Bacteria-templated ZIF-8 embedded in polyacrylonitrile nanofibers as a novel sorbent for thin film microextraction of benzoylurea insecticides.

In the present work, the rod-like ZIF-8 (ZIF8@E coli) was prepared by fast, easy and environmentally friendly method of biomimetic mineralization with Escherichia coli bacteria as a bio-template and was exploited for the first time in the microextraction. In this regard, electrospun nanofiber mats of polyacrylonitrile (PAN) and ZIF8@E coli were prepared by electrospinning method and used as a new sorbent for thin film microextraction (TFME) of benzoylurea insecticides such as Hexaflumuron and Teflubenzuron as model analytes. The PAN/ZIF8@E coli nanocomposite was characterized using electron scanning microscopy and various spectroscopy techniques. Factors affecting the proposed extraction method were screened and optimized using the experiment design strategy. Then, the model analytes were measured by high-performance liquid chromatography (HPLC) with ultraviolet (UV) detector after microextraction. Satisfactory figures of merit were obtained for suggested TFME-HPLC-UV under optimum conditions. The suitable linearity varied in the range of 0.5-200 µg L-1 with R2 greater than 0.9968. The limit of detections for Hexaflumuron and Teflubenzuron were 0.12 and 0.15 µg L-1, respectively. The application of the method in the real sample was investigated by analyzing the selected analytes in environmental water and food samples. The spiking recovery of the selected analytes varied in the range of 93.0-109.8 % (RSD≤7.68). The results confirm the efficient application of this new sorbent in TFME approach. Considering the high availability, ease of production, and environmental friendliness of bacteria along with the significant improvement of metal-organic framework (MOF) growth efficiency, biomimetic mineralization is expected to be efficient method for the synthesis of ordered MOFs for use in extraction fields.

Keggin-type polyoxometalate embedded polyvinylidene fluoride for thin film microextraction of organophosphorus pesticides.

The present research is the first report on the application of Keggin-type phosphotungstic acid/polyvinylidene fluoride membrane. This compound as a simple, cost-effective and novel sorbent was used for the extraction and pre-concentration of two organophosphorus pesticides in real samples in the thin film solid-phase microextraction (TFME) method. TFME as one of the sub-branches of solid phase microextraction resolves the problems of SPME methods, including their limited absorption capacity. These extraction methods have a high surface-to-volume ratio, which improves their sensitivity compared to other geometries. Under optimal conditions, the limit of detections (LODs), the limit of quantifications (LOQs), and relative standard deviation (RSD) of this method varied in the ranges of 0.29-0.31 µg L-1, 0.96-1.0 µg L-1, and 3.9%-6.2%, respectively. This method showed a linear dynamic range (LDR) of 1.0-500 µg L-1 with a coefficient of determination (r2) above 0.9978. This promising method was used to analyze malathion and diazinon.

Nanoporous carbon fiber derived from Cu-BDC metal organic framework @pencil graphite as a sorbent for solid phase microextraction of acetamiprid and imidacloprid.

Solid-phase microextraction (SPME) is a sample pretreatment technique for enrichment of trace level of compounds from complex matrices. The fiber coating, as an extraction phase, is the significant part of SPME, which specifying the analytical performance of the developed SPME. In this study, a novel in situ fabricated Cu@porous carbon fiber that derived from copper benzene-1,4-dicarboxylate framework@pencil graphite (Cu-BDC MOF@PG) fiber was prepared as a SPME fiber. The Cu-BDC MOF was electrodeposited on the surface of pencil graphite. The Cu@porous carbon fiber with nanoporous structure was constructed by the direct carbonization of the electrosynthesized fiber. The Cu@porous carbon fiber showed high analytical performance for direct immersion SPME (DI-SPME) of acetamiprid and imidacloprid in fruit and vegetable samples. The SPME method was coupled by high-performance liquid chromatography-ultraviolet detection (SPME-HPLC-UV) for determination of the analytes. Under the optimized condition, good linear ranges (1-500 µg L-1 and 0.5-200 µg L-1) and acceptable limits of detection (LODs = 0.30 and 0.15 µg L-1), appropriate spiking recoveries in the range 87-109.0% were attained for acetamiprid and imidacloprid, respectively. Intra- and inter-day relative standard deviations were found within the ranges of 2.35-3.46% and 3.30-3.70%, respectively. These results signify promising potential of the in situ fabricated porous carbon fiber for SPME applications. Considering that most of the pencil graphite is made of carbon, after the carbonization of the Cu-BDC MOF@PG fiber, a unified porous carbon fiber is obtained. Compared to other reported procedures, in situ direct carbonization of Cu-BDC MOF@PG fiber was a one-step and straightforward method to fabricate carbon fiber.

Keggin type phosphotungstic acid intercalated copper-chromium-layered double hydroxide reinforced porous hollow fiber as a sorbent for hollow fiber solid phase microextraction of selected chlorophenols besides their quantification via high performance liquid chromatography.

Herein, a copper-chromium-layered double hydroxide (Cu/Cr-LDH) was synthesized by the co-precipitation method. The Cu/Cr-LDH was intercalated to the Keggin-type polyoxometalate (H3PW12O40). The modified LDH accommodated in the pores of hollow fiber (HF), to prepare the extracting device for the HF-solid phase microextraction method (HF-SPME). The method was used for the extraction of 4-chlorophenol, 2,4-dichlorophenol, and 2,4,6- trichlorophenol from tap water, river water, and tea sample. The extracted target analytes were quantified via high-performance liquid chromatography-UV detection. The figures of merit of the method such as, linear dynamic ranges (LDRs), limit of detections (LODs) and, limit of quantifications (LOQs), were determined based on the obtained optimum condition. Based on the results, the LDR was between 1 and 500 µg L - 1 and r2 higher than 0.9960. The LODs and LOQs were obtained in the ranges of 0.28-0.36 µg L - 1 and 0.92-1.1 µg L - 1, respectively. The relative standard deviations ((RSDs% for inter-and intra-day) of the method for the extraction of target analytes were calculated in two different concentrations of (2 and 10 µg L - 1) and (5 and 10 µg L - 1) between 3.70% - 5.30% and 3.50% - 5.70%-respectively. The enrichment factors were obtained between 57 and 61. In order to investigate the accuracy of the method, also the relative recovery was obtained, between 93 and 105%. Finally, the proposed method was used for the extraction of the selected analytes in different water and tea samples.

Electrochemical aptasensor based on carboxylated graphene oxide modified carbon paste electrode for strontium ultrasensitive detection.

Determination of strontium ions (Sr2+) is crucial with regard to human health and environmental protection. In this work, an electrochemical aptasensor was designed using carboxylated graphene oxide (CGO)-modified carbon paste electrode (CGO/CPE) for ultrasensitive determination of Sr2+ ions. The electrochemical determination was accomplished with employing the constructed G-quadruplex (G4) aptamer at the surface of aptasensor in presence of carmoisine (CA) as an electrochemical label. Moreover, NH2-functionalized aptamer was immobilized onto CGO/CPE via carboxylic group. Hence, differential pulse voltammetry was applied for detection of any possible signal changes of CA on the aptasensor surface. The reduction peak currents of CA in the absence and presence of Sr2+ in solution were different and this difference was linearly dependent to the concentration of Sr2+ in solution. The analytical results revealed that our novel aptasensor showed two appropriate linear ranges (0.1-8.0 pM and 3.0-20.0 nM) versus to Sr2+ ion concentrations with the limit of detection of 0.06 pM (S/N = 3). Excellent stability, selectivity and reproducibility were achieved with this new electrochemical aptasensor. Additionally, the aptasensor showed good achievements in analysis of Sr2+ in aqueous and urine real samples, which making this proposed method a promising candidate for electrochemical detection of Sr2+ in real samples.

Combination of in-situ electro synthesized Zn-Al-LDH@ pencil graphite fiber and three phase hollow fiber LPME for microextraction of some antibiotics in urine samples and quantification via HPLC-UV.

In the present study, a combination of two useful extraction techniques including fiber solid phase microextraction based on the new synthesized sorbent and the porous hollow fiber liquid phase microextraction is reported. The selective anion-exchangeable Zn-Al-layered double hydroxide as a fiber was electrodeposited on the surface of pencil graphite substrate through simple and cost-effective method. The prepared fiber was characterized and put into the lumen of the porous hollow fiber, which was filled by alkaline solution. The obtained optimum condition for the method was as follows: donor phase HCl concentration of 0.10 mM, acceptor phase NaOH concentration of 7.60 mM and extraction time of 16 min. It is necessary to adjust the concentration of the donor phase in order to extract acidic analytes from an aqueous sample into an organic phase. The method was used for the quantification of three antibiotics including amoxicillin, ciprofloxacin and cefixime. The extracted antibiotics were analyzed by high performance liquid chromatography-ultraviolet detection (HPLC-UV). In the optimal conditions, the linearity of the proposed method was in the range of 0.50-500.00 µg L-1 for selected analytes in water and urine matrices. All calibration curves showed determination of coefficient higher than 0.9958. The limits of detection and limits of quantification were calculated to be between 0.08 and 0.16 µg L-1 and 0.28-0.56 µg L-1, respectively. In order to define the precision of the method, the inter-day and intra-day relative standard deviations were determined between 3.25 and 5.73% in the three selected concentrations. The enrichment factors (EFs) were between 46.20 and 55.81 for selected drugs. Moreover, the calculated absolute recoveries were between 69.30 and 83.71%. The relative recoveries were obtained in the range of 93.00-105.00%. The proposed method was also employed for analysis of various urine samples containing the selected drugs. The obtained recoveries indicated that the method was useful and applicable in complicated biological samples.

In situ electrodeposition of Cu-BDC metal-organic framework on pencil graphite substrate for solid-phase microextraction of some pesticides.

The study focuses on the electrochemical deposition of copper benzene-1,4-dicarboxylate framework (Cu-BDC MOF) on the surface of a very cheap pencil graphite (PG) substrate for utilization as the sorbent in fiber solid-phase microextraction (SPME) of two chosen pesticides, including abamectin and amitraz for the first time. The extracted pesticides were quantified by high-performance liquid chromatography-ultraviolet detection (HPLC-UV). The UV detector was set at 236 nm wavelength. Based on the optimized condition, the presented technique showed a good linear range (2-500 µg L-1 and 2-100 µg L-1), suitable limits of detections (LODs = 0.60 and 0.5 µg L-1), satisfactory enhancement factors (EFs = 128 and 105), good absolute recoveries (ARs% = 64% and 53%) and spiking recoveries in the range 87.4-110.0% for amitraz and abamectin, respectively. Intra- and inter-day relative standard deviations were found within the range 1.2-3.8% and 0.6-1.9%, respectively. The method was successfully employed for the quantification of the selected pesticides in strawberry juice, lemon juice, orange juice, tomato juice, and honey.

Phytic acid determination in food products using the extract of rice sprout and SBA@DABCO nanoparticle-modified filter paper as a novel electrochemical biosensor.

We outline the fabrication of a highly sensitive biosensor for phytic acid (PA) determination using the extract of rice sprout and SBA@DABCO nanoparticles. The nanoparticles were first added to the surface of small paper disks. After drying, the extract of rice sprout in phosphate buffered saline was immobilized on the paper disks. FT-IR spectroscopy, XRD, and SEM were employed for the characterization of the nanoparticles. The assembly process of the modified paper disks on top of graphite screen-printed electrodes was investigated by cyclic voltammetry and electrochemical impedance spectroscopy. PA measurements were performed by differential pulse voltammetry (DPV) with a small amount of sample (7 µL) for analysis. The cooperation of the rice sprout extract and the nanostructure of this biosensor led to the selective and sensitive electrochemical determination of PA. The limit of detection (S/N = 3) and linear dynamic range for PA determination by DPV were obtained at 0.04 µM and 0.1-10.0 µM, respectively. The biosensor showed excellent sensitivity for the determination of PA in real samples such as biscuits and wheat flour.

Designing a novel DNA-based electrochemical biosensor to determine of Ba2+ ions both selectively and sensitively.

This work describes a novel electrochemical biosensor based on G-quadruplex (G4) DNA for the sensitive and selective detection of Ba2+ ions using a Carbon Paste Electrode modified with Ag nanoparticles incorporated in reduced Graphene Oxide via a simple wet chemical method (Ag-rGO/CPE), in the presence of carmoisine (CA) as a new electrochemical indicator. The peak current of CA increased with increasing Ba2+ ions concentration and the DNA-based sensor showed linear ranges of 0.06-0.80 nM and 1.0-80 nM and a Limit of Detection (LOD) of 0.045 nM. The proposed biosensor showed a good selectivity toward Ba2+ ions in the presence of other metal ions such as Ag+, Hg2+, K+ and Na+ and was applied to the analysis of natural samples showing appropriate results.

A descrição matemática da análise eletroquímica do fármaco hidroxizina em soluções ácidas sobre um ácido sulfônico, baseado num polímero condutor / The mathematical description for the electrochemical analysis of hydroxyzine drug in acid solution over a conducting-polymer based sulfonic acid

RESUMO Um caso interessante da aplicação dos polímeros condutores funcionalizados na análise do fármaco hidroxizina em soluções ácidas vem sendo descrito do ponto de vista teórico. Um modelo matemático, correspondente ao caso, é desenvolvido e analisado mediante a teoria de estabilidade linear e da análise de bifurcações. Foi detectado que o uso de um polímero condutor de natureza ácida no processo pode deixar o uso das soluções menos ácidas do fármaco sem prejuízo para a eficiência eletroanalítica. Outrossim, foi avaliada a influência para o processo do comportamento dos grupos amina. A possibilidade das instabilidades oscilatória e monotônica também foi verificada.

SUMMARY An interesting case of the application of the functionalized conducting polymer in the analysis of hydroxyzine drug in acid solutions is described from the theoretical point of view. A mathematical model, correspondent to the case, is developed and analyzed by means of linear stability theory and bifurcation analysis. It was detected that the use of an acid conducting polymer may permit the use of less acid solution without mischief of the electroanalytical efficiency. Moreover, the influence of the aminogroups' behavior to the process was also evaluated. The possibility of the oscillatory and monotonic instabilities has also been verified.

Evaluación teórica del desempeño del electrodo, modificado por el oxihidróxido de cobalto (III) en la detección del ácido úrico / Theoretical evaluation of the work of the electrode, modified by cobalt (III) oxyhydroxide, in the uric acid detection

RESUMEN La posibilidad del empleo de oxihidróxido de cobalto como modificador del electrodo en la detección del ácido úrico se investigó desde el punto de vista teórico. Se sugiere el mecanismo del desempeño del compuesto inorgánico en el proceso, y el modelo, correspondiente al proceso, se analizó mediante la teoría de estabilidad lineal y análisis de bifurcaciones. Se concluye que el oxihidróxido de cobalto puede servir como un modificador eficiente, facilitando la oxidación del analito en medio neutro en el modo galvanostático. La inestabilidad monotónica para este caso no puede realizarse, y la oscilatoria es causada por el único factor.

SUMMARY The possibility of use of cobalt oxyhydroxide as an electrode modifier in the uric acid determination has been investigated from the theoretical point of view. The mechanism of the use of the inorganic compound in the process has been suggested, and the model, correspondent to the process, has been analyzed by means of linear stability theory and bifurcation analysis. It has been concluded that the cobalt oxyhydroxide may serve as an efficient modifier, making easier the analyte oxidation in neutral media in galvanostatic mode. The monotonic instability for this case isn't capable to realize, and the oscillatory behavior is caused by the unique factor.

An impedimetric biosensor for DNA damage detection and study of the protective effect of deferoxamine against DNA damage.

The detection and inhibition of DNA damage are of great importance in the prevention and treatment of diseases. Developing a simple and sensitive tool for this purpose would be a chance to monitor the DNA damage and could be helpful in introducing some drugs which can prevent this phenomenon. Here, we report a novel and sensitive electrochemical biosensor based on DNA/Au nanoparticles (AuNPs) modified screen printed gold electrode (DNA/AuNPs/SPGE) to investigate the DNA damage process and also to study the protective behavior of deferoxamine (DFO). The proposed biosensor was fabricated by electrodeposition of AuNPs onto SPGE, followed by chemical immobilisation of thiol-terminated DNA. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) have been used to characterise this biosensor. Hydroxyl radical (OH), which is generated during the Fenton reaction, is responsible for the induced damage to DNA. EIS technique was applied to monitor the DNA damage, and the increase in charge transfer resistance (Rct) following the DNA damage, was considered as an indicator. Furthermore, the ability of the electrochemical screening system was proved by the investigation of the antioxidant effect of DFO in prohibiting the DNA damage.

A detecção eletroquímica da lidocaína sobre o oxihidróxido de cobalto trivalente. Uma possibilidade teórica a ser avaliada / Lidocaine CoO(OH)-assisted electrochemical determination. A theoretical possibility to be evaluated

RESUMO O comportamento eletroquímico da lidocaína durante a sua eletrooxidação sobre o oxihidróxido de cobalto trivalente em meio levemente básico, realizada para fins eletroanalíticos, foi avaliado do ponto de vista mecanístico matemático. Da análise foi feita uma conclusão acerca do desempenho do CoO(OH) como modificador de elétrodo na eletrooxidação da lidocaína in vivo e in vitro. Foi, outrossim, verificada a possibilidade da realização das instabilidades oscilatória e monotônica no sistema.

Summary The electrochemical behavior of lidocaine during its electrooxidation over trivalent cobalt oxyhydroxide in lightly alkaline medium, realized for electroanalytical purposes, was evaluated from the mechanistic mathematical point of view. From analysis a conclusion has been made of the electroanalytical function of CoO(OH) as an electrode modifier for lidocaine electrooxidation in vivo and in vitro. Also, the possibility of oscillatory and monotonic instabilities has been verified in the system.

Development of a new paper based nano-biosensor using the co-catalytic effect of tyrosinase from banana peel tissue (Musa Cavendish) and functionalized silica nanoparticles for voltammetric determination of l-tyrosine.

In this paper, a new and facile method for the electrochemical determination of l-tyrosine was designed. First, 3-mercaptopropyl trimethoxysilane-functionalized silica nanoparticles were added to a paper disc. Then, the banana peel tissue and the mediator potassium hexacyanoferrate were dropped onto the paper, respectively. The modified paper disc was placed on the top of the graphite screen printed electrode and electrochemical characterization of this biosensor was studied by cyclic voltammetry and electrochemical impedance spectroscopy methods. The effective parameters like pH, banana peel tissue percentage, and the amount of mediator loading were optimized. l-tyrosine measurements were done by differential pulse voltammetry with a little sample (3 µL) for analysis. The biosensor showed a linear response for l-tyrosine in the wide concentration range of 0.05-600 µM and a low detection limit about 0.02 µM because of the co-catalytic effect of enzyme and nanoparticles. The stability of the biosensor and its selectivity were evaluated. This biosensor was applied for the voltammetric determination of l-tyrosine in the blood plasma sample. The results of the practical application study were comparable with the standard method (HPLC). In conclusion, a simple, inexpensive, rapid, sensitive and selective technique was successfully applied to the l-tyrosine analysis of the little samples.

Design of an electrochemical DNA-based biosensor for selective determination of cadmium ions using a DNA hybridization indicator.

A simple electrochemical DNA- based biosensor was designed for determination of Cd2+ using ethyl green (EG) as a DNA hybridization indicator on the surface of carbon paste electrode (CPE). The interaction of Cd2+ with double strand DNA (dsDNA) led to the destabilizing of dsDNA and the increase in the reduction peak currents of EG. The difference in the values of electrochemical responses of EG before and after DNA helix destabilization in the presence of Cd2+ (ΔI) was used for Cd2+ determination and was linearly related to the concentration of Cd2+ over the ranges of 1.0pM-1.0nM and 10.0nM-1.0µM. Detection limit was achieved as low as 0.3pM using simple and low cost working electrode and without applying any materials for modification of electrode or DNA. The proposed biosensor was utilized successfully to real sample analysis of Cd2+.

El mecanismo de la electrooxidación de procarbacina y su descripción matemática / The procarbazine electrooxidation mechanism and its mathematical description

RESUMEN Al proceso de la electrooxidación de procarbacina fue atribuido el mecanismo, incluyendo dos etapas electroquímicas y las dos químicas. También, ha sido desarrollado y analizado un modelo matemático, capaz de describir el comportamiento del sistema. Por su intermedio, se dio la posibilidad de comparar el comportamiento de este sistema con el de los semejantes y análogos, como con el sistema de la electrosíntesis de monómeros.

SUMMARY A mechanism, including two electrochemical and two chemical stages, has been attributed to the procarbazine electrooxidation. Also, a mathematical model, capable to describe the system's behavior, has been developed. My its means, it was possible to compare the behavior of this system with that of the monomers' electrosynthesis.

A descrição matemática da eletrooxidação de dopamina, acompanhada por sua eletropolimerização / The mathematical description for the dopamine electrooxidation, accompanied by its electropolymerization

RESUMO Um caso interessante da eletrooxidação de dopamina, acompanhada por sua eletropolimerização, em que tanto o monômero, como o polímero condutor resultante podem ser oxidados até à respectiva forma quinônica, foi investigado do ponto de vista teórico. A análise do modelo matemático, correspondente a este sistema, mostrou que o estado estacionário, neste sistema é fácil de manter estável, apesar de a zona topológica, correspondente a esta estabilidade, ser mais estreita. Já as instabilidades oscilatória e monotônica mostraram-se mais prováveis neste caso que em sistemas semelhantes.

SUMMARY An interesting case for dopamine electrooxidation, in which either a monomer, or a polymer may be oxidized to the correspondent quinonic form, has been investigated from the theoretical point of view. The analysis o the correspondent mathematical model has shown that in this system the steady-state is easy to maintain stable, despite of the more narrow extension of the topological zone, correspondent to this stability. Yet the oscillatory and monotonic instabilities may be more probable in this cast, than in the similar ones.

Construction of a highly sensitive signal-on aptasensor based on gold nanoparticles/functionalized silica nanoparticles for selective detection of tryptophan.

In this work, a highly sensitive, low-cost, and label-free aptasensor based on signal-on mechanisms of response was developed by immobilizing the aptamer on gold nanoparticles (AuNPs)/amine-functionalized silica nanoparticle (FSN)/screen-printed electrode (SPE) surface for highly selective electrochemical detection of tryptophan (Trp). The hemin (Hem), which interacted with the guanine bases of the aptamer, worked as a redox indicator to generate a readable electrochemical signal. The changes in the charge transfer resistance have been monitored using the voltammetry and electrochemical impedance spectroscopic (EIS) techniques. The peak current of Hem linearly increased with increasing concentration of Trp, in differential pulse voltammetry, from 0.06 to 250 nM with a detection limit of 0.026 nM. Also, the results obtained from EIS studies showed that the Trp was detected sensitively with the fabricated aptasensor in the range of 0.06-250 nM. The detection limit is 0.01 nM, much lower than that obtained by most of the reported electrochemical methods. The usage of aptamer as a recognition layer led to a sensor with high affinity for Trp, compared with control amino acids of tyrosine, histidine, arginine, lysine, valine, and methionine. The usability of the aptasensor was successfully evaluated by the determination of Trp in a human blood serum sample. Thus, the sensor could provide a promising plan for the construction of aptasensors. Graphical abstract Schematic outline the principle for tryptophan aptasensing.

A avaliação mecanística teórica da utilização de oxihidróxido de cobalto (III) em sensores eletroquímicos de tramadol / The mechanistic theoretical evaluation of the use of cobalt (III) oxyhydroxide in electrochemical sensors of tramadol

RESUMO A possibilidade da detecção eletroquímica de tramadol in vivo e in vitro por meio do sensor, baseado em oxihidróxido de cobalto trivalente e no seu compósito com polímeros condutores, foi avaliada do ponto de vista mecanístico. O modelo matemático, correspondente ao mecanismo de oxidação sugerido, foi desenvolvido e analisado, mediante a teoria de estabilidade linear e da análise de bifurcações. Foi detectado que CoO(OH) pode aplicar-se na detecção eletroquímica de tramadol nos valores de pH neutros e levemente alcalinos, correspondentes à oxidação mais eficiente do composto. A possibilidade da aparição de instabilidades oscilatória e monotônica também foi verificada.

SUMMARY The possibility of tramadol in vivo and in vitro electrochemical determination by means of the sensor, based on cobalt (III) oxyhydroxide and its composite with conducting polymers was evaluated from the mechanistic point of view. The mathematical model, correspondent to the suggested mechanism, was developed and analyzed by means of linear stability theory and bifurcation analysis. It was shown that CoO(OH) may be applied to the tramadol electrochemical determination in neutral and lightly alkaline pH values, correspondent to the more efficient oxidation of the compound. The possibility of oscillatory and monotonic instabilities has also been modified.

Design of a novel electrochemical biosensor based on intramolecular G-quadruplex DNA for selective determination of lead(II) ions.

An electrochemical DNA biosensor based on a G-quadruplex (G4) for the sensitive determination of Pb2+ was reported using a carbon paste electrode (CPE) or a multi-walled carbon nanotube paste electrode (MWCNTPE) as working electrodes, ethyl green (EG) as a new G4 intercalator, and a single-stranded nucleic acid sequence rich in guanine (G) as DNA probe. Electrochemical determination of Pb2+ relied on probe structural changes from single - stranded to the stabilized intramolecular G4 in the presence of Pb2+, which caused a change in the current of the EG reduction peak due to the intercalation of EG into the G4 structure. The change in the reduction peak of EG before and after its intercalation into the stabilized G4 (∆I) had a linear correlation to the concentration of Pb2+ ions. The linear ranges of 4.0 × 10-10-5.0 × 10-9 M and 2 × 10-7-1 × 1-5 M with a detection limit (LOD) of 1.04 × 10-10 M were obtained using CPE, while improved linear ranges of 4.0 × 10-11-1.0 × 10-9 M and 2 × 10-7-1 × 10-5 M with a lower LOD of 2.64 × 10-11 M were achieved using the MWCNTPE biosensor. The biosensors exhibited satisfactory results in terms of selectivity and practical applicability in the analysis of real samples. Graphical abstract The principle of the electrochemical sensing of Pb2+ based on intramolecular G-quadruplex using EG.