Fluorometric Probe Research Articles

Nitrogen-doped Ti3C2 MXene quantum dots as an effective FRET ratio fluorometric probe for sensitive detection of Cu2+ and D-PA

In this work, a ratiometric fluorescence sensing platform was established to detect Cu2+ and D-PA (d-penicillamine) based on nitrogen-doped Ti3C2 MXene quantum dots (N-MODs) that was prepared via a simple hydrothermal method and exhibited strong fluorescent and photoluminescence performance as well as excellent stability. Since the oxidation reaction between o-phenylenediamine (OPD) and Cu2+ induced the formation of 2,3-diaminophenazine (ox-OPD) which not only can emerge an emission peak at 570 nm, but also inhibit the fluorescence intensity of N-MQDs at 450 nm, a ratiometric reverse fluorescence sensor via fluorescence resonance energy transfer (FRET) was designed to sensitively detect Cu2+, where N-MQDs acted as energy donor and ox-OPD as energy acceptor. More importantly, another considerably interesting phenomenon was that their catalytic oxidation reaction can be restrained in the presence of D-PA because of the coordination of Cu2+ with D-PA, further triggering the obvious changes in ratio fluorescent signal and color, thus a ratiometric fluorescent sensor of determining D-PA was proposed also in this work. After optimizing various conditions, the ratiometric sensing platform showed rather low detection limits for Cu2+ (3.0 nM) and D-PA (0.115 μM), coupled with excellent sensitivity and stability.

Silicon nanoparticles as a fluorometric probe for sensitive detection of cyanide ion and its application in C. elegans bio-imaging

In recent years, silicon nanoparticles (Si NPs) have been explored as a promising alternative to traditional organic fluorophores in optical sensing and bioimaging applications owing to their exceptional optical properties and negligible toxicity. In this study, water-dispersible Si NPs were prepared from a 3-aminopropyl trimethoxysilane precursor using a facile one-pot process. The as-prepared Si NPs exhibited excitation-wavelength-dependent fluorescence properties and bright green fluorescence at 530 nm upon excitation at 420 nm. The fluorescence properties of Si NPs remained unperturbed under various physiological conditions, such as varying pH, ionic strength, and incubation time. A sensitive fluorometric turn-off sensor for cyanide ion (CN−) detection was devised based on the unique fluorescence properties of Si NPs. The Si NPs-based detection assay showed a good linear response toward CN− ranging between 0 and 33 μM, with a limit of detection as low as 0.90 nM. Caenorhabditis elegans is used as a model organism to evaluate the in vivo toxicity and molecular imaging capability of Si NPs.

Cell cycle-dependent Cu uptake explained the heterogenous responses of Chlamydomonas to Cu exposure

Growing evidence suggested that microorganisms exhibited heterogeneous sensitivity to toxicants, but their underlying mechanisms remain largely unknown. The asynchronous cell cycle progression in natural population implies the connection between cell cycle and heterogeneity. Here, the heterogenous responses of Chlamydomonas reinhardtii upon Cu stress were confirmed with the aid of a fluorometric probe for imaging Cu(I), implying the connection with cell cycle. Our results further indicated that the increase of labile Cu(I) was related to the cell division, leading to the fluctuation of labile Cu(I) with diurnal cycle and cell cycle, respectively. However, lack of Cu mainly influenced the cell division. We demonstrated that G2/M phase was the critical stage requiring high Cu quota during cell division. Specifically, algae at G2/M phase required 10-fold of Cu quota compared with that at G1 phase, which was related to the mitochondrial replication. Eventually, the heterogeneous Cu uptake ability of algae at different cell phases led to the heterogeneous responses to Cu exposure. Overall, Cu could influence the cell cycle through mediating the cell division, and in turn algae at different cell phases exhibited different Cu sensitivities. This study firstly uncovered the underlying mechanisms of heterogeneous Cu sensitivity for phytoplankton, which could help to evaluate the potential ecological risks of Cu.

A Dihydropyridine Derivative as a Highly Selective Fluorometric Probe for Quantification of Au3+ Residue in Gold Nanoparticle Solution.

Novel dihydroquinoline derivatives (DHP and DHP-OH) were synthesized in one pot via a tandem trimerization-cyclization of methylpropiolate. DHP and DHP-OH possess strong blue fluorescence with high quantum efficiencies over 0.70 in aqueous media. DHP-OH displays a remarkable fluorescence quenching selectively to the presence of Au3+ through the oxidation of dihydropyridine to pyridinium ion as confirmed by NMR and HRMS. DHP-OH was used to demonstrate the quantitative analysis of Au3+ in water samples with the limit of detection of 33 ppb and excellent recovery (>95%). This fluorescent probe was also applied for the determination of Au3+ residue in the gold nanoparticle solution and a paper-based sensing strip for the on-site detection of Au3+.

A Novel Composite of Zinc-based Metal Organic Framework Embedded with SnO2 Nanoparticle as a Photocatalyst for Methylene Blue Dye Degradation as well as Fluorometric Probe for Nitroaromatic Compounds Detection.

A facile bottom up synthesis technique is opted for the preparation of novel composite SnO2@Zn-BTC. This synthesized composite is fully characterized by Fourier Transform Infrared (FTIR) Spectroscopy, Powder X-Ray Diffraction (PXRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDS), and Elemental mapping techniques. Optical analysis was performed using UV-Visible absorption spectroscopy and fluorescence studies. Further this composite was utilized for the first time as a photocatalyst for methylene blue (MB) dye degradation under sunlight irradiation. This photocatalyst shows degradation efficiency of 89% within 100min of exposure of sunlight. In addition to that, the synthesized composite can be utilized as a fluorescence probe for detection of NACs via 'turn-off" quenching response. This composite is extremely sensitive towards 3-NA in aqueous medium with quenching efficiency of 75.42%, which is highest quenching rate till reported. There occurs no interference for detecting 3-NA in the presence of other NACs. The linear fitting of the Stern-Volmer plot for 3-NA shows large quenching constant (KSV) of 0.0115ppb-1 with correlation coefficient R2 = 0.9943 proves higher sensitivity of composite in sensing process. The outstanding sensitivity of composite for 3-NA is certified by the low detection limit (LOD) of 25ppb (0.18µM). Photoinduced Electron Transfer (PET)and Fluorescence Resonance Energy Transfer (FRET) are the mechanisms used for clarification of quenching response of PL intensity by NACs via density functional theory (DFT) calculations and extent spectral overlap, respectively. Hence, synthesized composite is verified as multi-component system to act as excellent photocatalyst as well as fluorescent sensor.

Development of novel fluorescent probes to detect and quantify specific reactive oxygen species

Hydrogen peroxide (H2O2) plays important roles in redox signaling and oxidative stress, and its dynamic concentration is critical to human health and diseases. Here we report the synthesis of a novel fluorescent probe based on pyridine-coumarin core 3-(2-pyridyl)-7-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)chromen-2-one (P182) for quantitative measurement of H2O2. This fluorometric probe displays a fluorescence turn-on response in the process of deprotection of arylboronate to phenol in the presence of H2O2. It could offer good performances in terms of sensitivity and response time. Moreover, cytotoxicity studies on various model cell lines proved the non-toxic activity of the tested sensor allowing its use in vivo studies. This study provides research on molecular fluorescence probe for the detection of H2O2.

A colorimetric and fluorometric molecular system for discriminative detection of palladium acetate and CO cell imaging

A novel fluorophore (NAP-PMA) has been constructed through appending 2-pyridinemethanamine to naphthalimide. The air and moisture stable fluorophore were adopted as a colorimetric and fluorometric probe for palladium cation, revealing simultaneously good selectivity, high sensitivity and low detection limit (22.5 nM). Moreover, NAP-PMA not only exhibited a visible naked-eye color change from yellowish green to pink, but also displayed highly selective recognition to palladium acetate. In addition, NAP-PMA could be used as paper strips to quantitatively detect Pd2+ in water. Surprisingly, the developed sensing platform NAP-PMA-Pd is capable of detecting CO in living cells by “turn on” mode with high selectivity and stability, providing a potential real-time monitor for CO-involved reactions in biological systems.

Spiropyran-Merocyanine Based Photochromic Fluorescent Probes: Design, Synthesis, and Applications.

Due to ever-increasing insights into their fundamental properties and photochromic behaviors, spiropyran derivatives are still a target of interest for researchers. The interswitching ability of this photochrome between the spiropyran (SP) and merocyanine (MC) isoforms under external stimuli (light, cations, anions, pH etc.) with different spectral properties as well as the protonation–deprotonation of its MC form allows researchers to use it suitably in sensing purposes by developing different colorimetric and fluorometric probes. Selective and sensitive recognition can be achieved by little modification of its SP moiety and functional groups. In this review, we emphasize the recent advancements (from 2019 to 2022) of spiropyran–merocyanine based fluorogenic and chromogenic probes for selective detection of various metal ions, anions, neutral analytes, and pH. We precisely explain their design strategies, sensing mechanisms, and biological and environmental applications. This review may accelerate the improvements in designing more advanced probes with innovative applications in the near future.

Synthesis and characterization of a novel colorimetric and fluorometric probe “Turn-on” for the detection of Cu2+ of derivatives rhodamine

A new Rhodamine-based “Turn On” fluorescent probe (E)- 3′,6′-bis(diethylamino)-2-((2,5-dimethoxybenzylidene)amino)spiro[isoindoline-1,9′-xanthen]-3-one (WGB) was synthesized. Results show that WGB is selective for Cu2+ cations, forming a WGB-Cu2+ complex in a 2:1 stoichiometry, confirmed through density functional theory (DFT) electronic structure calculations and reactive molecular dynamics (MD) simulations. Theoretical calculations agreed with the experimental data. The detection limit of WGB-Cu+2 complex is 6.76 × 10-8 M. Preliminary studies employing epifluorescence microscopy demonstrate that Cu2+ can be imaged in neuroblastoma SH-SY5Y cells treated with WGB.

A Turn-On Fluorescent Probe for Determination of Ascorbic Acid Based on CaF2:Yb3+, Er3+ Upconversion Nanoparticles

A turn-on fluorometric probe is designed for the determination of ascorbic acid (AA) based on the inner filter effect (IFE) between CaF2:[Formula: see text], [Formula: see text] upconversion nanoparticles (CaF2:[Formula: see text], [Formula: see text] NPs) and the oxidized 3, [Formula: see text], 5, [Formula: see text]-tetramethylbenzidine (oxTMB). The colorless TMB can be oxidized by H2O2/[Formula: see text] to blue oxTMB. Under 980 nm photoexcitation, CaF2:[Formula: see text], [Formula: see text] NPs can emit red light, which can be absorbed by the blue oxTMB, leading to the fluorescence quenching at 657 nm. As AA can reduce the blue oxTMB to colorless TMB, the fluorescence at 657 nm can be recovered with the addition of AA, which can accomplish the detection towards AA. The linear detection range of AA is from 1 to 30 [Formula: see text]M, and the limit of detection (LOD) of AA is 0.1 [Formula: see text]M.

A simple colorimetric and fluorometric probe for rapid detection of CN– with large emission shift

In this work, a novel probe R was synthesized via Knoevenagel reaction between 3H-benzo[f]chromium-2-formaldehyde and ethyl cyanoacetate for selective detection of CN– in both colorimetric and fluorescent signal channels. The recognition of CN– was through the nucleophilic reaction of CN– to C = C of probe R, which destroys π-conjugation and blocks the ICT effect of the probe, resulting in colorimetric and fluorometric responses. Probe R showed great sensitivity toward CN–, with large fluorescent emission (595 nm) and low detection limit (0.70 μM). Moreover, probe R can detect exogenous CN– in living cells.

Biocompatible Carbon Dot Decorated α-FeOOH Nanohybrid for an Effective Fluorometric Sensing of Cr (VI) in Wastewater and Living Cells.

This article reports the fluorometric detection of toxic hexavalent chromium Cr (VI)) in wastewater and Cr (VI) contaminated living cells using in-situ grown carbon quantum dots into the goethite (α-FeOOH) nano-matrix. The synthesized nano-hybrid shows enormous potential in determining the chromium contamination levels in various types of water samples. This selective fluorometric probe is enormously sensitive (LOD 81nM) toward hexavalent chromium, which makes it a dedicated chromium sensor. Moreover, the sensing mechanism has been assessed using Stern-Volmer's equation and fluorescence lifetime experiments showing the simultaneous occurrence of photoinduced electron transfer and the inner filter effect. This chromium sensor has also been employed to assess the contamination level in real-life industrial wastewater. The performance of this probe in a real-life wastewater sample is quite commendable. Further, this biocompatible fluorometric probe has been used to demonstrate the in-vitro sensing of Cr (VI) in HeLa cells. The rapid detection mechanism of hexavalent chromium in living cells has been validated using theoretical docking simulations. Henceforth, this fluorometric sensor material could open new avenues not only in wastewater monitoring but also in biomedical applications.

Development a coordination polymer based nanosensor for phenobarbital determination in exhaled breath condensate

In this study, a fluorometric probe based on luminol-terbium coordination polymer nanoparticles (luminol-Tb CP NPs) is validated for the quantification of phenobarbital in the exhaled breath condensate collected from expiratory circuit of the mechanical ventilator (MVEBC). It relies on the coordination of phenobarbital to luminol-Tb CP NPs which casing an aggregation-induced fluorescence enhancement of probe owing to the increasing the system rigidity and the decreasing the nonradiative decay rate. As the increase in response intensity is proportional to phenobarbital amount, a method is offered for its determination in MVEBC. This method presents a linear relationship with phenobarbital concentration in the range of 0.1–10.0 mg.L−1 with a limit of detection of 0.024 mg.L−1 and the relative standard deviation of 3.6%. The proposed method is used in MVEBC of the pre-term newborn babies receiving phenobarbital under mechanical ventilator.

High Quantum Yield Nitrogen-Doped Carbon Quantum Dot-Based Fluorescent Probes for Selective Sensing of 2,4,6-Trinitrotoluene

Fluorescent carbon quantum dots hold great promise for the determination of nitro-explosive 2,4,6-trinitrotoluene (TNT), a potential environmental pollutant. Here, a nitrogen-doped carbon quantum dot (N-CQD)-based fluorometric probe with high quantum yield (73.10%) was developed for the selective determination of TNT. N-CQDs were synthesized by the reflux method using citric acid (CA) as a carbon precursor and ethylenediamine (EDA) with diaminocyclohexane (DACH) as nitrogen precursors. N-CQDs, with excitation and emission wavelengths of 360 and 460 nm, respectively, were highly selective toward TNT among different types of explosives [i.e., tetryl, 2,4,6-trinitrophenol (TNP), 2,4-dinitrotoluene (DNT), 4-amino-2,6-dinitrotoluene (ADNT), HMX, 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), and pentaerythritol tetranitrate (PETN)]. As a result of the dominant FRET mechanism secondarily assisted by ground-state donor–acceptor complexation, the fluorescence of N-CQDs showed excellent quenching in the presence of TNT. The structure of N-CQDs was elucidated using X-ray photoelectron spectroscopy, X-ray diffraction, IR, Raman, high-resolution transmission electron microscopy, and dynamic light scattering techniques, and their interaction mechanism with TNT was resolved using the Gaussian (i.e., highest occupied molecular orbital–lowest unoccupied molecular orbital energy levels) program. The limit of detection and limit of quantification in aqueous media were 30.0 and 90.0 nM, respectively, while the Benesi–Hildebrand binding constant of N-CQDs was 2.22 × 103. In the presence of common soil ions, explosive mixtures, and camouflage materials, the N-CQDs could determine TNT with recoveries between 94.9 and 104.9%. In addition, sandy soil specimens were artificially contaminated with TNT as real samples, and the TNT extracted from these samples was determined by both N-CQDs and the reference liquid chromatography with tandem mass spectrometry method to validate the proposed fluorometric method. To design field detection techniques, two different support materials based on the thin layer chromatography-paper and hydrogel (N-CQD-gel) were developed, and TNT was determined visually at a μM level with both materials. The developed support materials make N-CQDs potentially useful in environmental sensor applications with their selective and sensitive sensing ability.

Benzothiazole tethered triazole based potential antibacterial agent as a selective fluorometric probe for the detection of Al3+ ions and phenylalanine

The excess of Al3+ ions in the biological and environmental samples have negative impact and Phenylalanine deficiency can cause serious neurological abnormalities. Hence, there is a need of a simple and cost-effective chemosensor for the detection of Al3+ ions and Phenylalanine. Herein, we have designed a ligand that shows selectivity and sensitivity towards Al3+ ions and phenylalanine in absorption spectroscopy without any interference of other metal ions and amino acids respectively. The linearity of the B-H plot confirms the 1:1 stoichiometry ratio of the ligand with the ions and amino acid. Further, fluorescence study demonstrated that ligand shows turn-on and turn-off fluorescence in the presence of Al3+ ions and Phenylalanine with LOD values of 4.08 × 10−9 M and 18.45 × 10−6 M, respectively. The complexes of the synthesized receptor with Al3+ ions and Phenylalanine were synthesized and characterized by the 1H NMR to confirm the binding mode. Moreover, prepared molecules were subjected to in vitro microbiology assay against gram-positive and gram-negative bacteria and the results gave potential evidence of antibacterial activity against Staphylococcus Aureus and Escherichia Coli at the minimum inhibitory concentration (MIC) of 0.039 mg/ml.

Highly selective and sensitive fluorometric probe for Cd2+ ions based on 4-(quinolin-2-ylmethylene)aminoanisole Schiff base

Herein, we report a reversible and easy assembled fluorometric probe (4-(quinolin-2-ylmethylene)aminoanisole, QMAA) for the highly selective and sensitive detection of cadmium ion (Cd2+) in DMF solution with PBS buffer (0.01 M, pH = 7.30). The strong fluorescence response of QMAA to Cd2+ along with a bright blue fluorescence was mainly ascribed to the formation of the complex QMAA–CdCl2. The results show that the complexation can inhibit the CN isomerisation and photo–induced electron transfer (PET), and further lead to the occurrence of chelation fluorescence enhancement. The 1:1 stoichiometry of the complex between QMAA and cadmium ion was studied by fluorescence titration, Job’s plot analysis, 1H NMR, FT–IR, and ESI–MS data, and was further confirmed by the single crystal structure of the complex QMAA–CdCl2. Density functional theory (DFT) calculations have verified the mechanism of fluorescence enhancement. In addition, the limit of detection of QMAA for Cd2+ was as low as 0.1547 µM (at 10–7 M level), which was lower than the acceptable limit of Cd2+ level in drinking water defined by World Health Organization. The analog experiments about nature contamination of Cd2+ in real samples were finished.

A soil-borne Mn(II)-oxidizing bacterium of Providencia sp. exploits a strategy of superoxide production coupled to hydrogen peroxide consumption to generate Mn oxides.

Bacterial non-enzymatic Mn(II) oxidation involving reactive oxygen species (ROS) (i.e., indirect oxidation), initially discovered from a marine alpha-proteobacterium, is believed to be of importance in controlling biogeochemical cycles. For soil-borne bacteria, however, evidence of indirect Mn(II) oxidation remains unclear. In this study, the indirect Mn(II) oxidation was evidenced in a soil-borne bacterium, Providencia sp. LLDRA6. First, with and without 50mM of Mn(II) exposure for LLDRA6, 300 differentially expressed genes were found to be linked to Mn(II) exposure via transcriptome sequencing. Among them, an operon, responsible for phenylacetic acid catabolism, was sharply upregulated in transcription, drawing us a special attention, since its transcriptional upregulation has recently shown to be important for withstanding ROS. Next, a fluorometric probe, 2',7'-Dichlorofluorescin diacetate (DCFDA), was used to qualitatively detect ROS from cells, showing a distinct increase in fluorescence intensities of ROS during Mn(II) exposure. Furthermore, concentrations of superoxide and hydrogen peroxide from cells were detected, respectively, with and without Mn(II) exposure, exhibiting that when Mn(II) oxidation occurred, superoxide concentration significantly increased but hydrogen peroxide concentration significantly decreased. Particularly, superoxide produced by LLDRA6 was proven to be the oxidant for Mn(II) in the formation of Mn oxides. Finally, we predicted links between phenylacetic acid metabolism pathway and ROS during Mn(II) exposure, proposing that the excessive ROS, generated in response to Mn(II) exposure, transcriptionally activate phenylacetic acid catabolism presumably by increasing concentrations of highly reactive oxepins.

Microwave-assisted facile synthesis of N, P co-doped fluorescent carbon dot probe for the determination of nifedipine.

A simple and fast microwave synthesis method was applied for the preparation of several carbon dots (CDs) from various combinations of urea, phosphoric acid, and B-alanine as nitrogen, phosphorus, and carbon precursors. The maximum quantum yield (44%) was obtained for nitrogen and phosphorus co-doped carbon dots (N, P-CDs) prepared from urea, B-alanine, and phosphoric acid. Furthermore, N, P-CDs were exploited to synthesize a simple and sensitive fluorometric probe to determine nifedipine (NFD). We determined that the analytical response of the designed sensor could be affected by the kind of dopant and synthesis precursors. It is worth mentioning that the fluorescence intensity of N, P-CDs was weakened by NFD, and no fluorescence quenching was observed for other prepared CDs. The NFD-developed sensor demonstrated a linear response range of 3.3 × 10-8-3.2 × 10-5mol/L, with the detection limit of 1.0 × 10-8mol/L. The sensor was successfully applied to measure NFD in human biological fluids.

Chalcone appended Organosilanes and their silica nanoparticles based UV–vis and fluorometric probes for Co2+ ions detection

Herein, we have designed heterocycle-based ligands having chalcone appended triazole silane in the scaffold by using a cost-effective and simple synthetic procedure. They were well characterized by using various spectroscopic techniques. In addition, organosilane was incapacitated on a silica nanosphere, and the resulting hybrid nanoparticles were thoroughly investigated using XRD, EDX, TGA, and SEM. Further, a recognition study of synthesized compounds was done by treating with different metal ions like Zn2+, Ni2+, Na+, Mg2+, K+, Ba2+, Ca2+, Ag+, Al3+ and Co2+ and it was observed in UV–Vis and fluorometric spectroscopy that ligand only shows selectivity and sensitivity towards Co2+ metal ions. Job’s plot confirms the binding of a ligand with the metal ion in 1:1 stoichiometry. From the B-H plot association constant for hybrid silica nanoparticles was 6.3 × 104 M−1. In the emission spectra for both organosilane and H-NP’s turn-off fluorescence behaviour was observed with detection limit value of 5.94 × 10−7 M and 6.06 × 10−8 M respectively. Moreover, by using Tauc’s plot band gap energy of the ligand and functionalized nanoparticles were calculated. In addition, DFT calculations were done to provide valuable information about the ligand interaction with Co2+ metal ions.

A novel reversible dual-mode probe based on amorphous carbon nanodots for the detection of mercury ion and glutathione

Fluorometric and colorimetric probes have attracted more and more attention in recent years. However, there are few reports on dual-mode reversible probes. We report the design of a novel colorimetric and fluorometric probe based on amorphous carbon nanodots (CND), which successfully realized the dual-mode and reversible detection of mercury (Hg2+) and glutathione (GSH). The limits of detection with fluorometric and colorimetric for Hg2+ were 6.8 nM and 0.38 μM, and for GSH were 10.9 nM and 0.56 μM, respectively. Furthermore, the probe could also effectively analyze Hg2+ and GSH in different practical water samples. These findings extend the application of CND in environment and biology.