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

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

A highly sensitive dual-mode detection platform based on the novel copper/molybdenum bimetallic nanoclusters and Co-Fe layered doubled hydroxide nanozyme for butyrylcholinesterase activity sensing

Herein, a novel copper/molybdenum bimetallic nanoclusters (Cu/Mo NCs) with intense blue emission were synthesized by using polyvinylpyrrolidone (PVP) as template and ascorbic acid as reducing agent. Owing to the synergistic effect between Cu and Mo, the fluorescence intensity of Cu/Mo NCs was significantly improved about 6-time than monometallic copper nanoclusters. A novel and sensitive ratiometric fluorescence and colorimetric dual-mode sensing platform for monitoring butyrylcholinesterase (BChE) was strategically constructed by the integration of Cu/Mo NCs with excellent optical properties and Co-Fe layered doubled hydroxide (CoFe-LDH) with superior peroxidase-like activity for the first time. In the presence of H2O2, nonfluorescent and colorless o-phenylenediamine (OPD) was oxidized to fluorescent and yellow 2,3-diaminophenazine (DAP) with maximum fluorescence emission peak at 564 nm and ultraviolet absorption peak at 418 nm by CoFe-LDH with peroxidase-like activity. Simultaneously, the generation of DAP could effectively quench Cu/Mo NCs fluorescence at 444 nm through the inner-filter effect (IFE). The hydrolysis of S-butyrylthiocholine iodide (BTCh) can be catalyzed by butyrylcholinesterase (BChE) to generate thiocholine (TCh) that could hinder the oxidation of OPD, leading to the fluorescence and ultraviolet absorption of DAP decreased, meanwhile, the fluorescence of Cu/Mo NCs recovered. The ratiometric fluorescence signal F564/F444 and colorimetric system both performed a satisfactory response to the concentration of BChE in the range 0.5 to 90 U L-1 and 1 to 100 U L-1 with the LOD of 0.18 U L-1 and 0.36 U L-1, respectively. The dual-mode sensing for BChE exhibited outstanding application potential in biosensing.

Ultrasensitive turn-off fluorescent sensor for estimation of the new influenza antiviral prodrug baloxavir marboxil in its pharmaceutical formulation

Carbon quantum dots (CQDs) are a recently developed class of fluorescent nanoparticles made from carbon. Co-doping with heteroatoms such as nitrogen and sulfur improved the properties and generated a high quantum yield. In the proposed study, we utilized a simple, cost-effective, single-stage hydrothermal approach to produce extreme photoluminescence co-doped, nitrogen and sulfur, CQDs (N,S-CODs). Thiosemicarbazide was used as a nitrogen and sulfur source, while citric acid was used as a carbon source to produce fluorescent probes. The prepared N,S-CQDs were subjected to extensive characterization. The generated N,S-CQDs yielded strong fluorescence emission at λ em 430.0 nm after excitation at λ ex 360.0 nm, with a relatively high quantum yield of 41.3% utilizing quinine sulfate as a reference fluorescent compound. These N,S-CQDs were applied as fluorescent nanosensors for the ultrasensitive spectrofluorimetric determination of baloxavir marboxil (BXM) directly without pre-derivatization for the first time. BXM effectively quenches the native fluorescence of N,S-CQDs. Considering the optimal conditions, the fluorescence intensity reduction of N,S-CQDs exhibited a 'turn-off' response to BXM at concentrations of 10.0-100.0 ng ml-1, with detection limits of 1.88 ng ml-1 and quantitation limits of 5.69 ng ml-1, respectively. The proposed method determined BXM successfully in its tablet dosage form and further expanded to confirm the content uniformity of the tablet units in agreement with USP guidelines.

Carbon Dot-Laponite Hybrid Nanocomposites as Selective Turn-Off Sensors for Hg2+ Detection and Photoluminescence Quenching Mechanism

Motivated by the importance of Hg2+ detection in water due to its harmful effect on the environment and human health, we investigated a recently developed nanocomposite based on carbon dots (CDs) and LAPONITE as an optical chemical sensor using photoluminescence emission. While several studies have reported the Hg2+ detection using CDs' photoluminescence emission, there is a lack of in-depth investigation into the quenching mechanisms involved in turn-off sensors. In this study, we propose a Stern-Volmer analysis at three different temperatures (288, 298, and 303 K). The results indicated selectivity for Hg2+ over that of the other evaluated metal. The optimum detection range for Hg2+ was found to be 1-40 μM, with limits of detection and quantification of 2.5 and 8.3 μM, respectively. Using the Stern-Volmer models, we found that static quenching dominates over collisional quenching, possibly due to the complexation between nanocomposite's carboxylate groups and Hg2+. Additionally, the modified Stern-Volmer model, which accounts for the fractional accessibility of the fluorophores by the quenchers, suggests that some parts of the sensor are inaccessible to the quencher.

Carbon dot-based fluorescent sensors for pharmaceutical detection: Current innovations, challenges, and future prospects

Environmental contamination by pharmaceuticals has become a matter of concern as they are released in sewage systems at trace levels, thus impacting biological systems. Increasing concerns about the low-level occurrence of pharmaceuticals in the environment demands sensitive and selective monitoring. Owing to their high sensitivity and specificity carbon dots (CDs) have emerged as suitable fluorescent sensors. This review discusses the current scenario of the status of pharmaceuticals in the environment, limitations associated with traditional techniques employed for their detection, and benefits offered by CDs like easy surface modification and tunable optical properties for sensing applications. Several representative means by which CDs interact with other molecules such as inner filter effect (IFE), dynamic quenching (DQ), static quenching (SQ), Förster resonance energy transfer (FRET), among others, are also discussed along with co-referencing fluorophores to design sensors. Based on developments described herein, CDs-based sensors can be expected to sense pharmaceuticals ranging from nanogram to picogram, target real-time industrial and spiked sample analysis, etc., which provides direction for future research.

Mechanistic insights into pH-sensitive photoluminescence of carbon dots: The role of carboxyl group

We present a mechanistic study of pH-sensitive photoluminescence (PL) in two deliberately designed systems of carbon dots (CDs), which are relatively poor and rich in carboxyl groups anchored on their surfaces, denoted CDs-COOH(p) and CDs-COOH(r), respectively. The underlying PL mechanisms for the two contrasting CD systems are revealed to be different. As for CDs-COOH(p), the pH response of PL exhibits an asymmetric volcano-shaped pattern featuring dynamic and static quenching under acidic and alkaline conditions, dominated by the effects of hydrogen bonding and non-emissive ground-state complex, respectively. As for CDs-COOH(r), however, the pH response exhibits an interesting sigmoid-shaped pattern featuring PL quenching under acidic conditions but PL enhancement under alkaline conditions, both of which become more pronounced with increasing photoexcitation energy, exhibiting a nearly symmetric trumpet-shaped pattern. Such patterns of PL response to acidity/alkalinity and photoexcitation energy can be understood in terms of the prominent effect of excited-state proton transfer that is coupled to the surface emissive centers of the carboxyl group and can be effectively modulated via pH-regulated protonation/deprotonation. Our comparative analyses of the pH-regulated surface-sensitive PL quenching/enhancement behaviors in the two CD systems allow for elucidating the different surface-state-controlled PL mechanisms, highlighting the specific role of carboxyl groups in the pH-sensitive PL of CDs. The mechanistic insights gleaned from this work would be useful for CDs-based applications such as luminescence, sensing, and bioimaging.

Fluorescent carbon quantum dots for heavy metal sensing

Many heavy metals pose significant threats to the environment and human health. Traditional methods for detecting heavy metals are often limited by complex procedures, high costs, and challenges in field monitoring. Carbon quantum dots (CQDs), a novel class of fluorescent carbon nanomaterials, have garnered significant interest due to their excellent biocompatibility, low cost, and minimal toxicity. This paper reviews the primary synthesis methods, luminescence mechanisms, and fluorescence quenching mechanisms of CQDs, as well as their recent applications in detecting heavy metals. In heavy metal sensing applications, the simplest hydrothermal method is commonly employed for the one-step synthesis and surface modification of CQDs. Various green reagents and biomass materials, such as citric acid, glutathione, orange peel, and bagasse, can be used for CQDs' preparation. Quantum confinement effects and surface defects give CQDs their distinctive luminescence properties, enabling the detection of heavy metals through fluorescence quenching or enhancement. Additionally, CQDs can be applied in biological imaging and smart detection, and when combined with adsorption materials, they can offer multifunctional capabilities. This review also discusses the future development prospects of CQDs.

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.

Curcumin-Derived (3-Aminopropyl)trimethoxysilane-Functionalized Carbon Quantum Dots: A Fluorometric and Colorimetric Nanoprobe for Picric Acid Detection, Antioxidant Activity, and Liposome Encapsulation

Creating an analytical probe to track extremely mutagenic picric acid (PA) is essential for human health and the environment. Here, we developed a straightforward and quick fluorescence analytical method utilizing 3-aminopropyltrimethoxysilane (3-APTMS)-functionalized curcumin carbon quantum dots (CQDs) for the fast and selective detection of PA. Solvothermal carbonization and functionalization of curcumin with 3-APTMS were used to create multifunctional CQDs, which were then characterized using UV-vis spectroscopy, Fourier transform infrared (FTIR), X-ray diffraction (XRD), ζ-potential, transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Our CQDs, as synthesized with an average diameter of 3.4 nm, exhibited excitation-dependent emission behavior, demonstrating 63.85% yield, 1.59% quantum yield, and fluorescence lifetime decay broader than a single exponential. The addition of picric acid significantly reduced the fluorescence (FL) emission intensity of CQDs and caused a noticeable color shift in visible as well as UV light. Throughout the 0.1-2.5 μM range, the calibration curve of the suggested assay demonstrated favorable linearity between quenched FL emission intensity and PA concentration, with the lowest detection limit of 88.96 nM. The CQD shows antioxidant activity at low concentrations (<0.07 mg/mL), measured by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay (colorimetry and electrochemically). Further, we encapsulated our CQDs in the liposome to make it biocompatible for cell imaging for future study. The results indicate the efficacy of CQDs as a nanoprobe for the selective detection of PA, retaining a few of the primary properties of natural curcumin-like antioxidant activity while having significantly higher bioavailability and water solubility; they can be used as a modifier in semiconductors for photocatalytic application and can also be a promising fluorescence probe in cell imaging.

Synthesis and applications of luminescent metal organic frameworks (MOFs) for sensing dipicolinic acid in biological and water samples: a review

The detection of trace quantities of 2,6-dipicolinic acid (DPA) in real-world samples is crucial for early disease diagnosis and routine health monitoring. Metal-organic frameworks (MOFs), recognized for their diverse structural architectures, have emerged as advanced multifunctional hybrid materials. One of the most notable properties of MOFs is their luminescence (L), which can arise from structural ligands, guest molecules, and emissive metal ions. Luminescent MOFs have shown significant promise as platforms for sensor design. This review highlights the application of luminescent MOFs in the detection of DPA in biological and aqueous environments. It provides a comprehensive discussion of the various detection strategies employed in luminescent MOF-based DPA sensors. Additionally, it explores the origins of L in MOFs, their synthesis, and the mechanisms underlying their sensing capabilities. The article also addresses key challenges and limitations in this field, offering practical insights for the development of efficient luminescent MOFs for DPA detection.

Carbon dots: synthesis, sensing mechanisms, and potential applications as promising materials for glucose sensors

The disruption of glucose (Glu) metabolism in the human body can lead to conditions such as diabetes and hyperglycemia. Therefore, accurately determining Glu levels is crucial for clinical diagnosis and other applications. Carbon dots (CDs) are a novel category of carbon nanomaterials that exhibit outstanding optical properties, excellent biocompatibility, high water solubility, low production costs, and straightforward synthesis. Recently, researchers have developed various carbon dot sensors for fast and real-time Glu monitoring. In this context, we provide a comprehensive introduction to Glu and CDs for the first time. We categorize the synthetic methods for CDs and the sensing mechanisms, further classifying the applications of carbon dot probes into single-probe sensing, ratiometric sensing, and visual detection. Finally, we discuss the future development needs for CD-based Glu sensors. This review aims to offer insights into advancing Glu sensors and modern medical treatments.

Development of silver-doped carbon dots sensor derived from lignin for dual-mode fluorometric and spectrophotometric determination of valsartan in a bulk powder and a commercial product

Doping of carbon dots (CDs) with heteroatoms has garnered growing attention in recent years as a useful method of controlling their physicochemical properties. In this study, a new dual-mode sensor based on silver-doped CDs (AgCDs) derived from lignin was developed for fluorometric and spectrophotometric determination of valsartan (VAL). The analysis of AgCDs revealed a structure that closely resembled graphene oxide, with the successful doping of Ag. The mean particle size of AgCDs was 3.50 ± 0.89 nm and it exhibited a reasonable fluorescence quantum yield of 28.1 %. The emission at 612 nm of AgCDs is quenched by VAL after being excited at 275 nm due to a combination of dynamic and static quenching mechanisms. The enhancement in the absorbance of AgCDs upon the addition of the medication was measured at 275 nm. The most favorable circumstances for the dual-mode sensing were achieved with a pH of 8 and a volume of 0.10 mL of AgCDs. The measurements were conducted using fluorometry after 3 min at 10 °C, followed by spectrophotometry after 7 min at 20 °C. The fluorometric data indicated a linear response within the range of 2.0-50.0 μg/mL, while the spectrophotometric results showed a dynamic range of 5.0-100.0 μg/mL. The limits of detection (LODs) were 0.57 and 1.38 μg/mL for the fluorometric and spectrophotometric methods, respectively. The limits of quantification (LOQs) were 1.72 and 4.19 μg/mL for the fluorometric and spectrophotometric methods, respectively. The nano sensor efficiently assessed the presence of VAL in pharmaceutical tablets and produced a favorable outcome with the mean of recovery of 98.91 % and 99.76 % with relative standard deviation (RSD%) of 0.79 and 0.78 for the fluorometric and spectrophotometric methods, respectively.

Spontaneous interactions between typical antibiotics and soil enzyme: Insights from multi-spectroscopic approaches, XPS technology, molecular modeling, and joint toxic actions

A large amount of antibiotics enters the soil environment and accumulates therein as individuals and mixtures, threatening the soil safety. However, there is little information regarding the influence of single and mixed antibiotics on key soil proteins at molecular level. In this study, setting sulfadiazine (SD) and tetracycline hydrochloride (TC) as the representative antibiotics, the interactions between these agents and α-amylase (an important hydrolase in soil carbon cycle) were investigated through multi-spectroscopic approaches, X-ray photoelectron spectrometry, and molecular modeling. It was found that both SD and TC spontaneously bound to α-amylase with 1:1 stoichiometry mainly via forming stable chemical bonds. The interactions altered the polarity of aromatic amino acids, protein backbone, secondary structure, hydrophobicity and activity of α-amylase. The SD-TC mixtures were designed based on the direct equipartition ray to comprehensively characterize the possible concentration distribution, and interactive effects indicated that the mixtures antagonistically impacted α-amylase. These findings reveal the binding characteristics between α-amylase and typical antibiotics, which probably influence the ecological functions of α-amylase in soil. This study clarifies the potential harm of antibiotics on soil functional enzyme, which is significant for the environmental risk assessment of antibiotics and their mixtures.

Facile synthesis of long-wavelength emission carbon dots for hypochlorite sensing and intracellular pH imaging

Hypochlorite (ClO-), a typical reactive oxygen species, plays an irreplaceable roles in various biological processes. In this work, long-wavelength emission carbon dots (LW-CDs) were fabricated through one-step hydrothermal method by using l-cysteine (cys) and neutral red (NR) as precursors for monitoring of hypochlorite and intracellular pH. Characterizations of as-prepared LW-CDs showed that they had excellent water solubility, high optical stability and sensitive response behavior. Fluorescence intensity of LW-CDs decayed in the presence of ClO- linearly from 10 to 162.5 μM (LOD = 1.021 μM) based on static quenching effect with ideal selectivity. Besides, LW-CDs revealed a pH responsive behavior in the pH range of 2.0 to 10.0, exhibited dual good linear relationships in the pH ranges of 4.2-5.8 and 5.8-7.4. The LW-CDs can also be utilized as imaging reagents in Hela living cells owing excellent biocompatibility and low cytotoxicity. These results demonstrated that the as-mentioned LW-CDs are expected to serve as excellent long wavelength emitting nanomaterials for fluorescence sensing and monitoring of cell fluctuations.

Development of an accurate synchronous transport signal hand-held sensing platform for fluorescence-based berberine on-site detection

BACKGROUND

Berberine is widely used in clinical treatment because of its wide antibacterial spectrum and low toxic side effects. However, its abuse could lead to bacterial resistance and several other adverse effects. In addition, measuring the content of berberine in environmental water samples helps to monitor its accumulation and metabolism in ecosystems. Traditional detection methods usually need to be carried out in the laboratory, involving complex processing procedures, which are not only time-consuming, but also unfavorable for rapid response and decision-making. Therefore, it is necessary to develop portable instruments to provide reasonable guidance on the addition and intake of berberine to reduce the harm caused by its abuse.

RESULTS

In this work, an accurate synchronous transport signal hand-held sensing platform (STSHSP) with a low-cost, easy-to-manufacture, independent use was developed by using photoelectric conversion technology, Bluetooth technology, remote synchronous signal technology, electrical technology, and 3D printing technology. To verify the performance of STSHSP, a 5-oxo-2,3-dihydro-5H-thiazolo [3,2-a] pyridine-3,7-dicarboxylic acid (TPDCA) with ultra-high quantum yield was designed and synthesized as a probe. TPDCA exhibited bright blue fluorescence under the ultraviolet light of 365 nm which could be quenched by berberine through the inner filter effect. In the range of 0.1-80 μg/mL, the voltage displayed by the prepared STSHSP has a good linearity with the berberine concentration (R2 = 0.9997) with a detection limit of 28.32 ng/mL. The portable sensor demonstrated good stability, accuracy, and reliability in detecting actual river water, urine, traditional Chinese medicine, and its preparation samples.

SIGNIFICANCE

The sensor with its compact structure, portability, and simple operation was suitable for in-situ detection with accurate, reliable, and feasible results, which is beneficial for improving drug quality and ensuring human health. Fortunately, the device could transmit the information to the control center and/or a third-party supervision institution in real-time, which could effectively eliminate the trust crisis. The sensor has broad application prospects in the field of environmental water quality detection and drug safety.

A molecular imprinted ratiometric fluorescence sensor based on blue/orange MXene quantum dots for visual detection of histamine

Histamine is a highly toxic biogenic amine in food, making its sensitive and rapid detection methods vital for the assurance of edible safety and human health. Here, we explored for the first time a smartphone-enabled ratiometric imprinted fluorescence sensor based on blue/orange MXene quantum dots (MQDs) for fluorescence and visual detection of histamine. A linear relationship between the concentration of histamine and the fluorescence response of the sensor was found in the range of 1-60 μM with a limit of detection (LOD) of 21.9 nM for fluorescence detection and 92.2 nM for visual detection. In addition, the method was validated for the detection of real samples with excellent recoveries from 96.52% to 105.32%. Therefore, this work greatly expands the application of MQDs in the fluorescence sensing field, as well as provides a visual strategy for in-situ detection of histamine in food.

Interfacial Assembly of Peptide Carbon Dot Hybrids Enables Photoinduced Electron Transfer with Improved Photoresponse

Assemblies at the interface represent a powerful tool for integrating organic and inorganic components into hybrid nanostructures. Carbon dots are both excellent electron donors and acceptors, offering opportunities for their potential uses in light-harvesting applications. To further improve their functions, integration of acceptor carbon dots into donor organic nanostructures is of great interest for improving photophysical properties useful for photoinduced electron transfer. Here, a one-step protocol for the interfacial assembly of a two-component hybrid consisting of carbon dots and perylene containing an l-phenylalanine-based dipeptide through noncovalent bonding is developed. The perylene-containing dipeptide derivative formed micrometer-long nanofibers on the water surface through J-aggregate formation. Spectroscopic studies reveal photoluminescence quenching of the donor dipeptide upon increasing the concentration of acceptor carbon dots in the hybrid, suggesting photoinduced electron transfer from the donor peptides to acceptor carbon dots. The hybrids integrated in a planar device architecture show a significantly improved photoresponse because of the favorable interactions between the donor-acceptor components. The one-step integration of donor-acceptor hybrids on the water surface offers opportunities for light harvesting and related applications.

Ampicillin-derived carbon dots as the sensitive probe for the detection of Fe3+ and Cu2+ in living cells and water samples

Water-soluble N-doped fluorescent (FL) carbon dots (ACDs) were successfully fabricated hydrothermally using ampicillin sodium as sole precursor. The produced ACDs exhibit satisfactory optical behavior, favorable photostability, and acceptable water solubility. With bright blue emission at 450 nm, the ACDs were utilized for multivariate sensing Fe3+ and Cu2+ based on the synergistic effect of the inner filter effect (IFE) and static quenching with detection limits of 0.31 μM and 0.26 μM, respectively. The practicality of ACDs has been verified by the successful determination  of Fe3+ and Cu2+ in real water and living cells. These findings confirm the feasibility of the proposed ACDs as FL sensors for efficient and selective detection of Fe3+ and Cu2+, which present promising prospects for real-time monitoring these two metal ions  in environmental and biological systems.