A Novel Multi-Functional Fluorescence Probe for the Detection of Al3+/Zn2+/Cd2+ and its Practical Applications

A novel multi-functional fluorescence probe HMIC based on hydrazide Schiff base has been successfully synthesized and characterized. It can distinguish Al3+/Zn2+/Cd2+ in ethanol, in which fluorescence emission with different colors (blue for Al3+, orange for Zn2+, and green for Cd2+) were presented. The limits of detection of HMIC towards three ions were calculated from the titration curve as 7.70 × 10- 9 M, 4.64 × 10- 9 M, and 1.35 × 10- 8 M, respectively. The structures of HMIC and its complexes were investigated using UV-Vis spectra, Job's plot, infrared spectra, mass spectrometry, 1H-NMR and DFT calculations. Practical application studies have also demonstrated that HMIC can be applied to real samples with a low impact of potential interferents. Cytotoxicity and cellular imaging assays have shown that HMIC has good cellular permeability and potential antitumor effects. Interestingly, HMIC can image Al3+, Zn2+ and Cd2+ in the cells with different fluorescence signals.

Highly selective and sensitive fluorescent probe possessing AIEE and ICT properties for rapid detection of Pb2+ in aqueous medium and its applications in living cells

In this paper, a novel rapid, highly selective and sensitive Pb²⁺ fluorescent probe (E)-N'-((2-(4'-(diphenylamino)-[1,1'-biphenyl]-4-yl)-2H-1,2,3-triazol-4-yl)methylene) (DBTBH) was synthesized. The probe DBTBH not only exhibited more excellent selectivity and sensitivity to Pb²⁺ detection compared with other analytes (include metal ions and anions) in H₂ O:THF solution (v:v = 9:1, 10 mM Tris-HCl, 1 mM KI, pH 7.4), but also had excellent optical properties such as aggregation-induced emission enhancement (AIEE) and intramolecular charge transfer (ICT). Detection limit of the probe DBTBH towards Pb²⁺ was 4.49 × 10^-8  M. The possible mechanism was verified by ¹ H NMR titration and HR-MS. Furthermore, the successful detection of Pb²⁺ by DBTBH in real water samples and HeLa cells indicated that DBTBH has great potential for selective recognition of Pb²⁺ in the natural environment and biological systems. These findings will provide a promising new idea for designing better Pb²⁺ fluorescent probes in the future.

A multi-binding site hydrazone-based chemosensor for Zn(ii) and Cd(ii): a new strategy for the detection of metal ions in aqueous media based on aggregation-induced emission

A multi-binding site chemosensor, N-(3-methoxy-2-hydroxybenzylidene)-3-hydroxy-2-naphthahydrazone (H₃L), with excited-state intramolecular proton transfer (ESIPT) behaviour was prepared and characterized. It possesses no aggregation-induced emission (AIE) characteristics but can detect Cd²⁺ and Zn²⁺ ions selectively in the "off-on" mode based on the AIE of their complexes in the media of THF/HEPES and THF/H₂O, respectively, which will provide a new strategy for target detection based on AIE. The detection limits of Zn²⁺ and Cd²⁺ were 9.85 × 10^-9 M and 1.27 × 10^-7 M, respectively. The aggregates of the complexes formed in the detection system were confirmed by DLS data and SEM images. The corresponding Zn²⁺ (1) and Cd²⁺ (2) complexes were prepared to investigate the response mechanism. Powder X-ray diffraction and single crystal X-ray diffraction proved that complex 1 is the species formed in the detection system. The chemosensor coordinates with the Cd²⁺ and Zn²⁺ ions in different formation and coordination modes, leading to the emission position of the aggregates at 560 and 645 nm, respectively, based on which Cd²⁺ ions were successfully differentiated from Zn²⁺ ions. Moreover, the detection of Cd²⁺ and Zn²⁺ ions was realized qualitatively via test paper and quantitatively in water.

Oxidation-Induced Differentially Selective Turn-On Fluorescence via Photoinduced Electron Transfer Based on a Ferrocene-Appended Coumarin-Quinoline Platform: Application in Cascaded Molecular Logic

Differentially selective molecular sensors that exhibit differential response toward multiple analytes are cost-effective and in high demand for various practical applications. A novel, highly differentially selective electrochemical and fluorescent chemosensor, 5, based on a ferrocene-appended coumarin-quinoline platform has been designed and synthesized. Our designed probe is very specific toward Fe³⁺ via a reversible redox process, whereas it detects Cu²⁺ via irreversible oxidation. Interestingly, it exhibits differential affinity toward the Cu⁺ ion via complexation. High-resolution mass spectrometry, ¹H NMR titration, and IR spectral studies revealed the formation of a bidentate Cu⁺ complex involving an O atom of the amide group attached to the quinoline ring and a N atom of imine unit, and this observation was further supported by quantum-chemical calculations. The metal binding responses were further investigated by UV-vis, fluorescence spectroscopy, and electrochemical analysis. Upon the addition of Fe³⁺ and Cu²⁺ ions, the fluorescence emission of probe 5 shows a "turn-on" signal due to inhibition of the photoinduced electron transfer (PET) process from a donor ferrocene unit to an excited-state fluorophore. The addition of sodium l-ascorbate (LAS) as a reducing agent causes fluorescence "turn off" for the Fe³⁺ ion because of reemergence of the PET process but not for the Cu²⁺ ion because it oxidizes the ferrocene unit to a ferrocenium ion with its concomitant reduction to Cu⁺, which further complexes with 5. Thermodynamic calculations using the Weller equation along with density functional theory calculations validate the feasibility of the PET process. A unique combination of Fe³⁺, LAS, and Cu²⁺ ions has been used to produce a molecular system demonstrating combinational "AND-OR" logic operation.

A ratiometric fluorogenic probe for the real-time detection of SO32- in aqueous medium: application in a cellulose paper based device and potential to sense SO32- in mitochondria

A new water soluble and fluorogenic probe (L) that can demonstrate a specific ratiometric detection of a SO₂ derivative (SO₃^2-) in 100% aqueous medium and live cells has been designed and synthesized. The detection process can be visualized by the naked eye, as the orange-red fluorescence of L turns into a strong blue fluorescence upon interaction with SO₃^2-. L displayed several beneficial attributes such as detection in complete aqueous medium, extremely fast response time along with high selectivity and sensitivity. The ratiometric sensing was attributed to the selective nucleophilic addition reaction of SO₃^2- with L. The probe was further used to develop a low cost microfluidic sensor device (μPAD). The probe was biocompatible and its potential to sense SO₃^2- in mitochondria was captured in live HeLa cells.

Twisted-Intramolecular-Charge-Transfer-Based Turn-On Fluorogenic Nanoprobe for Real-Time Detection of Serum Albumin in Physiological Conditions

Two cyanine-based fluorescent probes, ( E)-2-(4-(diethylamino)-2-hydroxystyryl)-3-ethyl-1,1-dimethyl-1 H-benzo[ e]indol-3-ium iodide (L) and ( E)-3-ethyl-1,1-dimethyl-2-(4-nitrostyryl)-1 H-benzo[ e]indol-3-ium iodide (L₁), have been designed and synthesized. Of these two probes, the twisted-intramolecular-charge-transfer (TICT)-based probe, L, can preferentially self-assemble to form nanoaggregates. L displayed a selective turn-on fluorescence response toward human and bovine serum albumin (HSA and BSA) in ∼100% aqueous PBS medium, which is noticeable with the naked eye, whereas L₁ failed to sense these albumin proteins. The selective turn-on fluorescence response of L toward HSA and BSA can be attributed to the selective binding of probe L with HSA and BSA without its interfering with known drug-binding sites. The specific binding of L with HSA led to the disassembly of the self-assembled nanoaggregates of L, which was corroborated by dynamic-light-scattering (DLS) and transmission-electron-microscopy (TEM) analysis. Probe L has a limit of detection as low as ∼6.5 nM. The sensing aptitude of probe L to detect HSA in body fluid and an artificial-urine sample has been demonstrated.

A multi-functional chemosensor for highly selective ratiometric fluorescent detection of silver(I) ion and dual turn-on fluorescent and colorimetric detection of sulfide

A multi-functional chemosensor 1 as silver and sulfide detector was synthesized by the combination of octopamine and 4-dimethylaminocinnamaldehyde. Sensor 1 exhibited a ratiometric fluorescence emission for Ag+ from blue to sky. The binding mode of 1 and Ag+ turned out to be a 1 : 1 ratio as determined using Job plot and electrospray ionization (ESI) mass spectral analyses. The sensing mechanism of 1 with silver ion was unravelled by 1H NMR titrations and theoretical calculations. Sensor 1 also discerned sulfide by enhancing fluorescence intensity and changing colour from yellow to colourless in aqueous solution. The sensing properties of 1 toward S2- were investigated by using ESI-mass analysis, Job plot and 1H NMR titrations. Moreover, 1 could be used as a detector for sulfide in a wide pH range.

Highly selective recognition of Al3+ and I- ions using a bi-functional fluorescent probe

A tripodal fluorescent probe L1 armed with Rhodamine B and 1-naphthaleneisothiocyanates was prepared in high yield. A study of the recognition properties revealed that probe L1 exhibited high sensitivity and selectivity towards Al³⁺ through a "FRET" fluorescence response and colorimetric response with low detection limits of the order of 10^-8 M. Meanwhile, probe L1 also possessed high recognition ability for I^- through fluorescence decay, which given there are comparatively few selective fluorescent probes for I^-, is significant. Furthermore, the complexation mechanisms were fully investigated by spectral titrations, ¹H NMR spectroscopic titrations and mass spectrometry. The utility of probe L1 as a biosensor in living cells (PC3 cells) towards Al³⁺ ions has also been demonstrated.

A highly selective and sensitive fluorescent chemosensor for distinguishing cadmium(ii) from zinc(ii) based on amide tautomerization

A naphthalimide-derived fluorescent sensor termed L2 was designed and synthesized.

A highly sensitive and selective chemosensor for Pb2+ based on quinoline–coumarin

In this study, a highly sensitive and selective fluorescent chemosensor, ethyl(E)-2-((2-((2-(7-(diethylamino)-2-oxo-2H-chromene-3-carbonyl)hydrazono)methyl)quinolin-8-yl)oxy)acetate (1), was synthesized and characterized by ¹H NMR, ¹³C NMR and ESI-MS. Sensor 1 showed an “on–off” fluorescence response to Pb²⁺ with a 1 : 1 binding stoichiometry in CH₃CN/HEPES buffer medium (9 : 1 v/v). The detection limit of sensor 1 to Pb²⁺ was determined to be 0.5 μM, and the stable pH range for Pb²⁺ detection was from 4 to 8.

A highly sensitive and selective fluorescent chemosensor 1 was synthesized and used for naked eye detection of Pb²⁺.

White-light emission from simple AIE–ESIPT-excimer tripled single molecular system

A rationally designed simple organic molecule exhibits white-light emission in methanol/water and acetonitrile/water mixtures.