Two birds with one stone: Multifunctional and highly selective fluorescent probe for distinguishing Zn2+ from Cd2+ and selective recognition of sulfide anion

Activity-Based Fluorescent Probes for Hydrogen Sulfide and Related Reactive Sulfur Species

Hydrogen sulfide (H2S) is not only a well-established toxic gas but also an important small molecule bioregulator in all kingdoms of life. In contemporary biology, H2S is often classified as a "gasotransmitter," meaning that it is an endogenously produced membrane permeable gas that carries out essential cellular processes. Fluorescent probes for H2S and related reactive sulfur species (RSS) detection provide an important cornerstone for investigating the multifaceted roles of these important small molecules in complex biological systems. A now common approach to develop such tools is to develop "activity-based probes" that couple a specific H2S-mediated chemical reaction to a fluorescent output. This Review covers the different types of such probes and also highlights the chemical mechanisms by which each probe type is activated by specific RSS. Common examples include reduction of oxidized nitrogen motifs, disulfide exchange, electrophilic reactions, metal precipitation, and metal coordination. In addition, we also outline complementary activity-based probes for imaging reductant-labile and sulfane sulfur species, including persulfides and polysulfides. For probes highlighted in this Review, we focus on small molecule systems with demonstrated compatibility in cellular systems or related applications. Building from breadth of reported activity-based strategies and application, we also highlight key unmet challenges and future opportunities for advancing activity-based probes for H2S and related RSS.

Sensitivity and Selectivity Analysis of Fluorescent Probes for Hydrogen Sulfide Detection

Hydrogen sulfide (H₂S) is a gasotransmitter known to regulate physiological and pathological processes. Abnormal H₂S levels have been associated with a range of conditions, including Parkinson's and Alzheimer's diseases, cardiovascular and renal diseases, bacterial and viral infections, as well as cancer. Therefore, fast and sensitive H₂S detection is of significant clinical importance. Fluorescent H₂S probes hold great potential among the currently developed detection methods because of their high sensitivity, selectivity, and biocompatibility. However, many proposed probes do not provide a gold standard for proper use and selection. Consequently, issues arise when applying the probes in different conditions. Therefore, we systematically evaluated four commercially available probes (WSP‐1, WSP‐5, CAY, and P3), considering their detection range, sensitivity, selectivity, and performance in different environments. Furthermore, their capacity for endogenous H₂S imaging in live cells was demonstrated.

Bio-inspired Track-Etched Polymeric Nanochannels: Steady-State Biosensors for Detection of Analytes

Bio-inspired polymeric nanochannel (also referred as nanopore)-based biosensors have attracted considerable attention on account of their controllable channel size and shape, multi-functional surface chemistry, unique ionic transport properties, and good robustness for applications. There are already very informative reviews on the latest developments in solid-state artificial nanochannel-based biosensors, however, which concentrated on the resistive-pulse sensing-based sensors for practical applications. The steady-state sensing-based nanochannel biosensors, in principle, have significant advantages over their counterparts in term of high sensitivity, fast response, target analytes with no size limit, and extensive suitable range. Furthermore, among the diverse materials, nanochannels based on polymeric materials perform outstandingly, due to flexible fabrication and wide application. This compressive Review summarizes the recent advances in bio-inspired polymeric nanochannels as sensing platforms for detection of important analytes in living organisms, to meet the high demand for high-performance biosensors for analysis of target analytes, and the potential for development of smart sensing devices. In the future, research efforts can be focused on transport mechanisms in the field of steady-state or resistive-pulse nanochannel-based sensors and on developing precisely size-controlled, robust, miniature and reusable, multi-functional, and high-throughput biosensors for practical applications. Future efforts should aim at a deeper understanding of the principles at the molecular level and incorporating these diverse pore architectures into homogeneous and defect-free multi-channel membrane systems. With the rapid advancement of nanoscience and biotechnology, we believe that many more achievements in nanochannel-based biosensors could be achieved in the near future, serving people in a better way.

A new class of fluorogenic thiazolo[2,3-b]quinazolinone receptor: selective detection towards mercury and hydrogen bisulfate ions in aqueous medium

A series of fluorophoric and structurally diverse thiazoloquinazoline derivatives were synthesized in a one-pot multicomponent cascade reaction using a microwave irradiation technique. The unique structural arrangement of the synthesized compounds encouraged us to design a new type of bioactive molecular receptor. This receptor interacts with HSO₄⁻ in 1 : 1 and Hg²⁺ in 1 : 2 binding stoichiometric ratios resulting in a change in fluorescence as well as absorption spectra in aqueous medium. The ion bonded receptor complex possibly enhances the fluorescence signal of the receptor via H-bonded complex formation with HSO₄⁻ ions and co-ordinate complex formation with Hg²⁺ ions.

Fluorophoric thiazoloquinazoline derivatives were synthesized under microwave assisted one-pot three-component cascade reaction. Owing to their unique structural arrangement, a new bioactive molecular receptor was developed for HSO⁴⁻ and Hg²⁺ ions.

Water-soluble fluorescent sensor for Zn2+ with high selectivity and sensitivity imaging in living cells

A new water-soluble 4-amino-1, 8-naphthalimide based fluorescent sensor, with iminoacetic acid and iminoethoxyacetic acid as receptor contained two different arms, was developed. Under physiological pH conditions, it demonstrates good water solubility, high selectivity and sensitivity for sensing Zn²⁺ with about 20-fold enhancement in aqueous solution, with a characteristic emission band of 4-amino-1, 8-naphthalimide with a green color centered at 550 nm. It was applied successfully to detect Zn²⁺ in living cells.

A dual-function probe based on naphthalene for fluorescent turn-on recognition of Cu2+ and colorimetric detection of Fe3+ in neat H2O

A simple naphthalene derivative, 6-hydroxy-2-naphthohydrazide (NAH), was designed and synthesized through two facile steps reactions with the 6-hydroxy-2-naphthoic acid (NCA) as the starting material. In neat H₂O (10% 0.01 M HEPES buffer, v/v, pH = 7.4), probe NAH showed a highly selective and sensitive response towards Fe³⁺ via perceptible color change and displayed "turn-on" dual-emission fluorescence response for Cu²⁺. The binding stoichiometry ratio of NAH/Cu²⁺ and NAH/Fe³⁺ were all confirmed as 1:1 by the method of fluorescence job's plot and UV-Vis job's plot, respectively. Probe NAH can be used over a wide pH range for the determination of Fe³⁺ (2.0-10.0) and Cu²⁺ (6.0-10.0) without interference from other co-existing metal ions. A possible detection mechanism was the hydrolysis of NAH upon the addition of Fe³⁺ or Cu²⁺, thereby leading to the formation of 6-hydroxy-naphthalene-2-carboxylic acid (NCA) which was further confirmed by the various spectroscopic techniques including FT-IR, ¹H NMR titration and HRMS. Moreover, NAH was successfully applied to the detection of Cu²⁺ and Fe³⁺ in tap water, ultrapure water and BSA.

Dual-Analyte Fluorescent Sensor Based on [5]Helicene Derivative with Super Large Stokes Shift for the Selective Determinations of Cu2+ or Zn2+ in Buffer Solutions and Its Application in a Living Cell

A new fluorescent sensor, M201-DPA, based on [5]helicene derivative was utilized as dual-analyte sensor for determination of Cu²⁺ or Zn²⁺ in different media and different emission wavelengths. The sensor could provide selective and bifunctional determination of Cu²⁺ in HEPES buffer containing Triton-X100 and Zn²⁺ in Tris buffer/methanol without interference from each other and other ions. In HEPES buffer, M201-DPA demonstrated the selective ON-OFF fluorescence quenching at 524 nm toward Cu²⁺. On the other hand, in Tris buffer/methanol, M201-DPA showed the selective OFF-ON fluorescence enhancement upon the addition of Zn²⁺, which was specified by the hypsochromic shift at 448 nm. Additionally, M201-DPA showed extremely large Stokes shifts up to ∼150 nm. By controlling the concentration of Zn²⁺ and Cu²⁺ in a living cell, the imaging of a HepG2 cellular system was performed, in which the fluorescence of M201-DPA in the blue channel was decreased upon addition of Cu²⁺ and was enhanced in UV channel upon addition of Zn²⁺. The detection limits of M201-DPA for Cu²⁺ and Zn²⁺ in buffer solutions were 5.6 and 3.8 ppb, respectively. Importantly, the Cu²⁺ and Zn²⁺ detection limits of the developed sensors were significantly lower than permitted Cu²⁺ and Zn²⁺ concentrations in drinking water as established by the U.S. EPA and WHO.

Photophysics of a coumarin based Schiff base in solvents of varying polarities

The present work reports detailed photophysics of a coumarin based Schiff base, namely, (E)-7-(((8-hydroxyquinolin-2-yl)methylene)amino)-4-methyl-2H-chromen-2-one (HMC) in different solvents of varying polarity exploiting steady state absorption, fluorescence and time resolved fluorescence spectroscopy. The dominant photophysical features of HMC are discussed in terms of emission from an intramolecular charge transfer (ICT) excited state. Molecular orbital (MO) diagrams as obtained from DFT based computational analysis confirms the occurrence of charge transfer from 8'-hydroxy quinoline moiety of the molecule to the coumarin part. The notable difference in the photophysical response of HMC from its analogous coumarin (C480) lies in a lower magnitude of fluorescence quantum yield of the former, particularly in the solvents of low polarity, which is rationalized by considering the higher rate of non-radiative decay of HMC in apolar solvents. Phosphorescence emission as well as phosphorescence lifetime of HMC has also been reported in 77K frozen matrix.

Selective and sensitive detection of cysteine in water and live cells using a coumarin–Cu2+ fluorescent ensemble

A coumarin–Cu²⁺ ensemble based fluorescent chemosensor was developed for the selective detection of cysteine in aqueous media and live cells.

A highly efficient and selective coumarin based fluorescent probe for colorimetric detection of Fe3+and fluorescence dual sensing of Zn2+and Cu2+

A new coumarin based Schiff-base chemosensor was synthesized and evaluated. Based on Job’s plot,¹H NMR titration, ESI-MS and B-H plot, the structure of ligand and its metal ion is 1 : 1 stoichiometry. It also exhibits a binary logic function.

A new diketopyrrolopyrrole-based probe for sensitive and selective detection of sulfite in aqueous solution

A new probe was synthesized by incorporating an α,β-unsaturated ketone to a diketopyrrolopyrrole fluorophore. The probe had exhibited a selective and sensitive response to the sulfite against other thirteen anions and biothiols (Cys, Hcy and GSH), through the nucleophilic addition of sulfite to the alkene of probe with the detection limit of 0.1 μM in HEPES (10 mM, pH 7.4) THF/H2O (1:1, v/v). Meanwhile, it could be easily observed that the probe for sulfite changed from pink to colorless by the naked eye, and from pink to blue under UV lamp after the sulfite was added for 20 min. The NMR and Mass spectral analysis demonstrated the expected addition of sulfite to the C=C bonds.

A highly selective fluorescent sensor for Al3+ and the use of the resulting complex as a secondary sensor for PPi in aqueous media: its applicability in live cell imaging

An “off–on–off” reversible fluorescent sensor has been developed for sequential detection of Al³⁺ and PPi in aqueous media, and has further been applied to live cell imaging.

Optical sensor: a promising strategy for environmental and biomedical monitoring of ionic species

In this review, we cover the recent developments in fluorogenic and chromogenic sensors for Cu²⁺, Fe²⁺/Fe³⁺, Zn²⁺and Hg²⁺.

NBD-based fluorescent chemosensor for the selective quantification of copper and sulfide in an aqueous solution and living cells

A fluorescent chemosensor (NL) has been developed for the selective quantification of copper and sulfide in aqueous solutions and living cells.

Chromogenic and fluorogenic chemosensors for hydrogen sulfide: review of detection mechanisms since the year 2009

The development of probes for the biologically important gas hydrogen sulfide (H₂S) has been an active area of research in recent years.

Fluorescent metal ion chemosensors via cation exchange reactions of complexes, quantum dots, and metal–organic frameworks

Overview of a new paradigm in the design of fluorescent chemosensors for detecting metal ions via cation exchange reactions of complexes, quantum dots, and metal–organic frameworks.

A novel coumarin based molecular switch for dual sensing of Zn(ii) and Cu(ii)

New coumarin based molecular switch for Zn²⁺ and Cu²⁺ presents a tunable system comprising of two INHIBIT logic gates with Zn²⁺ and Cu²⁺ or Zn²⁺ and EDTA as chemical inputs. IMPLICATION logic gate is obtained with Cu²⁺ and EDTA as chemical inputs.

Highly selective turn-on fluorescent sensor for nanomolar detection of biologically important Zn2+ based on isonicotinohydrazide derivative: application in cellular imaging

A new Zn(2+) selective chemosensor (3) was synthesized by condensation of commercially available substituted salicylaldehyde and isonicotinohydrazide, and characterized by single crystal X-ray crystallography. Receptor 3 with Zn(2+) exhibited a highly selective and pronounced enhancement in the fluorescence emission among different cations by forming a 2:1 complex. The receptor can detect Zn(2+) up to nanomolar level (6.75 nM) with good tolerance of other metal ions and can be used for in vitro cellular imaging.

Cascade reaction-based rapid and ratiometric detection of H2S/S2− in the presence of bio-thiols with live cell imaging: demasking of ESIPT approach

For the rapid, ratiometric, fluorogenic and “naked eye” detection of H₂S/S²⁻, a pro-excited state intramolecular proton transfer (ESIPT)-based receptor, 2-formyl-benzoic acid 2-benzothiazol-2-yl-phenyl ester (FBBP), has been designed.

Cascade OFF–ON–OFF fluorescent probe: dual detection of trivalent ions and phosphate ions

A new rhodamine B-based fluorescent probe was developed for the selective cascade signaling of trivalent cations (Fe³⁺, Al³⁺, Cr³⁺) and phosphate anion (PO₄³⁻).