Fluorescence Emission Wavelength Research Articles

Rational design of long wavelength solid-state fluorescent carbon dots based on zirconium

As a new type of zero dimensional carbon based fluorescent nanomaterial, carbon dots (CDs) have been studied and developed for many years. Various methods have been explored to prepare multicolor CDs to achieve tunable fluorescence of CDs. However, synthesizing fluorescent CDs located in the long wavelength emission region remains a challenge. Here, through a simple one-step solvothermal method using anhydrous citric acid (CA) as the raw material, ZrCl4 as both a metal element dopant and an inorganic salt matrix, and NH3·H2O as nitrogen source, Zr-doped CDs (Zr-CDs) solution with long wavelength fluorescence emission and solid powders with blue fluorescence can be obtained simultaneously. By optimizing the usage of ZrCl4, the fluorescence emission of the prepared CDs red shifted from 596 nm to 650 nm. The introduction of Zr4+ can cause a significant redshift. In addition, based on the sensitivity of CDs to oxygen, they can be used for the detection of trace amounts of H2O2. When using metal-organic framework (MOF) to encapsulate the Zr-CDs which is in the solution, optically stable CD@MOF powders can be obtained, which can be used for the construction of red light-emitting diodes (LEDs), demonstrating its potential application in the field of solid-state lighting. The synthesis technology is expected to provide favorable technical support for the future development of CDs.

Efficient preparation strategy of high quantum yield multicolor CDs for warm white LED

Multicolor carbon dots (CDs) possess tremendous potential applications, especially in optoelectronic devices. However, further applications in warm white LED have been constrained due to the extremely low quantum yield (QY) of multicolor CDs. In this work, fluorescence enhancement multicolor CDs (o-CDs(cat.) (emitted yellow, Em = 550 nm, QY = 85.4 %), m-CDs(cat.) (emitted blue, Em = 440 nm, QY = 35.7 %), p-CDs(cat.) (emitted red, Em = 610 nm, QY = 73.8 %)) with almost 15 % QY improvement, without changing the fluorescence emission wavelength, was successfully achieved by introducing MnSO4 into the reaction system. The relevant mechanism may be the catalytic effect of MnSO4, which leads to the increased content of C = N and pyridine N, further suppressing non radiative transitions, leading to the increasement of QY. Finally, the obtained high QY multicolor CDs were applied to warm white LED with the color coordinates (CIE) of (0.33,0.36), color rendering index (CRI) of 90, correlated color temperature (CCT) of 3473 K. Laying the foundation for the research methods and mechanisms of metal ion caused high QY of CDs.

Synthesis of Quinoline-based New Organic Chemosensors and its Application in Fluorophoric Detection of Metal-ions in Environmental Samples and Confirmation of Results using Molecular Modelling: A Complete Study

Quinoline-based two new ligands have been synthesized (QL1 and QL2) by reacting 8-quinoline carboxylic acid with derivatives of L-valine under a condensation reaction. The synthesized ligands were characterized by spectroscopic techniques such as 1H NMR, UV, IR, HRMS and CHNS. The 3D structures of both ligands were optimized for the lowest energy and the HOMO-LUMO orbitals were developed. The photoluminescence analysis of both ligands showed the fluorescence emission wavelengths on 492 and 508 nm, respectively for QL1 and QL2. The substituents on the quinoline ring influence the change in fluorescence emission wavelengths. Synthesized ligands acted as selective fluorescence turn-off chemosensors for Cu2+ ions and demonstrated the sensitive detection of Cu2+ ions in different water samples at the nanomolar scale. The interaction between metal ion and ligands were also studied by developing DFT structures.

Synthesis of 3‐Arylazoindoles through Iron(III)‐Catalyzed C−H Azolation of Indoles and Arylhydrazines

AbstractA variety of functionalized 3‐arylazoindoles were prepared in good to excellent yields through an iron(III)‐catalyzed C−H azolation of 2‐substituted indoles with arylhydrazines under mild reaction conditions. The reaction underwent an initial TBN‐mediated nitrosation, 1,5‐hydrogen migration, intramolecular condensation, and 1,5‐hydrogen migration over four steps in one pot. A paracyclophane‐derived 3‐phenylazoindole could be prepared in 25% yield over three steps and some prepared 3‐arylazoindoles showed a different fluorescence emission wavelength and existed obvious pH conditions response. The present method highlights broad substrate scope of easily available starting materials, wide range of functional group compatibility, gram scalable preparations, high atom economy, avoidance of unstable and explosive azolation reagents, and simple purification operations by extraction, washing, and recrystallization without flash column chromatography.

A novel pH-sensitive hemi-cyanine containing tetrahydropyridine ring near-infrared fluorescence probe with lysosome-targeting ability

In recent years, hemi-cyanine dyes have been widely used as biological probes due to their red-light emission characteristics and high fluorescence quantum yield. In this study, we synthesized a novel hemi-cyanine dye containing a tetrahydropyridine ring. A lysosomal target was introduced into its structure to create a new pH-sensitive near-infrared fluorescent probe that successfully targeted lysosomes. The results showed that when the probe solution was excited at the absorption wavelength of 650 nm, its fluorescence emission wavelength was about 700 nm, and the peak intensity changed with different pH values in a wide range. Therefore, this probe enabled non-invasive detection of changes in the acidic environment of lysosomes in living organisms and showed good imaging capabilities. Moreover, the probe displays high sensitivity and good stability. The theoretical calculation of a probe structure has also been completed to discuss the relationship between structure and property.

Tuning Optical Properties of Carbon Dots by Co‐doping Strategy for Versatile Applications

AbstractCarbon dots (CDs) with tunable photoluminescence was successfully prepared via selective co‐doping of three elements, including nitrogen, phosphorus and sulfur element by green one‐step hydrothermal method. Nitrogen‐sulfur‐doped CDs (red NS‐CDs), which emitted red fluorescence under UV excitation, were used to detect iron ions in the linear range 1–50 μM, yielding detectable limits as low as 94 nM. The nitrogen‐phosphorus‐doped CDs (blue NP‐CDs) exhibited blue fluorescence with quantum yields up to 34.5 %. When the concentration is 800 μg/mL, it showed excellent anticancer effect in vitro. The nitrogen‐sulfur‐phosphorus‐doped CDs (green NPS‐CDs) emitting green fluorescence showed a low cytotoxicity at a high concentration of 800 μg/mL and were used for intracelluar imaging of NCl−H292 cells. This study demonstrated the photoluminescent characteristics of carbon dots (CDs) and highlighted the ability to modify their peak fluorescence emission wavelengths through the flexible combination of specific reagents under comparable hydrothermal conditions. Additionally, it provided valuable insights into the efficient methodologies for synthesizing CDs suitable for various application scenarios.

Fluorescence spectral analysis and logistic regression modeling for diagnosing basal cell carcinoma on head and neck

The optical fluorescence method is distinguished by key features such as non-invasiveness, high sensitivity, and resolution, which are superior to traditional diagnostic approaches. Unlike histopathological examinations and biochemical analyses, optical diagnostic methods obviate the need for tissue sampling, enabling the analysis of virtually unlimited material.The research aims to examine the effectiveness of emission spectra analysis in the diagnosis of basal cell carcinoma (BCC) of the scalp and neck. The analysis was based on data provided by Specialized Hospital No. 2 in Bytom comprising a study sample of 10 patients. For each patient, fluorescence emission spectra were recorded from each of 512 points along a 5 mm line.The results obtained from the histopathological examination, the analysis and morphological evaluation of the tissue, and the diagnosis through microscopic observation were used to define a dichotomous variable (presence or absence of a cancerous lesion), adopted in the study as the modeled variable. The next step of the presented study involved constructing a logistic regression model for identifying cancerous lesions depending on the biochemical indicator's relative fluorescence value (RFV) and emission wavelength (ELW) within the 620 nm to 730 nm range. This wavelength range is often used in fluorescence diagnostics to detect various pathologies, including cancerous lesions.The resulting binary logistic regression model, logit(p)=−33.17+0.04ELW+0.01RFV, indicates a statistically significant relationship between wavelength and relative fluorescence values with the probability of detecting cancer. The estimated model exhibits a good fit and high predictive accuracy. The overall model accuracy is 84.8 %, with the correct classification rates at approximately 96 % for healthy individuals and 74 % for individuals with cancer. These findings underscore the potential of photodynamic diagnostics in cancer detection and monitoring.

An “on-off-on” fluorescent sensor based on TSPP-gallic acid: Visual detection of S2− in actual samples

A novel “on-off-on” switches fluorescence sensor based on TSPP-gallic acid (GA) for S[Formula: see text]-detecting was designed in this article. 5,10,15,20- (4-sulphonatophenyl) porphyrin (TSPP) was synthesized by a modified “one-pot” method. The synthesized TSPP was used as a fluorescence probe for the construction of a fluorescence sensing system. At room temperature, the maximum fluorescence emission wavelength could be obtained at 642 nm when the excitation wavelength was 515 nm when the fluorescence signal was in the “on” mode. The TSPP solution appeared pink in color at this moment. When GA was introduced into the TSPP solution, the fluorescence signal was turned off (fluorescence intensity was quenched) due to the protonation of TSPP, which was caused by the weak acidity of GA. The color of the TSPP solution changed from pink to green. Following that, an acid-base reaction between S[Formula: see text]and GA was initiated when S[Formula: see text]was introduced into the TSPP-GA system, leading to the liberation of TSPP and restoration of fluorescence intensity. The solution color reverted to red, indicating that the fluorescence sensing system had returned to the “on” mode. The TSPP-GA system had good selectivity and sensitivity to S[Formula: see text], the linear range was 4.52 × 10[Formula: see text] M [Formula: see text] 4.34 × 10[Formula: see text] M, and the detection limit (LOD) was 0.87 [Formula: see text] M. It could be used to detect sulfur ions in actual samples with satisfactory recoveries and RSD values.

Multistimuli-responsive diaryldibenzofulvene derivatives and fluorescent detection of volatile organic vapors

Through molecule design, the aromatic fused ring groups (naphthyl and anthracyl) were introduced into 9-benzylidene-9H-fluorene to prepare the diaryldibenzofulvene derivatives with asymmetric structures, which exhibited typical aggregation induced emission (AIE) behavior. To multiple stimuli such as grinding, solvent fuming, and heating, the anthracene-based compound (9-(anthracen-9-yl(phenyl)methylene)-9H-fluorene) powders displayed high contrast fluorescence response behavior, whose emission could convert among yellow (570 nm), yellow green (560 nm), green (526 nm), and cyan (478 nm). Meanwhile, four single crystals of the anthracene-based compound were obtained from different conditions, exhibiting polymorphism phenomena. Through the XRD patterns and the data of the monocrystalline analysis, the different fluorescent emissions originated from changes in the molecular packing. Based on this, two fluorescent detection papers (A) and (B) were prepared using the anthracene-based compound in different solvents. The detection paper showed significant fluorescence quenching for THF and obvious fluorescence enhancement for aromatic solvents. Based on changes in fluorescence intensity and emission wavelength, various volatile organic vapors could be detected accurately by using both detection papers simultaneously. Therefore, this multi stimulus responsive fluorescent compound has potential applications in detection, recognition, sensing and other fields.

B and N Co-doped carbon dots for the ratiometric fluorescence detection of riboflavin and information security with room temperature phosphorescence

Matrix-free room temperature phosphorescence (RTP) materials have generated considerable interest in sensing, anti-counterfeiting and bioimaging due to long lifetime and large Stokes shift. However, spin-forbidden transition and non-radiative transition make RTP challenging to implement. In this work, matrix-free RTP carbon dots (CDs) co-doped with boron and nitrogen were prepared through the microwave-assisted strategy. The CDs realize RTP without any protective matrix. This may be attributed to the stable and rigid structure formed during the heating polymerization process, which can protect the triplet excited state from being quenched by oxygen and water in the air environment. The fluorescence and phosphorescence emission wavelength of the as-prepared CDs were observed at 532 nm and 596 nm with the excitation wavelength of 476 nm and 514 nm, respectively, showing a long afterglow lifetime of 735.3 ms. Nitrogen doping has a crucial effect on the luminescence of RTP, and the increase of nitrogen content facilitates the n-π* transition and improve the efficiency of intersystem crossing (ISC). Importantly, the ratiometric fluorescence method for determining riboflavin has been established based on the Förster resonance energy transfer (FRET) between the CDs (Donor) and riboflavin (Acceptor), with a linear relationship in the range of 9.52–85.71 μM and the limit of detection (LOD) of 19.9 nM. Additionally, the phosphorescent property of the CDs was exploited to demonstrate the potential applications in the field of information encryption.

Modular Design Platform for Activatable Fluorescence Probes Targeting Carboxypeptidases Based on ProTide Chemistry.

Carboxypeptidases (CPs) are a family of hydrolases that cleave one or more amino acids from the C-terminal of peptides or proteins and play indispensable roles in various physiological and pathological processes. However, only a few highly activatable fluorescence probes for CPs have been reported, and there is a need for a flexibly tunable molecular design platform to afford a range of fluorescence probes for CPs for biological and medical research. Here, we focused on the unique activation mechanism of ProTide-based prodrugs and established a modular design platform for CP-targeting florescence probes based on ProTide chemistry. In this design, probe properties such as fluorescence emission wavelength, reactivity/stability, and target CP can be readily tuned and optimized by changing the four probe modules: the fluorophore, the substituent on the phosphorus atom, the linker amino acid at the P1 position, and the substrate amino acid at the P1' position. In particular, switching the linker amino acid at position P1 enabled us to precisely optimize the reactivity for target CPs. As a proof-of-concept, we constructed probes for carboxypeptidase M (CPM) and prostate-specific membrane antigen (also known as glutamate carboxypeptidase II). The developed probes were applicable for the imaging of CP activities in live cells and in clinical specimens from patients. This design strategy should be useful in studying CP-related biological and pathological phenomena.

A signal‐switchable fluorescent probe for detection of HPO42− based on 5,10,15,20‐(4‐sulphonatophenyl)porphyrin (TPPS4)

AbstractIn this study, 5,10,15,20‐(4‐sulphonatophenyl)porphyrin (TPPS4) was selected as a fluorescent probe due to its excellent characteristics including high quantum yield, good water solubility, and exceptional biocompatibility. With an excitation wavelength set at 515 nm, the optimal fluorescence emission wavelength for TPPS4 was measured at 642 nm. At this moment, the fluorescence signal of TPPS4 pink solution was in the ‘ON’ state. The fluorescence intensity of TPPS4 was quenched when ascorbic acid (AA) was introduced, which was due to the electron transfer quenching effect between AA and TPPS4. The colour of the corresponding solution changed from pink to green, and the fluorescence signal was in the ‘OFF’ state. When HPO42− was further introduced into the TPPS4–AA system, the quenched fluorescence intensity of TPPS4 was recovered due to the unique interaction between HPO42− and AA. At this time, the colour of the corresponding solution changed from green to red, and the fluorescence signal was in the ‘ON’ state. Therefore, an ‘ON–OFF–ON’ signal‐switchable fluorescent probe was constructed based on TPPS4 to detect HPO42−. The results showed that the linear range of HPO42− was 4.0 × 10−9 to 1.7 × 10−6 M, and the detection limit was 1.3 × 10−9 M (S/N = 3). The sensing system exhibited high accuracy and sensitivity, and it could be used successfully to detect HPO42− in real samples.

B, P, and S heteroatom doped, bio- and hemo-compatible 2D graphitic-carbon nitride (g-C3N4) with antioxidant, light-induced antibacterial, and bioimaging endeavors

The synthesis of two-dimensional (2D) graphitic g-C3N4 and heteroatom-doped graphitic H@g-C3N4 (H: B, P, or S) particles were successfully done using melamine as source compounds and boric acid, phosphorous red, and sulfur as doping agents. The band gap values of 2D g-C3N4, B50@g-C3N4, P50@g-C3N4, and S50@g-C3N4 structures were determined as 2.90, 3.03, 2.89, and 2.93 eV, respectively. The fluorescent emission wavelengths of 2D g-C3N4, B50@g-C3N4, P50@g-C3N4, and S50@g-C3N4 structures were observed at 442, 430, 441, and 442 nm, respectively upon excitation at λ Ex = 325 nm. There is also one additional new emission wavelength was found at 345 nm for B50@g-C3N4 structure. The blood compatibility test results of g-C3N4, B50@g-C3N4, P50@g-C3N4, and S50@g-C3N4 structures revealed that all materials are blood compatible with <2% hemolysis and >90% blood clotting indices at 100 μg ml−1 concentration. The cell toxicity of the prepared 2D graphitic structures were also tested on L929 fibroblast cells, and even the heteroatom doped has g-C3N4 structures induce no cytotoxicity was observed with >91% cell viability even at 250 μg ml−1 particle concentration with the exception of P50@g-C3N4 which as >75 viability. Moreover, for 2D g-C3N4, B50@g-C3N4, and S50@g-C3N4 constructs, even at 500 μg ml−1 concentration, >90% cell viabilities was monitored. As a diagnostic material, B50@g-C3N4 was found to have significantly high penetration and distribution abilities into L929 fibroblast cells granting a great potential in fluorescence imaging and bioimaging applications. Furthermore, the elemental doping with B, P, and S of g-C3N4 were found to significantly increase the photodynamic antibacterial activity e.g. more than half of bacterial elimination by heteroatom-doped forms of g-C3N4 under UVA treatment was achieved.

Atomic electronegativity-dependent intramolecular hydrogen bond and fluorescence characteristics of novel scaffold-based fluorophore: a TD-DFT study.

In this work, fluorescent properties and excited-state intramolecular proton transfer (ESIPT) processes of 2,5-bis(benzo[d]thiazol-2-yl)phenol (BTP) and its derivatives (BOP and BSeP) with different heteroatom atoms (O and Se) have been systematically explored by the density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. The calculated absorption and fluorescence emission peaks agree well with the experimental values in acetonitrile. From the data of structures, topological parameters, reduced density gradient analyses, and infrared (IR) vibrational frequencies, the intramolecular hydrogen bonds (IHBs) of BTP and its derivatives are enhanced upon light-excitation. The potential energy curves show that the ESIPT process occurs in BTP and its derivatives after surmounting 0.167-0.306eV energy barrier. The strength of intramolecular hydrogen bond, HOMO-LUMO energy gap, and red-shifted value of absorption and fluorescence emission wavelengths are dependent on the electron-withdrawing ability of heteroatom from O to S and Se. We believe that this work can pave the way for developing a new ESIPT-based fluorophore with better luminescent properties.

The full spectrum tuning of fluorescent molecules via a one-pot multicomponent reaction

Fluorogenic probes for imaging enable visualization and analysis of difficult-to-reach cells and organelles. However, there are limited efficient examples of tuning these fluorescent molecules to higher wavelengths. This is vital since different tissues are sensitive to varying wavelength emissions. To address this need, we report the discovery, tuning, structure-photophysical property relationships (SPPR), and time-dependent DFT (TD-DFT) computations of 400–700+ nm fluorescent pyrido[2′,1′:2,3]imidazo[4,5-c]isoquinolines and substituted imidazo[1,2-a]pyridin-3-amines. The syntheses involve the trimethylsilylcyanide (TMSCN) modified Groebke-Blackburn-Bienaymé (GBB) multicomponent reaction as well as the TMSCN modified GBB combined with subsequent condensation of an aldehyde, and Aza-Friedel-Crafts-Intramolecular Cyclization-Oxidation all in one pot. The SPPR reveals that electron-withdrawing strength in the para-position of the aminopyridine starting material has direct control over the absorption and fluorescence emission wavelengths of these molecules. The TD-DFT computations show the changes in the natural transition orbitals (NTOs) with differing substitutions to the parent molecule that dictate the observed excitations, emissions, and fluorescence intensities. These findings give insights and directions for tuning the fluorescent properties of these motifs for various uses as probes and imaging agents.

Hantzsch Ester Modified Asymmetric BODIPY Probe with Ultra‐high Sensitivity for Ultra‐fast Detection of Endogenous Hypochlorite in Living Cells

Comprehensive SummaryHypochlorite (ClO–) is an important reactive oxygen species produced by the immune system to fight off invading pathogens, but its over‐expression can interfere with normal physiological process and induce serious diseases. Although a variety of molecular probes have been reported for detecting ClO–, the development of advanced fluorescent tools with faster response and higher sensitivity to precisely monitor ClO– remains a challenge. In this work, two Hantzsch ester (a derivative of 1,4‐dihydropyridine) derived fluorescent probes MeDHP‐BCl and MeDHP‐PhBCl were constructed based on asymmetric BODIPY‐matrix. These probes exhibit significant fluorescence turn‐on in the ultra‐sensitive (detection limit &lt; 1 nmol/L) and ultra‐fast response (≤ 5 s) to ClO–. The reaction has been determined to be a highly selective N‐chlorination of Hantzsch ester which cannot be activated by various common bioactive species, including nitric oxide (NO) that could oxidize Hantzsch ester under aerobic physiological conditions in most reports. MeDHP‐PhBCl possessed a relatively longer fluorescence emission wavelength and higher quantum yield after activation, while more notably, MeDHP‐BCl displayed lower cytotoxicity and more remarkable fluorescence increment in the response to ClO–, enabling selective and precise visualization of endogenous ClO– over‐expression in living RAW264.7 cells.

Insights of the pH-dependent emission of carbon dots: a density functional theory study

The mechanism of luminescence in carbon dots has long been a topic of controversy, as accurately characterizing their structure has proven difficult. This has made it challenging to guide the design and synthesis of carbon dots, hindering the development of highly efficient fluorescent varieties. Understanding the mechanism and regulatory mechanisms of carbon dot luminescence at the molecular level is important not only from a theoretical perspective but also has practical value. Previous studies have suggested that the fluorescence emission wavelength of carbon dots can be altered by changing the pH of the carbon dot solution, but the mechanism behind this modulation is not yet fully understood. In this study, we used density functional theory calculations and excited state simulations with 2, 3-Diaminophenazine, a representative luminescent molecule found in molecular state luminescent carbon dots, to investigate the effect of protonation on the absorption and fluorescence emission spectra of carbon dots. We analyzed the electronic structure and spatial distribution of the luminescent molecules before and after protonation and found that the change in molecular dipole moment caused by protonation was responsible for the significant red shift in the fluorescence spectrum. To further verify our findings, we modified the substituted functional groups with different electron-pulling abilities in the corresponding luminescent molecules to modulate the molecular dipole. The results showed that the larger the dipole moment in the luminescent molecules with different substituted functional groups, the longer the fluorescence emission wavelength. Therefore, the protonation-induced change in molecular dipole is the main reason for the pH-dependent modulation of luminescence in molecular state luminescent carbon dots.

Single Quasi-Symmetrical LED with High Intensity and Wide Beam Width Using Diamond-Shaped Mirror Refraction Method for Surgical Fluorescence Microscope Applications.

To remove tumors with the same blood vessel color, observation is performed using a surgical microscope through fluorescent staining. Therefore, surgical microscopes use light emitting diode (LED) emission and excitation wavelengths to induce fluorescence emission wavelengths. LEDs used in hand-held type microscopes have a beam irradiation range of 10° and a weak power of less than 0.5 mW. Therefore, fluorescence emission is difficult. This study proposes to increase the beam width and power of LED by utilizing the quasi-symmetrical beam irradiation method. Commercial LED irradiates a beam 1/r2 distance away from the target (working distance). To obtain the fluorescence emission probability, set up four mirrors. The distance between the mirrors and the LED is 5.9 cm, and the distance between the mirrors and the target is 2.95 cm. The commercial LED reached power on target of 8.0 pW within the wavelength band of 405 nm. The power reaching the target is 0.60 mW in the wavelength band of 405 nm for the LED with the beam mirror attachment method using the quasi-symmetrical beam irradiation method. This result is expected to be sufficient for fluorescence emission. The light power of the mirror was increased by approximately four times.

Ultra small carbon dots from Crocus cancellatus as a highly fluorescence probe for synthetic Ponceau 4R dye sensing in food samples

In this work, for the first time, natural Crocus cancellatus was adopted for the green, low-cost, and simple synthesis of highly fluorescent ultra-small carbon dots (CDs) with well-distributed size using a one-pot hydrothermal treatment. As-synthesized CDs are used as fluorescence sensing probe for quantitative analysis of Ponceau 4R (E124) synthetic food dye, which is widely used. However, excessive consumption of Ponceau 4R poses potential health risks. To obtain better-quality performance of as-synthesized CDs, the time and temperature of the hydrothermal carbonization reaction of crocus were optimized simply. The as-prepared carbon dots exhibit exceptional advantages including excellent fluorescence, satisfactory chemical stability, low toxicity, and excellent biocompatibility. It produced a strong blue fluorescence when irradiated with UV light at 365 nm, which was subsequently effectively employed for Ponceau 4R sensing based on the quenching of fluorescence. The as-prepared CDs was characterized by EDX, XRD, FTIR, SEM, HRTEM, UV–Visible absorption spectrophotometry, and fluorescence. The effects of carbon dots fluorescence emission wavelength, CDs quantity, pH value, and reaction time were investigated to detect Ponceau 4R under optimum conditions. The synthesized carbon dot's fluorescence intensity allowed quantitative determination of Ponceau 4R in the linear range of 60–6000 nM with a detection limit of 40 nM that is lower than all previously published methods. Several soft drink samples were used to validate the potential use of this new fluorescent probe for P4R detection in actual samples with good precision and accuracy.

Dihydroxanthene-derived fluorescent probe with near-infrared excitation and emission maxima for detecting human carboxylesterase-2 and bioimaging

Carboxylesterases in human body play pivotal roles for catalyzing the hydrolysis of endogenous and exogenous substances such as lipids, thioesters and amides. Carboxylesterase-2 (CES2) as a major isoform of carboxylesterases is highly expressed in human digestive tract, and usually serves as an important mediator for pharmacokinetics and pharmacodynamics of ester medications or ester prodrugs. Therefore, developing effective strategies to detect and track CES2 in cells or tissues is of great significance for understanding its physiological and pharmacological effects on various diseases and therapeutic outcomes. In this study, we synthesized a fluorescent probe (CHQ-E) with near-infrared (NIR) excitation and emission maxima based on dihydroxanthene fluorophore for highly selective and sensitive detection of CES2. This probe exhibited rapid response (3 min), excellent sensitivity (detection limit = 0.35 ng/mL) and high binding affinity (Km = 9.4 μM) towards CES2, as well as low cytotoxicity towards living biosamples. Significantly, the maximum fluorescence excitation and emission wavelengths led to excellent optical properties of this probe including less photodamage, few autofluorescence and superior tissue penetration depth (180 µm). Moreover, CHQ-E has been applied to monitoring CES2 activity in drug-induced liver injury and its remediation models. Results of fluorescence imaging in vivo indicate the broad potential of CHQ-E for clinical diagnosis and evaluation of pharmaceuticals.