Dual Photoluminescence Emission Carbon Dots for Ratiometric Fluorescent GSH Sensing and Cancer Cell Recognition

Recent Progress of Fluorescent Carbon Dots and Graphene Quantum Dots for Biosensors: Synthesis of Solution Methods and their Medical Applications

In the fields of health and biology, fluorescent nanomaterials have emerged as highly potential and very useful candidates for use in biosensor applications. These typical highly powerful nanomaterials are carbon dots (CDs) and graphene quantum dots (GQDs) among many other metallic nanomaterials. In the context of medical biosensors, this review article investigates the techniques of synthesis, and many uses of these nanomaterials, the obstacles that they face, and the potential for their future. We cover the significance of fluorescent nanomaterials, their use in the medical field, as well as the several techniques of synthesis for CDs and GQDs, including ultrasonication, hydrothermal, electrochemical method, surface modification, and solvothermal. In addition, we also discuss their biomedical applications, which include biomolecule detection, disease diagnosis and examine the obstacles and prospective possibilities for development of ultra-bright, ultra-sensitive, and selective biosensors for use in in-vivo research.Fluorescent carbon dots and graphene quantum dots is synthesized by using several types of raw material and methods. These Carbon dots and graphene quantum dots are used in the medical field includes detection of biomaterials, detection of cancer, virus and mutation in DNA.

Polarity-sensitive dual emissive fluorescent carbon dots as highly specific targeting probes for lipid droplets in live cells

Polarity-sensitive fluorescent nanoparticles with intrinsic dual emission are invaluable tools for investigating microenvironmental polarity. Ratiometric fluorescent sensors, with their built-in self-calibration characteristics, offer higher sensitivity and more obvious visual detection in qualitative and quantitative analysis. In this context, we report the synthesis of polarity-sensitive, dual-emitting carbon dots via a solvothermal method and demonstrate their application in ratiometric polarity sensing. These carbon dots exhibit characteristic solvatochromic effects with emissions in both the blue and red spectral regions. Notably, we observed a remarkable 30-fold enhancement in the red-to-blue emission intensity ratio as the solvent polarity shifted from 0.245 to 0.318. The dual-emitting carbon dots demonstrate the highly sensitive and inherently reliable (self-calibration) polarity dependence of the emission spectra, facilitating their application in ratiometric polarity sensing. These dual-emitting carbon dots exhibited a strong affinity for lipid droplets in live cells, demonstrating their potential as highly specific targeting probes for imaging lipid droplets in live cells, without the need for additional targeting ligands. The characteristics of excellent biocompatibility, photostability, and good cellular imaging capabilities make these dual-emitting carbon dots highly promising for biomedical and sensing applications.

Smartphone-assisted fluorescence/colorimetric dual-mode sensing strategy for uranium ion detection using cerium-sulfonyl calix[4]arene

A novel fluorescence/colorimetric dual-mode detection strategy for uranium ions (UO22+) is presented based on a cerium-sulfonyl calix[4]arene (SC4A) platform. The exo- and endo-rim sites of SC4A can coordinate with Ce3+ and Ce4+ ions, respectively, quenching Ce3+ fluorescence and influencing the oxidase-like activity of Ce4+. In the absence of UO22+, the solution of 3,3,5,5-tetramethylbenzidine (TMB) remains blue, but upon UO22+ binding, Ce3+ dissociates from SC4A, restoring fluorescence, while UO22+ interacts with oxTMB, turning the solution from blue to colorless. This dual-mode system provides a linear fluorescence detection range of 30-800 nM with a detection limit of 20.20 nM, and a colorimetric range of 30-800 nM with a detection limit of 27.78 nM. By combining high-sensitivity fluorescence with visual colorimetric analysis, the proposed method possesses high sensitivity, accuracy, and reliability. Notably, smartphone-based color capture facilitates rapid and convenient sample analysis, enabling straightforward quantification at varying UO22+ concentrations. The method has been successfully applied to real water and urine samples, demonstrating its practical utility in environmental and biological monitoring of UO22+.

Picric Acid Incorporated Fluorescent Nitrogen Doped Carbon Dot for "Turn-On" Detection of Glutathione

Glutathione (GSH), a non-protein thiol in living cells whose abnormal level indicates the onset of diseases like Alzheimer's, HIV, diabetes, cancer, Parkinson's, Dementia, etc. Herein, we have synthesized a low-cost, selective, and sensitive detection platform by using citric acid and urea-derived fluorescent carbon dots (NCDs) via the microwave-assisted method, showing fluorescence at 444 nm. This fluorescence was quenched with picric acid (PA), and this probe, picric acid incorporated nitrogen doped carbon dot (NCDs@PA) was further used for the detection of GSH. The characterization of the probe was done by photoluminescence study, UV-Visible absorption studies, ATR-FTIR, SEM, and DLS analysis. GSH induced fluorescence recovery due to the competitive binding of GSH to PA. GSH was detected within a linear range of 0.31 mM- 2.43 mM with a Limit of Detection (LoD) and Limit of Quantification (LoQ) of 32.10 µM and 107.32 µM, respectively. The sensor exhibited good selectivity and sensitivity towards GSH among various co-existing ions and biomolecules. The paper-strip-based sensing of glutathione was conducted to check practical applicability of the probe, and a real sample analysis was also conducted from spiked human samples.

Enhanced Enantioselective Sensing of 1,1'-Bi-2-naphthol and Mandelic Acid by Proportional Fluorescence Sensor 3DOM Zn-MOF-74-l-Trp with Hierarchical Macro-Micropore Structure

The enantioselective performance of porous chiral metal-organic frameworks (CMOFs) is closely related to the pore size and uniformity of easily accessible active sites. The chiral recognition efficiency of microporous CMOFs is hindered by the restricted diffusion of the guest. Hierarchical porous chiral CMOFs with multiple pore size regimes ranging from micropores to macropores have emerged as potential candidates in chiral separation applications. 3DOM Zn-MOF-74 crystalline porous material with ordered macro-micropore structure was prepared with a general bottom-up strategy by carrying out the controllable confined growth of Zn-MOF-74 precursor in a removable three-dimensional ordered macroporous (3DOM) polystyrene (PS) template. Then l-tryptophan ( l -Trp) was introduced into MOFs by the strategy of postsynthetic modifications, and finally, a chiral hierarchical porous functional material 3DOM Zn-MOF-74-l-Trp was successfully fabricated. Based on the two luminescent centers from the achiral ligand H4DOBC and chiral ligand l-Trp, the proportional fluorescence sensor 3DOM Zn-MOF-74-l-Trp was hopeful to be applied in the field of enantioselective fluorescence sensing. The enantioselectivity factor values of microporous M-Zn-MOF-74-l-Trp for 1,1'-bi-2-naphthol (Binol) and mandelic acid (MA) were 1.08 and 1.12, respectively. In comparison, the construction of hierarchical porous structure greatly enhanced the chiral recognition performance, which may be due to the improved mass-transfer efficiency of chiral guest molecules and highly swelled accessibility to the chiral recognition sites in this CMOF composite, making the enantioselectivity factor values correspondingly increased to 1.29 and 2.26, respectively.

Convenient in situ self-assembled formation of dual-functional Ag/MXene nanozymes for efficient chemiluminescence sensing

MXenes are attracting increasing interest as a low-cost carrier for the development of nanozymes with enhanced peroxidase or oxidase-like activity. In this work, silver nanoparticles (AgNPs) were synthesized and loaded on Ti3C2 MXene nanosheets (denoted as Ag/MXene) by a simple method, using MXene as a support and reducing agent. The synthesized Ag/MXene composites exhibited satisfactory stability and the peroxidase activity was higher than that of the single components. In the presence of luminol and hydrogen peroxide (H2O2), Ag/MXene could catalyze H2O2 to produce reactive oxygen species (ROS) and act on luminol to generate strong chemiluminescent (CL) signals. Free radical scavenging experiments and electron paramagnetic resonance spectroscopy confirmed the production of these radicals. In this regard, we fabricated a facile biosensor for glutathione (GSH) and uric acid (UA) detection and the results showed good linear relationship between GSH and UA. The linear ranges of GSH and UA were 50 nM to 20 μM and 1 μM to 35 μM, respectively, with low detection limits of 0.83 nM and 0.37 μM. The sensor platform established in this study provides the possibility for developing MXene biosensors with high sensitivity and performance, and lays the solid foundation for expanding the application of MXene in biosensors.

A lantern-shaped fluorescent probe based on viologen/polyoxometalate for the detection of Ag+ in beverages and daily necessities

A lantern-shaped viologen/polyoxometalate (POM)-based compound [NiII(MSBP)2(H2O)2]·(β-Mo8O26)·H2O (Ni-POM) (MSBP = 1-(4-Methanesulfonyl-benzyl)-[4,4']bipyridinyl-1-ium) was successfully synthesized by a hydrothermal method for the efficient detection of Ag+. A strong affinity between Ag+ and SO in the viologen component of the Ni-POM structure made them interact, which led to blue fluorescence quenching. In the concentration range of 0.1-4 μM, a strong linear relationship was observed between the Ag+concentration and the fluorescence intensity ratio of Ni-POM, and the limit of detection (LOD) was 20.4 nM. Considering the widespread presence of Ag+ in various water sources, daily necessities and food preservatives, the utilization of Ni-POM for detecting the concentration of Ag+ in real samples (water, daily necessities and beverages) was proved to be highly effective. Moreover, a remarkable recovery rate ranging from 95.70 % to 103.60 % was achieved, indicating that the monitoring results of practical samples were satisfactory. A fluorescent ink based on Ni-POM was designed for the purpose of information confidentiality. More importantly, the hydrogel intelligent device for visual detection of Ag+ was developed, which could realize visual real-time on-site quantitative detection of Ag+ concentration in beverages and daily necessities. Therefore, Ni-POM provides an effective platform for the development of visually quantitative detection of Ag+ in food and daily necessities.

An artificial intelligence handheld sensor for direct reading of nickel ion and ethylenediaminetetraacetic acid in food samples using ratiometric fluorescence cellulose paper microfluidic chip

User-friendly in-field sensing protocol is crucial for the effective tracing of intended analytes under less-developed countries or resources-limited environments. Nevertheless, existing sensing strategies require professional technicians and expensive laboratory-based instrumentations, which are not capable for point-of-care on-site analyses. To address this issue, artificial intelligence handheld sensor has been designed for direct reading of Ni2+ and EDTA in food samples. The sensing platform incorporates smartphone with machine learning-driven application, 3D-printed handheld device, and cellulose paper microfluidic chip stained with ratiometric red-green-emission carbon dots (CDs). Intriguingly, Ni2+ introduction makes green fluorescent (FL) of CDs glow but red FL fade because of the coordination of Ni2+ with CDs verified by density functional theory (DFT), concurrently manifesting continuous FL colour transition from red to green. Subsequent addition of EDTA renders FL of CDs-Ni2+ recover owing to the capture of Ni2+ from CDs by EDTA based on strong chelation effect of EDTA on Ni2+ confirmed via DFT, accompanying with a noticeable colour returning from green to red. Inspired by above FL phenomena, CDs-based cellulose paper microfluidic chips are first fabricated to facilitate point-of-care testing of Ni2+ and EDTA. Designed fully-automatic handheld sensor is utilized to directly output Ni2+ and EDTA concentration in water, milk, spinach, bread, and shampoo based on wide linear ranges of 0-48 μM and 0-96 μM, and low limits of detection of 0.274 μM and 0.624 μM, respectively. The proposed protocol allows for speedy straightforward on-site determination of target analytes, which will trigger the development of automated and intelligent sensors in near future.

Amine-Rich Carbon Dots Synthesized from Kappa-Carrageenan and l-Lysine as a Dual Probe for Detection of Folic Acid and Tumor-Targeted Delivery of Therapeutics

Strategically designed, heteroatom-rich surface functionalized blue fluorescent carbon dots (CDs) were synthesized for high-throughput detection of folic acid (vitamin B9). The highly stable CDs could particularly detect vitamin B9 in the presence of 35 analytes, even up to 40 nM of the vitamin. The versatile CDs were found to have a high affinity for folic acid in wastewater, folic acid tablets, and food samples enriched with folic acid. The hemocompatibility of the CDs was also studied by using a hemolysis assay, confirming the CDs to be nontoxic to human blood samples up to 400 μg/mL. The CDs were then covalently conjugated to biotin, which possesses receptors that are overexpressed in tumor cells. The MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide dye) assay and confocal bioimaging studies proved the biotin-modified CDs (CDBT) were remarkably nontoxic in healthy cell lines (HEK-293) and highly target-specific toward tumor cells (HeLa), including triple-negative breast cancer cells (MDA-MB-231). The cytotoxicity assay of 5-fluorouracil encapsulated CDs (CDBTFu) showed the IC50 value to be 81 μM in HeLa cells and 185 μM in MDA-MB-231 cells, respectively, and significantly higher in HEK-293 cells (over 300 μM), owing to high specificity toward tumor cells.

Ratiometric Fluorescent pH Sensing with Carbon Dots: Fluorescence Mapping across pH Levels for Potential Underwater Applications

Ocean acidification has become a major climate change concern requiring continuous observation. Additionally, in the industry, pH surveillance is of great importance. Consequently, there is a pressing demand to develop robust and inexpensive pH sensors. Ratiometric fluorescence pH sensing stands out as a promising concept. The application of carbon dots in fluorescent sensing presents a compelling avenue for the advancement of pH-sensing solutions. This potential is underpinned by the affordability of carbon dots, their straightforward manufacturing process, low toxicity, and minimal susceptibility to photobleaching. Thus, investigating novel carbon dots is essential to identify optimal pH-sensitive candidates. In this study, five carbon dots were synthesized through a simple solvothermal treatment, and their fluorescence was examined as a function of pH within the range of 5-9, across an excitation range of 200-550 nm and an emission range of 250-750 nm. The resulting optical features showed that all five carbon dots exhibited pH sensitivity in both the UV and visible regions. One type of carbon dot, synthesized from m-phenylenediamine, displayed ratiometric properties at four excitation wavelengths, with the best results observed when excited in the visible spectrum at 475 nm. Indeed, these carbon dots exhibited good linearity over pH values of 6-9 in aqueous Carmody buffer solution by calculating the ratio of the green emission band at 525 nm to the orange one at 630 nm (I525nm/I630nm), demonstrating highly suitable properties for ratiometric sensing.

Luminescence performance and antioxidant properties of selenium carbon dots prepared from selenium-hyperaccumulating plants

Heteroatom doping has become an important method to enhance the performance of traditional carbon dots in modern times. Selenium (Se) is a nonmetallic trace element with excellent redox properties and is therefore essential for health. Previous studies have mainly used pure chemicals as selenium sources to prepare selenium-doped carbon dots (Se-CDs), but the precursor pure chemicals have the disadvantages of being expensive, difficult to obtain, toxic, and having low fluorescence yields of the synthesised Se-CDs. Fortunately, our team achieved successful synthesis of selenium carbon dots, exhibiting excellent luminescence and biocompatibility through a one-step hydrothermal method using selenium-enriched natural plant Cardamine, as an alternative to selenium chemicals. This approach aims to address the limitations and high costs associated with Se-CDs precursors. Electron spin resonance spectroscopy (ESR) and cellular antioxidant tests have confirmed the protective ability of Se-CDs against oxidative damage induced by excessive reactive oxygen species (ROS). A new concept and method for synthesizing selenium carbon dots on the basis of biomass, a rationale for the antioxidant effects on human health, and a wide range of development and application possibilities were offered in this work.

Aggregation-induced-emission red carbon dots for ratiometric sensing of norfloxacin and anti-counterfeiting

The detection of trace antibiotic residues holds significant importance because it's related to food safety and human health. In this study, we developed a new high-yield red-emitting carbon dots (R-CDs) with aggregation-induced emission properties for ratiometric sensing of norfloxacin. R-CDs were prepared in 30 min using an economical and efficient microwave-assisted method with tartaric acid and o-phenylenediamine as precursors, achieving a high yield of 34.4 %. R-CDs showed concentration-dependent fluorescence and aggregation-induced-emission properties. A ratiometric fluorescent probe for detecting the norfloxacin was developed. In the range of 0-40 μM, the intensity ratio of two emission peaks (I445 nm/I395 nm) towards norfloxacin show good linear relationship with its concentrations and a low detection limit was obtained (36.78 nM). In addition, complex patterns were developed for anti-counterfeiting based on different emission phenomenon at different concentrations. In summary, this study designed a novel ratiometric fluorescent probe for detection of norfloxacin, which greatly shortens the detection time and improves efficiency compared with high-performance liquid chromatography and other methods. The study will promote the application of carbon dots in anti-counterfeiting and other related fields, laying the foundation for the preparation of low-cost photosensitive anti-counterfeiting materials.

Fluorescent carbon dots for discriminating cell types: a review

Carbon dots (CDs) are quasi-spherical carbon nanoparticles with excellent photoluminescence, good biocompatibility, favorable photostability, and easily modifiable surfaces. CDs, serving as fluorescent probes, have emerged as an ideal tool for cellular differentiation owing to their outstanding luminescence performance and tunable surface properties. In this review, we summarize the recent research progress with CDs in the differentiation of cancer/normal cells, Gram-positive/Gram-negative bacteria, and live/dead cells, as well as the cellular differences used for differentiation. Additionally, we summarize the preparation methods, raw materials, and properties of the CDs used for cell discrimination. The differentiation mechanisms and the advantages or limitations of the differentiation methods are also introduced. Finally, we propose several research challenges in this field and future research directions that require extensive investigation. It is hoped that this review will help researchers in the design of new CDs as ideal fluorescent probes for realizing diverse cell differentiation applications.

Aggregation-Resistant, Turn-On-Off Fluorometric Sensing of Glutathione and Nickel (II) Using Vancomycin-Conjugated Gold Nanoparticles

Glutathione (GSH) and nickel (II) cation have an indispensable role in various physiological processes, including preventing the oxidative damage of cells and acting as a cofactor for lipid metabolic enzymes. An imbalance in the physiological level of these species may cause serious health complications. Therefore, sensitive and selective fluorescent probes for the detection of GSH and nickel (II) are of great interest for clinical as well as environmental monitoring. Herein, vancomycin-conjugated gold nanoparticles (PEI-AuNP@Van) were prepared and employed for the detection of GSH and nickel (II) based on a turn-on-off mechanism. The as-synthesized PEI-AuNP@Van was ~7.5 nm in size; it exhibited a spherical shape with face-centered cubic lattice symmetry. As compared to vancomycin unconjugated gold nanoparticles, GSH led to the turn-on state of PEI-AuNP@Van, while Ni2+ acted as a fluorescence quencher (turn-off) without the aggregation of nanoparticles. These phenomena strongly justify the active role of vancomycin conjugation for the detection of GSH and Ni2+. The turn-on-off kinetics was linearly proportional over the concentration range between 0.05-0.8 µM and 0.05-6.4 μM. The detection limits were 205.9 and 90.5 nM for GSH and Ni2+, respectively; these results are excellent in comparison to previous reports. This study demonstrates the active role of vancomycin conjugation for sensing of GSH and Ni2+ along with PEI-AuNP@Van as a promising nanoprobe.

The construction of dual-emissive ratiometric fluorescent probes based on fluorescent nanoparticles for the detection of metal ions and small molecules

With the rapid development of fluorescent nanoparticles (FNPs), such as CDs, QDs, and MOFs, the construction of FNP-based probes has played a key role in improving chemical sensors. Ratiometric fluorescent probes exhibit distinct advantages, such as resistance to environmental interference and achieving visualization. Thus, FNP-based dual-emission ratiometric fluorescent probes (DRFPs) have rapidly developed in the field of metal ion and small molecule detection in the past few years. In this review, firstly we introduce the fluorescence sensing mechanisms; then, we focus on the strategies for the fabrication of DRFPs, including hybrid FNPs, single FNPs with intrinsic dual emission and target-induced new emission, and DRFPs based on auxiliary nanoparticles. In the section on hybrid FNPs, methods to assemble two types of FNPs, such as chemical bonding, electrostatic interaction, core satellite or core-shell structures, coordination, and encapsulation, are introduced. In the section on single FNPs with intrinsic dual emission, methods for the design of dual-emission CDs, QDs, and MOFs are discussed. Regarding target-induced new emission, sensitization, coordination, hydrogen bonding, and chemical reaction induced new emissions are discussed. Furthermore, in the section on DRFPs based on auxiliary nanoparticles, auxiliary nanomaterials with the inner filter effect and enzyme mimicking activity are discussed. Finally, the existing challenges and an outlook on the future of DRFP are presented. We sincerely hope that this review will contribute to the quick understanding and exploration of DRFPs by researchers.

Carbon dots and MnO2 nanosheet nanocomposites sensing platform for sensitive detection of oxalate in urine samples of urolithiasis patients

In the human body, oxalate tends to form calcium oxalate with calcium ions, which can trigger the formation of stones in the urinary system. Therefore, oxalate in urine is usually utilized as a crucial biomarker in clinical urolithiasis diagnoses. In this work, a turn-on fluorescent nanoprobe was developed based on nitrogen-doped carbon dots (N-CDs) and MnO2 nanosheets (NSs) nanocomposites for oxalate sensing in urolithiasis patients. MnO2 NSs is a good sensing platform with high extinction coefficients and rich redox chemistry. The fluorescent N-CDs can be quenched efficiently by MnO2 NSs through the inner filter effect (IFE) to form N-CDs-MnO2 nanocomposites. The reductive oxalate could operate the decomposition of MnO2 NSs to Mn2+ resulting in the dissociation of the N-CDs-MnO2 nanocomposites and fluorescence recovery of N-CDs. Under optimal conditions, the developed sensor revealed good specificity toward oxalate with a limit of detection (LOD) of 0.69 μM. The developed sensor was successfully applied to quantify oxalate content in 47 urine samples (41 urolithiasis patients and 6 healthy persons). The results showed great consistency with clinical diagnostic reports and computed tomography images. This novel method retains several unique advantages, including affordable, rapid, and validating potential clinical application.

A Review of Dual-Emission Carbon Dots and Their Applications

Carbon dots (CDs), as a rising star among fluorescent nanomaterials with excellent optical properties and fascinating dual-emission characteristics, have attracted increasing attention in sensing, bio-imaging, drug delivery, and so on. The synthesis of dual-emission CDs (DE-CDs) and the establishment of ratiometric fluorescence sensors can effectively diminish background interference and provide more accurate results than single-emission CDs. Although DE-CDs have generated increased attention in many fields, the review articles about DE-CDs are still insufficient. Therefore, we summarized the latest results and prepared this review. This review first provides an overview of the primary synthesis route and commonly used precursors in DE-CDs synthesis. Then, the photoluminescence mechanism behind the dual-emission phenomenon was discussed. Thirdly, the application of DE-CDs in metal cation detection, food safety analysis, biosensing, cell imaging, and optoelectronic devices has been extensively discussed. Finally, the main challenges and prospects for further development are presented. This review presents the latest research progress of DE-CDs synthesis and its application in ratiometric sensing; hopefully, it can help and encourage researchers to overcome existing challenges and broaden the area of DE-CDs research.

Ultrahighly Sensitive and Selective Glutathione Sensor Based on Carbon Dot-Functionalized Solution-Gate Graphene Transistor

A new type of carbon dot (CD)-functionalized solution-gated graphene transistor (SGGT) sensor was designed and fabricated for the highly sensitive and highly selective detection of glutathione (GSH). The CDs were synthesized via a one-step hydrothermal method using DL-thioctic acid and triethylenetetramine (TETA) as sources of S, N, and C. The CDs have abundant amino and carboxyl groups and were used to modify the surface of the gate electrode of SGGT as probes for detecting GSH. Remarkably, the CDs-SGGT sensor exhibited excellent selectivity and ultrahigh sensitivity to GSH, with an ultralow limit of detection (LOD) of up to 10-19 M. To the best of our knowledge, the sensor outperforms previously reported systems. Moreover, the CDs-SGGT sensor shows rapid detection and good stability. More importantly, the detection of GSH in artificial serum samples was successfully demonstrated.

Artificial intelligence-integrated smartphone-based handheld detection of fluoride ion by Al3+-triggered aggregation-induced red-emssion enhanced carbon dots

Artificial intelligence (AI)-integrated smartphone-based handheld determination platform, based on 3D printed accessory, Al3+-triggered aggregation-induced red-emssion enhanced carbon dots (CDs) test strip, and smartphone with self-developed YOLO v3 AI algorithm-based application, proves the feasibility for intelligent real-time on-site quantitation of F- through tracking a consecutive fluorescence (FL) colour change. CDs, manifesting dual emission of moderate green emission at 512 nm and weak red one at 620 nm under 365 nm excitation, were synthesized hydrothermally from alizarin carmine and citric acid. CDs@Al3+, with distinct aggregation-induced red-emssion enhancement and green-emssion quenchment, were prepared by adding Al3+ to the CDs solution. Inspiringly, due to intrinsic ratiometric FL variation (I620/I512), CDs@Al3+ engender a successive FL colour variation from red to green in response to different concentrations of F- with low limit of detection of 7.998 μM and wide linear range of 150-1200 µM based on excellent linearity correlation between R/G value and F- concentration. Furthermore, F- content in tap water, toothpaste and milk could be intelligently, speedily, and straightforwardly analyzed through the AI-integrated smartphone-based handheld detection platform. It is fervently desired that our study will motivate a brand-new perspective for the promotion of efficacious detection strategy and the extension of practical application promise.

In situ and dynamic SERS monitoring of glutathione levels during cellular ferroptosis metabolism

Ferroptosis is a non-apoptotic cell death regulated by iron-dependent lipid peroxidation. Glutathione (GSH), a key antioxidant against oxidative damage, is involved in one of the most important metabolic pathways of ferroptosis. Herein, an excellent plasmonic nanoprobe was developed for highly sensitive, in situ, dynamic real-time monitoring of intracellular GSH levels during ferroptosis. A nanoprobe was prepared by functionalizing gold nanoparticles (AuNPs) with the probe molecule crystal violet (CV). The fluctuation in the SERS signal intensity of CV via the competitive displacement reaction can be used to detect GSH. The advantages of the plasmonic nanoprobe including low-cost production techniques, outstanding stability and biocompatibility, high specificity and sensitivity towards GSH with a detection limit of 0.05 μM. It enables real-time dynamic monitoring of GSH levels in living cells during erastin-induced ferroptosis. This approach is expected to provide important theoretical support for elucidating the GSH-related ferroptosis metabolic mechanism and advancing our understanding of ferroptosis-based cancer therapy. Overview of the workflow of sensing principle for highly sensitive, in situ and dynamic tracking of intracellular GSH levels during drug-triggered ferroptosis process.

Logic gate-driven dual-index balanced visualization strategy for tumor metastasis diagnosis

Exfoliated tumor cells are integral to malignant tumors diagnosis. The process of clinical cytology of exfoliation involves several complex steps that require at least two days of preparation. Here, we develop a balanced-etching visual kit based on concentration differences of Glutathione/Glucose (GSH/Glu) to distinguish normal from exfoliated tumor cells rapidly and accurately. The balanced-etching visualization kit can be used to obtain color cards and screen exfoliated tumor cells initially (within 10 min). Furthermore, by utilizing logic gates and machine learning algorithms for RGB extraction of the color card obtained from the kit, accurate screening of exfoliated tumor cells is achieved. Finally, a series of clinical tumor samples, such as urine, pleural fluids, ascites, and gastric fluids, have been validated. With effective experimental methods, accurate disease information, and appropriate therapeutic programs, the novel diagnostic strategy is expected to promote precision medicine.

Progress in construction and release of natural polysaccharide-platinum nanomedicines: A review

Natural polysaccharides are natural biomaterials that have become candidate materials for nano-drug delivery systems due to their excellent biodegradability and biocompatibility. Platinum (Pt) drugs have been widely used in the clinical therapy for various solid tumors. However, their extensive systemic toxicity and the drug resistance acquired by cancer cells limit the applications of platinum drugs. Modern nanobiotechnology provides the possibility for targeted delivery of platinum drugs to the tumor site, thereby minimizing toxicity and optimizing the efficacies of the drugs. In recent years, numerous natural polysaccharide-platinum nanomedicine delivery carriers have been developed, such as nanomicelles, nanospheres, nanogels, etc. Herein, we provide an overview on the construction and drug release of natural polysaccharide-Pt nanomedicines in recent years. Current challenges and future prospectives in this field are also put forward. In general, combining with irradiation and tumor microenvironment provides a significant research direction for the construction of natural polysaccharide-platinum nanomedicines and the release of responsive drugs in the future.

Luminescence of carbon quantum dots and their application in biochemistry

Similar to fullerenes, carbon nanotubes and graphene, carbon dots (CDs) are causing a lot of research work in their own right. CDs are a type of surface-passivated quantum dot that contain carbon atoms. Their distinctive characteristics, such as luminescent emission that varies with size and wavelength, resistance to photobleaching, easy biological binding, lack of toxicity, and economical production without the need for intricate synthetic processes, have led to a noteworthy surge in attention within the research community. Different techniques can be utilized to create these CDs, spanning from basic candle burning to laser ablation. This review article delves into the principles of fluorescence technology, providing insights into how different synthesis methods of quantum dots impact their luminescent properties. Additionally, it highlights the latest applications of quantum dots in catalysis and biomedical fields, with special emphasis on the current status of luminescent properties in biology and chemistry. Towards the end, the article discusses the limitations of quantum dots in current practical applications, pointing out that CDs hold promising potential for future applications.

Multicolor Photoluminescent Carbon Dots à La Carte for Biomedical Applications

Dual-emission fluorescence probes that provide high sensitivity are key for biomedical diagnostic applications. Nontoxic carbon dots (CDs) are an emerging alternative to traditional fluorescent probes; however, robust and reproducible synthetic strategies are still needed to access materials with controlled emission profiles and improved fluorescence quantum yields (FQYs). Herein, we report a practical and general synthetic strategy to access dual-emission CDs with FQYs as high as 0.67 and green/blue, yellow/blue, or red/blue excitation-dependent emission profiles using common starting materials such as citric acid, cysteine, and co-dopants to bias the synthetic pathway. Structural and physicochemical analysis using nuclear magnetic resonance, absorbance and fluorescence spectroscopy, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy in addition to transmission electron and atomic force microscopy (TEM and AFM) is used to elucidate the material's composition which is responsible for the unique observed photoluminescence properties. Moreover, the utility of the probes is demonstrated in the clinical setting by the synthesis of green/blue emitting antibody-CD conjugates which are used for the immunohistochemical staining of human brain tissues of glioblastoma patients, showing detection under two different emission channels.

Zero-Dimensional Carbon Nanomaterials for Fluorescent Sensing and Imaging

Advances in nanotechnology and nanomaterials have attracted considerable interest and play key roles in scientific innovations in diverse fields. In particular, increased attention has been focused on carbon-based nanomaterials exhibiting diverse extended structures and unique properties. Among these materials, zero-dimensional structures, including fullerenes, carbon nano-onions, carbon nanodiamonds, and carbon dots, possess excellent bioaffinities and superior fluorescence properties that make these structures suitable for application to environmental and biological sensing, imaging, and therapeutics. This review provides a systematic overview of the classification and structural properties, design principles and preparation methods, and optical properties and sensing applications of zero-dimensional carbon nanomaterials. Recent interesting breakthroughs in the sensitive and selective sensing and imaging of heavy metal pollutants, hazardous substances, and bioactive molecules as well as applications in information encryption, super-resolution and photoacoustic imaging, and phototherapy and nanomedicine delivery are the main focus of this review. Finally, future challenges and prospects of these materials are highlighted and envisaged. This review presents a comprehensive basis and directions for designing, developing, and applying fascinating fluorescent sensors fabricated based on zero-dimensional carbon nanomaterials for specific requirements in numerous research fields.

Portable smartphone-assisted ratiometric fluorescent test paper based on one-pot synthesized dual emissive carbon dots for visualization and quantification of mercury ions

Dual-emissive fluorescent carbon dots (CDs) were prepared through the solvothermal method with citric acid and urea as raw materials and dimethylformamide as the solvent. Two emission peaks were observed at 465 nm and 630 nm. Hg2+ could selectively quench the fluorescence at 630 nm, but the fluorescence intensity at 465 nm was less affected. Accordingly, a ratiometric fluorescence sensor for Hg2+ detection was developed, with a linear detection range of 0.5-40 μM and a limit of detection (LOD) of 37 nM. The dual-emissive CDs were loaded on the surface of the filter paper to fabricate Hg2+ detection test paper. The color of the test paper could be changed from pink purple to blue by the addition of Hg2+, and thus the qualitative and quantitative detection of Hg2+ could be realized. The concentration distinguishable by the naked eye reached 50 μM, and the quantitative detection range was 5-10,000 μM. This method shows excellent selectivity for Hg2+ and can be used to detect Hg2+ in real water samples, providing a highly potential sensing platform for rapid on-site detection of mercury ions.

The Preparation of Golgi Apparatus-Targeted Polymer Dots Encapsulated with Carbon Nanodots of Bright Near-Infrared Fluorescence for Long-Term Bioimaging

As a vital organelle in eukaryotic cells, the Golgi apparatus is responsible for processing and transporting proteins in cells. Precisely monitoring the status of the Golgi apparatus with targeted fluorescence imaging technology is of enormous importance but remains a dramatically challenging task. In this study, we demonstrate the construction of the first Golgi apparatus-targeted near-infrared (NIR) fluorescent nanoprobe, termed Golgi-Pdots. As a starting point of our investigation, hydrophobic carbon nanodots (CNDs) with bright NIR fluorescence at 674 nm (fluorescence quantum yield: 12.18%), a narrow emission band of 23 nm, and excellent stability were easily prepared from Magnolia Denudata flowers using an ultrasonic method. Incorporating the CNDs into a polymer matrix modified with Golgi-targeting molecules allowed for the production of the water-soluble Golgi-Pdots, which showed high colloidal stability and similar optical properties compared with pristine CNDs. Further studies revealed that the Golgi-Pdots showed good biocompatibility and Golgi apparatus-targeting capability. Based on these fascinating merits, utilizing Golgi-Pdots for the long-term tracking of the Golgi apparatus inside live cells was immensely successful.

In situ stimulus-responsive self-assembled nanomaterials for drug delivery and disease treatment

The individual motifs that respond to specific stimuli for the self-assembly of nanomaterials play important roles. In situ constructed nanomaterials are formed spontaneously without human intervention and have promising applications in bioscience. However, due to the complex physiological environment of the human body, designing stimulus-responsive self-assembled nanomaterials in vivo is a challenging problem for researchers. In this article, we discuss the self-assembly principles of various nanomaterials in response to the tissue microenvironment, cell membrane, and intracellular stimuli. We propose the applications and advantages of in situ self-assembly in drug delivery and disease diagnosis and treatment, with a focus on in situ self-assembly at the lesion site, especially in cancer. Additionally, we introduce the significance of introducing exogenous stimulation to construct self-assembly in vivo. Based on this foundation, we put forward the prospects and possible challenges in the field of in situ self-assembly. This review uncovers the relationship between the structure and properties of in situ self-assembled nanomaterials and provides new ideas for innovative drug molecular design and development to solve the problems in the targeted delivery and precision medicine.

Discrimination and Quantification of Glutathione by Cu+-Based Nanozymes

Glutathione (GSH) is the most abundant low-molecular-weight biological thiol in vivo and has been linked to several diseases. The accurate quantification of GSH is therefore crucial for disease diagnosis and monitoring. In this study, we prepared self-assembled Cu(I)-Cys (cysteine) nanozymes through a two-step procedure. The Cu(I)-Cys nanoparticles exhibited peroxidase-mimicking activity. Upon the addition of H2O2, they were able to oxidize 3,3,5,5-tetramethylbenzidine (TMB) into oxTMB, resulting in a measurable increase in UV-Vis absorption at 655 nm. However, in the presence of GSH, oxTMB was reduced back to TMB, leading to a decrease in UV-Vis absorption at 655 nm. By utilizing these changes in the absorption intensity, we achieved the sensitive detection of GSH with a detection limit of 2.13 μM. Moreover, taking advantage of the different peroxidase-mimicking activities of Cu(I)-Cys nanoparticles at various pH values, a sensor array with Cu(I)-Cys nanoparticles at pH 4 and pH 5 was constructed. The discrimination of GSH among Cys and ascorbic acid was achieved and the practicability of the sensor array in human serum was validated. This novel approach holds significant promise for the precise discrimination and quantification of GSH and its potential applications in disease diagnosis and therapeutics.

Dual-Functional Eu-Metal-Organic Framework with Ratiometric Fluorescent Broad-Spectrum Sensing of Benzophenone-like Ultraviolet Filters and High Proton Conduction

The construction of attractive dual-functional lanthanide-based metal-organic frameworks (Ln-MOFs) with ratiometric fluorescent detection and proton conductivity is significant and challenging. Herein, a three-dimensional (3D) Eu-MOF, namely, [Eu4(HL)2(SBA)4(H2O)6]·9H2O, has been hydrothermally synthesized with a dual-ligand strategy, using (4-carboxypiperidyl)-N-methylenephosphonic acid (H3L = H2O3PCH2-NC5H9-COOH) and 4-sulfobenzoic acid monopotassium salt (KHSBA = KO3SC6H4COOH) as organic linkers. Eu-MOF showed ratiometric fluorescent broad-spectrum sensing of benzophenone-like ultraviolet filters (BP-like UVFs) with satisfactory sensitivity, selectivity, and low limits of detection in water/ethanol (1:1, v/v) solutions and real urine systems. A portable test paper was prepared for the convenience of actual detection. The potential sensing mechanisms were thoroughly analyzed by diversified experiments. The synergistic effect of the forbidden energy transfer from the ligand to Eu3+, the internal filtration effect (IFE), the formation of a complex, and weak interactions between the KHSBA ligand and BP-like UVFs is responsible for the ratiometric sensing effect. Meanwhile, Eu-MOF displayed relatively high proton conductivity of 2.60 × 10-4 S cm-1 at 368 K and 95% relative humidity (RH), making it a potential material for proton conduction. This work provides valuable guidance for the facile and effective design and construction of multifunctional Ln-MOFs with promising performance.

Ratiometric Fluorescent Detection of Ultrasound-Regulated ATP Release: An Ultrasound-Resistant Cu,N-Doped Carbon Nanosphere

Focused ultrasound, as a protocol of cancer therapy, might induce extracellular adenosine triphosphate (ATP) release, which could enhance cancer immunotherapy and be monitored as a therapeutic marker. To achieve an ATP-detecting probe resistant to ultrasound irradiation, we constructed a Cu/N-doped carbon nanosphere (CNS), which has two fluorescence (FL) emissions at 438 and 578 nm to detect ultrasound-regulated ATP release. The addition of ATP to Cu/N-doped CNS was conducted to recover the FL intensity at 438 nm, where ATP enhanced the FL intensity probably via intramolecular charge transfer (ICT) primarily and hydrogen-bond-induced emission (HBIE) secondarily. The ratiometric probe was sensitive to detect micro ATP (0.2-0.6 μM) with the limit of detection (LOD) of 0.068 μM. The detection of ultrasound-regulated ATP release by Cu,N-CNS/RhB showed that ATP release was enhanced by the long-pulsed ultrasound irradiation at 1.1 MHz (+37%, p < 0.01) and reduced by the short-pulsed ultrasound irradiation at 5 MHz (-78%, p < 0.001). Moreover, no significant difference in ATP release was detected between the control group and the dual-frequency ultrasound irradiation group (+4%). It is consistent with the results of ATP detection by the ATP-kit. Besides, all-ATP detection was developed to prove that the CNS had ultrasound-resistant properties, which means it could bear the irradiation of focused ultrasound in different patterns and detect all-ATP in real time. In the study, the ultrasound-resistant probe has the advantages of simple preparation, high specificity, low limit of detection, good biocompatibility, and cell imaging ability. It has great potential to act as a multifunctional ultrasound theranostic agent for simultaneous ultrasound therapy, ATP detection, and monitoring.

Interfacial deposition of Ag nanozyme on metal-polyphenol nanosphere for SERS detection of cellular glutathione

The low polarization and low Raman cross section characteristics of glutathione (GSH) make it challenging to directly detect GSH molecules through surface enhanced Raman scattering (SERS) technology. Development of nanostructures for indirect detection of GSH applied to the SERS platform is of great interest. Herein, silver nanoparticles (Ag NPs)/copper-polyphenol colloidal spheres (denoted as CuTA@Ag) with adjustable Ag NPs coverage are prepared by deposition of Ag NPs on the metal-polyphenol colloidal spheres via an interfacial polyphenol reduction method. The size and density of the Ag NPs deposited on the out layer can be readily adjusted by tailoring the concentrations of silver precursor. It leads to activity difference for the nanozyme and SERS characteristics. The SERS properties of the obtained CuTA@Ag are studied using oxTMB, catalytic products of nanozyme, as the probing molecules. They provide satisfactory SERS performance with a low detection limit of 10^-7 M (S/N = 3) and linear determination in the 1-100 μM range for GSH. Moreover, it is further able to detect the glutathione content in cancer cells with well accurate and reproducible capability, catching the signs of rising cancer marker levels. This work proposes structurally tunable nanomaterials platform for a catalytic-based SERS assay, which is expected to utilize the high sensitivity of SERS tool for GSH detection in the cellular environment.

Tea-derived carbon dots with two ratiometric fluorescence channels for the independent detection of Hg2+ and H2O

Ratiometric fluorescence carbon dots (CDs) that serve as probes have attracted more attention on account of their unique optical properties, low toxicity, anti-interference, and internal reference. However, the facile fabrication of CDs with the aim of detecting multiple targets through mutually independent response channels is always a challenge. Herein, multifunctional label-free N-doped ratiometric fluorescence CDs (N-CDs) are developed from tea leaves extract and o-phenylenediamine by a mild solvothermal method. The prepared N-CDs are tailored with nitrogen- and oxygen-containing functional groups on the surface and contribute to splendid hydrophilia. Two completely independent ratiometric fluorescence channels of N-CDs, respectively, respond to Hg²⁺ and H₂O in a mutually independent manner. Based on the interactions of N-Hg and O-Hg, N-CDs achieve an excellently sensitive and selective detection for Hg²⁺ in the channel of I_{387 nm}/I_{351 nm}, giving a linear relationship in the range of 0-50 μM. Also, a wide range of Hg²⁺ concentration (0-100 μM) is linear to A_{374 nm} through UV-vis assay. Otherwise, the linear determination of H₂O content (0-30%) is realized in another channel (I_green/I_blue). The good performance in the independent testing of Hg²⁺ and H₂O, demonstrate that the proposed N-CDs have potential in multifunctional detection.

Efficient Eu3+-Integrated UiO-66 Probe for Ratiometric Fluorescence Sensing of Styrene and Cyclohexanone

The development of probes with sensitive and prompt detection of volatile organic compounds (VOCs) is of great importance for protecting human health and public security. Herein, we successfully prepared a series of bimetallic lanthanide metal-organic framework (Eu/Zr-UiO-66) by incorporating Eu³⁺ for fluorescence sensing of VOCs (especially styrene and cyclohexanone) using a one-pot method. Based on the multiple fluorescence signal responses of Eu/Zr-UiO-66 toward styrene and cyclohexanone, a ratiometric fluorescence probe using (I₆₁₇/I₃₂₀) and (I₆₁₇/I₃₃₀) as output signals was developed to recognize styrene and cyclohexanone, respectively. Benefitting from the multiple fluorescence response, the limits of detection (LODs) of Eu/Zr-UiO-66 (1:9) for styrene and cyclohexanone were 1.5 and 2.5 ppm, respectively. These are among the lowest reported levels for MOF-based sensors, and this is the first known material for fluorescence sensing of cyclohexanone. Fluorescence quenching by styrene was mainly owing to the large electronegativity of styrene and fluorescence resonance energy transfer (FRET). However, FRET was accounted for fluorescence quenching by cyclohexanone. Moreover, Eu/Zr-UiO-66 (1:9) exhibited good anti-interference ability and recycling performance for styrene and cyclohexanone. More importantly, the visual recognition of styrene and EB vapor can be directly realized with the naked eyes using Eu/Zr-UiO-66 (1:9) test strips. This strategy provides a sensitive, selective, and reliable method for the visual sensing of styrene and cyclohexanone.

Multifunctional carbon dots for glutathione detection and Golgi imaging

Glutathione (GSH) is present in almost every cell in the body and plays various integral roles in many biological processes. The Golgi apparatus is a eukaryotic organelle for the biosynthesis, intracellular distribution, and secretion of various macromolecules; however, the mechanism of GSH in the Golgi apparatus has not been fully elucidated. Here, specific and sensitive sulfur-nitrogen co-doped carbon dots (SNCDs) with orange-red fluorescence was synthesized for the detection of GSH in the Golgi apparatus. The SNCDs have a Stokes shift of 147 nm and excellent fluorescence stability, and they exhibited excellent selectivity and high sensitivity to GSH. The linear response of the SNCDs to GSH was in the range of 10-460 μM (LOD = 0.25 μΜ). More importantly, we used SNCDs with excellent optical properties and low cytotoxicity as probes, and successfully realized golgi imaging in HeLa cells and GSH detection at the same time.

Carbon Dots: Opportunities and Challenges in Cancer Therapy

Recently, carbon dots (CDs) have been actively studied and reported for their various properties. In particular, the specific characteristics of carbon dots have been considered as a possible technique for cancer diagnosis and therapy. This is also a cutting-edge technology that offers fresh ideas for treating various disorders. Though carbon dots are still in their infancy and have not yet shown their value to society, their discovery has already resulted in some noteworthy advancements. The application of CDs indicates conversion in natural imaging. Photography using CDs has demonstrated extraordinary appropriateness in bio-imaging, the discovery of novel drugs, the delivery of targeted genes, bio-sensing, photodynamic therapy, and diagnosis. This review seeks to provide a comprehensive understanding of CDs, including their benefits, characteristics, applications, and mode of action. In this overview, many CD design strategies will be highlighted. In addition, we will discuss numerous studies on cytotoxic testing to demonstrate the safety of CDs. The current study will address the production method, mechanism, ongoing research, and application of CDs in cancer diagnosis and therapy.

Construction of continuously enhanced fluorescent sensor for detection of glutathione in normal and cancer cells

In this paper, water-soluble cysteamine (CA)-capping CdSe quantum dots (CA-CdSe) could be used as a continuous fluorescent sensor. The CA-CdSe QDs can respond to Ag⁺ with a detection limit of 54.1 nM. Interestingly, CA-CdSe quantum dots combined with Ag⁺ to generate a new nano-fluorescence sensor-Ag⁺ modified CA-CdSe QDs (Ag⁺@CA-CdSe). Ag⁺@CA-CdSe can detect glutathione (GSH) with good sensitivity and anti-interference performance. The detection limit of Ag⁺@CA-CdSe fluorescenct sensor for GSH is as low as 0.74 μM. In addition, the novel nano-fluorescent sensor Ag⁺@CA-CdSe exhibited good cell permeability and was successfully applied to detect exogenous and endogenous GSH concentrations in cells. It could distinguish cancerous and normal cells by in vitro cell fluorescence imaging.

The synthesis of N-doped carbon dots for visual differentiating and detection of tetracyclines

N-doped carbon dots (N-CDs) were synthesized from L-glutamine and triethanolamine using a one-step hydrothermal method. The N-CDs emitting blue fluorescence had selective responses to tetracyclines (TCs) and could be used as a fluorescent probe to realize the quantitative detection and qualitative analysis of TCs. A method for the determination of TCs using the N-CDs in actual samples was successfully established. The recovery rate was maintained at 97.50-105.60%, and the relative standard deviation (RSD) was less than 3%. In addition, TCs can be visually distinguished using filter paper by the different fluorescence colours (light green, dark blue, and yellow-green) of the N-CDs/TCs system under ultraviolet light. This study provides a relatively simple method to detect and identify TCs.

Luminescent carbon dots with excellent peroxidase mimicking property for fluorometric and colorimetric detection of glucose

The luminescent carbon dots with peroxidase mimicking property had attracted considerable attention in biomedical field. In this work, iron-doped carbon dots (Fe-CDs) were prepared by one-pot hydrothermal method with 5, 10, 15, 20-tetra (4-borate phenyl)-21H, 23H-porphyrin Fe (II) (Fe-TBPP) as precursor. The obtained Fe-CDs emitted intense blue luminescence under ultraviolet light irradiation. Moreover, the Fe-CDs exhibited remarkable peroxidase mimicking property, which can efficiently catalyze the oxidation of 3, 3', 5, 5'-tetramethylbenzidine (TMB) into blue ox-TMB in the presence of hydrogen peroxide (H₂O₂). More importantly, the emission of Fe-CDs could be gradually quenched with the addition of H₂O₂. Based on these phenomena, a new optical dual-mode (colorimetric and fluorometric) method for the detection of H₂O₂ and glucose was successfully established. The detection limits of glucose were calculated to be 3.86 and 7.27 μM (S/N = 3) respectively based on the colorimetric and fluorometric methods. Furthermore, we combined this dual-mode detection method with smartphone imaging. The colorimetric and fluorescent images were collected by recognition software of smartphone, which were then transformed into the corresponding HSL values for quantitative determination of glucose. Finally, the dual-mode approach based on Fe-CDs was used for the detection of glucose content in human serum, demonstrating the potential application of carbon dots in the biological area.

Ligands engineering of gold nanoclusters with enhanced photoluminescence for deceptive information encryption and glutathione detection

Gold nanoclusters (Au NCs) have appeared as an essential alternative to traditional quantum dots and fluorescent molecules for the development of intelligent stimuli-responsive photoluminescence (PL), but the low PL emission of Au NCs restricts their broad applications. Herein, we reported a simple yet effective strategy for preparing Au NCs with high PL by ligands engineering of 4-hydroxy-2-mercapto-6-methylpyrimidine (MTU) and L-Arginine (Arg). Owing to the rigidified shell and the ligand-to-metal charge transfer (LMCT) effects, it was found that the assembly of Arg ligand on MTU-protected Au NCs (Arg/MTU-Au NCs) led to a significantly enhanced PL in the alkaline solution up to 30 times. Moreover, utilizing the tunable LMCT, the Arg/MTU-Au NCs displayed rapid responses to multi-type ionic interaction in a reversible manner, such as H+/OH- and Cu2+/glutathione (GSH) pairs. Inspired by these intriguing ions-responsive LMCT and the associated switchable PL emission, the Arg/MTU-Au NCs were successfully used as excellent stimuli-responsive PL probes for intriguing deceptive information encryption and biosensing as well. This work would provide new insight into regulating the PL emission of Au NCs by ligands engineering and advance their potential applications in information encryption and bioassay.

Fluorescent Sensing of Glutathione and Related Bio-Applications

Glutathione (GSH), as the most abundant low-molecular-weight biological thiol, plays significant roles in vivo. Abnormal GSH levels have been demonstrated to be related to the dysfunction of specific physiological activities and certain kinds of diseases. Therefore, the sensing of GSH is emerging as a critical issue. Cancer, with typical high morbidity and mortality, remains one of the most serious diseases to threaten public health. As it is clear that much more concentrated GSH is present at tumor sites than at normal sites, the in vivo sensing of GSH offers an option for the early diagnosis of cancer. Moreover, by monitoring the amounts of GSH in specific microenvironments, effective diagnosis of ROS levels, neurological diseases, or even stroke has been developed as well. In this review, we focus on the fluorescent methodologies for GSH detection, since they can be conveniently applied in living systems. First, the fluorescent sensing methods are introduced. Then, the principles for fluorescent sensing of GSH are discussed. In addition, the GSH-sensing-related biological applications are reviewed. Finally, the future opportunities in in the areas of fluorescent GSH sensing-in particular, fluorescent GSH-sensing-prompted disease diagnosis-are addressed.

Multifunctional N,S-doped and methionine functionalized carbon dots for on-off-on Fe3+ and ascorbic acid sensing, cell imaging, and fluorescent ink applying

Fluorescent carbon dots (CDs) have been identified as potential nanosensors and attracted tremendous research interests in wide areas including anti-counterfeiting, environmental and biological sensing and imaging in considering of the attractive optical properties. In this work, we present a CDs based fluorescent sensor from polyvinylpyrrolidone, citric acid, and methionine as precursors by hydrothermal approach. The selective quantifying of Fe3+ and ascorbic acid (AA) are based on the fluorescent on-off-on process, in which the fluorescent quenching is induced by the coordination of the Fe3+ on the surface of the CDs, while the fluorescence recovery is mainly attributed to redox reaction between Fe3+ and AA, breaking the coordination and bringing the fluorescence back. Inspired by the good water solubility and biocompatibility, significant photostability, superior photobleaching resistance as well as high selectivity, sensitivity, and interference immunity, which are constructed mainly from the N,S-doping and methionine surface functionalization, the CDs have not only been employed as fluorescence ink in multiple anti-counterfeiting printing and confidential document writing or transmitting, but also been developed as promising fluorescence sensors in solution and solid by CDs doped test strips and hydrogels for effectively monitoring and removing of Fe3+ and AA in environmental aqueous solution. The CDs have been also implemented as effective diagnostic candidates for imaging and tracking of Fe3+ and AA in living cells, accelerating the understanding of their function and importance in related biological processes for the prevention and treatment specific diseases.

Electronic Supplementary Material

Supplementary material (fluorescence spectra: UV and Xe irradiation, TG, thermo stability, ionic strength, relationship between fluorescence responses at different concentrations of Fe3+ and AA, reaction time-dependent fluorescent responses; XPS spectra of CDs + Fe3+ and Fe3+@CDs + AA; structural characterization; equations about fluorescence lifetime, quantum yield and LOD; comparison of the CDs for the detection of Fe3+ and AA with reported methods; detection of Fe3+ and AA in real samples; absorption of Fe3+ in environmental samples and MTT assay results) is available in the online version of this article at 10.1007/s12274-022-5107-7.