Fluorescent Carbon Dots: Aggregation-Induced Emission Enhancement, Application as Probe for CN- and Cr2O7-2, Sensing Strips and Bio-imaging Agent

Fluorescent carbon dots (Trp-CDs) were prepared using tryptophan as precursor and were characterized on the basis of elemental analysis, powder-XRD, IR, Raman spectroscopy, 13C-NMR, UV-Vis, fluorescence and TEM. Trp-CDs exhibit poor fluorescence in 100% water but showed strong Aggregation Induced Emission (AIE) in ethanol and higher alcohols. The anion sensing study of Trp-CD revealed that it selectively detects CN- and Cr2O7-2 and from fluorescence quenching titration study, quenching constant, LOD and range of detection were evaluated. The emission life-time of Trp-CD before and after addition of CN- and Cr2O7-2 were measured, the decay curve before addition of anion was best fitted with a bi-exponential function with life-time of τ1 2.79 ns (10.74%) and τ2 18.93 ns (89.26%). The mechanistic study revealed that for CN-, the fluorescence quenching is due to its interaction with protons attached to surface functional groups and for Cr2O7-2, it is due to inner filter effect (IFE). Sensing strips were prepared by coating Trp-CDs onto various solid surfaces including agarose films and were used for detection of CN- and Cr2O7-. Trp-CD was found to be nontoxic and biocompatible and used as staining agent for Artemia and Bacteria (Bacillus Subtilis, Pseudomonas) and detection of CN- and Cr2O7-.

Fabrication and Efficient Interfacial Assembly of Bright Red-Emitting Carbon Quantum Dots for Security-Warning Textiles

Carbon quantum dots (CQDs) have attracted more attentions due to their multiple performances. However, the fabrication of long-wavelength emitting CQDs with aliphatic precursors still remains a challenge, mainly because it is difficult to generate large sp2 domains to reduce energy gap, which is not conducive to a redshift of the luminescence peak. Hereon, by regulating the pH of citric acid and thiourea mixture, a N, S co-doped CQD emitting bright red fluorescence at 635 nm is successfully fabricated through the solvothermal reaction under acidic condition, achieving a high quantum yield of 32.66%. Solvatochromic effects of the CQDs are discussed through theoretical equations and models, which confirm that the hydrogen-bonding interaction dominates the fluorescence emission behavior of CQDs in polar solvents. Besides, a feasible strategy is proposed to prepare an anti-counterfeiting textile via the deposition of red-emitting CQDs onto cotton fibers, through rapidly evaporating the preferred organic solvent. As expected, the CQD-decorated textiles exhibit encouraging anti-counterfeiting and security-warning functions, along with underwater and long-distance detectability, washability, and sun resistance. It is worth noting that the present work is innovative in realizing the application of red-light-emitting CQDs in the fields of security-warning textiles.

Glutathione Modified silicon-doped Carbon Quantum dots as a Sensitive Fluorescent Probe for ClO- Detection

A selective and sensitive fluorescence method for hypochlorite (ClO-) was designed using glutathione (GSH) modified silicon-doped carbon quantum dots (GSH@Si-CDs). Then a dual emission ratio fluorescence probe (RF-probe) was obtained based on carbodiimide-activated coupling reaction between GSH and Si-CDs. i.e., when the excitation wavelength was kept at 360 nm, the GSH@Si-CDs exhibited strong blue and weak yellow fluorescence at 430 and 580 nm. Meanwhile, the fluorescence of GSH@Si-CDs could be selectively quenched at 430 nm and enhanced at 580 nm in the presence of ClO-, and corresponding limit of detection (LOD) and linear range were measured to be 0.35 µM and 1.0-33.3 µM. The sensing mechanism of the system was also investigated in detail. Moreover, the RF-probe with good accuracy was successfully employed to monitor ClO- in real samples with satisfactory results compared to the standard iodometric method.

Surface Modification Functionalized Carbon Dots

Carbon dots (CDs) smaller than 10 nm constitute a new type of fluorescent carbon-based nanomaterial. They have attracted much attention owing to their unique structures and excellent photoelectric properties. Primitive CDs usually comprise carbon and oxygen and are synthesized in one step from various natural products or synthetic organic compounds, usually via microwave or hydrothermal methods. However, the uniformity of surface functional groups often make CDs lack the diversity of active sites required for specific applications. Therefore, the functionalization of CDs by specific groups is a powerful strategy for improving their photophysical and photochemical properties. This paper reviews surface modification strategies to overcome these shortcomings. Functionalizing CDs using covalent or non-covalent modification can give them unique properties and broaden their applicability.

Carbon dots with aggregation-induced emission enhancement (AIEE) for detection of Zr4+/ Hf4+ and PTP1B activity

The frequent use of Zirconium (Zr) and Hafnium (Hf) in modern industries may result in serious environment issues, and thus developing analytical methods to facilitate the control of these two resembled metal elements is urgently needed. However, up to now, rapidly and conveniently detecting Zr⁴⁺ and Hf⁴⁺ is still full of challenge. In this study, nitrogen and sulfur co-doped carbon dots (N, S-Cdots) with aggregation-induced emission enhancement (AIEE) were prepared and used for turn-on detection of Zr⁴⁺ and Hf⁴⁺ within 10 min. The photoluminescent intensity of N, S-Cdots showed a good linear correlation with Zr⁴⁺ and Hf⁴⁺concentrations ranging from 0 to 30 μM with the limit of detection (LOD) of 0.47 and 0.53 μM, respectively. Furthermore, this fluorometric assay was successfully used for quantitative analysis of Zr⁴⁺ and Hf⁴⁺ in real water samples with satisfactory recoveries in the range of 91.16-108.50% and 90.28-106.49%, respectively. Finally, the developed N, S-Cdots sensing system was used for assay PTP1B activity and screening its inhibitor with Zr⁴⁺ as the medium. Our work demonstrated that the as-prepared N, S-Cdots with AIEE can offer a simple and reliable alternative for rapid detection of Zr⁴⁺ and Hf⁴⁺ in water samples, in addition to being potential useful in phosphatase analysis and drug discovery.

Peptide-modified carbon dot aggregates for ultrasensitive detection of lipopolysaccharide through aggregation-induced emission enhancement

This study fabricated yellow-emitting CDs (Y-CDs) by hydrothermal treatment of citric acid and urea and applied them as a fluorescence turn-on platform for sensitive and selective detection of lipopolysaccharide (LPS) based on the non-shifted AIEE of peptide-stabilized CD aggregates. The designed peptide (named K3) consisting of aggregation-active and LPS-recognition units triggered the aggregation of Y-CDs, switching on their fluorescence through the blue-shifted AIEE process. The formed K3-stabilized Y-CD aggregates (K3-YCDAs) specifically interacted with LPS at neutral pH, demonstrating that the sequence of the decorated peptide was highly connected with their selectivity and sensitivity. The K3-YCDAs provided a fast response time (within 5 min) to detect LPS with a quantification range of 0.5-100.0 nM and a limit of detection (LOD, signal-to-noise ratio of 3) of 300.0 pM. By integrating ultrafiltration membranes as a concentration device with K3-YCDAs as a sensing probe, the LOD for LPS was further reduced to 3.0 pM. The determination of picomolar levels of plasma LPS by the K3-YCDAs coupled to the centrifugation ultrafiltration was demonstrated to fall within the specificity range of clinical interest for sepsis patients. Also, the K3-YCDAs served as a fluorescent probe to selectively image and quantify E. coli cells. The distinct advantages of the K3-YCDAs for LPS include fast response time, wide linear range, low detection limit, and excellent selectivity compared to previously reported sensors.

The synthesis of carbon dots by folic acid and utilized as sustainable probe and paper sensor for Hg2+ sensing and cellular imaging

In this work, the blue emission carbon dots (FA-CDs) are synthesized by one-pot solvothermal method by using folic acid as precursor. The FA-CDs emitted bright emission at 445 nm when excited at 360 nm with the QY of 31.2 %. The FA-CDs exhibit sensitive quenching response to Hg²⁺ with variable concentrations systematically, which determined FA-CDs can be employed as fluorescent probe, with a reliable linear relationship between fluorescence intensity and Hg²⁺ concentration, and a limit of detection (LOD) of 1.29 nM. Notably, the quenched FA-CDs can be recovered by using EDTA saturated solution with the emission comparable to initial in succession. The FA-CDs based paper sensor can be explored with similar detection performance, and it can also be restored by EDTA saturated solution. Both the restored CDs and paper sensor can be reused in the next turn for detecting Hg²⁺, which allowed the FA-CDs and their paper sensor can be serviced as sustainable probe for Hg²⁺ detection. The visual LOD of paper sensor can be determined at 0.1 μM, notably, the paper sensor can be reused at least 3 times with good performance, which is beneficial to environmental protection and saving resources. Possess excellent water solubility and non-toxic properties, the cellular imaging of FA-CDs was evaluated with excellent quality fluorescent image results. The FA-CDs provide a promising convenient fluorescent probe for multi-application in detection and imaging.

Highly efficient red-emitting carbon dots as a "turn-on" temperature probe in living cells

Nanothermometers, which can precisely detect the intracellular temperature changes, have great potential to solve questions concerning the cellular processes. Thus, the temperature sensors that provide fluorescent "turn-on" signals in the biological transparency window are of highly desirable. To meet these criteria, this work reported a new "turn-on" carbon dot (CD)-based fluorescent nanothermometry device for sensing temperature in living cells. The CDs that emit bright red fluorescence (R-CDs; λ_max = 610 nm in water) were synthesized with o-phenylenediamine as carbon precursor via a facile solvothermal method. The R-CDs in water were almost nonfluorescent at 15 °C. As the temperature increased, the fluorescence intensity of R-CDs exhibited a gradual increase and the final enhancement factor was greater than 21-fold. The fluorescence intensity exhibited a linear response to temperature and a high-sensitive variation of ≈13.3 % °C^-1 was detected within a broad temperature range of 28-60 °C. Moreover, the R-CD thermal sensors also exhibited high storage stability, excellent response reversibility and superior photo- and thermo-stability. Due to its good biocompatibility and "intelligent" response to external temperature, the nanothermometer could be applied for sensing temperature changes in biological media.

One-step synthesis of highly fluorescent carbon dots as fluorescence sensors for the parallel detection of cadmium and mercury ions

Cadmium (Cd2+) and mercury ions (Hg2+) are essential for the quality control of food samples because of their serious toxicity to human health, but the effective and simple strategy for their parallel detection remains challenging. In this paper, a rapid and simple parallel detection method for Cd2+ and Hg2+ was developed using carbon dots (CDs) as fluorescent sensors. A one-step hydrothermal method with a single precursor l-arginine as both the carbon and nitrogen sources was employed to prepare nitrogen-doped CDs (N-CDs). N-CDs exhibited a uniform particle size and excitation-independent fluorescence emission. The maximum emission wavelength of N-CDs was observed at 354 nm with the excitation wavelength at 295 nm. The quantum yield of N-CDs reached as high as 71.6% in water. By using sodium diphosphate and phytic acid as masking agents, the fluorescent sensor can be quenched by Cd2+ and Hg2+ in the linear range of 0–26.8 μM and 0–49.9 μM within 5 min. Other common ions in farm products showed no significant effect on the fluorescence intensity of the sensing system. The results demonstrated that the sensing system had good selectivity and sensitivity for Cd2+ and Hg2+. The detection limits for Cd2+ and Hg2+ were 0.20 and 0.188 μM, respectively. In addition, the fluorescent sensor had been successfully applied for the detection of Cd2+ and Hg2+ in fruits and vegetables, and the recoveries were 86.44–109.40% and 86.62–115.32%, respectively. The proposed fluorescent sensor provides a rapid, simple, and sensitive detection method for Cd2+ and Hg2+ in food samples and thus a novel quantitative detection method for heavy metal ions in foods.

Polymer-Induced Emission-Active Fluorine-Embedded Carbon Dots for the Preparation of Warm WLEDs with a High Color Rendering Index

Exploration of many strategies has continuously contributed to producing aggregation-induced red-emissive carbon dots (CDs). In this work, we designed fluorine-embedded (F-embedded) CDs from 1,2,4-triaminobenzene, thiourea, and ammonium fluoride (NH₄F) exhibiting polymer-induced emission (PIE). The PIE phenomenon of fluorescent CDs is obtained in poly(vinyl alcohol) (PVA), showing emissions at 611 and 617 nm in the dispersed and solid states, respectively. The CDs exhibited a red shift of 28 nm in the PVA solution because PVA hydroxyl groups formed a robust bridge-like H-bonding network between CDs. The fluorine embedded in CDs enhanced the H-bond affinity toward PVA. It showed that this H-bond restricted the coupling of CDs' surface states and inhibited the nonirradiation transfer. For the solid state, surface PVA chains eliminated the π-π interaction of the conjugated core and constructed a self-quenching resistance polymeric system around CDs. As a result, CDs showed an unexpected red shift of fluorescence emission in PVA. Furthermore, white light-emitting diodes (WLEDs) have a correlated color temperature (CCT) of 5232 K, and a high color rendering index of 95 has been fabricated by integrating the red- and green-emissive films over the UV LEDs. Interestingly, the as-synthesized CDs showed room temperature phosphorescence (RTP), which enabled us to employ the CDs in double-security protection. Simultaneously, CDs have been used in fingerprint detection.

Novel nitrogen-doped carbon dots for "turn-on" sensing of ATP based on aggregation induced emission enhancement effect

In this work, a nitrogen-doped carbon dots (CDs) was successfully synthesized by hydrothermal synthesis of polyethylenimine (PEI) and citric acid. The as-prepared CDs suffered from aggregation-caused quenching (ACQ) with a high concentration, but after adding adenosine triphosphate (ATP), the CDs aggregated. The generation of aggregates caused the rotation of the surface groups on CDs and reduced the non-radiation decay. The QY of CDs in water was 9.25 %, and increased to 16.60 % and 63.38% in the addition of 100 and 1000 μM ATP. And then, the enhancement of the radiation rate led to the aggregation induced enhancement effect (AIEE). Moreover, we also found that the proportion of precursors for CDs synthesis was a key factor in the occurrence of AIEE. Therefore, such CDs would be excellent candidates as fluorescent probes for the label-free detection of ATP. Our proposed method exhibited simple and easy preparation of nanoprobe, quick response (3 min), wide range of linear rage (1-2000 μM) and eco-friendly. In addition, the method performed successfully as a "turn-on" sensor for detection of ATP in the tablet with a recovery of 100.1~106.9% and RSD below 3.5%.

A Review on the Catalytic Remediation of Dyes by Tailored Carbon Dots

Water polluted with dyes has become a serious global concern during the twenty-first century, especially for developing countries. Such types of environmental contaminant pose a severe threat to biodiversity, ecosystems, and human health globally; therefore, its treatment is an utmost requirement. Advanced technologies including the use of nanomaterials represent a promising water treatment technology with high efficiencies, low production costs, and green synthesis. Among the nanomaterials, carbon dots, as a new class of carbon-based nanoparticles, have attracted attention due to their unique features and advantages over other nanomaterials, which include high water solubility, easy fabrication and surface functionalisation, excellent electron-donating ability, and low toxicity. Such properties make carbon dots potential nanocatalysts for the Fenton-like degradation of environmental pollutants in water. Although recent studies show that carbon dots can successfully catalyse the degradation of dyes, there are still limited and controversial studies on the ecotoxicity and fate of these nanoparticles in the environment. In this review, the authors aim to summarise the recent research advances in water remediation by technologies using carbon dots, discuss important properties and factors for optimised catalytic remediation, and provide critical analysis of ecotoxicity issues and the environmental fate of these nanoparticles.

Cadmium induced aggregation of orange-red emissive carbon dots with enhanced fluorescence for intracellular imaging

Cadmium is a notorious toxic heavy metal, that poses serious threat to human health. Sensitive and selective detection of cadmium in cells is of great significance in poison screening and disease diagnosis. Orange-red emissive carbon dots (OR-CDs), prepared from the calcination of selected carbon sources 5-amino-1, 10-phenanthroline (Aphen) and salicylic acid (SA), were found to act as a "turn on" type fluorescence probe for Cd²⁺ detection. The structure and optical properties of OR-CDs were comprehensively investigated by both experimental characterizations and density functional theory (DFT) calculations. The OR-CDs consist of a basic unit of nine aromatic rings, and the N/O binding sites on the OR-CDs can specifically bind with Cd²⁺, leading to aggregation induced enhanced emission (AIEE). A detection limit of 0.30 μM was achieved for Cd²⁺ with a linear range of 0.80-100 μM. OR-CDs can not only be used for intracellular Cd²⁺ imaging but also have the potential to alleviate cadmium poison in living organisms.

N-gene-complementary antisense-oligonucleotide directed molecular aggregation of dual-colour carbon dots, leading to efficient fluorometric sensing of SARS-COV-2 RNA

The early stages of the COVID-19 pandemic punctuated the need for rapid, mass testing for early detection of viral infection. Carbon dots are easily synthesized, cost-effective fluorescent nanoparticles whose surface functionalities enable facile conjugation with biorecognition elements suitable for  molecular detection of viral RNA. Herein, we report that a pair of complementary antisense oligonucleotide (ASO) sequences can lead to a highly specific molecular aggregation of dual colour carbon dots (CDs) in the presence of SARS-CoV-2 RNA. The nanoprobes used ASOs highly specific to the N-gene of SARS-COV-2. When the ASOs are conjugated to blue and yellow citric acid-derived CDs, the combination of the ASO-CD pairs facilitates aggregation-induced emission enhancement (AIEE) of the measured fluorescence after hybridization with SARS-CoV-2 RNA. We found the sensor capable of differentiating between MERS-CoV and SARS-CoV-2 samples and was found to have a limit of detection of 81 copies per μL. Additionally, we used dialysis to demonstrate that the change in emission upon aggregation is dependent on the compositional heterogeneity of the conjugated-carbon dot mixture.

The highly sensitive “turn-on” detection of morin using fluorescent nitrogen-doped carbon dots

Graphic diagram of the synthesis of the N-CDs and the N-CDs based fluorescent sensor for the determination of morin.

Quaternary Ammonium-Mediated Delamination of Europium-Based Metal-Organic Framework into Ultrathin Nanosheets for the Selective Photoelectrochemical Sensing of Fe3

Structural delamination of bulk layered metal-organic frameworks (MOFs) remains a great challenge, largely owing to a lack of general synthetic strategies. Here, we reported a simple solvent-free intercalation strategy for the delamination of rare-earth-based MOF (RE-MOF) with a topology structure of MIL-78 by tuning the chain length of quaternary ammonium salts. Four types of quaternary ammonium salts, involving tetraethylammonium bromide (TEAB), tetrapropylammonium bromide (TPAB), tetrabutylammonium bromide (TBAB), and hexadecyl trimethyl ammonium bromide (CTAB) were introduced to investigate their intercalation capabilities. It is evident in our case that the interruption/intercalation behavior of quaternary ammonium salts differs with their steric structures, and the chain-like CTAB can induce obvious delamination of MIL-78 crystals. Particularly, the CTAB-intercalated ultrathin Eu-based MIL-78 nanosheets exhibited unique selective photoelectrochemical sensing property toward trace amounts of Fe³⁺ ions in aqueous solution with a detection limit of 0.0899 μM at a signal-to-noise ratio of 3. These results demonstrated a green bottom-up strategy to obtain high-quality RE-MOF nanosheets for potential photocurrent response applications.

Stimuli-Responsive AIEgens

The unique advantages and the exciting application prospects of AIEgens have triggered booming developments in this area in recent years. Among them, stimuli-responsive AIEgens have received particular attention and impressive progress, and they have been demonstrated to show tremendous potential in many fields from physical chemistry to materials science and to biology and medicine. Here, the recent achievements of stimuli-responsive AIEgens in terms of seven most representative types of stimuli including force, light, polarity, temperature, electricity, ion, and pH, are summarized. Based on typical examples, it is illustrated how each type of systems realize the desired stimuli-responsive performance for various applications. The key work principles behind them are ultimately deciphered and figured out to offer new insights and guidelines for the design and engineering of the next-generation stimuli-responsive luminescent materials for more broad applications.

[Synthesis of zwitterionic dual-functional metal-organic framework nanocomposite with ultra-hydrophilicity for selective enrichment of glycopeptides]

蛋白糖基化是生物体中普遍发生且重要的生物学过程,其参与多种分子生物学的功能和途径,是临床诊断重要的生物标志物。但是,糖肽因其丰度低、离子化效率低、糖链异质性等难点,使糖蛋白分析一直面临巨大的挑战。因此,研究合成了一种新型的两性离子双功能化纳米金(AuGC)修饰的超亲水性沸石咪唑骨架(ZIF-8)纳米复合材料(AuGC/ZIF-8),并建立了亲水相互作用色谱(HILIC)和基质辅助激光解吸电离-飞行时间质谱(MALDI-TOF MS)联用选择性富集糖肽的分析方法。谷胱甘肽和半胱氨酸双功能化的协同作用,使MOF具有超亲水性和低空间位阻,为糖肽选择性富集提供了更多的亲和位点。研究以辣根过氧化物酶(HRP)为模式糖蛋白,通过AuGC/ZIF-8富集后,MALDI-TOF MS分析。结果表明,AuGC/ZIF-8对HRP糖肽的富集能力高达250 μg/mg,且在与牛血清白蛋白(BSA)混合溶液中(HRP-BSA (1∶200,质量比))显示出对HRP糖肽的高选择性,以及极低含量下(0.3 ng/μL)的高灵敏度。因此,在复杂生物样品糖蛋白的富集分离中具有很大的应用潜力。

Effects of Sonication and Hydrothermal Treatments on the Optical and Chemical Properties of Carbon Dots

In our study, we have tested the effects of sonication and hydrothermal treatments on the properties of carbon dots synthesized from a microwave-assisted method (C-dotsMW). When the carbon dots are sonicated in an aerobic environment, the fluorescence quantum yield decreases drastically because the molecular fluorophores attached to the surface of the carbon dots are oxidized during the sonication process. Meanwhile, the sonicated C-dotsMW also lose their Hg2+ ion sensing and photoreduction activity due to the oxidization of surface functional groups. After the hydrothermal treatment, the fluorescence quantum yield of C-dotsMW increases due to the formation of new fluorophores; however, the Hg2+ ion sensitivity and photoreduction activity of C-dotsMW decrease significantly due to the oxidization of surface functional groups. By autoclaving the C-dotsMW at 100 °C, we have demonstrated that we can enhance the fluorescence quantum yield of C-dotsMW without losing their Hg2+ ion sensitivity. This finding can be used to improve the fluorescence quantum yield of the fluorescent ion sensor based on C-dots.

Glutathione-decorated fluorescent carbon quantum dots for sensitive and selective detection of levodopa

Levodopa has been a standard drug for treating Parkinson's disease since the 1960s, but it has caused many side effects such as wearing-off, motor fluctuation, and dystonia. In this work, we developed glutathione-conjugated carbon quantum dots (GSH-CQDs) as a novel fluorescent sensor for sensitive and selective detection of levodopa. The GSH-CQDs were prepared by EDC/NHS coupling reaction of glutathione (GSH) with amine-functionalized CQDs (N-CQDs) synthesized using meta-phenylenediamine and ethylenediamine. The synthesized GSH-CQDs emitted bright green fluorescence with a high quantum yield (QY) of 22.42 ± 6.88%. However, upon the addition of levodopa to GSH-CQDs under alkaline conditions, the fluorescence of GSH-CQDs was quenched. Since levodopa is converted to dopaquinone in an alkaline environment, it is presumed that thiol groups of GHS-CQDs form covalent bonds with dopaquinone, causing fluorescence quenching through photoinduced electron transfer. Therefore, as the concentration of levodopa increased, the fluorescence intensity of GSH-CQDs was gradually decreased. Under optimal conditions, a linear response was observed in the range of 0.05-1 μM, and limit of detection (LOD) was determined to be 0.057 μM. The GSH-CQDs exhibited high specificity to levodopa over other non-target biological substances, quinone derivatives, and Parkinson's medications. Furthermore, the capability of this GSH-CQDs sensor for monitoring levodopa in human serum were validated with excellent precision and recovery rates of 100.20-103.33%.

Ratiometric determination of Cr(VI) based on a dual-emission fluorescent nanoprobe using carbon quantum dots and a smartphone app

A simple dual-colour fluorescent nanoprobe has been designed composed of blue and yellow emission carbon quantum dots (CQDs). This system is inexpensive and easy to operate and was successfully employed for on-site measurements based on a smartphone app. The designed nanoprobe exhibited increased selectivity for Cr(VI), leading to a double stable response of the two CQDs. The dual-emission nanoprobe showed blue-violet fluorescence upon UV irradiation, and the fluorescent emission peaks were located at 418 nm and 552 nm. The blue light emission of CQDs was quenched with increasing Cr(VI) concentration due to the inner filter effect, whereas the yellow light emission was enhanced due to the aggregation-induced emission effect. The different responses of the dual emissions to Cr(VI) resulted in a fluorescent colour variation, thus enabling facile macroscopic visualization. With a smartphone, the change in the fluorescence colour could be observed more apparently than that of a single fluorescence nanoprobe, and the response increased linearly so that the nanoprobe could be applied to instantaneous measurements. Furthermore, the dual-emission nanoprobe was successfully employed for analysing food and water samples. Accurate concentrations were obtained by constructing a calibration plot using a fluorescence spectrometer and a smartphone app; the recoveries were 81.6% to 107.7%, and the relative standard deviation was below 3.6%. Therefore, this smartphone-integrated dual-emission detection system is promising as a new portable method for the on-site measurement of Cr(VI) ions. * Y-CQDs: yellow emission carbon quantum dots. B-CQDs: blue emission carbon quantum dots. B/Y-CQDs: a mixture of B-CQDs and Y-CQDs.

N,S-co-doped carbon dots for rapid acid test paper and bioimaging

Fluorescent N,S-CDs with a quantum yield of 37.8% were synthesized via a one-pot solvothermal method. Detailed characterizations on physical, chemical and optical properties have been investigated. N,S-CDs demonstrated remarkably quenched and enhanced fluorescence in acidic and basic media. Direct qualitative analysis in pH sensor and cell imaging were preliminarily studied.

"Luminescent carbon nanodots: Current prospects on synthesis, properties and sensing applications"

"Nanocarbon science" ignited interest owing to its substantial scope in biomedicine, energy and environment-beneficial applications. Carbon dots (C-dots), a multi-faceted nanocarbon material, emerged as a homologue to graphene and henceforth geared extensive investigation both on its properties and applications. Eximious properties like excitation-wavelength tunable fluorescence emission, up-converted photoluminescence, photon-induced electron transfer, low cytotoxicity, chiroptical behavior, high chemical and photostability set the ground for astounding applications of carbon dots. Abundant availability of raw "green" precursors complementary to other molecular/graphitic precursors make them environmentally benign, inexpensive and ultimately "nanomaterials of the current decade". This review focuses on the synthesis of carbon dots not only from natural sources but also from other carbonaceous precursors and contemplates the inherent but controversial properties. We also aim to garner the attention of readers to the recent progress achieved by C-dots in one of its prestantious area of applications as nanosensors.

Developing fluorescent copper nanoclusters: Synthesis, properties, and applications

Metal nanoclusters exhibit strong fluorescence emission, providing immense potential for developments in biological labeling and imaging. Copper nanoclusters in particular, due to their unique optical properties such as molecular-like absorption and strong luminescence, represent a novel fluorescent nanomaterial for sensing and bioimaging applications. This review describes research progress on Cu nanoclusters in recent years, investigating the synthesis techniques, their properties, and their promising applications. A concluding summary provides an outlook on the future research challenges for Cu nanoclusters and their corresponding synthesis techniques.

Review of Carbon and Graphene Quantum Dots for Sensing

Carbon and graphene quantum dots (CQDs and GQDs), known as zero-dimensional (0D) nanomaterials, have been attracting increasing attention in sensing and bioimaging. Their unique electronic, fluorescent, photoluminescent, chemiluminescent, and electrochemiluminescent properties are what gives them potential in sensing. In this Review, we summarize the basic knowledge on CQDs and GQDs before focusing on their application to sensing thus far followed by a discussion of future directions for research into CQDs- and GQD-based nanomaterials in sensing. With regard to the latter, the authors suggest that with the potential of these nanomaterials in sensing more research is needed on understanding their optical properties and why the synthetic methods influence their properties so much, into methods of surface functionalization that provide greater selectivity in sensing and into new sensing concepts that utilize the virtues of these nanomaterials to give us new or better sensors that could not be achieved in other ways.

Surface States Induced Photoluminescence Enhancement of Nitrogen-Doped Carbon Dots Via Post-Treatments

The tunable photoluminescence (PL) of nitrogen-doped carbon dots (NCDs) has attracted much attention in recent years while the specific mechanism is still in dispute. Herein, NCDs with yellow emission were successfully synthesized via a facile hydrothermal approach. Three kinds of post-treatment routes were investigated to verify the influence of surface states on the PL emission of NCDs including solvent-dependent, reduced-reaction and metal-enhanced effect. The interaction mechanism was studied by absorption spectrum, structural characterizations, steady-state and time-resolved spectroscopy. When dispersed in different solvents, the as-prepared NCDs show tunable emission and PL enhancement attributed to hydrogen bonding between solvents and NCDs. Besides, the addition of NaBH4 can induce the reduction of the C=O bonds existing in original NCDs to C-O bonds and thus result in the enhancement of the intrinsic (n-π*) emission. Moreover, metal-enhanced fluorescence of NCDs can also be observed when adding Ag+ into initial NCD solution, which might be ascribed to aggregation-induced emission enhancement. These results for post-treated NCDs demonstrate that surface functional groups are responsible for PL emission and provide new possibilities like multi-image sensing and lighting application.

A dual-zwitterion functionalized ultra-hydrophilic metal–organic framework with ingenious synergy for enhanced enrichment of glycopeptides

A rational strategy was introduced for the synthesis of a novel dual functionalized metal–organic framework nanocomposite (AuGC/ZIF-8) with ultra-hydrophilicity to enhance glycopeptide enrichment.

Biogreen Synthesis of Carbon Dots for Biotechnology and Nanomedicine Applications

Over the past decade, carbon dots have ignited a burst of interest in many different fields, including nanomedicine, solar energy, optoelectronics, energy storage, and sensing applications, owing to their excellent photoluminescence properties and the easiness to modify their optical properties through doping and functionalization. In this review, the synthesis, structural and optical properties, as well as photoluminescence mechanisms of carbon dots are first reviewed and summarized. Then, we describe a series of designs for carbon dot-based sensors and the different sensing mechanisms associated with them. Thereafter, we elaborate on recent research advances on carbon dot-based sensors for the selective and sensitive detection of a wide range of analytes, including heavy metals, cations, anions, biomolecules, biomarkers, nitroaromatic explosives, pollutants, vitamins, and drugs. Lastly, we provide a concluding perspective on the overall status, challenges, and future directions for the use of carbon dots in real-life sensing.

Facile Fluorescence "Turn on" Sensing of Lead Ions in Water via Carbon Nanodots Immobilized in Spherical Polyelectrolyte Brushes

Heavy metal detection has become very important for the protection of water resource. In this work, a novel controllable probe is presented for the sensitive detection of Pb2+ in aqueous solutions. The probe was synthesized via the immobilization of surface functionalized carbon dots (named as CAEA-Hs) into the shell of the spherical polyelectrolyte brushes (SPB). The fluorescence of CAEA-H was firstly "turned off" via electrostatic interaction induced quenching. Based on the aggregation induced emission enhancement (AIEE), the fluorescence of the immobilized CAEA-H could be specifically turned on via the aggregation of the SPB particles. This fluorescence "turn on" sensor could selectively detect Pb2+ among five different metal ions with a relatively wide detecting range (0-1.67 mM) and good linear relationship (R 2 = 0.9958). Moreover, the aggregating behavior and nano-structure of CAEA-H loaded SPB have been systematically analyzed via small angle X-ray scattering, turbidity titration, and Zeta-potential measurement. Based on a series of control experiments, we finally gain an insight into the sensing mechanism of this novel sensing probe. This contributed a proof of concept demonstration that sensitive and selective chemical detection can be achieved via a C-dot/SPB synergistic platform.

Green Synthesis of Red-Emitting Carbon Nanodots as a Novel "Turn-on" Nanothermometer in Living Cells

Temperature measurements in biology and medical diagnostics, along with sensitive temperature probing of living cells, is of great importance; however, it still faces significant challenges. Herein, a novel "turn-on" carbon-dot-based fluorescent nanothermometry device for spatially resolved temperature measurements in living cells is presented. The carbon nanodots (CNDs) are prepared by a green microwave-assisted method and exhibit red fluorescence (λem =615 nm) with high quantum yields (15 %). Then, an on-off fluorescent probe is prepared for detecting glutathione (GSH) based on aggregation-induced fluorescence quenching. Interestingly, the quenched fluorescence could be recovered by increasing temperature and the CNDs-GSH mixture could behave as an off-on fluorescent probe for temperature. Thus, red-emitting CNDs can be utilized for "turn-on" fluorescent nanothermometry through the fluorescence quenching and recovery processes, respectively. We employ MC3T3-E1 cells as an example model to demonstrate the red-emitting CNDs can function as "non-contact" tools for the accurate measurement of temperature and its gradient inside a living cell.

Dual-emitting quantum dot/carbon nanodot-based nanoprobe for selective and sensitive detection of Fe(3+) in cells

A novel dual-emitting fluorescence probe is developed for rapid and ultrasensitive detection of Fe(3+). The nanoprobe is prepared by coating CdSe semiconductor quantum dots (SQDs) onto the surface of carbon nanodot (CND) doped TiO2 microspheres. The as-prepared nanoprobe exhibits the corresponding dual emissions at 436 and 596 nm for CNDs and CdSe, respectively, under a single excitation wavelength. The blue fluorescence of the CNDs is insensitive to Fe(3+), whereas the orange emission of the CdSe SQDs is functionalized to be selectively quenched by Fe(3+). The intensity ratio of I436/I596 shows a good linear relationship with the concentration of Fe(3+) in the range of 10(-9) to 10(-5) M. The nanoprobe provides an effective platform for the reliable detection of Fe(3+) with a detection limit as low as 10 nM. Besides, this ratiometric nanosensor exhibits good selectivity for Fe(3+) over other metal ions. The results reveal that the nanoprobe could provide a sensitive sensor for rapid detection of Fe(3+) with high selectivity and sensitivity. Moreover, 293T cells are used as models to achieve a potential application as a probe for monitoring Fe(3+) in cells. Thus, these dual-emitting nanoprobes could work as an alternative to conventional fluorescence probes for biolabeling, sensing and other applications.

A hydrothermal route for synthesizing highly luminescent sulfur- and nitrogen-co-doped carbon dots as nanosensors for Hg2+

Sulfur- and nitrogen-co-doped carbon dots were synthesized by the one step hydrothermal treatment of pyritinol hydrochloride in the presence of graphene oxide, and could be used as an effective fluorescent probe for the detection of Hg²⁺.