Facile preparation and characterization of new green emitting carbon dots for sensitive and selective off/on detection of Fe3+ ion and ascorbic acid in water and urine samples and intracellular imaging in living cells

Reductive carbon dots for reduction, ratiometric fluorescence determination, and intracellular imaging of Au3

Many studies show that ortho-phenylenediamine (OPD) produces an oxidized fluorescent product when exposed to an oxidizing agent that enables the direct or indirect fluorescence detection of a range chemical and biochemical analytes. However, there is no report on this unique optical behavior for other two isomers of phenylenediamine. This study demonstrates that a simple hydrothermal treatment of para-phenylenediamine (PPD) in the presence of sulfuric acid results in the formation of fluorescent N, S-doped carbon dots (CDs) with triple functionalities including the reduction of Au3+ into gold nanoparticles (AuNPs), the stabilization of the produced AuNPs, and the determination of Au3+ concentration through an intrinsic ratiometric fluorescence signal. In the presence of Au3+, the blue emission of CDs at 437 nm quenched, and a green emission at 540 nm emerged. The linear concentration range for the determination of Au3+ was 20 nM-16 µM with a detection limit of 16 nM. Additionally, the dual emissive CDs-AuNPs hybrid probe showed potential for the indirect fluorescence ratiometric determination of cysteine and sulfide ions. The linear concentration range for cysteine and sulfide ions were 0.25-8 μM and 0.1-6 μΜ, with detection limits of 0.095 μM and 0.041 μM, respectively. Accordingly, CDs were applied to detect Au3+ and S2- in real water samples. Moreover, the synthesized CDs showed no cytotoxicity for HeLa cells up to 300 µg mL-1, as determined by the MTT assay. Therefore, their potential for intracellular imaging of Au3+ in living cells was also investigated.

Continuous monitoring of temperature and freshness in cold chain transport based on the dual-responsive fluorescent hydrogel

Comprehensive attention should be paid to the potential food spoilage in food transport. However, there is a problem of freshness destruction by repeated freezing and thawing during the cold chain transport. Herein, a fluorescent hydrogel with N-doped green-emitting carbon dots (N-GCDs), bovine serum albumin-gold nanoclusters (BSA-AuNCs) as fluorescent probes and polyvinyl alcohol-sodium alginate hydrogel as carrier matrix was developed to continuously detect temperature and freshness. Due to the solvatochromic effect of N-GCDs, when the temperature surpassed the threshold, the mixture of water and dimethyl sulfoxide underwent a phase transition and melted into the gel, changing the fluorescence color to realize the temperature monitoring. Then, due to the pH effect of BSA-AuNCs, the gel could respond to pH changes in food deterioration to monitor the food freshness. Thus, the changes of both fluorescence color and intensity of the hydrogel provides a new method for visual and portable authenticity of food freshness.

A single atom cobalt anchored MXene bifunctional platform for rapid, label-free and high-throughput biomarker analysis and tissue imaging

Few of single-atom materials have been served as platform to analyze small molecules for surface assisted laser desorption/ionization mass spectrometry (SALDI-MS). Herein, a novel single Co atom-anchored MXene (Co-N-Ti3C2) is prepared to achieve enhanced SALDI-MS and mass spectrometry imaging (MSI) performance for the first time. The Co-N-Ti3C2 films were prepared by a simple in situ self-assembly strategy to generate an efficient SALDI-MS platform. Compared to typical inorganic/organic matrices, Co-N-Ti3C2 films exhibit superior performance in small molecules detection with ultra-high sensitivity (LOD at amol level), excellent repeatability (CV <4%), clean background and wide analyte coverage, enabling accurate quantitative analysis of various low-concentration metabolites from 1 μL biofluid in seconds. Its usage efficiently enhanced SALDI-MS detection of various small-molecule biomarkers such as amino acids, succinic acid, itaconic acid, arachidonic acid, citrulline, prostaglandin E2, creatinine, uric acid, glutamine, D-mannose, cholesterol and inositol in positive ion mode. The blood glucose level in humans was successfully determined from a linearity concentration range (0.25-10 mM). Notably, the Co-N-Ti3C2 assisted SALDI-MSI enables study the spatial distribution of small molecules covering the range central to metabolomics at a high resolution on a tissue section. Furthermore, Co-N-Ti3C2 platform revealed a specific peak profile that distinguishes osteoarthritis (OA) from rheumatoid arthritis (RA) tissue. Density functional theory theoretical investigation revealed that single Co atoms anchored on Ti3C2 could highly enhanced the ionization ability of metabolites, resulting in high-sensitivity and heterogeneous metabolome coverage.

A sensitive sensor based on carbon dots for the determination of Fe3+ and ascorbic acid in foods

To develop a feasible, sensitive, and essential sensor is important for the identification of Fe3+ ions and ascorbic acid (AA). Herein, highly fluorescent heteroatom co-doped carbon dots (N,S-CDs) with a quantum yield (QY) of 24.6% were synthesized, using hydrothermal treatment of L-cysteine (Cys) and 1-amino-2-naphthol-4-sulfonic acid (ANSA). The fluorescence emission of the as-prepared N,S-CDs was quenched strongly by Fe3+ ions, and this was further recovered by the reduction effect of AA on Fe3+. Based on this, continuous fluorescence sensing of Fe3+ and AA with an "on-off-on" style was developed. The detection of Fe3+ and AA were in relatively wider linear ranges of 5.00-105 μmol L-1 and 4.97-54.8 μmol L-1, with a detection limit of 0.10 μmol L-1 and 2.4 nmol L-1 (S/N = 3), respectively. Then, the N,S-CDs were successfully used to measure Fe3+ ions and AA in some daily food samples, and this method exhibited some advantages over most other reported techniques in the term of response speed, quantum yield, and detection limit.

Development of a fluorometric and colorimetric dual-mode sensing platform for acid phosphatase assay based on Fe3+ functionalized CuInS2/ZnS quantum dots

BACKGROUND

The spectral dual-mode response towards analyte has been attracted much attention, benefiting from the higher detection accuracy of such strategy in comparison to single signal readout. However, the currently reported dual-mode sensors for acid phosphatase (ACP) activity are still limited, and most of them more or less exist some deficiencies, such as complicated construction procedure, high-cost, poor biocompatibility, aggregation-caused quenching and limited emission capacity.

RESULTS

Herein, we employed Fe3+ functionalized CuInS2/ZnS quantum dots (CIS/ZnS QDs) as nanosensor to develop a novel fluorometric and colorimetric dual-mode assay for ACP activity, combing with ACP-triggered hydrolysis of ascorbic acid 2-phosphate (AAP) into ascorbic acid (AA). The Fe3+ binding to CIS/ZnS QDs can be reduced into Fe2+ during the determination, resulting in the dramatically weakened photoinduced electron transfer (PET) effect and the disappearance of competition absorption. Thus, a highly sensitive ACP assay in the range of 0.22-12.5 U L-1 through fluorescence "turn-on" mode has been achieved with a detection of limit (LOD) of 0.064 U L-1. Meanwhile, the ACP activity can also be quantified by spectrophotometry based on the chromogenic reaction of the formed Fe2+ with 1,10-phenanthroline (Phen). Moreover, the designed nanosensor with good biocompatibility was successfully applied to image and monitor the ACP levels in living cells.

SIGNIFICANCE

We believe that the proposed method has remarkable advantages and potential application for ACP assay in terms of the high accuracy, simplicity, low cost, as well as its adequate sensitivity.

Carbon dots-based fluorescence enhanced probe for the determination of glucose

In this work, a novel "turn-on" fluorescence sensor for the detection of H2O2 and glucose was developed based on green fluorescent carbon dots (CDs). The CDs was newly prepared by a facile one-pot hydrothermal method with Eosin Y and branched polyethylenimine as precursors. Interestingly, in the presence of H2O2 and HRP, the fluorescence of the CDs enhanced significantly with a red-shift emission due to their "aggregation". Meanwhile, the oxidation of glucose catalyzed by glucose oxidase could generate H2O2. Thus, a simple sensing system based on the CDs as fluorescent probes was constructed for H2O2 and glucose determination, avoiding the fluorescence quenching and subsequent recovery process in conventional turn-on strategy. The method showed good selectivity and sensitivity for glucose sensing with the detection limit of 0.12 μM. The method was further applied to glucose detection in real samples. The obtained results demonstrated the simplicity, selectivity and practicality of the method. This work expands the carbon nanomaterials with fluorescence emission enhancement properties. It provides a new and direct "turn-on" strategy for H2O2 and glucose detection, which could be a simple and effective tool for screening biological substances involved in H2O2-generation reaction.

Guar gum-enhanced emission of gold nanoclusters for α-glucosidase activity detection and anti-diabetic agents screening in plant extracts

The development of efficient fluorescent methods for α-glucosidase (α-Glu) detection and α-Glu inhibitor screening plays a critical role in the therapy of type 2 diabetes (T2D). Herein, guar gum (GG), a high-abundant and non-toxic natural polymer originated from the seeds of a drought-tolerant plant, Cyamposis tetragonolobus, was found to be able to enhance the fluorescence emission of gold nanoclusters (AuNCs) probe. The emission enhancement effect was achieved by using GG at very low concentrations (<1.0 wt%) and presented in a viscosity-dependent manner through increasing solvent reorientation time and inhibiting intramolecular motions of AuNCs. Furthermore, the enhanced emission of the AuNCs was quenched by Fe³⁺via dynamic quenching and then restored by α-Glu. Accordingly, a fluorimetric method was proposed for the determination of α-Glu. Owing to the fluorescence enhancement effect of GG on the AuNCs probe, the detection limit of the approach was 0.13 U L^-1 and the detection range was up to 5 orders of magnitude from 0.2 to 4000 U L^-1, which was much better than most current α-Glu detection methods. The approach was further applied to α-Glu inhibitors screening from natural plant extracts, providing great prospects for the prevention and treatment of T2D.

Preparation of carbon quantum dots from ionic liquid modified biomass for the detection of Fe3+ and Pd2+ in environmental water

A new type of green carbon quantum dots (ILB-CQDs) was prepared by hydrothermal method using ionic liquid as a modifier and grape skin as carbon source, and was obtained from hydrogen-bonded lattice structure ionic liquid preparation, which makes the CQDs in a ring-like stable structure with a stability period of more than 90 day. There is also the catalytic effect of the ionic liquid on cellulose, which makes the prepared CQDs show good advantages, such as uniform particle size, high quantum yield (26.7%), and very good fluorescence performance. This is a smart material for the selective detection of Fe³⁺ and Pd²⁺. It has a detection limit of 0.001 nM for Fe³⁺ and 0.23 µM for Pd²⁺ in pure water. It has a detection limit of 3.2 nmol/L for Fe³⁺ and 0.36 µmol/L for Pd²⁺ in actual water, both of which meet the requirements of WHO drinking water standards. And there is to achieve more than 90% of water restoration effect.

Water-soluble long afterglow carbon dots/silica composites for dual-channel detection of alkaline phosphatase and multi-level information anti-counterfeiting

Water-soluble carbon dots/silica (CDs/SiO₂) composites with an ultra-long lifetime of 846.9 ms and an ultra-high afterglow quantum yield of 12.1% were successfully obtained by incorporating CDs into a SiO₂ network. Within the aqueous solution, the SiO₂ layer isolates CDs from the surrounding oxygen. Meanwhile, hydrogen bonds and covalent bonds are formed between the CDs and SiO₂, and these bonds restrict the movement and vibration of the CDs. Accordingly, the non-radiative inactivation rate of the triplet excitons of the CDs is reduced, thereby enhancing the room-temperature phosphorescence of the CDs and triggering thermally activated delayed fluorescence. The multiple properties of the material effectively protect the CDs from the external environment, making CDs/SiO₂ emit a long afterglow in the solid and liquid phases. The prepared CDs/SiO₂ composites have exceptional stability against strong oxidants, acids, bases, and polar solvents. The composites were successfully used in the dual-optical mode detection of alkaline phosphatase, as an anti-counterfeiting ink, and in multi-level information anti-counterfeiting and encryption.

A Review on Carbon Dots: Synthesis, Characterization and Its Application in Optical Sensor for Environmental Monitoring

The development of carbon dots (CDs), either using green or chemical precursors, has inevitably led to their wide range application, from bioimaging to optoelectronic devices. The reported precursors and properties of these CDs have opened new opportunities for the future development of high-quality CDs and applications. Green precursors were classified into fruits, vegetables, flowers, leaves, seeds, stem, crop residues, fungi/bacteria species, and waste products, while the chemical precursors were classified into acid reagents and non-acid reagents. This paper quickly reviews ten years of the synthesis of CDs using green and chemical precursors. The application of CDs as sensing materials in optical sensor techniques for environmental monitoring, including the detection of heavy metal ions, phenol, pesticides, and nitroaromatic explosives, was also discussed in this review. This profound review will offer knowledge for the upcoming community of researchers interested in synthesizing high-quality CDs for various applications.

Tellurium-based chemical sensors

The various tellurium-based chemical sensors are described. This article focuses on four types of Tellurium sensors such as CdTe quantum dots-based sensor, Te thin films-based sensor, Te nanostructures or nanoparticles-based sensor, and TeO2-based sensor.

Fluorescent Carbon Dot-Supported Imaging-Based Biomedicine: A Comprehensive Review

Carbon dots (CDs) provide distinctive advantages of strong fluorescence, good photostability, high water solubility, and outstanding biocompatibility, and thus are widely exploited as potential imaging agents for in vitro and in vivo bioimaging. Imaging is absolutely necessary when discovering the structure and function of cells, detecting biomarkers in diagnosis, tracking the progress of ongoing disease, treating various tumors, and monitoring therapeutic efficacy, making it an important approach in modern biomedicine. Numerous investigations of CDs have been intensively studied for utilization in bioimaging-supported medical sciences. However, there is still no article highlighting the potential importance of CD-based bioimaging to support various biomedical applications. Herein, we summarize the development of CDs as fluorescence (FL) nanoprobes with different FL colors for potential bioimaging-based applications in living cells, tissue, and organisms, including the bioimaging of various cell types and targets, bioimaging-supported sensing of metal ions and biomolecules, and FL imaging-guided tumor therapy. Current CD-based microscopic techniques and their advantages are also highlighted. This review discusses the significance of advanced CD-supported imaging-based in vitro and in vivo investigations, suggests the potential of CD-based imaging for biomedicine, and encourages the effective selection and development of superior probes and platforms for further biomedical applications.

Reuse of waste Myrica rubra for green synthesis of nitrogen-doped carbon dots as an "on-off-on" fluorescent probe for Fe3+ and ascorbic acid detection

As one kind of high nutrition fruits, abandoned Myrica rubra causes great waste due to short storage period. For resource utilization, we herein fabricated the Myrica rubra-based N-doped carbon dots (MN-CDs) by a facile/green hydrothermal method. MN-CDs, fabricated from four regions of China, displayed significant differences in their corresponding fluorescence intensities (FIs). Interestingly, different batches of waxberry samples from the same region (Wenzhou, China) exhibited slight differences in their FIs, and also an excellent anti-photobleaching and anti-salt capacity. Based on Fe³⁺-triggered quenching effect and fluorescent recovery by redox reaction of AA and Fe³⁺, MN-CDs were employed to construct an "on-off-on" switch probe for sequential detection of Fe³⁺ and ascorbic acid (AA). Through Zeta potential, UV spectrum, Stern-Volmer equation, and valence-conduction band theory, the Fe³⁺-triggered quenching belonged to a static quenching process, which resulted from the synergistic contribution of inner filtering effect and photo-induced electron transfer mechanisms. The linear ranges for Fe³⁺ and AA detections were 1-1000 and 0.1-1000 mM. The limits of detection were 0.3 μM for Fe³⁺ in environmental waters, and 0.03 μM for AA in pharmaceutical tablets and fruit juice samples. Under 365-nm UV lamp, the color changes of test papers were easily observed from dark blue and bright blue in the presence of Fe³⁺ and AA, and thus the MN-CDs-based switch probe could be satisfactorily used for visually qualitative detection of Fe³⁺ and AA outdoor with our naked eyes. To sum up, MN-CDs not only realize resource reutilization of abandoned Myrica rubra, but also offer an convenient outdoor approach for qualitative detection of Fe³⁺ and AA in complex matrices.

Facile Preparation of Fluorescent Carbon Dots from Glutathione and l-Tryptophan for Sensitive and Selective Off/On Detection of Fe3+ Ions in Serum and Their Bioimaging Application

In the past decade, carbon dots (CDs) have attracted considerable attention due to their excellent properties such as low toxicity, good biocompatibility, good fluorescence imaging, etc. Here, glutathione and l-tryptophan were used as carbon sources to hydrothermally synthesize CDs for sensitive and selective off/on detection of Fe³⁺ ions. The CDs are spherical nanoparticles with an average particle size of 3.8 nm and the presence of organic groups such as hydroxyl, carboxyl, sulfhydryl, and amino groups on their surface. The experiment results display that Fe³⁺ ions can be selectively and sensitively detected by quenching the fluorescence of CDs. Moreover, the fluorescence of the CDs+Fe³⁺ system can be restored after adding ascorbic acid. Thus, an off/on fluorescent probe for the determination of Fe³⁺ can be formed using the as-synthesized CDs solution. The CDs show a good linear range of 0-13.89 mM and a 0.0331 μM limit of detection for Fe³⁺, and the most probable mechanism concluded from ultraviolet-visible spectroscopy, electrospray ionization-mass spectrometry, and fluorescence spectrophotometry is a mixed static and dynamic quenching. Furthermore, the cytotoxicity experiment results show that CDs have low toxicity and can be used for intracellular imaging.

Molecular Probes, Chemosensors, and Nanosensors for Optical Detection of Biorelevant Molecules and Ions in Aqueous Media and Biofluids

Synthetic molecular probes, chemosensors, and nanosensors used in combination with innovative assay protocols hold great potential for the development of robust, low-cost, and fast-responding sensors that are applicable in biofluids (urine, blood, and saliva). Particularly, the development of sensors for metabolites, neurotransmitters, drugs, and inorganic ions is highly desirable due to a lack of suitable biosensors. In addition, the monitoring and analysis of metabolic and signaling networks in cells and organisms by optical probes and chemosensors is becoming increasingly important in molecular biology and medicine. Thus, new perspectives for personalized diagnostics, theranostics, and biochemical/medical research will be unlocked when standing limitations of artificial binders and receptors are overcome. In this review, we survey synthetic sensing systems that have promising (future) application potential for the detection of small molecules, cations, and anions in aqueous media and biofluids. Special attention was given to sensing systems that provide a readily measurable optical signal through dynamic covalent chemistry, supramolecular host-guest interactions, or nanoparticles featuring plasmonic effects. This review shall also enable the reader to evaluate the current performance of molecular probes, chemosensors, and nanosensors in terms of sensitivity and selectivity with respect to practical requirement, and thereby inspiring new ideas for the development of further advanced systems.

Chitosan and κ-carrageenan-derived nitrogen and sulfur co-doped carbon dots "on-off-on" fluorescent probe for sequential detection of Fe3+ and ascorbic acid

This study develops a high sensitive and selective "on-off-on" fluorescent probe for sequential detection of iron ion (Fe³⁺) and ascorbic acid (AA) based on nitrogen and sulfur co-doped carbon dots (N, S-CDs), which were synthesized by using chitosan and κ-carrageenan as raw materials through one-step hydrothermal protocol. The synthesized N,S-CDs possess particularly high quantum yield (QY = 59.31%), excellent stability and excitation dependent behavior, showing great potential for practical applications. Furthermore, N,S-CDs provided high selectivity and strong anti-interference to Fe³⁺ due to its fluorescence quenching performance, revealing a wide linear concentration range from 1 to 100 μM for the detection of Fe³⁺ ion with an extremely low limit of detection of 57 nM, and presented reliable and accurate results in actual sample detection of Fe³⁺. The overall fluorescence quenching mechanism of N,S-CDs with Fe³⁺ was due to the formation of N,S-CDs/Fe³⁺ initiated to the aggregation and electron transfer of N,S-CDs, resulting in the static quenching of fluorescence. More interestingly, AA could reduce Fe³⁺ to Fe²⁺ and efficaciously recover the quenched fluorescence of N,S-CDs/Fe³⁺. N,S-CDs/Fe³⁺ as "turn-on" fluorescent probe was further applied for detecting AA in a linear range of 0.5-90 μM with a detection limit of 38 nM.

A yellow-emitting carbon quantum dot-based fluorescent logic gate for the continuous detection of Au3+ and biothiols

Yellow-emitting carbon quantum dots, named Y-CQDs, were synthesized from O-phenylenediamine and ethylene glycol via a one-pot hydrothermal method. A fluorescent IMPLICATION logic gate for the continuous and "on-off-on" detection of Au³⁺ and biothiols in tap water at the nanoscale level was constructed based on these QDs. It showed promise in real sample detection and also as a fluorescent ink.

Carbon Dots: Classification, Properties, Synthesis, Characterization, and Applications in Health Care-An Updated Review (2018-2021)

Carbon dots (CDs) are usually smaller than 10 nm in size, and are meticulously formulated and recently introduced nanomaterials, among the other types of carbon-based nanomaterials. They have gained significant attention and an incredible interest in the field of nanotechnology and biomedical science, which is merely due to their considerable and exclusive attributes; including their enhanced electron transferability, photobleaching and photo-blinking effects, high photoluminescent quantum yield, fluorescence property, resistance to photo-decomposition, increased electrocatalytic activity, good aqueous solubility, excellent biocompatibility, long-term chemical stability, cost-effectiveness, negligible toxicity, and acquaintance of large effective surface area-to-volume ratio. CDs can be readily functionalized owing to the abundant functional groups on their surfaces, and they also exhibit remarkable sensing features such as specific, selective, and multiplex detectability. In addition, the physico-chemical characteristics of CDs can be easily tunable based on their intended usage or application. In this comprehensive review article, we mainly discuss the classification of CDs, their ideal properties, their general synthesis approaches, and primary characterization techniques. More importantly, we update the readers about the recent trends of CDs in health care applications (viz., their substantial and prominent role in the area of electrochemical and optical biosensing, bioimaging, drug/gene delivery, as well as in photodynamic/photothermal therapy).

Providing multicolor plasmonic patterns with graphene quantum dots functionalized d-penicillamine for visual recognition of V(V), Cu (II), and Fe(III): Colorimetric fingerprints of GQDs-DPA for discriminating ions in human urine samples

In this study, a novel fluorescent probe (graphene quantum dots functionalized d-penicillamine [GQDs-DPA]) was developed for the selective identification of Cu²⁺ , V⁵⁺ , and Fe³⁺ among 26 types of metal ions, which considerably quench the fluorescence intensity of GQD. So, GQDs-DPA was applied as a simple fluorescent probe for facile metal ions recognition in standard solution. The proposed DPA-GQD supported amino acids respond to Cu²⁺ , V⁵⁺ , and Fe³⁺ , with high sensitivity. The intensity of the fluorescence histogram of this probe significantly diminished in exposure to metal ions such as Cu(II), V(V), and Fe(III). Moreover, a microfluidic paper-based device (μPAD) was fabricated through a facile and cost-effective protocol. Cu²⁺ , V⁵⁺ , and Fe³⁺ can be selectively recognized by GQDs-DPA using μPAD by naked eye. Also, GQDs-DPA exhibits a linear response for the detection of ions in concentrations ranging from 0.01 to 1 ppm, with a low limit of quantification of 0.01 ppm in standards samples. The boosted color uniformity, low instrumental needs of the stamp, and disposability of μPADs enable the application of the proposed device for commercial applications in environmental science and technology.

Simple and Sensitive Multi-components Detection Using Synthetic Nitrogen-doped Carbon Dots Based on Soluble Starch

Although carbon dots (CDs) as fluorescent sensors have been widely exploited, multi-component detection using CDs without tedious surface modification is always a challenging task. Here, two kinds of nitrogen-doped CDs (NCD-m and NCD-o) based on soluble starch (SS) as carbon source were prepared through one-pot hydrothermal process using m-phenylenediamine and o-phenylenediamine as nitrogenous dopant respectively. Through fluorescence "on-off" mechanism of CDs, NCD-m and NCD-o could be used as a fluorescence sensor for detection of Fe 3+ and Ag + with LOD of 0.25 and 0.51 μM, respectively. Additionally, NCD-m could be used for indirect detection of ascorbic acid (AA) with LOD of 5.02 μM. Moreover, fluorescence intensity of NCD-m also exhibited the sensitivity to pH change from 2 to 13. More importantly, Both NCD-m and NCD-o had potential application for analysis of complicated real samples such as tap water, Vitamin C tablets and orange juice. Ultimately, the small size of NCD-m could contribute to reinforcing intracellular endocytosis, which allowed them to be used for bacteria imaging. Obviously, these easily obtainable nitrogen-doped CDs were able to be used for multi-components detection. Strategy for synthesis of nitrogen-doped carbon dots (NCDs) and a schematic for fabrication of as-prepared NCDs for detection of Fe 3+, Ag + and ascorbic acid (AA).

Molecularly imprinted polymer grafted on paper and flat sheet for selective sensing and diagnosis: a review

Molecularly imprinted polymers are efficient and selective adsorbents which act as artificial receptors for desired compounds with the ability to recognize the size, shape, and functional groups of the compounds simultaneously. A molecularly imprinted polymer is prepared by the polymerization of functional monomers around a template (analyte) molecule. Afterward, the removal of the template from the polymer matrix leaves a selective cavity behind. The fabrication and development of molecularly imprinted polymers grew rapidly, due to their low cost, simple preparation, selectivity, sensitivity, and stable physicochemical properties. Traditionally, molecularly imprinted polymers can be synthesized using two main methods, namely bulk and surface imprinting. For more efficient use of the latter method, researchers have developed molecularly imprinted polymers grafted on the solid-phase matrix (substrate). This grafting technique would be particularly useful for surface imprinting of macromolecules, such as proteins. Cellulose fibers of papers with unique properties such as being abundant, retaining a porous structure, having good adsorption properties, and possessing hydroxyl groups naturally have gained much attention as substrate. The goal of this review is to introduce molecularly imprinted polymer-grafted or molecularly imprinted polymer-coated paper, as an interesting, simple, and efficient method in the detection and separation of small and large molecules. Therefore, in the present paper, several recent preparation techniques and applications of molecularly imprinted polymer-grafted paper are reviewed and discussed in detail. Green, cost-effective, selective, and sensitive paper-based sensor prepared via grafting molecularly imprinted polymer on paper surface with the potential use for online detection trace of analytes in the point-of-care testing.

Cancer cell identification by facile imaging of intracellular reductive substances with fluorescent nanosensor

Ascorbic acid (AA) and glutathione (GSH), the most abundant intracellular reductive substances, have been widely used as biomarkers for cancer cells identification. The current methods relying on imaging of AA or GSH alone to identify cancer cells may cause systematic errors, since a mutual conversion relationship exists between AA and GSH. In this work, we propose a fluorescent nanosensor for the simultaneous imaging of intracellular reductive substances including AA and GSH. Biocompatible fluorescent silicon nanoparticles (SiNPs) with rich surface amine and carboxyl groups were synthesized. The fluorescence of the SiNP was initially quenched by chelation of Fe³⁺ ions, forming SiNP/Fe³⁺ complex as the fluorescent nanosensor. Upon the redox reaction with reductive substances, the nanosensor showed sensitively fluorescent recovery. Moreover, benefited from the efficient cellular uptake of the SiNP/Fe³⁺ and the overexpressed intracellular reductive substances in cancer cells, the fluorescent nanosensor was used to accurately identify the human breast carcinoma (MCF-7) cells from normal mammary epithelial (MCF-10A) cells by imaging of intracellular AA and GSH simultaneously. This strategy would be promising in imaging-guided precision cancer diagnosis.

Simple and eco-friendly synthesis of crude orange-peel-derived carbon nanoparticles for detection of Fe3+ and ascorbic acid

Although fluorescence sensors based on carbon dots (CDs) have been developed widely, multicomponent detection using CDs without extra and tedious surface modification remains a challenge. Here, the crude carbon nanoparticles (CPs) as a fluorescence sensor were prepared through one-pot hydrothermal process using orange peel as the precursor. The method was simple, rapid, economical, and eco-friendly given that such extra steps as dialysis and lyophilization were not required. By adding ethanol into the reaction solvent, the fluorescence properties of orange-peel-derived CPs as well as their sensitivity of detecting Fe³⁺ with a limit of detection of 0.25 μM were improved. Additionally, orange-peel-derived CPs could be used as a fluorescence sensor for detection of ascorbic acid (AA) with a LOD of 5 μM. More importantly, the proposed fluorescence methods were successfully used to qualitatively and quantitatively analyze Fe³⁺ and AA in real samples. Recovery of Fe³⁺ from tap water was within the range 97.2-105.4%. Conversely, recovery of AA from vitamin C tablets and orange juices laid within the ranges 97.7-99.3% and 93.2-97.6%, respectively.

Dual-emission ratio fluorescence for selective and sensitive detection of ferric ions and ascorbic acid based on one-pot synthesis of glutathione protected gold nanoclusters

A fluorometric method was proposed for the determination of Fe³⁺ and ascorbic acid (AA) based on blue and red dual fluorescence emissions of glutathione (GSH) stabilized-gold nanoclusters (AuNCs). AuNCs were synthesized from GSH and tetrachloroauric acid. The fluorescence peaks of AuNCs were at 425 nm and 585 nm, respectively. In the presence of Fe³⁺, the fluorescence peak at 425 nm can be enhanced and that at 585 nm can be quenched. There is a good linear relationship between the fluorescence intensity ratio for the 425 and 585 nm peaks (F ₄₂₅/F ₅₈₅) and the concentration of Fe³⁺ in the range of 0.75-125 μM. However, when AA was added to the AuNCs-Fe³⁺ system, the value of F ₄₂₅/F ₅₈₅ decreased consistently with the concentration of AA in the range of 0.25-35 μM. The limit of detection for Fe³⁺ and AA was 227 and 75.8 nM, respectively. The interaction between AuNCs and Fe³⁺ can induce the ligand-metal charge transfer (LMCT) effect leading to the fluorescence increment at 425 nm, while AA can reduce Fe³⁺ to Fe²⁺. The production of Fe²⁺ can not enhance or quench the fluorescence of AuNCs. By comparison with previous literature, the AuNCs prepared here show two fluorescence peaks without additional fluorescence labels. Furthermore, the method was successfully applied in the determination of Fe³⁺ and AA in some real samples, such as water, human serum and tablets.

A multifunctional near-infrared fluorescent sensing material based on core-shell upconversion nanoparticles@magnetic nanoparticles and molecularly imprinted polymers for detection of deltamethrin

The construction of multifunctional sensors has attracted considerable attention due to their multifunctional properties, such as high sensitivity and rapid detection. Herein, near-infrared multifunctional fluorescent sensing materials based on core-shell upconversion nanoparticle@magnetic nanoparticle and molecularly imprinted polymers were synthesized for rapid detection of deltamethrin. The difunctional core-shell upconversion nanoparticle@magnetic nanoparticle was introduced as the optical signal and rapid separator. Firstly, the difunctional core-shell materials were prepared through solvothermal method. Then, molecularly imprinted polymers (MIPs) as recognition elements for deltamethrin were coated on the surface of upconversion nanoparticle@magnetic nanoparticle through polymerization. The structure and recognition characterizations of multifunctional fluorescent sensing materials were evaluated. Under optimal condition, the imprinting factor of sensing materials was 3.63, and the fluorescence intensity of sensing materials decreased linearly with increasing concentration of deltamethrin from 0.001 to 1 mg L^-1 with a detection limit of 0.749 μg L^-1, and a relative standard deviation of 3.10% was obtained with 5 mg L^-1 deltamethrin. The sensing materials showed a high selectivity and were successfully utilized for the detection of deltamethrin in grapes and cabbages; the results showed that the recoveries for two samples obtained were 95.6-102% and 91.8-105%.

On-off-on nanosensors of carbon quantum dots derived from coal tar pitch for the detection of Cu2+, Fe3+, and L-ascorbic acid

Novel nitrogen-doped carbon quantum dots (N-CQDs) were synthesized by a chemical oxidation method using medium-low temperature coal tar pitch as the raw material. Such quantum dots were developed as a highly sensitive fluorescent "on-off-on" switch sensor for the selective and simultaneous sensing of Cu²⁺ and Fe³⁺. The as-prepared N-CQDs, which emit blue light, were characterized by TEM images, FT-IR spectra, Raman spectroscopy, XPS analysis, fluorescence spectra, and UV-vis absorption spectra. The results showed that the N-CQDs exhibit outstanding optical properties and high optical stability within the pH range of 4-10, with a quantum yield of approximately 7%. Additionally, the material performed as an "on-off" sensor which can be dramatically extinguished by Cu²⁺ and Fe³⁺. A linear relationship between Cu²⁺ and Fe³⁺ ion concentration and fluorescence intensity was observed in the range from 0 to 50 μM. The limits of detection of the fluorescent sensor toward Cu²⁺ and Fe³⁺ were 0.16 μM and 0.173 μM, respectively. The Fe³⁺-quenched N-CQDs were restored after adding L-ascorbic acid, due to the redox reaction between Fe³⁺ and L-ascorbic acid, which resulted in the detachment of Fe³⁺ from the surface of the N-CQDs. The linear range for the detection of L-ascorbic acid was 0-28 μM. Therefore, the amount of L-ascorbic acid can be measured by using the sensing system consisting of Fe³⁺ and N-CQDs. In consequence, N-CQDs are considered an important material for the detection of Cu²⁺ and Fe³⁺ in water samples or L-ascorbic acid in drugs.

Rapid microwave-assisted green synthesis of guanine-derived carbon dots for highly selective detection of Ag+ in aqueous solution

In this work, a simple and green synthetic approach of novel guanine decorated carbon dots (G-CDs) using guanosine 5'-monophosphate and ethylenediamine through a domestic microwave oven was established for the first time. The as-prepared fluorescent G-CDs were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, UV-vis spectroscopy, and fluorescence spectroscopy. The obtained fluorescent G-CDs with a uniform morphology had desirable functional groups and excellent optical performances. Furthermore, the fluorescence intensity of G-CDs was remarkably quenched by Ag⁺ than that of other nucleotides-derived CDs. The density functional theory calculations were performed to confirm that the strong interaction of guanine-Ag⁺ was responsible for the remarkable fluorescence response of G-CDs towards Ag⁺. In addition, as a label-free fluorescence probe, the G-CDs displayed a good linear detection for highly selective Ag⁺ sensing over the range of 0-80 μM with the low detection limit of 90 nM. Therefore, the proposed G-CDs had the capacity for Ag⁺ detection in the real samples.

Iodine-doped carbon dots with inherent peroxidase catalytic activity for photocatalytic antibacterial and wound disinfection

A new type of nitrogen-iodine co-doped carbon dot (N/I-CD) was synthesized by a one-step hydrothermal method with a fluorescence quantum yield of 37%. The prepared N/I-CDs exhibit peroxidase-like activity, can catalyze bio-safety levels of H2O2 to generate hydroxyl radicals (•OH) under visible light and enhance the level of reactive oxygen species (ROS) in bacteria cells. All in vitro experiments showed that the designed system has strong photocatalytic antibacterial activity against both E. coli and S. aureus bacteria. The light-induced antibacterial function of N/I-CDs was evaluated under the conditions of changing other experimental parameters. When the visible light irradiation time was extended to 60 min, the antibacterial efficiency of N/I-CDs (0.21 mg·mL-1) against S. aureus and E. coli reached 100% in the presence of exogenous H2O2 (0.07 mM). More importantly, wound disinfection in vivo demonstrates the high antibacterial efficiency, low toxicity and application potential of good biocompatibility due to the nanozyme activity of N/I-CDs.

Red fluorescent carbon dots excited by visible light: cell imaging and visual detection of ammonia gas using PVB films

Red fluorescent carbon dots are used in cell imaging and detection of ammonia gas using PVB films under visible light.

N-doped carbon dots modified with the epithelial cell adhesion molecule antibody as an imaging agent for HepG2 cells using their ultra-sensitive response to Al3

Carbon dots (CDs) are emerging as an ideal multifunctional materials due to their ease of preparation and excellent properties in medical imaging technology, environmental monitoring, chemical analysis and other fields. N-doped CDs modified with the epithelial cell adhesion molecule antibody (anti-EpCAM-NCDs) were synthesized in an ingenious and high-output approach. Due to the fluorescence enhancement effect of the introduced N atoms, the obtained anti-EpCAM-NCDs exhibited a strong green emission with an absolute quantum yield of up to 32.5%. Anti-EpCAM-NCDs have immunofluorescent properties and an active targeting function. The fluorescence effect and fluorescence quenching of anti-EpCAM-NCDs are used to image cells and detect Al³⁺, respectively. Experimental results show that this probe exhibited a wide linear response to Al³⁺over a concentration range of 0-100μM with a detection limit and quantification limit of 3 nM and 6 nM, respectively. Significantly, anti-EpCAM-NCDs, which have negligible cytotoxicity, excellent biocompatibility and high photostability, could be used for the intracellular imaging of HepG2 cells and the detection of Al³⁺in environmental and biological samples. As an efficient multifunctional material, anti-EpCAM-NCDs hold great promise for a number of applications in biological systems.

One-pot synthesis of fluorescent non-conjugated polymer dots for Fe3+ detection and temperature sensing

The facile preparation of highly fluorescent polymer dots (PDs) still attracts substantial interest. Here, temperature/Fe³⁺ dual-responsive PDs are synthesized under mild conditions via the amidation reaction and self-assembly between hyperbranched polyethyleneimine and 5-aminosalicylic acid. The prepared PDs display strong green fluorescence with quantum yield of 15.5% and 53.3% in water and dimethylsulfoxide, respectively. The PDs also possess unique features, including excellent solubility, solvent polarity-dependent emission, remarkable photostability, as well as good salt-tolerance. Interestingly, the fluorescence intensity of PDs exhibits a reversible and sensitive response to temperature within 20-65 °C, which renders the PDs useful as a thermometer probe. Importantly, Fe³⁺ ion has the specific coordination ability toward the surface groups of PDs, leading to the aggregation and fluorescence quenching of PDs. Thus, the PDs are employed as a fluorescence probe for sensitive detecting Fe³⁺. The fluorescent intensity linearly decreases with increasing Fe³⁺ from 2 to 60 μM. Besides, Fe³⁺ concentration in river water samples is successfully assayed with this developed probe. The non-conjugated PDs with facile preparation, sensitive response to temperature and Fe³⁺ may hold potential applications in environmental monitoring.

High quantum yield photoluminescent N-doped carbon dots for switch sensing and imaging

Stable blue fluorescent nitrogen doped carbon dots (N-CDs) with a very high quantum yield up to 81% has been reported for the first time. Novel N-CDs were synthesized through an efficient and rapid one-step hydrothermal synthesis process from diethylenetriamine as nitrogen source and a novel carbon source trans-aconitic acid. The nanosized particles of N-CDs were in the range of 2-8 nm and uniformly distributed in molecular level. The N-CDs showed high selectivity toward Fe³⁺ with low detection limit of 10.42 nmol L^-1 (with corresponding linear range of 2-50 μmol L^-1) enabling them for ion detection application and also exhibited high fluorescence stability in extreme pH conditions. Novel N-CDs also presented a green emission shift under acidic condition (pH~2) which makes them a potential sensing probe for security papers, food packaging and bio-medical detection sensors. A security paper sensor device has been fabricated and its operation function has been validated by making real time detection of color. The novel and facile to manufacture carbon dots has potential applications ranging from biological nano-sensors for security document to color-switch sensing and bio-imaging.

Carbon quantum dots derived from the extracellular polymeric substance of anaerobic ammonium oxidation granular sludge for detection of trace Mn(vii) and Cr(vi)

Carbon quantum dots (CQDs) were synthesized via a hydrothermal method, in which extracellular polymeric substance (EPS) from anaerobic ammonium oxidation (anammox) granular sludge was used as a carbon precursor, while citric acid and ethylenediamine were applied as auxiliary carbon source and passivation agent, respectively. The synthesized CQDs, with orderly spherical shape and mean size of 7.15 nm, emitted blue fluorescent light under UV radiation of 365 nm. The CQDs had a high fluorescence yield (40.84%), with good water solubility and excellent spectroscopic properties. In addition, the CQDs exhibited selective, sensitive and distinctive fluorescence quenching behaviors for Cr(vi) and Mn(vii) in a PBS buffer solution (NaH₂PO₄–Na₂HPO₄) of pH 7, with a detection limit of 5.8 nM for Cr(vi) and 2.3 nM for Mn(vii). Owing to the nitrogen components from the EPS of anammox granules, the CQDs were well nitrogen-doped, promoting electron-transfer and leading to reduction between the CQDs and Mn(vii)/Cr(vi). These results indicate that CQD-based chemical sensing is a simple and efficient means for the fluorescence detection of Mn(vii) and Cr(vi).

Fluorescence detection of trace Mn(vii) or Cr(vi) by the CQDs prepared from anaerobic ammonium oxidation granular sludge.

MPA-CdTe quantum dots as "on-off-on" sensitive fluorescence probe to detect ascorbic acid via redox reaction

Mercaptopropionic acid (MPA) capped CdTe quantum dots (MPA-CdTe QDs) were synthesized in aqueous medium by hydrothermal method, which modified by Fe³⁺ could be used as a fluorescent probe to detect ascorbic acid (AA). MPA-CdTe QDs fluorescence probe could be used as successive sensor for metal ions and AA with "on-off-on" process. The fluorescence of QDs was quenched after adding Fe³⁺ to MPA-CdTe QDs. Then, the fluorescence of the Fe³⁺@MPA-CdTe QDs can be sensitively turned on by AA to give an "on-off-on" fluorescence response according to the oxidation-reduction between Fe³⁺ and AA. There was a linear relationship between fluorescence intensity quenching value and the concentration of Fe³⁺ in the range of 2-10 μM since Fe³⁺ sensitively reacted with CdTe QDs. The linear detection range for AA was 0.1-1 μM with a limit of detection of 6.6 nM. The principle is proved by fluorescence emission spectroscopy, nuclear magnetic resonance spectroscopy. The proposed method is successfully used to detect the AA in human plasma sample.

Economical, green and rapid synthesis of CDs-Cu2O/CuO nanotube from the biomass waste reed as sensitive sensing platform for the electrochemical detection of hydrazine

Reeds live widely in swamp and wetland and have an important ecological balance functions in environmental protection. However, the use of reeds is not effectively. The carbon dots (CDs) have been developed as the family of 0D nanocarbon materials and have all the advantages of the carbon family. In this work, we prepared CDs via hydrothermal method using reed. It is surprising that the reed-derived CDs are an effective reducing agent. A highly catalytically active composite material CDs-Cu₂O/CuO was synthesized using economical, green, one-step ultrasonic method and used for the detection of hydrazine. The electrochemical detection of hydrazine was investigated by cyclic voltammetry. The result shows that the CDs-Cu₂O/CuO exhibited good electrocatalytic activity for the oxidation of hydrazine. The fabricated sensor presented a wide linear range from 0.99 μM to 5903 μM and a detection limit of 0.024 μM. In addition, the CDs-Cu₂O/CuO exhibited good sensitivity, stability and repeatability. Therefore, the CDs-Cu₂O/CuO provides a new idea for the utilization of reed and low-cost electrocatalytic nanocomposite.

Two-Step Hydrothermal Preparation of Carbon Dots for Calcium Ion Detection

It is well known that the calcium ion is essential for maintaining life activities in living organisms, and it is of great significance to detect the intracellular calcium concentration. For the detection of calcium ions, we developed a new type of fluorescent carbon dots (CDs), whose surface was modified by ethylenebis(oxyethylenenitrilo)tetraacetic acid (EGTA) through a secondary hydrothermal method. This is a simple and convenient chemical preparation method because all reactions are carried out in the same autoclave, and the final product is directly the EGTA-modified CDs. The CDs exhibit bright blue fluorescence, and as the calcium concentration increases, the fluorescence intensity drops sharply. The fluorescence quenching correlates with the concentration of calcium ions and has a good linearity in the range of 15-300 μM with a detection limit of 0.38 μM. The experimental results confirmed that the detection of calcium ions by CDs is a static fluorescence quenching process. Also, cytotoxicity test and cellular imaging experiments have shown that the CDs are nontoxic and biocompatible.

Carbon dots derived from lychee waste: Application for Fe3+ ions sensing in real water and multicolor cell imaging of skin melanoma cells

Exploit of biomass as an inexhaustible resource has accepted much more curiosity to the present research world. Herein, a simple, one-step solvothermal action has been used to synthesize an ascendable amount of fluorescent carbon dots (CDs) with an average size of~3.13 nm, from Low-reasonable and green source lychee waste. The excitation/emission maxima of CDs have 365/443 nm with high quantum yield (23.5%). The present ingredient predominantly contained carboxylic acid and hydroxyl group that acted as a passive agent for stabilizing the CDs. The structural and optical properties were evaluated through HRTEM, FTIR, UV-vis, zeta potential, XPS, fluorescence, and fluorescence lifetime experiments. We investigated the manoeuvre of our synthesized CDs as a probe for detection of Fe³⁺ ions in water bodies; This sensing approach showed impressive selectivity and sensitivity towards Fe³⁺ions with LOD 23.6 nM. The sensing mechanism took place through static quenching which was entrenched through fluorescence lifetime measurements. Fe³⁺ ions detection was basically carried out with efficacy in real water. For its lofty Photo-stability, low cytotoxicity and cell viability the probe were substantially applied for bio-imaging experiment i.e. intracellular multi-color cell imaging in skin melanoma cells (A375 cells) with and without Fe³⁺ ions exemplifying its real applications in living cells.

Synthesis of Multicolor Carbon Dots Based on Solvent Control and Its Application in the Detection of Crystal Violet

The adjustment of the emitting wavelength of carbon dots (CDs) is usually realized by changing the raw materials, reaction temperature, or time. This paper reported the effective synthesis of multicolor photoluminescent CDs only by changing the solvent in a one-step solvothermal method, with 1,2,4,5-tetraaminobenzene as both the novel carbon source and nitrogen source. The emission wavelengths of the as-prepared CDs ranged from 527 to 605 nm, with quantum yields (QYs) reaching 10.0% to 47.6%, and it was successfully employed as fluorescence ink. The prepared red-emitting CDs (R-CDs, λ_em = 605 nm) and yellow-emitting CDs (Y-CDs, λ_em = 543 nm) were compared through multiple characterization methods, and their luminescence mechanism was studied. It was discovered that the large particle size, the existence of graphite Ns, and oxygen-containing functional groups are beneficial to the formation of long wavelength-emitting CDs. Y-CDs responded to crystal violet, and its fluorescence could be quenched. This phenomenon was thus employed to develop a detection method for crystal violet with a linear range from 0.1 to 11 µM and a detection limit of 20 nM.

Microwave-assisted Synthesis of N,S-co-carbon Dots as Switch-on Fluorescent Sensor for Rapid and Sensitive Detection of Ascorbic Acid in Processed Fruit Juice

To achieve a rapid, sensitive, and economical method for the detection of ascorbic acid (AA) in the presence of Fe³⁺, a nitrogen and sulfur co-doped carbon dots (N,S-co-CDs) based fluorescence sensing system was developed. In this work, N,S-co-CDs were successfully synthesized via a one-step microwave-assisted method within 2.5 min using ammonium citrate and L-cysteine as precursors. The fluorescence of N,S-co-CDs was quenched (off ) by Fe³⁺ through a static-quenching mechanism. Subsequently, the fluorescence was recovered (on) after introducing AA into the quenched system, which was attributed to the reduction effect of AA for Fe³⁺. Therefore, a switch-on sensor (N,S-co-CDs/Fe³⁺ system) was developed for AA detection. Under optimal conditions, the limit of detection (LOD) of 2.31 μmol/L for AA was obtained over a linear range from 0 to 150 μmol/L. Furthermore, the proposed sensing method was successfully applied to detect AA in processed fruit juice with satisfactory results. The most important is that the sensor derived from a microwave-assisted method has simple and eco-friendly synthesis processes, is rapid, and has high detection efficiency. Therefore, such a switch-on sensor may be a promising candidate sensor for AA detection in processed fruit samples.