An enzymeless organophosphate pesticide sensor using Au nanoparticle-decorated graphene hybrid nanosheet as solid-phase extraction

A sensitive enzymeless organophosphate pesticides (OPs) sensor is fabricated by using Au nanoparticles (AuNPs) decorated graphene nanosheets (GNs) modified glassy carbon electrode as solid phase extraction (SPE). Such a nanostructured composite film, combining the advantages of AuNPs with two dimensional GNs, dramatically facilitates the enrichment of nitroaromatic OPs onto the surface and realizes their stripping voltammetric detection of OPs by using methyl parathion (MP) as a model. The stripping voltammetric performances of captured MP were evaluated by cyclic voltammetric and square-wave voltammetric analysis. The combination of the nanoassembly of AuNPs-GNs, SPE, and stripping voltammetry provides a fast, simple, and sensitive electrochemical method for detecting nitroaromatic OPs. The stripping analysis is highly linear over the MP concentration ranges of 0.001-0.1and 0.2-1.0 μg mL⁻¹ with a detection limit of 0.6 ng mL⁻¹. This designed enzymeless sensor exhibits good reproducibility and acceptable stability.     

Ultrasensitive electrochemical sensor for p-nitrophenyl organophosphates based on ordered mesoporous carbons at low potential without deoxygenization

p-Nitrophenyl organophosphates (OPs) including paraoxon, parathion and methyl parathion, etc, are highly poisonous OPs, for which sensitive and rapid detection method is most needed. In this work, an ultrasensitive electrochemical sensor for the determination of p-nitrophenyl OPs was developed based on ordered mesoporous carbons (OMCs) modified glassy carbon electrode (GCE) (OMCs/GCE). The electrochemical behavior and reaction mechanism of p-nitrophenyl OPs at OMCs/GCE was elaborated by taking paraoxon as an example. Experimental conditions such as buffer pH, preconcentration potential and time were optimized. By using differential pulse voltammetry, the current response of the sensor at −0.085 V was linear with concentration within 0.01–1.00 μM and 1.00–20 μM paraoxon. Similar linear ranges of 0.015–0.5 μM and 0.5–10 μM were found for parathion, and 0.01–0.5 μM and 0.5–10 μM for methyl parathion. The low limits of detection were evaluated to be 1.9 nM for paraoxon, 3.4 nM for parathion and 2.1 nM for methyl parathion (S/N = 3). Common interfering species had no interference to the detection of p-nitrophenyl OPs. The sensor can be applicable to real samples measurement. Therefore, a simple, sensitive, reproducible and cost-effective electrochemical sensor was proposed for the fast direct determination of trace p-nitrophenyl OPs at low potential without deoxygenization.     

A Highly Efficient ZrO2 Nanoparticle Based Electrochemical Sensor for the Detection of Organophosphorus Pesticides

A sensitive electrochemical method for square‐wave voltammetric detection of organophosphate (OP) compounds was developed based on zirconia (ZrO₂) nanoparticles modified electrode. The electrode was fabricated using electrochemical deposition and characterized by scanning electron microscopy (SEM), which confirmed the successful formation of nanoparticles. Due to the strong affinity of ZrO₂ with the phosphoric group, nitroaromatic OPs can strongly bind to the surface of ZrO₂ nanoparticles (ZrO₂NPs). Under optimized operational conditions, SWV was employed for Omethoate (a model of OP compounds) detection with 5 min absorption, which showed a wide detection range from 98.5 pmol·L^?1 to 985 nmol·L^?1, with a detection limit as low as 52.5 pmol·L^?1. This electrochemical sensor has good selectivity, stability and reproducibility, and great potential in the detection of OP compounds in agriculture area.     

Stripping voltammetric analysis of organophosphate pesticides based on solid-phase extraction at zirconia nanoparticles modified electrode

A sensitive electrochemical stripping voltammetric method for analyzing organophosphate (OP) compounds was developed based on solid-phase extraction (SPE) at zirconia (ZrO₂) nanoparticles modified electrode. ZrO₂ nanoparticles were proved as a new sorbent for SPE of OP pesticides. Because of the strong affinity of ZrO₂ for the phosphoric group, nitroaromatic OPs can strongly bind to the ZrO₂ nanoparticle surface. The combination of SPE with square-wave voltammetry (SWV) provided a fast, sensitive, and selective electrochemical method for nitroaromatic OP compounds using methyl parathion (MP) as a model. The stripping response was highly linear over the MP range of 0.003–2.0 μg/mL, with a detection limit of 0.001 μg/mL. The fast extraction ability of ZrO₂ nanoparticles makes it promising sorbent for various solid-phase extractions.     

A novel nonenzymatic hydrogen peroxide sensor based on multi-wall carbon nanotube/silver nanoparticle nanohybrids modified gold electrode

A novel strategy to fabricate hydrogen peroxide (H₂O₂) sensor was developed based on multi-wall carbon nanotube/silver nanoparticle nanohybrids (MWCNT/Ag nanohybrids) modified gold electrode. The process to synthesize MWCNT/Ag nanohybrids was facile and efficient. In the presence of carboxyl groups functionalized multi-wall carbon nanotubes (MWCNTs), silver nanoparticles (Ag NPs) were in situ generated from AgNO₃ aqueous solution and readily attached to the MWCNTs convex surfaces at room temperature, without any additional reducing reagent or irradiation treatment. The formation of MWCNT/Ag nanohybrids product was observed by transmission electron microscope (TEM), and the electrochemical properties of MWCNT/Ag nanohybrids modified gold electrode were characterized by electrochemical measurements. The results showed that this sensor had a favorable catalytic ability for the reduction of H₂O₂. The resulted sensor could detect H₂O₂ in a linear range of 0.05-17 mM with a detection limit of 5 × 10⁻⁷ M at a signal-to-noise ratio of 3. The sensitivity was calculated as 1.42 μA/mM at a potential of −0.2 V. Additionally, it exhibited good reproducibility, long-term stability and negligible interference of ascorbic acid (AA), uric acid (UA), and acetaminophen (AP).     

Electrodeposition of silver nanoparticles on a zinc oxide film: improvement of amperometric sensing sensitivity and stability for hydrogen peroxide determination

A strategy to fabricate a hydrogen peroxide (HP) sensor is developed by electrodepositing silver nanoparticles (Ag NPs) on a modified glassy carbon electrode (GCE) with a zinc oxide (ZnO) film. The Ag NPs/ZnO/GCE has been characterized by scanning electron microscopy, cyclic voltammetry, and chronoamperometry. It has been found that the Ag NPs synthesized in the presence of ZnO film provide an electrode with enhanced sensitivity and excellent stability. The sensitivity to HP is enhanced 3-fold by using Ag NPs/ZnO/GCE compared to Ag NPs/GCE. The HP sensor exhibits good linear behavior in the concentration range 2 µM to 5.5 mM for the quantitative analysis of HP with a detection limit of 0.42 µM (S/N?=?3).     

Fast functionalization of silver decahedral nanoparticles with aptamers for colorimetric detection of human platelet-derived growth factor-BB

Aptamer-silver decahedral nanoparticles (Ag₁₀NPs-aptamer) based detection was developed for protein. Ag₁₀NPs were synthesized by photochemical method. The advantage of Ag₁₀NPs was its tolerance of NaCl which facilitates the functionalization of silver nanoparticles with all kinds of ssDNA. Attaching aptamers to Ag₁₀NPs could be achieved within 2 h, much faster than traditional methods. Human platelet-derived growth factor-BB (PDGF-BB) was used as a model protein to test the binding capacity of aptamers attached on Ag₁₀NPs. Our data showed that the aptamer-Ag₁₀NPs conjugates were successful in detecting human PDGF-BB. Furthermore, we developed an aptamer-Ag₁₀NPs conjugates-based colorimetric sensor to detect PDGF-BB. The results showed a linear relationship between PDGF-BB concentrations (5 ng mL⁻¹–200 ng mL⁻¹) and ΔOD with excellent detection specificity in serum. Therefore, the sensor based on aptamer-Ag₁₀NPs conjugates was highly effective and sensitive and had great promise for further development and applications.     

Sensitive DNA biosensor improved by Luteolin copper(II) as indicator based on silver nanoparticles and carbon nanotubes modified electrode

A novel and sensitive electrochemical DNA biosensor has been developed for the detection of DNA hybridization. The biosensor was proposed by using copper(II) complex of Luteolin C₃₀H₁₈CuO₁₂ (CuL₂) as an electroactive indicator based on silver nanoparticles and multi-walled carbon nanotubes (Ag/MWCNTs) modified glassy carbon electrode (GCE). In this method, the 4-aminobenzoic acid (4-ABA) and Ag nanoparticles were covalently grafted on MWCNTs to form Ag/4-ABA/MWCNTs. The proposed method dramatically increased DNA attachment quantity and complementary ssDNA detection sensitivity for its large surface area and good charge-transport characteristics. DNA hybridization detection was performed using CuL₂ as an electroactive indicator. The CuL₂ was synthesized and characterized using elemental analysis (EA) and IR spectroscopy. Cyclic voltammetry (CV) and fluorescence spectroscopy were used to investigate the interaction between CuL₂ and ds-oligonucleotides (dsDNA). It was revealed that CuL₂ presented high electrochemical activity on GCE, and it could be intercalated into the double helices of dsDNA. The target ssDNA of the human hepatitis B virus (HBV) was quantified in a linear range from 3.23 × 10⁻¹² to 5.31 × 10⁻⁹ M (r = 0.9983). A detection limit of 6.46 × 10⁻¹³ M (3σ, n = 11) was achieved.     

Amperometric sulfite sensor based on multiwalled carbon nanotubes/ferrocene-branched chitosan composites

A novel amperometric sensor for the determination of sulfite was fabricated based on multiwalled carbon nanotubes (MWCNTs)/ferrocene-branched chitosan (CHIT-Fc) composites-covered glassy carbon electrode (GCE). The electrochemical behavior of the sensor was investigated in detail by cyclic voltammetry. The apparent surface electron transfer rate constant (K_s) and charge transfer coefficient (α) of the CHIT-Fc/MWCNTs/GCE were also determined by cyclic voltammetry, which were about 1.93 cm s⁻¹ and 0.42, respectively. The sensor displayed good electrocatalytic activity towards the oxidation of sulfite. The peak potential for the oxidation of sulfite was lowered by at least 330 mV compared with that obtained at CHIT/MWCNTs/GCE. In optimal conditions, linear range spans the concentration of sulfite from 5 μM to 1.5 mM and the detection limit was 2.8 μM at a signal-to-noise ratio of 3. The proposed method was used for the determination of sulfite in boiler water. In addition, the sensor has good stability and reproducibility.     

Analytical sensing of hydrogen peroxide on Ag nanoparticles–multiwalled carbon nanotube-modified glassy carbon electrode

A sensor based on silver nanoparticles (NPs)/multiwalled carbon nanotube (CNT)-modified glassy carbon electrode (GCE) was prepared and employed for accurate and rapid determination of hydrogen peroxide (H₂O₂). In summary, by using a mechanochemical method, multiwalled CNTs dispersed in ethanol and used for modification of GCE. After that, by using a double-pulse technique, silver NPs are electrodeposited on surface of multiwalled CNTs/ GCE. Parameters that are affected by electrocatalytic reduction of H₂O₂ on the modified electrode, such as multiwalled CNT concentration and double-pulse parameters, were optimized using Minitab software. The optimal modified electrode was characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and cyclic voltammetry. The proposed H₂O₂ sensor exhibited excellent characteristics for the sensing of H₂O₂, such as wide linear range from 0.1 to 10 mM, a low detection limit of 2 μM, high repeatability, and no interference by a number of substances.     

An ultrasensitive electrochemical immunosensor for CA72-4 based on a signal amplification strategy of MoS2 nanoflower-supported Au nanoparticles

Accurate detection of cancer antigen 72-4 (CA72-4), a tumor-associated glycoprotein, is of great significance for gastric cancer diagnosis and immunotherapy monitoring. Modification of noble metal nanoparticles on transition metal dichalcogenides can significantly enhance functions, such as electron transport. Molybdenum disulfide gold nanoparticles nanocomposites (MoS₂-Au NPs) were prepared in this study and a series of characterization studies were carried out. In addition, a label-free, highly sensitive electrochemical immunosensor molybdenum disulfide -Au nanoparticles/Glassy carbon electrode (MoS₂-Au NPs/GCE) was also prepared and used for the detection of CA72-4. The electrochemical performance of the immunosensor was characterized by electrochemical techniques, such as cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). The results indicated that better MoS₂-Au NPs nanomaterials have been synthesized, and the prepared electrochemical immunosensor, MoS₂-Au NPs/GCE, showed excellent electrochemical performance. The sensor exhibited high detection sensitivity under optimal conditions, including an incubation time of 30 min, an incubation temperature of 25 °C, and a pH of 7.0. The electrochemical immunosensor also had a low detection limit of 2.0 × 10^?5 U/mL (S/N = 3) in a concentration range of 0.001–200 U/mL, with good selectivity, stability, and repeatability. In conclusion, this study provided a theoretical basis for the highly sensitive detection of tumor markers in clinical biological samples.     

Ag nanoparticles decorated Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/chitosan nanocomposite: synthesis,characterization and application toward electrochemical sensing of hydrogen peroxide

We studied a rapid, sensitive and selective amperometric sensor for determination of hydrogen peroxide by electrodeposited Ag NPs on a modified glassy carbon electrode (GCE). The modified GCE was constructed through a step by step modification of magnetic chitosan functional composite (Fe₃O₄–CH) and high-dispersed silver nanoparticles on the surface. The resulted Ag@Fe₃O₄–CH was characterized by various analytical methods including Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, scanning electron microscopy and cyclic voltammetry. The proposed sensor employed Ag@Fe₃O₄–CH/GCE as the working electrode with a linear current response to the hydrogen peroxide concentration in a wide range from 0.01 to 400 µM with a low limit of detection (LOD = 0.0038 µM, S/N = 3). The proposed sensor showed superior reproductivity, sensitivity and selectivity for the detection of hydrogen peroxide in environmental and clinical samples.     

Colorimetric detection of iron ions (III) based on the highly sensitive plasmonic response of the N-acetyl-l-cysteine-stabilized silver nanoparticles

We report here a facile colorimetric sensor based on the N-acetyl-l-cysteine (NALC)-stabilized Ag nanoparticles (NALC–Ag NPs) for detection of Fe³⁺ ions in aqueous solution. The Ag NPs with an average diameter of 6.55 ± 1.0 nm are successfully synthesized through a simple method using sodium borohydride as reducing agent and N-acetyl-l-cysteine as protecting ligand. The synthesized silver nanoparticles show a strong surface plasmon resonance (SPR) around 400 nm and the SPR intensity decreases with the increasing of Fe³⁺ concentration in aqueous solution. Based on the linear relationship between SPR intensity and concentration of Fe³⁺ ions, the as-synthesized water-soluble silver nanoparticles can be used for the sensitive and selective detection of Fe³⁺ ions in water with a linear range from 80 nM to 80 μM and a detection limit of 80 nM. On the basis of the experimental results, a new detection mechanism of oxidation–reduction reaction between Ag NPs and Fe³⁺ ions is proposed, which is different from previously reported mechanisms. Moreover, the NALC–Ag NPs could be applied to the detection of Fe³⁺ ions in real environmental water samples.     

Assessment of Melamine in Different Water Samples with ZnO-doped Co3O4 Nanoparticles on a Glassy Carbon Electrode by Differential Pulse Voltammetry

In this investigation, a melamine electrochemical sensor has been developed by using wet-chemically synthesized low-dimensional aggregated nanoparticles (NPs) of ZnO-doped Co₃O₄ as sensing substrate that were decorated onto flat glassy carbon electrode (GCE). The characterization of NPs such as UV-Vis, FTIR, XRD, XPS, EDS, and FESEM was done for detailed investigations in optical, functional, structural, elemental, and morphological analyses. The ZnO-doped Co₃O₄ NPs decorated GCE was used as a sensing probe to analyze the target chemical melamine in a phosphate buffer at pH 5.7 by applying differential pulse voltammetry (DPV). It exhibited good performances in terms of sensor analytical parameters such as large linear dynamic range (LDR; 0.15–1.35 mM) of melamine detection, high sensitivity (80.6 μA mM⁻¹ cm⁻²), low limit of detection (LOD; 0.118±0.005 mM), low limit of quantification (LOQ; 0.393 mM), and fast response time (30 s). Besides this, the good reproducibility (in several hours) and repeatability were investigated under identical conditions. Moreover, it was implemented to measure the long-time stability, electron mobility, less charge-transfer resistance, and analyzed diffusion-controlled process for the oxidation reaction of the NPs assembled working GCE electrode, which showed outstanding chemical sensor performances. For validation, real environmental samples were collected from various water sources and investigated successfully with regard to the reliability of the selective melamine detection with prepared NPs coated sensor probe. Therefore, this approach might be introduced as an alternative route in the sensor technology to detect selectively unsafe chemicals by an electrochemical method with nanostructure-doped materials for the safety of environmental, ecological, healthcare fields in a broad scale.     

Selective detection of dopamine in the presence of uric acid using a gold nanoparticles-poly(luminol) hybrid film and multi-walled carbon nanotubes with incorporated β-cyclodextrin modified glassy carbon electrode

Gold nanoparticles-poly(luminol) (Plu-AuNPs) hybrid film and multi-walled carbon nanotubes with incorporated β-cyclodextrin modified glassy carbon electrode (β-CD-MWCNTs/Plu-AuNPs/GCE) was successfully prepared for simultaneous determination of dopamine (DA) and uric acid (UA). The surface of the modified electrode has been characterized by X-ray photo-electron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS), field-emission scanning electron microscope (SEM) and transmission electron microscope (TEM). Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV) have been used to investigate the β-CD-MWCNTs/Plu-AuNPs composite film. Gold nanoparticles anchored into poly(luminol) film exhibited catalytic activity for DA. MWCNTs with incorporated β-CD can greatly promote the direct electron transfer. In 0.10 M phosphate buffer solution (PBS, pH 7.0), the DPV response of the β-CD-MWCNTs/Plu-AuNPs/GCE sensor to DA is about 8-fold as compared with the Plu-AuNPs/GCE sensor, and the detection limit for DA is about one order of magnitude lower than the Plu-AuNPs/GCE sensor. The steady-state current response increases linearly with DA concentration from 1.0 × 10⁻⁶ to 5.6 × 10⁻⁵ M with a low detection limit (S/N = 3) of 1.9 × 10⁻⁷ M. Moreover, the interferences of ascorbic acid (AA) and uric acid (UA) are effectively diminished. The applicability of the prepared electrode has been demonstrated by measuring DA contents in dopamine hydrochloride injection.     

Electrochemical deoxyribonucleic acid biosensor based on carboxyl functionalized graphene oxide and poly-l-lysine modified electrode for the detection of tlh gene sequence related to vibrio parahaemolyticus

A carboxyl functionalized graphene oxide (GO-COOH) and electropolymerized ploy-l-lysine (PLLy) modified glassy carbon electrode (GCE) was fabricated and used for the construction of an electrochemical deoxyribonucleic acid (DNA) biosensor. The NH₂ modified probe ssDNA sequences were immobilized on the surface of GO-COOH/PLLy/GCE by covalent linking with the formation of amide bonds, which was stable and furthur hybridized with the target ssDNA sequence. Differential pulse voltammetry (DPV) was used to monitor the hybridization events with methylene blue as electrochemical indicator, which gave a sensitive reduction peak at −0.287 V (vs. SCE). Under the optimal conditions the reduction peak current was proportional to the concentration of tlh gene sequence in the range from 1.0 × 10⁻¹² to 1.0 × 10⁻⁶ mol L⁻¹ with a detection limit as 1.69 × 10⁻¹³ mol L⁻¹ (3σ). The polymerase chain reaction products of tlh gene from oyster samples were detected with satisfactory results, indicating the potential application of this electrochemical DNA sensor.     

Copper hexacyanoferrate multilayer films on glassy carbon electrode modified with 4-aminobenzoic acid in aqueous solution

4-Aminobenzoic acid (4-ABA) was covalently grafted on a glassy carbon electrode (GCE) by amine cation radical formation during the electrooxidation process in 0.1 M KCl aqueous solution. X-ray photoelectron spectroscopy (XPS) measurement proves the presence of 4-carboxylphenylamine on the GCE. Electron transfer processes of Fe(CN)₆³⁻ in solutions of various pHs at the modified electrode are studied by both cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Changing the solution pH would result in the variation of the terminal group's charge state, based on which the surface pK_a values were estimated. The copper hexacyanoferrate (CuHCF) multilayer films were formed on 4-ABA/GCE prepared in aqueous solution, and which exhibit good electrochemical behavior with high stability.     

A Hafnium Oxide Based Voltammetric Platform for the Sensitive Determination of Octopamine

An electrochemical sensor was constructed by modification of a glassy carbon electrode (GCE) with nanoparticles of hafnium oxide (HfO₂) and multi-walled carbon nanotubes (MWCNTs) for the sensitive determination of octopamine. The platform (HfO₂NPs/MWCNTs/GCE) presented an improved anodic peak for octopamine at 0.65 V. The combination of HfO₂ and MWCNTs resulted in outstanding catalytic activity and enhanced the magnitude of the peak response. Results suggest that a three-electron oxidation occurs for the process of octopamine. Voltammetry of octopamine exhibited a dynamic linear response in the concentration range of 1.6×10⁻⁶∼4.8×10⁻⁵ M with a detection limit of 5.4×10⁻⁷ M for octopamine.     

Sensitive Determination of Terbutaline Using a Platform Based on Nanoparticles of Europium Oxide and Carbon Nanotubes

This study presents a sensitive voltammetric determination of terbutaline (TER) on a platform based on carbon nanotubes (CNTs) and europium oxide nanoparticles (Eu₂O₃NPs) coated glassy carbon electrodes (GCEs). An ultrasonic bath was performed for the preparation of composite material. The material was characterized by energy dispersive X‐ray spectroscopy (EDX), X‐ray diffraction method (XRD) and scanning electron microscopy (SEM). The Eu₂O₃NPs/CNTs/GCE system was assessed for the oxidation of terbutaline (TER). A broad oxidation peak was appeared at 0.71 V using a bare GCE. However, the voltammetry of TER has been improved at a GCE coated with CNTs and a well‐defined anodic peak exhibited at 0.61 V. Furthermore, the nanoparticles of Eu₂O₃ and CNTs coated GCE has greatly improved the electrochemical behaviour of TER and a sharp peak was appeared at 0.59 V. Cyclic voltammetry at Eu₂O₃NPs/CNTs/GCE also reveals a high catalytic effect for the oxidation of TER with an oxidation peak that is distinctly enhanced compared to GCE and CNTs/GCE. Eu₂O₃ nanoparticles were utilized to enhance the surface area of GCE and then improve the sensitivity of the procedure. The response of TER was linear over a concentration range of 2.0×10^?8 M ?9.5×10^?6 M with an LOD of 3.7×10^?9 M. Square wave voltammetric analysis of tablets by Eu₂O₃NPs/CNTs/GCE yielded a recovery of 99.2 % with an RSD% of 3.2. The modified electrode (EuO₂NPs/CNTs/GCE) provides accuracy and precision to the analysis of samples.     

Using a photochemical method and chitosan to prepare surface-enhanced Raman scattering–active silver nanoparticles

In this paper, we report a new strategy for the preparation of surface-enhanced Raman scattering (SERS)-active silver nanoparticles (Ag NPs), using a photochemical method and the presence of chitosan (Ch). First, Ag substrates were subjected to electrochemical oxidation/reduction cycles (ORCs) in deoxygenated aqueous solutions containing 0.1 M HNO₃ and 1 g L⁻¹ Ch (pH 6.9, adjusted by adding 1 M NaOH), resulting in Ag⁺–Ch complexes. These substrates were then irradiated with UV light at various wavelengths to yield the SERS-active Ag NPs. A stronger SERS effect was observed on the SERS-active Ag NPs prepared by using UV irradiation at 310 nm. The pH of the solution and the presence of Ch during the preparation process both affected the resulting SERS activities.