Unveiling of a smartphone-mediated ratiometric chemosensor towards the nanomolar level detection of lethal CN-: combined experimental and theoretical validation with the proposition of a molecular logic circuitry

A promising naphthalene-functionalized ratiometric chemosensor (E)-1-((naphthalen-5-yl) methylene)-2-(2,4-dinitrophenyl) hydrazine (DNMH) is unveiled in the present work. DNMH demonstrates brisk discernible colorimetric response from yellow to red in the presence of CN⁻, a lethal environmental contaminant, in a near-perfect aqueous medium with a LOD of 278 nM. The “key role marker” controlling the electrochemical and non-covalent H-bonding interaction between DNMH and CN⁻ is through the commendable role of acidic –NH functionalities. Kinetic studies reveal a pseudo second order reaction rate and the formation of an unprecedented photostable adduct. The negative value of ΔG as evaluated from ITC substantiates the spontaneity of the DNMH⋯CN⁻ interaction. The sensing mechanism was further reinforced with state-of-the-art theoretical investigations, namely DFT, TDDFT and Fukui indices (FIs). Moreover, the proposition of a reversible multi-component logic circuitry implementing Boolean functions in molecular electronics has also been triggered by the turn-over spectrophotometric response of the ditopic ions CN⁻ and Cd²⁺. The cytotoxicity of DNMH towards Bacillus thuringiensis and Escherichia coli is successfully investigated via the MTT assay. Impressively, “dip stick” and “easy to prepare” test paper device and silica gel-based solid-phase CN⁻ recognition validate the on-site analytical application of DNMH. Furthermore, the involvement of a synergistic approach between ‘chemistry beyond the molecule’ and ‘engineering’ via an exquisitely implemented smartphone-assisted colorimetric sensory prototype makes this work unprecedented among its congeners and introduces a new frontier in multitudinous material-based functional product development.

A ratiometric chemosensor (DNMH) is unveiled herein, demonstrating selective chromogenic response towards CN⁻, with a LOD of 278 nM. Consequently, molecular logic circuitry and a smartphone-based colorimetric sensory prototype has been explored.

Coumarin functionalized molecular scaffolds for the effectual detection of hazardous fluoride and cyanide

Fluoride and cyanide contamination in drinking water imposes detrimental impacts on human health above their permissible limits. Hence, the quantitative detection of these colourless water-soluble toxins has attracted attention. Even though a plethora of chemosensors have been reported so far for the detection of fluoride and cyanide from various matrices, still their applicability is limited to a few examples. Nevertheless, recent advances in the syntheses of coumarin derivatives have shown significant impact on fluoride and cyanide detection. Therefore, this present review provides a brief overview of the application of coumarin-coupled molecular scaffolds towards the detection of perilous fluoride and cyanide along with their sensing mechanisms in order to develop more innovative, simple, sensitive, real-time responsive and cost-effective coumarin-based supramolecular chemosensors to promote next generation approaches towards the ultra-trace quantitative detection of these toxic anions.

A simple colorimetric and ratiometric fluoride ion probe with large color change

Two colorimetric and ratiometric fluoride ion probes SHJ-1 and SHJ-2 based on the acylhydrazone skeleton have been developed. Among the eight anions (F-, Cl-, Br-, I-, ClO4 -, H2PO4 -, HSO4 -, CH3COO-), the present probes showed high selectivity and sensitivity toward fluoride ion detection with obvious color change. Notably, the probe SHJ-1 exhibited a red shift of 145 nm upon fluoride sensing, which is the largest value among fluoride ion probes based on acylhydrazone derivates to date. 1HNMR titration study and theoretical calculations suggested that the strong binding of the probe SHJ-1 to fluoride as well as the further deprotonation may facilitate the intramolecular charge transfer transition. These two probes are 1 : 1 complexed with fluoride ions, and the detection limits were calculated to be 1.24 μM for SHJ-1 and 15.73 μM for SHJ-2.

A Chemodosimetric Approach for Fluorimetric Detection of Hg2+ Ions by Trinuclear Zn(II)/Cd(II) Schiff Base Complex: First Case of Intermediate Trapping in a Chemodosimetric Approach

The present work discloses the application of two fluorescent zinc and cadmium complexes (1 and 2) for sensing of Hg(II) ions through a chemodosimetric approach. The ligand under consideration in this work is a N₂O donor Schiff base ligand (E)-4-bromo-2-(((2-morpholinoethyl)imino)methyl)phenol (HL), which has been harnessed to generate complexes [Zn₃L₂(OAc)₄] (1) and [Cd₃L₂(OAc)₄] (2). X-ray single crystal diffraction studies unveil the trinuclear skeleton of complexes 1 and 2. Both complexes have been found to be highly fluorescent in nature. However, the quantum efficiency of Zn(II) complex (1) dominates over the Cd(II) analogue (2). The absorption and emission spectroscopic properties of the complexes have been investigated by density functional theory. Complexes 1 and 2 can detect Hg²⁺ ions selectively by fluorescence quenching, and it is noteworthy to mention that the mechanism of sensing is unique as well as interesting. In the presence of Hg²⁺ ions, complexes 1 and 2 are transformed to mononuclear mercuric intermediate complex (3) and finally to a trinuclear mercuric complex (4) by hydrolysis. We have successfully trapped the intermediate complex 3, and we characterized it with the aid of X-ray crystallography. Transformation of complexes 1 and 2 to intermediate complex 3 and finally to 4 has been established by UV-vis spectroscopy, fluorescence spectroscopy, ESI-MS spectroscopy, ¹H NMR spectroscopy, and X-ray crystallography. The spontaneity of the above conversion is well supported by thermodynamic aspects as reflected from density functional theoretical calculations.

Tandem Detection of Sub-Nano Molar Level CN- and Hg2+ in Aqueous Medium by a Suitable Molecular Sensor: A Viable Solution for Detection of CN- and Development of the RGB-Based Sensory Device

An inimitable urea-based multichannel chemosensor, DTPH [1,5-bis-(2,6-dichloro-4-(trifluoromethyl)phenyl)carbonohydrazide], was examined to be highly proficient to recognize CN- based on the H-bonding interaction between sensor -NH moiety and CN- in aqueous medium with explicit selectivity. In the absorption spectral titration of DTPH, a new peak at higher wavelength was emerged in titrimetric analytical studies of CN- with the zero-order reaction kinetics affirming the substantial sensor-analyte interaction. The isothermal titration calorimetry (ITC) experiment further affirmed that the sensing process was highly spontaneous with the Gibbs free energy of -26 × 104 cal/mol. The binding approach between DTPH and CN- was also validated by more than a few experimental studies by means of several spectroscopic tools along with the theoretical calculations. A very low detection limit of the chemosensor toward CN- (0.15 ppm) further instigated to design an RGB-based sensory device based on the colorimetric upshots of the chemosensor in order to develop a distinct perception regarding the presence of innocuous or precarious level of the CN- in a contaminated solution. Moreover, the reversibility of the sensor in the presence of CN- and Hg2+ originated a logic gate mimic ensemble. Additionally, the real-field along with the in vitro CN- detection efficiency of the photostable DTPH was also accomplished by using various biological specimens.

A highly sensitive and selective Schiff-base probe as a colorimetric sensor for Co2+ and a fluorimetric sensor for F- and its utility in bio-imaging, molecular logic gate and real sample analysis

In this work, we designed a novel Schiff-base probe from the condensation reaction of 3,5-diiodosalicylaldehyde with isoniazid. Treatment of the sensor molecule with different metal ions like K⁺, Ba²⁺, Ca²⁺, Mg²⁺, Fe²⁺, Mn²⁺, Co²⁺, Cu²⁺, Cd²⁺, Ni²⁺, Hg²⁺, Zn²⁺, Pb²⁺ and Al³⁺ in visual inspection and absorption measurements explained its colorimetric sensing ability. The sensor DISN displays a remarkable color variation from pale yellow to brownish-orange towards Co²⁺ ion. The absorption and emission spectra of DISN, upon treating with various anions including F^-, Br^-, Cl^-, I^-, HSO₄^-, NO₃^-, H₂PO₄^-, and CN^- were tested. The addition of the fluoride ion to the receptor caused not only the intense color variation from pale yellow to orange but also a significant fluorescence turn-on response. Job's plot method fixed the binding of Co²⁺ and F^- to DISN separately, in 2:1 and 1:1 binding stoichiometry, respectively. The detection limit of 1.24 × 10^-7 M and 0.108 × 10^-6 M was attained for Co²⁺ and F^-, respectively. The TD-DFT calculations further supported the photophysical properties involved in the free probe and its complexes. The YES and INHIBIT logic function was found to operate from modulation in the absorbance and fluorescence behavior of Co²⁺ and F^- ions with DISN. Furthermore, DISN displays its practical applicability in filter-paper strips, live cell imaging, and real sample analyses.

Engineering diformyl diaryldipyrromethane into a molecular keypad lock

A diaryldipyrromethane-based acyclic system acts as a photolabile sequential chemosensor for both anions and cations via ESIDPT and deprotonation, which is engineered into a fluorescent molecular keypad lock system.

Engineering bio-molecular device with biocompatible sensor via symmetric encryption–decryption of spectroscopic signals towards F− detection and Zn2+ recognition by the imine hydrolysis pathway

A small molecular probe was synthesized and its response towards biologically significant ions Zn²⁺ and F⁻ with low detection threshold (Zn²⁺: 50 nM & F⁻: 3 μM) was investigated as well as Bio-molecular device designing was performed.

A simple urea-based multianalyte and multichannel chemosensor for the selective detection of F−, Hg2+ and Cu2+ in solution and cells and the extraction of Hg2+ and Cu2+ from real water sources: a logic gate mimic ensemble

Herein, a hydrazine-based chromogenic, fluorogenic and electrochemical chemosensor BCC [1,5-bis(4-cyanophenyl) carbonohydrazide] was reported.

A Journey towards Salivary Fluoride Level Detection by Suitable Low Cost Chemosensor: From Molecule to Product

Fluoride is a ubiquitous anion and essential for us owing to its ability to protect human body from several health related issues. The safe limit of Fluoride ion for human body is 1.5 ppm, above it the ion becomes toxic and can cause dental-skeletal fluorosis or urolithiasis. Several countries are facing such health hazard owing to the naturally abundant excess fluoride in ground water. As a consequence, habitants of such fluoride enriched zone needs to monitor the concentration of fluoride in their body by periodic analysis. In this regard, development of a chemosensor which can detect fluoride from human body fluid at easy-instant-economic way is an obvious mandate. For the first time, our group has developed a sensor kit and sensor station device as a deliverable product for individual and batch scale detection of salivary fluoride level by colorimetric method. The sensor station is the first device made by interfacing chemical output with electronics and the encrypted signal in digital version could be used as a level of fluoride in saliva. Our journey towards the development of suitable chemosensor for recognition of fluoride from human body fluid is summarized in this account.

A pyrene-benzimidazole composed effective fluoride sensor: potential mimicking of a Boolean logic gate

A highly selective fluoride sensor based on a pyrene benzimidazole unit was developed and studied for recyclable memory function.

Nanomolar-level selective dual channel sensing of Cu2+and CN−from an aqueous medium by an opto-electronic chemoreceptor

A novel chromogenic and fluorogenic chemoreceptor exhibiting a proclivity towards Cu²⁺and CN⁻, with applications in bioimaging and molecular electronics, was developed.

Photoinduced Electron Transfer Switching Mechanism of a Naphthalimide Derivative with its Solvatochromic Behaviour: An Experimental and Theoretical Study with In Cell Investigations

The sole existence of a t-bone-shaped naphthalimide derivative [2-(2-aminoethyl)-1H-benzo[de]isoquinoline-1,3(2H)dione] (NAP), which gives rise to a photoinduced electron transfer (PET) mechanism, has been established using a combination of experimental and theoretical studies. In parallel an in vitro-in cell PET mechanism has also been shown. To understand the photophysics of NAP, solvent studies have been carried out in different solvents. In addition, theoretical calculations have been conducted to explain the spectroscopic properties through optimized structures. A "turn off" PET mechanism has also been observed in the presence of specific metal ions, namely, Cr³⁺ , Fe³⁺ and Hg²⁺ among a series of metal ions. Theoretical studies reveal that NAP-Cr³⁺ , NAP-Fe³⁺ and NAP-Hg²⁺ have their HOMO energy states lying in between a HOMO-LUMO energy state of the t-bone-type NAP molecule. On the contrary, the HOMO state of the other metal ion-NAP conjugate (NAP-Mⁿ⁺ ) does not lie in between the HOMO-LUMO energy gap of the t-bone-type NAP molecule. Coupled with in vitro studies, in cell investigations reveal an enhancement of fluorescence intensity of NAP upon cytosolic metal sensing. Furthermore, a very high cell viability of NAP treated cells as tested by MTT assay and a fast permeation of the said compound as revealed by flow cytometry suggest NAP to be a potential candidate in metal sensing and bioimaging applications.

A highly selective chromogenic sensor for Mn2+, turn-off fluorometric for Hg2+ ion, and turn-on fluorogenic sensor for F- ion with the practical application

A colorimetric and fluorometric probe (E)-2-((8-hydroxy-1,2,3,5,6,7-hexahydropyrido[3,2,1-ij]quinolin-9-yl)methylene)hydrazinecarbothioamide based on thiosemicarbazide and julolidine moieties has been synthesised in pure crystalline form and characterized by ¹H NMR, UV-vis, elemental analysis and single crystal XRD. The probe functioned as multitarget ion sensor, detect biologically important metal ions Hg²⁺ and Mn²⁺ in dual channel mode. Meanwhile, in mixed solvent media DMF/H₂O [8:2], probe displayed selectivity for Hg²⁺ over other cations by the emission spectrum. Interestingly probe has been explored to recognize F^- anion in DMF through ESIPT mechanism. The 1:1 binding stoichiometry of probe with Hg²⁺ and Mn²⁺ is confirmed by Job's plot through emission titration and UV-vis titration respectively. Probe is selective and sensitive to Hg²⁺ and Mn²⁺ with detection limit as low as 15μM and 0.2μM respectively. The sensing mechanism for selective ions was also scrutinized using ¹H NMR experiments and computational studies.

Small molecular probe as selective tritopic sensor of Al3+, F- and TNP: Fabrication of portable prototype for onsite detection of explosive TNP

Schiff base organic compound (SOC) has been prepared as a tritopic chemosensor for selective sensing by fluorescence signalling towards ions like Al³⁺, F^- and explosive molecule like TNP. In general, fluorescence like photophysical property has been used for selective detection of analyte where Al³⁺ and F^- show turn-on fluorescence signal at different wavelengths (nm) however, quenching was found with TNP. As a consequence, the chemosensor has become a selective sensor for Al³⁺, F^- and TNP. Reversibility of fluorescence responses for Al³⁺ and F^- are observed in presence of ammonium nitrate and H⁺ respectively. Similar to the detection of TNP, the detection of explosive like NO₃^- salts is also essential from homeland security point of view. In the present work, the finding of reversible sequential fluorescence response can be promoted for fabrication of next generation AND-NOT-OR-NAND-XOR-XNOR-NOR based complex logic circuit which is applicable in photonics, security and other fields including inorganic and material science. In the case of TNP recognition, the pathway mainly depends on non-covalent interaction (quenching constant: 4.4 × 10⁵ M^-1) which is even better than the recently reported materials. Detection limit for Al³⁺, F^- and TNP is 1 μM, 3 μM and 500 nM respectively. DFT-D3 has been carried out to explore the host⋯guest interaction along with the structure-property correlation of the present host-guest system. All three guest analytes have been detected inside the living cell at a certain level and in its consequence, the successful in vitro recognition ability of the SOCs inside human cell line HeLa has been explored too. In real time stepping, an easy to operate and an economically affordable pocket prototype has also been fabricated for on spot detection of TNP like explosive.

Hydrazine functionalized probes for chromogenic and fluorescent ratiometric sensing of pH and F−: experimental and DFT studies

Two novel hydrazine based sensors, BPPIH (N¹,N³-bis(perfluorophenyl)isophthalohydrazide) and BPBIH (N^1′,N^3′-bis(perfluorobenzylidene)isophthalohydrazide), are presented here.

A simple naphthalene-based fluorescent probe for high selective detection of formaldehyde in toffees and HeLa cells via aza-Cope reaction

A simple naphthalene-based fluorescent probe (AENO) for formaldehyde (FA) was successfully synthesized, which exhibited a significant fluorescence turn-on response towards FA in aqueous solution. The probe could quantitatively determine the concentration of FA (0-1.0mM) with excellent selectivity, high sensitivity and low limit of detection (0.57µM). The sensing mechanism was proposed as 2-aza-Cope rearrangement for AENO after reaction with FA, which was confirmed by (1)H NMR, HR-MS, FT-IR, UV-vis and fluorescence spectra. The probe has been employed to determine the FA contents in several commercially available toffee samples with satisfactory performance. Thus, AENO might be used as a promising tool for quantitative detection of FA in food. Furthermore, fluorescence imaging of HeLa cells indicated that the probe was cell membrane permeable and could be used for visualizing/imaging the FA trace/transportation in cancer cells.

Novel Schiff-base molecules as efficient corrosion inhibitors for mild steel surface in 1 M HCl medium: experimental and theoretical approach

In order to evaluate the effect of the functional group present in the ligand backbone towards corrosion inhibition performances, three Schiff-base molecules namely, (E)-4-((2-(2,4-dinitrophenyl)hydrazono)methyl)pyridine (L(1)), (E)-4-(2-(pyridin-4-ylmethylene)hydrazinyl)benzonitrile (L(2)) and (E)-4-((2-(2,4-dinitrophenyl)hydrazono)methyl)phenol (L(3)) were synthesized and used as corrosion inhibitors on mild steel in 1 M HCl medium. The corrosion inhibition effectiveness of the studied inhibitors was investigated by weight loss and several sophisticated analytical tools such as potentiodynamic polarization and electrochemical impedance spectroscopy measurements. Experimentally obtained results revealed that corrosion inhibition efficiencies followed the sequence: L(3) > L(1) > L(2). Electrochemical findings showed that inhibitors impart high resistance towards charge transfer across the metal-electrolyte interface and behaved as mixed type inhibitors. Scanning electron microscopy (SEM) was also employed to examine the protective film formed on the mild steel surface. The adsorption as well as inhibition ability of the inhibitor molecules on the mild steel surface was investigated by quantum chemical calculation and molecular dynamic (MD) simulation. In quantum chemical calculations, geometry optimized structures of the Schiff-base inhibitors, electron density distribution in HOMO and LUMO and Fukui indices of each atom were employed for their possible mode of interaction with the mild steel surfaces. MD simulations revealed that all the inhibitors molecules adsorbed in parallel orientation with respect to the Fe(110) surface.

Construction of a novel INHIBIT logic gate through a fine-tuned assembly of anthryl fluorophores via selective anion recognition and host–guest interactions

A novel ligand containing of anthryl fluorophore was achieved. The assembly and disassembly of anthryl fluorophore by Pi and β-CD as chemical inputs and emission around 500 nm as output resulted in the construction of novel INHIBIT gate.

Fluorescence “on–off–on” chemosensor for selective detection of Hg2+ and S2−: application to bioimaging in living cells

A phenothiazine based diamino-malenonitrile-linked (P-1) chromogenic and fluorogenic probe was synthesized and characterized for the specific detection of Hg²⁺ and S²⁻. The probe P-1 can be used for selective imaging of Hg²⁺ and S²⁻ in living cells.

How paramagnetic and diamagnetic LMOCs detect picric acid from surface water and the intracellular environment: a combined experimental and DFT-D3 study

Diamagnetic and paramagnetic luminescent metal organic complexes (LMOCs) have been reported for explosive and pollutant nitro aromatic (epNAC) recognition.

Phenothiazine based sensor for naked-eye detection and bioimaging of Hg(ii) and F− ions

The design and development of new phenothiazine-based fluorescent probes, which displays selective fluorescence response to Hg²⁺ and F⁻ ions in a reversible manner. The probe is the first example that facilitates the detection of Hg²⁺ at nanomolar concentration.