A gold nanorod based colorimetric probe for the rapid and selective detection of Cu2+ ions

A gold nanorod (AuNR) based colorimetric probe was reported for the rapid and selective detection of Cu(2+) ions. The probe was fabricated by functionalizing cysteine (Cys) onto AuNR (Cys-AuNR) with an aspect ratio of 2.3. The strong coordination of Cu(2+) with cysteine resulted in a stable Cys-Cu-Cys complex, and induced the aggregation of the colloidal nanorods along with a rapid colour change from blue-green to dark gray. Potential factors affecting the performance of the probe for the detection of Cu(2+) were carefully optimized, including the pH value of the buffer media, the concentration of cysteine, and the kinetics for the coordination of Cu(2+) with Cys-AuNR. Under optimal conditions, the developed colorimetric method gave a linear range of 1-100 μM for Cu(2+), and a detection limit (3s) of 0.34 μM. Moreover, the developed method exhibited excellent selectivity for Cu(2+), and quantitative spike-recoveries from 90% to 107% in environmental water samples. The proposed colorimetric approach can in principle be used to detect other metal ions by functionalizing various specific ligands onto the AuNR that can selectively bind the other target metal ions.     

Visual detection of copper(II) ions in blood samples by controlling the leaching of protein-capped gold nanoparticles

We have developed a simple, low-cost, paper-based probe for the selective colorimetric detection of copper ions (Cu(2+)) in aqueous solutions. The bovine serum albumin (BSA)-modified 13.3-nm Au nanoparticle (BSA-Au NP) probe was designed to detect Cu(2+) ions using lead ions (Pb(2+)) and 2-mercaptoethanol (2-ME) as leaching agents in a glycine-NaOH (pH 12.0) solution. In addition, a nitrocellulose membrane (NCM) was used to trap the BSA-Au NPs, leading to the preparation of a nanocomposite film consisting of a BSA-Au NP-decorated membrane (BSA-Au NPs/NCM). The BSA-Au NPs probe operates on the principle that Cu deposition on the surface of the BSA-Au NPs inhibits their leaching ability, which is accelerated by Pb(2+) ions in the presence of 2-ME. Under optimal solution conditions (5 mM glycine-NaOH (pH 12.0), Pb(2+) (50 μM), and 2-ME (1.0 M)), the Pb(2+)/2-ME-BSA-Au NPs/NCM enabled the detection of Cu(2+) at nanomolar concentrations in aqueous solutions by the naked eye with high selectivity (at least 100-fold over other metal ions). In addition, this cost-effective probe allowed for the rapid and simple determination of Cu(2+) ions in not only natural water samples but also in a complex biological sample (in this case, blood sample).     

Solvent controlled sugar-rhodamine fluorescence sensor for Cu(2+) detection

A "turn-on" fluorescence probe for Cu(2+) detection has been reported according to a Cu(2+) triggered spirolactam ring-opening reaction. The probe is a double-responsive fluorescent and colorimetric Cu(2+)-specific sensor in aqueous solution containing 20% of acetonitrile with high selectivity and excellent sensitivity (limit of detection is 12 μg L(-1)). Furthermore, the significant color changes visible to the naked eye at the concentration of 3 μM (ca. 0.20 mg L(-1)) are about ten times lower than the WHO (World Health Organization) recommended level (2.0 mg L(-1)) for Cu(2+) ions in drinking water.     

Label-free colorimetric sensing of cobalt(II) based on inducing aggregation of thiosulfate stabilized gold nanoparticles in the presence of ethylenediamine

As a sensitive and selective analytical technique, gold nanoparticles-based colorimetric sensing was characterized by its simplicity and cost-effectiveness. Specific methods have been extensively developed for different targets in diverse samples. In this study, a label-free method for sensing Co(2+) in aqueous solutions was described. The target was achieved by the induced aggregation of thiosulfate (S(2)O(3)(2-)) stabilized gold nanoparticles (AuNPs) in the presence of ethylenediamine (en). Co(2+) first reacted with en and formed complexes of Co(en)(3)(2+) in aqueous solutions, which was followed by the oxidation of Co(en)(3)(2+) to Co(en)(3)(3+) by dissolved oxygen. Co(en)(3)(3+) then attacked S(2)O(3)(2-) ligands adsorbed on the AuNPs' surfaces, forming positively charged (en)(2)CoS(2)O(3)(+) on the AuNPs' surfaces, which reduced the surface charges of AuNPs and induced the aggregation of AuNPs. The process was accompanied by a red-shift in the adsorption spectrum and a visible colour change from wine red to blue. Potential effects of relevant experimental conditions, including pH, concentrations of S(2)O(3)(2-) and en, and incubation time were evaluated for optimization of the method. The proposed method is sensitive (LOD = 0.0 4 μM or 2.36 ppb) and selective (by at least 100-fold over other metal ions except for Cu(2+)) toward Co(2+) with a linear range from 0.1 to 0.7 μM. The cost-effective method allows rapid and simple determination of the concentrations of Co(2+) ions in drinking water.     

Multifunctional modified silver nanoparticles as ion and pH sensors in aqueous solution

Silver nanoparticles capped with mercaptoacetic acid and 2-aminoethanethiol short-chain alkanethiols were prepared by a one-step method in aqueous solution for monitoring pH and a range of heavy metal ions. The mode of transduction is optical, based on the change in aggregation of the nanoparticles in solution. Because of the different ionic interactions between the modified nanoparticles, these nanoparticle sensors can rapidly detect Pb(2+), Cu(2+) and Fe(2+), with detection limits as low as 1 × 10(-5) M, 5 × 10(-7) M and 5 × 10(-5) M respectively, as well as having the ability to detect Cu(2+) ions from Pb(2+) and Fe(2+). Furthermore, the same functionalised nanoparticles are also sensitive to pH; exhibiting a good linear dynamic response between pH 1 and 10.     

Colorimetric assay for parallel detection of Cd2+, Ni2+ and Co2+ using peptide-modified gold nanoparticles

A colorimetric assay has been developed for parallel detection of Cd(2+), Ni(2+) and Co(2+) utilizing peptide-modified gold nanoparticles (P-AuNPs) as a sensing element based on its unique surface plasmon resonance properties. The functional peptide ligand, CALNNDHHHHHH, was self-assembled on gold nanoparticles (AuNPs) to produce P-AuNPs probe. The P-AuNPs probe could be used to simultaneously detect and showed different responses to the three ions Cd(2+), Ni(2+) and Co(2+) in an aqueous solution based on the aggregation-induced color change of AuNPs. The method showed good selectivity for Cd(2+), Ni(2+) and Co(2+) over other metal ions, and detection limit as low as 0.05 μM Cd(2+), 0.3 μM Ni(2+) or 2 μM Co(2+). To simultaneously (or parallel) detect the three metal ions coexisting in a sample, EDTA and imidazole were applied to mask Co(2+) and Ni(2+) for detecting Cd(2+), glutathione and EDTA were applied to mask Cd(2+) and Co(2+) for detecting Ni(2+), and glutathione and imidazole were applied to mask Cd(2+) and Ni(2+) for detecting Co(2+). Finally, the simple and cost-effective probe could be successfully applied for simultaneously detecting Cd(2+), Ni(2+), and Co(2+) in river water. Because this novel P-AgNPs-based probe design offers many advantages, including simplicity of preparation and manipulation compared with other methods that employ specific strategies, the sensing system shows potential application in the developing region for monitoring water quality.     

Colorimetric detection of Cd2+ using gold nanoparticles cofunctionalized with 6-mercaptonicotinic acid and L-cysteine

We have developed a colorimetric assay for the highly sensitive and selective detection of Cd(2+) using gold nanoparticles (AuNPs) cofunctionalized with 6-mercaptonicotinic acid (MNA) and L-Cysteine (L-Cys) through the formation of an Au-S bond. In the presence of Cd(2+), the aggregation of functionalized AuNPs occurred by means of a metal-ligand interaction that led to visible color changes. Most importantly, cofunctionalized AuNPs had better responses for Cd(2+) than that functionalized by either MNA or L-Cys. Cd(2+) could be detected by the colorimetric response of AuNPs that could be detected by the naked eye or a UV-vis spectrophotometer. The absorbance ratio (A(620)/A(523)) was linear with the Cd(2+) concentration in the range of 2.0 × 10(-7) to 1.7 × 10(-6) M. Under optimum conditions (2.0 × 10(-5) M MNA, 2.0 × 10(-6) M L-Cys and 0.020 M NaCl at pH 10.0), the detection limit (3σ) of Cd(2+) could be as low as 1.0 × 10(-7) M. Interference experiments showed that Pb(2+) and Cu(2+) caused a slight interference for Cd(2+) determination while other metal ions caused no interference. The proposed method was successfully applied to determine the concentration of Cd(2+) in environmental samples (lake water).     

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.     

A colorimetric sensor based on catechol-terminated mixed self-assembled monolayers modified gold nanoparticles for ultrasensitive detections of copper ions

A colorimetric sensor for Cu(II) ions has been developed based on mixed self-assembled monolayers (SAMs) modified gold nanoparticles (AuNPs). The AuNPs were modified with mixed SAMs consisting of mercaptosuccinic acid and the product of electrochemically triggered Michael addition reaction of 4-thiouracil and catechol. In the presence of Cu(II) ions, the coordination of Cu(2+) to catechol-terminated AuNPs leads to aggregation-induced changes of surface plasmon resonance. The cost-effective chemical sensor allows rapid, sensitive and selective detection of Cu(2+) ions, indicating its potential application in environmental field.     

Visual determination of Cu(2+) through copper-catalysed in situ formation of Ag nanoparticles

A new strategy was explored for the visual determination of Cu(2+) using copper-catalysed in situ formation of Ag nanoparticles. In this method, only common reagents were used and the pre-synthesis and modification of nanoparticles are avoided. Ag(+) can form a milk-white suspension (AgBr) with Br(-) in an aqueous solution composed of AgNO(3), cetyltrimethylammonium bromide, ascorbic acid, bovine serum albumin, and NaNO(3). The reaction will be stopped by addition of Cu(2+), accompanied by a colour change from milk-white to orange or brilliant yellow. Cu(+) (the reduction product of Cu(2+)) consumes the dissolved O(2) and prevents the O(2) from oxidizing the newly reduced Ag atoms (by ascorbic acid) back to Ag(+), facilitating the further aggregation of Ag atoms to become Ag nanoparticles. The visible colour change was shown to be specific towards Cu(2+) over most other metal ions. The limit of detection was 0.75 μM Cu(2+) by the naked eye and 0.25 μM by spectrometer. Quantitation of Cu(2+) was achieved in a linear range from 0.25 to 2.0 μM. This method was validated by measuring real water and serum samples, giving results agreeing well with the data reported and measured by inductively coupled plasma mass spectrometry. The recovery was 95.6-106% for untreated tap water and 96.0-100% for resin-pre-treated water and serum samples.     

Selective and sensitive optical chemosensor for detection of Ag(I) ions based on 2(4-hydroxy pent-3-en-2-ylideneamine) phenol in aqueous samples

A selective and sensitive chemosensor, based on the 2(4-hydroxy pent-3-en-2-ylideneamine) phenol (HPYAP) as chromophore, has been developed for colorimetric and visual detection of Ag(I) ions. HPYAP shows a considerable chromogenic behavior toward Ag(I) ions by changing the color of the solution from pale-yellow to very chromatic-yellow, which can be easily detected with the naked-eye. The chemosensor exhibited selective absorbance enhancement to Ag(I) ions in water samples over other metal ions at 438 nm, with a linear range of 0.4–500 μM (r² = 0.999) and a limit of detection 0.07 μM of Ag(I) ions with UV–vis spectrophotometer detection. The relative standard deviation (RSD) for 100 μM Ag(I) ions was 2.05% (n = 7). The proposed method was applied for the determination Ag(I) ions in water and waste water samples.     

Colorimetric filtrations of metal chelate precipitations for the quantitative determination of nickel(II) and lead(II)

A colorimetric filtration method has been developed for the highly selective and sensitive determination of Ni(2+) and Pb(2+) ions. Determinations of Ni(2+) and Pb(2+) follow the filtration using nioxime (1,2-cyclohexanedione dioxime) and rhodizonic acid disodium salt, respectively, as colorimetric reagents. Different from regular instrumentation techniques, the metal chelate precipitations are continuously pumped into a home-made flow cell at a constant flow rate, and filtered by a cellulose acetate/nitrate membrane. The color changes of the membrane are imaged using a conventional flatbed scanner, and digitized. The special selection of individual channels in the red, green, and blue channels of the images filters the influences of coexisting ions and provides a highly selective detection of Ni(2+) and Pb(2+) cations. The linear relationship between the colorimetric response of the chosen channel and Ni(2+) or Pb(2+) concentrations indicates a quantitative detection. The detection limit for Pb(2+) is 3 μM (almost half of the Chinese wastewater discharge standard concentration), and is well below the nM level (94 nM) for Ni(2+) (a quarter of the WHO drinking water safe-exposure standard for Ni(2+)). The determinations take five to ten minutes. No shelf life issue exists because the chelating indicators react with metal directly without any pre-immobilizations.     

Rhodamine-based highly sensitive colorimetric off-on fluorescent chemosensor for Hg2+ in aqueous solution and for live cell imaging

A novel rhodamine-based highly sensitive and selective colorimetric off-on fluorescent chemosensor for Hg(2+) ions is designed and prepared by using the well-known thiospirolactam rhodamine chromophore and furfural hydrazone as signal-reporting groups. The photophysical characterization and Hg(2+)-binding properties of sensor RS1 in neutral N, N-dimethylformamide (DMF) aqueous solution are also investigated. The signal change of the chemosensor is based on a specific metal ion induced reversible ring-opening mechanism of the rhodamine spirolactam. The response of the chemosensor for Hg(2+) ions is instantaneous and reversible. And it successfully exhibits a remarkably "turn on" response toward Hg(2+) over other metal ions (even those that exist in high concentration). Moreover, this sensor is applied for in vivo imaging in Rat Schwann cells to confirm that RS1 can be used as a fluorescent probe for monitoring Hg(2+) in living cells with satisfying results, which further demonstrates its value of practical applications in environmental and biological systems.     

Quantitative analysis of multiple urinary biomarkers of carcinoid tumors through gold-nanoparticle-assisted laser desorption/ionization time-of-flight mass spectrometry

A highly selective and sensitive coumarin-based chemodosimeter 1 for Cu(2+) in water is reported in this work. 1 was designed and facilely synthesized by a one-step reaction with coumarin as a fluorophore and 2-picolinic acid as the binding moiety, which showed very week fluorescence in buffer solution, and its fluorescence was considerably enhanced by the addition of Cu(2+) at room temperature in 5 min. Mechanism study suggested that Cu(2+) promoted the hydrolysis of 1 via the catalytic sensing cycle, generating a highly fluorescent product 7-hydroxycoumarin with fluorescence signal greatly amplified. The probe exhibited remarkably selective fluorescence enhancement to Cu(2+) over other metal ions at 454 nm, with a detection limit of 35 nM Cu(2+). Under optimal condition, 1 was successfully used for the determination of Cu(2+) in fetal equine serum and two water samples.     

Two-photon excited fluorescent chemosensor for homogeneous determination of copper(II) in aqueous media and complicated biological matrix

In the present work, a two-photon excited fluorescent chemosensor for Cu(2+) was prepared. The probe was constructed on the basis of internal charge transfer (ICT) principle with macrocyclic dioxotetraamine as the Cu(2+) receptor. The good water-solubility of the molecule enabled recognition and assay of Cu(2+) ions in biological media. The photophysical properties of the chemosensor were investigated in detail, exhibiting favorable fluorescence quantum yield and moderate two-photon absorption cross-section. The studies on binding thermodynamics demonstrated the formation of 1?:?1 complex between the chemosensor and Cu(2+) and an association constant of ca. 1.04 × 10(5) M(-1). Due to the rational design of the molecular structure, the sensor was highly specific to Cu(2+), which ensured high selectivity in Cu(2+) determination. Upon Cu(2+) binding, the intramolecular charge-transfer extent within the chromophore was weakened resulting in a remarkable quenching of fluorescence, based on which quantitative determination of Cu(2+) was performed. Good linearity was obtained between the fluorescence quenching value and Cu(2+) concentration ranging from 0.04 to 2.0 μM in aqueous solution. Benefiting from the merits of two-photon excitation, the chemosensor was free of interference from background luminescence in serum. A homogeneous quantitative determination of Cu(2+) was achieved in the serum medium with a linear range of 0.04 to 2.0 μM. Considering the structural flexibility of the sensor, this work also opens up the possibility to construct other two-photon excited chemosensors for direct homogeneous assay of various molecules/ions in complicated biological sample matrices.     

Terbium hybrid particles with spherical shape as luminescent probe for detection of Cu2+ and Fe3+ in water

A novel green emissive terbium inorganic-polymeric hybrid particle was designed and this material could detect cations in water. Polyvinyl alcohol as an amphiphilic surfactant rendered the powders dispersible in water with regular round shape (10-20 μm). Interestingly, we noticed that not only Cu(2+) (detection limit 10(-4)M) but also Fe(3+) (detection limit 10(-4) M) can give rise to emission quenching to this target material in comparison with K(+), Na(+), Fe(2+), Mn(2+), Pd(2+), Cd(2+) and Co(2+) (10(-3) mol L(-1)). We regarded that the coordination interactions between ligand and metal ions resulted in these quenching processes. Additionally, it was found that the sensing material can be repeatedly used at least 5 cycles. More importantly, this novel material demonstrated higher thermal-stability in aqueous media than pure silica hybrid material.     

Selective removal and quantification of Cu(II) using fluorescent iminocoumarin-functionalized magnetic nanosilica

A newly prepared iminocoumarin-functionalized magnetic nanosilica (Ni@SiO(2)-1) was found to form a selective stable complex with Cu(2+) over other metal ions. Quantification of Cu(2+) ions in aqueous solution using Ni@SiO(2)-1 is demonstrated through a fluorescent demetallization ensemble process.     

A bi-ligand co-functionalized gold nanoparticles-based calcium ion probe and its application to the detection of calcium ions in serum

In this study, the use of bi-ligand co-functionalized gold nanoparticles in a highly selective and sensitive colorimetric probe for Ca(2+) ions is demonstrated and this probe also determined the concentrations of Ca(2+) ions in serum samples.     

An indicator-displacement assay for naked-eye detection and quantification of histidine in human urine

A simple and efficient colorimetric method for the naked-eye detection and quantification of histidine in biological fluids was developed based on an indicator-displacement assay (IDA) and the Ni(2+)-histidine affinity pair. In this IDA approach, a commercially available dye, murexide, was used as the indicator and the selective detection of histidine was achieved based on the competition between indicator and histidine for the binding with Ni(2+). The competition of histidine with murexide for Ni(2+) resulted in an obvious color change of the solution from yellow to purple, and the permitted naked-eye detection of trace histidine. The developed bioassay allows the rapid, sensitive and selective detection of histidine in urine samples, and does not need complicated sample pretreatment. The detection limit was 0.4 μM with a linear range from 2 to 30 μM. The relative standard deviation for 11 replicate detections of 8 μM histidine was 2.0%. The developed sensor was successfully applied to the determination of histidine in human urine samples with recoveries from 97 to 105%.     

Highly sensitive and selective turn-on fluorescent and chromogenic probe for Cu2+ and ClO- based on a N-picolinyl rhodamine B-hydrazide derivative

A new rhodamine B-based dual-function chromo- and fluorogenic probe for Cu(2+) and ClO(-) has been designed, synthesized, and characterized. The probe comprises a spectroscopic unit of rhodamine B and a Cu(2+)-specific chelating unit of pyridinecarboxamide as well as a ClO(-)-specific reactive moiety of diacylhydrazine, and is a highly selective and extremely sensitive fluorescent and colorimetric sensor for Cu(2+) and ClO(-) in different pH conditions. Compared with the reported probes for Cu(2+) or ClO(-), this is the first chemosensor based on a small molecule that can detect both Cu(2+) and ClO(-), respectively, at 1 nM level.