Chelation-enhanced Fluorescence Research Articles

Eu-doped carbon dots-MOF based turn-on fluorescent probe for trace Hg2+ and Pb2+ and construction of the simultaneous detection model

Multiple trace heavy metal pollutants present a serious threat to the aquatic environment, and their coexistence also affected the detection efficiency. This work prepared Eu doped metal organic framework (MOF) complexed with S-containing carbon dots (CD(s)) exhibited dual-emission fluorescence. Its chelation-enhanced fluorescence with heavy metals replaced the original agglomerative fluorescence quenching of pure CD(s), which was utilized to construct a “turn on” fluorescence sensing probe. Based on the XPS, DFT and fluorescence lifetime results, the N, S functional groups on the surface of the materials could bind specifically to Hg2+ and Pb2+ with enhanced sensitivity. The limit of detection reached 76.67 nM for Hg2+ and 5.12 nM for Pb2+ within 2 min detection time. Furthermore, due to the different response mechanism of the two signal peaks to Hg2+ and Pb2+, a three-dimensional data model was developed for simultaneous detection in the co-existence system. The model had been successfully applied to actual Hg2+-Pb2+ containing water samples with recoveries ranged from 93.15 ∼ 105.08 %. The results provided a new strategy for simultaneous detection of trace environmental pollutants.

The crystal structures of Imine-Enamine ‘tautomerism’ in solid state and “turn on” sensing for Zn2+: spectroscopy, DFT and cell imaging studies

The crystallographically established ligand 2-((E)-(benzyl imino)methyl)-4-bromophenol (HL) (existing keto at 296 K and enol at 120 K in the solid state), which is in equilibrium of interconversion (ΔE) = 4.39Kcal) with its tautomer, showed weak emission in the excited state, due to the fact of PET but in the presence of Zn2+, PET was blocked and chelation-enhanced fluorescence (CHEF) was set up. It exhibits 'turn on' sensor with the coordination of Zn2+. Among various metal ions, the synthesised probe HL selectively detected Zn2+ and LOD was about to ∼ 1.63 µM. The Zn(II) coordinated complex and the relative stabilities of the tautomers of HL were thoroughly calculated by spectroscopic and computational studies. Furthermore, cell imaging was also performed to validate the sensing property as well as cyto-toxicity of the probe.

A novel peptide fluorescent chemical sensor capable of detecting Cu2+, Zn2+, and S2.

A novel peptide-based chemical fluorescence sensor L (Dansyl-His-Pro-Thr-Cys-NH2) was designed and synthesized. This sensor exhibits an "On-Off-On" detection cycle to detect Cu2+, Zn2+, and S2- in solution. According to the chelation-enhanced fluorescence (CHEF) mechanism, when Zn2+ is present, the fluorescence is significantly enhanced and a blue shift occurs, representing a "Turn-On" phase of the fluorescence detection mode. Because copper ions (Cu2+) have a paramagnetic quenching sensing mechanism, the fluorescence of L quenches rapidly with the formation of the L-Cu system, representing the "Turn-Off" phase. The subsequent introduction of S2- to the L-Cu system results in the recovery of the L-fluorescence, thereby representing the second "Turn-On" phase. As a peptide molecule, the sensor L has several advantages over other types of sensors, including water solubility, high sensitivity, and good biocompatibility, with a very low detection limit. The detection lines of Zn2+ and Cu2+ are 97 nM (R = 0.993) and 75 nM (R = 0.995), respectively. Additionally, the sensor does not exhibit any obvious cell toxicity. These results indicate that this peptide chemiluminescent sensor has the potential to be applied in in vivo detection.

Silver induced self-assembly of a rhodanine derived reversible fluorescent chemosensor: Applications in smart-phone color assist app, logic gate, real sample analysis and bio-imaging

An innovative chemosensor, Rhodanine-appended benzaldehyde (RB), was developed and analyzed using spectroscopic methods to detect silver ions (Ag+) in a THF–H2O buffer solution via fluorimetry. The RB probe exhibited low fluorescence due to C-N free rotation and inhibition of electron transfer. However, interaction with Ag+ ions resulted in a noteworthy redshift of approximately 6 nm and increased fluorescence intensity owing to the chelation-enhanced fluorescence (CHEF) effect, which hindered the Intramolecular Charge Transfer (ICT) process. The binding ratio between RB and Ag+ ions was determined to be 2:1 using the job plot method. The association constant (Ka) was calculated to be 4.84 × 105 M−1 and further confirmed through ESI-TOF spectroscopic and DFT analyses. The limit of detection (LOD) and quantification (LOQ) for RB in binding with Ag+ ions were found to be 1.7 × 10−8 M and 5.4 × 10−8 M, respectively. Additionally, the color changes of RB when binding with Ag+ ions were effectively leveraged in an RGB-assisted smartphone color analysis app for precise sample analysis for Ag+ ion detection. Most importantly, the RB probe’s ability to detect silver ions in the E. coli pathogen was successfully demonstrated, providing reassurance about its practical application, using a confocal scanning electron microscope via the green channel.

Unlocking multi-mode sensing potential: Phosphorus-doped graphitic carbon nitride quantum dots for Ag+, ciprofloxacin, and riboflavin analysis in environment and food matrices

The simultaneous detection of multiple analytes through a single fluorescence sensor is highly attractive. In this study, phosphorus-doped graphitic carbon nitride quantum dots (P-CNQDs) were developed, achieving multi-mode sensing through three distinct response mechanisms. The preparation involved using melamine as the carbon and nitrogen source and ammonium dihydrogen phosphate as the phosphorus source. Uniform and narrowly distributed P-CNQDs were successfully synthesized through chemical oxidation and hydrothermal methods, with an average size of 2.4 nm. These unique P-CNQDs exhibited fluorescence quenching through photo-induced electron transfer (PET) in response to Ag+. Additionally, the formation of hydrogen bonds and coordination interactions between P-CNQDs-Ag+ and ciprofloxacin (CIP) led to a pronounced fluorescence response to CIP by the chelation enhanced fluorescence (CHEF) mechanism. Furthermore, leveraging the principle of fluorescence resonance energy transfer (FRET), P-CNQDs-CIP served as a ratio fluorescence sensor for riboflavin (RF), enabling ultra-sensitive detection of RF. The combination of PET, CHEF, and FRET response mechanisms successfully facilitated multi-mode sensing for Ag+, CIP, and RF. The detection ranges were 0.05–100 μM, 0.002–2 μM, and 0.05–60 μM, with corresponding lowest detection limits of 17.1 nM, 1.1 nM, and 29.2 nM, respectively. This versatile sensor has been effectively applied to real samples, including the detection of river water and vitamin B2 tablets.

A Novel AIE-Active Salicylaldehyde-Schiff Base Probe with Carbazole Group for Al3+ Detection in Aqueous Solution.

A donor-acceptor Schiff-base fluorescent probe BKS with chelation enhanced fluorescence (CHEF) mechanism was designed and synthesized via benzophenone(Acceptor), salicylaldehyde and carbazole(Donor) for Al3+ detection, which exhibited typical aggregation-induced emission (AIE) characteristic. BKS probe could provide outstanding selectivity to Al3+ with a prominent fluorescence "turn-on" at 545nm in a wide pH range from 2 to 11. By the Job's plot, the binding stoichiometry ratio of probe BKS to Al3+ was determined 1:1. The proposed strategy offered a very low limit of detection at 1.486 µM in THF/H2O(V/V = 1:4, HEPBS = 10 mM, pH = 7.40),which was significantly lower than the standard of WHO (Huang et al., Microchem J 151:104195, 2019)-(Yongjie Ding et al., Spectrochim Acta Mol Biomol Spectrosc 167:59-65, 2021) guidelines for drinking water. BKS probe could provide a wider linear detection range of 50 to 500 µM. Furthermore, the probe could hardly be interfered by other examined metal ions. The analysis of Al3+ in real water samples with appropriate recovery (100.72 to 102.85) with a relative standard deviation less than 2.82% indicated the accuracy and precision of BKS probe and the great potential in the environmental monitoring of Al3+.

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 420nm emission (bCQDs) and a p-phenylenediamine-derived fluorescence probe with 550nm emission (yprobe) is constructed for the detection of Mn2+. The presence of Mn2+ results in the enhanced absorption band at 400nm 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 × 10-6M, and the limit of detection is 1.76 × 10-9M. 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.

A ratiometric, turn-on fluorosensor for specific detection of Zn2+ ions

A potentially active fluorescent chemosensor (E)-2-(((2-(1H-benzo[d]imidazol-2-yl)phenyl)imino)methyl)-5-(diethylamino)phenol (BMDP) is developed by the condensation of 2-(2-aminophenyl)-1H-benzimidazole and 4-(diethylamino)salicylaldehyde. It shows an exceptional ratiometric fluorescence behavior when exposed to Zn2+ ions and the photoluminescence color is changed from blue to cyan under the exposure of a 365 nm UV light which is also strongly evident from the color chromaticity diagram. The exceptional ratiometric fluorescence behavior in the presence of Zn2+ ions is found to be due to the chelation-enhanced fluorescence (CHEF). The 1:1 stoichiometry of BMDP and Zn2+ ions in Zn2+ ions chelated BMDP complex is confirmed through Job’s plot analysis. Remarkably, Cd2+ does not interfere with the selective ratiometric fluorescence behavior induced by Zn2+ ions. The lowest detection limit and quantification limit are estimated to be 28 nM and 92 nM respectively. The cyan fluorescence of the Zn2+ ions chelated BMDP complex is interestingly reversed to the original BMDP in the presence of ethylenediamine tetraacetic acid (EDTA). At the molecular level, this can be thought of as a complimentary “INHIBIT” logic gate. Furthermore, it is possible to utilize the probe for on-site identification in test strips with improved Zn2+ ions selectivity. We have also used a smartphone-based method to demonstrate the usefulness of BMDP for the immediate quantification and detection of Zn2+ ions. In light of this, probe BMDP is a trustworthy fluorescence probe for on-site monitoring that can accurately identify Zn2+ ions even when some other metals and anions compete.

A twistable aggregation induced emission enhancement active multisite fluorescent sensor for targeted sensing of zinc ions, 4-nitrophenol and chloroform in diverse conditions

Excessive utilization of Zn2+ and 4-nitrophenol (4-NP) in multiple fields has been becoming a serious threat to the environment and human health from a long time. Considering this, a multipurpose, extremely sensitive and selective fluorescent sensor BMP has been developed for the sensing of Zn2+, 4-NP and chloroform. Chalcone based sensor BMP was easily synthesized through simple aldol condensation reaction that possessed remarkable aggregation induced emission enhancement (AIEE) features along with the formation of J-aggregates. The particle size of aggregates was measured by DLS analysis. Sensor BMP showed strong emission at wavelength 430 nm. Moreover, sensor BMP showed different emissive behavior in various solvents. Sensor BMP selectively detected the Zn2+ through Chelation Enhanced Fluorescence (CHEF) intensity. BMP sensor has selectively sensed the 4-NP through photo-induced electron transfer (PET) quenching mechanism. Along with Zn2+ and 4-NP the sensor BMP has interestingly detected the percentage of chloroform in DCM. The calculated values of limit of detection for Zn2+, 4-NP and chloroform is 43 nM, 18 nM and 0.1 % v/v, respectively. UV–Visible, 1H NMR, LC-MS titration, and SEM experiments were also executed to verify the interaction of BMP sensor with respective analytes. Furthermore, the experimental findings were further justified through the theoretical studies including energy calculation of orbitals and nature of interactions. BMP sensor was employed in both solution and solid state for successful sensing of Zn2+, 4-NP and chloroform in real samples.

Solid-state brightness and Al3+ ions-triggered flower-shaped nano-luminogen for cascade detection of Al3+ and PO43− ions

Solid-state photoluminescence materials have come out as an emergent material for their versatile optoelectronic applications. In the present contribution, a novel fluorescent probe, HMNS has been introduced which exhibits bright orange color photoluminescence when exposed to a 365 nm UV lamp and with a few drops of dimethyl sulfoxide (DMSO), it can be used as photoluminescence security ink. Further, HMNS is utilized for quickly and accurately detecting Al3+ ions in a water-DMSO (1:1, v/v) media displaying Al3+ ions-triggered aggregation-induced emission (AIE). Scanning electron microscopy and dynamics light scattering investigations revealed that HMNS from Al3+ ions triggered flower-shaped nano-luminogen. Probe HMNS can detect Al3+ ions within μM range and also the probe binds with Al3+ ions under physiological pH. The reaction time to Al3+ ions is only a few minutes (around 6–7 min). The development of J-aggregates and chelation-enhanced fluorescence (CHEF) in the water-DMSO (1:1, v/v) media may be responsible for the AIE behavior. Additionally, using the Al3+ ions triggered HMNS nano-luminogen could be used as a "marker-ink" which could be used as printing material to decipher secret data under UV light. Also, to determine its reversibility and reusability, the tested paper was washed with a PO43− ions solution. A notable decrease in the code's intensity indicates that this material can be used repeatedly. Moreover, the probe is suitable for on-site identification when employed in test strips with better Al3+ ions selectivity. We have also used a smartphone-based method to demonstrate the usefulness of HMNS for the immediate quantification and detection of Al3+ ions. In light of this, probe HMNS is a trustworthy on-site monitoring fluorescence probe that can accurately identify Al3+ and PO43− ions successively even when some other metals and anions compete.

Synthesis and logic gate application of quinoline schiff base probe for fluorescence detection of mercury ions

Herein, we report the synthesis of a small molecule quinoline Schiff-base “turn-on” fluorescence probe L, denoted as (2-NC9H6)C(H)=N(C6H4OCH3-p), utilizing 4-aminoanisole and quinoline-2-carboxaldehyde as precursors. The synthesized probe was comprehensively characterized through EA,1H/13C NMR, FT-IR, and ESI-MS spectral analysis. In a CH3CN/H2O solution (1/1, v/v, 0.01 M PBS buffer, pH = 7.30), probe L responded to Hg(II) with high sensitivity (LOD = 2.98 × 10−7 M) and selectivity. Upon binding to Hg(II), the fluorescence of the probe shifted from being initially off to a distinct blue emission. The probe L to Hg(II) binding ratio was 1:1 and the binding constant was 1.955 × 104 M−1. The detection mechanism of Hg(II) by probe L is due to the complex formation between the metal ion and imine nitrogen (–CH = N), thus causing chelation-enhanced fluorescence. TD-DFT studies at the B3LYP/6-31G(d) level of theory further confirmed that the complexation of L and Hg(II) occurred. Finally, probe L could reversibly identify Hg(II) upon adding EDTA, thus developing a molecular logic gate. In addition, this probe was successfully used to detect Hg(II) in actual water samples.

Synthesis of an Antipyrine-Based Fluorescent Probe with Synergistic Effects for the Selective Recognition of Zinc Ion

A novel fluorescent probe containing an imine structure was synthesized through a condensation reaction based on the skeleton of antipyrine. Due to the synergistic effect of photoinduced electron transfer (PET), excited-state intramolecular proton transfer (ESIPT), and E/Z isomerization, the probe itself has weak fluorescence. When zinc ions are added to the ethanol solution of the probe, the formed complex inhibits PET, ESIPT, and E/Z isomerization while activating chelation-enhanced fluorescence (CHEF), resulting in fluorescent “turn-on” at 462 nm. Under optimal detection conditions, the probe can rapidly respond to zinc ions within 3 min, with a linear range of 60–220 μM and a lower limit of detection (LOD) of 0.63 μM. It can also specifically identify zinc ions in the presence of 13 common metal ions.

Fluorescence turn-on detection of arsenite in rice and seawater samples using bisphosphonate-functionalised carbon quantum dots

ABSTRACT In this paper, we illustrate an efficient and simple fluorescence (FL) sensing approach for the specific determination of arsenite (As(III)) in aqueous solution by alendronate-functionalised carbon quantum dots (A-CQDs) as a turn-on fluorescent probe. A-CQDs exhibit linear FL turn-on response towards the increasing concentration of As(III) analyte with a limit of detection of 0.007 µM and a linear range of 0.03–1.87 µM. The selectivity study demonstrates that the A-CQDs are very selective for As(III) detection, even at a higher concentration of other interfering ions. The sensing pathway for the sensitivity of A-CQDs assay to quantify As(III) ions is expected to rely on the chelation-enhanced FL (CHEF) mechanism between A-CQDs and the analyte. This mechanism is verified by the density functional theory methodology. The practical application of this simple and reliable sensor is demonstrated by assaying As(III) in rice and seawater samples, which confirms that A-CQDs have good potential for real sample analysis in food and environmental samples.

A simple fluorescent “Turn-Off” Schiff base sensor for Cu2+ and Fe2+ ions and its applications in real water sample analysis and logic gate construction

A novel imidazole-based Schiff base ligand (Z)-N’-((1H-imidazol-2-yl)methylene)-2-hydroxybenzohydrazide (IMBH), was effectively synthesized and characterized using spectroscopic methods. Chemosensor IMBH’s chelation enhanced fluorescence (CHEF) is responsible for its extremely selective and sensitive detection of Cu2+ and Fe2+ ions in DMSO solutions. Adding different metal ions (30 μM) allowed for the determination of the fluorescence behaviour of IMBH (50 μM). The findings showed that, only for Cu2+ and Fe2+ ions, a notable fluorescence quenching in the emission was seen at 465 nm with an excitation at 320 nm. Furthermore, the Job’s plot and mass spectral analysis showed that IMBH bound Cu2+ and Fe2+ ions at a 2:1 (Ligand:Metal) ratio. For the Cu2+ and Fe2+ ions, the limit of detection (LOD) was found to be 0.204 × 10−9 M and 0.201 × 10−9 M, respectively. On the other hand, IMBH was successfully utilized for the quantitative analysis of Cu2+ and Fe2+ ions in real water samples and logic gate construction. In addition, optoelectronic and structural properties of the IMBH and Fe(II) and Cu(II) complexes were determined by solvent phase DFT calculations.

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.

An AIE dynamic a highly selective and expeditious benzothiazole-pyrazine based colorimetric chemosensor for Ni2+and fluorogenic chemosensor for Cu2+ and Al3+ detection

Considerable research focus has been devoted to the advancement of single-component sensors that can identify several analytes. In this regard, a complex chemosensor called BPA was created by building an imine link between benzothiazole and pyrazine. On the flexible imine link, the nitrogen atoms with lone pair electrons were arranged as possible coordination sites to enable changes in molecular configurations and charge transfer. In the aqueous acetonitrile environment, BPA displayed the discriminative identification of Ni2+ by a chromogenic response (color transition from colorless to yellow) and a fluorescence “decreasing” response for Cu2+ via ligand–metal charge transfer. Additionally, BPA exhibited recognition of Al3+ through a “turn-on” fluorogenic response facilitated by the chelation-enhanced fluorescence effect. The detection limits for Ni2+, Al3+, and Cu2+ were remarkably low, measuring 5.19 nM, 16 nM, and 214 nM, respectively. A 1:1 binding stoichiometry and precise complex modes between BPA and the target metal ions were successfully determined using extensive investigations, which encompassed the utilization of Job's plot, mass spectra, NMR, and DFT analysis. The deduced coordination mechanisms were corroborated by computational and experimental methodologies. BPA's potential practical uses were demonstrated by subsequently evaluating its ability to identify Ni2+, Al3+, and Cu2+ in actual water samples and validating its performance on-site using test strips.

Ferrocene-based chemosensor creates molecular logic circuit for selective detection of Hg2+ and Cu2+

A cation sensor, R, with multi-channel signaling was developed by creating a covalent connection between a ferrocene unit and pyridyl-pyrazole rings. Spectroscopic techniques and single-crystal X-ray diffraction were employed to characterize sensor R. The examination revealed a dihedral angle of 140.09° for the pyridyl-pyrazole rings. The receptor R functions as a highly selective multi-channel chemosensor, exhibiting chromogenic, fluorogenic, and electrochemical capabilities. In a CH3CN/water (9:1) solvent mixture, receptor R operates as a multi-channel signaling chemosensor, selectively detecting Hg2+ and Cu2+ ions in water. The original pale-yellow solution turned orange upon Hg2+ addition and green upon Cu2+ addition. A new low energy (LE) band at 460 nm was detected after adding one equivalent of Hg2+. In cyclic voltammetry (CV), the half-wave potential (E1/2) of 462 mV shifted to 622 mV, whereas in differential pulse voltammogram (DPV), the oxidation peak underwent an anodic shift (ΔE1/2 = 155 mV). The maximum emission at 423 nm was lowered by more than 90 % when the concentration of Hg2+ ions reached one equivalent. One equivalent addition of Cu2+ results in a new LE band at 740 nm. Cu2+ ions suppress the oxidation peak current in both the CV and DPV of R. It also demonstrates chelation-enhanced fluorescence effect (CHEF) with Cu2+. The interaction between cations and R was elucidated through 13C NMR titration. DFT calculations revealed the binding mode. Its distinctive fluorescence demonstrates a 'turn-on' response to Cu2+ and a 'turn-off' response to Hg2+ with selectivity. This concept has been applied to create a molecular combinatorial logic circuit.

A highly selective and sensitive rhodamine B-based chemosensor for Sn4+ in water-bearing and biomaging and biosensing in zebrafish

A novel colorimetric-fluorescent dual-mode chemosensor (JT5) based on rhodamine B has been produced for monitoring Sn4+ in the DMSO/H2O (4:1, v/v) medium. It has high sensitivity, a low detection limit, a short response time (1 s) and high stability, and can still be maintained after two weeks with the red dual fluorescence/ colorimetric response. Enhancement of red fluorescence (591 nm) and red colorimetric (567 nm) response of JT5 by Sn4+ addition. The electrostatic potential of the sensor JT5 molecule was simulated to speculate on the sensing mechanism, and the IR, mass spectrometry and 1H NMR titration were utilized to further demonstrate that JT5 was coordinated to Sn4+ with a 1:1 type, the rhodamine spironolactam ring of JT5 opens up to form a penta-membered ring with Sn4+, meanwhile, its system may have chelation enhanced fluorescence (CHEF) effect. In addition, theoretical calculations were carried out to give the energy gaps of JT5 and [JT5 + Sn4+] as well as to simulate the electronic properties of the maximal absorption peaks. Notably, the sensor JT5 was successfully applied to monitoring Sn4+ in zebrafish, and the JT5-loaded filter paper provided a solid-state platform for detecting Sn4+ by both naked eye and fluorescent methods. In summary, this work contributes to monitoring Sn4+ in organisms and solid-state materials and promotes understanding of Sn4+ functions in biological systems, environments, and solid-state materials.

Heterocyclic fluorescent Schiff base chemosensors for the detection of Fe(III) and Cu(II) ions.

Two new Schiff bases were synthesized from 1-(2,4-dihydroxyphenyl)ethanone and pyridine derivatives. Both compounds were characterized using infrared, UV-Vis., 1H NMR, 13C NMR and mass spectral studies. Density functional theory (DFT) calculations were performed for both the Schiff bases with 6-31G(d, p) as the basis set. Vibrational frequencies calculated using the theoretical method were in good agreement with the experimental values. Both the Schiff bases were highly fluorescent in nature. The cation-recognizing profile of the compounds was investigated in aqueous methanol medium. The Schiff base 4-(1-(pyridin-4-ylimino)ethyl)benzene-1,3-diol (PYEB) was found to interact with Fe(III) and Cu(II) ions, whereas the Schiff base 4,4'-((pyridine-2,3-diylbis(azanylylidene))bis(ethan-1-yl-1-ylidene))bis(benzene-1,3-diol) (PDEB) was found to detect Cu(II) ions. The mechanism of recognition was established as combined excited state intramolecular proton transfer (ESIPT)-chelation-enhanced fluorescence (CHEF) effect and chelation-enhanced quenching (CHEQ) process for the detection of Fe(III) and Cu(II) ions, respectively. The stability constant of the metal complexes formed during the sensing process was determined. The limit of detection for Fe(III) and Cu(II) ions with respect to Schiff base PYEB was found to be 1.64 ×10-6 and 2.16 ×10-7M, respectively. With respect to Schiff base PDEB, the limit of detection for Cu(II) ion was found to be 4.54 ×10-4M. The Cu(II) ion sensing property of the Schiff base PDEB was applied in bioimaging studies for the detection of HeLa cells.

A novel triphenylamine-furan hydrazone-based sensing of Cu2+ ions and imaging in cancer cells

A novel fluorescent probe (TPA-TF) was designed and synthesized, incorporating triphenylamine-thiophene moieties coupled with furan and a hydrazone. First, the TPA-TF can be used as a sensor to detect Cu2+ in the environment/biosystem through an effective fluorescence quenching due to chelation-enhanced fluorescence quenching (CHEQ) and inhibiting the photoinduced electron transfer (PET) process. Various fluorescence spectra and density functional theory (DFT) computations were used to clarify the TPA-TF to Cu2+ detection characteristics. The Cu2+ sensor TPA-TF exhibited a fast response time of one minute. In this study, the linear range concentration for the Cu2+ ion detection was 0–1000 μM, with a broad pH working range (pH 2.7–7.4), and the detection limit of the sensor was 6.08 μM. With its broad applicability, the TPA-TF sensor was successfully used to detect and photograph Cu2+ in live cells, demonstrating its considerable potential for applications in biological imaging.