Fluorescence tuning behavior of carbon quantum dots with gold nanoparticles via novel intercalation effect of aldicarb

Development of a novel HPLC-CDCL method utilizing nitrogen-doped carbon dots for sensitive and selective detection of dithiocarbamate pesticides in tea

In this study, S-methyl derivatives of dithiocarbamates (DTCs) were shown to significantly enhance chemiluminescence (CL) between Ce(IV) and efficient and environmentally friendly nitrogen-doped carbon dots (NCDs). Based on the elucidation of the CL mechanisms, an innovative approach involving high-performance liquid chromatography coupled with N-CDs and CL detection (HPLC-CDCL) was proposed. The developed method was successfully applied to the highly sensitive detection of three DTC fungicides (dimethyl dithiocarbamate, ethylene bisdithiocarbamate, and propylene bisdithiocarbamate) in tea. The recovery of the established method ranged 70.51-116.45%, with relative standard deviations (RSD) of <9.40%. The limit of detection (S/N = 3) was as low as 0.19 μg/L (as CS2), which is superior to the previous methods and comparable to UPLC-tandem mass spectrometry (MS/MS). Moreover, the proposed approach does not require solid-phase extraction and offers excellent selectivity. This study proposes a novel method for the detection of DTCs in the food safety and environmental fields.

Polyvinyl alcohol-derived-carbon quantum dots based fluorometric "On-Off" probe for moxifloxacin detection in milk and egg samples

Unconditional use of antibiotics triggered the process of bacterial resistance and causes major health problems. Nowadays, antibiotics majorly used in animals not only for infection treatment but also as mass promotor. The excess amount of antibiotics residue in animal derived foods which accelerate antibiotic resistance (ABR). So, here, a simple and quick carbon quantum dots(CQDs) based fluorometric "On-Off" probe was developed for detection of moxifloxacin (MOXI) in milk and egg samples. The CQDs emits blue emission and are uniformly distributed with average particle size 5.9 ± 0.22 nm. With MOXI, fluorescence intensity of CQDs at 372 nm decreased due to inner filter effect (IFE) and a new peak appeared at 508 nm correspondence to MOXI. The probe shows linear response with MOXI concentration varies as 0.025 µM - 15.0 µM with lower detection limit (LOD) of 6.34 nM. The real sample applicability test proved that the sensors have excellent efficacy for food applications.

Fluorescence enhancing and quenching signal based on new approach for selective detection of multiple organochlorine pesticides using blue emissive-carbon dot

Measuring the concentration of organochlorine pesticides (OCPs) in agriculture has engaged significant awareness for healthcare investigation since OCPs are harmful to many physiological processes. Excessive usage of these compounds can result in major contamination of the environment and food supply chains. As a result, more accurate and rapid ways to detect pesticide residues in food are required. In this work, we have portrayed the surface-engineered fluorescent blue emissive-carbon dot (B-CD) with a high quantum yield (49.3 %) via the hydrothermal method for fluorescent sensing of OCPs on real samples. The amine group functionalities of carbon dots have supported the direct coordination with -Cl and -OH groups of HEP, ENS, CDF and 2,4-DPAC for the sensitive detection of OCPs, by switching in the fluorescent intensity of B-CD. The functional group of OCPs exhibits a variety of binding interactions with B-CD to contribute a complex formation, which leads to static quenching via an insubstantial restricted electron transfer process. The synthesized carbon dots exhibit individuality in binding nature towards different OCPs. Fluorescence studies help to distinguish the target OCPs and their low detection limits (LODs) were 0.002, 0.099, 0.16 and 0.082 μM for Heptachlor (HEP - turn "on"), Endosulfan (ENS), Chlordimeform (CDF) and 2,4-dichlorophenoxyacetic acid (2,4-DPAC - turn "off") OCPs respectively. The real water samples and agriculture food samples were effectively investigated and the OCP toxicity was noted. Thus, the design of the fluorescence sensor is established as an easy and proficient sensing method for detecting OCPs.

Structural Features of Carbon Dots and Their Agricultural Potential

Carbon dots (CDs) have drawn attention due to their enticing physical, chemical, and surface properties. Besides, good conductivity, low toxicity, environmental friendliness, simple synthetic routes, and comparable optical properties are advantageous features of CDs. Further, recently, CDs have been explored for biological systems, including plants. Among biological systems, only plants form the basis for sustainability and life on Earth. In this Review, we reviewed suitable properties and applications of CDs, such as promoting the growth of agricultural plants, disease resistance, stress tolerance, and target transportation. Summing up the available studies, we believe that the applications of CDs are yet to be explored significantly for innovation and technology-based agriculture.

A highly sensitive fluorescence nanosensor for determination of amikacin antibiotics using composites of carbon quantum dots and gold nanoparticles

Amikacin is an aminoglycoside antibiotic widely used to treat various bacterial infections in humans. However, elevated concentrations of amikacin can damage the cochlear nerve. Thus, accurate and rapid amikacin detection is crucial. In this study, we developed an "on-off" fluorescence nanosensor for highly sensitive amikacin determination based on a composite of carbon quantum dots (CQDs) and gold nanoparticles (AuNPs). The method quenches CQD fluorescence (turn-off) when they bind to AuNPs but restores it (turn-on) when amikacin binds and releases the CQDs. Adding Cu2+ enhances sensitivity by cross-linking amikacin-coated AuNPs. Under optimal conditions (pH 4, 1 mM Na2SO4, 1 mM CuSO4), the method achieved a low detection limit of 3.5 × 10-11 M (0.02 ppb), a wide linear range (10-10 to 10-8 M), high precision (RSD < 5 %), and a rapid 2-minute response time. Exceptional selectivity was observed over other antibiotics. The CQDs/AuNPs-based sensor successfully detected amikacin in pharmaceutical and surface water samples. This approach offers a fast on-site analytical method for amikacin detection, with potential applications in clinical and environmental settings.

Gold@Carbon Quantum Dots Nanocomposites Based Two-In-One Sensor: A Novel Approach for Sensitive Detection of Aminoglycosides Antibiotics in Food Samples

Antibiotics are life-saving drugs for humans, but their unwanted use leads to antibacterial resistance (ABR) and causes serious health problems. The excess of these antibiotics entered to the food chain and caused food contamination. Here, Au@CQDs nanocomposites (NCs) was used as a two-in-one sensor to detect two antibiotics. The color change of AuNCs and fluorescence resonance energy transfer are two distance-dependent phenomena used as sensing mechanisms. In the sensing process, Au@CQDs NCs change their color, enhancing the fluorescence intensity of NCs in the presence of Gentamicin (GENTA) and Kanamycin (KMC) antibiotics. The limit of detection of 116 nM and 133 nM for GENTA and 195 nM and 120 nM for KMC have been achieved with colorimetric and fluorimetric readout, respectively. The practicality of the reported sensor was evaluated in real spiked samples and showed excellent recovery efficiency. Therefore this two-in-one sensor can be used for the food monitoring system.

A smart ratiometric fluoresence and colorimetry dual-responsive sensor for morin determination based on the complex between carbon quantum dots and polyethyleneimine

As a representative flavonoid, morin exhibits multi-biological activities, but its abuse endangers human health. Developing advanced technology for morin determination is urgently needed. In this study, a dual-responsive approach was reported for morin based on the complexing of carbon quantum dots (CQDs) and polyethyleneimine (PEI). The CQDs were fabricated via an improved hydrothermal method employing tyrosine and malic acid. Binding with PEI induced an 8-fold emission enhancement and a slight red-shift to 445 nm of CQDs because of the complexing of PEI and CQDs. Further morin introduction led to the blue emission (445 nm) quenching of CQDs-PEI and a yellow emission (560 nm) generation, which contributed a ratiometric fluorescence approach for morin determination between 2.0 and 32 μM, with a limit of detection (LOD) of 45 nM. Meanwhile, under sunlight the color of CQDs-PEI became yellow upon morin addition, which developed a colorimetric method for morin determination in a wide range between 2.0 and 100 μM (LOD = 69 nM). The developed dual-responsive method either displayed accurate results for morin in diluted human and bovine serum, being potential for actual sample analysis. Finally, a visual detection based on the smartphone was constructed and applied for the real-time determination of morin.

A dual-mode ratiometric fluorescence and smartphone-assisted colorimetric sensing platform based on bifunctional Fe,Co-CQD for glucose analysis at physiological pH

Diabetes is a common and fatal chronic metabolic disease characterized by hyperglycemia, and thus monitoring blood glucose level is essential for early screening and timely control of disease. Herein, we have prepared the bifunctional iron and cobalt co-doped carbon quantum dot (Fe,Co-CQD) with good optical properties and peroxidase-mimetic catalytic activity toward specific substrate o-phenylenediamine (OPD) under alkaline condition. Glucose oxidase (GOx) specifically catalyzes the oxidation of glucose into H₂O₂, and Fe,Co-CQD subsequently triggers a reaction between H₂O₂ and OPD to form yellow product DAP with a distinct UV absorption peak at 420 nm. Simultaneously, the generated DAP also appears a well-defined fluorescence signal at 555 nm, which can suppress the intrinsic fluorescence peak of Fe,Co-CQD (439 nm) owing to the inner filter effect (IFE). Based on this principle, a dual-mode ratiometric fluorescence and colorimetric sensing platform has been constructed for glucose analysis at physiological pH, which reveals the advantages of excellent accuracy, high throughput, simple operation, and low cost. More importantly, a smartphone-assisted colorimetric sensing system based on a portable visual detection kit and a 3D printing smartphone-based device has been constructed, which enables on-site detection of glucose in complex serum samples without laboratory instruments, indicating its potential practical application prospect.

A fluorescent probe based on FRET effect between carbon nanodots and gold nanoparticles for sensitive detection of thiourea

Illegal abuse results in the presence of thiourea (TU) in soil, wastewater, and even fruits, which is harmful for the environment and human health. It has urgent practical significance to design an efficient and reliable probe for TU detection. Herein, a sensitive fluorescent probe with off-on response for harmful TU was reported. The probe was designed with fluorescent carbon nanodots (CNDs) and gold nanoparticles (AuNPs) based on fluorescence resonance energy transfer (FRET) effect. Firstly, the CNDs were pre-combined with AuNPs and the fluorescence of CNDs was quenched due to the FRET effect. Upon addition of TU, the fluorescence of CNDs recovered due to the unbinding of CNDs and AuNPs, since the coordination interaction between TU and AuNPs is stronger than the electrostatic interaction among CNDs and AuNPs. Under the optimum parameters, a linear relationship was found between the relative fluorescence intensity of the probe and the concentration of TU in the range of 5.00 × 10^-8-1.00 × 10^-6 M (R² = 0.9958), with the limit of detection (LOD) calculated to be 3.62 × 10^-8 M. This proposed method is easy to operate and has excellent selectivity and sensitivity for TU, which can be effectively applied in environmental water and compound fruit-vegetable juice.

Electrospinning membranes with Au@carbon dots: Low toxicity and efficient antibacterial photothermal therapy

As bacterial infections continue to pose a significant challenge to healthcare globally, new therapeutic strategies, interventions, and complementary approaches that address both infection prevention and treatment are needed. As one such strategy, photothermal therapy (PTT) as a non-chemotherapeutic approach is considered a safe and potentially efficient strategy to combat bacterial infections, particularly for antibiotic-resistant pathogens given that PTT operates via a temperature-dependent process against which the development of bacterial resistance is unlikely. Here, we prepared Au@CDs composite nanoparticles (Au@CD) comprised of gold nanoparticles (AuNPs) and carbon dots (N,S-CDs), and investigated their use as a photothermal agent in PTT. The presence of the CDs as surface decorations conferred improved photothermal conversion efficiency, photostability, and biocompatibility to the Au@CD when compared to the parent AuNPs. To investigate if the Au@CD could serve as a PTT wound dressing and accelerate tissue repair, they were embedded within a PVA membrane via electrospinning. The resultant Au@CD membrane exhibited excellent biocompatibility and photothermal antimicrobial activity. In vitro photothermal antibacterial inactivation studies confirmed their efficacy against S. aureus and E. coli (99 + % inactivation of both pathogens under NIR irradiation). Moreover, in vivo studies employing Kunming male mice with S. aureus-infected wounds on their backs were chosen as a trauma model, with the Au@CD membranes serving as wound dressings. The results showed that a local temperature increased up to 50 °C upon NIR irradiation could effectively eradicate bacteria at the wound site, reduce the risk of bacterial infection, suppress inflammation as well as improve collagen deposition and angiogenesis, all of which together facilitated wound closure and resulted in a better therapeutic effect than the controls. Taken together, this work confirms that NIR-irradiated Au@CD-based membranes and related materials are promising photothermal antimicrobial platforms for wound dressings and related healthcare applications.

Enhanced detection of ascorbic acid with cascaded fluorescence recovery of a dual-nanoquencher system

An innovative strategy with target-triggered cascade fluorescence recovery of a dual-nanoquencher system was developed to detect ascorbic acid (AA). Herein, manganese dioxide (MnO₂) nanosheets and gold nanoparticles (AuNPs) were used as nanoquenchers simultaneously. Owing to their synergistic effects, the fluorescence of 2,3-diaminophenazine (DAP) was decreased efficiently, thus minimizing the background fluorescence. The introduction of AA triggered the decomposition of MnO₂ into Mn²⁺, which induced the aggregation of AuNPs. Both the decomposed MnO₂ and aggregated AuNPs possess weak quenching abilities towards DAP. Such a cascade amplification strategy enhanced the detection sensitivity for AA with a LOD as low as 6.7 nM, which was two orders of magnitude lower than that of MnO₂-based fluorescence assay. Furthermore, this amplification strategy was successfully applied to detect AA in food samples.

Hapten designs based on aldicarb for the development of a colloidal gold immunochromatographic quantitative test strip

The common carbamate insecticide aldicarb is considered one of the most acutely toxic pesticides. Herein, rational design was used to synthesize two haptens with spacers of different carbon chain lengths. The haptens were then used to immunize mice. The antibodies obtained were evaluated systematically, and a colloidal gold immunochromatographic strip was developed based on an anti-aldicarb monoclonal antibody. The 50% inhibition concentration and linear range of anti-aldicarb monoclonal antibody immunized with Hapten 1 were 0.432 ng/mL and 0.106–1.757 ng/mL, respectively. The cross-reactivities for analogs of aldicarb were all <1%. The limit of detection of the colloidal gold immunochromatographic strip was 30 μg/kg, and the average recoveries of aldicarb ranged from 80.4 to 110.5% in spiked samples. In the analysis of spiked samples, the test strip could accurately identify positive samples detected by the instrumental method in the GB 23200.112-2018 standard but produced some false positives for negative samples. This assay provides a rapid and accurate preliminary screening method for the determination of aldicarb in agricultural products and environments.

Colorimetric and fluorescent probes for the rapid detection of profenofos in farmland system

Colorimetric and fluorescent sensors were developed for the detection of profenofos. The colorimetric assay relied on the aggregation of cysteine modified gold nanoparticles (Au-cys) composite caused by the hydrogen bond and Au-S bond between profenofos and Au-cys. The further addition of S, N-doped carbon quantum dots (CDs) (fluorescence quantum yield up to 98%) into the Au-cys system depended on the change of fluorescence intensity of Au-cys-CDs owing to the inner filter effect between Au-cys and CDs. Under the optimal conditions, the sensor exhibits good linearity within 0.2-1.2 mg L^-1 and 20-320 μg L^-1, and limit of detection of 21.7 μg L^-1 and 5.5 μg L^-1 in colorimetry and fluorescence mode, respectively. The developed sensor did not only possess favorable selectivity and sensitivity, but also feasibility of usage in the actual detection of profenofos in farmland system samples.

Rapid qualitative and quantitative detection of Salmonella typhimurium using a single-step dual photometric/fluorometric assay

A dual-signal photometric/fluorometric assay was established for rapid, qualitative, and quantitative detection of Salmonella typhimurium (S. typhimurium). This method was composed of two parts: (1) a single-step photometric (SSC) assay containing gold nanoparticles (AuNPs), poly-diallyldimethylammonium chloride (PDDA), and S. typhimurium-specific aptamer, and (2) a fluorescence (FL) assay containing carboxyl-modified CdSe/ZnS quantum dots (QDs-_COOH). Users just need to drop samples contaminated with S. typhimurium into SSC assay; the apparent color change from red to blue can be observed in a short time (20 min). A smartphone app was developed to read the semiquantitative result. By subsequently adding one drop of FL assay into the reaction mixture, the generated fluorescence intensity reflected the concentration of S. typhimurium. The naked eye limit of detection (LOD) and fluorescent LOD were 10³ cfu/mL and 10 cfu/mL, respectively. This method exhibited good selectivity. The reliability and practicability were verified by testing contaminated food, drinking water, and pets' urine.

Green synthesis of fluorescent carbon nanospheres from chrysanthemum as a multifunctional sensor for permanganate, Hg(II), and captopril

A simple and green method for the synthesis of fluorescent carbon nanospheres (CNs) was proposed using chrysanthemum as a natural precursor and ethylenediamine as the co-reagent. The prepared CNs show strong blue fluorescence in water with quantum yield of 13.7 %, and distinguished fluorescent stability against photobleaching and ion strength. Meanwhile, the fluorescence signal of CNs is reversible and sensitive to temperature in the range of 20-80 °C, which makes CNs useful as a temperature sensor. More importantly, the CNs can serve as excellent fluorescent sensors for detecting MnO₄^- and Hg²⁺ with the detection limit of 0.72 and 0.26 μM, respectively. MnO₄^- quenches the fluorescence of CNs through inner filter effect and static quenching mechanism, while Hg²⁺ forms a stable complex with the amino group on the surface of CNs, resulting in the fluorescence quenching of CNs. However, the stronger affinity between Hg²⁺ and captopril (Cap) results in the fluorescence quenched by Hg²⁺ recovery after the addition of Cap. Thus, the CNs-Hg²⁺ system is employed as a novel sensitive and selective fluorescence "turn-on" sensor for Cap in the range of 0-75 μM. Inspired by the sensing results, the developed sensors were successfully used for the determination of MnO₄^-, Hg²⁺ in river water samples and Cap in the pharmaceutical and urine samples.

"Off-on" fluorescence probe based on green emissive carbon dots for the determination of Cu2+ ions and glyphosate and development of a smart sensing film for vegetable packaging

An ultra-sensitive glyphosate nanosensor, based on carbon dots (CDs), was successfully developed with excellent long-wavelength emission (530 nm), a high quantum yield (41.3%), and an impressive detection limit (0.8 ng·mL-1). This is the lowest value for glyphosate detection achieved by CD-based fluorescence analysis. The sensor was derived from a separate precursor, 1,4-dihydroxyanthraquinone, and was based on the "off-on" fluorescence analysis, where Cu2+ acts as a dynamic quencher and glyphosate as a fluorescence restorer (excitation wavelength 460 nm). Trace detection of glyphosate is possible with a wide detection range of 50-1300 ng·mL-1 and spiked recoveries between 93.3 and 110.0%. Exploration in depth confirmed that (1) the fluorescence of CDs was derived from the carbon core, (2) the large sp2 conjugated domain consisting of graphitic carbon and nitrogen contributed to the long-wavelength emission, and (3) CDs had an impressive binding interaction with Cu2+, which endow high sensitivity to glyphosate detection. The nanosensor has also be used as a dual-mode visual sensor and a smart sensing membrane that can identify glyphosate on the surface of vegetables, thus showing good practical applicability. Synthetic methods of G-CDs and its detection mechanisms for glyphosate.

A Competitive Assay Based on Dual-Mode Au@Pt-DNA Biosensors for On-Site Sensitive Determination of Carbendazim Fungicide in Agricultural Products

Carbendazim (CBZ), a systemic, broad-spectrum benzimidazole fungicide, is widely used to control fungal diseases in agricultural products. Its residues might pose risks to human health and the environment. Therefore, it is warranted to establish a rapid and reliable method for its residual quantification. Herein, we proposed a competitive assay that combined aptamer (DNA) specific recognition and bimetallic nanozyme gold@platinum (Au@Pt) catalysis to trace the CBZ residue. The DNA was labeled onto bimetallic nanozyme Au@Pt surface to produce Au@Pt probes (Au@Pt-DNA). The magnetic Fe₃O₄ was functionalized with a complementary strand of DNA (C-DNA) to form Fe₃O₄ probes (Fe₃O₄-C-DNA). Subsequently, the CBZ and the Fe₃O₄ probes competitively react with Au@Pt probes to form two Au@Pt-DNA biosensors (Au@Pt-ssDNA-CBZ and Au@Pt-dsDNA-Fe₃O₄). The Au@Pt-ssDNA-CBZ biosensor was designed for qualitative analysis through a naked-eye visualization strategy in the presence of CBZ. Meanwhile, Au@Pt-dsDNA-Fe₃O₄ biosensor was developed to quantitatively analyze CBZ using a multifunctional microplate reader. A competitive assay based on the dual-mode Au@Pt-DNA biosensors was established for onsite sensitive determination of CBZ. The limit of detection (LOD) and recoveries of the developed assay were 0.038 ng/mg and 71.88-110.11%, with relative standard deviations (RSDs) ranging between 3.15 and 10.91%. The assay demonstrated a good correlation with data acquired from liquid chromatography coupled with mass spectrometry/mass spectrometry analysis. In summary, the proposed competitive assay based on dual-mode Au@Pt-DNA biosensors might have a great potential for onsite sensitive detection of pesticides in agro-products.

Graphene Quantum Dot-Based Optical Sensing Platform for Aflatoxin B1 Detection via the Resonance Energy Transfer Phenomenon

An optical sensing platform for the detection of an important mycotoxin, aflatoxin B1 (AFB1), in the absence of a bioactive environment is explored. In this work, a fluorescence-based sensing technique was designed by combining graphene quantum dots (GQDs) and AFB1 via fluorescence quenching, where AFB1 acts as the quencher of GQD fluorescence. GQDs were synthesized through a single-step hydrothermal reaction from the leaves of "curry tree" (Murraya Koenigii) at 200 °C. The fluorescent GQDs were quenched by AFB1 (quencher), which itself is detecting the analyte. Hence, this study reports the direct sensing of the mycotoxin AFB1 without the involvement of inhibitors or biological entities. The possible mode of quenching is the nonradiative resonance energy transfer between the GQDs and the AFB1 molecules. This innovative sensor could detect AFB1 in the range from 5 to 800 ng mL^-1 with a detection limit of 0.158 ng mL^-1. The interferent study was also carried out in the presence of different mycotoxins and carbohydrates (d-fructose, cellulose, and starch), which demonstrated the high selectivity and robustness of the sensor in the complex sample matrix. The recovery percentage of the spiked samples was also calculated to be up to 106.8%. Thus, this study reports the first GQD based optical sensor for AFB1.

Recent advances in synthesis and modification of carbon dots for optical sensing of pesticides

Serious threat from pesticide residues to the ecosystem and human health has become a global concern. Developing reliable methods for monitoring pesticides is a world-wide research hotspot. Carbon dots (CDs) with excellent photostability, low toxicity, and good biocompatibility have been regarded as the potential substitutes in fabricating various optical sensors for pesticide detection. Based on the relevant high-quality publications, this paper first summarizes the current state-of-the-art of the synthetic and modification approaches of CDs. Then, a comprehensive overview is given on the recent advances of CDs-based optical sensors for pesticides over the past five years, with a particular focus on photoluminescent, electrochemiluminescent and colorimetric sensors regarding the sensing mechanisms and design principles by integrating with various recognition elements including antibodies, aptamers, enzymes, molecularly imprinted polymers, and some nanoparticles. Novel functions and extended applications of CDs as signal indicators, catalyst, co-reactants, and electrode surface modifiers, in constructing optical sensors are specially highlighted. Beyond an assessment of the performances of the real-world application of these proposed optical sensors, the existing inadequacies and current challenges, as well as future perspectives for pesticide monitoring are discussed in detail. It is hoped to provide powerful insights for the development of novel CDs-based sensing strategies with their wide application in different fields for pesticide supervision.

“Turn on” Fluorescence Sensor of Glutathione Based on Inner Filter Effect of Co-Doped Carbon Dot/Gold Nanoparticle Composites

Glutathione (GSH) is a thiol that plays a significant role in nutrient metabolism, antioxidant defense and the regulation of cellular events. GSH deficiency is related to variety of diseases, so it is useful to develop novel approaches for GSH evaluation and detection. In this study we used nitrogen and phosphorus co-doped carbon dot-gold nanoparticle (NPCD–AuNP) composites to fabricate a simple and selective fluorescence sensor for GSH detection. We employed the reductant potential of the nitrogen and phosphorus co-doped carbon dots (NPCDs) themselves to form AuNPs, and subsequently NPCD–AuNP composites from Au3+. The composites were characterized by using a range of spectroscopic and electron microscopic techniques, including electrophoretic light scattering and X-ray diffraction. The overlap of the fluorescence emission spectrum of NPCDs and the absorption spectrum of AuNPs resulted in an effective inner filter effect (IFE) in the composite material, leading to a quenching of the fluorescence intensity. In the presence of GSH, the fluorescence intensity of the composite was recovered, which increased proportionally to increasing the GSH concentration. In addition, our GSH sensing method showed good selectivity and sensing potential in human serum with a limit of detection of 0.1 µM and acceptable results.

Fabrication of a 2D metal-organic framework (MOF) nanosheet colloidal system and investigation of its fluorescence response to pesticide molecules

Pesticides, as a type of toxic chemicals widely used for a long time, not only pollute the environment but also affect people's health and cause serious harm to the human body, soil and environment. Therefore, it is very necessary to exploit a portable and environmentally friendly method to detect pesticides with high sensitivity. Herein, a new luminescent metal-organic framework ([Zn(TPYBDC)·H₂O]_n, TPYBDC^2- = 4'-(pyridin-4-yl)-[2,2':6',2''-terpyridine]-4,4''-dicarboxylate) with 2D coordination layers has been designed and assembled using 4'-(pyridin-4-yl)-[2,2':6',2''-terpyridine]-4,4''-dicarboxylic acid as the ligand. The as-synthesized Zn-LMOF was exfoliated to ultrathin 2D nanosheets (4-5 nm) to form a luminescence colloidal sensor by destroying the weak interaction between the coordination layers such as H-bonding between the matrix H₂O and the coordination carboxyl oxygen, and the π-π interactions among the interlayer conjugated aromatic rings. Investigation of its recognition and detection ability towards chemical pesticides shows that it can sensitively detect pesticides such as imidacloprid, nitenpyram and dinotefuran via fluorescence quenching effect with very low detection limit (LOD). Using imidacloprid as a typical case, a LOD value of 0.562 μM and recoveries for the simulated agricultural environmental samples in the range of 94-115% suggests that the as-fabricated 2D Zn-MOF nanosheet colloidal sensor (Zn-LMOF probe) is a most promising candidate for sensing chemical pesticides.

A Review of Green Synthesis of Metal Nanoparticles Using Algae

The ability of algae to accumulate metals and reduce metal ions make them a superior contender for the biosynthesis of nanoparticles and hence they are called bio-nano factories as both the live and dead dried biomass are used for the synthesis of metallic nanoparticles. Microalgae, forming a substantial part of the planet's biodiversity, are usually single-celled colony-forming or filamentous photosynthetic microorganisms, including several legal divisions like Chlorophyta, Charophyta, and Bacillariophyta. Whole cells of Plectonema boryanum (filamentous cyanobacteria) proved efficient in promoting the production of Au, Ag, and Pt nanoparticles. The cyanobacterial strains of Anabaena flos-aquae and Calothrix pulvinate were used to implement the biosynthesis of Au, Ag, and Pt nanoparticles. Once synthesized within the cells, the nanoparticles were released into the culture media where they formed stable colloids easing their recovery. Lyngbya majuscule and Chlorella vulgaris have been reported to be used as a cost-effective method for Ag nanoparticle synthesis. Dried edible algae (Spirulina platensis) was reported to be used for the extracellular synthesis of Au, Ag, and Au/Ag bimetallic nanoparticles. Synthesis of extracellular metal bio-nanoparticles using Sargassum wightii and Kappaphycus alvarezi has also been reported. Bioreduction of Au (III)-Au (0) using the biomass of brown alga, Fucus vesiculosus, and biosynthesis of Au nanoparticles using red algal (Chondrus crispus) and green algal (Spyrogira insignis) biomass have also been reported. Algae are relatively convenient to handle, less toxic, and less harmful to the environment; synthesis can be carried out at ambient temperature and pressure and in simple aqueous media at a normal pH value. Therefore, the study of algae-mediated biosynthesis of metallic nanoparticles can be taken toward a new branch, termed phyco-nanotechnology.

A colorimetric and fluorescence turn-on probe for the detection of ascorbic acid in living cells and beverages

A colorimetric and fluorescence turn-on dual-signal assay was developed for the determination of ascorbic acid (AA). Because the ultraviolet absorption of the oxidized 3,3',5,5'-tetramethylbenzidine (oxTMB) overlapped with the fluorescence emission of glutathione stabilized Au nanoclusters (AuNCs), the fluorescence of AuNCs can be quenched by oxTMB. When AA was added, the blue oxTMB was reduced to colorless TMB, and the fluorescence of AuNCs was restored simultaneously. The decrease in absorbance and increase in fluorescence signal depended on the concentration of AA. In the determination range of 0.5 to 200 μM, the detection limits (LOD) for AA were as low as 0.15 µM and 0.22 µM for fluorometric and colorimetric, respectively. The established probe was used successfully for AA detection in living cells and beverages.

Highly Sensitive and Selective Detection Toward Melamine in Dairy Product by Turn-On Fluorescence of Ultrathin Graphitic Carbon Nitride Nanosheet

It is meaningful and promising to develop a practical sensor toward melamine in dairy products with high sensitivity and selectivity. However, complicated composition and environment in milk necessitate stable luminophore as sensor with excellent photophysical properties. Herein, ultrathin graphitic carbon nitride nanosheet (CNNS) is prepared via successive thermal polymerization and acid exfoliation. The photophysical property of CNNS states its strong ultraviolet absorption and intense blue-light emission. Noteworthily, the CNNS could act as a chemo-sensor to detect trace melamine in dairy products. The high stability, eminent sensitivity, powerful selectivity and competitiveness substantiates that this CNNS luminophore is a promising sensor for melamine in dairy products, being of potentially practical value on monitoring milk quality.