Ferrocene-based novel electrochemical In sensor

A new ferrocene-based electrochemical sensor 1 for In³⁺ with amide and thiourea as binding sites was synthesized and characterized by X-ray crystal analysis. Among various metal ions, 1 displays highly selective electrochemical signal changes for In³⁺ over other metal ions, with its color changing from yellow to orange.     

Boron-dipyrromethene based specific chemodosimeter for fluoride ion

3,5-Bis(trimethylsilylethynyl)-4,4-difluoro-8-(4-tolyl)-4-bora-3a,4a-diaza-s-indacene [BODIPY(CCTMS)₂] has been synthesized by coupling of 3,5-dibromo-4,4-difluoro-8-(4-tolyl)-4-bora-3a,4a-diaza-s-indacene with trimethylsilylacetylene under pd(0) coupling conditions. The BODIPY(CCTMS)₂ was used as a selective colourimetric and fluorescent chemodosimeter for fluoride ion, following the F⁻ ion induced cleavage of trimethylsilyl group, the protecting group of ethyne functionality by monitoring the changes in UV-vis and fluorescence properties. The dosimeter BODIPY(CCTMS)₂ display clear changes in colour, absorption and emission bands selectively for F⁻ ion over other anions such as Cl⁻, Br⁻, I⁻, ClO₄⁻ and HPO₄²⁻.     

Ferrocene-based derivatization in analytical chemistry

Ferrocene-based derivatization has raised considerable interest in many fields of analytical chemistry. This is due to the well-established chemistry of ferrocenes, which allows rapid and easy access to a large number of reagents and derivatives. Furthermore, the electrochemical properties of ferrocenes are attractive with respect to their detection. This paper summarizes the available reagents, the reaction conditions and the different approaches for detection. While electrochemical detection is still most widely used to detect ferrocene derivatives, e.g., in the field of DNA analysis, the emerging combination of analytical separation methods with electrochemistry, mass spectrometry and atomic spectroscopy allows ferrocenes to be applied more universally and in novel applications where strongly improved selectivity and limits of detection are required.     

A new colorimetric chemodosimeter for Hg2+ based on charge-transfer compound of N-methylpyrrole with TCNQ

Reaction of N-methylpyrrole and 7,7,8,8-tetracyanoquinodimethane (TCNQ) furnishes an intense blue unsymmetrical charge-transfer compound through regioselective attachment of tricyanoquinodimethane at the 2-position of N-methylpyrrole which was found to be selective chemodosimeter for Hg²⁺ ions in CH₃CN:H₂O mixture (1:1 v/v, pH = 7.0, 0.01 M HEPES, 0.15 M NaCl) as well as in the solid state when supported on silica, over a variety of metal ions. A plausible mechanism for the sensing process has been proposed and supported through the characterization of the resulting Hg²⁺ complex and the density functional theory (DFT) studies.     

Fluorescent coumarinyldithiane as a selective chemodosimeter for mercury(II) ion in aqueous solution

A coumarin-based dithiane (1) was synthesized for the selective detection of Hg²⁺ with respect to dual chromo- and fluorogenic changing events in an aqueous solution by the mercury-promoted transformation of a dithiane group into an aldehyde functional unit. The Hg²⁺-selective response of the chemodosimeter was clearly observed in aqueous buffer as well as in human blood plasma medium.     

Rhodamine-based chemodosimeter for fluorescent determination of Hg in 100% aqueous solution and in living cells

A rhodamine spirolactam derivative (1) bearing a hydrophilic carboxylic acid group is developed as a fluorescent chemodosimeter for bivalent mercury ions (Hg²⁺) in 100% aqueous solution. It exhibits a highly sensitive “turn-on” fluorescent response toward Hg²⁺ with a 42-fold fluorescence intensity enhancement under 1 equiv. of Hg²⁺ added. The chemodosimeter can be applied to the quantification of Hg²⁺ with a linear range covering from 3.0 × 10⁻⁷ to 1.0 × 10⁻⁵ M and a detection limit of 9.7 × 10⁻⁸ M. Most importantly, the fluorescence changes of the chemodosimeter are remarkably specific for Hg²⁺ in the presence of other metal ions, which meet the selective requirements for practical application. Moreover, the experiment results show that the response behavior of 1 towards Hg²⁺ is pH independent in neutral condition (pH 5.0–8.0) and the response is fast (response time less than 3 min). Furthermore, the ring-opening mechanism of the rhodamine spirolactam induced by Hg²⁺ was supported by NMR, MS, and DFT theoretical calculations. In addition, the proposed chemodosimeter has been used to detect Hg²⁺ in water samples and image Hg²⁺ in living cells with satisfying results.     

Target-induced formation of gold amalgamation on DNA-based sensing platform for electrochemical monitoring of mercury ion coupling with cycling signal amplification strategy

Heavy metal ion pollution poses severe risks in human health and environmental pollutant, because of the likelihood of bioaccumulation and toxicity. Driven by the requirement to monitor trace-level mercury ion (Hg²⁺), herein we construct a new DNA-based sensor for sensitive electrochemical monitoring of Hg²⁺ by coupling target-induced formation of gold amalgamation on DNA-based sensing platform with gold amalgamation-catalyzed cycling signal amplification strategy. The sensor was simply prepared by covalent conjugation of aminated poly-T₍₂₅₎ oligonucleotide onto the glassy carbon electrode by typical carbodiimide coupling. Upon introduction of target analyte, Hg²⁺ ion was intercalated into the DNA polyion complex membrane based on T–Hg²⁺–T coordination chemistry. The chelated Hg²⁺ ion could induce the formation of gold amalgamation, which could catalyze the p-nitrophenol with the aid of NaBH₄ and Ru(NH₃)₆³⁺ for cycling signal amplification. Experimental results indicated that the electronic signal of our system increased with the increasing Hg²⁺ level in the sample, and has a detection limit of 0.02 nM with a dynamic range of up to 1000 nM Hg²⁺. The strategy afforded exquisite selectivity for Hg²⁺ against other environmentally related metal ions. In addition, the methodology was evaluated for the analysis of Hg²⁺ in spiked tap-water samples, and the recovery was 87.9–113.8%.     

A new fluorogenic chemodosimetric system for mercury ion recognition

A new probe system for fluorogenic sensing of mercury ions has been designed and synthesized. It is the first intermolecular reaction-based fluorogenic chemodosimetric probe system for Hg(II) ion recognition. High and low concentrations of mercury ions gave different fluorescence responses that could easily be distinguished by the naked eye. This unique system allows detection of the concentration and presence of the mercury ion.     

A selective fluorescent ratiometric chemodosimeter for mercury ion

A selective fluorescent chemodosimeter for mercury ion based on the mercury-promoted intramolecular cyclic guanylation of thiourea connected on 1, 8-naphthalimide is described.     

Synthesis and electrochemical studies of disubstituted ferrocene/dipeptide conjugates with sulfur-containing side chains

A series of 1,1′-disubstituted ferrocenoyl peptides incorporating dipeptide sidearms has been synthesized and studied electrochemically. The target peptides include ferrocene as an electrochemical reporter, sulfur-containing amino acids (l-methionine, S-methyl-l-cysteine, S-trityl-l-cysteine, S-benzhydryl-l-cysteine) as metal binding agents, and amino acids with non-polar side chains (l-alanine, l-valine, l-phenylalanine) as spacers between reporter and metal binding groups. Ferrocene/dipeptide conjugates were prepared using solution phase peptide synthesis methods employing a BOC-protecting group strategy and HBTU- (O-(benzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium hexafluorophosphate) mediated peptide coupling. The electrochemical properties of these 1,1′-substituted ferrocenoyl peptides have been characterized using cyclic voltammetry. All exhibit fully reversible one electron oxidation steps; forward sweep half wave peaks (E_F), reverse sweep half wave peaks (E_R), peak separations (ΔE_P) and half wave potentials (E_1/2) are reported. Finally, towards the goal of utilizing ferrocenoyl peptides to detect heavy metals in solution, the response of these ferrocene/dipeptide conjugates to metal cations (zinc(II), mercury(II), cadmium(II), lead(II), silver(I)) has been examined. Monitoring changes in the potential of the Fe(II)/Fe(III) redox couple to follow peptide/metal interactions, we have probed the influence of the spacer unit between the redox reporter and the metal-binding amino acid, and shown that these systems respond to mercury(II) more strongly than to other heavy metal ions.     

Doubly activated coumarin as a colorimetric and fluorescent chemodosimeter for cyanide

A new α,β-unsaturated nitro group and coumarin conjugate-based fluorescent chemodosimeter 1 was developed for the selective detection of cyanide anions. The chemodosimeter has shown a selective and sensitive response to cyanide anions over other various anions through a nucleophilic aromatic substitution reaction of the cyanide to 1. When cyanide anions were added, the enhanced fluorescence intensity as well as the color changes of 1 was observed so that micromolar concentrations of cyanides were detectable by the naked eye.     

A novel retro-reaction strategy toward designing a selective fluorescence Cu(II) chemodosimeter

A novel C9 acridane-adduct, featuring ketobenzimidazole chelate, functions as a highly selective fluorescent chemodosimeter for Cu²⁺, while other metal ions pose little interferences, if any. The signaling strategy operates via the Cu²⁺-mediated retro-reaction, generating a strongly fluorescent acridinium ion at the expense of the weakly emitting probe.     

Magnetic bead-based hybridization assay for electrochemical detection of microRNA

Aberrant expression of microRNAs (miRNAs), short non-coding RNA molecules regulating gene expression, is often found in tumor cells, making the miRNAs suitable candidates as cancer biomarkers. Electrochemistry is an interesting alternative to current standard methods of miRNA detection by offering cheaper instrumentation and faster assays times. In this paper, we labeled miRNA in a quick, simple, two-step procedure with electroactive complex of osmium(VI) and 2,2′-bipyridine, Os(VI)bipy, which specifically binds to the ribose at the 3′-end of the miRNA, and hybridized such labeled miRNA with biotinylated capture probe attached to the streptavidin magnetic beads. Labeled miRNA was then detected at hanging mercury drop electrode at femtomole level due to an electrocatalytic nature of the peak from the Os(VI)bipy label. We obtained good selectivity of the assay using elevated hybridization temperatures for better discrimination of perfect duplex from single and double mismatches. After optimization of the protocol, we demonstrated feasibility of our assay by detecting target miRNA in real total RNA samples isolated from human cancer cells.     

A fluorescein-based fluorogenic and chromogenic chemodosimeter for the sensitive detection of sulfide anion in aqueous solution

A highly sensitive chromo- and fluorogenic chemodosimeter for sulfide anion was developed based on its nucleophilicity. 2,4-Dinitrobenzenesulfonyl-fluorescein (I) is a weakly fluorescent compound. Upon mixing with sulfide anion in aqueous acetone solution, the 2,4-dinitrobenzenesulfonyl group of I was efficiently removed and highly fluorescent fluorescein was released, hence leading to the dramatic increases in both fluorescence and absorbance of the reaction solution. The fluorescence increment is linear with sulfide anion concentration in the range 50-1000 nmol L⁻¹ with a detection limit of 4.3 nmol L⁻¹ (3σ). The proposed chemodosimeter showed excellent selectivity toward sulfide anion and was successfully applied to the determination of sulfide anion in synthetic wastewater samples.     

A highly selective and femto-molar sensitive fluorescence ‘turn-on’ chemodosimeter for Hg

A selective fluorescence ‘turn-on’ chemodosimeter N,N′-bis-(4-cyanobenzylidene)-2,4,6-trimethylbenzene-1,3-diamine (3) based on a Schiff base for femto-molar detection of the Hg²⁺ has been described. It presents the highest level of detection limit for Hg²⁺ through Schiff base hydrolysis.     

Unprecedented intramolecular cyclization of pyridinium to pyrido[1,2-a]benzimidazole: a novel chemodosimeter for fluoride ions

Pyridinium 1a underwent an efficient intramolecular cyclization initiated by fluoride ions to form highly fluorescent 1,3,4-triphenylpyrido[1,2-a]benzimidazole, providing a novel chemodosimeter for fluoride ions detection.     

A ratiometric fluorescent chemodosimeter for Cu(II) in water with high selectivity and sensitivity

Coumarin derivative 1 was synthesized as an efficient ratiometric chemodosimeter for the detection of Cu(II) in 99% water/DMSO (v/v) at pH 7.0. Mechanism studies suggested that 1 formed a complex with Cu(II) at 2:1 ratio accompanied by quenching of green fluorescence at 524 nm; when the solution was heated to 50 °C for 30 min, Cu(II)-promoted hydrolysis of coumarin lactone moiety of 1 occurred with bright blue fluorescence at 451 nm emerged. With fluorescence intensity ratio detection at 451 nm and 524 nm, 1 features an excellent sensitivity with the detection limit of 15 nmol L⁻¹ toward Cu(II) and a good selectivity over other metal ions.     

One-pot electrochemical synthesis of functionalized fluorescent carbon dots and their selective sensing for mercury ion

We propose a simple, economical, and one-pot method to synthesize water-soluble functionalized fluorescent carbon dots (C-Dots) through electrochemical carbonization of sodium citrate and urea. The as-prepared C-Dots have good photostability and exhibit a high quantum yield of 11.9%. The sizes of the C-Dots are mainly distributed in the range of 1.0–3.5 nm with an average size of 2.4 nm. It has been further used as a novel label-free sensing probe for selective detection of Hg²⁺ ions with detection limit as low as 3.3 nM. The detection linear range is 0.01–10 μM. The as-prepared C-Dots are also successfully applied for the determination of Hg²⁺ in real water samples.     

A ratiometric chemodosimeter for highly selective naked-eye and fluorogenic detection of cyanide

A simple indole-based chemosensor (1) with a very low molecular weight of 207 g mol⁻¹ has been synthesized for the highly reactive and selective detection of CN⁻ in aqueous media, even in the presence of other anions, such as F⁻, Cl⁻, Br⁻, AcO⁻, S₂⁻${{\mathrm{S}}_2}^{-}$, SCN⁻, NO₂⁻${{\text{NO}}_2}^{-}$, NO₃⁻${{\text{NO}}_3}^{-}$, CO₃⁻${{\text{CO}}_3}^{-}$, BzO⁻, H₂PO₄⁻${{\mathrm{H}}_2{\text{PO}}_4}^{-}$, and HSO₄⁻${{\text{HSO}}_4}^{-}$. The sensor achieves rapid detection of cyanide anion in 2 min, and the pseudo-first-order rate constant is estimated as 1.576 min⁻¹. The colorimetric and ratiometric fluorescent response of the sensor to CN⁻ is attributable to the addition of CN⁻ to the electron-deficient dicyanovinyl group of 1, which prevents intramolecular charge transfer. The sensing mechanism is supported by density functional theory and time-dependent density functional theory calculations. Moreover, sensor 1 exhibits both high accuracy in determining the concentration of CN⁻ in real samples and 1-based test strips can conveniently detect CN⁻ without any additional equipment. The detection limit of the sensor 1 (1.1 μM) for cyanide is lower than the maximum permissible level of CN⁻ (1.9 μM) in drinking water.     

Biosourced 3-formyl chromenyl-azo dye as Michael acceptor type of chemodosimeter for cyanide in aqueous environment

A simple water-soluble aldehyde functionalized chromone 5 was utilized as a doubly activated Michael acceptor type of chemodosimeter for cyanide in water. The water solubility of the probe 5 is due to the incorporation of two glycerol units on the starting prepared chemodosimeter. This sensory system is able to selectively distinguish cyanide among fluoride and many other anions at micromolar concentrations and instantly detect cyanide in water at ambient temperatures with a detection limit down to 1.0 mM. Thus, the chemodosimeter 5 was applied to the quantitative determination of cyanide anion in drinking water sample (drinking water from commence).