Sensor For Heavy Metal Ions Research Articles

Biogenic fabrication of a gold nanoparticle sensor for detection of Fe3+ ions using a smartphone and machine learning.

In recent years, smartphones have been integrated into rapid colorimetric sensors for heavy metal ions, but challenges persist in accuracy and efficiency. Our study introduces a novel approach to utilize biogenic gold nanoparticle (AuNP) sensors in conjunction with designing a lightbox with a color reference and machine learning for detection of Fe3+ ions in water. AuNPs were synthesized using the aqueous extract of Eleutherine bulbosa leaf as reductants and stabilizing agents. Physicochemical analyses revealed diverse AuNP shapes and sizes with an average size of 19.8 nm, with a crystalline structure confirmed via SAED and XRD techniques. AuNPs exhibited high sensitivity and selectivity in detection of Fe3+ ions through UV-vis spectroscopy and smartphones, relying on nanoparticle aggregation. To enhance image quality, we developed a lightbox and implemented a reference color value for standardization, significantly improving performance of machine learning algorithms. Our method achieved approximately 6.7% higher evaluation metrics (R 2 = 0.8780) compared to non-normalized approaches (R 2 = 0.8207). This work presented a promising tool for quantitative Fe3+ ion analysis in water.

Explanation based on thermodynamic parameters regarding effect of sensing film thickness and amount of graphene oxide on sensor performance in aniline, N-phenylglycine and graphene oxide based electrochemical heavy metal ion sensor

Background: To construct a heavy metal ion sensor, selectivity and sensitivity are the key important parameters to be taken care of. In our earlier work, film thickness and amount of graphene oxide (GO) content in a novel composite ANGO, synthesized from aniline, N-phenylglycine and GO was varied and sensing parameters including sensitivity, limit of detection (LOD), thermodynamic parameter which includes -∆Gad and charge transport parameter including barrier width (BW), d, of charge transfer based on Simmon’s model were evaluated and compared and an LOD of 800 ppt for Cd2+ was achieved using square wave voltammetry (SWV) withstanding interference from several ions. Methods: In this work, thermodynamic factors such as -∆Gad, ∆H, reorganization energy, partition coefficient and solvated ionic radius were used to explain the sensor performance with respect to film thickness and amount of GO. All the parameters were analyzed for different film thicknesses and amount of GO and a correlation was achieved. Finally, effect of electrochemical surface area of different polyaniline-based material on thermodynamic properties of detection process of Cd2+ was studied. Results: The variation of the thermodynamic properties for Cd2+ sensing with respect to film thickness and amount of GO were examined. Similarly, variation of thermodynamic properties for polyaniline based different sensing materials were examined. Correlation coefficients were developed from the thermodynamic parameters and the d values to explain the underlying mechanism behind improved sensor performance. Conclusions: This study can provide information on the thermodynamic properties which can be predicted from BW technique. The correlation coefficients would help in designing polyaniline based novel sensing film material with the need of lesser number of experiments.

Synthesis of Modified Polyvinyl Pyrrolidone (PVP) Silver Nanoparticles Using Soursop (Annona muricata Linn) Leaf Extract and Its Application as a Heavy Metal Colorimetric Sensor

This study aims to analyze the characteristics and performance of silver nanoparticles (AgNP) synthesized using soursop leaf extract bioreductor modified with the addition of polyvinyl pyrrolidone (PVP) stabilizer as a colorimetric sensor for heavy metal ions. The synthesis of silver nanoparticles was carried out by reducing AgNO3 using soursop leaf extract (Annona muricata Linn) bioreductor modified with the addition of PVP as stabilizer. The results showed that the optimum synthesis volume ratio of AgNP synthesis was 0.7 mL of soursop leaf extract: 10 mL AgNO3 with the addition of 3% PVP stabilizer. The formation of AgNP was characterized by a change in the color of the solution from yellow to brownish with a surface plasmon resonance peak at a maximum wavelength of 438 nm. Fourier-transform infrared spectroscopy studies showed hydroxyl groups (-OH) and carbonyl groups (C=O) play a role in the reduction process of silver ions. Particle size analysis results demonstrated an average particle size of 71.5 nm with a polydispersity index value of 0.364. The results of the colorimetric analysis showed that the synthesized AgNPs proved to be highly selective towards Cu metal ions.

Tungsten Oxide Coated Liquid Metal Electrodes via Galvanic Replacement as Heavy Metal Ion Sensors.

Gallium liquid metals (LMs) like Galinstan and eutectic Gallium-Indium (EGaIn) have seen increasing applications in heavy metal ion (HMI) sensing, because of their ability to amalgamate with HMIs like lead, their high hydrogen potential, and their stable electrochemical window. Furthermore, coating LM droplets with nanopowders of tungsten oxide (WO) has shown enhancement in HMI sensing owing to intense electrical fields at the nanopowder-liquid-metal interface. However, most LM HMI sensors are droplet based, which show limitations in scalability and the homogeneity of the surface. A scalable approach that can be extended to LM electrodes is therefore highly desirable. In this work, we present, for the first time, WO-Galinstan HMI sensors fabricated via photolithography of a negative cavity, Galinstan brushing inside the cavity, lift-off, and galvanic replacement (GR) in a tungsten salt solution. Successful GR of Galinstan was verified using optical microscopy, SEM, EDX, XPS, and surface roughness measurements of the Galinstan electrodes. The fabricated WO-Galinstan electrodes demonstrated enhanced sensitivity in comparison with electrodes structured from pure Galinstan and detected lead at concentrations down to 0.1 mmol·L-1. This work paves the way for a new class of HMI sensors using GR of WO-Galinstan electrodes, with applications in microfluidics and MEMS for a toxic-free environment.

Versatile MXenes as electrochemical sensors for heavy metal ions and phenolic moiety-containing industrial chemicals: recent development and prospects

MXenes and their hybrid materials, with good physicochemical traits, have exhibited excellent performance across numerous applications.

Detection of Fe(III) ion based on bifunctionalized silver nanoparticles: Sensitivity, selectivity and environmental safety

Functionalized silver nanoparticles (AgNPs) are widely used as optical sensors for heavy metal ions in water, due to their versatile, easy and cheap preparations and due to their peculiar physico-chemical properties. Surface functionalization plays a key role in AgNPs chemical-physical behavior as capping agents can affect sensitivity, selectivity but alsoenvironmental safety. In this framework, AgNPs are synthetised and properly functionalized using two capping agents to induce hydrophilic behavior and selectivity, respectively citrate (cit) and glutathione (GSH). The opportune choice of these capping agents induces size control and stability for AgNPs-cit-GSH in water (Ø = 4 ± 0.2 nm; ζ-potential = - 60 ± 1 mV) and make available selectively detection of Fe (III) in the range 0.5–10.0 ppm. Environmental safety was also evaluated using standardized ecotoxicity assays (ecosafety) with freshwater and marine microalgae which show a low-to-negligible effects, with exception only at the highest tested concentration (10 mg/L) but only for the freshwater one.

Molybdenum disulfide (MoS[formula omitted]) and reduced graphene oxide (rGO) nanocomposite based electrochemical sensor for detecting mercury(II) ions

In this study, a two-dimensional (2D) layered nanocomposite of molybdenum disulfide and reduced graphene oxide (rGO) was synthesized through a facile single-step hydrothermal method. Internal structure and morphological studies have shown that the vertical layered structure of MoS2 has grown over the horizontally aligned layer of reduced graphene oxide. The XRD analysis proved that the structure is multi-layered with 68.8 % crystallinity. Despite the highly crystalline nanocomposite structure, very few defects are also present in the network, as shown through Raman spectroscopy. Further, the presence of CS, RSR, CO, CO, MoO and MoS bonds, identified through XPS, indicates the successful synthesis of the MoS2-rGO nanocomposite. The nanocomposite was further evaluated for its electrochemical properties and applications regarding the sensing of mercury ions. Cyclic voltammetry shows that the oxidation peak current response increased by ∼103 % with the MoS2-rGO modified electrode compared to a bare electrode. The sensor has shown an excellent detection limit (LOD) of 1.6 μM, while the sensitivity and limit of quantification obtained from the sensor are 76.302 μM μA−1 cm−2 and 5.4 μM, respectively. The enhanced sensing performance of the MoS2-rGO modified sensor is attributed to the synergistic effect of MoS2 and rGO. The as-synthesized sensor also exhibits excellent stability, as only a 13% drop in current was observed after 60 days. This work proves that MoS2-rGO possesses enormous potential for developing next-generation heavy metal ion sensors.

Synthesis of 4-(1-(2-(2,4-dinitrophenyl)hydrazineylidene)-5-phenylpenta-2,4-dien-1-yl)-1-(4-methoxyphenyl)-5-methyl-1H-1,2,3-triazole as optical sensor for the toxic heavy metal ions in an aqueous medium

Heavy metal ions represented as highly toxic pollutants for the environment. In the search for new optical sensors for heavy metals, here, new organic linker [4-(1-(2-(2,4-dinitrophenyl)hydrazineylidene)-5-phenylpenta-2,4‑dien-1-yl)-1-(4-methoxyphenyl)-5-methyl-1H-1,2,3-triazole] was prepared in 87% yield by simple and facile method. The techniques of synthesis follow the formation of chalcone then condensation with hydrazine moiety to perform hydrazone derivatives. It was synthesized from addition of 1-(1-(4-Methoxyphenyl)-5-methyl-1H-1,2,3-triazol-4-yl)-5-phenylpenta-2,4‑dien-1-one to 2,4-dinitrophenylhdrazine. The chemical structure of prepared linker was established by the IR and NMR spectral data in addition to single-crystal X-ray crystallography. The new linker was used for detection of various metal ions (Cu2+, Zn2+, Cr3+, Co2+, Cd2+, and Hg2+). Interestingly, the new linker showed highly detection level and selectivity toward Hg2+ions. The color of the Hg2+ ions solution was turned from colorless to green when adding the title compound performed excellent naked-eye detection. The binding stoichiometry of the linker to the Hg2+ ions was found to be 1:1, which was confirmed by Job plot. For industrial application, the new linker was mixed with filter paper and used for detection of Hg2+ions. The new fabricated filter paper was identified using scanning electron microscopy (SEM). The present fabricated filter paper produced naked eye colorimetric detection of Hg2+ions.

Bi-functional aqueous starch capped CdS quantum dots synthesis and their application as sensor of heavy metal-ions as well as photocatalytic dye degradation

CdS quantum dots (QDs) have emerged as the promising nanomaterial for various applications. This study reported bi-functional usage of aqueous starch capped CdS QDs as heavy metal-ion sensor for selective detection of Hg2+ and Cu2+ in aqueous medium as well as sunlight driven photocatalyst for degradation of organic dyes. CdS QDs exhibited colorimetric, spectroscopic, and compositional change with Hg2+ and Cu2+ via cation exchange reaction (CER). The CER of yellow color CdS QDs solution with Hg2+ showed rapid colour change to orange, red and white with composition Cd1-xSHgxS, HgS/CdS, and mixture of HgS and Hg sol, respectively whereas, CER of CdS QDs with Cu2+ resulted in pale brown, brown and greenish brown with composition Cd1-xCuxS, CuxS/CdS and Cu2-xS, respectively. Further, CdS QDs displayed excellent sunlight driven photocatalytic degradation of cationic, anionic and hair dye with good efficiency, reusability, and stability.

A compact dication source for Ba2+ tagging and heavy metal ion sensor development

We present a tunable metal ion beam that delivers controllable ion currents in the picoamp range for testing of dry-phase ion sensors. Ion beams are formed by sequential atomic evaporation and single or multiple electron impact ionization, followed by acceleration into a sensing region. Controllability of the ionic charge state is achieved through tuning of electrode potentials that influence the retention time in the ionization region. Barium, lead, and cadmium samples have been used to test the system, with ion currents identified and quantified using a quadrupole mass analyzer. Realization of a clean Ba2+ ion beam within a bench-top system represents an important technical advance toward the development and characterization of barium tagging systems for neutrinoless double beta decay searches in xenon gas. This system also provides a testbed for investigation of novel ion sensing methodologies for environmental assay applications, with dication beams of Pb2+ and Cd2+ also demonstrated for this purpose.

Ultrasensitive Real-Time Detection of Pb2+ Ions Using g-C3N4 Nanosheets

The quick and easy monitoring of heavy metals in drinking water is utmost important due to their harmful effects on human health. In this work, GaN based high electron mobility transistor (HEMT) sensor has been fabricated using optical lithography and explored as a prospective sensor for the determination of trace Pb <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> ions present in the water. Graphitic carbon nitride was synthesized by single step combustion method. The g-C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> nanosheets were used to functionalise the gate area of the fabricated GaN HEMT sensor to investigate the presence of Pb <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> metal ions in water. The g-C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> functionalized sensor exhibited sensitivity of around 0.46 μA/ppb with 0.32 ppb as Limit of detection (LoD) much below the international set standards. Moreover, the real time measurements on lake water were performed using the developed GaN HEMT sensor to detect the presence of Pb <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> ions in real samples in a fast and ultrasensitive manner. We anticipate that the reported work will certainly serve as proof-of-concept to develop heavy metal ion sensors.

Development of in-situ electrochemical heavy metal ion sensor using integrated 1D/0D/1D hybrid by MWCNT and CQDs supported MnO2 nanomaterial

An integrated 1D/0D/1D hybrid nanomaterial was prepared from MWCNT supported carbon quantum dots @ MnO2 nanomaterial for a sensitive and selective electrochemical heavy metal ion sensor by hydrothermal methods. The developed nanomaterials were characterized by various analytical methods such as FESEM, HRTEM, XRD, FTIR, EDX and elemental mapping study, and also its electrochemical properties of the prepared samples were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) analysis. Differential pulse voltammetry (DPV) analysis has been used to investigate the quantitative detection of heavy metal ions such as cadmium and chromium on modified electrodes under optimal conditions. The in-situ electrochemical sensitivity and selectivity of the samples were determined by varying various parameters, such as the concentration of heavy metal ions, different electrolytes and electrolyte pH. The observed DPV results show that prepared MWCNT (0.05 wt%) and CQD (0.1 wt%) supported MnO2 nanoparticles show effective detection response for chromium (IV) metal ion. In particular, 0D CQD, 1D MWCNT, and MnO2 hybrid nanostructures produced a synergistic effect among them, resulting in strong electrochemical performance of the prepared samples against the target metal ions.

Development of boron doped diamond electrodes material for heavy metal ion sensor with high sensitivity and durability

We report on the optimized substrate pretreatment and deposition process conditions for boron-doped diamond (BDD) electrodes fabricated by hot-filament chemical vapor deposition (HFCVD). The optimized BDD electrode with a doping concentration of 8000 ppm showed high accuracy and precision in detecting Cd(II), Pb(II), and Cu(II) ions. In addition, this demonstrates excellent selectivity against external metal ions under the optimized stripping voltammetry measurement conditions. The detection limits of the target ions of Cd(II), Pb(II), and Cu(II) were 0.55 (±0.05), 0.43 (±0.04), and 0.74 (±0.06) μg/L (S/N = 3), respectively. In real samples spiked with 100 μg/L Cd(II), Pb(II), and Cu(II), both the accuracy and precision of the BDD electrode were within 5%; the interference with organic matter was also negligible. The excellent selectivity and long-term stability indicate that the BDD electrode developed in this study are potentially useful for online water environment monitoring systems.

Ternary nanocomposite-based smart sensor: Reduced graphene oxide/polydopamine/alanine nanocomposite for simultaneous electrochemical detection of Cd2+, Pb2+, Fe2+, and Cu2+ ions

Heavy metal ion (HMI) sensors are the most sought commercial devices for environmental monitoring and food analysis research due to serious health concerns associated with HMI overdosage. Herein, we developed an effective electrochemical sensor for simultaneous detection of four HMI (Cd2+, Pb2+, Fe2+, and Cu2+) using a ternary nanocomposite of reduced graphene oxide functionalized with polydopamine and alanine (ALA/pDA/rGO). Comprehensive spectroscopic and microscopic characterizations were performed to ensure the formation of the ternary nanocomposite. The developed nanocomposite on glassy carbon electrode (GCE) yields >2-fold higher current than GO/GCE electrode with excellent electrochemical stability and charge transfer rate. Using DPV, various chemical and electrochemical parameters, such as supporting electrolyte, buffer pH, metal deposition time, and potential, were optimized to achieve highly sensitive detection of targeted HMI. For Cd2+, Pb2+, Fe2+, and Cu2+ sensing devised sensor exhibited detection limits of 1.46, 2.86, 50.23, and 17.95 ppb and sensitivity of 0.0929, 0.0744, 0.0051, and 0.0394 μA/ppb, respectively, with <6% interference. The sensor worked similarly well for real water samples with HMI. This study demonstrates a novel strategy for concurrently detecting and quantifying multiple HMI in water and soil using a smart ternary nanocomposite-based electrochemical sensor, which can also detect HMI in food samples.

Hybrid hierarchically porous carbon micron tubes for trace cadmium and lead ions electrochemical detection

The nitrogen, sulfur codoped hierarchical porous carbon tubes were synthesized using oxidized asphaltene, melamine and trithiocyanuric acid, it showed excellent performance in the detection of trace amounts of Cd2+/Pb2+ thanks to its rich sulfur and nitrogen functional groups as well as hierarchical porous tube structure. The introduction of oxidized asphaltene increased the conductivity of the resultant carbon material while retaining a high sulfur content (6.13 wt%). Under the optimum conditions, the resultant porous carbon tube was used as electrochemical detection sensor for heavy metal ions. The sensitivities and detection limits for individual Cd2+ and Pb2+ were 19.4802 and 33.2850 μA/μM, 2.80 and 1.38 nM; while the sensitivities and detection limits for simultaneous Cd2+ and Pb2+ were 14.5474 and 37.3337 μA/μM, 3.75 and 1.23 nM, respectively. This sensor also was utilized to detect actual water samples, and it was successful in measuring environmental heavy metal contaminants with acceptable recoveries of 97.34–102.83% for Cd2+ and 97.46–106.47% for Pb2+.

Synthesis of carbon dots based on corn cobs as heavy metal ion sensors using the microwave method

&lt;p class="Abstract"&gt;Carbon dots (CDots) are nanomaterials that can be applied as a heavy metal ion sensor. CDotss ware synthesized from corncobs which are abundant and underutilized. This study aims to determine the effect of variations in the concentration of corncobs on optical properties of CDots and their application as Fe&lt;sup&gt;3+&lt;/sup&gt; ion sensors. CDots were synthesized with variations of corncobs’ mass 5, 10, 15, and 20 g and variations in metal ion concentrations 10&lt;sup&gt;-7&lt;/sup&gt;, 10&lt;sup&gt;-6&lt;/sup&gt;, 10&lt;sup&gt;-5&lt;/sup&gt;, 10&lt;sup&gt;-4&lt;/sup&gt;, and 10&lt;sup&gt;-3&lt;/sup&gt; M. The success of CDots synthesis was indicated by luminescence green when exposed to UV light. UV-Vis characterization showed that the greater the concentration of CDots could cause a shift in the absorbance peak towards longer wavelengths and peaks at wavelengths of 290, 291, 295, 298, and 323 nm, respectively. Photoluminescence (PL) characterization showed CDots emission peaks at 511, 504, 503, and 495 nm. The greater the concentration of CDots can cause a shift in the emission peak towards a shorter wavelength and increase the intensity. The PL characterization can identify the presence of Fe&lt;sup&gt;3+&lt;/sup&gt; metal ions with a wavelength shift that indicates a change in the CDots structure. The synthesis of CDots from corncobs have great potential to be applied as sensors.&lt;/p&gt;

3D printing MOFs‐based fiber electrodes: A novel platform as electrochemical sensors for heavy metal ions

AbstractPb2+ probes play an important part in environments and human health. We developed a new free‐standing electrochemical probe by 3D printing UiO‐66‐NH2 with @rGO. This free‐standing fiber electrochemical sensor exhibited good structural stability and Pb2+ sensing performance with enhanced conductivity. This MOFs‐based hybrid probe showed an excellent sensing sensitivity for Pb2+ with a very low detection limit of 0.041 μM, significantly lower than the standard for Pb2+ in drinking water as a result of the porous structure of UiO‐66‐NH2 and the good conductivity of rGO. This study highlighted a simple strategy for MOFs‐based hybrid sensor formation and accelerated the MOFs‐based materials for Pb2+ electrochemical detection in future practical applications.

Metal Ion Complex Compound Fe(III) with Pyrazoline Derivative Ligand as Cd(II) and Zn(II) Heavy Metal Ion Sensor Based on Fluorescence

&lt;p&gt;The purpose of this research is to synthesize the complex compound of ion Fe&lt;sup&gt;3+&lt;/sup&gt; with para-di-2-(1-phenyl-3-pyridyl-4,5-dihydro-1H-pyrazole-5-yl)benzene ligand and its potentials as the sensor of Cd&lt;sup&gt;2+&lt;/sup&gt; and Zn&lt;sup&gt;2+&lt;/sup&gt; heavy metal ions based on fluorescence. Complex compounds are characterized with a Fourier-Transform Infrared (FTIR) Spectrophotometer, Ultraviolet-Visible (UV-Vis) Spectrophotometer and Spectrofluorometer. Then, a complex compound fluorosensor study is conducted by adding Cd&lt;sup&gt;2+&lt;/sup&gt; and Zn&lt;sup&gt;2+&lt;/sup&gt; heavy metal ions using a UV-Vis Spectrophotometer and Spectrofluorometer. The results show that the synthesis of the complex compound formed by reacting Fe metal and pyrazoline derived ligands generates brown precipitate with a yield of 51.25% and a range of melting points of 252.2-253.2 . The result of characterization with FTIR (cm&lt;sup&gt;-1&lt;/sup&gt;) generates 3380.20 (tertiary amine), 2922.31-2852.42 (C-H pyridine), 2360.38 (C=C aromatic), 1595.93-1451.88 (C=N), 1232.25-982.66 (C-N pyrazoline), 751.61-690.29 (C-H aromatic) and 366.54-339.44 (Fe-N). The Uv-Vis spectrophotometer study with a concentration of 5x10&lt;sup&gt;-5 &lt;/sup&gt;M showed two absorption peaks at 246 nm, 354 nm, and 440 nm. The resulting fluorescence intensity of 813.1 a.u. at the wavelenght of 500 nm. The study of complex compound fluorescence shows that the addition of Cd&lt;sup&gt;2+&lt;/sup&gt; heavy metal ion can be made as fluorosensor with turn-on (enhancement) type, while the complex compound in the addition of Zn&lt;sup&gt;2+&lt;/sup&gt; heavy metal ion can be made as fluorosensor with turn off-on (quenching-enhancement) type.&lt;/p&gt;

Fully inkjet-printed paper-based Pb2+ optodes for water analysis without interference from the chloramine disinfectant.

We developed a paper-based colorimetric sensor for facile and cost-effective detection of Pb2+ in drinking and environmental water samples. The Pb2+ ion-selective optodes are fabricated by inkjet printing of ionophore, chromoionophore, and ion exchanger on cellulose paper. Pb2+ in water samples induces deprotonation of the pH chromoionophore and changes the optode color, which is acquired and analyzed by a smartphone. The paper-based optode without any plasticizer or polymer has a dynamic range and selectivity comparable to those of traditional optodes using PVC polymer and/or plasticizer. Furthermore, the response time of the plasticizer/polymer-free paper-based optode is much shorter than those of plasticized PVC-based optodes on paper and glass (5min vs. 15 and 50min). Moreover, the plasticizer/polymer-free optode preserves the water-wicking capability of porous cellulose paper, allowing for the design of pump-free microfluidic devices. Chloramine, a widely used disinfectant in drinking water, was found to be a strong and generic interference species for heavy metal ion detection via ion-selective optodes. A fully inkjet-printed lateral-flow paper-based device consisting of a sodium thiosulfate-based chloramine elimination zone and a plasticizer/polymer-free sensing zone was designed for Pb2+ detection in tap water disinfected by chloramine. The dynamic range of the Pb2+ sensor may be shifted from the current 10-6 to 10-5M to lower concentrations by using stronger ionophores, but this work lays a foundation for the design of paper-based heavy metal ion sensors without detrimental interference from disinfectants.

Electrosynthesis of poly(2,5-dimercapto-1,3,4-thiadiazole) films and their composites with gold nanoparticles at a polarised liquid|liquid interface

The organosulfur compound 2,5-dimercapto-1,3,4-thiadiazole (DMcT) finds widespread applications in batteries, lubricant fluids, heavy metal ion sensors, waste-water purification and as a biocide. In this article, we demonstrate the untapped versatility inherent to using biphasic systems for electrosynthesis by showcasing several successful approaches to the electrosynthesis of poly(DMcT) films at a polarised interface between two immiscible electrolyte solutions (ITIES) by cyclic voltammetry (CV) cycling using either I 2 , Hg 2+ or O 2 as the oxidising agents. AC voltammetry is demonstrated as an effective in situ method to monitor poly(DMcT) film formation by I 2 or Hg 2+ as a function of the aqueous electrolyte anion and pH. DMcT is further shown to act as a binder molecule to promote interfacial gold nanoparticle (AuNP) assembly into floating films at an immiscible liquid|liquid (L|L) interface. Exploiting the electrocatalysis of DMcT oxidation by O 2 in the presence of adsorbed interfacial AuNPs yields AuNP/poly(DMcT) composite films. Raman spectroscopy suggests the latter were a coordination polymer of poly(DMcT) with AuNPs and surface enhanced Raman spectroscopy (SERS) active. The dielectric nature of the poly(DMcT) films suppresses the capacitance at the ITIES, yet the AuNP/poly(DMcT) films show a very high interfacial capacitance, with an ability to efficiently adsorb cations. Thus, these films open opportunities to selectively modulate the interfacial capacitance, potentially forming the basis of novel “soft” capacitors at a polarised L|L interface.