Comparative studies of neodymium (III)-selective PVC membrane sensors

Electrochemical determination of zinc(II) using N1-hydroxy-N1,N2-diphenylbenzamidine and multi-walled carbon nanotubes modified carbon paste electrode

In this study, a new carbon paste electrode modified with a laboratory-synthesized ligand, N¹-hydroxy-N¹,N²-diphenylbenzamidine (HDPBA) and multi-walled carbon nanotubes (MWCNTs) (HDPBA‒MWCNTs/CPE) has been developed. The modified electrode was applied for preconcentration and voltammetric determination of zinc ions (Zn(II)) by square wave anodic stripping voltammetry (SWASV). The preconcentration of Zn(II) on the electrode surface was performed in 0.1 M Brinton Robinson (B-R) buffer solution (pH 6) at an applied potential of -1.30 V versus Ag/AgCl for 120 s, followed by stripping in the positive potential scan of the SWASV after a quit time of 10 s. Under optimized experimental conditions, the proposed electrode exhibited a wider linear dynamic response for Zn(II) in a concentration range of 0.02-10.00 μM with a detection limit of 2.48 nM. This is due to the excellent metal-chelation property of the ligand, and the good conductivity and large surface area of MWCNTs which significantly improved the sensing performance of the nanocomposite modified electrode. The selectivity of the electrode was studied by evaluating the interference effects of various foreign ions on the peak current of Zn(II). The method exhibited high reproducibility with a relative standard deviation (RSD) of 3.1%. The present method was applied for the determination of zinc ions in water samples. The recovery values in the tested samples were found to be 98.50-106.0%, indicating a good accuracy of the proposed electrode. Furthermore, the electrochemical behavior of HDPBA in acetonitrile and aqueous solutions has been studied.

All solid-state miniaturized potentiometric sensors for flunitrazepam determination in beverages

Flunitrazepam is one of the frequently used hypnotic drugs to incapacitate victims for sexual assault. Appropriate diagnostic tools should be available to victims regarding the growing concern about "date-rape drugs" and their adverse impact on society. Miniaturized screen-printed potentiometric sensors offer crucial point-of-care devices that alleviate this serious problem. In this study, all solid-state screen-printed potentiometric flunitrazepam sensors have been designed. The paper device was printed with silver and carbon ink. Formation of an aqueous layer in the interface between carbon-conducting material and ion-sensing membrane nevertheless poses low reproducibility in the solid-contact electrodes. Accordingly, poly(3,4-ethylenedioxythiophene) (PEDT) nano-dispersion was applied as a conducting hydrophobic polymer on the electrode surface to curb water accumulation. Conditioning of ion-sensing membrane in the vicinity of reference membrane has been considered carefully using special protocol. Electrochemical characteristics of the proposed PEDT-based sensor were calculated and compared favorably to PEDT-free one. The miniaturized device was successfully used for the determination of flunitrazepam in carbonated soft drinks, energy drink, and malt beverage. Statistical comparison between the proposed sensor and official method revealed no significant difference. Nevertheless, the proposed sensor provides simple and user-friendly diagnostic tool with less equipment for on-site determination of flunitrazepam.

Highly selective fluorescent peptide-based chemosensors for aluminium ions in aqueous solution

Two novel fluorescent peptide-based chemosensors, including A (2-amino-benzoyl-Ser-Glu-Glu-NH₂) and B (2-amino-benzoyl-Ala-Glu-Pro-Glu-Ala-Glu-Pro-NH₂) were synthesized and characterized by nuclear magnetic resonance (NMR) spectra. These fluorescent probes exhibited excellent selective and sensitive responses to Al³⁺ ions over other metal ions in aqueous buffered solutions. The limits of detection for both chemosensors towards the Al³⁺ ions were in the order of ∼10^-7 M (A: 155 nM and B: 195 nM), which clearly indicates that these probes have significant potential for biological applications. They also displayed high binding affinity (1.3029 × 10⁴ M^-1 and 1.7586 × 10⁴ M^-1 relevant to A and B respectively). These two chemosensors are great analytical probes that produce turn-on responses upon binding to Al³⁺ ions through an intramolecular charge transfer (ICT) mechanism. In addition, the application of both chemosensors was examined over a wide range of pH. The fluorescent peptide-based probes and Al³⁺ form a 1:1 coordination complex according to the ESI-MS and Job's plot analysis. Notably, upon addition of Al³⁺ to these chemosensors, a fluorescence enhancement of approximately 8-fold was observed and the binding mode was determined using NMR titration and fluorescence emission data.

Simultaneous electrochemical sensing of dihydroxy benzene isomers at cost-effective allura red polymeric film modified glassy carbon electrode

Background

A simple and simultaneous electrochemical sensing platform was fabricated by electropolymerization of allura red on glassy carbon electrode (GCE) for the interference-free detection of dihydroxy benzene isomers.

Methods

The modified working electrode was characterized by electrochemical and field emission scanning electron microscopy methods. The modified electrode showed excellent electrocatalytic activity for the electrooxidation of catechol (CC) and hydroquinone (HQ) at physiological pH of 7.4 by cyclic voltammetric (CV) and differential pulse voltammetric (DPV) techniques.

Results

The effective split in the overlapped oxidation signal of CC and HQ was achieved in a binary mixture with peak to peak separation of 0.102 V and 0.103 V by CV and DPV techniques. The electrode kinetics was found to be adsorption-controlled. The oxidation potential directly depends on the pH of the buffer solution, and it witnessed the transfer of equal number of protons and electrons in the redox phenomenon.

Conclusions

The limit of detection (LOD) for CC and HQ was calculated to be 0.126 μM and 0.132 μM in the linear range of 0 to 80.0 μM and 0 to 110.0 μM, respectively, by ultra-sensitive DPV technique. The practical applicability of the proposed sensor was evaluated for tap water sample analysis, and good recovery rates were observed.

Graphical abstract

Electrocatalytic interaction of ALR/GCE with dihydroxy benzene isomers.

A Simple Method for Developing a Hand-Drawn Paper-Based Sensor for Mercury; Using Green Synthesized Silver Nanoparticles and Smartphone as a Hand-Held-Device for Colorimetric Assay

Mercury ions are highly toxic at trace levels, and its pollution has posed a significant threat to the environment and public health, where current detection methods mainly require laborious operation and expensive instrumentation. Herein, a simple, cost-effective, instrument-free approach for selective detection of Hg2+ based on a hand-drawn paper-based naked-eye colorimetric device is developed. To develop a hand-drawn paper-based device, a crayon is used to build hydrophobic barriers and a paper puncher is applied to obtain patterns as a sensing zone. A green method for the synthesis of silver nanoparticles (AgNPs) is applied using Achillea Wilhelmsii (Aw) extract. The sensing ability of Aw-AgNPs toward Hg2+ is investigated in both solution-phase and paper substrate loaded with Aw-AgNPs using colorimetric methods. For the paper-based sensor, the quantification of the target relies on the visual readout of a color-changed sensing zone modified with Aw-AgNPs. Under optimal conditions, the color of Aw-AgNPs in aqueous solution and on the coated paper substrate can change from brown to colorless upon addition of target, with a detection limit of 28 × 10-9 m and 0.30 × 10-6 m, respectively. In conclusion, the present study indicates the potential of this hand-drawn eco-friendly paper-based sensor for monitoring of mercury.

Conventional and Nanotechnology-Based Sensing Methods for SARS Coronavirus (2019-nCoV)

Ongoing pandemic coronavirus (COVID-19) has affected over 218 countries and infected 88,512,243 and 1,906,853 deaths reported by Jan. 8, 2021. At present, vaccines are being developed in Europe, Russia, USA, and China, although some of these are in phase III of trials, which are waiting to be available for the general public. The only option available now is by vigorous testing, isolation of the infected cases, and maintaining physical and social distances. Numerous methods are now available or being developed for testing the suspected cases, which may act as carriers of the virus. In this review, efforts have been made to discuss the conventional as well as fast, rapid, and efficient testing methods developed for the diagnosis of 2019-nCoV.Testing methods can be based on the sensing of targets, which include RNA, spike proteins and antibodies such as IgG and IgM. Apart from the development of RNA targeted PCR, antibody and VSV pseudovirus neutralization assay along with several other diagnostic techniques have been developed. Additionally, nanotechnology-based sensors are being developed for the diagnosis of the virus, and these are also discussed.

Highly selective and sensitive chemosensor for Al(III) based on isoquinoline Schiff base

As a colorimetric and fluorescent turn-on sensor to Al³⁺, N'-(2-hydroxybenzylidene)isoquinoline-3-carbohydrazide (HL) has been easily synthesized. The fluorescence intensity increases by 273 times in the presence of Al³⁺ at 458 nm. Meanwhile, the experiment data indicate that the limit of detection for Al³⁺ is 1.11 × 10^-9 M. Remarkably, the blue fluorescence signal of HL-Al³⁺ could be specially observed by the naked eye under UV light and is significantly different from those of other metal ions. Fluorescence switch based on the control of Al³⁺ and EDTA proved HL could act as a reversible chemosensor. According to ESI-MS result and the Job's plots, the 2:1 coordination complex formed by HL and Al³⁺ could be produced. Density functional theory calculations were performed to illustrate the structures of HL and complex. The cell imaging experiment indicates that HL can be applied for monitoring intracellular Al³⁺ levels in cells.

A novel isatin-based probe for ratiometric and selective detection of Hg2+ and Cu2+ ions present in aqueous and environmental samples

A novel isatin derivative (1) is UV-Visible active and displays about 90 nm bathochromic shift upon interaction with only Hg²⁺ and Cu²⁺, but not with other common metal ions. Also, the colorless probe 1 turns to brick-red and yellow in the presence of Hg²⁺ and Cu²⁺, respectively. Addition of increasing amounts of Hg²⁺ or Cu²⁺ to 1 leads to the emergence of a new absorption at ~470 nm (due to LMCT), with a concomitant decrease in the intensity of absorption of 1 at ~380 nm, and thereby provides a ratiometric response. Common metal ions and anions do not interfere with the interactions of 1 with Hg²⁺or Cu²⁺ ions. Probe 1 shows very high sensitivity and selectivity towards Hg²⁺ and Cu²⁺ as revealed by their very low detection limits 0.95 × 10^-9 M and 1.5 × 10^-9 M, respectively. Formation of 1:1 complex with Hg²⁺ and 2:1 complex with Cu²⁺ is confirmed using NMR, ESI-MS and FT-IR techniques, Job plot and DFT calculations. Selective detection of Hg²⁺ from Cu²⁺ is established from the ratiometric response caused by β-mercaptoethanol. Advantages of the probe 1 in terms of high sensitivity, stability in the physiological pH and suitability for dual detection are presented. Probe impregnated silica plates for onsite detection of Hg²⁺ and Cu²⁺ present in environmental samples is also demonstrated.

A novel profuse color card for convenient visual determination of iodide in human urine based on catalytic oxidation reaction

In this work, we reported a novel and convenient profuse color card for naked eye determination of iodide (I^-) in urine using chromogenic substrate 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS). I^- catalyzed the oxidation of ABTS by peroxyacetic acid causing ABTS to yield cyan product ABTS⁺ with a new absorption peak at 730 nm. The addition of rose-red dye rhodamine B (RhB) changes the overall color of the solution from pink to purple and finally to blue, which makes the solution multicolor and easy to distinguish. A good linear relationship for I^- was obtained ranging from 10.0 to 500.0 μg/L with the detection limit of 9.2 μg/L. Importantly, the sensor can semi-quantitatively estimate the concentration of I^- in human urine with naked eye through the standard color card and assess the deficiency or excess of iodine in human body. The proposed profuse color card opens up a new colorimetric method for the rapid, simple and reliable determination of I^- in clinic, and has promising applications in developing assay kit for the clinical diagnosis of I^- in urine.

Ultrasensitive detection of ochratoxin A based on biomimetic nanochannel and catalytic hairpin assembly signal amplification

In this paper, an ultrasensitive nanochannel sensor has been proposed for label-free Ochratoxin A (OTA) assay in combination with graphene oxide (GO) and catalyzed hairpin assembly (CHA). The high-performance sensor is segmented into two parts. One is composed of graphene oxide (GO) and DNA probes. In the presence of target OTA, OTA works as a catalyst to trigger the self-assembly pathway of the two probes and initiate the cycling of CHA circuits, which results in numerous double-stranded DNAs (dsDNA) in solution. The excess ssDNA probes are removed by GO. The other part is composed of biomimetic nanochannel coated with polyethyleneimine (PEI) and Zr⁴⁺, which can quantify the concentration of OTA by detecting the dsDNA in solution. The nanofluidic device has a detection limit of as low as 6.2 pM with an excellent selectivity. The nanochannel based assay was used to analyse food samples (red wine) with satisfied results. Thus, the proposed analytical method will provide a new approach the detection of OTA and can be applied for quality control to ensure food safety.

Green synthesis and characterization of DyMnO3-ZnO ceramic nanocomposites for the electrochemical ultratrace detection of atenolol

The present study is a first report about magnetic, optical and electrical as well as drug sensing properties of DyMnO₃-ZnO green-nanocomposites that are synthesized by Pechini modified method. Three natural compounds containing Vitis vinifera, Hibiscus sabdariffa and rhus juices are used as green and eco-friendly reagents for synthesis of the nanostructures. The nanostructures are characterized by various techniques containing Fourier transform infrared spectra (FT-IR), X-ray diffraction (XRD), energy dispersive X-ray (EDX), field emission scanning electron microscopes (FESEM), high resolution transmission electron microscopy (HR-TEM), vibrating sample magnetometer (VSM) and diffuse reflectance spectroscopy (DRS). The calcination temperature, type of chelating agent and pH are optimized to achieve the best structural and smallest crystallite sizes of the systems via an eco-friendly approach. The studies show that the Vitis vinifera juice creates the best homogeneous sphere-like nanostructures. Therefore, the samples that are synthesized by Vitis vinifera juice are used for fabrication of a carbon paste electrode modified with DyMnO₃-ZnO nanocomposites (DMZN/CPE). The nanostructured modified electrode exhibits an excellent electrocatalytic effect for determination of atenolol (ATN) using voltammetry techniques. The results reveal that the DyMnO₃-ZnO green-nanocomposites have potential applications as a sensitive material in the drug analysis in biological samples.

Single-step fluorescence recognition of As3+, Nd3+ and Br− using pyrene-linked calix[4]arene: application to real samples, computational modelling and paper-based device

A new fluorescence sensor has been synthesized for its selective recognition of As³⁺ (11.53 nM), Nd³⁺ (0.65 nM) and Br⁻ (11.25 nM).

Selectivity enhancement of Arsenazo(III) reagent towards heavier lanthanides using polyaminocarboxylic acids: a spectrophotometric study

A new study has been conducted to quantify lanthanide(III) ions using Arsenazo III-polyaminocarboxylic acid (PACA) system. The study disclosed two different analytically important information: (i) λmax of lanthanide-Arsenazo III complexes for lighter lanthanides like Ce(III) and Nd(III) did not shift from its original position on addition of PACA and (ii) for heavier lanthanides like Dy(III), Tm(III) and Lu(III) a new λmax at 538 nm was observed, while wavelengths at 610 nm and 654 nm were disappeared in presence of ethylenediaminetertracetic acid (EDTA) and trans-1,2-Diaminocyclohexane-N,N,N',N'-tetraacetic acid (DCTA), further the intensity of peak decreased with increase in lanthanide(III) ion concentration. Effect of ethylene glycol-bis(2-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA) and N-(2-hydroxyethyl) ethylenediamine-N,N',N'-triacetic acid (EDTA-OH) on Arsenzo(III)-Ln(III) complex is very weak and there is no analytically importance of such interaction. Moreover, this work confirms that Nd(III) and heavy lanthanides can be successfully determined with high accuracy in the working range of concentration of these metal ions.

Titanium (III) cation selective electrode based on synthesized tris(2pyridyl) methylamine ionophore and its application in water samples

The introduction of low detection limit ion selective electrodes (ISEs) may well pave the way for the determination of trace targets of cationic compounds. This research focuses on the detection of titanium (III) cation using a new PVC-membrane sensor based on synthesized tris(2pyridyl) methylamine (tpm) ionophore. The application and validation of the proposed sensor was done using potentiometric titration, inductively coupled plasma atomic emission spectrometry (ICP-AES), and atomic absorption spectrometry (AAS). The membrane sensor exhibited a Nernstian response to the titanium (III) cation over a concentration range of 1.0 × 10⁻⁶–1.0 × 10⁻² M and pH range from 1–2.5. The Nernstian slope, the lower of detection (LOD), and the response time (t_95%) of the proposed sensor were 29.17 ± 0.24 mV/dec, 7.9 × 10−7 M, and 20 s, respectively. The direct determination of 4–39 μg/ml of titanium (III) standard solution showed an average recovery of 94.60 and a mean relative standard deviation of 1.8 at 100.0 μg/ml. Finally, the utilization of the electrodes as end-point indicators for potentiometric titration with EDTA solutions for titanium (III) sensor was successfully carried out.