Neutral carriers based polymeric membrane electrodes for selective determination of mercury (II)

Ultrasensitive green spectrofluorimetric approach for quantification of Hg(II) in environmental samples (water and fish samples) using cysteine@MnO2 dots

Mercury (Hg²⁺ ) is a natural element present in foods such as fish, water and soil. Exposure to mercury leads to severe toxic effects on the nervous, digestive, and immune systems. Here, a novel, green, and environmentally friendly fluorescent probe decorated with cysteine/MnO₂ quantum dots (Cys@MnO₂ QDs) was synthesized. This synthesis was carried out using a simple ultrasound technique with the aid of cysteine for fabricating Cys@MnO₂ QDs to estimate Hg levels in fish and water samples. In this morphological study, Cys@MnO₂ QDs were fully characterized using high-resolution transmission electron microscopy, zeta potential analysis, fluorescence, ultraviolet-visible and infrared spectroscopy. The fluorescence of the synthesized Cys@MnO₂ QDs was significantly quenched by gradually increasing the Hg(II) concentration. The quenching mechanism based on the Hg-S bonds strengthened the utility of the Cys@MnO₂ QDs as a novel luminescent nanoprobe. The estimation of Hg was linear in the concentration range 0.7-100.0 ng mL^-1 with a limit of quantitation equal to 0.30 ng mL^-1 . The Cys@MnO₂ QDs are fluorescent probes with various benefits such as speed, ease of use, cost- effective, and being environmentally friendly; they are easily applied in food manufacturing and for public health improvement.

Lignosulfonate-Based Conducting Flexible Polymeric Membranes for Liquid Sensing Applications

In this study, lignosulfonate (LS) from the acid sulfite pulping of eucalypt wood was used to synthesize LS-based polyurethanes (PUs) doped with multiwalled carbon nanotubes (MWCNTs) within the range of 0.1-1.4% w/w, yielding a unique conducting copolymer composite, which was employed as a sensitive material for all-solid-state potentiometric chemical sensors. LS-based PUs doped with 1.0% w/w MWCNTs exhibited relevant electrical conductivity suitable for sensor applications. The LS-based potentiometric sensor displayed a near-Nernstian or super-Nernstian response to a wide range of transition metals, including Cu(II), Zn(II), Cd(II), Cr(III), Cr(VI), Hg(II), and Ag(I) at pH 7 and Cr(VI) at pH 2. It also exhibited a redox response to the Fe(II)/(III) redox pair at pH 2. Unlike other lignin-based potentiometric sensors in similar composite materials, this LS-based flexible polymeric membrane did not show irreversible complexation with Hg(II). Only a weak response toward ionic liquids, [C2mim]Cl and ChCl, was registered. Unlike LS-based composites comprising MWCNTs, those doped with graphene oxide (GO), reduced GO (rGO), and graphite (Gr) did not reveal the same electrical conductivity, even with loads up to 10% (w/w), in the polymer composite. This fact is associated, at least partially, with the different filler dispersion abilities within the polymeric matrix.

Design and Characterization of Electrochemical Sensor for the Determination of Mercury(II) Ion in Real Samples Based upon a New Schiff Base Derivative as an Ionophore

The present paper provides a description of the design, characterization, and use of a Hg2+ selective electrode (Hg2+-SE) for the determination of Hg2+ at ultra-traces levels in a variety of real samples. The ionophore in the proposed electrode is a new Schiff base, namely 4-bromo-2-[(4-methoxyphenylimino)methyl]phenol (BMPMP). All factors affecting electrode response including polymeric membrane composition, concentration of internal solution, pH sample solution, and response time were optimized. The optimum response of our electrode was obtained with the following polymeric membrane composition (% w/w): PVC, 32; o-NPOE, 64.5; BMPMP, 2 and NaTPB, 1.5. The potentiometric response of Hg2+-SE towards Hg2+ ion was linear in the wide range of concentrations (9.33 × 10-8-3.98 × 10-3 molL-1), while, the limit of detection of the proposed electrode was 3.98 × 10-8 molL-1 (8.00 μg L-1). The Hg2+-SE responds quickly to Hg2+ ions as the response time of less than 10 s. On the other hand, the slope value obtained for the developed electrode was 29.74 ± 0.1 mV/decade in the pH range of 2.0-9.0 in good agreement with the Nernstian response (29.50 mV/decade). The Hg2+-SE has relatively less interference with other metal ions. The Hg2+-SE was used as an indicator electrode in potentiometric titrations to estimate Hg2+ ions in waters, compact fluorescent lamp, and dental amalgam alloy and the accuracy of the developed electrode was compared with ICP-OES measurement values. Moreover, the new Schiff base (BMPMP) was synthesized and characterized using ATR-FTIR, elemental analysis, 1H NMR, and 13C NMR. The PVC membranes containing BMPMP as an ionophore unloaded and loaded with Hg(II) are reported by scanning electron microscope images (SEM) along with energy-dispersive X-ray spectroscopy (EDX) spectra.

Amino acid recognition by a fluorescent chemosensor based on cucurbit[8]uril and acridine hydrochloride

A new fluorescent chemosensor comprised of cucurbit[8]uril (Q[8]) and acridine hydrochloride (AC) has been designed and utilized for the recognition of amino acids. The AC was encapsulated by the Q[8] cavity and formed a 1:2 host-guest inclusion complex both in solution (aqueous) and in the solid-state. Whilst free AC is known to be strongly fluorescent, this strong fluorescence was quenched in the inclusion complex Q [8]-AC. This non-fluorescent complex Q[8]-AC was capable of serving as a fluorescence "off-on" probe, and was able to recognize either L-Phe or L-Trp via the competitive interaction between L-Phe or L-Trp. Moreover, the pH responsive nature of the probe allowed for the detection of basic amino acids, namely L-Arg, L-His, or L-Lys). As a result, a fluorescence method for the detection of five amino acids using a single system has been developed.

A review on nanostructure-based mercury (II) detection and monitoring focusing on aptamer and oligonucleotide biosensors

Heavy metal ion pollution is a severe problem in environmental protection and especially in human health due to their bioaccumulation in organisms. Mercury (II) (Hg²⁺), even at low concentrations, can lead to DNA damage and give permanent harm to the central nervous system by easily passing through biological membranes. Therefore, sensitive detection and monitoring of Hg²⁺ is of particular interest with significant specificity. In this review, aptamer-based strategies in combination with nanostructures as well as several other strategies to solve addressed problems in sensor development for Hg²⁺ are discussed in detail. In particular, the analytical performance of different aptamer and oligonucleotide-based strategies using different signal improvement approaches based on nanoparticles were compared within each strategy and in between. Although quite a number of the suggested methodologies analyzed in this review fulfills the standard requirements, further development is still needed on real sample analysis and analytical performance parameters.

Fabrication of a Cu(II)-Selective Electrode in the Polyvinyl Chloride Matrix Utilizing Mechanochemically Synthesized Rhodamine 6g as an Ionophore

A Cu(II)-selective electrode has been fabricated by utilizing a mechanochemically synthesized copper-specific ionophore "L" embedded in a poly(vinyl chloride) membrane. 2-Nitrophenyloctylether and sodium tetraphenylborate have been used as a plasticizer and as a solvent mediator, respectively, and found to be enhancing the sensitivity of the fabricated ion-selective electrode (ISE). A range of membranes (S1-S7) with varying compositions were casted and investigated in ISE. Results revealed an excellent Nernstian response of 29.38 ± 0.55 mV/dec for the ISE S6. The fabricated ISE operates well in the pH window 4.0-7.5, and the limit of detection was found to be 5 μM (0.3 ppm). Quick response time (15 s), long shelf-life, and selectivity (on the order of 10^-4 and 10^-5) over a number of interfering cations enabled S6 promising for real off laboratory sample analysis and can be employed to detect copper ion in various industrial as well as biological and environmental samples. To demonstrate the practical application of these ISE, the Cu concentration in the digested printed circuit board has been estimated using the standard calibration plot. The fabricated ISE has been regenerated through extracting copper by chelating with ethylenediaminetetraacetic acid.

Fluorescence chemosensor containing 4-methyl-7-coumarinyloxy, acetylhydrazono and N-phenylaza-15-crown-5 moieties for K+ and Ba2+ ions

A new aza-15-crown-5 derivative 1 bearing coumarin and hydrazone moieties was synthesized and characterized. The fluorescent sensing behavior and selectivity of 1 toward different metal ions in ethanol were investigated. There are 4-fold and 2-fold fluorescence enhancements of 1 at λem=406 nm upon addition of five equivalents of K+ and Ba2+, respectively. The fluorescence titration revealed the stoichiometry of 1:1 for 1-K+1-Ba2+ complexes and the binding constants (lgKs) of 4.11 for 1-K+ and 3.61 for 1-Ba2+. Compound 1 can be used as a fluorescent chemosensor for K+ and Ba2+ through discriminable photoresponse signals. The calculated detection limits for K+ and Ba2+ are 2.28 μm and 5.21 μm, respectively.

Controlled Growth of N-Doped and Large Mesoporous Carbon Spheres with Adjustable Litchi-Like Surface and Particle Size as a Giant Guest Molecule Carrier

N-doped mesoporous carbon nanospheres (NMCNs) with tunable particle size, pore size, surface roughness, and inner cavity are extremely important for the future development of new carriers for nanoencapsulation, high-performance giant molecule transport, and cell uptake. However, constructing such a multifunctional material via a simple method still remains a great challenge. Herein, a controlled growth technology was developed for the first time to synthesize such NMCNs based on the initial reaction temperature (IRT) and solution polarity. In this strategy, the IRT not only can adjust the micelle aggregation to obtain NMCNs with large mesopores but also can make the F127 micelle more lyophobic to prepare hollow N-doped mesoporous carbon spheres, which is a great breakthrough. Inspiringly, by varying the solution polarity to make nonuniform growth of nanoparticles, the litchi-like rough surface of NMCNs was obtained, which could significantly improve the cell uptake performance of NMCNs. The current understanding of nucleation and growth mechanism of nanospheres was further extended and realized the development of NMCNs with large mesopores and litchi-like rough surface, which provided a new and interesting fundamental principle for the synthesis of NMCNs. The mesoporous structure of NMCNs was successfully reverse-replicated by nanocasting of tetraethylorthosilicate to obtain mesoporous silica spheres (MSNs), revealing the easy transformation between NMCNs and MSNs. Insulin as a peptide drug cannot be directly administered orally. But it can be used as oral preparation after being loaded into NMCNs, which has never been reported before. Interestingly, the results of the animal experiment showed an excellent in vivo hypoglycemic activity. This finding provides a new paradigm for the fabrication of structurally well-defined NMCNs with a great promise for drug carriers.

Electrochemical Sensor for the Determination of Paracetamol at Carbamazepine Film Coated Carbon Paste Electrode

The electrochemical behavior of paracetamol (PC) was investigated at carbamazepine (CBZ) film coated carbon paste electrode in 0.2 M PBS of pH 7.4 by cyclic voltammetric technique. The modified electrode was exhibited a good electrochemical activity towards the oxidation of paracetamol, which results in a noticeable improvement of the peak currents and feasible oxidation as compared to the bare carbon paste electrode. Under optimal experimental conditions the electrochemical response to PC was linear in the concentration range from 1.0×10−4M to 3.94×10−4M with a detection limit of 0.24 μM by cyclic voltammetric technique. The sensitivity, long-term stability, reproducibility was shown by the modified electrode. Finally, the proposed method was successfully applied to determine PC in pharmaceutical samples.

A turn-on chemiluminescence biosensor for selective and sensitive detection of adenosine based on HKUST-1 and QDs-luminol-aptamer conjugates

In this work, HKUST-1 and QDs-luminol-aptamer conjugates were prepared. The QDs-luminol-aptamer conjugates can be adsorbed by graphene oxide through π-π conjugation. When the adenosine was added, the QDs-luminol-aptamer conjugates were released from magnetic graphene oxide (MGO), the chemiluminescent switch was turned on. It was reported that HKUST-1 can catalyze the chemiluminescence reaction of luminol-H₂O₂ system in an alkaline medium, and improve the chemiluminescence resonance energy transfer (CRET) between chemiluminescence and QDs indirectly. Thus, the adenosine can be detected sensitively. Based on this phenomenon, the excellent platform for detection of adenosine was established. Under the optimized conditions, the linear detection range for adenosine was 1.0 × 10^-12-2.2 × 10^-10 mol/L with a detection limit of 2.1 × 10^-13 mol/L. The proposed method was successfully used for adenosine detection in biological samples.

The first highly selective turn “ON” fluorescent sensor for vanadyl (VO2+) ions: DFT studies and molecular logic gate behavior

We report the first antipyrine-derived fluorescent chemosensor for highly selective and sensitive detection of vanadyl ions by an inhibited PET mechanism, with DFT studies.

Simultaneous sensitive determination of benzenediol isomers using multiwall carbon nanotube–ionic liquid modified carbon paste electrode by a combination of artificial neural network and fast Fourier transform admittance voltammetry

A novel electrochemical method for the simultaneous determination of catechol, hydroquinone, and resorcinol.

A chalcohalide glass/alloy based Ag+ ion - selective electrode with nanomolar detection limit

In this paper, a silver ion-selective electrode material with lower detection limit is presented. The electrode is based on 22.5As₂S₃-22.5Ag₂S-55AgCl chalcohalide glass membranes. The low detection limit decreases from the micromolar range of the original Ag₂S-As₂S₃ electrode to the nanomolar level (1.89 nM) by introducing AgCl. The addition of AgCl increases the conductivity of the glasses and improves the analytical properties of electrodes because of the joint effects of Ag⁺ and Cl^- on network structure of the glass. The super-Nernstian response behavior was observed for the partially crystallized electrode. The electrode containing AgCl also possesses a high selectivity (except for Hg²⁺), fast response and good stability.

A review: Aptamer-based analytical strategies using the nanomaterials for environmental and human monitoring of toxic heavy metals

Recent developments in biotechnology offer the new methods for the sensitive detection of heavy metals based on the affinity and specificity of aptamers, as nucleic acid ligands selected from random sequence pools in vitro. Heavy metals have received considerable importance as the most toxic metallic pollutants which may cause serious environmental damages. They are classified as trace elements because of their presence in trace concentrations in various environmental matrices. Thus, the precise and sensitive methods to detect heavy metals are important to ensure human and environment safety. Aptamers as the biological probes, show high binding affinity which can often be directly translated into high detection sensitivity. On the other hand, high selectivity and stability make them possible to detect a wide range of targets, especially metallic ions. This review provides current progress of aptamers for environmental and biological monitoring of heavy metals using the nanomaterials mainly in two groups: (i) aptamer based biosensors (aptasensors) and (ii) aptamer based biosorbents (aptasorbents). The introduction of nanomaterials can efficiently increase the immobilization quantity of aptamers. Furthermore, they play an important role in the orientation and assembly density controlling of aptamers for the optimized recognition ability.