Sub-ppt detection limits for copper ions with Gly-Gly-His modified electrodes

Development of a new electrochemical method for the determination of copper(ii) at trace levels in environmental and food samples

This paper presents the fabrication of a new modified carbon paste electrode (CPE) with N 1-hydroxy-N 1,N 2-diphenylbenzamidine (HDPBA) and functionalized multi-walled carbon nanotubes (MWCNTs) (HDPBA-MWCNTs/CPE) for highly sensitive and selective determination of Cu(ii) using the square wave anodic stripping voltammetry (SWASV) technique. The fabricated electrode was characterized using various spectroscopic techniques to study its morphological, structural, and electrochemical properties. The accumulation of Cu(ii) on the surface of HDPBA-MWCNTs/CPE was done in 0.1 M ammonium chloride (NH4Cl, pH 5) solution at an applied potential of -0.70 V versus Ag/AgCl for 180 s, followed by electrochemical stripping in the positive scan of the voltammetry after a resting time of 10 s. The developed HDPBA-MWCNTs/CPE was found to be highly selective, sensitive and reproducible. At optimal conditions of the experiment, the proposed method exhibited a very low limit of detection (0.0048 nM Cu(ii)), a wide linear dynamic range (0.00007-1.5000 μM Cu(ii)), and good reproducibility with relative standard deviation (RSD) value of 3.7%. The effect of various foreign ions on the voltammetric response of Cu(ii) was investigated and the electrode was found to be highly selective to Cu(ii). The practical applicability of the proposed HDPBA-MWCNTs/CPE was studied by applying the electrode for the quantification of Cu(ii) contents in environmental water (wastewater and tap water), soft drink (Fanta and Sprite), and food supplement (commercially available multi-mineral/vitamin tablets) samples. The present method was validated with atomic absorption spectrometry (AAS). The results found from the two methods are in good agreement with a 95% confidence level.

Tuning the Sensing Properties of N and S Co-Doped Carbon Dots for Colorimetric Detection of Copper and Cobalt in Water

In this study, nitrogen and sulfur co-doped carbon dots (NS-CDs) were investigated for the detection of heavy metals in water through absorption-based colorimetric response. NS-CDs were synthesized by a simple one-pot hydrothermal method and characterized by TEM, STEM-coupled with energy dispersive X-ray analysis, NMR, and IR spectroscopy. Addition of Cu(II) ions to NS-CD aqueous solutions gave origin to a distinct absorption band at 660 nm which was attributed to the formation of cuprammonium complexes through coordination with amino functional groups of NS-CDs. Absorbance increased linearly with Cu(II) concentration in the range 1–100 µM and enabled a limit of detection of 200 nM. No response was observed with the other tested metals, including Fe(III) which, however, appreciably decreased sensitivity to copper. Increase of pH of the NS-CD solution up to 9.5 greatly reduced this interference effect and enhanced the response to Cu(II), thus confirming the different nature of the two interactions. In addition, a concurrent response to Co(II) appeared in a different spectral region, thus suggesting the possibility of dual-species multiple sensitivity. The present method neither requires any other reagents nor any previous assay treatment and thus can be a promising candidate for low-cost monitoring of copper onsite and by unskilled personnel.

Design and optimization of sensitive analytical spectrophotometric method for micro determination of copper(II) from e-waste by using of novel chromogenic extractant

In this article, a novel spectrophotometric reagent 1-(pyrimidine)-4, 4, 6-trimethyl-1,4-dihydropyrimidine-2-thiol [PTPT] has been synthesized for liquid-liquid extraction and spectrophotometric determination of copper(II). The as-synthesized ligand has been selectively forms stable complex with copper(II) in basic medium (pH 9.0), in presence of mild pyridine the extraction and color stability has found to be synergistically enhanced. The equilibrium time is 10 min for effective extraction of copper(II) from organic phase and absorbance of colored organic complex in carbon tetrachloride is measured spectrophotometrically at λ_max 615 nm against reagent blank. The ternary complex of Cu(II)-PTPT-Py having molar ratio 1:2:2 (M:L:Py) showed green colored complex. The main factors influencing the achievement of synergistic extraction; i.e. pH, ligand concentration, type and volume of the dispersive organic solvents, equilibrium time, synergent concentration and foreign ions were investigated. The Beer's law was obeyed in the concentration range 1-20 μg mL^-1 of copper(II) and optimum concentration range is evaluated by Ringbom's plot and it is found that 2.5-25 μg mL^-1. In presence of pyridine, molar absorptivity and Sandell's sensitivity of copper(II)-PTPT complex is 2.80 × 10³ L mol^-1 cm^-1 and 0.226 μg cm^-2, respectively and in absence of pyridine, molar absorptivity and Sandell's sensitivity of copper(II)-PTPT complex is 1.35 × 10³ L mol^-1 cm^-1 and 0.469 μg cm^-2, respectively. The stoichiometry of the copper(II)-PTPT-pyridine complex was calculated by slope ratio method, mole ratio method and Job's method of continuous variation and it has been found as 1:2:2. No significant effects of potentially interfering species i.e. cations and anions were observed. The optimized method was applied for the determination of copper(II) in binary, synthetic mixtures and successfully applied for determination of copper(II) from e-waste samples. The standard deviation (R.S.D.) is 0.11% for n = 5 repetition. The reliability of the developed method is confirmed by comparison of experimental results with atomic absorption spectrophotometer.

Anchoring zinc-doped carbon dots on a paper-based chip for highly sensitive fluorescence detection of copper ions

In this work, zinc-doped carbon dots (Zn-CDs) were anchored on a three-dimensional wheel type paper-based microfluidic chip, and were decorated with 6-mercaptonicotinic acid (MNA) and L-cysteine (L-Cys) for highly sensitive and rapid fluorescence detection of Cu²⁺. Zn-CDs were first anchored on paper through the amide bonds between the carboxyl groups of the Zn-CDs and the amino groups of the paper. Afterwards, Zn-CDs were decorated with MNA and L-Cys, effectively preventing the Zn-CDs from aggregation. The nitrogen atom on the pyridine ring and the carboxylic acid groups in MNA and L-Cys coordinated with Cu²⁺ to form a nonfluorescent ground-state complex, causing the fluorescence quenching of the Zn-CDs. The three-dimensional rotary design could simplify the operation process and achieve simultaneous analysis of multiple samples with different concentrations. Under optimal conditions, the fluorescent sensor exhibits linear response for the determination of Cu²⁺ in the range from 0.1 to 60 μg L^-1 with the detection limit (LOD) of 0.018 μg L^-1. The proposed strategy provides a novel way for the highly sensitive detection of Cu²⁺ in a complex water environment.

Ion-Imprinted Polymer Modified with Carbon Quantum Dots as a Highly Sensitive Copper(II) Ion Probe

Fluorescence analysis technology and ion imprinting technology are combined to prepare a copper ion fluorescence sensor. Carbon quantum dots (CQDs), with a quantum yield of 79%, were synthesized by a hydrothermal process using citric acid as the carbon source. The prepared CQDs, acting as the fluorophore, were grafted onto the surface of an SBA-15 mesoporous molecular sieve by an amidation reaction. Then, the fluorescent sensor CQDs@Cu-IIP was prepared using a surface imprinting technique with the modified SBA-15 as the substrate, copper ions as a template, tetraethoxysilane as the crosslinker, and 3-aminopropyl-3-ethoxysilane as the functional monomers. The sensor showed strong fluorescence from CQDs and high selectivity due to the presence of Cu(II)-IIP. After the detection conditions were optimized, the fluorescence intensity of the sensor had good linearity with Cu(II) concentration in a linear range of 0.25-2 mg/L and 3-10 mg/L. This CQDs@Cu-IIP was applied to the determination of traces Cu(II) in real water samples and good recoveries of 99.29-105.42% were obtained. The present study provides a general strategy for fabricating materials based on CQDs for selective fluorescence detection of heavy metals.

Building Tailored Interfaces through Covalent Coupling Reactions at Layers Grafted from Aryldiazonium Salts

Aryldiazonium ions are widely used reagents for surface modification. Attractive aspects of their use include wide substrate compatibility (ranging from plastics to carbons to metals and metal oxides), formation of stable covalent bonding to the substrate, simplicity of modification methods that are compatible with organic and aqueous solvents, and the commercial availability of many aniline precursors with a straightforward conversion to the active reagent. Importantly, the strong bonding of the modifying layer to the surface makes the method ideally suited to further on-surface (postfunctionalization) chemistry. After an initial grafting from a suitable aryldiazonium ion to give an anchor layer, a target species can be coupled to the layer, hugely expanding the range of species that can be immobilized. This strategy has been widely employed to prepare materials for numerous applications including chemical sensors, biosensors, catalysis, optoelectronics, composite materials, and energy conversion and storage. In this Review our goal is first to summarize how a target species with a particular functional group may be covalently coupled to an appropriate anchor layer. We then review applications of the resulting materials.

Electrochemical Activation of Self-Assembled Monolayers for the Binding of Effectors

A self-assembled monolayer (SAM) on gold was prepared from a diaminoterephthalate (DAT) derivative as functional molecule and 1-decanthiol as a backfiller. The DAT derivative is N-protected by a tert-butyloxycarbonyl (Boc) group and is anchored to the gold surface via a liponic acid as a stable anchor group. The terminal DAT moiety exhibits interesting effector properties such as fluorescence and electrochemical activity. Irreversible oxidation of the monolayer at 0.4 V (Hg|Hg₂SO₄) in 0.1 M HClO₄ triggers deprotection of the DAT group and subsequent chemical reactions, during which 10% of the DAT groups of the original SAM are transformed to a new surface-bound, quasi-reversible redox couple with a formal potential of 0.0 V (Hg|Hg₂SO₄) and a standard rate constant of 8 s^-1 in 0.1 M HClO₄. Immersion of the mixed SAM in 0.1 M HClO₄ at open circuit potential or oxidation in 0.1 M H₂SO₄ did not produce this surface-bound redox couple. The monolayers were thoroughly characterized by X-ray photoelectron spectroscopy (XPS) and polarization modulation infrared reflection absorption spectroscopy (PM IRRAS) after the different preparation steps indicating only minor changes in the overall composition of the monolayer, in particular, the preservation of the heteroatoms. The new redox couple is likely a diimine, in agreement with its ability to bind nucleophiles such as anilines by conjugate addition that could be followed by multicycle voltammetry and XPS. The DAT effector group is especially interesting because it can also report the binding reaction by changed electrochemical and fluorescence signals.

A zinc selective oxytocin based biosensor

Oxytocin is a peptide hormone with high affinity to both Zn²⁺ and Cu²⁺ ions compared to other metal ions. This affinity makes oxytocin an attractive recognition layer for monitoring the levels of these essential ions in biofluids. Native oxytocin cannot differentiate between Cu²⁺ and Zn²⁺ ions and hence it is not useful for sensing Zn²⁺ in the presence of Cu²⁺. We elucidated the effect of the terminal amine group of oxytocin on the affinity toward Cu²⁺ using theoretical calculations. We designed a new Zn²⁺ selective oxytocin-based biosensor that utilizes the terminal amine for surface anchoring, also preventing the response to Cu²⁺. The biosensor shows exceptional selectivity and very high sensitivity to Zn²⁺ in impedimetric biosensing. This study shows for the first time an oxytocin derived sensor that can be used directly for sensing Zn²⁺ in the presence of Cu²⁺.

Selective Detection of Pyrophosphate Anions in Aqueous Medium Using Aggregation of Perylene Diimide as a Fluorescent Probe

A water-soluble perylene diimide, aspartic acid-functionalized perylene diimide (APDI), has shown significant sequential "turn-off" and "turn-on" responses toward Cu2+ and inorganic pyrophosphate (PPi), respectively. APDI was found to show selectivity toward Cu2+ and inorganic PPi over adenosine monophosphate, adenosine diphosphate, and adenosine triphosphate. The detection has been studied by absorption and emission spectroscopy techniques. Incorporation of Cu2+ into the solution of APDI results in a distinct quenching of the fluorescence intensity, while there was no spectral change in the presence of other metal ions. The formed APDI-Cu2+ ensemble can turn on its fluorescence signal when PPi is present. The detection of PPi could be traced by looking at the change in color of the solution under the naked eye. No interference was observed from other anions, making the APDI-Cu2+aggregate a highly selective biosensor for PPi.

Detection of Cu2+ Ions with GGH Peptide Realized with Si-Nanoribbon ISFET

The presence of heavy metal ions such as copper in the human body at certain concentrations and specific conditions can lead to the development of different diseases. The currently available analytical detection methods remain expensive, time-consuming, and often require sample pre-treatment. The development of specific and quantitative, easy-in-operation, and cost-effective devices, capable of monitoring the level of Cu²⁺ ions in environmental and physiological media, is necessary. We use silicon nanoribbon (SiNR) ion-sensitive field effect transistor (ISFET) devices modified with a Gly-Gly-His peptide for the detection of copper ions in a large concentration range. The specific binding of copper ions causes a conformational change of the ligand, and a deprotonation of secondary amine groups. By performing differential measurements, we gain a deeper insight into the details of the ion-ligand interaction. We highlight in particular the importance of considering non-specific interactions to explain the sensors' response.

Diaminoterephthalate-α-lipoic acid conjugates with fluorinated residues

Two bifunctional diaminoterephthalate (DAT) fluorescence dyes were prepared in a three-step sequence including one deprotection reaction. One functional unit is α-lipoic acid (ALA) for binding the dye to gold surfaces. It was introduced to the DAT scaffold by an amidation reaction. The other functional unit is a para-(trifluoromethyl)benzyl group for facile detection of the surface-bound material by X-ray photoelectron spectroscopy (XPS). This residue was introduced by reductive amination of the DAT scaffold with the respective benzaldehyde derivative. In one compound (60% yield over three steps) the ALA unit is directly bound to the DAT as a relatively electron-withdrawing amide. In solution (CH2Cl2), this material shows strong fluorescence (quantum yield 57% with emission at 495 nm, absorption maximum at 420 nm). The other compound (57% yield over three steps) possesses a propylene spacer between the ALA and the DAT units for electronic decoupling, thus, bathochromic shifts are observed (absorption at 514 nm, emission at 566 nm). The quantum yield is, however, lower (4%). Self-assembled monolayers on a gold surface of both compounds were prepared and characterized by high-resolution XPS of the C 1s, O 1s, S 2p, N 1s and F 1s emissions. The high signal-to-noise ratios of the F 1s peaks indicated that trifluoromethylation is an excellent tool for the detection of surface-bound materials by XPS.

Integrated optical and electrochemical detection of Cu2+ ions in water using a sandwich amino acid–gold nanoparticle-based nano-biosensor consisting of a transparent-conductive platform

In this paper, an optical-electrochemical nano-biosensor was introduced for measuring Cu²⁺ ion concentrations in water. A multi-step procedure was used to fabricate the transparent-conductive biosensor platform consisting of an l-cysteine–gold nanoparticle-based sandwich structure. First, colloidal gold nanoparticles (GNPs) were synthesized according to the Turkevich–Frens method with some modifications and then functionalized with l-cysteine molecules (GNP/l-cys). Then, cyclic voltammetry was preformed in buffered solutions containing HAuCl₄·3H₂O for gold nanoparticle electrodeposition on cleaned ITO glasses. The GNP-electrodeposited ITO glasses (ITO/GNPs) were thermally treated in air atmosphere for 1 hour at a temperature of 300 °C. Following the procedure, the gold nanoparticles on ITO/GNPs substrates were functionalized with l-cysteine to prepare ITO/GNPs/l-cys substrates. Finally, the sandwich-type substrates of ITO/GNPs/l-cys⋯Cu²⁺⋯l-cys/GNPs were fabricated by accumulation of Cu²⁺ ions using an open circuit technique performed in copper ion buffer solutions in the presence of previously produced colloidal GNP/l-cys nanoparticles. The effective parameters including GNP/l-cys solution volume, pre-concentration pH and pre-concentration time on the LSPR and SWV responses were investigated and optimized. The fabricated transparent-conductive platforms were successfully assessed as a nano-biosensor for detection of copper ions using two different methods of square wave voltammetry (SWV) and localized surface plasmon resonance (LSPR). As a result, the proposed biosensor showed a high sensitivity, selectivity and a wide detectable concentration range to copper ions. The total linear range and the limit of detection (LOD) of the nano-biosensor were 10–100 000 nM (0.6–6354.6 ppb) and below 5 nM (0.3 ppb), respectively. The results demonstrated the potential of combining two different optical and electrochemical methods for quantitation of the single analyte on the same biosensor platform and obtaining richer data. Also, these results indicated that the developed LSPR-SWV biosensor was superior to many other copper biosensors presented in the literature in terms of linear range and LOD. The developed nano-biosensor was successfully applied in the determination of trace Cu²⁺ concentration in actual tap water samples.

The transparent-conductive platforms of ITO/GNPs/l-cys⋯Cu²⁺⋯l-cys/GNPs were fabricated for quantitation of Cu²⁺ ions in water samples using combined LSPR and SWV methods.

Peptides, Peptidomimetics, and Carbohydrate-Peptide Conjugates as Amyloidogenic Aggregation Inhibitors for Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder accounting for 60-80% of dementia cases. For many years, AD causality was attributed to amyloid-β (Aβ) aggregated species. Recently, multiple therapies that target Aβ aggregation have failed in clinical trials, since Aβ aggregation is found in AD and healthy patients. Attention has therefore shifted toward the aggregation of the tau protein as a major driver of AD. Numerous inhibitors of tau-based pathology have recently been developed. Diagnosis of AD has shifted from measuring late stage senile plaques to early stage biomarkers, amyloid-β and tau monomers and oligomeric assemblies. Synthetic peptides and some derivative structures are being explored for use as theranostic tools as they possess the capacity both to bind the biomarkers and to inhibit their pathological self-assembly. Several studies have demonstrated that O-linked glycoside addition can significantly alter amyloid aggregation kinetics. Furthermore, natural O-glycosylation of amyloid-forming proteins, including amyloid precursor protein (APP), tau, and α-synuclein, promotes alternative nonamyloidogenic processing pathways. As such, glycopeptides and related peptidomimetics are being investigated within the AD field. Here we review advancements made in the last 5 years, as well as the arrival of sugar-based derivatives.

A Photoswitchable Colorimetric Sensor for Fluoride Based on a Dithienylethene Unit

A novel dithienylethene amide-based photoswitchable anion receptor was synthesised by amidation of 4,4′-(cyclopent-1-ene-1,2-diyl) bis(5-methylthiophene-2-carboxylic acid) with 4-nitroaniline in 56% yield under mild conditions; its structure was confirmed by NMR, MS and elemental analysis. Investigation of its photochromic properties indicated that 4,4′-(cyclopent-1-ene-1,2-diyl)bis[5-methyl-N-(4-nitrophenyl) thiophene-2-carboxamide] had good reversibility and excellent fatigue resistance upon irradiation with UV or visible light and can serve as a colorimetric sensor for fluoride, resulting in a significant change in the absorption spectrum.

Developing on-site paper colorimetric monitoring technique for quick evaluating copper ion concentration in mineral wastewater

With the reinforce of the copper mining, the on-site monitoring of the accompanied effluent discharge is highly demanded for the emergency response to minimize the negative effect of the effluent on the surrounding ecosystem. On the basis of the specific interaction between Cu²⁺ and l-Cysteine (l-Cys), which was modified on gold nanoparticles (Au NPs), and the aggregation dependent surface plasmon resonance (SPR) of Au NPs, we developed an easy-on-going paper colorimetric method for the quick evaluating the copper ion concentration in the waste water excreted from the copper mine. The color change of l-Cys modified Au NPs (l-Cys-Au NPs)immobilized on a filter paper was very sensitive to the Cu²⁺ concentration and free of interference from other metal ions typically in waste water. The proposed paper colorimetry has the LOD of 0.09mg/L and the linear range of 0.1-10mg/L, respectively, with the RSD (n=5) was 6.6% for 1mg/L Cu²⁺ and 3.5% for 5mg/L Cu²⁺. The quantitative analysis results for the mineral wastewater is in good agreement the China National Environmental Protection Standards HJ485-2009, which indicates the current method could be developed to the on-site detection technique for the emergency response in monitoring Cu²⁺ in industrial wastewater or polluted water.

Gly–Gly–His tripeptide- and silver nanoparticle-assisted electrochemical evaluation of copper(ii) ions in aqueous environment

A sensitive and selective electrochemical sensor for Cu²⁺ assay is developed using tripeptide-based recognition and silver nanoparticle-modified electrode.

Copper Induced Conformational Changes of Tripeptide Monolayer Based Impedimetric Biosensor

Copper ions play a major role in biological processes. Abnormal Cu²⁺ ions concentrations are associated with various diseases, hence, can be used as diagnostic target. Monitoring copper ion is currently performed by non-portable, expensive and complicated to use equipment. We present a label free and a highly sensitive electrochemical ion-detecting biosensor based on a Gly-Gly-His tripeptide layer that chelate with Cu²⁺ ions. The proposed sensing mechanism is that the chelation results in conformational changes in the peptide that forms a denser insulating layer that prevents RedOx species transfer to the surface. This chelation event was monitored using various electrochemical methods and surface chemistry analysis and supported by theoretical calculations. We propose a highly sensitive ion-detection biosensor that can detect Cu²⁺ ions in the pM range with high SNR parameter.

Selective recognition of Cu (II) and Fe (III) using a pyrene based chemosensor

A pyrene-based colorimetric chemosensor 1-(pyren-1-yl)-N,N-bis-(pyridine-2-ylmethyl)methanamine (1) was synthesised for selective detection of Cu (II) and Fe (III) over the other metal cations Ni²⁺, Mg²⁺, Cd²⁺, Hg²⁺, Na⁺, K⁺, Ca²⁺, Co²⁺, Cr³⁺, Pb²⁺ and Zn²⁺. The significant changes in UV-vis absorption band of receptor 1 and the emergence of 660nm band in presence of Cu²⁺ ion indicates the selective binding of Cu²⁺ ion as compared to other metal cations which could easily be identified from the naked eye strong colour change. Job plots suggest a 1:1 and 2:1 stoichiometric binding of Cu²⁺ and Fe³⁺, respectively, which was evidenced by ESI-MS analysis. Chemosensor 1 explores a cost-effective and selective colorimetric sensor for naked eye detection of trace amount of Cu²⁺ and Fe³⁺ ions in presence of other metal cations.

A highly sensitive and fast responsive naphthalimide-based fluorescent probe for Cu2+ and its application

The response of the probe L to Cu²⁺ is reversible and very fast (20 s). L has a low detection limit of 49 nM and was used for imaging of Cu²⁺ in MCF-7 cells with satisfying results. The sensor L can be analyzed with a molecular logic gate.

Tripeptide GGH as the Inhibitor of Copper-Amyloid-β-Mediated Redox Reaction and Toxicity

The Aβ complexes of some redox-active species, such as Cu, cause oxidative stress and induce severe toxicity by generating reactive oxygen species (ROS). Thus, Cu chelation therapy should be considered as a valuable strategy for the treatment of Alzheimer's disease (AD). However, more attention should be paid to the specific chelating ability of these chelating agents. Herein, a tripeptide GGH was used to selectively chelate the Cu(2+) in Aβ-Cu complex in the presence of other metal ions (e.g., K(+), Ca(2+), Ni(2+), Mg(2+), and Zn(2+)) as shown by isothermal titration calorimetry results. GGH decreased the level of HO(•) radicals by preventing the formation of intermediate Cu(I) ion. Thus, the Cu species completely lost its catalytic activity at a superequimolar GGH/Cu(II) ratio (4:1) as observed by UV-visible spectroscopy, coumarin-3-carboxylic acid fluorescence, and BCA assay. Moreover, (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) (MTT) assay indicates that GGH increased PC-12 cell viability from 36% to 63%, and neurotoxicity partly triggered by ROS decreased. These results indicate potential development of peptide chelation therapy for AD treatment.

A phthalazine-based two-in-one chromogenic receptor for detecting Co(2+) and Cu(2+) in an aqueous environment

A new multifunctional and highly selective chemosensor for Co(2+) and Cu(2+) was designed and synthesized. could simultaneously detect both Co(2+) and Cu(2+) by changing its color from pale yellow to pink and to orange in a near-perfect aqueous solution. The binding modes of to Co(2+) and Cu(2+) were determined to be a 2 : 1 complexation stoichiometry through Job's plot, ESI-mass spectrometry analysis and (1)H NMR titration. The detection limits (1.5 and 2.1 μM) of for Co(2+) and Cu(2+) were lower than the DEP guidelines (1.7 μM for Co(2+)) and the WHO guidelines (31.5 μM for Cu(2+)) for drinking water. The chemosensor could be used to quantify Co(2+) and Cu(2+) in water samples. Moreover, could be used as a practical, visible colorimetric test kit for both Co(2+) and Cu(2+). The sensing mechanisms of Co(2+) and Cu(2+) by were supported by theoretical calculations.

Study of a Bifunctional Aβ Aggregation Inhibitor with the Abilities of Antiamyloid-β and Copper Chelation

In this study, a bifunctional Aβ aggregation inhibitor peptide, GGHRYYAAFFARR (GR), with the abilities to bind copper and antiamyloid was designed to inhibit the neurotoxicity of the Aβ-Cu(II) complex. The thioflavin T (ThT) assay, turbidimetric analysis, transmission electron microscopy (TEM), and (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) (MTT) assay were used to study its potential inhibitory effect on Aβ aggregation. Our findings indicate that GGH was the specific chelating sequence and that the RYYAAFFARR (RR) component acted as an aggregation inhibitor. More importantly, GR significantly decreased the cytotoxicity of the Aβ-Cu(II) complex. The cell viability improved to 88%, which was higher than with the single functional peptide GGH and RR by 39% and 20%, respectively. Moreover, the qualitative effect of Cu(II) on the Aβ-Cu(II) complex was also studied. Our results indicate that Cu(II) induces the formation of the β-sheet structure with a subequimolar Cu(II):Aβ molar ratio (0.25:1) but led to increased ROS production at a supra-equimolar ratio.

Dual-channel detection of Cu(2+) and F(-) with a simple Schiff-based colorimetric and fluorescent sensor

A simple and easily synthesized colorimetric and fluorescent receptor 1, based on 4-diethylaminosalicylaldehyde moieties as a binding and signaling unit, has been synthesized and characterized. The receptor 1 has a selective colorimetric sensing ability for copper (II) ion by changing color from colorless to yellow in aqueous solution, and could be utilized to monitor Cu(II) over a wide pH range of 4-11. In addition, the detection limit (12μM) of 1 for Cu(2+) is much lower than that (30μM) recommended by WHO in drinking water, and its copper complex could be reversible simply through treatment with a proper reagent such as EDTA. Moreover, receptor 1 exhibited both a color change from colorless to yellow and fluorescence enhancement with a red shift upon addition to F(-) in DMSO. The recognition mechanism was attributed to the intermolecular proton transfer between the hydroxyl group of the receptor and the fluoride.

Tunnelling current recognition through core–satellite gold nanoparticles for ultrasensitive detection of copper ions

The addition of copper ions induces the formation of GNP/l-cysteine/Cu²⁺/l-cysteine/GNP molecular junctions and generates a significant decrease in the resistance through the networks.

Malonamide dithiocarbamate functionalized gold nanoparticles for colorimetric sensing of Cu2+ and Hg2+ ions

In this study, a colorimetric probe was developed based on malonamide dithiocarbamate functionalized gold nanoparticles (MA–DTC–Au NPs) for the simultaneous colorimetric detection of Cu²⁺ and Hg²⁺ ions.

Label-free detection of Cu(ii) in a human serum sample by using a prion protein-immobilized FET sensor

We report a simple and label-free detection of Cu²⁺utilizing prion proteins as the recognition molecules, which can provide highly sensitive and selective performance at the nanomolar level in a human serum sample.

Chromogenic naked-eye detection of copper ion and fluoride

Colorimetric chemosensor was reported for detection of Cu²⁺ and F⁻via the color change from colorless to yellow and to orange.

A diaminomaleonitrile based selective colorimetric chemosensor for copper(ii) and fluoride ions

A chemosensor showed colorimetric sensing for copper(ii) and fluoride by changing color from yellow to colorless and to orange.

Click chemistry-mediated catalytic hairpin self-assembly for amplified and sensitive fluorescence detection of Cu2+in human serum

Cu⁺-mediated click ligation of DNA leads to catalytic self-assembly of hairpins and amplified fluorescent signals for sensitive detection of Cu²⁺.

Environment-sensitive fluorescent supramolecular nanofibers for imaging applications

The combination of an environment-sensitive fluorophore, 4-nitro-2,1,3-benzoxadiazole (NBD), and peptides have yielded supramolecular nanofibers with enhanced cellular uptake, brighter fluorescence, and significant fluorescence responses to external stimuli. We had designed and synthesized NBD-FFYEEGGH that can form supramolecular nanofibers and emit brighter than its counterpart of NBD-EEGGH without the self-assembling property. The nanofibers of NBD-FFYEEGGH could specifically bind to Cu(2+), leading to the formation of fluorescence quenched elongated nanofibers. This fluorescence quenching property was enhanced in self-assembling nanofibers and could be applied for detection of Cu(2+) in vitro and within cells. In a further step, an enzyme-cleavable DEVD peptide was placed between NBD-FFY and the copper binding tripeptide GGH. The resulting self-assembling peptide NBD-FFFDEVDGGH also showed strong fluorescence quenching to Cu(2+). Upon the enzymatic cleavage to remove the Cu(2+)-binding GGH tripeptide from the peptide, the fluorescence was restored. The cellular uptake of nanofibers was better than that of free molecules because of endocytosis. The supramolecular nanofibers with fluorescence turn-on property could therefore be applied for detection of caspase-3 activity in vitro and within cells. We believe that the combination of environment-sensitive fluorescence and fast responses of supramolecular nanostructures would lead to a useful platform to detect many important analytes.

A Nano-Silver Enhancement Effect on the Luminescence of a Ligand–Eu3+ Complex via a SiO2 Spacer

Luminescent rare earth complex (REC) nanocomposites, Eu(TTA)3Phen attached onto Ag@SiO2 nanoshells, were fabricated by facile wet chemistry and self-assembly techniques. Transmission electron microscopy, and fourier transform infrared and UV–Vis spectroscopy were used to investigate the step-by-step fabrication. The luminescence of REC was significantly enhanced using a silver core (size: 45 nm) surrounded by a 20-nm thick silica shell. Thicker or thinner silica shells afforded tuning of the metal-enhanced luminescence. The thiophene-TTA-containing REC fluorophore was able to etch the silver core, resulting in hollow silica shells, consequently displaying no luminescence enhancing capabilities. The etching efficiency was proportional to the concentration of Eu(TTA)3Phen, and decreased with increasing shell thickness.