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A novel platform of a polydiacetylene combined with rhodamine B (PDA-Rho) colorimetric chemosensor array was prepared from a diacetylene monomer and rhodamine B derivative. Rhodamine B derivative as the ion-recognition element was embedded in the polydiacetylene matrix. To fabricate chemosensor, diacetylene monomer connected rhodamine B derivatives (DA-Rho) was coated onto a filter paper surface via drop-casting technique and transformed to polydiacetylene by polymerisation through ultraviolet (UV) irradiation. From the result, PDA-Rhoen exhibited high sensitivity and selectivity for Au3+ and could be monitored directly by naked eyes providing a fast, portable and easy-to-use as a molecular device in the real system. The DFT calculation results showed a stable complex between PDA-Rho and Au3+. We believe that, this method offers a sensitive and accurate process for Au3+ ion detection in real environmental and biological applications.

A novel platform of a polydiacetylene combined with rhodamine B (

2-Chloro-N-(2,4-dinitrophenyl) acetamide, 1, was synthesized and characterized by 1H and 13C NMR spectroscopy, ESI–MS, X-ray crystallography, and elemental analysis. This compound crystallizes in the monoclinic space group P21/n. The crystal structure of compound 1 revealed the intramolecular H-bonding with the S(6) motif between H atom of the amide group and the nitro group at the ortho position. Several intermolecular C–H⋯O interactions hold different molecules of the compound 1 together resulting in the crystal packing. Red faint spots observed in the Hirshfeld surface of the compound 1 confirm the presence of N–H⋯O hydrogen bond as well as C–H⋯O interactions. According to the Hirshfeld surface, C–H⋯Cl interaction is also found, of which distance is relatively longer than the C–H⋯O distance. Moreover, the analysis of the corresponding fingerprint plots indicates the significant interactions within the crystal namely H⋯O/O⋯H (39.0%), C⋯O/O⋯C (10.6%), H⋯Cl/Cl⋯H (8.5%), H⋯H (7.3%), and H⋯C/C⋯H (5.9%) contacts. The optical properties of compound 1 in various solvents were investigated using UV–vis spectrophotometry. Compound 1 showed solvatochromic effects upon the varying polarity of the solvent. Time-dependent DFT calculations (TD-DFT) of compound 1 suggest that the deprotonation process occurs in polar solvents such as DMF. Crystal structure of 2-Chloro-N-(2,4-dinitrophenyl) acetamide (1) revealed the intramolecular N–H⋯O hydrogen bonding with the S(6) motif within the molecule as well as several intermolecular C–H⋯O interactions between molecules. Moreover, the compound 1 exhibited solvatochromic effects upon the varying polarity of the solvents.

Copper nanoparticles fabricated onto reduced graphene oxide (Cu NPs/rGO) were successfully synthesized via a one-pot dimethylformamide (DMF) reduction approach with an addition of nominal water. Th...

A new paper-based analytical device based on bulk ion-selective optodes (ISOs) for dual Ag+ and Hg2+ detection has been developed. A plasticized PVC hydrophobic phase composed of 25,27-di(benzothiazolyl)-26,28-hydroxycalix[4]arene (CU1) as an ion-selective ionophore, potassium tetrakis(4-chlorophenyl)borate as an ion-exchanger and chromoionophore XIV as a lipophilic pH indicator was entrapped in the pores of cellulose paper. This paper strip showed higher selectivity for Ag+ and Hg2+ over common alkali, alkaline earth and some transition metal ions with a color change from blue to yellow. With the proposed sensor, Ag+ and Hg2+ can be measured with the range of 1.92 × 10−6 to 5.00 × 10−3 M for Ag+ and 5.74 × 10−7 to 5.00 × 10−5 M for Hg2+ with a limit of detection of 1.92 × 10−6 M for Ag+ and 5.74 × 10−7 M for Hg2+. The proposed sensor was successfully applied to determine the amount of mercury in various water sources and the amount of silver in cleaning product samples containing silver nanoparticles (AgNPs). The results were in good agreement with inductively couple plasma-optical emission spectrometric measurements (ICP-OES).

A novel naked eye fluorescence sensor (ANI) based on naphthalimide and imidazolium moieties for fluoride detection has been designed and synthesized by multiple step synthesis. The fluorescence response of ANI sensor was significantly quenched in the presence of fluoride ion upon the interaction between an acidic amide proton and acidic C2 proton (-C(2)H-) of imidazolium compound. The binding behavior of ANI and F− ion was extensively explored by using NMR titration. Comparison of binding ability of ANI and AN sensors addressed the dominant electrostatic and hydrogen bonding interaction with F− ion. Consequently, ANI sensor highlights a strong binding with F− ions with a high selectivity over AN. Interestingly, ANI demonstrated a naked-eye response with colorimetric and fluorometric assay.

Modification of graphene oxide (GO) with porphyrins, TPP and ZnTPP (TPP = 5,10,15,20-tetraphenyl-21H,23H-porphine), was achieved by facile synthesis through a self-assembly process. GO–porphyrins composites were characterized by scanning electron microscopy, and UV-visible, fluorescence, photoluminescence and Raman spectroscopy, which confirmed the successful attachment of TPP and ZnTPP onto the GO surface via π–π stacking. The coordination of oxygen functional groups on GO to the Zn center of ZnTPP was also observed. The latter interaction was proposed to account for the lower catalytic activity of the GO–ZnTPP composite compared to that of the GO–TPP one because it hindered the accessible active sites on the GO surface, i.e. epoxy groups. Compared to unmodified GO and pristine porphyrins, the GO–porphyrin composites exhibited remarkable photocatalytic enhancement under irradiation using a light emitting diode. Moreover, the GO–TPP composite was shown to be a competent and reusable photocatalyst for selective alcohol oxidation under mild conditions, affording desired products in moderate to excellent yields.

A novel paper-based sensor using graphene quantum dots (GQDs) as a colorimetric probe for Au3+ determination has been developed. The paper sensor was fabricated by the adsorption of GQDs onto cellulose filter paper and then coating with a PVC membrane. The PVC membrane was plasticized with o-NPOE containing potassium tetrakis(4-chlorophenyl)borate (KTpClPB) as a lipophilic cation-exchanger. According to the ion-exchanged mechanism between the lipophilic phase and aqueous phase, Au3+ in the aqueous solution was extracted to the lipophilic phase on the paper layer. Then, adsorbed GQDs on the paper could selectively reduce Au3+ to elemental gold (Au0). The generated gold nanoparticles (AuNPs) resulted in the color of the paper turning from pale yellow to pink, which was recorded by using CIE L*a*b* color space. Under optimized conditions, the change in the color difference (ΔE) was related to the concentration of Au3+ in a working linear range of 200–1000 μM and the detection limit was found to be 70 μM. The proposed sensor was successfully applied to the determination of Au3+ in real water samples. The results were in favorable agreement with standard inductively coupled plasma-optical emission spectrometry (ICP-OES) results.

The title compound possesses crystallographically imposed twofold symmetry with the two C atoms of the central benzene ring and the C atom of its methyl substituent lying on the twofold rotation axis. The two dansyl groups are twisted away from the plane of methyl­phenyl bridging unit in opposite directions. The crystal packing features weak C—H⋯O hydrogen bonds., The title compound, C31H30N2S2O6, possesses crystallographically imposed twofold symmetry with the two C atoms of the central benzene ring and the C atom of its methyl substituent lying on the twofold rotation axis. The two dansyl groups are twisted away from the plane of methyl­phenyl bridging unit in opposite directions. The three-dimensional arrangement in the crystal is mainly stabilized by weak hydrogen bonds between the sulfonyl oxygen atoms and the hydrogen atoms from the N-methyl groups. Stacking of the dansyl group is not observed. From the DFT calculations, the HOMO–LUMO energy gap was found to be 2.99 eV and indicates n→π* and π→π* transitions within the mol­ecule.

A highly sensitive and selective optical chemosensor (Arg-Rhoen) for determination of Au3+ was prepared by covalent immobilization of rhodamine ethylenediamine on agarose gel. Spectrophotometric studies of complex formation, chemical structures and purity of the hydrogel sensor were carried out using TGA, NMR, TEM, and IR. The complexation study results indicated that this probe can selectively detect Au3+ via a metal ion chelation-induced ring-opening reaction, and then caused a remarkable colour change from colourless to pink and a strong fluorescence enhancement. Theoretical DFT calculation results suggested that the hydrogel sensor Arg-Rhoen formed stable complexes with Au3+ through a large number of cation-dipole interactions. Reusability has been established by repeatedly dipping and rinsing the hydrogel in aqueous Au3+ and EDTA in basic solutions. We believe that this approach may provide an easily measurable and inherently sensitive method for Au3+ detection in environmental and biological applications.

Histamine poisoning from fish is a worldwide problem. It occurs when bacteria convert high levels of naturally occurring histidine into histamine resulting that when people eat fish containing high levels of histamine, they suffer allergic type reactions. Deeply considering, histamine and histidine consist of the primary amine and imidazole unit in their structures. As a result, the selectively discriminate detection of each species has been a greatly challenge task for determining the freshness of seafood. In the present work, the successful development of a new fluorescence sensors based on the superior Histamine blue (HB) doped in nanoporous silica (NPS) and surface modification with FC to provide FRET On-Off process and highly discriminate detection of histamine among other biogenic amines through the charge repulsion of FC and histidine and the specific reaction of mesoionic acid fluoride based Histamine blue (HB) with the amine group of Him via self-catalytic reaction of imidazole group in Him. This simple HB@NPS@FC sensory platform allows accurate determination of histamine in the linear response ranges of 29.12-166.67 μM of Him. The detection limit of the sensor was calculated equal to 8.55 μM. This HB@NPS@FC platform was investigated with success on real salmon and tuna samples. On the discovery of highly selective Him detection, the couple of two sensors and surface selector offers the potentially specific detection of Him in the field of food chemistry.

A very simple, highly sensitive and selective method for the determination of trace amounts of Cr3+ in real systems using the solvatochromic properties of a rhodamine-based sensor has been developed. This solvatochromic-based sensor is established using commercially available rhodamine dissolved in different solvents to produce rhodamine lactone (RhoL) via the rhodamine lactone–zwitterion equilibrium. Complexation studies using fluorescence spectroscopy showed that RhoL exhibited the highest colorimetric and fluorescence selectivity and sensitivity to Cr3+ in aqueous medium when compared to other metal ions. Importantly, RhoL could directly and rapidly detect Cr3+ through filter paper without resorting to additional instrumental analysis.

A novel magnetic hydroxyapatite-supported nickel oxide nanocomposite (NiO–HAP@γ-Fe2O3) was successfully prepared using a combination of co-precipitation and wet impregnation methods and was applied to the adsorption of methylene blue from aqueous solution. The presence of HAP, γ-Fe2O3, NiO and all elements in NiO–HAP@γ-Fe2O3 was confirmed by XRD, SEM–EDX and ICP-AES. The structure of the resulting nanocomposite was shown by TEM and SEM–EDX to be rod-shaped, measuring 55.8 ± 16.5 nm in length and 27.1 ± 6.2 nm in width, and on the surface of which was uniformly interspersed with NiO nanoparticles (about 21.4 nm average crystallite size) and γ-Fe2O3 nanoparticles (6.7 ± 2.6 nm in diameter). The novel NiO–HAP@γ-Fe2O3 exhibited a high adsorption rate during the first 20 min and reached an equilibrium within 3 h. The adsorption capacity of NiO–HAP@γ-Fe2O3 was significantly higher than that of its precursors (7.20 mg g−1 vs 0.79–1.31 mg g−1). The superior adsorption performance of the novel nanocomposite, which occurred despite its relatively low surface area, is likely attributable to the synergistic mechanisms facilitated by the presence of mixed metal oxides (NiO and γ-Fe2O3) on the adsorbent as well as by the Lewis acidity and basicity of the components of the adsorbent and the adsorbate. The adsorption kinetics and isotherms were well-fitted by the pseudo-second-order kinetic model and the Langmuir isotherm model, respectively.

In this work, a highly sensitive colorimetric paper-based optode for the determination of thiocyanate in urine samples was developed for the first time. The cocktail solution of the optode was composed of 5,10,15,20-tetrakis(4-octyloxyphenyl)porphyrin cobalt(II) complex (L), tridodecylmethylammonium chloride (TDMACl), 2-nitrophenyl octyl ether, and polyvinyl chloride as an ionophore, an ion exchanger, a plasticizer, and a polymer, respectively. The paper-based optode responded to thiocyanate by increasing the blue component in the RGB index and a visible change, with the naked-eye, of the optode color from pink to green was observed. From the central composite design, the optimized conditions that yielded the highest sensitivity were 4.70 mmol/kg TDMACl and 13.75 mmol/kg L. The developed optode sensor was highly selective and responded to thiocyanate over other anions, with a working range of 0.001–5 mM and with a coefficient of determination (R2) of 0.9915. The limits of detection using naked-eye and camera were determined to be 50.0 μM and 1.26 μM, respectively. In addition, the LOD and LOQ estimated from the standard deviation of the blank were 0.65 and 1.87 μM, respectively. Furthermore, this sensor was successfully applied to the detection of thiocyanate in urine samples from non-smokers and smokers. The results were in good agreement with the standard ion chromatography (IC) technique. This developed paper-based optode sensor was simple, low-cost, portable, and easy to use as a sensing device without any complicated instrument.

A paper-based colorimetric sensor was fabricated using polymethylacrylic acid-templated silver nanoclusters (AgNCs) as a sensing probe for the detection of Fe 2+ and employing an ion exchange polymeric membrane as a coating layer. AgNCs were impregnated on a cellulose filter paper. The AgNC-impregnated filter paper was then lacquered with a hydrophobic membrane of polyvinyl chloride plasticized with o -NPOE incorporating a hydrophobic cation exchanger. Due to the ion exchange phenomenon at the membrane surface, Fe 2+ was extracted into the paper layer, and the bound Ag + on the AgNCs was reduced by Fe 2+ . The growth of the cluster could be observed by measuring the increase in the silver nanoparticle (AgNP) plasmon band. The maximum plasmon band on the paper at 447 nm increased as a linear function of the increasing Fe 2+ concentration. The proposed sensor was highly selective to Fe 2+ over Fe 3+ and other cations. The proposed sensor was optimized and could be used to detect Fe 2+ solution concentrations as low as 50 μM, with a wide working linear concentration range of 0.2–1.0 mM. The sensor was applied to determine Fe 2+ in iron supplement tablet samples with satisfactory results.

We demonstrate an advance in the fabrication of circular dichroism (CD) sensors for detection of Cd2+ and S2- based on chiral CdS quantum dots (QDs) generated by a facile in-situ reaction. The chiral quantum dots are generated in solutions composed of Cd2+, S2-, cysteamine (CA) and L-penicillamine (L-PA), with the number of the generated particles limited by either the Cd2+ or S2- concentration. We show that the magnitude of the CD signal produced by the QDs is linearly related to the initial concentration of Cd2+ and S2-, with excellent selectivity over other ions. Our sensor functions over concentration ranges of 65-200μM and 7-125μM with detection limits of 59.7 and 1.6μM for Cd2+ and S2-, respectively. The sensor is applied in real water samples with results comparing favorably with those obtained from ICP-OES (for Cd2+) and HPLC (for S2-).

We described a turn-on fluorescence sensor for the determination of Cu(2+) ions, utilizing the quantum confinement effect of cadmium sulfide quantum dots capped with cysteamine (Cys-CdS QDs). The fluorescence intensity of the Cys-CdS QDs was both enhanced and red shifted (from blue-green to yellow) in the presence of Cu(2+). Fluorescence enhancement was linearly proportional to the concentration of Cu(2+) in the concentration range 2 to 10μM. Other cations at the same concentration level did not significantly change the intensity and spectral maxima of Cys-CdS QDs, except Ag(+). The limit of detection was 1.5μM. The sensor was applied to the determination of Cu(2+) in (spiked) real water samples and gave satisfactory results, with recoveries ranging from 96.7 to 108.2%, and with RSDs ranging from 0.3 to 2.6%.

A highly sensitive and selective optical membrane for determination of Au3+ was synthesized by immobilization of a rhodamine derivative on agarose hydrogel. The sensing dye was synthesized by solva...

MCM-41- and Al-MCM-41-supported nickel phosphide nanomaterials were synthesized at two different initial molar ratios of Ni/P: 10:2 and 10:3 and were tested as heterogeneous catalysts for the one-pot conversion of cellobiose to sorbitol. The catalysts were characterized by X-ray diffractometer (XRD), N2 adsorption-desorption, scanning electron microscope (SEM), transmission electron microscope (TEM), 27Al-magnetic angle spinning-nuclear magnetic resonance spectrometer (27Al MAS-NMR), temperature programmed desorption of ammonia (NH3-TPD), temperature-programmed reduction (H2-TPR), and inductively coupled plasma optical emission spectrophotometer (ICP-OES). The characterization indicated that nickel phosphide nanoparticles were successfully incorporated into both supports without destroying their hexagonal framework structures, that the catalysts contained some or all of the following Ni-containing phases: Ni0, Ni3P, and Ni12P5, and that the types and relative amounts of Ni-containing phases present in each catalyst were largely determined by the initial molar ratio of Ni/P as well as the type of support used. For cellobiose conversion at 150 &deg, C for 3 h under 4 MPa of H2, all catalysts showed similarly high conversion of cellobiose (89.5&ndash, 95.0%). Nevertheless, sorbitol yield was highly correlated to the relative amount of phases with higher content of phosphorus present in the catalysts, giving the following order of catalytic performance of the Ni-containing phases: Ni12P5 &gt, Ni3P &gt, Ni. Increasing the reaction temperature from 150 &deg, C to 180 &deg, C also led to an improvement in sorbitol yield (from 43.5% to 87.8%).

A new and facile approach to stabilise copper(I) complexes in aqueous solution by the addition of zinc(II) ions in combination with acetate ions (OAc−) was demonstrated. This stability enhancement toward the aerobic oxidation of copper(I) species was investigated by various techniques including UV-vis spectroscopy, 1H-NMR, FT-IR, and ESI-MS. Our experimental results together with DFT calculations led to a proposed structure of [(adpa)Cu-OAc-Zn(OAc)(H2O)2]+/2+. It was also postulated that zinc(II) with its Lewis acidity may attract electrons from the Cu centre through the bridging ligands (OAc−), resulting in the lower reactivity of Cu(I) with O2. In addition, this strategy was shown to be applicable to ascorbic acid detection by monitoring a change in the redox states of copper complexes using fluorescence spectroscopy. Moreover, it was demonstrated that the method was sensitive and accurate for the quantitative analysis of ascorbic acid in vitamin C tablets.

In this work, a facile and controllable method to fabricate high-density silver nanofilaments (Ag NFs) from β -silver sulfide ( β -Ag 2 S) for surface-enhanced Raman scattering (SERS) substrates was reported. The β -Ag2S crystal structure affects the growth of Ag NF significantly. The optimal silver nanofilaments with a density of 5.93 × 109 NF/cm 2 and length of 0 . 46 ± 0 . 04 μ m were formed when the β -Ag2S substrate was irradiated by a 20kV electron beam for 10 min. The Ag NF substrate possesses the SERS enhancement factor (EF) of 1.57 × 106 at 1 mM Methylene blue (MB), nevertheless, the detection limit for Methylene blue can reach up to 1.18 × 10−11 M. It was found that by controlling the accelerating voltage and irradiation time, the surface morphology of the Ag NFs as SERS substrates can be tailored to obtain the optimal SERS EF. The simple yet controllable method presented here opens a new path to fabricate Ag nanofilament SERS substrates for ultra-low chemical concentration analysis.

In the present work, water-soluble cysteamine capped-CdS quantum dots (Cys-CdS QDs) modulated with Ag+ were employed as fluorescence sensors for the determination of Hg2+ ion. The synthesized Cys-CdS QDs exhibit relatively weak fluorescence emission, however, the emission was enhanced exclusively in the presence of Ag+ compared to other metal ions. Moreover, the fluorescence intensity of the Ag+ modulated Cys-CdS QDs (Ag+@Cys-CdS QDs) was significantly quenched in the presence of trace amounts of Hg2+ due to high-affinity metallophilic interactions between Hg2+ and Ag+. Based on this specific interaction, good selectivity towards the detection of Hg2+ over other metal ions was achieved. To gain the best sensing performance, parameters affecting the Hg2+ detection sensitivity were studied and optimized in detail. Under the optimized conditions, the fluorescence intensity of Ag+@Cys-CdS QDs decreased linearly with Hg2+ concentration in the range of 0.1–3.5 μM, with a limit of detection of around 0.09 μM. The applicability of this sensor was demonstrated by the determination of Hg2+ in drinking water samples, corresponding well with results of cold-vapor atomic absorption spectrometry.

Rhodamine chemosensors based on excimer-fluorescent resonance energy transfer (Em-FRET), combined with energy donor from excimer emission (naphthalene excimer) and energy acceptor from dye absorption (rhodamine dye) (L1) and fluorescent chemosensor (L2) were designed and synthesized. Complexation studies using UV–vis absorption and fluorescence spectroscopy showed that L1 and L2 were chemosensors selective for AcO−. Allowing the chemosensors L1 and L2 to complex with Cu2+ resulted in a hyperchromic shift of UV–vis absorption and a quenching of fluorescence in the presence of anions such as AcO−, F−, BzO− and H2PO4−. The incremental stability constants of anion complexation upon addition of Cu2+ were illustrated due to the allosteric effect and inductive effect from Cu2+ complexation. The adduct L1·Cu2+ could still be used to detect AcO−, whilst the adduct L2·Cu2+ turned out to bind BzO−.

A series of copper complexes bearing polypyridyl tridentate ligands have been prepared to fine tune their reactivity toward the oxygen reduction reaction (ORR). During the process of preparation of our copper complexes, we successfully obtained two new crystal structures which are [Cu2(μ-Cl)2(adpa)2](ClO4)2 (2b) and [Cu2(addpa)(CH3CN)2(ClO4)2](ClO4)2 (3a) and a new structure [Cu2(addpa)(CH3CN)2(H2O)2](ClO4)4 (3b) captured after the catalytic ORR. Electrochemical studies and stoichiometric chemical reduction of copper(ii) complexes by ascorbic acid indicated that the presence of an anthracene unit helps to facilitate the reduction of Cu(ii) as well as the stabilisation of Cu(i) species. Regarding oxygen activation, the dinuclear Cu(i) complex 3a showed significantly higher ORR activity than its analogous mononuclear complex 2a. Complex 3a was also found to be relatively robust and competent in catalytic O2 reduction. The observed H2O2 product after this catalysis, together with the data obtained from DFT calculations supported that 3a exhibited a 2H+, 2e- catalytic activity towards the ORR as opposed to the expected 4H+, 4e- process usually found in copper complexes with tridentate ligands. The proton (H+) source for this process was expected from ascorbic acid which also serves as a reducing agent in this reaction. This work highlighted an approach for tuning the ORR activity of the copper complexes by the introduction of a conjugated-π moiety to the supporting ligand.

A selective cobalt ion sensor derived from l -Cysteine modified on fluorescence nanomaterials including silver nanoclusters ( l -Cyst-AgNCs) and cadmuim sulfide quantum dots ( l -Cyst-CdS QDs) were proposed. In the presence of Co 2+ , the fluorescence intensity of both nanomaterials were efficiently quenched. However, in the case of l -Cyst-CdS QDs, other metal ions can also quench the fluorescence intensity of l -Cyst-CdS QDs. On the other hand, the fluorescence intensity of l -Cyst-AgNCs can be quenched exclusively in the presence of Co 2+ suggested the role of the fluorescence core material towards the detection selectivity. Circular dichroism spectroscopy revealed that only Co 2+ could interact with l -Cyst-AgNCs by coordinating with l -Cysteine modified on AgNCs surface. Thus, l -Cyst-AgNCs were used as a sensor to detect Co 2+ by measuring the fluorescence quenching. In addition, the degree of fluorescence quenching was linearly increased with the increasing of Co 2+ concentration. The proposed l -Cyst-AgNCs sensor can be used to detect Co 2+ in a wide working linear concentration range of 14–150 μM. Furthermore, the proposed sensor can be efficiently used for detection of Co 2+ in real water samples with satisfactory results.

A new circular dichroism sensor for detecting Ni 2+ and Co 2+ was proposed for the first time using chiral chelating quantum dots. The detection principle was based on changing of circular dichroism signals of the chiral quantum dots when forming a chiral complex with Ni 2+ or Co 2+ . l -Cysteine capped cadmium sulfide quantum dots ( l -Cyst-CdS QDs) were proposed as a chiral probe. The CD spectrum of l -Cyst-CdS QDs was significantly changed in the presence of Ni 2+ and Co 2+ . On the other hand, other studied cations did not alter the original CD spectrum. Moreover, when increasing the concentration of Ni 2+ or Co 2+ , the intensity of the CD spectrum linearly increased as a function of concentration and could be useful for the quantitative analysis. The proposed CD sensor showed linear working concentration ranges of 10–60 μM and 4–80 μM with low detection limits of 7.33 μМ and 1.13 μM for the detection of Ni 2+ and Co 2+ , respectively. Parameters possibly affected the detection sensitivity such as solution pH and incubation time were studied and optimized. The proposed sensor was applied to detect Ni 2+ and Co 2+ in real water samples, and the results agreed well with the analysis using the standard ICP-OES.

This review focuses on colorimetric and visual assays for determination of mercury(II) (Hg2+) ions based on gold nanoparticles (AuNPs), fluorescent gold nanoclusters (AuNCs), gold nanorods (AuNRs), gold nanoflowers (AuNFs) and gold nanostars (AuNSs). The analytical colorimetric approaches based on AuNPs can be categorized according to the aggregation or disaggregation mechanisms of functionalized or unmodified AuNPs. The colorimetric concept involves change of the color of a solution of AuNPs from deep red to purple or blue. Disaggregation assays involve reversing the color from blue to red. Detection using AuNCs is based on Hg2+-induced fluorescence quenching of functionalized AuNCs and label-free AuNCs. The benefits of these systems are simplicity, rapidity, cost-effective production, ease of usage, easy visualization of the color change, and detection using spectrophotometry, fluorometry and the naked eye. We summarize applications to real samples, limits of detection, and the development of test strips.

A highly selective colorimetric sensor for detecting Fe 2+ was proposed using the water-soluble silver nanoclusters (AgNCs) for the first time. AgNCs were synthesized via a one-pot reaction by using polymethacrylic acid (PMAA) as both a template and a reducing agent. The as-prepared AgNCs showed highly selective and sensitive detection toward Fe 2+ over Fe 3+ and other cations. Upon addition of Fe 2+ , the absorbance at 447 nm increased as a linear function of the increasing concentration of Fe 2+ . Parameters possibly affected the sensor sensitivity were investigated and optimized. The proposed sensor could efficiently be used for Fe 2+ sensing at very low concentration with the limit of detection of 76 nM and the linear working concentration range of 5–100 μM. The feasibility of the proposed sensor for determining Fe 2+ in the iron supplement tablet samples was also studied and compared with 1,10-phenanthroline method as well as inductively couple plasma–optical emission spectroscopy (ICP–OES). The Fe 2+ content obtained from three methods were not significantly different signifying the high accuracy of the proposed sensor.

A selective colorimetric assay for detecting formaldehyde (FA) was proposed based on silver nanoclusters (AgNCs) templated by polymethacrylic acid (PMAA). The chemodosimeter was easily fabricated by the formation of Tollens’ reagent in the presence of AgNCs (AgNCs@Tollens). The detection principle was based on the change in the color caused by the change in the particle size from nanoclusters (no LSPR) to nanoparticles (with LSPR) upon the reduction of Tollens’ reagent by FA. In the presence of FA, the intensity of a new absorbance band with a maximum at a wavelength of 430 nm corresponding to the LSPR of the AgNPs linearly increased as a function of the FA concentration, exhibiting a color change that could be observed by the naked eye. This method provided a working range of 30–50 µM with lower detection limit (LOD) of 27.99 µM. The proposed method exhibited excellent selectivity towards FA over other aldehyde-containing compounds.

At present, strategies to disperse hydrophobic molecules in water without altering their chemical structures include conventional surfactant-based micellar and vesicular systems, encapsulation into water dispersible polymeric nanoparticles, and loading onto the surface of various metal nanoparticles. Here, we report a simple and low cost platform to incorporate hydrophobic molecules into a stable water dispersible nanostructure that can significantly increase the stability of the encapsulated materials. The platform is based on the incorporation of hydrophobic molecules into the self-assembled complex of gadolinium ion (Gd

Herein we report the synthesis, and optical and electrochemical properties of a rhodamine-appended polyterthiophene network thin film which demonstrates ion selective potentiometric, chromic and fluorescent responses. The rhodamine-appended terthiophene monomer (RhoT) was electropolymerized and deposited on an ITO electrode. Ion selective potentiometric studies have shown that the potentials of the conducting polymer films decreased upon adding Hg2+ because interactions of Hg2+ with the rhodamine-appended conducting polymer film may increase charge carrier transport properties on a conjugated polymer through rhodamine-bound Hg2+, reduce the doping states by interfering with ions through ion–ion interactions, and perturb the π-extended conjugated polymer through π–π interactions. Moreover, the lower detection limit of the ultrathin film sensor toward Hg2+ (0.10 μM) was less than that obtained from RhoT (1.34 μM), and the response time was less than 30 seconds. Reusability was evaluated by repeating dipping and rinsing cycles in aqueous Hg2+ and EDTA solutions. This approach may provide an easily measurable and inherently sensitive method for Hg2+ ion detection in environmental and biological applications.

An inkpen-based reversible biodegradable sensor (IRBS) has been developed for the detection of mercuric ions (Hg2+). The colour response can be tuned to allow detection with the naked eye based on Hg2+-induced opening of the rhodamine spirocycle, leading to an increase in fluorescence and other colour changes. After dipping in water, the colour change in the IRBS paper can be quantified by visual comparison with standard images of IRBS papers, allowing the concentration of Hg2+ to be determined over the concentration range 4.0 × 10−8 M to 1.0 × 10−6 M. Reusability has been established by repeatedly dipping and rinsing the paper in aqueous Hg2+ and EDTA solutions. This approach provides a sensitive and accurate method for the estimation of Hg2+ in environmental and biological applications.

The silica gel modified with benzothiazole calix[4]arene (APS-L1) via Schiff's base reaction was applied as a sorbent in an online system for preconcentration and determination of silver ion by flame atomic absorption spectrometry (FAAS). APS-L1 was used as an effective sorbent for solid phase extraction (SPE) of silver(I) ion in both batch and column methods. The optimum experimental parameters such as pH, eluent type, sample flow rate, eluent volume and eluent flow rate including the effect of interfering ions were investigated. Silver(I) ion was determined at pH 6-7. The capacity of APS-L1 sorbent was found to be 12.2 mg/g of sorbent. The high affinity was obtained without interference from the interfering ions. The optimum conditions of the online flow injection preconcentration coupled with the FAAS (FI-FAAS system) were evaluated. The sample flow rate was 3.0 mL min(-1) using sample volume of 5-10 mL. Elution was performed with 250 μL of 0.1 mol L(-1) thiosulfate at the flow rate of 1.5 mL min(-1). The analytical characteristics and performance of the FI-FAAS system were studied under optimum conditions using a solution spiked with standard silver(I) ion at 20 and 50 μg L(-1). The detection limit of 0.44 μg L(-1) was obtained. The accuracy of the proposed method was evaluated and percentages of recovery at 20 and 50 μg L(-1) were 100.2 and 99.5%, respectively. The percent relative standard deviations (%RSD) at 20 and 50 μg L(-1) were 6.1 and 3.3%, respectively. The developed method was successfully applied to determine trace silver(I) ion in drinking and tap water samples.

A new fluorescence sensor for detection of cyanide ions (CN(-)) in aqueous media based on the recovered fluorescence of cysteamine capped CdS quantum dots [Cys-CdS QDs]-Cu(2+) system was proposed. The fluorescence intensity of Cys-CdS QDs was quenched by Cu(2+) due to the binding of Cu(2+) to cysteamine on the surface of the QDs. The degree of fluorescence quenching was proportional to the concentration of Cu(2+). However, in the presence of CN(-), the fluorescence intensity of Cys-CdS QDs was found to be efficiently recovered. Experimental results showed that the pH of the buffer solution and the concentration of Cu(2+) affected the fluorescence intensity upon adding CN(-). Under the optimal condition, the recovered fluorescence intensity was linearly proportional to the increasing CN(-) concentration in the range 2.5-20 μM. The limit of detection and the limit of quantification were found to be 1.13 μM and 3.23 μM, respectively. In addition, among the tested ions, only CN(-) could turn on the fluorescence intensity suggesting that the [Cys-CdS QDs]-Cu(2+) system was a highly selective sensor for CN(-). Moreover, this proposed sensor was demonstrated to detect CN(-) in drinking water with satisfactory results.

We demonstrate an advance in the fabrication of circular dichroism (CD) sensors for detection of Cd

A podand containing urea units ( L ) was found to form interlocked structures with 2,5-dihexylamide imidazolium salts ( 3 · X ), 2,5-dihexyl imidazolium salts ( 4 · X ), and 2,5-dihexyl benzoimidazolium salts ( 5 · X ), where X=Cl − , Br − , and PF 6 − using anions as templates. The binding ability of L and guest molecules was evaluated by 1 H NMR titrations in CDCl 3 . It was found that L could form complexes with guest molecules in the following order, 3 · X > 5 · X > 4 · X . Stabilities of the complexes also depended on shape of the templated anions: Cl − >Br − ≫PF 6 − . Hydrogen bonding and π–π stacking interactions played an important role in the self-assembling of these interlocked molecules.