Fluorescent detection of zinc in biological systems: recent development on the design of chemosensors and biosensors

A highly selective indole-based sensor for Zn2+, Cu2+, and Al3+ ions with multifunctional applications

A wide range of chemosensors has been developed for detecting specific metal ions at trace levels, attracting considerable research interest. However, despite the significant role of indole-based molecules in the biological domain, only a few chemosensors incorporating this moiety have been reported. In this work, a novel indole-based receptor [R = (Z)-3-((((1H-indol-4-yl)methyl)imino)methyl)benzene-1,2-diol], was synthesized and characterized using single-crystal X-ray diffraction, NMR, IR, and ESI-MS techniques. Sensing studies conducted in a CH3CN/H2O (7 : 3, v/v) solvent system demonstrated that the receptor R exhibits selectivity towards Zn2+, Cu2+, and Al3+ ions, with turn-on fluorescence and UV-Vis spectral responses while showing insensitivity to other cations and anions. Binding studies revealed the formation of 1 : 2 stoichiometric complexes between R and the respective metal ions. The interaction with Zn2+ resulted in enhanced fluorescence emission at 497 nm, whereas Al3+ and Cu2+ ions caused significant bathochromic shifts in the absorption maxima from 290 nm to 308 nm and 318 nm, respectively. The calculated detection limits were 0.056 μM for Zn2+, 0.57 μM for Cu2+, and 0.45 μM for Al3+. Density functional theory (DFT) calculations confirmed that R coordinates effectively with these metal ions, stabilizing the complexes by reducing the HOMO-LUMO energy gap. Molecular docking studies further indicated strong binding affinities of R and its metal complexes to DNA and bovine serum albumin (BSA), elucidating the potential binding sites within these biomolecules. The receptor R exhibits outstanding potential for detecting Zn2+ ions in the Caenorhabditis elegans model system. Its excellent membrane permeability and biocompatible nature enable efficient intracellular uptake, ensuring accurate and reliable detection of Zn2+ ions in living organisms. Furthermore, the receptor was employed in designing molecular logic gates and keypad lock systems, demonstrating its utility in developing functional molecular devices.

Synthesis of novel sulphonamide derivatives from tunable quinolines with computational studies

The synthesis of new quinoline-sulphonamide derivatives was accomplished through a meticulous five-step molecular assembly utilizing Suzuki, acid-amine cross-coupling reactions and N-alkylation. The integrity of each derivative was thoroughly confirmed via comprehensive spectroscopic analyses, including 1H and 13C NMR, DEPT-135, 1H-1H COSY, HSQC NMR and HRMS techniques. Subsequently, the absorbance and emission spectra of the newly synthesized derivatives were thoroughly investigated. Absorbance spectra were determined to be restricted within the range of 337 nm to 341.73 nm, with compound 10j exhibiting the maximum wavelength of 341.73 nm; conversely, emission spectra were uniformly detected within the range of 411.70 nm to 429.90 nm upon excitation at 340 nm, with compound 10f demonstrating the highest wavelength of 429.90 nm. Notably, these fluorophores displayed impressive characteristics, with high intensity and significant molar extinction coefficients; quantum yield ranging from 0.015 to 0.558 along with the highest stokes shifts in 10h compound (0.6237 × 10-4) in acetonitrile solvent. Additionally, compound 10p showed strong binding affinity and favorable pharmacokinetic properties through molecular docking studies and ADMET calculations. The electronic structure of the molecules was elucidated using techniques such as density functional theory (DFT) and molecular electrostatic potential (MEP) mapping. Additionally, the calculated global reactivity parameters provided valuable insights. Compound 10p exhibited a distinctly low energy gap compared to other compounds, demonstrating its exceptional properties. The comparison between experimental and theoretical UV-vis spectra with major contribution transition in percentage also showcased the remarkable consistency and quality of the synthesized derivatives, highlighting the significant potential of this work in the field of fluorophore and biological application.

New Fluorescent Dye for the Detection of Zn2+ in Living Cells and Fixed Sections of the Rat Pancreas

We report the synthesis and characterization of a new 4-methoxyphenyl-2,2'-bipyridine-based ligand, such as 12, bearing dipicolylaminomethyl core as a receptor unit, as a probe for the fluorescence "turn-on" detection of Zn2+. Thus, in the presence of Zn2+ the probe 12 exhibited a fluorescence enhancement with a Stokes shift of ~ 180 nm and photoluminescence quantum yields value of ~ 1.0. In addition, 12 exhibited higher binding constant for Zn2+ (~ 2 × 105 M-1) with the LOD reaching the nanomolar level (~ 0.1 × 10-9 M) compare to the previously reported probe 1. The stoichiometry and structure of the [Zn(12)]2+ and [Zn(1)]2+ complexes were supported by XRD analysis, DFT calculations and 1H NMR experiments. It was postulated that, as a result of binding of Zn2+, the sample exhibited a bright "on" state via the PET-ICT processes. Molecular docking studies and confocal fluorescence microscopy experiments demonstrated that the probe 12 could be used for the fluorescence detection of Zn2+ not only in artificially enriched with zinc salts live cells, but also in fixed tissues with cations are in a bound state. The high binding constant of compound 12 to Zn2+ cation allows it to be used for the accurate localization of pancreatic beta cells (islets of Langerhans).

A Fluorometric Method for Zinc Estimation: Applications in the Estimation of Plasma Zinc and in Assessing Zinc Bioaccessibility from Rice

Sensitive and precise methods for the estimation of zinc (Zn) in biological fluids and foods are important tools in understanding the various aspects related to Zn nutrition. Estimation of serum/plasma Zn was suggested for assessing the population Zn status while assessing the bioaccessible Zn following simulated gastrointestinal digestion of crop varieties such as rice helps in ranking the crops. Atomic absorption spectrometry (AAS) or inductively coupled plasma-mass spectrometry (ICP-MS) are widely used for Zn estimation. Zinquin, a Zn fluorophore, has been used for the localization of cellular Zn and labile Zn pools in biological fluids with extremely high sensitivity. However, it was not tested for its use in Zn estimation in serum/plasma or in assessing the Zn bioaccessibility from foods. In the current study, we demonstrate a sensitive method for Zn estimation in human plasma and validate it against the reference method (AAS) by comparing the paired measurements on the same samples. The method-related bias between zinquin with AAS was negligible (0.48 µg/dL), and the precision (CV) of the assay was < 5% across different Zn concentrations. In addition, we also demonstrated the utility of zinquin assay in estimating the bioaccessibility of Zn from rice varieties and showed that the method is again comparable to AAS. The zinquin method is capable of discriminating the differences in zinc bioaccessibility between polished and unpolished rice varieties. In the context of required low plasma volume (100 µL Vs 400 µL), excellent comparability of the results with the reference method and analytical simplicity could be particularly useful.

Fluorogenic selective detection of Zn2+ using a pyrazole-ortho-vanillin conjugate: insights from DFT, molecular docking, bioimaging and anticancer applications

A fluorescent sensor, (E)-N'-(2-hydroxy-3-methoxybenzylidene)-3,5-dimethyl-1H-pyrazole-1-carbohydrazide (HMPC), was designed and synthesized for the selective fluorescence recognition of Zn2+ in semi-aqueous media. Notably, HMPC exhibited a red-shifted, two-fold fluorescence "turn-on" enhancement in response to Zn2+ at 490 nm, with a detection limit of 1.68 μM, which is significantly lower than the WHO guideline (76.0 μM). The binding constant of HMPC with Zn2+ was calculated to be 5 × 104 M-1. The fluorescence enhancement of HMPC in the presence of Zn2+ is attributed to the suppression of the PET process and the enhancement of ICT, leading to fluorescence via the CHEF mechanism. The sensing mechanism was demonstrated through UV-vis, fluorescence spectroscopy, Job plots, ESI-MS, and DFT calculations. For biological applications, cytotoxicity and cell imaging studies were performed using MCF-7 cells. Molecular docking studies revealed a high binding energy of HMPC (ΔG = -7.1 kcal mol-1) with the 4,5-diaryl isoxazole HSP90 chaperone protein, suggesting its potential as an anticancer agent. Additionally, its binding energy of -6.5 kcal mol-1 with the HDAC8 protein indicates greater efficacy than suberoylanilide hydroxamic acid (SAHA) in inhibiting HDAC, as it binds more strongly to the HDAC8 protein than SAHA (-7.4 kcal mol-1). Furthermore, due to its favorable ADME profile, HMPC may be suitable for oral administration, enhancing its potential as an anticancer drug.

V. A New Biphenol-bis(polyazacyclophane) Receptor with Unusual Photophysical Properties Towards Zn2

The new ligand 3,3'-bis(((2-(3,6,9-triaza-1(2,6)-pyridinacyclodecaphane-6-yl)ethyl)amino)methyl)-[1,1'-biphenyl]-2,2'-diol (L) has been synthesized and characterized. It contains two pyridinacyclophane macrocycles spaced by a 2,2'-biphenol moiety. The acid-base behaviour of L as well as its binding properties towards Zn2+ ion have been investigated. This work is inserted in the field of fluorescent ditopic receptors, formed by two polyamines spaced by a aromatic fragments. This ligand represents a new example of a peculiar case of polyamine fluorescent receptor in which the interaction with Zn2+ is translated into a deactivation of the emission. Enough data to describe and explain this unusual behaviour was obtained through potentiometric, UV-Vis, fluorescence and NMR titrations as well as theoretical calculations. This studies have shown that the metal cation is indirectly affecting the emission favouring a conformation in which the fluorophore is at stacking distance from the electron poor pyridine moieties. This gives rise to an oxidative photoinduced electron transfer from the excited state of the fluorophore to the electron-poor Zn2+ coordined pyridine.

Targeted imaging of lysosomal zinc ions with a tetrahedral DNA framework fluorescent reporter

Abnormal levels of zinc ions within endo-lysosomes have been implicated in the progression of Alzheimer's disease (AD), yet the detection of low-concentration zinc ions at the organelle level remains challenging. Here we report the design of an endo-lysosome-targeted fluorescent reporter, Znluorly, for imaging endogenous zinc ions. Znluorly is constructed from an amphiphilic DNA framework (DNF) with programmable size and shape, which can encapsulate zinc-responsive fluorophores within its hydrophobic nanocavity. We find that the tetrahedral DNFs of 20 bp in the edge length are effectively located within endo-lysosomes, which can detect zinc ions with a detection limit of ∼31.9 nM (a sensitivity that is ∼2.5 times that of the free fluorophore). Given the organelle-targeting ability and high zinc sensitivity of Znluorly, we employ it to detect endogenous endo-lysosomal zinc ions in neuron cells. We monitor the dynamics of zinc levels in AD model cells and zebrafish, corroborating the positive correlation between zinc levels and AD hallmarks including Aβ aggregates and learning/memory impairments. Our study provides a generalizable strategy for organelle-specific theranostic applications.

L-Tryptophan-based pyrene conjugate for intracellular zinc-guided excimer emission and controlled nano-assembly

This article describes intracellular zinc-induced excimer emission and tuning of self-assembly from L-tryptophan-pyrene conjugate (1). The zinc-guided excimer formation is due to the interaction of the pyrene moiety in an excited state. AFM studies show the structural modification in the supramolecular nano-assembly of 1 from dome-shaped to porous surface after complexation with zinc ions. Further, the interaction of 1 with Zn(II) ion is also studied using DFT, Job's plot, NMR titration and HRMS. The results of Zn(II) ion determination in natural water samples and RAW 264.7 cells demonstrate the practical utility of 1.

A Julolidine Aldehyde Dansyl Hydrazine Schiff Base as Fluorescence Chemosensor for Zn2+ ions Recognition and its Application

The Schiff base fluorescent probe (Dz-Jul), containing julolidine aldehyde and dansyl hydrazine, was derived using a simple condensation. This chemosensor showed high selectivity towards Zn2+ and quick response (170 s) in DMSO/H2O solutions (8/2, v/v, pH 7.2 buffer). A fluorometric titration determined that Dz-Jul-Zn2+ has a binding ratio of 1:1, and the association constant (Ka) is 1.03 × 105 M-1. The Dz-Jul detection limit of Zn2+ ions was 15 nM, much lower than the WHO standard (76.0 nM). DFT, ESI mass, and FTIR spectral demonstrated a plausible complexation mode between Dz-Jul and Zn2+ ions. In actual water samples, Zn2+ has been detected with good detection performance using Dz-Jul. Additionally, Dz-Jul-coated test strips allowed for rapid and qualitative monitoring of Zn2+ ions in a visible manner.

Unexpected enrichment of DNA aptamers for Zn2+ ions from an insulin selection

We serendipitously discovered Zn2+-binding DNA aptamers when selecting insulin aptamers. The Zn-1 aptamer binds to Zn2+ with a dissociation constant (Kd) of ∼1 μM, and has 450-fold higher selectivity for Zn2+ over Cd2+. A strand-displacement based fluorescent sensor achieved a limit of detection of 0.2 μM Zn2+.

Pyridine appended pyrimidine bis hydrazone: Zn2+/ATP detection, bioimaging and functional properties of its dinuclear Zn(II) complex

A pyridine functionalized pyrimidine-based system, H2P was successfully synthesized, characterized, and evaluated for its remarkable selective characteristics towards Zn2+ and ATP ions. The chemical sensing capabilities of H2P were demonstrated through absorption, fluorescence, and NMR spectroscopic techniques. The probe exhibited outstanding sensitivity when interacting with the ions, demonstrating relatively strong association constants and impressively low detection limits. The comprehensive binding mechanism of H2P with respect to Zn2+ and ATP ions was investigated using a combination of analytical methods, including Job's plot, NMR spectroscopy, mass spectrometry, and density functional theory (DFT) experiments. The interesting sensing ability of H2P for Zn2+/ATP ions was harnessed for live cell bioimaging and other diverse on-site detection purposes, including paper strips, cotton swabs, and applications involving mung bean sprouts. Further, the fluorescent probe demonstrated its effectiveness in detecting Zn2+ and ATP within live cells, indicating its significant potential in the realm of biological imaging applications. Moreover, the molecular configuration of the zinc complex (H2P-Zn2Cl4), derived from H2P, was elucidated using X-ray crystallography. This complex exhibited intriguing multifunctional attributes, encompassing its capability for detecting picric acid and for reversible acid/base sensing responses. The enhanced conducting behavior of the complex as well as its resistance properties were investigated by performing I-V characteristics and electrochemical impedance spectroscopic (EIS) experiments respectively.

An environmentally sensitive zinc-selective two-photon NIR fluorescent turn-on probe and zinc sensing in stroke

A two-photon near infrared (NIR) fluorescence turn-on sensor with high selectivity and sensitivity for Zn2+ detection has been developed. This sensor exhibits a large Stokes' shift (∼300 nm) and can be excited from 900 to 1000 nm, with an emission wavelength of ∼785 nm, making it ideal for imaging in biological tissues. The sensor's high selectivity for Zn2+ over other structurally similar cations, such as Cd2+, makes it a promising tool for monitoring zinc ion levels in biological systems. Given the high concentration of zinc in thrombi, this sensor could provide a useful tool for in vivo thrombus imaging.

Picomolar level sensorial dual colorimetric gold nanoparticle sensor for Zn2+ and Hg2+ ions synthesized from bark extract of Lannea Grandis Coromandelica and its wide range applications in real sample analysis

In this work a facile, rapid, reproducible and non-toxic approach has been demonstrated for synthesis of most stable AuNPs from bark extract of Lannea Grandis Coromandelica. UV-Visible spectroscopy, FTIR, TEM, SAED, EDX, XRD, DLS, Zeta Potential, FE-SEM, AFM and XPS techniques were employed for the characterization of synthesized LGC-AuNPs. The UV-Vis spectra of LGC-AuNPs gave SPR peak at 536 nm while the TEM analysis revealed LGC-AuNPs have 20.75 nm size with spherical in shape. DLS study showed the AuNPs have average diameter 50.18 nm. The synthesized AuNPs exhibited very high selectivity, rapid response in recognition towards Zn2+ and Hg2+ ions by changing its color within 20 sec. This proposed sensor can detect very low picomolar level of Zn2+ and Hg2+ ions (LOD value for Zn2+ and Hg2+ were found 1.36 pM and 24.60 pM respectively). Here we also studied effect of several factors such as variation of conc of gold, temperature, incubation time, pH, salt, solvent (polar protic and polar aprotic) to know in which condition AuNPs have high stability and sensitivity. The data revealed that synthesized AuNPs was stable up to two years at pH 6.5 at room temperature in water media and under this condition, it shows maximum sensitivity and reactivity. Moreover, here interference study was carried out to identify high selectivity of synthesized LGC-AuNPs probe in presence of different metal ions. The real sample analyses also revealed the great applicability of this probe. Therefore, this simple, rapid, low-cost, sensing activity appeared to hold great sensibleness for detection of heavy metal ions in real sample.

A trinuclear Zn (II) schiff base dicyanamide complex attenuates bacterial biofilm formation by ROS generation and membrane damage and exhibits anticancer activity

A trinuclear Zn (II) complex, [(ZnL{N(CN)2})2Zn], termed complex 1 has been synthesized by the reaction of an aqueous solution of sodium dicyanamide to the methanolic solution of Zn (CH3COO)2, 2H2O and corresponding Schiff base (H2L) which is derived from 1:2 condensation of 1, 4 butane diamine with 3-ethoxy salicylaldehyde. Complex 1 is characterized by elemental analysis, IR, UV and Single X-ray diffraction study. Drug resistance is a growing global public health concern that has prompted researchers to look into advanced alternative treatment modalities. In this context, complex 1 has shown promising antibacterial and antibiofilm efficacy against gram-positive Staphylococcus aureus and Methicillin-resistant Staphylococcus aureus strains. Complex 1 attenuated Staphylococcal biofilm formation by reducing several virulence factors including the formation of extracellular polysaccharide matrix, slime, haemolysin, staphyloxanthin, auto-aggregation, cell surface hydrophobicity, and motility. Notably, complex 1 mechanistically potentiated Reactive Oxygen Species (ROS) generation within the bacterial cells, leading to the damage of bacterial cell membrane followed by DNA leakage and thereby impeding the growth of Staphylococcus aureus. Furthermore, complex 1 significantly exhibited anticancer activity by reducing the growth of prostate adenocarcinoma cells. It obstructed the migration of cancer cells by potentiating apoptosis and arresting the cell cycle at the G2/M phase. In summary, complex 1 could act as a potent candidate for the generation of novel antibacterial, antibiofilm as well as anticancer treatment regimens for the management of drug-resistant biofilm-mediated Staphylococcus aureus infection and lethal prostate malignancy.

A novel chromone Schiff base as Zn2+ turn-on fluorescent chemosensor in a mixed solution

In this study, a novel fluorescent chemosensor 1 based on chromone-3-carboxaldehyde Schiff base was synthesized and featured through nuclear magnetic resonance (NMR) and mass spectra. Spectroscopic investigation indicated that the fluorescent sensor showed high selectivity toward Zn2+ over other metal ions and that the detection limit of 1 could reach 10-7  M. These indicated that 1 acted as a highly selective and sensitive fluorescence chemosensor for Zn2+ .

Water Solvated Zn(II)-Guanine Complex: Structural Aspects and Luminescence Properties

Understanding the role of metal ions in living organisms and their interactions with biological compounds is fundamental for our health and for developing technological devices for bioinorganic applications. In this work, structural aspects and photophysical mechanisms involved in the luminescence of the Zn(II)-guanine complex in water were studied by using computational quantum chemical methods, providing molecular-level explanations for reported experimental findings. Structural aspects were investigated with def2-SVP basis sets, Density Functional Theory, Resolution of Identity Algebraic Diagrammatic Construction in Second-Order (RI-ADC(2)), Polarizable Continuum Model (PCM), and Conductor-like Screening Model (COSMO) methods. Spectroscopic properties and photophysical deactivation mechanisms were explored with the atomic natural orbital basis sets including relativistic and semicore correlation (ANO-RCC-VDZP) basis sets, Multistate Complete-Active-Space Second-Order Perturbation Theory (MS-CASPT2), and Polarizable Continuum Model (PCM) methods. Our results indicate that Zn(II) ions bind preferentially to the N7 position, and three water molecules in its coordination sphere are sufficient for describing the photophysical properties. The complexation with Zn(II) ions and solvation effects favor fluorescence because the minimum energy region of the S1 (La) (1ππ*) ((La)min) potential energy hypersurface is stabilized, the (La/GS) crossing region is destabilized, and a high energetic barrier along the pathway from the (La)min and (La/GS) regions hampers fast nonradiative return of the electronic population to the ground state, as observed for isolated 9H-guanine.

Fluoranthene-terminated terpyridine ensemble for fluorescence light up and ratiometric chemical sensor for multi toxic metals

A novel π-electron rich fluoranthene embellished with a phenyl spacer and coupled with terpyridine (TS1) was developed through Diels-Alder reaction. Single crystal X-ray structure evidences the variations in dihedral angles between the fluoranthene and the phenyl unit responsible for development of non-coplanar interactions and stabilized by a wave-like molecular packing in the crystal lattice with weak π-π interaction of 4.125 Å. The peripheral terpyridine of TS1 endows an efficient binding with multiple metal ions by colorimetric and fluorometric methods. TS1 exhibits a ratiometric fluorescence response from sky blue to yellow colour upon the addition of Zn²⁺ ions with a limit of detection (LOD) of 0.05 ppm. The other metal ions such as Cu²⁺, Co²⁺ and Fe²⁺ demonstrate fluorescence quenching behaviour with LODs of 0.1, 0.3 and 0.7 ppm, respectively. The intramolecular charge transfer (ICT) shows the variation in TS1 emission behaviour upon metal ions interaction and quantitatively discriminates the metal ion concentrations. TS1 conferred a visual colorimetric change from colourless to magenta, enabling naked-eye detection of Fe²⁺ and showing clear discrimination between Fe²⁺ and Fe³⁺ ions for the real-time water samples. Furthermore, we have investigated the effect of TS1 in Zebrafish larvae/embryos and cytotoxicity in human urinary tract transitional cell carcinoma cells (UM-UC-3).

Design and Synthesis of Poly(2,2'-Bipyridyl) Ligands for Induction of Cell Death in Cancer Cells: Control of Anticancer Activity by Complexation/Decomplexation with Biorelevant Metal Cations

Chelation therapy is a medical procedure for removing toxic metals from human organs and tissues and for the treatment of diseases by using metal-chelating agents. For example, iron chelation therapy is designed not only for the treatment of metal poisoning but also for some diseases that are induced by iron overload, cancer chemotherapy, and related diseases. However, the use of such metal chelators needs to be generally carried out very carefully, because of the side effects possibly due to the non-specific complexation with intracellular metal cations. Herein, we report on the preparation and characterization of some new poly(bpy) ligands (bpy: 2,2'-bipyridyl) that contain one-three bpy ligand moieties and their anticancer activity against Jurkat, MOLT-4, U937, HeLa S3, and A549 cell lines. The results of MTT assays revealed that the tris(bpy) and bis(bpy) ligands exhibit potent activity for inducing the cell death in cancer cells. Mechanistic studies suggest that the main pathway responsible for the cell death by these poly(bpy) ligands is apoptotic cell death. It was also found that the anticancer activity of the poly(bpy) ligands could be controlled by the complexation (anticancer activity is turned OFF) and decomplexation (anticancer activity is turned ON) with biorelevant metal cations. In this paper, these results will be described.

Benzil Bis-Hydrazone Based Fluorescence 'Turn-on' Sensor for Highly Sensitive and Selective Detection of Zn(II) Ions

In this study, a novel Benzil Bis-Hydrazone (BBH) sensor with two C = N-N = C moieties was designed and synthesized based on the condensation reaction between benzil-dihydrazone (b) and cinnamaldehyde. The BBH probe in dimethylsulfoxide showed extremely weak fluorescence. However, the same solution exhibited an intensive fluorescence enhancement (152-fold) with the introduction of Zn(II) ions. In contrast, no or negligible fluorescence changes were observed when other ions were added. The fluorogenic behavior of BBH towards the examined cations indicated an excellent selectivity of the BBH sensor for Zn(II) cations without any interference from other cations like Fe(II), Mg(II), Cu(II), Co(II), Mn(II), Cr(III), Hg(II), Sn(II), Al(I), La(III), Ca(II), Ba(II), Na(I), K(I), and especially Cd(II). Moreover, the UV-vis spectrophotometric titrations revealed that a 1:1 stoichiometric complex BBH-Zn(II) was formed during the Zn(II) sensing and the binding constant value for this complex was calculated to be equal to 106.8. Further, in order to show the affinity of the BBH sensor for Zn(II) cations, it was deemed necessary to determine the limit of detection (LOD) which was found to equal to 2.5 10-4 M.

Prospects of Microfluidic Technology in Nucleic Acid Detection Approaches

Conventional diagnostic techniques are based on the utilization of analyte sampling, sensing and signaling on separate platforms for detection purposes, which must be integrated to a single step procedure in point of care (POC) testing devices. Due to the expeditious nature of microfluidic platforms, the trend has been shifted toward the implementation of these systems for the detection of analytes in biochemical, clinical and food technology. Microfluidic systems molded with substances such as polymers or glass offer the specific and sensitive detection of infectious and noninfectious diseases by providing innumerable benefits, including less cost, good biological affinity, strong capillary action and simple process of fabrication. In the case of nanosensors for nucleic acid detection, some challenges need to be addressed, such as cellular lysis, isolation and amplification of nucleic acid before its detection. To avoid the utilization of laborious steps for executing these processes, advances have been deployed in this perspective for on-chip sample preparation, amplification and detection by the introduction of an emerging field of modular microfluidics that has multiple advantages over integrated microfluidics. This review emphasizes the significance of microfluidic technology for the nucleic acid detection of infectious and non-infectious diseases. The implementation of isothermal amplification in conjunction with the lateral flow assay greatly increases the binding efficiency of nanoparticles and biomolecules and improves the limit of detection and sensitivity. Most importantly, the deployment of paper-based material made of cellulose reduces the overall cost. Microfluidic technology in nucleic acid testing has been discussed by explicating its applications in different fields. Next-generation diagnostic methods can be improved by using CRISPR/Cas technology in microfluidic systems. This review concludes with the comparison and future prospects of various microfluidic systems, detection methods and plasma separation techniques used in microfluidic devices.

Multicomponent synthesis of chromophores – The one-pot approach to functional π-systems

Multicomponent reactions, conducted in a domino, sequential or consecutive fashion, have not only considerably enhanced synthetic efficiency as one-pot methodology, but they have also become an enabling tool for interdisciplinary research. The highly diversity-oriented nature of the synthetic concept allows accessing huge structural and functional space. Already some decades ago this has been recognized for life sciences, in particular, lead finding and exploration in pharma and agricultural chemistry. The quest for novel functional materials has also opened the field for diversity-oriented syntheses of functional π-systems, i.e. dyes for photonic and electronic applications based on their electronic properties. This review summarizes recent developments in MCR syntheses of functional chromophores highlighting syntheses following either the framework forming scaffold approach by establishing connectivity between chromophores or the chromogenic chromophore approach by de novo formation of chromophore of interest. Both approaches warrant rapid access to molecular functional π-systems, i.e. chromophores, fluorophores, and electrophores for various applications.

Synthesis of a BINOL-Based C3 Symmetric Schiff Base and Its Fluorescence Response to Zn2

A novel C₃ symmetric 1,1'-bi-2-naphthol-based Schiff base (R,R,R)-6 has been synthesized which shows highly selective fluorescence enhancement with Zn²⁺ among 21 metal cations examined. Its sensitivity and selectivity are found to be greater than other related C₂ (1) and C₁ [(R)-9] symmetric compounds in the fluorescent recognition of Zn²⁺ . The mechanistic study reveals that the selective fluorescence enhancement of the probe can be attributed to the formation of a unimolecular multidentate 6-coordinated Zn²⁺ complex.

Coordination of Distal Carboxylate Anion Alters Metal Ion Specific Binding in Imidazo[1,2-a]pyridine Congeners

Imidazo[1,2-a]pyridine derivatives have excellent potential for chelation with transition metal ions. Two new imidazo[1,2-a]pyridine-8-carboxylates were synthesized and characterized by ¹H NMR, ¹³C NMR, HRMS, and single crystal-XRD techniques. Methyl carboxylate (probe 1) turns on fluorescence upon coordination with Zn²⁺, while sodium carboxylate (probe 2) turns off its fluorescence upon coordination with Co²⁺ or Cu²⁺ ions present in aqueous acetonitrile medium. ¹³C NMR study revealed that the change in metal ion specific binding was due to the involvement of carboxylate anion in complex formation with Co²⁺ or Cu²⁺ ions. The carboxylate anion at 8-position also enhanced the sensitivity of detection of probe 2 by an order of magnitude (detection limits: 3.804 × 10^-7 M, probe 1/Zn²⁺; 0.420 × 10^-7 M, probe 2/Co²⁺ and 0.304 × 10^-7 M, probe 2/Cu²⁺). The detection limits of probes 1 and 2 comply well with the World Health Organization (WHO) and US Environmental Protection Agency (US-EPA) guidelines for detection of heavy metal ions present in drinking water and ground water. Both the probes form a 1:1 complex with Zn²⁺, Co²⁺ or Cu²⁺, and the stoichiometry was verified by Job plot and ESI-mass analysis. The sensing mechanism is explained using ¹³C NMR experiments, ESI-mass analytical data and theoretical DFT calculations. The suitability of probes 1 and 2 for on-site detection and quantitative determination of Zn²⁺, Co²⁺ and Cu²⁺ ions present in biological, environmental and industrial samples is demonstrated. In addition, both 1 and 2 are used for detection of intracellular contamination of Zn²⁺, Co²⁺ or Cu²⁺ ions in onion epidermal cells.

Smart sensory polymer for straightforward Zn(II) detection in pet food samples

We report on an innovative method to measure the Zn(II) concentration in commercial pet food samples, both wet and dry food. It is based on a colorimetric sensory polymer prepared from commercial monomers and 0.5 % of a synthetic monomer having a quinoline sensory core (N-(8-(2-azidoacetamido)quinolin-5-yl)methacrylamide). We obtained the sensory polymer as crosslinked films by thermally initiated bulk radical polymerization of the monomers of 100 μm thickness, which we punched into Ø6 mm sensory discs. The immersion of the discs in water solutions containing Zn(II) turned the fluorescence on, allowing for the titration of this cation using the G parameter of a digital picture taken to the discs. The limits of detection and quantification were 29 and 87 µg/L, respectively. Furthermore, we measured the concentration of Zn(II) even in the presence of other cations, detecting no significant interferences. Thus, in a further step, we obtained the concentration of Zn(II) from 15 commercial pet food samples, ranging from 19 to 198 mg/kg, following a simple extraction procedure and contacting the extractant with our sensory discs. These results were contrasted with that obtained by ICP-MS as a reference method.

Ratiometric Zinc Biosensor Based on Bioluminescence Resonance Energy Transfer: Trace Metal Ion Determination with Tunable Response

Determination of metal ions such as zinc in solution remains an important task in analytical and biological chemistry. We describe a novel zinc ion biosensing approach using a carbonic anhydrase-Oplophorus luciferase fusion protein that employs bioluminescence resonance energy transfer (BRET) to transduce the level of free zinc as a ratio of emission intensities in the blue and orange portions of the spectrum. In addition to high sensitivity (below nanomolar levels) and selectivity, this approach allows both quantitative determination of "free" zinc ion (also termed "mobile" or "labile") using bioluminescence ratios and determination of the presence of the ion above a threshold simply by the change in color of bioluminescence, without an instrument. The carbonic anhydrase metal ion sensing platform offers well-established flexibility in sensitivity, selectivity, and response kinetics. Finally, bioluminescence labeling has proven an effective approach for molecular imaging in vivo since no exciting light is required; the expressible nature of this sensor offers the prospect of imaging zinc fluxes in vivo.

Terminalia chebula: a novel natural product colorimetric sensor for Fe2+ and Fe3+ ions

Natural product like Terminalia chebula as Fe2+ and Fe3+ ions sensor was not reported in the literature till now. Herein, we first reported Terminalia chebula (T. chebula), a natural product used in Ayurveda, as a highly sensitive, simple, and cost-effective colorimetric sensor for the detection of Fe2+ and Fe3+ ions. Terminalia chebula showed a selective colorimetric sensing ability for iron (2+/3+) by changing color from green and pale yellow to blue, having limit of detection level of 43.7 μM and 60.8 μM for Fe2+ and Fe3+ ions, respectively. The concentration-dependent colorimetric determination of iron (2+/3+) was carried out, and the color change to distinguish between different concentrations was excellent. Using High Performance Liquid Chromatography, the fraction having sensing ability was isolated and purified. From the mass spectra of the purified fraction, it was concluded that, the major component responsible for the sensing ability was tri-O-galloyl-β-D-glucose. This chemosensor could be used to detect and quantify Fe2+ and Fe3+ in water samples, which is particularly a useful tool.

A dual-channel visual sensing system for recognition of multiple metal ions

Here, we propose a simple, rapid, and effective colorimetric sensor array for discrimination of metal ions. The sensor array was constructed using two sensing channels, i.e., gold nanoparticles (AuNPs)- Tetramethylbenzidine (TMB)-H₂O₂ and AuNPs-O-phenylenediamine (OPD)-H₂O₂ reaction systems. The presence of metal ions with positive charges would lead to the corresponding surface charge change of negatively charged AuNPs, resulting in diverse catalytic performances of citrate-modified AuNPs, accompanied by a substantial colorimetric performance of oxidation products of TMB and OPD. Employing the diversity of colorimetric responses of metal ions to the two sensing channels, nine metal ions including Cr³⁺, Fe³⁺, Cu²⁺, Co²⁺, Ni²⁺, Pb²⁺, Mg²⁺, K⁺, and Cd²⁺ were well distinguished with a discrimination accuracy of 100% at a concentration as low as 50 nM. Further experiment showed that the sensor array was also capable of discriminating and quantifying metal ions at various concentrations, as well as the identification of metal ion mixtures. The feasibility of the sensor array was also verified by the successful identification of the nine metal ions in river water samples.

Turn on Fluorescence Sensing of Zn2+ Based on Fused Isoindole-Imidazole Scaffold

Optical chemosensors caused a revolution in the field of sensing due to their high specificity, sensitivity, and fast detection features. Imidazole derivatives have offered promising features in the literature as they bear suitable donor/acceptor groups for the selective analytes in the skeleton. In this work, an isoindole-imidazole containing a Schiff base chemosensor (1-{3-[(2-Diethylamino-ethylimino)-methyl]-2-hydroxy-5-methyl-phenyl}-2H-imidazo[5,1-a]isoindole-3,5-dione) was designed and synthesized. The complete sensing phenomena have been investigated by means of UV-Vis, fluorescence, lifetime measurement, FT-IR, NMR and ESI-MS spectroscopic techniques. The optical properties of the synthesized ligand were investigated in 3:7 HEPES buffer:DMSO medium and found to be highly selective and sensitive toward Zn²⁺ ion through a fluorescence turn-on response with detection limit of 0.073 μm. Furthermore, this response is effective in gel form also. The competition studies reveal that the response of the probe for Zn²⁺ ion is unaffected by other relevant metal ions. The stoichiometric binding study was performed utilizing Job’s method which indicated a 1:1 sensor–Zn²⁺ ensemble. Computational calculations were performed to pinpoint the mechanism of sensing.

Development of Transition-Metal-Free Lewis Acid-Initiated Double Arylation of Aldehyde: A Facile Approach Towards the Total Synthesis of Anti-Breast-Cancer Agent

This work describes a mild and robust double hydroarylation strategy for the synthesis of symmetrical /unsymmetrical diaryl- and triarylmethanes in excellent yields using Lambert salt (0.2-1.0 mol%). Despite the anticipated challenges associated with controlling selective product formation, unsymmetrical diaryl- and triarylmethanes products are obtained unprecedentedly. A highly efficient gram scale reaction has also been reported (TON for symmetrical product=475 and for unsymmetrical product=390). The synthetic utility of the methodology is demonstrated by the preparation of several unexplored diaryl- and triarylmethane-based biologically relevant molecules, such as arundine, vibrindole A, turbomycin B, and certain anti-inflammatory agents. A total synthesis of an anti-breast-cancer agent is also demonstrated. Control experiments, Hammett analysis, HRMS and GC-MS studies reveal the reaction intermediates and reaction mechanism.

Zn2+-Schiff's Base Complex as an "On-Off-On" Molecular Switch and a Fluorescence Probe for Cu2+ and Ag+ Ions

The present study presents a thorough theoretical analysis of the electronic structure and conformational preference of Schiff's base ligand N,N-bis(2-hydroxybenzilidene)-2,4,6-trimethyl benzene-1,3-diamine (H₂L) and its metal complexes with Zn²⁺, Cu²⁺ and Ag⁺ ions. This study aims to investigate the behavior of H₂L and the binuclear Zn²⁺ complex (1) as fluorescent probes for the detection of metal ions (Zn²⁺, Cu²⁺ and Ag⁺) using density functional theory (DFT) and time-dependent density functional theory (TDDFT). The six conformers of the H₂L ligand were optimized using the B3LYP/6-311 +  + G** level of theory, while the L^-2-metal complexes were optimized by applying the B3LYP functional with the LANL2DZ/6-311 +  + G** mixed basis set. The gas-phase and solvated Enol-cis isomer (E-cis) was found to be the most stable species. The absorption spectra of the E-cis isomer and its metal complexes were simulated using B3LYP, CAM-B3LYP, M06-2X and ωB97X functionals with a 6-311 +  + G** basis set for C, O, N and H atoms and a LANL2DZ basis set for the metal ions (Zn²⁺, Cu²⁺ and Ag⁺). The computational results of the B3LYP functional were in excellent agreement with the experimental results. Hence, it was adopted for performing the emission calculations. The results indicated that metal complex (1) can act as a fluorescent chemosensor for the detection of Ag⁺ and Cu²⁺ ions through the mechanism of intermolecular charge transfer (ICT) and as a molecular switch "On-Off-On" via the replacement of Cu²⁺ by Ag⁺ ions, as proved experimentally.

Fluorescence 'turn-on' probe for nanomolar Zn (II) detection in living cells and environmental samples

Herein, a Schiff base ligand FHE was synthesized by condensing 5-allyl-2-hydroxy-3-methoxybenzaldehyde, a eugenol derivative with a derivative furan-2-carbohydrazide. FHE alone showed low fluorescence signals due to the intramolecular charge transfer...

M, Patra M, Butcher RJ, Manjare ST. Selective detection of hypochlorous acid in living cervical cancer cells with an organoselenium-based BOPPY probe

The synthesis and crystal structure of the first selenium-containing BOPPY probe. The probe is selective for exogenous and endogenous HOCl detection in HeLa cells with a “turn-on” fluorescence response.

A Novel Imidazole Bound Schiff Base as Highly Selective "Turn-on" Fluorescence Sensor for Zn2+ and Colorimetric Kit for Co2

An imidazole based Schiff base (2-[(1H-imidazole-2-ylmethylene)-amino]-4-methyl-phenol) (IMP), with an imine unit, has been designed and characterized by various standard methods. The evaluation of the probe as a fluorogenic sensor for Zn²⁺ and a chromogenic sensor for Co²⁺ has been rationalized in terms of the PET mechanism. In the presence of Zn²⁺, a light yellow colored solution of IMP with maximum absorption of 364 nm becomes bright yellow with maximum absorption of 410 nm and a measurable fluorescent signal at 612 nm with bathochromic enhancement. The sensitivity of the fluorescent based assay (6.78 × 10^-9 M) for Zn²⁺ is far below the limit in the World Health Organization (WHO) guidelines for drinking water (7.6 × 10^-5 M) and therefore it is capable of being a practical system for the monitoring of Zn²⁺ concentrations in aqueous samples. Moreover, IMP showed a highly selective colorimetric response to Co²⁺ by displayed an obvious pink color upon addition of metal solution immediately without any interference from other ions. These results provide a new approach for selectively recognizing the two most important trace elements in the human body simultaneously, for Zn²⁺ by emission spectra and Co²⁺ by the naked eye.

Novel Benzothiazole-Based Highly Selective Ratiometric Fluorescent Turn-On Sensors for Zn2+ and Colorimetric Chemosensors for Zn2+, Cu2+, and Ni2+ Ions

Metal ions play a very important role in environmental as well as biological fields. The detection of specific metal ions at a minute level caught much attention, and hence, several probes are available in the literature. Even though benzothiazole-based molecules have a special place in the medicinal field, only very few chemosensors are reported based on this moiety. The current work describes the design and synthesis of the benzothiazole-based chemosensor for a highly selective and sensitive detection of biologically important metal ions such as Zn2+, Cu2+, and Ni2+. The sensing studies of compound-1 showed a ratiometric as well as colorimetric response toward Zn2+, Cu2+, and Ni2+ ions and color changes from colorless to yellow and is found to be insensitive toward various metal ions (Cd2+, Cr3+, Mn2+, Pb2+, Ba2+, Al3+, Ca2+, Fe2+, Fe3+, Mg2+, K+, and Na+). Further, compound-1 exhibited ratiometric as well as turn-on-enhanced fluorescence response toward Zn2+ ions and turn off response for Cu2+ and Ni2+ ions. The Job plots revealed that the binding stoichiometry of compound-1 and metal ions is 2:1. The detection limits were found to be 0.25 ppm for Zn2+, while it was 0.30 ppm and 0.34 ppm for Ni2+ and Cu2+, respectively. In addition, density functional theory results strongly support the colorimetric response of metals, and the reversibility studies suggested that compound-1 can be used as a powerful chemosensor for the detection of Zn2+, Cu2+, and Ni2+ ions. The bioimaging data illustrated that compound-1 is a very effective ratiometric sensor for Zn2+ ions in live cells.