Construction of Cyan Blue Fluorescence Probe based on Nitrogen-Doped Carbon Dots for Detecting Nitrite Ion in Ham Sausage.

Nitrite ion is one of the materials widely used in human life, and the accurate, sensitive and stable detection of nitrite ions is of great significance to people's healthy life. In this study, nitrogen-doped fluorescent carbon dots (N-CDs) for detecting nitrite salt solutions were prepared using citric acid monohydrate and Chrysoidin as precursors through a one-pot hydrothermal method. Under the condition of pH = 3, a noticeable quenching phenomenon occurred in the carbon dot solution with the increase in nitrite ion concentration. This quenching effect might be attributed to the diazonium effect. N-CDs have been successfully used as fluorescence probes for NO2- detection. NO2- can effectively quench the fluorescence intensity of N-CDs, providing a linear response to fluorescence quenching efficiency with respect to NO2- concentration within the range of 0-10µM and 10-30µM, and a detection limit of 52nM, showing high sensitivity. In addition, the probe was applied to the determination of NO2- in ham sausage samples with a detection limit of 0.67µM and recoveries in the range of 99.5-102.3%, the fluorescent probe showed satisfactory reliability.

o-phenylenediamine Derived Fluorescent Carbon Quantum dots for Detection of Hg(II) in Environmental Water.

With the expansion of human activities, the consequent influx of mercury (Hg) into the food chain and the environment is seriously threatening human life. Herein, nitrogen and sulfur co-doped fluorescent carbon quantum dots (yCQDs) were prepared via a hydrothermal method using o-phenylenediamine (OPD) and taurine as precursors. The morphological characteristics as well as spectral features of yCQDs indicated that the photoluminescence mechanism should be the molecular state fluorophores of 2, 3-diaminophenothiazine (oxOPD), which is the oxide of OPD. The as-synthesized yCQDs exhibited sensitive recognition of Hg2+. According to the investigation in combination of UV-Vis absorption spectra, time-resolved fluorescence spectra and quantum chemical calculations, the abundant functional groups on the surface of yCQDs allowed Hg2+ to bind with yCQDs through various interactions, and the formed complexes significantly inhibited the absorption of excitation light, resulting in the static fluorescence quenching of yCQDs. The proposed yCQDs was utilized for Hg2+ sensing with the limit of detection calculated to be 4.50 × 10- 8 M. Furthermore, the recognition ability of yCQDs for Hg2+ was estimated in tap water, lake water and bottled water, and the results indicated that yCQDs have potential applications in monitoring Hg2+.

Nitrogen and Sulfur co-doped Carbon dots as an "on-off-on" Fluorescent Sensor for the Detection of Hg2+ and Ampicillin.

Herein, a fluorescent "on-off-on" nanosensor based on N,S-CDs was developed for highly precise and sensitive recognition of Hg2+ and ampicillin (AMP). Nitrogen and sulfur co-doped carbon dots with blue fluorescence were synthesized by one-pot hydrothermal method using ammonium citrate and DL-methionine as precursors. N,S-CDs exhibited a surface abundant in -OH, -COOH, and -NH2 groups, aiding in creating non-fluorescent ground state complexes when combined with Hg2+, leading to the suppression of N,S-CDs' fluorescence. Subsequent to additional AMP application, the mixed system's fluorescence was restored. Based on this N,S-CDs sensing system, the thresholds for detection for AMP and Hg2+ were discovered to be 0.121 µM and 0.493 µM, respectively. Furthermore, this methodology proved effective in identifying AMP in real samples of tap and lake water, yielding satisfactory results. Consequently, in the area of bioanalysis in intricate environmental sample work, the sensing system showed tremendous promise.

Investigation of the Application and Mechanism of Nitrogen and Phosphorus Co-doped Carbon Dots for Mercury Ion Detection.

In this paper, we obtained nitrogen and phosphorus co-doped carbon dots through a hydrothermal method using o-phenylenediamine and citric acid in a 40% phosphoric acid environment. The carbon dots emitted fluorescence at 476 nm under excitation at 408 nm and exhibited good selectivity and high sensitivity towards mercury ions. These carbon dots showed excellent dispersibility in water and maintained stable fluorescence even in high concentration salt environments. The interaction between mercury ions and functional groups on the carbon dots surface through electrostatic interaction resulted in static quenching. Simultaneously, by detecting the lifetime and transient absorption spectra of the carbon dots, we observed that the coordination of mercury ions with the carbon dots broadened the band structure of the carbon dots, and the existing photoinduced electron transfer process increased the non-radiative transition channel. The combined effect of dynamic quenching and static quenching significantly reduced the fluorescence intensity of the carbon dots at 476 nm. The carbon dots exhibited linear detection of mercury ions in the range of 0.01-1 µM, with a detection limit as low as 0.0245 µM. In terms of practical water environmental detection applications, these carbon dots were able to effectively detect mercury ions in tap water and lake water, demonstrating their broad application prospects in the field of environmental metal analysis.

Non-enzymatic Detection of Uric Acid in Serum and Urine by Fluorescent and Visual Dual-Mode Sensor Based on 3-aminophenylboric Acid Functionalized Carbon Dots.

Herein, we developed a sophisticated dual-mode sensor that utilized 3-aminophenylboric acid functionalized carbon dots (APBA-CDs) to accurately detect uric acid (UA). Our innovative process involved synthesizing APBA-CDs that emitted at 369 nm using a one-step hydrothermal method with 3-aminophenylboric acid and L-glutamine as precursors, ethanol and deionized water as solvents. Once UA was introduced to the APBA-CDs, the fluorescence of the system became visibly quenched. The results of Zeta potential, Fourier transformed infrared (FTIR) spectra, fluorescence lifetime, and other characteristics were analyzed to determine that the reaction mechanism was static quenching. This meant that after UA was mixed with APBA-CDs, it combined with the boric acid function on the surface to form complexes, resulting in a decrease in fluorescence intensity and a blue shift in the absorption peak at about 295 nm in the Ultraviolet-visible (UV-vis) absorption spectra. We were pleased to report that we have successfully used the dual-reading platform to accurately detect UA in serum and human urine. It provided a superior quantitative and visual analysis of UA without the involvement of enzymes. We firmly believe that our innovative dual-mode sensor has immense potential in the fields of biosensing and health monitoring.

Dual-mode colorimetric and fluorescent detection of cobalt ions based on N, B co-doped carbon quantum dots and p-phenylenediamine derived nanoparticles.

Nitrogen, boron co-doped carbon quantum dots (gCQDs), and a coloration probe (PPD-NPs) with response to cobalt ions (Co2+) were prepared by using 4-hydroxyphenylboric acid as the common precursor, with ethylenediamine and p-phenylenediamine (PPD) adopted as nitrogen-doped reagents, respectively. A noticeable brown-to-purple color change can be observed with the addition of Co2+, and a broad absorption band emerges at 535 nm. At the same time, gCQDs, which is introduced as the fluorescence signal source, will be significantly quenched due to the enhanced inner filtration effect, induced by the overlap between the emission spectrum of gCQDs and the emerging absorption band. Therefore, a colorimetric/fluorescent dual-mode sensing probe for Co2+ is constructed by combining the recognition unit PPD-NPs and the fluorescent gCQDs into PPD-NP/gCQD. Under the optimized experimental conditions, the calculated limits of detection are 1.51 × 10-7 M and 3.75 × 10-7 M for the colorimetric mode and the fluorescence mode, respectively, well qualified for the determination of Co2+ maximum permitted level in drinking water. The feasibility of the proposed method has been verified in tap water, lake water, and black tea samples.

Ratiometric fluorescence probe based on carbon dots and p-phenylenediamine-derived nanoparticles for the sensitive detection of manganese ions.

A ratiometric fluorescence probe based on carbon quantum dots with 420 nm emission (bCQDs) and a p-phenylenediamine-derived fluorescence probe with 550 nm emission (yprobe) is constructed for the detection of Mn2+. The presence of Mn2+ results in the enhanced absorption band at 400 nm of yprobe, and the fluorescence of yprobe is significantly enhanced based on the chelation-enhanced fluorescence mechanism. The fluorescence of bCQDs is then quenched based on the inner filtration effect. The ratio (I550/I420) linearly increases with the increase of Mn2+ concentration within 2.00 × 10-7-1.50 × 10-6 M, and the limit of detection is 1.76 × 10-9 M. Given the fluorescence color changing from blue to yellow, the visual sensing of Mn2+ is feasible based on bCQDs/yprobe coupled with RGB value analysis. The practicability of the proposed method has been verified in tap water, lake water, and sparkling water beverage, indicating that bCQDs/yprobe has promising application in Mn2+ monitoring.

Detection of mercury(II) and glutathione using a carbon dots-based "off-on" fluorescent sensor and the construction of a logic gate.

In this paper, we proposed an efficient method for mercury(II) and glutathione detection using a fluorescent nanoprobe as a sensor. Carbon dots were synthesized from polyethyleneimine and ammonium citrate via a one-step hydrothermal method. The fluorescence of carbon dots was quenched since electron transfer occurred due to the interaction between mercury(II) and functional groups on the surface of carbon dots. Adding glutathione to the carbon dots-mercury(II) system, the fluorescence was recovered due to the stronger binding ability of glutathione to mercury(II). Based on the above-mentioned principle, this "off-on" fluorescent sensor can easily achieve the detection of mercury(II) and glutathione, which provided limits of detection of 22.45 nM and 61.89 nM, respectively. In this paper, the proposed method has been applied to detect mercury(II) and glutathione in real lake water and serum, respectively, and a logic gate for sensing glutathione was presented. The developed "off-on" fluorescent sensor with high sensitivity and selectivity has shown great potential for mercury(II) and glutathione detection in environmental and biosensing fields.

Regulation of aggregation-induced emission properties of Ag(0)@Ag(I) rich-thiolate core-shell nanoclusters: Ligand assembly dominated.

Aggregation-induced emission (AIE) is an effective strategy for improving the photoluminescence (PL) performance of metal nanoclusters (MNCs). However, the origin of AIE in MNCs is still not fully understood, which is pivotal for the design of AIE luminogens (AIEgens). Here, water soluble silver nanoclusters (Ag NCs) with AIE properties were synthesized. These as-synthesized non-luminescent Ag NCs will become photoluminescent when transferred from water to ethanol, and the emission peak was redshifted from ∼560 to ∼600 nm and largely intensified with the addition of Cu2+. The addition of Cu2+ makes a big difference in the PL properties of Ag NCs. That is, the PL will be enhanced if Cu2+ is added with the sequence "Ag NCs + Cu2++EtOH." In contrast, the PL will be quenched if Cu2+ is added with the sequence "Ag NCs + EtOH + Cu2+." The PL was from the supramolecular clusters formed by the assembly of capping ligands on the confined surface of individual silver clusters through weak interactions. The addition of Cu2+ could regulate the assembly structure and further affect the energy lever (p-band) through space electron interactions. These results provide new insights into the AIE process in metal nanoclusters.

Hydrated Hydroxide Complex Dominates the AIE Properties of Nonconjugated Polymeric Luminophores.

Nontraditional intrinsic luminescence (NTIL) which always accompanied with aggregation-induced emission (AIE) features has received considerable attention due to their importance in the understanding of basic luminescence principle and potential practical applications. However, the rational modulation of the NTIL of nonconventional luminophores remains difficult, on account of the limited understanding of emission mechanisms. Herein, the emission color of nonconjugated poly(methyl vinyl ether-alt-maleic anhydride) (PMVEMA) can be readily regulated from blue to red by controlling the alkalinity during the hydrolysis process. The nontraditional photoluminescence with AIE property is from the new formed p-band state, resulting from the strong overlapping of p orbitals of the clustered O atoms through space interactions. Hydrated hydroxide complexes embedded in the entangled polymer chain make big difference on the clustering of O atoms which dominates the AIE property of nonconjugated PMVEMA. These new insights into the photoluminescence mechanism of NTIL should stimulate additional experimental and theoretical studies and can benefit the molecular-level design of nontraditional chromophores for optoelectronics and other applications.

Synthesis and photoluminescence properties of orange-red carbon dots from the paper tissues as the precursor.

In recent years, stable and photoluminescence (PL) tunable fluorescent materials known as carbon dots (CDs) have seen rapid development. Here, a simple, low-cost, and environmentally friendly approach has been developed to synthesize the orange-red CDs (OR-CDs) with paper tissues as the precursor in the presence of ethanol and concentrated sulfuric acid. The average diameter of the OR-CDs was measured at around 1.25 nm. The as-prepared OR-CDs are composed of carbon cores with the graphite structure distributed in the middle and wrapped or entangled by polymers for the outside. Moreover, the PL characteristics of the OR-CDs under the dilute solution state and the concentrated solution state, respectively, were explored. The former with the blue light showed prominent excitation-dependent characteristics in the range from 365 to 420 nm; the latter rendered the excitation-independent property with distinguished orange-red fluorescence emission. With an increase in the concentration, the emission fluorescence intensities gradually increased under the excitation wavelength of 540 nm, which can be attributed to the aggregation-induced emission property of the OR-CDs. By virtue of their excellent PL properties and low toxicity, we believe that the OR-CDs have potential applications in various optoelectronic areas, especially in white LED fields.

Dendritic and Core-Shell-Corona Mesoporous Sister Nanospheres from Polymer-Surfactant-Silica Self-Entanglement.

Mesoporous nanospheres are highly regarded for their applications in nanomedicine, optical devices, batteries, nanofiltration, and heterogeneous catalysis. In the last field, the dendritic morphology, which favors molecular diffusion, is a very important morphology known for silica, but not yet for carbon. A one-pot, easy, and scalable co-sol-gel route by using the triphasic resol-surfactant-silica system is shown to yield the topologies of dendritic and core-shell-corona mesoporous sister nanospheres by inner radial phase speciation control on a mass-transfer-limited process, depending on the relative polycondensation rates of the resol polymer and silica phases. The trick was the use of polyolamines with different catalytic activities on each hard phase polycondensation. The self-entanglement of phases is produced at the {O- , S+ , I- } organic-surfactant-inorganic interface. Mono- and biphasic mesoporous sister nanospheres of carbon and/or silica are derivatized from each mother nanospheres and called "syntaxic" because of similar sizes and mirrored morphologies. Comparing these "false twins", or yin and yang mesoporous nanospheres, functionalized by sulfonic groups provides evidence of the superiority of the dendritic topologies and the absence of a shell on the diffusion-controlled catalytic alkylation of m-cresol.

Sensitive Detection of Polycyclic Aromatic Molecules: Surface Enhanced Raman Scattering via π-π Stacking.

We report silver nanoparticles (Ag NPs) with high stability, sensitivity, and no surface enhanced Raman scattering (SERS) background. The Ag NPs were synthesized via a one-step process with polysodium styrenesulfonate (PSSS) templates, and they could efficiently adsorb polycyclic aromatic molecules via π-π stacking. The adsorption mechanisms and applicability were systematically studied by experimental measurements and theoretical simulations. When the polycyclic aromatic analytes were adsorbed on the PSSS-templated Ag NPs, the vibrations of π-π stacking-bound moieties were attenuated, yet those of the other unbound aromatic moieties increased. Most importantly, when the analytes had more than two π-π stacking binding sites, the PSSS-templated Ag NPs could trap the analytes by focusing through the optical force induced or via the simultaneously formed analyte-Ag NPs aggregates. This afforded high SERS intensity and very low detection limits.

[Precise and Rapid Detection of Glutathione by Using Novel Fluorescent Ag Nanoclusters].

Glutathione (GSH) is an important three-peptide molecule, which has the functions of antioxidation and detoxification, and plays a crucial role in the fields of biology, medicine and food science. It is involved in many important biochemical reactions in cells and body fluid, and the changes of GSH content reflect the specific health problems of human body. Current methods of GSH detection are always complicated, time-consuming and expensive instrument depended, such as surface enhanced Raman spectroscopy (SERS), electrochemical analysis, high performance liquid chromatography (HPLC) and so on. The probe's photochemical properties can be modified by the reaction between GSH and nanoclusters, which will result in the changes of fluorescence intensity and wavelength. In this paper, a new method to realize precise and rapid GSH detection is developed by using silver na-noclusters as a fluorescent probe, and simultaneously measures the probe's fluorescence intensity and wavelength. The synthesis of the fluorescence probe reported in this paper possesses the advantages of steps-simple and pollution free, and the GSH detection method has faster response, more accurate measurement and smaller relative error over the traditional methods. The good specificity of GSH detection among other molecules with the similar structure is further proved in control group experiments by comparing the differences of their fluorescence intensities and wavelength. The measurement accuracy is fully assured due to the insensitivity of the probe to a variety of salt ions and amino acids. This technique can be further employed in the intracellular detection and imaging of GSH.

Photoemission mechanism of water-soluble silver nanoclusters: ligand-to-metal-metal charge transfer vs strong coupling between surface plasmon and emitters.

Using carboxylate-protected silver nanoclusters (Ag-carboxylate NCs) as a model, we separately investigated the contribution of the ligand shell and the metal core to understand the nature of photoluminescence of Ag NCs. A new Ag(0)NCs@Ag(I)-carboxylate complex core-shell structural model has been proposed. The emission from the Ag-carboxylate NCs could be attributed to ligand-to-metal-metal charge transfer from Ag(I)-carboxylate complexes (the oxygen atom in the carboxylate ligands to the Ag(I) ions) to the Ag atoms and subsequent radiative relaxation. Additionally, we found that the emission wavelength of the Ag NCs depends on the excitation wavelength implying a strong coupling between surface plasmon and emitter in Ag NCs. The strong coupling between the surface plasmon and the emitter determines the quantum yield and lifetime. The emission mechanism of Ag NCs and its relation to the organic templates and metal cores were clearly clarified. The results should stimulate additional experimental and theoretical research on the molecular-level design of luminescent metal probes for optoelectronics and other applications.

Carbon quantum dots as a turn-on fluorescent probe for the sensitive detection of Cd2.

In this study, fluorescent carbon dots were synthesized for the first time using ammonium citrate and glutamic acid as precursors via a one-pot hydrothermal method. The synthesized carbon dots emit blue fluorescence at 436 nm (excited at 320 nm) and demonstrate excellent photobleaching resistance and fluorescence stability in high salt environments. Within the range of 1-25 µM, the fluorescence of CDs gradually increases with the increasing concentration of Cd2+, reaching a limit of detection as low as 13 nM. This phenomenon could be ascribed to the chelation-enhanced fluorescence, a result of Cd2+ forming complexes with the abundant surface functional groups such as CN-, -COOH, -OH, -NH2 in CDs. Furthermore, this turn-on fluorescent probe has been successfully used for the detection of Cd2+ in tap water and lake water, providing an efficient and sensitive method for the analysis of environmental metals.

SERS substrate based on COF@Ag for detecting amoxicillin in honey and lake water.

This study presents the design of a Surface-enhanced Raman scattering (SERS) substrate, COF@Ag, for the sensitive detection of Amoxicillin (AMX) in lake water and honey. Furthermore, the study investigates the role of covalent organic frameworks (COFs) in SERS detection. The characterization results demonstrate the capability of COFs to efficiently enrich Ag nanoparticles (AgNPs), resulting in a more concentrated distribution of hotspots and an enhanced electromagnetic field on the substrate. By employing density functional theory (DFT) simulation, the frontier electronic orbitals of COFs and AMX were analyzed, and the chemical bonds and weak interactions in the system were examined using the Interaction Region Indicator (IRI) method to propose potential enhancement mechanisms. In aqueous solutions, the linear range is 1 µg/L-30 µg/L, with a limit of detection (LOD) 0.279 µg/L. In lake water, the linear range span from 100 µg/L to 500 µg/L, with a detection limit of 8.244 µg/L. For honey, the linear range extend from 20 ng/g to 100 ng/g, with a detection limit of 2.917 ng/g. This method holds key significance in facilitating the rapid detection of amoxicillin and advancing the application of COFs in SERS.

Boric acid-functionalized silver nanoparticles as SERS substrate for sensitive and rapid detection of fructose in artificial urine.

The accurate detection of fructose in human urine can help prevent and screen for diseases such as fructokinase deficiency and hereditary fructose intolerance. Surface-enhanced Raman spectroscopy (SERS) is an analytical technique with selectivity and high sensitivity, which has been widely applied to the detection of targets with complex backgrounds. In this work, 4-mercaptophenylboronic acid (4-MPBA) was modified on the surface of silver nanoparticles (AgNPs) under mild conditions to obtain a boronic acid-functionalized SERS substrate for the detection of fructose in artificial urine. The detection mechanism was based on the deboronization reaction of 4-MPBA on the surface of AgNPs, which was induced by fructose, and the Raman signal of the generated thiophenol (TP) molecules was significantly enhanced by the silver nanoparticles, with a linear increase in SERS peak intensity at 1570 cm-1. We achieved the detection limits of 0.084 µmol/L in water and 0.535 µmol/L in urine by this method. The relative standard deviation (RSD) in the recovery experiments of urine ranged from 1.01 % to 2.22 %, and the whole detection time was less than 10 min, which indicated that this method is highly reliable for fructose detection and has a good prospect in bioassay and clinical medicine.

Effect of Zn2+ on emodin molecules studied by time-resolved fluorescence spectroscopy and quantum chemical calculations.

Emodin is a natural drug for treating neurodegenerative diseases and plays a vital role in the mitigation of nerve damage. Metal ions can modify the drug properties of emodin, where Zn2+ can synergize with the emodin molecule and enhance the drug effect of emodin. Besides, complex changes can be observed in the fluorescence intensity and fluorescence lifetime of the emodin molecule as the concentration of Zn2+ increases. Herein, the synergistic effects of ligand structural in Zn(II)-Emodin complexes and the electronic effects of metal elements on the antioxidant properties of the complexes are discussed in detail based on UV-vis absorption spectroscopy, fluorescence spectroscopy, time-correlated single photon counting (TCSPC) technique and quantum chemical calculations at the B3LYP/6-31G(d) level. The experimental results confirm that Zn2+ can coordinate with the hydroxyl groups on the emodin to make the molecule structure more rigid, thus inhibiting the non-radiative processes such as high-frequency vibrations of the emodin molecule in solution. The suppression of non-radiative processes leads to an increase in the average fluorescence lifetime of the emodin molecule, and finally results in the enhanced fluorescence intensity. The chemical softness of Zn(II)-Emodin is then confirmed to be higher than that of emodin by Gaussian calculations, indicating its higher chemical reactivity and lower stability. The stronger electron donating ability of Zn(II)-Emodin compared to emodin may explain the higher antioxidant activity of Zn(II)-Emodin, which gives it a stronger pharmacological activity. The results of this study show that emodin can well complex with Zn2+ to remove excess Zn2+ in human body and the resulting complex has better antioxidant properties, which helps to understand the role of Zn2+ in drug-metal coordination and provides guidance for the design of new drugs.

Al2O3@Ag composite structure as SERS substrate for sensitive detection of sodium thiocyanate.

Sodium thiocyanate (NaSCN) can be added to fresh milk to enhance the sterilization ability of the lactoperoxidase system (LP system) in milk, extending shelf life. However, excessive intake of NaSCN can be harmful to human health because it can prevent absorption of iodine leading to disease. Also NaSCN can be used as a marker to distinguish smokers from non-smokers. In this work, we successfully synthesized meatball-like Al2O3@Ag composite structures as surface-enhanced Raman scattering (SERS) substrates using a simple wet chemical method adapted to conventional laboratory conditions. The substrate exhibited strong SERS enhancement for NaSCN. Under the optimal experiment conditions, we obtained a detection limit of 0.28 µg L-1 and a quantification limit of 1 µg L-1, R2 = 0.992. Based on the analysis of the intensity of SERS characteristic peak, the substrate had good reproducibility and uniformity. In summary, the Al2O3@Ag composite structure achieved sensitive SERS detection of NaSCN. Combining the facile and low-cost methods, we believe that the SERS detection method developed in this work can be used as a potential candidate for biosensing applications in the future.