscopic preparation and scale up synthetic of CQDs is still in its infancy. Here, we report a facile, green, kilogram-scale synthesis of high quality fluorescent CQDs derived from poplar leaves via a one-step hydrothermal method. Notably, the throughput of CQDs can reach a level up to as high as 1.4975 kg in one pot. The structure and properties of the as-prepared CQDs were assessed through TEM, XRD, XPS and various spectroscopic methods. The obtained high quality CQDs with a photoluminescent quantum yield of 10.64% showed remarkable stability in aqueous media, rich functional groups, high photostability, consistent photoluminescence within biological pH range and low cytotoxicity. On account of these good properties, we demonstrated the multifunctional application to electrocatalytic water splitting, Fe³⁺ sensing and bioimaging. It showed remarkable electrocatalytic activity, Fe³⁺ sensitivity and good biocompatibility. This study provides a green, facile, inexpensive and large-scale method for producing high quality CQDs, which provides application value for large-scale production of CQDs.     

Electrochemistry in Carbon‐based Quantum Dots

Electrochemistry belongs to an important branch of chemistry that deals with the chemical changes produced by electricity and the production of electricity by chemical changes. Therefore, it can not only act a powerful tool for materials synthesis, but also offer an effective platform for sensing and catalysis. As extraordinary zero‐dimensional materials, carbon‐based quantum dots (CQDs) have been attracting tremendous attention due to their excellent properties such as good chemical stability, environmental friendliness, nontoxicity and abundant resources. Compared with the traditional methods for the preparation of CQDs, electrochemical (EC) methods offer advantages of simple instrumentation, mild reaction conditions, low cost and mass production. In return, CQDs could provide cost‐effective, environmentally friendly, biocompatible, stable and easily‐functionalizable probes, modifiers and catalysts for EC sensing. However, no specific review has been presented to systematically summarize both aspects until now. In this review, the EC preparation methods of CQDs are critically discussed focusing on CQDs. We further emphasize the applications of CQDs in EC sensors, electrocatalysis, biofuel cells and EC flexible devices. This review will further the experimental and theoretical understanding of the challenges and future prospective in this field, open new directions on exploring new advanced CQDs in EC to meet the high demands in diverse applications.     

Biomass‐Derived Carbon Quantum Dot Sensitizers for Solid‐State Nanostructured Solar Cells

New hybrid materials consisting of ZnO nanorods sensitized with three different biomass‐derived carbon quantum dots (CQDs) were synthesized, characterized, and used for the first time to build solid‐state nanostructured solar cells. The performance of the devices was dependent on the functional groups found on the CQDs. The highest efficiency was obtained using a layer‐by‐layer coating of two different types of CQDs.     

Synthesis and surface photochemistry of graphitized carbon quantum dots

Graphitized carbon quantum dots (CQDs) were synthesized by a simple hydrothermal process with cetyltrimethylammonium bromide (CTAB) as the starting material and nitric acid as surface oxidant. The photoluminescent quantum yield (QY) of CQDs could be greatly enhanced through surface esterification with glycol. Based on the structure characterization, we proposed that the CQDs consisted of the stack of graphene sheets sized several nanometers and their excitation-dependent photoluminescence (PL) should be attributed to the n→π* transition of CO bond of surface carboxylic groups. And the PL of CQDs was obviously enhanced by the esterification of carboxylic groups, possibly due to the increase of the molecular coplanarity or the rigidity.     

Ethanol‐Precipitable,Silica‐Passivated Perovskite Nanocrystals Incorporated into Polystyrene Microspheres for Long‐Term Storage and Reusage

Perovskite nanocrystals (PNCs) are emerging luminescent materials due to their fascinating physic‐optical properties. However, their sensitive surface chemistry with organic polar solvents, oxygen, and moisture greatly hinders their developments towards practical applications. Herein we promote silica‐passivated PNCs (SP‐PNCs) by in situ hydrolyzing the surface ligands of (3‐aminopropyl) triethoxysilane. The resultant SP‐PNCs possesses a high quantum yield (QY) of 80 % and are precipitable by polar solvents, such as ethanol and acetone, without destroying their surface chemistry or losing QY, which offers an eco‐friendly and efficient method for separation, purification, and phase transfer of PNCs. Moreover, we further promoted a swelling–deswelling encapsulation process to incorporate the as‐made SP‐PNCs into non‐crosslinked polystyrene microspheres (PMs), which can largely increase the stability of the SP‐PNCs against moisture for long‐term storage.     

Ethanol‐Precipitable,Silica‐Passivated Perovskite Nanocrystals Incorporated into Polystyrene Microspheres for Long‐Term Storage and Reusage

Perovskite nanocrystals (PNCs) are emerging luminescent materials due to their fascinating physic‐optical properties. However, their sensitive surface chemistry with organic polar solvents, oxygen, and moisture greatly hinders their developments towards practical applications. Herein we promote silica‐passivated PNCs (SP‐PNCs) by in situ hydrolyzing the surface ligands of (3‐aminopropyl) triethoxysilane. The resultant SP‐PNCs possesses a high quantum yield (QY) of 80 % and are precipitable by polar solvents, such as ethanol and acetone, without destroying their surface chemistry or losing QY, which offers an eco‐friendly and efficient method for separation, purification, and phase transfer of PNCs. Moreover, we further promoted a swelling–deswelling encapsulation process to incorporate the as‐made SP‐PNCs into non‐crosslinked polystyrene microspheres (PMs), which can largely increase the stability of the SP‐PNCs against moisture for long‐term storage.     

Highly Photoluminescent Amino‐Functionalized Graphene Quantum Dots Used for Sensing Copper Ions

Herein, we report a new kind of highly fluorescent probe for Cu²⁺ sensing generated by hydrothermal treatment of graphene quantum dots (GQDs). After hydrothermal treatment in ammonia, the greenish‐yellow fluorescent GQDs (gGQDs) with a low quantum yield (QY, 2.5 %) are converted to amino‐functionalized GQDs (afGQDs) with a high QY (16.4 %). Due to the fact that Cu²⁺ ions have a higher binding affinity and faster chelating kinetics with N and O on the surface of afGQDs than other transition‐metal ions, the selectivity of afGQDs for Cu²⁺ is much higher than that of gGQDs. Furthermore, afGQDs are biocompatible and eco‐friendly, and the afGQDs with a positive charge can be easily taken up by cells, which makes it possible to sense Cu²⁺ in living cells. The strategy presented here is simple in design, economical, and offers a “mix‐and‐detect” protocol without dye‐modified oligonucleotides or complex chemical modification.     

Facile Preparation of Bright‐Fluorescent Soft Materials from Small Organic Molecules

Highly fluorescent and biocompatible soft materials are desirable for many potential applications, but their synthetic processes are somehow complicated. Herein, we have explored the feasibility of synthesis of unconventional fluorescence soft materials from small organic molecules under mild conditions. A new blue‐fluorescent soft material with high quantum yield (89.6 %) and eutectic feature prepared by simple heat treatment of citric acid (CA) and cysteine (Cys) aqueous mixtures below 100 °C in air was reported. The as‐prepared fluorescent material has the features of facile preparation, low cost, scalable production and easy to process, making it suitable for applications like fluorescent labeling and light‐emitting devices. This new finding opens a new venue for the preparation of fluorescent soft materials.     

Efficient Solid‐State Light‐Emitting CuCdS Nanocrystals Synthesized in Air

Semiconductor nanocrystals (NCs) possess high photoluminescence (PL) typically in the solution phase. In contrary, PL rapidly quenches in the solid state. Efficient solid state luminescence can be achieved by inducing a large Stokes shift. Here we report on a novel synthesis of compositionally controlled CuCdS NCs in air avoiding the usual complexity of using inert atmosphere. These NCs show long‐range color tunability over the entire visible range with a remarkable Stokes shift up to about 1.25 eV. Overcoating the NCs leads to a high solid‐state PL quantum yield (QY) of ca. 55 % measured by using an integrating sphere. Unique charge carrier recombination mechanisms have been recognized from the NCs, which are correlated to the internal NC structure probed by using extended X‐ray absorption fine structure (EXAFS) spectroscopy. EXAFS measurements show a Cu‐rich surface and Cd‐rich interior with 46 % Cu^I being randomly distributed within 84 % of the NC volume creating additional transition states for PL. Color‐tunable solid‐state luminescence remains stable in air enabling fabrication of light‐emitting diodes (LEDs).     

Gold Doping of Silver Nanoclusters: A 26‐Fold Enhancement in the Luminescence Quantum Yield

A high quantum yield (QY) of photoluminescence (PL) in nanomaterials is necessary for a wide range of applications. Unfortunately, the weak PL and moderate stability of atomically precise silver nanoclusters (NCs) suppress their utility. Herein, we accomplished a ≥26‐fold PL QY enhancement of the Ag₂₉(BDT)₁₂(TPP)₄ cluster (BDT: 1,3‐benzenedithiol; TPP: triphenylphosphine) by doping with a discrete number of Au atoms, producing Ag_29?xAu_x(BDT)₁₂(TPP)₄, x=1–5. The Au‐doped clusters exhibit an enhanced stability and an intense red emission around 660 nm. Single‐crystal XRD, mass spectrometry, optical, and NMR spectroscopy shed light on the PL enhancement mechanism and the probable locations of the Au dopants within the cluster.     

Protein‐Sized Bright Fluorogenic Nanoparticles Based on Cross‐Linked Calixarene Micelles with Cyanine Corona

The key challenge in the field of fluorescent nanoparticles (NPs) for biological applications is to achieve superior brightness for sizes equivalent to single proteins (3–7 nm). We propose a concept of shell‐cross‐linked fluorescent micelles, in which PEGylated cyanine 3 and 5 bis‐azides form a covalently attached corona on micelles of amphiphilic calixarene bearing four alkyne groups. The fluorescence quantum yield of the obtained monodisperse NPs, with a size of 7 nm, is a function of viscosity and reached up to 15 % in glycerol. In the on‐state they are circa 2‐fold brighter than quantum dots (QD‐585), which makes them the smallest PEGylated organic NPs of this high brightness. FRET between cyanine 3 and 5 cross‐linkers at the surface of NPs suggests their integrity in physiological media, organic solvents, and living cells, in which the NPs rapidly internalize, showing excellent imaging contrast. Calixarene micelles with a cyanine corona constitute a new platform for the development of protein‐sized ultrabright fluorescent NPs.     

Synthesis of Aqueous CdTe Nanocrystals with High Efficient Blue‐Green Emission of Exciton

As one of the most popular nanocrystals (NCs), aqueous CdTe NCs have very weak green emission under conventional synthesis conditions. In this work, we report the first example of blue‐emitting CdTe NCs directly synthesized in aqueous solution by slowing down the growth rate after nucleation. The key for the synthesis is the optimization of NC growth conditions, namely pH range of 7.5 to 8.5, TGA/Cd ratio of 3.6, Cd/Te ratio of 10, and Te concentration of 2×10^?5 mol/L, to get a slow growth rate after nucleation. The as‐prepared blue‐emitting CdTe NCs have small size (as small as 1.9 nm) and bright emission [with 4% photoluminescence quantum yield (PL QY) at 486 nm and 17% PLQY at 500 nm]. Transmission electron microscopy (TEM) images of the as‐prepared CdTe show monodispersed NCs which exhibit cubic zinc blend structure. Moreover, time‐resolved PL decay and X‐ray photoelectron spectroscopy (XPS) results show the as‐prepared NCs have better surface modification by ligand, which makes these luminescent small CdTe NCs have higher photoluminescence quantum yield, compared with NCs synthesized under conventional conditions.     

Study on the Ultrahigh Quantum Yield of Fluorescent P,O‐g‐C3N4 Nanodots and its Application in Cell Imaging

Graphitic carbon nitride nanodots (g‐C₃N₄ nanodots), as a new kind of heavy‐metal‐free quantum dots, have attracted considerable attention because of their unique physical and chemical properties. Although various methods to obtain g‐C₃N₄ nanodots have been reported, it is still a challenge to synthesize g‐C₃N₄ nanodots with ultrahigh fluorescence quantum yield (QY). In this study, highly fluorescent phosphorus/oxygen‐doped graphitic carbon nitride (P,O‐g‐C₃N₄) nanodots were prepared by chemical oxidation and hydrothermal etching of bulk P‐g‐C₃N₄ derived from the pyrolysis of phytic acid and melamine. The as‐prepared P,O‐g‐C₃N₄ nanodots showed strong blue fluorescence and a relatively high QY of up to 90.2 %, which can be ascribed to intrinsic phosphorus/oxygen‐containing groups, and surface‐oxidation‐related fluorescence enhancement. In addition, the P,O‐g‐C₃N₄ nanodots were explored for cell imaging with excellent stability and biocompatibility, which suggest that they have great potential in biological applications.