Rapid detection of trace Cu2+ using an l‐cysteine based interdigitated electrode sensor integrated with AC electrokinetic enrichment

Copper is an indispensable trace element for human health. Too much or too little intake of copper ion (Cu²⁺) can lead to its own adverse health conditions. Therefore, detection of Cu²⁺ is always of vital importance. In this work, a simple sensor was developed for rapid detection of trace Cu²⁺ in water, in which L‐cysteine (Cys) as a molecular probe was self‐assembled on a gold interdigital electrode to form a monolayer for specific capture of Cu²⁺. The interfacial capacitance of interdigital electrode was detected to indicate the target adsorption level under an AC signal working as the excitation to induce directed movement and enrichment of Cu²⁺ to the electrode surface. This sensor reached a limit of detection of 4.14 fM and a satisfactory selectivity against eight other ions (Zn²⁺, Hg²⁺, Pb²⁺, Cd²⁺, Mg²⁺, Fe²⁺, As³⁺, and As⁵⁺). Testing of spiked tap water was also performed, demonstrating the sensor's usability. This sensor as well as the detection method shows a great application potential in fields such as environmental monitoring and medical diagnosis.     

Carbazole‐based colorimetric and fluorescent probe for Cu2+ and its utility in bio‐imaging and real water samples

A new carbazole functionalized Schiff base CBM was synthesized and characterized. CBM can selectively recognize Cu²⁺ via UV–vis and fluorescence signal among common biologically relevant metal ions. When Cu²⁺ was added to CBM, there was a significant enhancement at the maximum absorption wavelength of 393 nm and with a distinct blue shift. The maximum emission peak was significantly attenuated by a factor of about 15 times at 535 nm and the blue shift of emission wavelength was observed. When other metal ions were added, there was no remarkable change at the maximum absorption and emission peak. Under the illumination of 365 nm ultraviolet lamp, the color of the CBM solution changed from light blue to dark blue after the addition of Cu²⁺. The combination mechanism of CBM with Cu²⁺ was nicely explored by density functional theory studies. The probe CBM has good cell permeability, fluorescence electron microscopy experiments show that CBM can be used as a fluorescent probe to detect the presence or absence of Cu²⁺ in Hela cells. Furthermore, the probe CBM can also be used for the detection of copper ions in actual water samples.     

Highly sensitive and selective optical chemosensor for determination of Cu2+ in aqueous solution

A highly selective and sensitive rhodamine-based colorimetric chemosensor (1) for quantification of divalent copper in aqueous solution has been investigated in this work. It was designed using salicylaldehyde hydrazone and rhodamine 6G as copper-chelating and signal-reporting groups, respectively. In environmentally friendly media (50% (v/v) water/ethanol and 10 mM NaAc–HAc neutral buffer (pH 7.0)), the sensor exhibited selective absorbance enhancement to Cu²⁺ over other metal ions at 529 nm, with a dynamic working range of 0.05–5.00 μM and a detection limit of 10 nM Cu²⁺, respectively. To achieve fluorometric determination of Cu²⁺, the Cu²⁺-induced absorbance enhancement of 1 was efficiently converted to fluorescence quenching by fluorescence inner filter effects using rhodamine B (RB) as a fluorophore. The selectivity and sensitivity of fluorescence analysis were similar to those of absorptiometric measurement. Both absorptiometric and fluorometric methods were successfully applied to the detection of Cu²⁺ in three water samples.     

Highly sensitive and selective chemosensor for Cu2+ detection based on a N-propargyl rhodamine 6G-hydrazide derivative

A novel fluorescence "turn-on" probe for Cu2+ detection has been designed based on a Cu2+ triggered spirolactam ring-opening reaction.The synthetic probe is a double-responsive fluorescent and colorimetric Cu2+-specific sensor.In aqueous solution,it exhibits high selectivity and excellent sensitivity.With a significant color change visible to the naked eye at the concentration of 3 μM(ca.0.19 mg/L),about one magnitude lower than the WHO(World Health Organization) recommended level(2.0 mg/L) for Cu2+ ions in drinking water,the probe could be used to monitor Cu2+ ions in drinking water.     

Naked-eye detection of cyanide ions in aqueous media based on an azo-azomethine chemosensor

The optical and colorimetric properties of a new chemosensor 4-((2,4-dichlorophenyl)diazenyl)-2-(3-hydroxypropylimino)methyl)phenol (L) for cyanide ions were investigated by the naked-eye detection and UV–vis spectroscopy. This receptor reveals visual changes toward CN⁻ anions in aqueous media. No significant color changes were observed upon the addition of any other anions. The cyanide recognition properties of the receptor through proton-transfer were monitored by UV–vis titration and ¹H NMR spectroscopy. The binding constant (K_a) and stoichiometry of the formed host–guest complex were calculated by the Benesi–Hildebrand (B–H) plot and Job's plot method, respectively. The detection limit of the probe towards CN⁻ was 1.03 × 10⁻⁶ mol L⁻¹, which is lower than the maximum value of cyanide (1.9 × 10⁻⁶ mol L⁻¹) permitted by the World Health Organization in drinking water. Thus, this chemosensor was sensitive enough to detect cyanide in aqueous solutions. ¹H NMR experiments were conducted to investigate the nature of interaction between the receptor and CN⁻ anions. Notably, the designed sensor can be applied for the rapid detection of cyanide anions in the basic pH range and also under physiological conditions, for practical purposes for a long duration. The sensing behavior of the receptor was further emphasized by computational studies. Quantum-chemical calculations and molecular studies via Density Functional Theory (DFT) were carried out to supplement the experimental results.     

A dual-function chemosensor based on coumarin for fluorescent turn-on recognition of Hg2+ and colorimetric detection of Cu2+ in aqueous media

A novel coumarin derivative CTT was synthesized via the condensation of 7-(N,N-diethylamino) coumarin-3-aldehyde with 5-amino-1,3,4-thiadiazole-2-thiol and its structure was characterized using infrared spectroscopy (IR), ¹H NMR, mass spectrometry (MS) techniques, and elemental analysis. The recognition properties of CTT with metal ions were investigated in CH₃CN–H₂O (v/v = 1/1) solution using UV–vis absorption and fluorescence emission spectrum method. The results showed that CTT could monitor Cu²⁺ and Hg²⁺ simultaneously as a dual-function chemosensor in CH₃CN–H₂O (v/v = 1/1). CTT could be used to detect Cu²⁺ colorimetrically; when using CTT, a color change from yellowish-brown to yellowish-green could be readily observed by the naked eye. CTT showed turn-on fluorescent recognition of Hg²⁺, the fluorescence enhancement was attributed to the inhibited C=N isomerization and the obstructed excited state intramolecular proton transfer (ESIPT) of CTT. The recognition mechanism of CTT for Cu²⁺ and Hg²⁺ was studied by experiments and theoretical calculations, respectively. Therefore, CTT has the ability to be a “single chemosensor for dual targets.”     

"Off-On" based fluorescent chemosensor for Cu2+ in aqueous media and living cells

A novel Cu²⁺-specific “off-on” fluorescent chemosensor of naphthalimide modified rhodamine B (naphthalimide modified rhodamine B chemosensor, NRC) was designed and synthesized, based on the equilibrium between the spirolactam (non-fluorescence) and the ring-opened amide (fluorescence). The chemosensor NRC showed high Cu²⁺-selective fluorescence enhancement over commonly coexistent metal ions or anions in neutral aqueous media. The limit of detection (LOD) based on 3 × δ_blank/k was obtained as low as 0.18 μM of Cu²⁺, as well as an excellent linearity of 0.05-4.5 μM (R = 0.999), indicating the chemosensor of high sensitivity and wide quantitation range. And also the coordination mode with 1:1 stoichiometry was proposed between NRC and Cu²⁺. In addition, the effects of pH, co-existing metal ions and anions, and the reversibility were investigated in detail. It was also demonstrated that the NRC could be used as an excellent “off-on” fluorescent chemosensor for the measurement of Cu²⁺ in living cells with satisfying results, which further displayed its valuable applications in biological systems.     

Quantitation of Cu+‐catalyzed Decomposition of S‐Nitrosoglutathione Using Saville and Electrochemical Detection: a Pronounced Effect of Glutathione and Copper Concentrations

S‐nitrosothiols (RSNOs) are composed of nitric oxide (NO) bound to the sulfhydryl group of amino acids of peptides or proteins. There is a great interest for their quantitation in biological fluids as they have a crucial impact on physiological and pathophysiological events. Most analytical methodologies for quantitation of RSNOs are based on their decomposition followed by the detection of the released NO. In order to obtain the optimal sensitivity for each detection method, the total decomposition of RSNOs is highly desired. The decomposition of RSNOs can be obtained by using catalytically active metal ions, such as Cu⁺, obtained from CuSO₄ in presence of a reducing agent such as glutathione (GSH) that is naturally present in biological environment. In this work, we have re‐investigated the decomposition of S‐nitrosoglutathione (GSNO) which is the most abundant in vivo low molecular weight RSNO, with a special emphasis on the effect of CuSO₄, GSH, and GSNO concentrations and of their ratio. To this aim, GSNO decomposition optimization was performed by both indirect (Griess assay) and direct (real time electrochemical detection of NO at NO‐microsensor) quantitation methods. Our results show that the ratio between CuSO₄, GSH and GSNO should be adjusted to tune the highest decomposition rate of GSNO and the most efficient electrochemical detection of released NO; also it shows the deleterious effect of very high GSH concentration on the detection of GSNO.     

Highly selective colorimetric naked-eye Cu2+ detection using new bispyrazolone silver nanoparticle-based chemosensor

In this work, we have successfully developed novel silver nanoconjugates of pyrazolone analogue and screened its chemosensing potential in aqueous medium. Bispyrazolone silver nanoparticles (Bispyra-AgNPs) were synthesised and characterised through FTIR, UV-visible spectroscopy and atomic force microscopy. The sensing ability was explored towards Ca²⁺, Cd²⁺, Co²⁺, Cu²⁺, Fe²⁺, Li⁺, Pb²⁺, La³⁺, Hg²⁺, Mg²⁺, Ni²⁺ and Ba²⁺ metal ions, respectively. Bispyra-AgNPs showed a highly quenching potential in selective recognition of Cu²⁺and colour of the solution immediately turned from yellow to purple, after the addition of Cu²⁺ in to the solution. The developed method also displayed a remarkable selectivity for Cu²⁺ over others interfering metal ions. The binding ratio and stoichiometry of host-guest complex was found to be 1:1 and determined by Job’s method. The propose method is facile and sensitive to detect Cu²⁺ with detection limit of 10 µM.     

Colorimetric detection of Ni2+ based on an anionic triphenylmethane dye and a cationic polyelectrolyte in aqueous solution

The combination of xylenol orange (XO) and poly(diallyldimethylammonium chloride) (PDADMAC) has been utilized as a colorimetric sensor for selective recognition of Ni²⁺ in aqueous solution. Upon addition of Ni²⁺, the chemosensor exhibited the significant color change from red to purple with a bathochromic shift, whereas these change was not induced by other metal ions. XO alone did not recognize Ni²⁺ colorimetrically, indicating that PDADMAC was required for detecting Ni²⁺. This study can provide the facile method for the construction of new chemosensors by a simple mixture of an anionic water-soluble dye and cationic polyelectrolyte.     

Synthesis and Characterization of Newly Designed and Highly Solvatochromic Double Squaraine Dye for Sensitive and Selective Recognition towards Cu2+

Synthesis and characterization of a novel and zwitterionic double squaraine dye (DSQ) with a unique D-A-A-D structure is being reported. Contrary to the conventional mono and bis-squaraine dyes with D-A-D and D-A-D-A molecular frameworks reported so far, DSQ dye demonstrated strong solvatochromism allowing for the multiple ion sensing using a single probe by judicious selection of the suitable solvent system. The DSQ dye exhibited a large solvatochromic shift of about 200 nm with color changes from the visible to NIR region with metal ion sensitivity. Utilization of a binary solvent consisted of dimethylformamide and acetonitrile (1:99, v/v), highly selective detection of Cu²⁺ ions with the linearity range from 50 μM to 1 nM and a detection limit of 6.5 × 10⁻¹⁰ M has been successfully demonstrated. Results of the Benesi–Hildebrand and Jobs plot analysis revealed that DSQ and Cu²⁺ ions interact in the 2:1 molecular stoichiometry with appreciably good association constant of 2.32 × 10⁴ M⁻¹. Considering the allowed limit of Cu²⁺ ions intake by human body as recommended by WHO to be 30 μM, the proposed dye can be conveniently used for the simple and naked eye colorimetric monitoring of the drinking water quality.     

A facile ratiometric and colorimetric azo-dye possessing chemosensor for Ni2+ and AcO− detection

A new tailor-made colorimetric chemosensor 1, containing pyridine and benzothiazole moieties connected through an azo (–N = N–) linkage has been synthesised. In 9:1 (v/v) aqueous THF (pH 7.0 HEPES buffer), it showed a conspicuous naked-eye colour change upon binding to Ni²⁺ (colourless to light green) and AcO^?  (colourless to orange) resulting in their ratiometric sensing. The cation and anion recognition property of the chemosensor 1 was monitored by UV–vis spectral analysis and ¹H NMR titrations.     

A novel colorimetric chemosensor based on quinoline for the sequential detection of Fe3+ and PPi in aqueous solution

A novel quinoline-functionalized Schiff-base derivative PY was designed and synthesized. Sensor PY displayed highly selective and sensitive fluorescence enhancement and naked-eye color change to Fe³⁺ in the presence of other competing cations. The mechanisms have been supported by Job’s plot evaluation, FT-MS and theoretical calculations. The in situ generated PY-Fe³⁺ complex solution exhibited a high selectivity toward PPi via Fe³⁺ displacement approach. The detection limits of sensor PY to Fe³⁺ and PY-Fe³⁺ complex to PPi were estimated to be 4.24 × 10^?8 M and 8.18 × 10^?8 M, respectively. This successive recognition feature of sensor PY makes it has a potential utility for Fe³⁺ and PPi detection in aqueous solution. A B3LYP/6-31G(d,p) basis set was employed for optimization of PY and PY-Fe³⁺ complex.     

Naphthalene-derived Al3+-selective fluorescent chemosensor based on PET and ESIPT in aqueous solution

A simple fluorescent chemosensor HL based on naphthalene with high selectivity and sensitivity towards Al³⁺ over other commonly coexisting metal cations in fully aqueous solution to enhance the potential applications of the fluorescent chemosensor was developed. HL exhibited a significant fluorescence enhancement at 475?nm in the presence of Al³⁺ over other competitive metal ions with a low detection limit of 0.43?μM due to the inhibition of the photo induced electron transfer (PET) and the excited-state intramolecular proton transfer (ESIPT). The 1:1 binding stoichiometry between HL and Al³⁺ was corroborated by the Job plot and the ESI-MS spectrum. Importantly, the reversible recognition process of HL to Al³⁺ will make HL could be used circularly and repeatedly in practical applications by addition of Na₂EDTA. In addition, the binding behavior and sensing mechanism of HL to Al³⁺ were illustrated in detail by the ¹H NMR titration experiment.     

Versatile trifunctional chemosensor of rhodamine derivative for Zn2+, Cu2+ and His/Cys in aqueous solution and living cells

On the basis of rhodamine, a versatile trifunctional chemosensor RP has been synthesized. It can selectively and sensitively recognize Cu(2+) and Zn(2+) in different solutions. Based on the zinc-containing [RP@Zn(2+)] complex, it shows highly selective recognition for His/Cys. Fluorescent imaging of Zn(2+) in living cells was also obtained.     

Anthroneamine based chromofluorogenic probes for Hg2+ detection in aqueous solution

Anthroneamine derivatives 1–3 (H₂O:DMSO; 9:1, HEPES buffer, pH 7.0 ± 0.1) undergo highly selective fluorescence quenching with Hg²⁺. The observed linear fluorescence intensity change allows the quantitative detection of Hg²⁺ between 200 nM/40 ppb—12 μM/2.4 ppm even in the presence of interfering metal ions viz. Na⁺, K⁺, Mg²⁺, Ca²⁺, Ba²⁺, Cr³⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Ag⁺, Cd²⁺, Pb²⁺. Probes 1–3 and their Hg²⁺ complexes also show the broad pH resistance for their practical applicability.     

Fabrication of reusable sensor for detection of Cu2+ in an aqueous solution using a self-assembled monolayer with surface plasmon resonance spectroscopy

The proposed procedure for recycling the sensor surface consists of (1) the self-assembly of 2-aminoethanethiol hydrochloride (AET) on the Au substrate, (2) the neutralization of zwitterion-like species, -NH3+Cl- to -NH2 by treatment with a NaOH solution (pH 11), (3) the detection of Cu2+ on the NaOH-treated AET-Au substrate, and finally (4) regeneration of the sensor surface from [-NH2--> Cu2+] to [-NH3+Cl-] by treatment with 1 M HCl.     

Water‐soluble cationic polypyrrole based probe for fluorometric and voltammetric detection of base pair mismatched oligonucleotides

Water‐soluble cationic polypyrrole, poly(N‐(4‐butyl‐(1‐methylimidazole)) pyrrole bromide) (PNBMIP‐Br), was synthesized and applied for base pair mismatched oligonucleotides detection. Interactions between PNBMIP‐Br and a series of oligonucleotides, including ss‐DNA and base pair mismatched ds‐DNA were studied by fluorometric spectra, circular dichroism spectra and voltammetric detection. The results showed that the electrostatic attraction and fluorescence resonance energy transfer of PNBMIP‐Br/DNA complexes resulted in an amplification and effective recognition of the fluorescence signals. The results of cyclic voltammograms indicate that voltammetric detection is an effective method to distinguish ss‐DNA and ds‐DNA. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1600–1605