Synthesis and application of a novel nanostructured ion-imprinted polymer for the preconcentration and determination of thallium(I) ions in water samples

Development of highly sensitive dual-enhanced fluorescence quenching immunochromatographic test strips based on Pt nanoprobes

The fluorescence-quenching method is crucial in vitro analysis, particularly for immunochromatographic test strips (ICTs) using noble metal nanoparticles as probes. However, ICTs still fall short in meeting the requirements for the detection of traces biomarkers due to the noble metal nanoparticles can only quench fluorescence of the dyes within a confined distance. Interestingly, noble metal nanoparticles, such as Pt NPs cannot only perform fluorescence-quenching ability based on the Förster resonance energy transfer (FRET), but also show perfect oxidase-like catalytic performance on many kinds of substrates, such as 3,3',5,5' -tetramethylbenzidine (TMB). We observed that the oxTMB (the oxidation products of TMB) exhibited notable effectiveness in quenching Cy5 fluorescence by the strong inner filter effect (IFE), which obviously improved the fluorescence-quenching efficiency with extremely low background signal. Through the dual-enhanced fluorescence quenching mechanism, the fluorescence quenching constant (Kn) was 661.24-fold that of only Pt NPs on the NC membrane. To validate the feasibility of this technique, we employed two types of biomarkers, namely microRNA (miR-15a-5p) and the signature protein (PSA). The sensitivity of miR-15a-5p was 9.286 × 10-18 mol/L and 17.5-fold more than that based on Pt NPs. As for the PSA, the LOD (0.6265 pg/mL) was 15.5-fold enhancement more sensitive after catalysis. Overall, the dual-enhanced fluorescence quenching rFICTs could act as a practical detection for biomarker in real samples.

Anodic Stripping Voltammetric Procedure of Thallium(I) Determination by Means of a Bismuth-Plated Gold-Based Microelectrode Array

This article presents a new working electrode based on a bismuth-plated, gold-based microelectrode array, which is suitable for determining thallium(I) species using anodic stripping voltammetry (ASV). It allowed a significant increase in the sensitivity as compared to other voltammetric sensors. The main experimental conditions and the instrumental parameters were optimized. A very good proportionality between the Tl(I) peak current and its concentration was evidenced in the range from 5 × 10-10 up to 5 × 10-7 mol L-1 (R = 0.9989) for 120 s of deposition and from 2 × 10-10 up to 2 × 10-7 mol L-1 (R = 0.9988) for 180 s. A limit of detection (LOD) of 8 × 10-11 mol L-1 for a deposition time of 180 s was calculated. The effects of interfering ions on the Tl(I) analytical signal were studied. The proposed method was applied for quantitative Tl(I) detection in water certified reference material TM 25.5 as well as in spiked real water samples, for which satisfactory recovery values between 98.7 and 101.8% were determined.

Determination of thallium in water samples via solid sampling HR-CS GF AAS after preconcentration on chromatographic paper

A method for determining thallium in water samples via solid sampling high-resolution continuum source graphite furnace atomic absorption spectrometry (SS HR-CS GF AAS) after preconcentration using chromatographic filter paper as a solid support was proposed. The effects of pH, stirring time, and sample volume in the analyte preconcentration step were studied. The presence of potential interferences in the sample and the type of masking agent were also examined. In the proposed procedure, the sample was placed in contact with the solid phase in a polypropylene tube, and after stirring for 3 min, thallium determination was performed via HR-CS GF AAS directly on chromatographic filter paper. A preconcentration factor of 55, a precision of 9.4% (n = 10; 10 μg L-1), a limit of detection of 0.018 μg L-1, and a limit of quantification of 0.059 μg L-1 were achieved. Analyte addition and recovery tests were performed, and the results ranged from 91% to 110%. The accuracy of the method was evaluated by analyzing a water reference material. The procedure was used to determine thallium in water samples collected in Barreiras, Bahia, Brazil. The results were compared with those obtained using inductively coupled plasma‒mass spectrometry (ICP‒MS). Thallium concentrations in the analyzed samples ranged from <0.059 to 0.80 μg L-1.

Metal-organic frameworks modified melamine foam in pipette-tip for rapid solid-phase extraction of organophosphorus pesticides in fruits and vegetables

In this work, metal-organic frameworks (MOFs) including Fe-MIL-101 and Ti-MIL-125 were prepared and fixed on the melamine foam (MF) by polyvinylidene fluoride (PVDF) to prepare MF/PVDF/MOFs, which was used as adsorbents in pipette-tip solid-phase extraction (PT-SPE) for rapid extraction of organophosphorus pesticides (OPPs). Then, a gas chromatograph-flame thermionic detector (GC-FTD) was used for simultaneous analysis of Dimethoate (DMT), Iprobenfos (IBF), Parathion-methyl (PAM), and Chlorpyrifos (CPF). The morphology, crystal structure, and functional groups of MF/PVDF/MOFs were characterized, indicating that Ti-MIL-125 and Fe-MIL-101 were successfully synthesized and distributed on MF. The Fe-MIL-101 and Ti-MIL-125 showed good extraction ability for OPPs, which was mainly due to the π-π interaction and the multiple porous structures. Under the optimal conditions, the limit of detection (LODs) of four OPPs was 0.03-0.14 μg L-1 and the RSDs were less than 9.9%. The developed PT-SPE method showed a short extraction time (<3 min). The recoveries in fruits and vegetables (Celery, cabbages, and oranges) ranged from 75.3%-118.8% (RSDs<9.6%). The prepared MF/PVDF/MOFs demonstrated the efficient extraction performance of OPPs, contributing to the rapid pretreatment of OPPs from food and the environment.

Voltammetric sensing of Cd(II) at ZIF-8/GO modified electrode: Optimization and field measurements

In this work, a metal-organic framework/graphene oxide (MOF(ZIF-8)/GO) nanocomposite was utilized for the electroanalysis of trace level of Cd(II) after modification of a cheap graphite rod electrode (GRE). After closed circuit process on the modified electrode, the differential pulse anodic stripping voltammetry (DPASV) technique was used for measuring of Cd(II). In optimal conditions, the sensor showed a linear dependence of current with concentration range 0.1-30 ppb for Cd(II). Moreover, limit of detection 0.03 ppb were obtained. Besides good selectivity, the sensor also indicated good reproducibility (below 5%). Moreover, the sensor showed satisfactory sensing performance in river, dam and wastewater samples with recovery ranging from 97.2% to 102.4%. Additionally, possible interfering cations were examined, but no significant interference was found. For the detection of trace Cd(II) in real matrices, this sensor illustrated other good merits like high stability, rapidity and simplicity.

Fully optimized new sensitive electrochemical device for the selective determination of 6-thioguanine anticancer drug in wastewater and biological samples

In present work, a novel voltammetric sensor for the determination of 6-thioguanine (6-TG) was fabricated. First, a graphite rod electrode (GRE) surface was modified via drop-coating of graphene oxide (GO) to increase the surface area of the electrode. Subsequently, molecularly imprinted polymer (MIP) network was prepared using a facile electro-polymerization procedure, using o-aminophenol (as functional monomer) and 6-TG (as template molecule). Influences of test solution pH, dropped GO concentration and incubation time on the performance of GRE-GO/MIP were studied, and their values determined as 7.0, 1.0 mg/mL and 90 s, respectively. Using GRE-GO/MIP, 6-TG was measured in the range of 0.5-60 μM with a low detection limit (DL) of 80 nM (based on S/N = 3). In addition, the electrochemical device demonstrated good reproducibility (3.8%) and anti-interference ability toward 6-TG monitoring. The as-prepared sensor illustrated satisfactory sensing performance in real samples with recovery ranging from 96.5% to 102.5%. For the determination of trace amounts of anticancer drug (6-TG) in real matrices (biological samples and pharmaceutical wastewater sample), this study is expected to provide an effective strategy with high selectivity, stability, and sensitivity.

Novel Chemoresistive Sensor for Sensitive Detection of Pb2+ Ions Using an Interdigital Gold Electrode Fabricated with a Reduced Graphene Oxide-Based Ion-Imprinted Polymer

This study presents novel chemoresistive reduced graphene oxide-ion-imprinted polymer (IIP-rGO)-based sensors for detection of lead (Pb2+) ions. The ion-imprinted polymer was synthesized by bulk polymerization and modified with a variable amount of rGO incorporated to form an IIP-rGO composite. The amount of rGO in the polymer matrix affected the sensor's relative response, and 1:3 mass ratio produced excellent results, with a consistent trend as the concentration of Pb2+ ions increased in the solution. The decrease in relative resistance (ΔR/R o) followed an exponential decay relationship between the ΔR/R o response and the concentration of Pb2+ ions in aqueous solutions. After solving the exponential decay function, it is observed that the sensor has the upper limit of ΔR/R o >1.7287 μg L-1, and the limit of detection of the sensor is 1.77 μg L-1. A nonimprinted polymer (NIP)-based sensor responded with a low relative resistance of the same magnitude although the concentration was varied. The response ratio of the IIP-based sensor to the NIP-based sensor (ΔR/R o)IIP/(ΔR/R o)NIP as a function of the concentration of Pb2+ ions in the solution shows that the response ratios recorded a maximum of around 22 at 50 μg L-1 and then decreased as the concentration increased, following an exponential decay function with the minimum ratio of 2.09 at 200 μg L-1 but never read 1. The sensor showed excellent selectivity against the bivalent cations Mn2+, Fe2+, Sn2+, and Ti2+. The sensor was capable of exhibiting 90% ΔR/R o response repeatability in a consecutive test.

High Performance Zinc Oxide Nanorod-Doped Ion Imprinted Polypyrrole for the Selective Electrosensing of Mercury II Ions

A biomimetic, ion-imprinted polymer (IIP) was prepared by electropolymerization of pyrrole at the surface of gold electrodes decorated with vertically grown ZnO nanorods. The vertical growth of the nanorods was achieved via an ultrathin aryl monolayer grafted by reduction of diazonium salt precursor. Pyrrole was polymerized in the presence of L-cysteine as chelating agent and Hg2+ (template). Hg2+-imprinted polypyrrole (PPy) was also prepared on a bare gold electrode in order to compare the two methods of sensor design (Au-ZnO-IIP vs. Au-IIP). Non-imprinted PPy was prepared in the same conditions but in the absence of any Hg2+ template. The strategy combining diazonium salt modification and ZnO nanorod decoration of gold electrodes permitted us to increase considerably the specific surface area and thus improve the sensor performance. The limit of detection (LOD) of the designed sensor was ~1 pM, the lowest value ever reported in the literature for gold electrode sensors. The dissociation constants between PPy and Hg2+ were estimated at [Kd1 = (7.89 ± 3.63) mM and Kd2 = (38.10 ± 9.22) pM]. The sensitivity of the designed sensor was found to be 0.692 ± 0.034 μA.pM-1. The Au-ZnO-IIP was found to be highly selective towards Hg2+ compared to cadmium, lead and copper ions. This sensor design strategy could open up new horizons in monitoring toxic heavy metal ions in water and therefore contribute to enhancing environmental quality.

A Critical Review on the Synthesis and Application of Ion-Imprinted Polymers for Selective Preconcentration, Speciation, Removal and Determination of Trace and Essential Metals from Different Matrices

The presence of toxic trace metals and high concentrations of essential elements in the environment presents a serious threat to living organism. Various methods have been used for the detection, preconcentration and remediation of these metals from biological, environmental and food matrices. Owing to the complexicity of samples, methods with high selectivity have been used for detection, preconcentration and remediation of these trace metals. These methods are achieved by the use of ion-imprinted polymers (IIPs) due to their impressive properties such as selectivity, high extraction efficiency, speciation capability and reusability. Because of the increase of toxic trace and essential metals in the environment, IIPs have attracted great use in analytical chemistry. This review, provide a brief background on IIPs and polymerization method that are used for their preparation. Recent applications of IIPs as adsorbents for preconcentration, removal, speciation and electrochemical detection of trace and essential metal is also discussed.

A modified method of separating Tl(I) and Tl(III) in aqueous samples using solid phase extraction

In spite of the development of new measurement techniques in recent years, the rapid and accurate speciation of thallium in environmental aqueous samples remains a challenge. In this context, a novel method of solid phase extraction (SPE), involving the anion exchange resin AG1-X8, is proposed to separate Tl(I) and Tl(III). In the presence of diethylene triamine pentacetate acid (DTPA), Tl(III) and Tl(I) can be separated by selective adsorption of Tl(III)-DTPA onto the resin, Tl(III) is then eluted by a solution of HCl with SO₂. The validity of this method was confirmed by assays of standard solutions of Tl(I) and Tl(III). The proposed method is shown to have an outstanding performance even in solutions with a high ratio of Tl(I)/Tl(III), and can be applied to aqueous samples with a high concentration of other electrolytes, which could interfere with the measurement. Portable equipment and reagents make it possible to use the proposed method routinely in the field.

Synthesis and application of a novel core-shell-shell magnetic ion imprinted polymer as a selective adsorbent of trace amounts of silver ions

Ion-imprinted polymer (IIP) technology has received considerable attention for its greatest potential application. In this work, a novel magnetic nano ion-imprinted polymer (MIIP) for the selective and sensitive pre-concentration of silver (I) ions were used. It was obtained using Fe3O4@SiO2@TiO2 nanoparticles as a magnetic support of adsorbent, Ag(I)-2,4-diamino-6-phenyl-1,3,5-triazine (DPT) complex as the template molecule and methacrylic acid (MAA), 2,2′-azobisisobutyronitrile (AIBN), ethylene glycol dimethacrylate (EGDMA), as the functional monomer, the radical initiator and crosslinker, respectively. The synthesized polymer nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM) and Brunauer-Emmett-Teller (BET). Silver ions were separate from the polymer and measured by flame atomic absorption spectrometry (FAAS). The maximum adsorption capacity of the novel imprinted adsorbent for Ag(I) was calculated to be 62.5 mg g−1. The developed method was applied to the preconcentration of the analyte in the water, radiology film and food samples, and satisfactory results were obtained.