Yellow Fluorescence Emission Research Articles

Construction of carbon dot-embedded fluorescent hydrogels based on oxidized gum arabic-gelatin Schiff base for Cr(VI) detection applications.

In this study, a novel nitrogen-doped carbon quantum dot/oxidized gum arabic-gelatin-based fluorescent probe (NAH) was prepared using gelatin (GL) and gum arabic (AG) biomolecules. The primary network structure of this hydrogel consisted of polyacrylamide (PAM), while a secondary network structure was constructed between oxidized gum arabic and gelatin through the reaction of the Schiff base, which significantly enhanced the mechanical properties, the stress and strain of NAH reached 266.47KPa and 2175.75%. Nitrogen-doped carbon dots (NCDs) with yellow fluorescence emission properties were synthesized by hydrothermal method using salicylic acid as the carbon source and o-phenylenediamine as the nitrogen source. The fluorescent sensor obtained by compounding NCDs with hydrogel was able to selectively detect Cr(VI). The linear range of its detection was 0-90μM, and the detection limit was 0.19μM. The maximum theoretical adsorption capacity of the NAH hydrogel was 169.4mg/g, and its adsorption isotherm conformed to the Langmuir adsorption isotherm model, and the adsorption kinetics conformed to the quasi-secondary kinetic model. Compared with the NCDs solution, the NAH hydrogel showed superior comprehensive performance, especially in solving the problem of recovery of NCDs. Meanwhile, this hydrogel provides an effective insight into the efficient detection and adsorption of environmental pollutants.

Smartphone-based ratiometric fluorescence sensor for sensitive visual detection of H2O2 and glucose based on B-CDs-Ag NPRs-OPD ternary system

A straightforward and highly sensitive ratiometric fluorescence sensor comprising blue emissive carbon dots, silver nanoprisms, and o-phenylenediamine (B-CDs-Ag NPRs-OPD) was developed for the detection of H2O2 and glucose. Ag NPRs were etched into Ag+ ions upon exposure to H2O2, which caused non-fluorescent OPD to be oxidized and produce 2,3-diaminophenazine (DAP), resulting in intense yellow fluorescence emission at 555 nm. DAP can quench the B-CDs based on inner filter effect (IFE), leading to a decrease in their fluorescence intensity at 435 nm. Because glucose oxidase may catalyze the oxidation of glucose to produce H2O2, this approach can also be used to detect glucose. The unique triangular structure leads to the easy etching of the edge and tip of Ag NPRs by H2O2 into Ag+ ions, allowing for the high sensitivity of detection of H2O2 and glucose with limit of detection (LOD) of 0.12 μM and 0.6 μM, respectively. Furthermore, with the increase of the concentrations of H2O2 and glucose, a visible color shift from blue to yellow-green occurs, which can be detected using a smartphone's color recognition application that captures the RGB channel values of the image. Real-time and on-spot detection of H2O2 and glucose were achieved based on smartphone sensing platform, presenting vast potential for applications in various fields.

Unraveling two yellow fluorescence emission mechanisms and color-changing afterglow characteristics of Dy-doped Mg2SnO4 luminescent materials

In this work, Dy ion doped Mg2SnO4 (Mg2SnO4:Dy3+) with monochromatic yellow fluorescence and color-changing long afterglow properties are prepared by the high-temperature solid-phase method. Mg2SnO4:Dy3+ shows the best luminescence performance under the preparation conditions of 1550 °C and 0.02 Dy3+ concentration. The samples are able to achieve yellow fluorescence emission (λem = 575 nm) under 350 nm and 291 nm excitation, and the emission intensity of the samples under 350 nm excitation is much higher than that of 291 nm excitation. Under 254 nm excitation, the sample not only emits bright white fluorescence but also has the ability of obvious afterglow after excitation. Moreover, the afterglow also has the color change function of transition from bright white to yellow. The luminescence mechanism study shows that Mg2SnO4:Dy3+ contains two emission centers, Dy3+ and lattice defects. Combining the results of spectroscopic measurements with the Dy3+ energy level distribution data, two different fluorescence emission processes under 291 and 350 nm excitation as well as the afterglow discoloration mechanism due to 254 nm excitation are discussed in detail.

Metal-organic frame material encapsulated Rhodamine 6G: A highly sensitive fluorescence sensing platform for the detection of picric acid contaminants in water

As a water pollutant with excellent solubility, 2,4,6-trinitrophenol (also known as picric acid, PA) poses a potential threat to the natural environment and human health, so it is crucial important to detect PA in water. In this study, a novel composite material (MIL-53(Al)@R6G) was successfully synthesized by encapsulating Rhodamine 6G into a metal-organic frame material, which was used for fluorescence detection of picric acid (PA) in water. The composite exhibits bright yellow fluorescence emission with a fluorescence quantum yield of 58.23 %. In the process of PA detection, the composite has excellent selectivity and anti-interference performance, and PA can significantly quench the fluorescence intensity of MIL-53(Al)@R6G. MIL-53(Al)@R6G has the advantages of fast detection time (20 s), wide linear range (1–100 µM) and low detection limit (4.8 nM). In addition, MIL-53(Al)@R6G has demonstrated its potential for the detection of PA in environmental water samples with satisfactory results.

Chromo-Fluorogenic Rhodamine-Based Amphiphilic Probe as a Selective and Sensitive Sensor for Intracellular Cu(I) in Living Cells.

Fluorescent probes are widely studied for metal ion detection because of their multiple favorable properties such as high sensitivity and selectivity, quick response, naked eye detection, and in situ monitoring. However, optical probes that can effectively detect the Cu(I) level in cell interiors are rare due to the difficulty associated with selectively and sensitively detecting this metal ion in a cell environment. Therefore, we designed and synthesized three water-soluble probes (1-3) with a 1,3,5-triazine core decorated by three substituents: a hydrophobic alkyl chain, a hydrophilic maltose, and a rhodamine B hydrazine fluorophore. Among the probes, probe 1, which has an octyl chain and a branched maltose group, was the most effective at sensing Cu+ in aqueous solution. Upon addition of Cu+, this probe showed a dramatic color change from colorless to pink in daylight and displayed an intense yellow fluorescence emission under 365 nm light. The limit of detection and dissociation constant (Kd) of this probe were 20 nM and 1.1 × 10-12 M, respectively, which are the lowest values reported to date. The two metal ion-binding sites and the aggregation-induced emission enhancement effect, endowed by the branched maltose group and the octyl chain, respectively, are responsible for the high sensitivity and selectivity of this probe for Cu+ detection, as demonstrated by 1H NMR, dynamic light scattering, and transmission electron microscopy studies. Furthermore, the probe successfully differentiated the Cu(I) level of cancer cells from that of the normal cells. Thus, the probe holds potential for real-time monitoring of Cu(I) level in biological samples and bioimaging of cancer cells.

Designing of multifunctional graphene quantum dot-polyvinyl alcohol-polyglycerol luminescent film for fluorescence detection of pH in sweat

BackgroundWound infection, skin disease, renal failure, cancer, cystic fibrosis, and other pathologies may induce obvious pH changes in sweat. Thus, tracking skin pH changes can help monitor human health in a convenient manner. Owing to their biocompatibility, easy preparation, and sensitive response to pH changes, graphene quantum dots (GQDs) have received increased attention in the optical detection of pH changes. However, their poor luminescent efficiency under visible light excitation and lack of functional diversification limit their application in skin pH monitoring. Therefore, the development of GQDs with excellent ultraviolet protection ability and antibacterial and luminescence performance is essential. ResultsFolic acid-, histidine-, and serine-functionalized boron-doped graphene quantum dots (FHSB-GQDs) were designed and synthesized via thermal treatment. The resulting FHSB-GQDs exhibit strong yellow fluorescence emission under excitation with 490-nm visible light and sensitive pH responsiveness. The peak fluorescence intensity linearly decreases with increasing pH from 4 to 9. Furthermore, the FHSB-GQDs were integrated with polyvinyl alcohol and polyglycerol to form a luminescent film via hydrogen bond interactions. The film exhibits high transparency, mechanical flexibility, ultraviolet protection ability, and antibacterial activity. The presence of polyvinyl alcohol and polyglycerol restricts the free movement of the FHSB-GQDs and improves fluorescence behavior. The film was successfully applied in an intelligent pH-sensing system for monitoring pH changes in human sweat. SignificanceThe graphene quantum dot–polyvinyl alcohol–polyglycerol luminescent film offers excellent transparency, mechanical flexibility, ultraviolet protection ability, antibacterial activity, and luminescence performance. It was successfully applied in an intelligent pH sensing system for the detection of pH changes in human sweat. This study provides a new strategy for the design and construction of wearable sensing systems for health monitoring, facial masks, and medical dressings.

A ratiometric fluorescence assay for the detection of DNA methylation based on an alkaline phosphatase triggered in situ fluorogenic reaction.

The accurate and sensitive quantification of DNA methylation is significant for the early diagnosis of cancer. In this work, an alkaline phosphatase (ALP) triggered in situ fluorogenic reaction between ascorbic acid (AA) and 2,3-DAN was employed as a ratiometric fluorescent probe for the accurate and sensitive detection of DNA methylation with the assistance of ALP encapsulated liposomes. The quinoxaline derivative with a yellow fluorescence emission (I525) was generated from the reaction between AA and 2,3-DAN. Meanwhile, the consumption of 2,3-DAN declined its fluorescence intensity (I386). A ratiometric fluorescent probe (I525/I386) constructed by the above in situ fluorogenic reaction was applied for the accurate detection of DNA methylation. The methylated DNA was first captured by its complementary DNA in 96-well plates. Then, 5mC antibody (Ab) linked liposomes that were encapsulated with ALP recognized and combined with the methylation sites of the target DNA. After the liposomes were lysed by Triton X-100, the released ALP triggered the hydrolysis of ascorbic acid diphosphate (AAP) to form AA, participating in the fluorogenic reaction with 2,3-DAN to produce a quinoxaline derivative. Thus, the ratiometric fluorescence detection of DNA methylation was achieved using I525/I386 values. Using the ALP-enzyme catalyzed reaction and liposomes as signal amplifiers, a low detection limit of 82 fM was obtained for DNA methylation detection. Moreover, the accuracy of the assay could be improved using ratiometric fluorescent probes. We hope that the proposed assay will pave a new way for the accurate determination of low-abundance biomarkers.

Myricetin-based fluorescence probes with AIE and ESIPT properties for detection of hydrazine in the environment and fingerprinting

BackgroundHydrazine (N2H4) is a highly toxic and versatile chemical raw material, which poses a serious threat to the environment and human health when used in large quantities. However, the traditional methods for the detection of N2H4 have the disadvantages of time-consuming, complicated operation and expensive instruments. In contrast, fluorescence probes have many advantages, such as simple operation, high sensitivity, good selectivity, and fast response time. Therefore, there is an urgent need for a fluorescence probe that can rapidly and accurately detect the presence of N2H4 and monitor the changes in its concentration. ResultsFor this purpose, we designed and synthesized a series of myricetin fluorescence probes 3-(substituent group)-5,7-dimethoxy-4-oxo-2-(3,4,5-trimethoxy.phenyl)-4H-chromen-4-one (Myr-R) for N2H4 detection. In the presence of N2H4, the probe 5,7-dimethoxy-3-(2,3,4,5,6-pentafluorobenzoate)-2-(3,4,5-trimethoxyphen-yl).-4H-chr-omen-4-one (Myr-3) shows significant fluorescence changes, double emission properties and a large Stokes shift (183 nm), and exhibits high selectivity and sensitivity to N2H4 (The detection limit is 93 nM). Importantly, the qualitative and quantitative analysis of N2H4 in water, soil, and air can be accomplished using fluorescence, smartphone, and UV lamps coupled with Myr-3. In addition, Myr-3 can be used for monitoring and imaging intracellular N2H4. Meanwhile, the fluorophore 3-hydroxy-5,7-dimethoxy-2-(3,4,5-trimethoxyphenyl)-4H-benzopyran-4-one (Myr-Me) was applied to fingerprinting of different substrate materials due to the fact that it exhibits strong yellow fluorescence emission in the solid state and shows excellent contrast and high resolution. SignificanceThe probe Myr-3 is not only able to rapidly detect N2H4 in complex environments, but also can be used for imaging intracellular N2H4. In addition, the fluorophore Myr-Me can be used as an effective imaging agent for visual fingerprinting. These properties enable the probe Myr-3 and the fluorophore Myr-Me for a wide range of potential applications in related fields.

Rose Bengal‐Derived Carbon Quantum Dots as a Fluorescence Probe for the Highly Sensitive Detection of Fe3+ Ions

AbstractIn this study, rose bengal‐derived carbon quantum dots (RB‐CQDs) was synthesized by a one‐step solvothermal method using rose bengal and 1,2‐phenylenediamine as precursors in ethanol at 180 °C for 10 h and purified by silica gel chromatography. The as‐synthesized RB‐CQDs disperses well in water with particle sizes ranging from 0.78 to 2.46 nm and exhibits excitation‐independent yellow fluorescent emission (529 nm), high quantum yield (44.3 %) and good biocompatibility. More importantly, the fluorescence of RB‐CQDs can be selectively quenched by Fe3+ ions with good linear correlation and the detection limit is 19.9 nM. The recoveries of this method in actual water samples are 90 % to 110 % with relative standard deviations less than 5 %.

Long wavelength emission multicolor fluorescent carbon quantum dots for the detection of pH, amino acids, and metal ions

Carbon quantum dots are widely used in the field of analysis and detection due to their excellent optical properties. At present, many studies have focused on the preparation of multi-color fluorescent quantum dots by simple methods. Inspired by this, carbon quantum dots with green (G-CQDs) and yellow fluorescence (YN-CQDs) emission were prepared by hydrothermal method using PTCDA and urea as precursors. After characterizing their morphology, structure, and optical properties, fluorescent probes for different purposes were constructed according to their different fluorescence characteristics. Since green G-CQDs are sensitive to acidic environments, pH detection kits are developed. In addition, G-CQDs can also efficiently detect Asp. YN-CQDs are used to detect metal ions and can specifically detect Fe3+. Both of them were applied to the detection of actual samples, showing high efficiency and reliability. It provides a new idea for the multi-purpose detection of carbon quantum dot fluorescent probes.

A selectivity-enhanced fluorescence imprinted sensor based on yellow-emission peptide nanodots for sensitive and visual smart detection of λ-cyhalothrin

The development of precise and efficient detection technologies to recognize λ-cyhalothrin (LC) in agricultural products has attracted attention worldwide due to its widespread use and notable toxic effects on humans. Herein, a novel fluorescence biomimetic nanosensor was elaborately designed based on Zn(II)-doped cyclo-ditryptophan (c-WW)-type peptide nanodots and incorporating molecularly imprinted polymer (c-WW/Zn-PNs@MIP) for LC assays. C-WW/Zn-PNs obtained by self-assembly with aromatic cyclic dipeptides as basic building blocks and coordination with Zn(II) have low-toxicity, photostability, and bright yellow fluorescence emission, as a sensitive signal transducer. High-affinity imprinting sites further endow c-WW/Zn-PNs@MIP with superior selectivity and reusability. Based on prominent merits, c-WW/Zn-PNs@MIP demonstrated a good linear range (1–360 μg/L) with a low limit of detection (LOD) (0.93 μg/L), fast kinetics in target capture (10 min), and strong practicability in the capture of LC from real samples (spiked recovery of 81.0–107.7%). Additionally, to attain onsite profiling of LC, a visual platform was developed by integrating c-WW/Zn-PNs@MIP with a smartphone-assisted optical device. This smart evaluation system can capture concentration-dependent fluorescent images and accurately digitize them, enabling quantitative analysis of LC. This study developed a fluorescent c-WW/Zn-PNs@MIP-based smart evaluation system as a novel platform for LC monitoring applications, which not only has enormous economic value but also great environmental health significance.

Erasable Photopatterning of Stilbene-Based Metal-Organic Framework Films.

The development of photosensitive materials for erasable photopatterning is of significant interest in anti-counterfeiting and information storage applications. Herein two kinds of stilbene-based metal-organic framework (MOF) films with layer by layer method for studying photopatterning is reported. The resulting 2D Zn2 (sdc)2 MOF film (sdc = 4,4'-stilbenedicarboxylate) exhibits excellent photosensitive features with a very short photoconversion time (<35s) while the 3D MOF Zn4 O(sdc)6 film does not have the property due to the fact that only parallel and short distance arrangement of olefin groups in the adjacent MOF layers can trigger [2+2] photocycloaddition. Furthermore, the Zn2 (sdc)2 film indicates obvious reversible fluorescent photoswitch behavior between yellow and blue fluorescence emission, which can achieve high-efficient, erasable photopatterning with various sizes (ca. 20 microns to decimeter). This study not only develops a new kind of photosensitive crystalline network film but also provides erasable photopatterning from macroscopic to microscopic in optical applications.

Water-based fluorescent flexo-ink for security applications

UV-readable fluorescent ink formulations find versatile applications in various fields including information encryption, automated identification systems, security markers and optical devices. In this context, a new bithiophene-based chalcone (BTCF) that exhibits good solution phase and solid-state fluorescence was synthesized as a colourant for formulating an eco-friendly UV fluorescent ink. The molecule demonstrated good thermal stability and photophysical features including intramolecular charge transfer, confirmed through emission studies in THF–hexane mixtures with varying hexane content. The intense greenish yellow solid-state fluorescence emission displayed by BTCF was exploited by using it as a colourant in a water-based fluorescent ink formulation. Further, the ink was used to print a fast-drying solid patch on an UV dull paper substrate using flexography technique. The analysis of colorimetric, densitometric and rub resistance properties of the printed paper samples demonstrated good fluorescence, moderate photostability and good rub resistance, and hence could be used for security printing applications.Graphical abstract

A dicyanoisophorone-based ICT fluorescent probe for the detection of Hg2+ in water/food sample analysis and live cell imaging

Mercury ions are notoriously difficult to biodegradable, and its abnormal bioaccumulation in the human body through the food chain can cause various diseases. Therefore, the quantitative and real-time detection of Hg2+ is very extremely important. Herein, we have brilliant designed and synthesized (E)-O-(4-(2-(3-(dicyanomethylene)-5,5-dimethylcyclohex-1-en-1-yl)vinyl)phenyl) O-phenyl carbonothioate (ICM-Hg) as a selective fluorescent probe for Hg2+ detection in real samples and intracellular staining. ICM-Hg displayed high specificity toward Hg2+ by activating the intramolecular charge transfer (ICT) process, resulting in distinguished color change from colorless to bright yellow along with noticeable switch on yellow fluorescence emission. The fluorescent intensity of ICM-Hg at 585 nm shows a well linear relationship in the range of Hg2+ concentration (0–45 μM), and the detection of limit for Hg2+ is calculated to be 231 nM. Promisingly, ICM-Hg can efficiently detect Hg2+ in real samples including tap water, tea, shrimp, and crab with quantitative recovery as well as the intracellular fluorescence imaging.

Dual-template molecularly surface imprinted polymer on fluorescent metal-organic frameworks functionalized with carbon dots for ascorbic acid and uric acid detection

In this work, dual-template molecularly imprinted polymer surfaces imprinted on blue fluorescent Cr-based MOF (Cr-MOF) functionalized with yellow emissive carbon dots (Y-CDs) were prepared using l-ascorbic acid (AA) and uric acid (UA) as templates for simultaneous selective recognition of AA and UA. The as-prepared nanocomposite probe (Y-CDs/Cr-MOF@MIP) contains two recognition site cavities and emits a dual well-resolved fluorescence spectra when excited at 390 nm; blue emission (λem 450 nm) is due to Cr-MOF, and yellow emission (λem 560 nm) is due to Y-CDs. The yellow fluorescence emission of Y-CDs was quenched upon the addition of ascorbic acid, while Cr-MOF’s emission remained unaffected. In the same way, the blue fluorescence emission of the Cr-MOFs was quenched in the presence of uric acid, while the yellow emission remained constant. Both emissions were quenched in a sample containing both AA and UA. This can be exploited to design a dual-template biosensor to detect UA and AA simultaneously. The Y-CDs/Cr-MOF@MIP sensor displayed a dynamic linear response for AA in the range 25.0 µM – 425.0 µM with a detection limit of 1.30 µM, and for UA in the range 25.0 µM – 425.0 µM with a detection limit of 1.10 µM. The dual-target probe Y-CDs/Cr-MOF@MIP was highly selective and sensitive for the detection of UA and AA in human urine samples due to the selectivity of the two recognition sites.

A fluorescence-based sweat test sensor in a proof-of-concept clinical study for COVID-19 screening diagnosis.

During the corona virus disease 2019 (COVID-19) pandemic period, rapid screening of covid-19 patients has been of great interest by developing a fluorescent sensor for complexation with nonanal, which is a marker for Covid-19 detection in sweat. Solid phase micro-extraction gas chromatography-mass spectrometry (SPME GC-MS) was initially used to quantify nonanal in armpit sweat samples based on an external calibration curve. A sample containing a nonanal content above the threshold of 1.04 μL is expected to be COVID-19 positive with a sensitivity and specificity of 87% and 89%, respectively, validated by comparison with RT-PCR results. For more practical applications, helicene dye-encapsulated ethyl cellulose, namely EC@dyeNH, was applied to screen 140 sweat samples collected from the foreheads of volunteers. The mixed sensor and sweat solution droplets were then visualized and imaged under blacklight. The COVID-19 positive droplets exhibited yellow fluorescence emission, the brightness of which could be measured by using ImageJ in the grey scale. With the optimum color intensity of >73 for positive results, the screening performance was observed with a sensitivity and specificity of 96% and 93%, respectively. The overall test time of this method is approximately less than 15 min. This alternative method offers a promising practical screening approach for the diagnosis of COVID-19 in sweat.

Preparation of fluorescein-modified polymer dots and their application in chiral discrimination of lysine enantiomers.

Fluorescein-functionalized fluorescent polymer dots (F-PDs) were prepared by a facile one-pot method by magnetic stirring under mild conditions based on carboxymethylcellulose (CMC) and fluorescein as the precursors. The obtained F-PDs exhibited a nanoscale size of 3.2 ± 1.1nm, excellent water solubility, and bright yellow fluorescence emission with a fluorescence quantum yield of 12.0%. The fluorescent probe displays rapid and sensitive chiral discrimination for lysine focused on different complexation abilities between lysine enantiomers and Cu2+. The concentration of L-lysine in the range4 to 14mM (R2 = 0.997) wasmeasured by the fluorescence intensity ratio (I513/I429); the exitation wavelength was set to λex = 365nm. The detection limit was 0.28mM (3σ/slope). Importantly, this sensor accurately predicted the enantiomeric excess (ee) of lysine enantiomers at the designed concentration (lysine: 20mM; Cu2+: 10mM) ranges. Theproposed sensor was successfully applied to determineL-lys (recovery: 95.8-101%; RSD: 0.465-3.34%) and ee values (recovery: 98.5-102%; RSD: 2.61-3.21%) in human urine samples using the standard addition method.

Fabrication of hydrophilic luminescent zinc oxide quantum dots for selective detection of copper ions and efficient inhibition of harmful fungi

In this study, we have successfully prepared surface modified zinc oxide quantum dots (M-ZnO QDs) with ultra-stable fluorescence and excellent hydrophilicity through introducing (3-aminopropyl)triethoxysilane (APTES). The as-prepared M-ZnO QDs under the optimum condition presented strong yellow fluorescence emission under 355 nm excitation and showed satisfied reproducibility. Physical and chemical properties of the synthesized ZnO QDs were further studied by various characterization techniques. Transmission electron microscopy showed homogeneous distribution of spherical M-ZnO QDs with the average particle size of 4.03 nm. According to the characteristic that metal ions can quench fluorescence, M-ZnO QDs-based fluorescence sensor for the detection of Cu 2+ in aqueous solution is developed in this work, which has the advantages of excellent selectivity, good sensitivity and a wide linear range. The limit of detection was 0.51 μM and the linear detection range was 1–200 μM for Cu 2+ determination. The practicability of the fluorescent probe is further validated in the lake water and the satisfactory spiked recoveries of Cu 2+ ranges from 99.1 % to 108.8 %. Besides, M-ZnO QDs displayed concentration inhibition effect and strain effect on the growth of fungi. Thus, the as-prepared M-ZnO QDs are demonstrated to be promising for Cu 2+ determination and anti-fungal applications.

Carbon dot-decorated metal-organic framework composite for Fe3+ detection in the aqueous environment

The contamination of heavy metal ions in the aqueous environment constitutes an important threat to human survival. Hence, the development of simple, effective, and cheap detection of heavy metals and pesticide residues is essential for environmental control. Here, we synthesized a yellow carbon dots-linked ZIF-8 (yCDs/ZIF-8) composite, which was prepared with excellent photoluminescence properties and aqueous stability, and characterized by strong yellow fluorescence emission. The ratio metric fluorescence sensor has been constructed using its stable light blue carbon dots. The fluorescence sensor has excellent selectivity and sensitivity as a sensing probe for Fe3+ ions, with a detection limit of 0.3690 μM. In addition, the fluorescence quench mechanism was investigated. It has been shown that the yCDs/ZIF-8 fluorescence could be quenched by Fe3+ via static quenching and absorption competition mechanisms. The probe has high-quality application potential in terms of food safety and environmental monitoring due to the fact of its simplicity, high yield, and low cost.

A ratiometric fluorescence method based on nitrogen-doped carbon quantum dots for the determination of the activity of alkaline phosphatase.

Herein, a simple and sensitive ratiometric fluorescence sensing platform to detect alkaline phosphatase (ALP) activity is developed on the basis of yellow fluorescent nitrogen-doped carbon quantum dots (YNCDs). The hydrolysis of ascorbic acid 2-phosphate (AAP) into ascorbic acid (AA) is catalyzed by ALP. Then, AA will react with o-phenylenediamine (OPD) to form 3-(1,2-dihydroxyethyl)furo[3,4b]-quinoxaline (QXD) which is a blue fluorescent quinoxaline derivative with emission at 435nm in the presence of Cu2+. YNCDs have yellow fluorescence emission at 555nm, and can maintain stable in QXD reaction system. Therefore, by utilizing the fluorescence of YNCDs at 555nm as reference signal and the fluorescence of QXD at 435nm as report signal, we can detect the ALP activity by monitoring the fluorescence ratio (F435/F555). The linear range is 0.5-5 U/L, and the limit of detection is 0.14 U/L. An application of this method for the analysis of ALP in human serum has given satisfactory results. A ratiometric fluorescent nanoprobe for ascorbic acid and alkaline phosphatase detection with excellent biocompatible and high sensitivity was successfully constructed based on YNCDs and QXD.