The quenching of the fluorescence of carbon dots: A review on mechanisms and applications

A novel fluorescent nanoprobe based on platinum nanoclusters with the characteristic of aggregation-induced emission for the detection of Cu2+ and D-penicillamine

In this work, platinum nanocluster (Pt NCs) with AIE property using L-glutathione (L-GSH) as the protecting ligand are reported. The solid-state photoluminescence quantum yields of obtained Pt NCs powder is as high as 8.0 %. The as-prepared Pt NCs exhibited solvent-induced emission. Specifically, they exhibited gradually enhanced red fluorescent emission as the volume ratio of ethanol to H2O increases. Additionally, the obtained Pt NCs presented excellent stability and resistance to photobleaching in the mixed solvent of ethanol and H2O. Based on the fluorescent quenching effect of Pt NCs induced by Cu2+ and the strong coordination interaction between Cu2+ and thiol group of D-penicillamine (D-Pen), a novel "off-on" fluorescent nanoprobe was proposed for quantifying the labelling amount percentage of commercially available D-penicillamine tablets. Experimental results demonstrated the fluorescent quenching from our proposed Pt NCs-based nanoprobe was linearly correlated with Cu2+ concentration within the range from 1 to 28 μM, with a limit of detect (LOD) of 0.13 μM. Besides, upon addition of D-Pen into a mixed system containing Pt NCs and Cu2+, fluorescent intensities of Pt NCs were recovered and exhibited concentration-dependent responses within a concentration of D-Pen from 1 to 120 μM, with an LOD of 0.058 μM. Spiked sample experiment validated that our proposed nanoprobe possessed an outstanding accuracy, which expands the potential application of metal nanoclusters exhibiting AIE effects in pharmaceutical analysis.

FeCuS multilayer nanoflowers loaded with N-CDs dual-mode method for the detection of uric acid and gout risk prediction with the aid of chemometrics

Transition metal sulfides have attracted much attention due to their low cost, high stability, adjustable performance, diverse morphology and good catalytic activity. In this work, nitrogen-doped carbon dots (N-CDs) were loaded onto bimetallic sulfides (FeCuS) and FeCuS/N-CDs could act as catalyst and fluorescent probe, which applied to the detection of uric acid (UA) in human blood and urine using dual-model assay (colorimetry and ratiometric fluorescence). The nanozyme has excellent peroxidase-like activity and steady-state kinetic results showed that the material prepared under optimized conditions had better affinity (Km = 0.42 mM) for the substrate and faster reaction rate (Vmax = 14.1 × 10-8 M s-1). •OH and O2•- were involved in the catalytic process of o-phenylenediamine (OPD) by FeCuS/N-CDs nanozymes. A profound discussion and quantitative analysis about the sensing mechanism of UA and fluorescence quenching mechanism between FeCuS/N-CDs and diaminophenazine (DAP) was performed. According to Parker equation, the inhibition efficiency of DAP in FeCuS/N-CDs was as high as 83 % of the total inhibition efficiency, confirming that the inhibition efficiency mainly came from internal filtering effect (IFE). The detection limits of ratiometric fluorescence method and colorimetric method were as low as 0.13 μM and 0.27 μM, respectively. Finally, principal component analysis was used to successfully distinguish three groups of people (healthy people, potential people and gout patients) and the model has potential value in clinical applications.

High quantum yield AIE covalent organic frameworks for sensitive pH monitoring, and copper toxicosis Diagnosis&Remission

The luminescence properties of covalent organic frameworks (COFs) have attracted significant attention for biomedical applications. However, conventional fluorescent COFs often suffer from weak fluorescence due to aggregation-caused quenching (ACQ), limiting their utility. Given the critical need for highly efficient and sensitive biosensing tools, herein, we propose an aggregation-induced emission (AIE) COF, named COF-Bpy, with the quantum yield up to 25%. Benefiting from the active nitrogen sites within the bipyridine unit, COF-Bpy demonstrates remarkable pH monitoring capabilities across a wide pH range and displays strong coordination affinity towards Cu2+, achieving satisfactory detection and efficient adsorption of Cu2+. These properties make COF-Bpy superior in cellular pH imaging, and diagnosis&remission of copper toxicosis at both cellular and nematode levels, as it reduces the late apoptotic cells, improves nematode survival and locomotor states. Additionally, the fluorescence quenching mechanism of dynamic quenching with metal-to-ligand charge transfer is clarified. Briefly, this study not only presents a novel strategy for fabrication of AIE-COFs, but also provides a promising avenue for early diagnosis of pH-related diseases, and offers a theranostics for copper toxicosis management.

An agar hydrogel-CuNPs/N@CQDs dual-mode colorimetric/fluorescent indicator for non-destructive monitoring of banana ripening

A colorimetric-fluorescence ripeness indicator, based on copper nanoparticles and carbon quantum dots doped with nitrogen (CuNPs/N@CQDS) immobilized in agar hydrogel (AGH-CuNPs/N@CQDs) for ethylene gas detection, was developed for detecting the ripening of bananas. Ethylene could reduce the fluorescence intensity of CuNPs/N@CQDs and cause a red shift of the LSPR peak. The prepared AGH-CuNPs/N@CQDs indicator had an irreversible response to ethylene with LOD and LOQ of 9.94 and 30.12 μM, respectively. The results of XPS and FTIR confirmed the formation of Cu-OH bonds. The color of the AGH-CuNPs/N@CQDs indicator changed from pale green to yellow and ultimately to brown during banana ripening. There was a strong correlation between the decrease in firmness of banana tissue, the increase in reducing sugars, and the change in the indicator's color. Therefore, the AGH-CuNPs/N@CQDs indicator is capable of simple, low-cost, high-accuracy, and naked-eye identification of the fruit's ripening in intelligent packaging.

A novel fluorescent sensor for highly sensitive detection of ascorbic acid in food based on inhibiting phosphatase-like activity of Zr-based MOF

Nanozyme-based sensors for detecting ascorbic acid (AA) generally depend on the reducibility of the analyte. However, these sensors are susceptible to interference from reducing substances in food. Herein, a novel fluorescent sensor for AA detection was developed based on inhibiting the phosphatase-like activity of a Zr-based metal-organic framework (Zr-CAU-28). Hydroxyl-rich AA molecules adsorb on the surface of Zr-CAU-28 through hydrogen bonding with [Zr6O4(OH)4] cluster, leading to a decrease in the relative content of terminal hydroxyl groups within the catalytic sites. The constructed sensor exhibits a wide detection range (0.08-11 μg·mL-1) and low detection limit of 0.025 μg·mL-1. Potential interfering studies demonstrated the good selectivity of the sensor. Moreover, the fluorescent sensor can effectively detect AA in juices and vitamin C tablets, with the recovery rate ranging from 96.25 % to 108.50 %. This work represents the first application of phosphatase mimics for AA detection, offering a new strategy for food analysis.

A simply designed quasi-ratiometric fluorescence probe for the visual and on-site detection of levofloxacin (LVF) residues in milk and fish sample

An europium metal organic framework (Eu-DBPA-Phen) was synthesized using 2,5-dibromoterephthalic acid (H2DBPA) and 1-10-phenanthroline (Phen) as ligands. A straightforwardc quasi-ratiometric fluorescence probe was then developed for the detection of levofloxacin (LVF) by the simplistic combination of red-emitting Eu-DBPA-Phen and the inherent blue auto-fluorescence of the target. The probe exhibits the advantages of wide linear range (0.01-50 and 50-175 μM), good selectivity, low detection limit (4.53 nM) and fast response time. In addition, a smartphone-assisted fluorescent test strip analysis platform was established for the visual and on-site detection of LVF in milk and fish samples, achieving satisfactory recovery rates ranging from 101.7 % to 103.4 % and low standard deviations (RSD ≤2.890, n = 3). Furthermore, a hierarchical clustering algorithm integrating machine learning and smartphone-test strip platform was devised to streamline the detection process. The proposed intelligent detection platform introduces a novel approach for LVF detection, thereby enhancing food safety and human health.

Self-cascade catalytic system constructed using carbon dots and Au nanoparticles co-assembled on MIL-53(Fe)-NH2 as a three-in-one fluorescent nanozyme for multimodal detection of glucose and maltose in food

Determination of glucose and maltose is crucial for food production and human health. Herein, a novel Au/CD@MIL-53(Fe)-NH2 self-cascade nanozyme was constructed via host-guest assembly with "three-in-one" features, including blue fluorescence, H2O2 production as an oxidase mimic, and •OH generation as a peroxidase mimic. Theoretical and experimental results proved that the incorporation of carbon dots renders the composite with high peroxidase-like activity and extremely high affinity for H2O2 (Km: 0.011 mM), 336 times higher than that of the natural enzyme. The self-cascade catalytic process could oxidize colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue ox-TMB, which further quenched the fluorescence and produced a photothermal effect. Consequently, colorimetric/fluorescence/photothermal-based multimodal detection of glucose and maltose was first achieved, obtaining low detection limits of 12/7.5/1.1 and 18/11.3/1.4 μM, respectively. This study offers a promising strategy for designing efficient nanozyme-based cascade systems that help enhance food quality determination.

pH-regulated CQDs@Eu/GMP ICP sensor array and its fingerprinting on 96-well plates: Toward point-of-use/specific identification and quantitation of six tetracyclines in animal farm wastewater, milks and milk-derivative products

Herein, a "lab-on-an-AIE@Ln/ICP" sensor array was constructed by employing aggregation-induced emission carbon quantum dots (AIE-CQDs) as the guest and Eu/GMP ICP as the host. Based on the antenna effect (AE) and reductive photo-induced electron transfer (r-PET) between CQDs@Eu/GMP ICPs and tetracyclines (TCs), the as-constructed sensor produced satisfactorily dual-emitting fluorescence. By combining pH regulation with principal component analysis (PCA), the underlying fingerprinting patterns realized the specific identification and quantitation of six TCs in animal farm wastewater, milks and milk-derivative products. Through the aggregation-induced quenching of CQDs@Eu/GMP ICPs on test strips, the discernible fluorescence alterations were successfully utilized for developing smartphone-based visual assay. To sum up, the prominent novelty of this study lies in that based on the comprehensive principles of AE and r-PET along with combination of pH-adjustment and PCA, the pioneered sensor assay achieves specifically identifying and sensing individual TCs for their rapid and on-site detection in animal-derived matrices.

L-tryptophan carbon dots as a fluorescent probe for malachite green detection

Development of a rapid and sensitive detection method for hazardous dyes attracts considerable research interest. In this work, L-Tryptophan-based Carbon dots were developed as a fluorescence sensor for the detection of Malachite green (MG). Green fluorescent L-Trp-C-dots were synthesized by a simple pyrolysis technique using L-Trp as the starting precursor. L-Trp-C-dots exhibited different quenching responses to MG, and other interfering species, consequently offering a selective strategy to detect MG. The proposed sensor shows a limit of detection (LOD) of 0.06 μM and a limit of quantification (LOQ) of 0.22 μM with in the linearity range of 0 to 60 µM concentration. Additionally, the relative standard deviation (RSD) was found to be below 1.7 %. Furthermore, the recovery of MG from the real-time samples (green peas) was investigated.

Green synthesis of red-emitting carbon dots for bioimaging, sensing, and antibacterial applications

It is a highly desirable and formidable challenge to synthesize carbon dots with long-wavelength emission using green synthesis. In this work, we explored red-emitting carbon dots (rCDs) via a hydrothermal strategy and their multifunctional application for bioimaging in vivo/vitro, curcumin sensing, and antibacterial materials. As-prepared rCDs were water-soluble and monodispersed with an average diameter of 2.34 nm. Significantly, these rCDs exhibited low toxicity and outstanding biocompatibility, which was consistent with the excellent bioimaging performance in living cells, zebrafish, and nude mice, providing them a promising prospect for clinical applications. Meanwhile, the obtained rCDs were also used as a fluorescent probe for sensitive detection of curcumin in a wide linear range of 0.03-135.73 μM with a limit of detection of 29.37 nM. Furthermore, quaternized rCDs were designed and used as antibacterial material with minimum inhibitory concentrations against Staphylococcus aureus and Escherichia coli of 0.15 mg/mL and 0.5 mg/mL, respectively, which advanced the development of novel antibacterial agents and broadened the applications of red-emitting CDs. Therefore, this work provided multifunctional CDs with red emission for use in the fields of biological imaging, fluorescence sensing, and antibacterial materials.

A dual-mode biosensor based on metal organic framework-coated upconversion composites with near-infrared luminescence and peroxidase-like activity for the detection of alkaline phosphatase and glucose

An abnormal level of alkaline phosphatase (ALP) in serum is related to many diseases, such as breast cancer, prostate cancer, hepatitis, and diabetes. The level of glucose in the blood is related to diabetes or hypoglycemia. Given the close correlation between ALP and glucose in various diseases, it is essential to establish an accurate, sensitive, and selective assay for monitoring the levels of ALP and glucose in serum. As luminescent materials, upconversion nanoparticles (UCNPs) stand out in the design of biosensors because of their high photostability, large anti-Stokes shifts and low background interference. Additionally, metal organic frameworks (MOFs) are a class of functional porous materials, and their adjustable pore size structure and high specific surface area expose many catalytic sites, making MOFs excellent catalysts and ideal materials for constructing artificial enzymes. Herein, a fluorescent and colorimetric dual-mode probe based on a multifunctional composite (UCNP@MOF) with upconversion luminescence and peroxidase-like activity was proposed for the detection of ALP and glucose. Under the optimal conditions, the detection limits of ALP and glucose by the fluorescence method were 0.046 U/L and 0.079 μM, respectively. Furthermore, the method was used to determine ALP and glucose in serum samples, and the detection results were similar to those of commercial kits; moreover, the recoveries were in the range of 92.7-105.4 %, indicating great potential for accurate and sensitive detection of ALP and glucose in biological samples.

Integration of Eu-based metal-organic frameworks and carbon dots for multicolor visual intelligent detection of phosphate

Phosphate (Pi) has an important influence on the water environment and physiological processes. Therefore, developing fluorescent probe for quantitative detection of Pi is crucial for water environment monitoring and human health assessment. This work designed a dual-emission ratio nano-fluorescent probe GCDs/Eu-BDC based on europium-based metal-organic frameworks (Eu-MOFs) and blue carbon dots (GCDs) for multicolor fluorescence detection of Pi. The GCDs/Eu-BDC realized multicolor fluorescence detection of Pi based on the red-to-blue fluorescence change. The probe has high selectivity and a detection limit of 70 nM in the range of 0-45 μM. GCDs/Eu-BDC can be used to detect Pi in environmental water samples and serum samples, proving the feasibility of quantitative analysis of Pi in real samples. In addition, a portable paper-based sensor was prepared in this work. Combined with the chromaticity analysis App in smartphones, the intelligent real-time detection of Pi can be realized, which has certain practical application potential.

Selective Identification and Quantification of Microplastics Using Solid Fluorescent Green Carbon Dots (SFGCDs) - A Novel, Naked Eye Sensing Fluoroprobe

The current work presents a Novel, Carbon Dot fluoroprobe to selectively identify and quantify Microplastics (MPs) released from Surgical facemask and Cosmetic Personal Cleansers. Solid Fluorescent Green Carbon Dots (SFGCDs) are synthesized for the first time from a high carbon source natural resin, obtained from Araucaria araucana (Monkey puzzle tree). The increased carbon content is responsible for the green colour of the CDs. SFGCDs function as a TURN OFF fluoroprobe on detection of MPs through dynamic quenching mechanism, which is confirmed from Stern Volmer Plot with an R2 value of. The minimum LOD being 0.0063 g/l for ≥ 6 μm diameter MPs. The agglomeration of microplastics released from surgical mask and cosmetic cleansers on functions as an insulator on the surface of SFGCDs, forbidding ease of electron- hole transfer between the donor- SFGCDs and acceptor-MPs. The release of MPs from the donor surface results in reappearance of fluorescence obeying FRET mechanism. The detection of MPs/ microfibres released by disposable surgical mask is studied by the degradation of the surgical face mask for a period of 50 days, followed by detection. Turn- OFF in fluorescence of SFGCDs observed in presence of micro fibre Turns On, as remediation of MPs is done by a simple filtration technique. The results demonstrate the potential of the fluoroprobe towards real time detection of MPs and simple remediation of MPs to conserve the ecosystem. The SFGCDs is stable and can be reused for nearly 3 cycles for the detection of MPs. A single PL peak obtained on detection of MPs in presence of monovalent, divalent trivalent ions and biomolecules authenticates the selectivity and stability of SFGCDs to function as an efficient fluoroprobe towards sensing of MPs.

Counterexample to Luminescent Metal Nanocluster Paradigm: Reactive Au(I) Complexes from His-Au(III) Synthetic Reactions and Their Chemistry for Direct Analysis of d-Penicillamine

There is a widely accepted material characterization paradigm in the success of synthesis of luminescent metal nanoclusters (NCs) in the aqueous phase: new emission, metal reduction, and ultrasmall particles (size < 3 nm). Herein, we falsified well-known fluorescent histidine (His)-directed Au NCs and a new model of metastable His-Au(I) complexes with emissive His oxidation products has been established. The redox reaction of His and Au(III) yields His oligomers with blue-green fluorescence and reducible Au(I) self-assemblies, which can form ultrasmall particles at electron bombardment. The resultant Au(I) complexes can be further reduced by d-penicillamine (DPA) via forming anisotropic Au nanoparticles with distinct local surface plasmon resonance absorption. The emerging absorption can quench the fluorescence of the His oxidation products through the inner filter effect pathway. A facile dual-model analytical approach is thus proposed to directly detect DPA fluorometrically and colorimetrically without interference from common biothiols, including cysteine and glutathione. Thus, with the help of a smartphone app, a highly sensitive and selective point-of-care testing for DPA direct detection can be realized. Our study warrants the importance of thinking twice about characterization results and supports corrective models for finding new reactions and possible applications.

Fluorophore-labeled molecule recognition peptide: Static quenching in metal-organic frameworks for ultrasensitive ratiometric fluorescence biosensing of ochratoxin a in grain products

Ochratoxin A (OTA) is a notable mycotoxin prevalent in grain products. In this paper, we computationally designed a high-affinity molecular recognition peptide (MRP, KQRLKCASLQKFGERAF) targeted at OTA according to structural analysis and molecular dynamics with a dissociation constant (Kd) of 12.18 ± 6.59 nM. A novel fluorescent probe, RhB-MRP (MRP-lysine-rhodamine B), was synthesized to convert the binding of MRP and OTA into optical signals. Based on RhB-MRP, we constructed a ratiometric fluorescence biosensor utilizing the classic blue fluorescent MOFs (NH2-MIL-88(Fe)). The fluorescence of NH2-MIL-88(Fe) was strongly quenched by RhB-MRP, which formed a ground state complex leading to static quenching. The developed biosensor exhibited exceptional sensitivity with detection limit of 0.32 pg mL-1 and rapid response time (11 min). A good recovery rate of 87.3-114.1 % was achieved in grain products. Although there are currently few MRPs that can specifically recognize small molecules, this highly sensitive and selective biosensor demonstrates the great potential of MRPs for detecting other molecules.

Poria cocos-derived carbon dots for parallel detection of Cr6+/Fe3+ in complex environments with superior sensitivity

Multifunctional sensor capable of parallel sensing is of great importance thanks to their wide applications and great practicality. In this report, Poria cocos-derived carbon dots (CDs) were adopted for the development of multifunctional sensor for the parallel detection of Cr6+ and Fe3+ with superior sensitivity and applicability. Specifically, extremely low limit of detection (LOD) of 1.07 × 10-3 nM and 1.98 × 10-3 nM were achieved for Cr6+ and Fe3+, respectively. Systematic mechanism explorations revealed that the highly sensitive detection of Cr6+ was attributed to an efficient inner filter effect (IFE), while the sensing of Fe3+ was realized due to a strong static quenching process. Furthermore, the assay was found to be extremely versatile, achieving the reliable detection of Cr6+ and Fe3+ in multiple natural water environments and even biological environment. Utilizing the different reactions of Cr6+ and Fe3+ towards masking reagents, a logic gate that could effectively eliminate the mutual interference of Cr6+ and Fe3+ was successfully designed.

High acid-base tolerance and long storage time lanthanum cerium co-doped carbon quantum dots for Fe3+ detection

In this paper, lanthanum and cerium co-doped carbon quantum dots (LaCe-CQDs) was firstly synthesized by one step hydrothermal method. The obtained LaCe-CQDs shown sable fluorescence properties with pH values from 3 to 9 and after 4 weeks of storage. The average particle size of LaCe-CQDs, with excitation and emission wavelengths of 350 nm and 446 nm, is 3.27 ± 0.12 nm. Selective analysis of various metal ions revealed the sensitivity of LaCe-CQDs towards Fe3+ ions. Within the 0-60 μM, the fluorescence intensity exhibits a strong linear correlation with the concentration of Fe3+. The limit of detection (LOD) was determined to be 0.753 μM. Additionally, the accuracy of LaCe-CQDs were demonstrated in natural water samples. Therefore, LaCe-CQDs are a promising sensor for Fe3+ detection.

Carbon dot-based fluorescent sensor for selective and sensitive detection of persulfate

Persulfate, a powerful oxidizing agent, is extensively employed in numerous industries. Accurate and rapid detection of persulfate (S2O8 2-) is essential. This study reports the development of a fluorescent sensor based on Am-CDs. It is synthesized from ascorbic acid (AA) and m-phenylenediamine (m-PD) through a one-step hydrothermal method. The fluorescence of Am-CDs demonstrated selective sensitivity to S2O8 2- via static quenching. A sensitive fluorescent sensor was constructed for S2O8 2-, exhibiting a linear detection range of 1.96 to 15.59 μM with a limit of detection (LOD) of 0.94 μM. This fluorescence method was successfully applied to detect S2O8 2- in water samples, achieving recoveries of 98.07% to 102.33%. The fluorescent sensor developed in this study offers a simple and effective method for quantifying S2O8 2- in aquatic environments.

A fluorescent nanocomposite probe of quantum dots and zinc oxide embedded in polymer for smartphone-assisted on-site determination of diflunisal

A fluorescent sensor based on nitrogen-doped graphene quantum dots (N-GQDs) was developed for the smartphone-assisted colorimetric determination of diflunisal. The fluorescence source was embedded with zinc oxide (ZnO) in a molecularly imprinted polymer (ZnO@N-GQDs@MIP). The quantitative analysis was based on the fluorescence quenching caused by electron transfer from the nanoprobe to diflunisal. The sensor demonstrated linearity in the range of 0.10-50.0 μg L-1 with a limit of detection of 0.03 μg L-1. Smartphone-assisted on-site determination produced linearity in the range of 1.0-50.0 µg/L with a limit of detection of 0.30 μg L-1. The developed sensor was applied to determine diflunisal in milk, egg and yogurt samples. Recoveries ranging from 94.8 to 103.7 % were achieved with a RSD below 2.0 % measured by fluorescence spectroscopy, and from 94.9 to 106.9 % with a RSD of <6 % smatphone-assisted measurement. Comparison of the detection outcomes of both methods with those of high-performance liquid chromatography revealed consistent results, demonstrating the accuracy of the developed method, which was also sensitive, selective, and fast. Notably, the portable and easy-to-read smartphone-assisted method is suitable for on-site application.

Molybdenum disulfide quantum dots for rapid fluorescence detection of glutathione and ascorbic acid

A method for the specific detection of glutathione (GSH) and ascorbic acid (AA) using 3-aminophenylboronic acid functionalized molybdenum disulfide quantum dots (APBA-MoS2 QDs) was reported. The APBA-MoS2 QDs synthesized using the hydrothermal method showed the strongest fluorescence intensity at an emission wavelength of 375 nm with the optimum excitation wavelength of 320 nm. The detection method was constructed by the combination of the dynamic and static quenching and the inner filter effect (IFE) of APBA-MoS2 QDs by permanganate (MnO4-) and the rapid redox reaction (1 min) of MnO4- by GSH or AA. The concentrations of GSH and AA showed good linear ranges of 10-500 μM and 10-100 μM, respectively, with limits of detection (LOD) of 0.476 μM and 0.185 μM, respectively. The spiked recovery tests in human serum and fresh fruit samples showed that APBA-MoS2 QDs had significant potential in the construction of fluorescent biological detection methods.

Nanowire-like phosphorus modulated carbon-based iron nanozyme with oxidase-like activity for sensitive detection of choline and dye degradation

Choline is mainly supplemented through food intake, lack of choline would result in diseases like liver cirrhosis, hardening of the arteries, or neurodegenerative disorders. The accurate detection of choline is important for human health. Herein, a novel nanowire-like phosphorus/nitrogen co-doped carbon-based iron nanozyme (Fe-NPC) with outstanding oxidase-like activity was synthesized, and the influence of phosphorus doping on oxidase-like activity was explored. Proper phosphorus doping was found to enhance the oxidase-like activity of Fe-NPC by increasing surface defects, promoting iron loading, and modulating chemical environment of central site. The oxidase-like activity of Fe-NPC was successfully applied to colorimetric-fluorescent dual mode detection of choline, and good linear relationship in the ranges of 3-200 μM were achieved with LODs of 1.95 and 1.50 μM, respectively. The fluorescent detection was constructed based on the fluorescence quenching of silicon quantum dots (Si QDs) by quinone-imine. The quenching mechanism was attributed to FRET due to the large spectra overlap, reduced fluorescence lifetime and proper donor-acceptor distance. The successful application to the detection of choline in milk proved the practicability of the proposed sensing method. The oxidase-like properties of Fe-NPC was further used in the degradation of cationic dye methyl blue, high degradation efficiency of 74 % was achieved within 5 min under optimal conditions, proving the enormous potential of Fe-NPC for application in environment protection.

A novel colorimetric and fluorometric dual-signal identification of crude baijiu based on La-CDs

The correct classification of strong-flavored crude baijiu affects its quality and overall standard and is crucial for the intelligent development of the baijiu industry. In this work, we developed a novel optical sensing array using lanthanum-doped carbon dots (La-CDs). Using La-CDs with three metal complex dyes-chromium black T, alizarin red, and dimethylphenol orange-we were able to detect organic acids and tannic acid (TA) in crude baijiu in a way that was both colorimetric and fluorescent for the first time. Based on the indicator displacement (IDA) principle, organic acids competitively replace the dyes' binding sites on La3+, causing the dye colors to change to varying degrees. TA quenches the fluorescence of quantum dots through an internal filtering effect. We analyzed the data using pattern recognition algorithms such as HCA, PCA, and LDA, successfully classifying and identifying 16 types of strong-flavored crude baijiu, which included 10 types of carboxylic acids and various grades. In blind tests of 32 crude baijiu samples, the colorimetric method achieved a 94 % accuracy rate, while the fluorescence method achieved 100 %. The sensor demonstrates significant advantages in response speed.

High sensitivity distinguishing detection of fluoroquinolones with a cage-based lanthanide metal-organic framework in food

Sensitive and selective detection of fluoroquinolones, especially from different sources, is challenging. This study reported an uncommon three-cage lanthanide metal-organic framework (1-Eu) with a Eu3+ cluster as its structural primitive using a C2-symmetric 5,5-(Pyrazine-2,6-diyl) diisophthalic acid ligand. The 1-Eu probe effectively detected four fluoroquinolones through distinct color changes and spectral emission bands, demonstrating excellent performance with low detection limits: moxifloxacin (LOD: 9.3 nM), danofloxacin (LOD: 33.7 nM), gatifloxacin (LOD: 67.9 nM), and ofloxacin (LOD: 238.6 nM). Mechanistic studies revealed that internal filtration and photoinduced electron transfer (a-PET) effects were key factors. Furthermore, 1-Eu was successfully used to detect fluoroquinolones in food samples. Additionally, portable paper-based sensors were developed to quickly semi-quantify analyte concentrations using a smartphone color recognition app, underscoring the practical potential of this probe. This study introduces a novel methodology for the identification and detection of fluoroquinolones to enhance food safety.

Fast and eco-friendly synthesis of carbon dots from pinecone for highly effective detection of 2,4,6-trinitrophenol in environmental samples

2,4,6-Trinitrophenol (TNP) has high explosive risks and biological toxicity, and there has been considerable concern over the determination of TNP. In the present work, fluorescent carbon dots (CDs) stemmed from a green carbon source of pinecone by the facile hydrothermal approach. A novel environment- friendly fluorescent probe was developed to efficiently detect TNP by using the obtained CDs with remarkable fluorescence stability. The fluorescent CDs exhibited obvious excitation dependence with the highest peaks for excitation and emission occurring at 321 and 411 nm, respectively. The fluorescence intensity is significantly reduced by TNP owing to the inner filter effect with the CDs. The probe exhibited good linearity with TNP concentrations in the range of 0.025-20 μg mL-1, and the limit of detection was as low as 8.5 ng mL-1. Additionally, the probe proved successful in sensing TNP quantitatively in actual environmental samples with satisfied recoveries of 95.6-99.6%. The developed fluorescent probe offered an environment-friendly, efficient, rapid, and reliable platform for detecting trace TNP in the environmental field.Highlights Novel carbon dots were synthesised from green precursors of pineal powder.The highly effective quenching process was put down to the inner filter effect.The as-constructed fluorescent probe was successfully utilised for sensing 2,4,6-trinitrophenol in environmental samples.The proposed method was simple, rapid, efficient, economical, and eco-friendly.

Synthesis of Yellow Fluorescence Carbon Dots for the Applications of Vitamin B12 Detection and Cell Imaging

In this work, bright yellow fluorescent and multifunctional carbon dots (N-CDs) were prepared by hydrothermal method from O-phenylenediamine and 4-aminobenzoic acid. The fluorescence characterization showed that the N-CDs possessed good optical properties (QY = 32%) and excitation dependent multi-color emission. By exciting with 390 nm, the strong selective interaction of VB12 with N-CDs could result in a sharp decrease in the luminescence of N-CDs at 567 nm. An efficient fluorescence sensor in aqueous solution was constructed which could linearly respond VB12 in wide concentration ranges of 0-90 μM and 140-250 μM. The linear correlation coefficients of N-CDs and VB12 were 0.9950 and 0.9968, respectively, and the detection limit was 0.119 μM. N-CDs were performed for sensitive determination of VB12 in real samples. Moreover, the N-CDs were exploited to image cell. This N-CDs was a sensitive fluorescence probe to monitor VB12 and presented prospective potential in living cells imaging.

Construction of eco-friendly dual carbon dots ratiometric fluorescence probe for highly selective and efficient sensing mercury ion

In present work, blue carbon dots (b-CDs) were derived from ammonium citrate and guanidine hydrochloride, and red carbon dots (r-CDs) were stemmed from malonate, ethylenediamine and meso‑tetra (4-carboxyphenyl) porphin based on facile hydrothermal method. Eco-friendly ratiometric fluorescence probe was innovatively constructed to effectively measure Hg2+ utilizing b-CDs and r-CDs. The developed probe displayed two typical emission peaks at 450 nm from b-CDs and 650 nm from r-CDs under the excitation at 360 nm. Mercury ion has strong quenching effect on the fluorescence intensity at 450 nm due to the electron transfer process and the fluorescence change at 450 nm was used as the response signal, whereas the fluorescence intensity at 650 nm kept unchangeable which resulted from the chemical inertness between Hg2+ and r-CDs, serving as the reference signal in the sensing system. Under optimal circumstances, this probe exhibited an excellent linearity between the fluorescence response values of ΔF450/F650 and Hg2+ concentrations over range of 0.01-10 µmol/L, and the limit of detection was down to 5.3 nmol/L. Furthermore, this probe was successfully employed for sensing Hg2+ in practical environmental water samples with satisfied recoveries of 98.5%-105.0%. The constructed ratiometric fluorescent probe provided a rapid, environmental-friendly, reliable, and efficient platform for measuring trace Hg2+ in environmental field.

Encapsulation of fluorescent carbon dots into mesoporous SiO2 colloidal spheres by surface functionalization-assisted cooperative assembly for high-contrast latent fingerprint development

Exploiting solid powder fluorescence holds significant potential in diverse domains including medicine and forensics. Conventional fingerprint detection methods often fall short due to low contrast, sensitivity, and high toxicity. To addressing these challenges, we present a novel method for latent fingerprint detection using fluorescent carbon dots (CDs) encapsulated into conventional or mesoporous SiO2 colloidal spheres (CD@SiO2 or CDs@m-SiO2) through a surface functionalization-assisted cooperative assembly process. The synthesized monodisperse CDs@SiO2 and CDs@m-SiO2 spheres, with tuning particle size, adjustable porosity and pore size, and highly dispersed CDs, exhibit improved fingerprint visibility and contrast on various substrates such as glass, stainless steel, and plastic. CDs located in SiO2 with excellent affinity effectively avoids their solid-state self-quenching phenomenon, which, coupling with mesoporous SiO2 shell, maximumly retains their fluorescence properties. Our method demonstrates a high contrast, selectivity, and sensitivity in fingerprint detection, offering an environmentally friendly and healthy alternative to conventional techniques, and showcasing a facile route to novel solid-state CDs-based fluorescent materials for forensic analysis.

Deep eutectic solvent-assisted carbon quantum dots from biomass Triticum aestivum: A fluorescent sensor for nanomolar detection of dual analytes mercury (Ⅱ) and glutathione

Deep eutectic solvents (DESs) have attracted significant attention in recent years due to its environment friendly characteristics and its participation in the multi-heteroatom doping of carbon quantum dots (CQDs). In this work, we present a simple, fast, and environment-friendly microwave synthesis approach for the synthesis of DES-assisted nitrogen and chloride co-doped CQDs (N,Cl-CQDs) using a choline chloride-urea based DES. A biomass-based precursor, i.e., wheatgrass (Triticum aestivum), has been used as a carbon source. Transmission electron microscopy (TEM) showed the spherical shape with average 1.75 nm particle diameter of prepared CQDs. The surface functionality and chemical composition of prepared N,Cl-CQDs were determined by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopic techniques. The N,Cl-CQDs obtained a high quantum yield (QY), i.e., 36 %, compared to undoped CQDs, which were synthesized in an aqueous medium (QY = 15 %). The prepared N,Cl-CQDs showed significant properties such as excellent photostability, favorable water solubility, and high optical stability. N,Cl-CQDs were used as sensing platform for the detection of Hg2+ ions and GSH with LOD value of 39 nM and 43 nM, respectively. The fluorescence quenching mechanism was confirmed by several photophysical parameters, such as average lifetime values, radiative rate constant (k r ), non-radiative rate constant (knr) and others. Furthermore, the current sensing system's viability is also tested in a river water sample for the detection of Hg2+. The N,Cl-CQDs prepared in this study exhibited a reduced detection limit and a broad linear range by an easy, environmentally friendly, and rapid method for detecting GSH and Hg2+ ions.

The Effect of the Position of a Phenyl Group on the Luminescent and TNP-Sensing Properties of Cationic Iridium(III) Complexes

Three cationic Ir(III) complexes, 1, 2, and 3, were successfully synthesized and characterized by tuning the position of a phenyl group at the pyridyl moiety in 2-phenylpyridine. All three complexes exhibited typical aggregation-induced phosphorescence emission (AIPE) properties in CH3CN/H2O. The AIPE property was further utilized to achieve the highly sensitive detection of 2,4,6-trinitrophenol (TNP) in aqueous media with low limit of detection (LOD) values of 164, 176, and 331 nM, respectively. This suggests that the different positions of the phenyl group influence the effectiveness of 1, 2, and 3 in the detection of TNP. In addition, 1, 2, and 3 showed superior selectivity and anti-interference properties for the detection of TNP and were observed to have the potential to be used to detect TNP in practical applications. The changes in the luminescence lifetime and UV-Vis absorption spectra of 1, 2, and 3 before and after the addition of TNP indicate that the corresponding quenching process is a combination of static and dynamic quenching. Additionally, the proton nuclear magnetic resonance spectra and results of spectral studies show that the detection mechanism is photo-induced electron transfer (PET).

Combining digital imaging and quantum dots for analytical purposes

This review provides a critical assessment of the most recent advances in digital imaging (DI) methods, applied for the development of analytical methodologies combining quantum dots (QDs). The state-of-the-art, treatment of data, instrumental considerations, software, sensing approaches, and optimization of the resulting methods are reported. Applications of the technology for the analysis of food and beverages, biomedically relevant analytes, drugs, environmental samples and forensic samples are also discussed. These examples aim to highlight the advantages of DI over traditional instrumentation, that in combination with QDs represents a powerful option for low-cost and on-site analyses. Moreover, some of these DI methods have been explored in the context of green chemistry principles, demonstrating a sustainable approach to modern analytical challenges.

White Fluorescent Carbon Dots for Specific Fe3+ Detection and Imaging Applications

In recent years, carbon dots (CDs) with fluorescence imaging function have been widely used in biomedicine, electronic manufacturing and environmental monitoring. However, monochromatic fluorescence is often limited by the application environment and loses its effectiveness. Here, we carefully designed white fluorescent CDs (WF-CDs) by solvothermal method, which is used for fluorescence imaging applications under different environmental conditions. WF-CDs based on nitrogen doping can produce obvious emission peaks at 640 nm, 490 nm and 400 nm, respectively, corresponding to red, green and blue (RGB) bands in the three primary colors. The full wavelength emission was realized by changing the solvent types and pH values to adjust the emission peak intensity. WF-CDs can accurately detect Fe3+ concentration according to fluorescence extinction degree (fluorescence elimination rate reaches 95.34 %). Furthermore, WF-CDs has practical applications in cell-level fluorescence imaging, near-infrared fluorescence imaging and ultraviolet anti-counterfeiting, and has broad application prospects in the fields of nano-medicine and industrial manufacturing.

Rapid and dual-mode nitrite detection with improved sensitivity by nanointerface-regulated ultrafast Griess assay

BACKGROUND

The rapid and sensitive detection of nitrite is important to human health protection due to its carcinogenic and teratogenic risks with excessive intake. The Griess assay is widely applied for the design of nitrite detection system. However, its relatively slow reaction kinetics and sole colorimetry mode might limit it's the sensitivity and practical application. Therefore, it is highly desirable to explore new detection method with rapid kinetics and multi-mode recognition characters.

RESULTS

We report a rapid and colorimetry and fluorimetry dual-mode sensing of nitrite by using N-(1-naphthalene)-ethylenediamine-derivated carbon dots (NETH-CDs) as the reporters. NETH-CDs show maximum excitation and emission around 359 nm and 431 nm, accompanying with a quantum yield of 27.1 %. The carbonization of NETH not only increases the fluorescence sensing mode, but also promotes the nanointerfacial Griess assay reaction kinetics within 1 min. High selectivity of dual-mode sensing is exhibited due to the specific reaction. The linear ranges in colorimetry and fluorimetry modes are 0.2-100 μM, and the corresponding limit of detection values are determined to be 0.10 and 0.08 μM, respectively. In addition, the accurate nitrite analysis in urine and serum samples with NETH-CDs nanoprobes. Moreover, the visual nitrite detection is achieved based on NETH-CD-loaded test strips.

SIGNIFICANCE

This work reports a new dual mode nitrite detection method for the first time by NETH-CDs supported ultrafast interfacial Griess assay, it not only explores sensitive nitrite detection probe, but also provides deep understanding of the relationship between chemical reaction kinetics and interfacial interaction on nanosurface. We believe our findings would benefit the exploration of rapid and sensitive detection systems toward various targets by regulating interfacial chemistry.

Design of Fluorescence Enhancing Sensor for Mercury Detection via Bamboo Cellulose-Derived Carbon Dots

Mercury contamination of the environment is extremely hazardous to human health because of its significant toxicity, especially in water. Biomass-derived fluorophores such as carbon dots (CDs) have emerged as eco-friendly and cost-effective alternative sensors that provide comparable efficacy while mitigating the environmental and economic drawbacks of conventional methods. In this work, we report the fabrication of a selective fluorescence-enhancing sensor based on sulfur-doped carbon dots (SCDs) using waste bamboo-derived cellulose and sodium thiosulfate as the soft base dopant, which actively complexes with mercury ions for detection. SCDs with an average size of 4 nm were synthesized hydrothermally, and the sulfur doping was confirmed quantitatively with an atomic percentage of 6.5%. Optical studies reveal an abnormal fluorescence enhancement of SCD in the presence of mercury due to the aggregation of carbon dots via sulfur-containing functional groups. The fabricated sensor exhibits a low detection limit of 5.16 nM, suggesting its application potential as a reliable mercury sensor. Real-time analyses carried out using tap water samples spiked with mercury and industry samples showed high efficiency for Hg(II) detection. The sensing performance was also demonstrated by using SCD-coated filter paper strips.

Smartphone-Assisted Fluorescence Determination of Inorganic Phosphorus Using a Samarium Metal-Organic Framework

Inorganic phosphori are widely used in food, whose quantitative detection method is of significance. This work presents a Sm-DDB (H4DDB = 1,3-di(3',5'-dicarboxylphenyl)benzene), which acts as a ratiometric fluorescence sensor to monitor PO43-, H2PO4-, and (PO3)66- with high sensitivity. The determination factors of pH, MOF dosage, and fluorescence response time are optimized as 7.35, 1 mg, and 2 min, respectively. The sensitivity tests show the linear fitting equations of I465/I598 = 0.00363·CP + 1.49183 (I465 and I598: the emission intensities at 465 and 598 nm; Cp = inorganic phosphorus concentration) for PO43-, I465/I598 = 0.00272·CP + 1.55944 for H2PO4-, and I465/I598 = 0.00957·CP + 1.55122 for (PO3)66- with LODs being 1.00 μM for PO43-, 1.33 μM for H2PO4-, and 0.38 μM for (PO3)66-. The detection method was applied in frozen shrimp, marine fish, and bacon, whose fluorescence recoveries of around 100% demonstrate its reliability. The analytical results are close to those determined by the phosphomolybdenum blue method. The Sm-DDB test paper shows an obvious emission color change, whose blue/red (B/R) values can be recognized by a smartphone APP. This work provides a smartphone-assisted visualization detection method for PO43-, H2PO4-, and (PO3)66-.

Carbon-dot pequi-nut in the development of immunosensor to detect pathogenic bacteria

Carbon dots in biosensing have advanced significantly, adding improvements to different detection techniques. In this study, an amperometric immunosensor for Salmonella Thyphimurium was designed using antibodies labeled with carbon dots (Cdots) from pequi almond (Caryocar brasiliensis). Cdots were synthesized by pyrolysis and characterized by FTIR, UV/fluorescence, electrochemistry, zeta potential, and transmission electron microscopy (TEM). A particle size of 6.80 ± 2.13 nm was estimated, and the zeta potential was - 47.4 mV, indicating the preponderant presence of acidic groups, as confirmed by FTIR. The impedance evaluation of the response of biosensors assembled for live (Rct = 13.4 kΩ) and dead (Rct = 499.7 Ω) Salmonella showed a significant difference in their values, in agreement with chronoamperometric analyses, which had their current values drastically reduced from - 2.2 mA (live) to 0 mA (dead). An analytical curve for Salmonella was established with the limit of detection lower than 1 CFU/mL. This electrochemical biosensor using pequi carbon dots for antibody labeling showed promising results for detecting the pathogen. Thus, carbon dots can be used as substitutes for enzymes in labeling antibodies used in the design and production of sensors.

Unlocking multi-mode sensing potential: Phosphorus-doped graphitic carbon nitride quantum dots for Ag+, ciprofloxacin, and riboflavin analysis in environment and food matrices

The simultaneous detection of multiple analytes through a single fluorescence sensor is highly attractive. In this study, phosphorus-doped graphitic carbon nitride quantum dots (P-CNQDs) were developed, achieving multi-mode sensing through three distinct response mechanisms. The preparation involved using melamine as the carbon and nitrogen source and ammonium dihydrogen phosphate as the phosphorus source. Uniform and narrowly distributed P-CNQDs were successfully synthesized through chemical oxidation and hydrothermal methods, with an average size of 2.4 nm. These unique P-CNQDs exhibited fluorescence quenching through photo-induced electron transfer (PET) in response to Ag+. Additionally, the formation of hydrogen bonds and coordination interactions between P-CNQDs-Ag+ and ciprofloxacin (CIP) led to a pronounced fluorescence response to CIP by the chelation enhanced fluorescence (CHEF) mechanism. Furthermore, leveraging the principle of fluorescence resonance energy transfer (FRET), P-CNQDs-CIP served as a ratio fluorescence sensor for riboflavin (RF), enabling ultra-sensitive detection of RF. The combination of PET, CHEF, and FRET response mechanisms successfully facilitated multi-mode sensing for Ag+, CIP, and RF. The detection ranges were 0.05-100 μM, 0.002-2 μM, and 0.05-60 μM, with corresponding lowest detection limits of 17.1 nM, 1.1 nM, and 29.2 nM, respectively. This versatile sensor has been effectively applied to real samples, including the detection of river water and vitamin B2 tablets.

d-arginine-functionalized carbon dots with enhanced near-infrared emission and prolonged metabolism time for tumor fluorescent-guided photothermal therapy

Carbon dots (CDs) have garnered significant interest owing to their distinctive optical properties. However, their bioimaging and biomedical applications are limited by pronounced fluorescence (FL) quenching in aqueous media and low tumor accumulation efficacy associated with their ultra-small size. This study proposes a simple surface modification approach using functioning d-arginine on CDs (d-Arg@CDs) to improve their near-infrared (NIR) FL in aqueous solution and maintain their high photothermal conversion properties. Because of the low utilization rate of dextral amino acids in animals, modifying CDs with low molecular weight d-arginine did not increase particle size but extended the metabolism time in blood circulation, thereby leading to enhanced accumulation efficacy at tumor sites in the mice model. The enhanced tumor accumulation of d-Arg@CDs resulted in significantly superior tumor NIR FL imaging and photothermal therapy performance compared with pure CDs and l-arginine functionalized CDs. This dextral amino acid modification approach is expected to be an effective tool for enhancing the biomedical applications of CDs.

Surface State-Based panchromatic luminescent carbon dots

Carbon dots have shown a broad application prospect in the fields of sensing and detection, biological imaging, and optoelectronic devices. However, it is still challenging to adopt a simple and green synthesis route and to develop new precursor systems to prepare full-color luminescent carbon dots. This study proposes a mechanism for fine regulation of carbon dot fluorescence spectra based on surface states of CN, COC, and OH, among which CN play a major role in long wavelength emission while COC and OH are responsible for the blue shift of emission wavelength. Using 4,4-bipyridine and p-phenylenediamine as precursors in safe and environmentally friendly glycol and water as solvents for the first time, the fine spectral carbon dots with full spectrum luminescence from purple (441 nm) to red (627 nm) were successfully synthesized by simply changing the composition of the reaction solvent and using a short reaction time. Compared with other reports on regulating polychromatic carbon dots, our method is more refined and has a wider distribution of luminescent colors. In addition, the obtained carbon dots based on such surface state luminescence mechanism have shown good application prospects in specific detection of Fe3+and cell labeling.

A smartphone-integrated ratiometric fluorescent sensor for ascorbic acid determination using microplasma-enabled carbon dots and rhodamine B

A switchable ratiometric fluorescent smartphone-assisted sensing platform based on nitrogen-doped carbon dots (N-CDs) and Rhodamine B was fabricated for the determination of the ascorbic acid (AA) content in fruits by quenching the fluorescence of N-CDs with Hg2+ (turn-off) and recovering with AA (turn-on). The blue-emission N-CDs was synthesized by liquid dielectric barrier discharge microplasma with an average size of 3.65 nm and an absolute quantum yield of 18 % (excited at 345 nm). In addition, the fluorescence color was converted to RGB values, enabling visual and quantitative determination of AA. Under optimal parameters, the linear ranges for detecting AA were found to be 3-170 μM and 5-170 μM for fluorescence spectrometer and smartphone sensing platform. The detection limits were 0.98 μM and 2.90 μM, respectively. Furthermore, the satisfactory recoveries in fruits were obtained by RF probe and smartphone platform. This smartphone-assisted platform will facilitate sensitive and visual determination for AA.

Novel quantum dots-based assay for the determination of anti-hypertensive drugs minoxidil and timolol in different matrices

The present work reports a sensitive, affordable, and ecologically friendly spectrofluorimetric method for the assessment of two antihypertensive medications, namely minoxidil and timolol. Blue-emitting sulfur and nitrogen co-doped carbon quantum dots (S,N-CQDs) were generated by exposing soluble starch and thiourea to a 15-minute microwave treatment. The so- prepared nanodots displayed fluorescence at 276/430 nm with a quantum yield of 22 %. Inspection of the so-prepared nano-sensor verified their doping with nitrogen and sulfur, and their size was in the range of 4.5-9.03 nm. The proposed method was found to be rectilinear in the range of 0.20-5.0 and 2.0-30.0 µg/mL, with LOQs of 0.16 and 0.82 µg/mL for minoxidil and timolol, respectively. The developed method was employed to assess the concentrations of minoxidil and timolol in their pharmaceutical formulations, with %recoveries varying between 99.00 % and 101.94 %, and low RSD values (less than 2 %). The high sensitivity of the developed method allowed its use for timolol measurement in artificial aqueous humor, with % recoveries between 97.60 %.and 101.57 %. The study further examined how each analyte interacted with the prepared dots, leading to a quenching of their fluorescence. Additionally, an interference study was utilized to evaluate the specificity of the proposed approach through determining analyte levels in the existence of common additives, co-formulated drugs, and co-administered drugs. The analytical eco-scale, GAPI and AGREE assessment techniques were utilized to confirm the suggested method greenness.

Safeguarding food safety: Nanomaterials-based fluorescent sensors for pesticide tracing

Pesticide residue contamination has emerged as a critical concern due to its potential negative effects on both public health and the natural environment. Consequently, the detection of pesticide residue is of utmost importance. Nanomaterial-based fluorescence sensors, including metal nanoparticles (MNPs), metal nanoclusters (MNCs), carbon dots (CDs), and quantum dots (QDs), are particularly effective for detecting pesticide residues. Herein, we provide a comprehensive review of the recent advances (2018-2024) in fluorescence-based sensors utilizing MNPs, MNCs, CDs and QDs and their composites for the purpose of detecting various pesticides including organophosphates, carbamates, organochlorines, and pyrethroids in food. This review delves into the evolution of nanomaterials, their corresponding fluorescence-based sensing mechanisms, including Förster resonance energy transfer (FRET), photoinduced electron transfer (PET), inner filter effect (IFE), aggregation induced emission (AIE), and the detection principle, focusing on aspects of sensitivity and specificity. We also address the challenges and future perspectives of nanomaterials-based fluorescence sensors.

Smart Luminescent Materials for Emerging Sensors: Fundamentals and Advances

Smart luminescent materials have drawn a significant attention owing to their unique optical properties and versatility in sensor applications. These materials, encompassing a broad spectrum of organic, inorganic, and hybrid systems including quantum dots, organic dyes, and metal-organic frameworks (MOFs), offer tunable emission characteristics that can be engineered at the molecular or nanoscale level to respond to specific stimuli, such as temperature, pH, and chemical presence. This adaptability makes them crucial in developing advanced sensor technologies for environmental monitoring, biomedical diagnostics, and industrial applications with the help of the luminescence mechanisms, such as fluorescence, phosphorescence, and upconversion. Recent advancements have been driven by the integration of nanotechnology, which enhances the sensitivity and selectivity of luminescent materials in sensor platforms. The development of photoluminescent and electrochemiluminescent sensors, for instance, has enabled real-time detection and quantification of target analytes with high accuracy. Additionally, the incorporation of these materials into portable, user-friendly devices, such as smartphone-based sensors, broadens their applicability and accessibility. Despite their potential, challenges remain in optimizing the stability, efficiency, and biocompatibility of these materials under different conditions. This review provides a comprehensive overview of the fundamental principles of smart luminescent materials, discusses recent innovations in their use for sensor applications, and explores future directions aimed at overcoming current limitations and expanding their capabilities in meeting the growing demand for rapid and cost-effective sensing solutions.

Smartphone-assisted hydrogel sensing platform based on double emission carbon dots for portable on-site tetracycline detection

Innovative double-emission carbon dots (DE-CDs) were synthesized via a one-step hydrothermal method using fennel and m-phenylenediamine (m-PD) as precursors. These DE-CDs exhibited dual emission wavelengths at 432 and 515 nm under different excitations, making them highly versatile for fluorescence-based applications. The fluorescence of the DE-CDs was efficiently quenched by tetracycline (TC) through the inner filter effect (IFE), allowing for the construction of a sensitive dual-response fluorescent sensor. This sensor demonstrated a strong exponential correlation with TC concentrations in the range 0.99-118 μM, achieving a low detection limit of 53.4 nM, which is appropriate for environmental monitoring. To further enhance its practicality, a smartphone-integrated fluorescent hydrogel film sensing platform was developed. This portable and user-friendly system enabled rapid, on-site TC detection in water samples, combining high sensitivity with convenience for real-world applications. The integration of the DE-CD-based sensor into a hydrogel platform addressed the challenge of translating laboratory precision into field-ready tools. This study revealed the potential of DE-CDs as a robust and efficient solution for bridging the gap between laboratory-based analysis and portable, on-site environmental monitoring.

N-Doped Carbon Nanodots as Temperature Sensors and Fluorescent Probes for the Detection of Tinidazole in Milk

In this study, nitrogen-doped carbon nanodots (N-CDs) with temperature and fluorescence sensing were prepared via hydrothermal method using L-lysine and ethylenediamine as precursors. The synthesized N-CDs exhibited spherical morphology with sizes ranging from 2.8 to 5.2 nm, with an average diameter of 4.03 nm. Maximum fluorescence emission was observed at 390 nm upon excitation at 320 nm, with the excitation spectrum closely overlapping the absorption spectrum of tinidazole (TNZ). In the temperature range of 20 ~ 50 °C, the fluorescence intensity of N-CDs decreased linearly with the increase of temperature. TNZ was detected based on inner filter effect (IFE) using N-CDs as a fluorescent probe. The fluorescence quenching degree had a good linear correlation with the TNZ concentration in the range of 1~100 µM (r = 0.9970), and the detection limit was 0.362 µM. In addition, the detection limits of other nitroimidazole antibiotics, including metronidazole (MNZ), Ornidazole (OMZ) and Seknidazole (SNZ), were 0.324 µM, 0.345 µM and 0.341 µM, respectively. Importantly, this method exhibits minimal interference from ions present in milk and has been validated in real milk samples, with recovery rates ranging from 92.56 to 107.27%. These results highlight the method's strong potential for application in food analysis.

Copper and nickel doped carbon dots for rapid and sensitive fluorescent turn-off detection of bilirubin

Carbon dots doped with metals and non-metals have gained much popularity due to the enhancement in their optical and electronic properties. In this study, polyethyleneimine-functionalized transition metal (nickel or copper) doped carbon dots (CD, NiCD and CuCD) were synthesized through hydrothermal method. The carbon dots exhibited a blue fluorescence at 470 nm when excited at 350 nm. The as-synthesized carbon dots were utilised for the fluorimetric detection of bilirubin in the range 0.5 µM - 280 µM, with CuCD exhibiting the highest sensitivity of 155.38 a.u/log µM in the concentration range 0.5 to 10 µM and 84.01 a.u/ log µM in the concentration range 10 to 280 µM. CuCD also exhibited the lowest limit of detection of 0.0907 µM and the lowest limit of quantification of 0.3023 µM. All the carbon dots showed negligible interference in the presence of biomolecules and metal ions present in human serum implying the remarkable selectivity of the method to bilirubin detection. Further, the carbon dots were successfully tested for their real-time application in human serum using bilirubin-spiked serum samples.

Ethylenediamine assist preparation of carbon dots with novel biomass for highly sensitive detection of levodopa

Levodopa (l-Dopa), a precursor drug for dopamine has been widely used to treat Parkinson's disease. However, excess accumulation of l-Dopa in the body may cause movement disorders and uncontrollable emotions. Therefore, it is vital to monitor l-Dopa levels in patients. In this study, a carbon dot (CD)-based fluorescence sensing system was developed for sensitive detection of l-Dopa. The CDs were prepared using a novel biomass, Pandanus amaryllifolius Roxb., as a carbon source via a simple hydrothermal method. Interestingly, it was found that ethylenediamine doping in the preparation system increased the quantum yield of CDs, as well as their fluorescence response sensitivity to l-Dopa. After optimizing the preparation and sensing conditions, the detection limit of l-Dopa decreased from 1.54 μM to 0.05 μM. A complete methodological validation was conducted and the probe was successfully applied to the determination of l-Dopa in fetal bovine serum with excellent precision (RSD ≤ 2.99%) and recoveries of 88.50-99.71%. Overall, this work provides an effective strategy for the regulation of properties of CDs derived from biomass and an innovative method for clinical l-Dopa monitoring.

Dual-recognition driven sensing platform based on a BSA-Cu NP nanozyme combined with smartphone-assistance for fluorometric/colorimetric monitoring of dopamine

Developing a highly sensitive approach for neurotransmitter analysis is of vital significance due to their essential role in clinical diagnosis and treatment of disease. Herein, bovine serum albumin templated copper nanoparticles (BSA-Cu NPs) with peroxidase-mimicking activity are designed and synthesized for dopamine detection through the fluorometric/colorimetric dual-mode technique. The experimental results suggest that as-fabricated BSA-Cu NPs can strongly catalyze the decomposition of hydrogen peroxide to produce oxidized substances, accompanied by remarkable color changes of chromogenic agent 3,3',5,5'-tetramethylbenzidine from colorless to blue, revealing peroxidase-like activities of BSA-Cu NPs. However, owing to the strong binding affinity between dopamine (DA) and BSA-Cu NPs, the catalytic activities of synthesized BSA-Cu NPs are inhibited, leading to a significant decrement of absorption peak signal. Meanwhile, the strong fluorescence of BSA-Cu NPs exhibits remarkable quenching due to photo-induced electron transfer. Besides, by integrating paper strips and smartphone software analysis, an intelligent recognition of DA is also fabricated. On the basis of these phenomena, a fluorometric/colorimetric approach based on the BSA-Cu NP nanozyme combined with smartphone-assisted analysis is constructed for detecting dopamine with a detection limit of 5 nM, and 5 nM, respectively. Moreover, the recognition of dopamine in human serum samples is also successfully realized which is verified using high performance liquid chromatography, demonstrating its promising potential in bioanalysis and clinical disease diagnosis.

Deep eutectic solvent-based magnetic molecular nanomaterials coupled with fluorescent carbon dots as a new strategy to highly enrich and sensitively detect doxycycline in food matrices

The highly selective enrichment and sensitive detection of antibiotics in food are crucial for human health, environmental monitoring, and management. In this study, deep eutectic solvents (DESs) were used as eco-friendly functional monomers, a magnetic molecular nanomaterial (DES-MMIP) coupled with carbon dots (CDs) was developed as a sensitive fluorescent probe for the selective enrichment and detection of trace amounts of doxycycline (DOX). Under optimal conditions, the method exhibited good linearity within 0.5-50 μg·L-1, a low detection limit of 0.34 nM for DOX detection. Furthermore, the DES-MMIP displayed excellent reusability and storage stability. With responsive, excellent selectivity and an eco-friendly nature, the established method is successful in detecting DOX in food matrices, with an average spiked recovery of 87.5 %-97.8 %. This strategy of integrating CDs and DES-MMIP for DOX detection conforms to the green concept of environmental protection and provides a new material and research approach for efficient analysis of DOX in complex matrices.

Redox interference-free bimodal paraoxon sensing enabled by an aggregation-induced emission nanozyme catalytically hydrolyzing phosphoesters specifically

In view of the current serious situation of organophosphorus pesticides (OPs) residue contamination, developing rapid and accurate OPs sensors is a matter of urgency. Redox-nanozyme based colorimetric sensors have been widely researched and utilized in OPs residue determination, but overcoming the interference of external redox substances and the effect of single-signal modes on detection performance is still a challenge. Here we fabricated a Zr-based metal-organic framework (MOF) featuring specific phosphatase-like activity and strong aggregation-induced emission (AIE) fluorescence for redox interference-free bimodal pesticide sensing. In the MOF, the activity-tunable Zr4+ node offered high hydrolytic activity and affinity toward P-O containing substrates, and the rigid framework structure effectively enhanced the fluorescence emission of the ligand 1,1,2,2-tetra(4-carboxylphenyl)ethylene. The developed AIEzyme could efficiently catalyze the hydrolysis of paraoxon to yellow p-nitrophenol, which further reduced the intrinsic AIE fluorescence of AIEzyme through internal filtration effect. Thereby, a natural enzyme-free dual-mode colorimetric/fluorescence approach was established for paraoxon detection with no interference from redox substances, and a smartphone-assisted portable platform was further developed to enable the facile, rapid, and high-performance sensing of the pesticide in complex practical matrices.

Fabrication of Highly Fluorescent Nitrogen and Phosphorus Dual-Doped Carbon Dots for Selective Sensing of Rutin

Based on nitrogen and phosphorus co-doped carbon dots (NP-CDs), a direct, quick, and selective sensing probe for fluorometric detection of rutin has been developed. Utilizing ethylene diamine tetra acetic acid (EDTA) as a carbon and nitrogen source and diammonium hydrogen phosphate (NH4)2HPO4 as a nitrogen and phosphorus source. The NP-CDs were synthesized in less than 3 min with a straightforward one-step microwave pyrolysis process with a high quantum yield (63.8%). After being excited at λ = 360 nm, the produced NP-CDs displayed a maximum bluish fluorescence at λem of 420 nm. Rutin quenched the fluorescence of the produced NP-CDs based on the inner filter effect and static quenching processes. Along with the International Council of Harmonization (ICH) requirements, the developed spectrofluorometric method was validated. The linearity range was 0.50-35.00 μg/mL of rutin. The developed NP-CDs were successfully employed to determine rutin concentrations in marketed tablets. The developed method is quick, simple, consistent, sensitive, and selective, and it does not require expensive chemicals or specialized instruments. This study paves the path for future application of NP-CD in pharmaceutical analysis.