Synthesis of nano-sized cyanide ion-imprinted polymer via non-covalent approach and its use for the fabrication of a CN−-selective carbon nanotube impregnated carbon paste electrode

Efficient cyanide sensing using plasmonic Ag/Fe3O4 nanoparticles

In the line of our previous studies, we have reported a developed sensitive and selective probe for cyanide detection based on Ag/Fe3O4 nanoparticles (NPs) with an extremely low limit of detection at the level of ng per milliliter. Herein, we report the improvement of the easy-to-make magnetic silver nanoparticle-based sensor system for cyanide determination in an extended calibration range with higher selectivity and precision. As far as our knowledge is concerned, the detectable linear range from 1.0 nM to 160 μM (0.026 ng mL-1 to 4.16 μg mL-1) of the improved simple highly precise technique represents the widest assay that has been reported so far. The method is based on strong enhancement of scattered light of the plasmonic nanoparticles and simultaneously cyanide fluorescence quenching. Although the fluorescence of cyanide is highly selective and precise, its intensity is poor. On the other hand, the strongly enhanced Rayleigh signal has a low repeatability. We proposed a method to remove the interference and obtained an effective factor that is directly proportional to cyanide concentration utilizing both above signals simultaneously. In this work, Ag/Fe3O4 NPs have been synthesized easily using a green preparation method and the NPs were consequently characterized using powder XRD, UV-Vis absorption spectroscopy, transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX). A combination of absorption, Rayleigh and fluorescence characteristics were used for detection of cyanide in real samples and an overview of recently reported sensors for cyanide was also provided.

A comparative study on selectivity and sensitivity of new chromium and copper electrodes

4-Methylcoumarin-7-yloxy-N-phenyl acetamide and 4-methylcoumarin-7-yloxy-N-4-nitrophenyl acetamide were synthesized and used as new ionophores in the carbon paste matrix to produce two novel potentiometric modified electrodes. The selectivity of the electrode changed from copper (II) to chromium (III) with the addition of a nitro group to the phenyl ring of the ionophore. The ionophores’ tendency to ions was confirmed by UV–visible spectrophotometry. Both electrodes were modified by multi-walled carbon nanotubes (MWCNTs) as an excellent modifier of carbon paste electrode (CPE). The best sensor response in the case of copper (II) selective CPE was obtained by 5% ionophore, 65% graphite powder, 5% MWCNT, and 25% paraffin oil. In addition, in the case of chromium (III) selective CPE, these conditions are 20% ionophore, 50% graphite powder, 5% MWCNT, and 25% paraffin oil. The copper (II) selective CPE showed a Nernstian slope of 32.15 mV/decade within the concentration range of 1.0 × 10^–10–1.0 × 10^–1 mol L⁻¹, while chromium (III) selective CPE showed a Nernstian slope of 19.28 mV/decade over the concentration range of 1.0 × 10^–10–7.0 × 10^–3 mol L⁻¹. The electrodes have short response time of less than 5 s and were used successfully to determine copper (II) in wastewater and to speciation of chromium (III) and chromium (VI).

A novel chloride selective potentiometric sensor based on graphitic carbon nitride/silver chloride (g-C3N4/AgCl) composite as the sensing element

In this research, AgCl anchored graphitic carbon nitride (g-C₃N₄) was introduced as a novel potentiometric sensing element. A g-C₃N₄/AgCl-modified carbon paste electrode (CPE) was fabricated and used as an outstandingly selective potentiometric sensor to determine Cl^- in water samples. The g-C₃N₄/AgCl nanocomposite was characterized with SEM, XRD and FT-IR techniques. It was demonstrated that, the incorporation of 5% of g-C₃N₄/AgCl, as a chloride ionophore in a CPE, results in a stable potential response of the electrode to chloride ion. The Nernstian slope of the electrode response was 55.4 (±0.3) mVdecade^-1, over a wide linear concentration range of 1 × 10^-6-1 × 10^-1 mol L^-1 and the detection limit of the electrode was estimated to be 4.0 × 10^-7 mol L^-1. The g-C₃N₄/AgCl-modified CPE electrode provided fast response time and long-term stability (more than 2 months) while the potential interfering ions such as I^-, Br^-, and CN^- showed no significant effect on the potential response. Since these interfering ions affected the response of the CPE electrode, modified with AgCl, highlighting the interesting effect of g-C₃N₄ on the sensor performance. This innovative electrode was shown to be a sensitive and accurate sensor for chloride ion content estimation in water samples.

Development of an anion imprinted polymer for high and selective removal of arsenite from wastewater

A novel cyclic functional monomer (CFM) was used to develop an As(III)-ion imprinted polymer (As-IIP). CFM possesses a positively charged imidazolium moiety and its specific cyclic size matches that of As(III). Batch adsorption experiments showed that the As-IIP has a maximum As(III) adsorption capacity of 55 mg/g, while that of the control polymer (CP) is only 25 mg As(III)/g. Adsorption isotherms for As(III) agree with the Langmuir model, suggesting monolayer adsorption. Kinetic studies showed that the adsorption process followed pseudo-second-order kinetics. The relative selectivity coefficients of As-IIP compared to CP for Cl^-/H₂AsO₃^-, SO₄^2-/H₂AsO₃^-, HPO₄^2-/H₂AsO₃^-, NO₃^-/H₂AsO₃^-, and Mo₇O₂₄^6-/H₂AsO₃^- are 1.03, 1.95, 2.55, 1.52 and 2.51, respectively. The removal efficiency of As-IIP for As(III) in actual industrial wastewater was nearly 100%, which confirms that As-IIP has a high adsorption capacity as well as selectivity for the removal of As(III) from wastewater.

Dendrimer-like amino-functionalized hierarchical porous silica nanoparticle: A host material for 2,4-dichlorophenoxyacetic acid imprinting and sensing

In this work, a novel molecularly imprinted electrochemical sensor based on the amino-functionalized silica nanoparticles was built for the sensitive and selective detection of 2,4-dichlorophenoxyacetic acid (2,4-D). The hierarchical porous dendrimer-like silica nanoparticles (HPSNs-NH₂) were synthesized by an ethyl ether emulsion method. The selective molecularly imprinted polymers (MIP) was prepared on the HPSNs-NH₂ modified electrode via electropolymerization by using 2,4-D as the template and o-phenylenediamine (OPD) as the monomer. The porous structure of HPSNs-NH₂ reduced the diffusion limitations of the analytes, enhanced the accessibility and increased the surface area of the sensor, while the MIP layer offered the ability to recognize and quantify target 2,4-D by using ferro/ferricyanide as probes. Several significant experimental parameters on the analytical performance of the MIP/HPSNs-NH₂ sensor were explored and optimized. Under the optimized condition, the sensor displayed an appreciable selectivity over structurally related compounds and good sensitivity toward 2,4-D. The linear range of 2,4-D detection was from 1.00 × 10^-10 to 2.50 × 10^-8M and the detection limit was down to 1.17 × 10^-11M according to the 3S_a/b criteria. This method has been applied to detect 2,4-D in bean sprout samples with satisfying results.

Synthesis of hydrophilic and conductive molecularly imprinted polyaniline particles for the sensitive and selective protein detection

In this work, a novel kind of water-dispersible molecular imprinted conductive polyaniline particles was prepared through a facile and efficient macromolecular co-assembly of polyaniline with amphiphilic copolymer, and applied as the molecular recognition element to construct protein electrochemical sensor. In our strategy, an amphiphilic copolymer P(AMPS-co-St) was first synthesized using 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) and styrene (St) as monomer, which could co-assemble with PANI in aqueous solution to generate PANI particles driven by the electrostatic interaction. During this process, ovalbumin (OVA) as template protein was added and trapped into the PANI NPs particles owing to their interactions, resulting in the formation of molecular imprinted polyaniline (MIP-PANI) particles. When utilizing the MIP-PANI particles as recognition element, the resultant imprinted PANI sensor not only exhibited good selectivity toward template protein (the imprinting factor α is 5.31), but also a wide linear range over OVA concentration from 10^-11 to 10^-6mgmL^-1 with a significantly lower detection limit of 10^-12mgmL^-1, which outperformed most of reported OVA detecting methods. In addition, an ultrafast response time of less than 3min has also been demonstrated. The superior performance is ascribed to the water compatibility, large specific surface area of PANI particles and the electrical conductivity of PANI which provides a direct path for the conduction of electrons from the imprinting sites to the electrode surface. The outstanding sensing performance combined with its facile, quick, green preparation procedure as well as low production cost makes the MIP-PANI particles attractive in specific protein recognition and sensing.

Synthesis of Water-Dispersible Molecularly Imprinted Electroactive Nanoparticles for the Sensitive and Selective Paracetamol Detection

A novel kind of water-dispersible molecularly imprinted electroactive nanoparticles was prepared combining macromolecular self-assembly with molecularly imprinting technique employing paracetamol (PCM) as template molecule. An amphiphilic electroactive copolymer (P(NVC-EHA-AA), PNEA) containing carbazole group was first synthesized through a one-pot free radical copolymerization. The coassembly of the electroactive copolymers with the template molecules (PCM) in aqueous solution generated nanoparticles embedded with PCM, leading to the formation of molecularly imprinted electroactive nanoparticles (MIENPs). A robust MIP film was formed on the surface of electrode by electrodeposition of MIENPs and subsequent electropolymerization of the carbazole units in MIENPs. After the extraction of PCM molecules, a MIP sensor was successfully constructed. It should be noted that electropolymerization of the electroactive units in MIENPs creates cross-conjugated polymer network, which not only locks the recognition sites but also significantly accelerates the electron transfer and thus enhances the response signal of the MIP sensor. These advantages endowed the MIP sensor with good selectivity and high sensitivity for PCM detection. The MIP sensor could recognize PCM from its possible interfering substances with good selectivity. Under the optimal conditions, two linear ranges from 1 μM to 0.1 mM and 0.1 to 10 mM with a detection limit of 0.3 μM were obtained for PCM detection. The MIP sensor also showed good stability and repeatability, which has been successfully used to analyze PCM in tablets and human urine samples with satisfactory results.

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

A novel synthesized nanostructured ion-imprinted polymer (IIP) was investigated for the determination of trace amount of thallium(I). For this purpose, the thallium(I) IIP particles were synthesized using methacrylic acid (MAA) as the functional monomer, ethylene glycol dimethacrylate (EGDMA) as the cross-linker, methyl-2-[2-(2-2-[2-(methoxycarbonyl) phenoxy] ethoxyethoxy) ethoxy] benzoate as the chelating agent and 2,2-azobisisobutyronitrile (AIBN) as the initiator. The prepared IIP particles were characterized by field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FT-IR) and thermo gravimetric analysis (TGA). Various experimental factors such as pH, the amount of IIP particles, sorption and desorption time, sample volume, elution condition, and potentially interfering ions systematically examined. Under the optimum conditions, a sensitive response to Tl(I) within a wide concentration range (0.05-18 μg L(-1)) was achieved. The limit of detection (LOD, 3Sb/m) was 6.3 ng L(-1). The maximum adsorption capacity of the novel imprinted adsorbent for Tl(I) was calculated to be 18.3 mg g(-1). The relative standard deviation (RSD) for eight replicate detections of 0.1 μg L(-1) of thallium(I) was found to be 4.0%. An enrichment factor (EF) of 100 was obtained by this method. The proposed technique was successfully applied to monitoring thallium in different water samples and the certified reference material.

A Ca2+ selective membrane electrode based on calcium-imprinted polymeric nanoparticles

In this work, a Ca²⁺ selective PVC-membrane electrode, utilizing nano-sized Ca²⁺ imprinted polymers as the ionophore, was introduced.