Sensitive and selective electrochemical determination of quinoxaline-2-carboxylic acid based on bilayer of novel poly(pyrrole) functional composite using one-step electro-polymerization and molecularly imprinted poly(o-phenylenediamine)

A facile and efficient molecularly imprinted polymer (MIP) recognition element of electrochemical sensor was fabricated by directly electro-polymerizing monomer o-phenylenediamine (oPD) in the presence of template quinoxaline-2-carboxylic acid (QCA), based on one-step controllable electrochemical modification of poly(pyrrole)-graphene oxide-binuclear phthalocyanine cobalt (II) sulphonate (PPY-GO-BiCoPc) functional composite on glassy carbon electrode (GCE). The MIP film coated on PPY-GO-BiCoPc functional composite decorated GCE (MIP/PPY-GO-BiCoPc/GCE) was presented for the first time. The synergistic effect and electro-catalytic activity toward QCA redox of PPY-GO-BiCoPc functional composite were discussed using various contrast tests. Also, the effect of experimental variables on the current response such as, electro-polymerization cycles, template/monomer ratio, elution condition for template removal, pH of the supporting electrolyte and accumulation time, were investigated in detail. Under the optimized conditions, the proposed MIP sensor possessed a fast rebinding dynamics and an excellent recognition capacity to QCA, while the anodic current response of square wave voltammetry (SWV) was well-proportional to the concentration of QCA in the range of 1.0 × 10⁻⁸–1.0 × 10⁻⁴ and 1.0 × 10⁻⁴–5.0 × 10⁻⁴ mol L⁻¹ with a low detection limit of 2.1 nmol L⁻¹. The established sensor was applied successfully to determine QCA in commercial pork and chicken muscle samples with acceptable recoveries (91.6–98.2%) and satisfactory precision (1.9–3.5% of SD), demonstrating a promising feature for applying the MIP sensor to the measurement of QCA in real samples.     

A novel high selective and sensitive metronidazole voltammetric sensor based on a molecularly imprinted polymer-carbon paste electrode

The design and construction of a highly selective voltammetric sensor for metronidazole by using a molecularly imprinted polymer (MIP) as recognition element were introduced. A metronidazole selective MIP and a nonimprinted polymer (NIP) were synthesized and then incorporated in the carbon paste electrodes (CPEs). The sensor was applied for metronidazole determination using cathodic stripping voltammetric method. The MIP-CP electrode showed very high recognition ability in comparison to NIP-CPE. Some parameters affecting the sensor response were optimized and then the calibration curve was plotted. Two dynamic linear ranges of 5.64 × 10⁻⁵ to 2.63 × 10⁻³ mg L⁻¹ and 2.63 × 10⁻³ to 7.69 × 10⁻² mg L⁻¹ were obtained. The detection limit of the sensor was calculated as 3.59 × 10⁻⁵ mg L⁻¹. This sensor was used successfully for metronidazole determination in biological fluids.     

A novel molecularly imprinted sensor for selectively probing imipramine created on ITO electrodes modified by Au nanoparticles

A sensitive molecularly imprinted electrochemical sensor was created for selective detection of a tricyclic antidepressant imipramine by combination of Au nanoparticles (Au-NPs) with a thin molecularly imprinted film. The sensor was fabricated onto the indium tin oxide (ITO) electrode via stepwise modification of Au-NPs by self-assembly and a thin film of molecularly imprinted polymers (MIPs) via sol-gel technology. It was observed that the molecularly imprinted film displayed excellent selectivity towards the target molecule imipramine. Meanwhile, the introduced Au-NPs exhibited noticeable catalytic activities towards imipramine oxidation, which remarkably enhanced the sensitivity of the imprinted film. Due to such combination, the as-prepared sensor responded quickly to imipramine, within only 1 min of incubation. The differential voltammetric anodic peak current was linear to the logarithm of imipramine concentration in the range from 5.0 × 10⁻⁶ to 1.0 × 10⁻³ mol L⁻¹, and the detection limits obtained was 1.0 × 10⁻⁹ mol L⁻¹. This method proposed was successfully applied to the determination of imipramine in drug tablets, and proven to be reliable compared with conventional UV method. These results reveal that such a sensor fulfills the selectivity, sensitivity, speed and simplicity requirements for imipramine detection, and provides possibilities of clinical application in physiological fluids.     

A novel high selective and sensitive para-nitrophenol voltammetric sensor, based on a molecularly imprinted polymer-carbon paste electrode

By using a molecularly imprinted polymer (MIP) as a recognition element, the design and construction of a high selective voltammetric sensor for para-nitrophenol was formed. Para-nitrophenol selective MIP and a non-imprinted polymer (NIP) were synthesized, and then used for carbon paste (CP) electrode preparation. The MIP-CP electrode showed greater recognition ability in comparison to the NIP-CP. It was shown that electrode washing after para-nitrophenol extraction led to enhanced selectivity, without noticeably decreasing the sensitivity. Some parameters affecting sensor response were optimized and a calibration curve was plotted. A dynamic linear range of 8 × 10⁻⁹ to 5 × 10⁻⁶ mol L⁻¹ was obtained. The detection limit of the sensor was calculated as 3 × 10⁻⁹ mol L⁻¹. Thus, this sensor was used successfully for the para-nitrophenol determination in different water samples.     

Electrochemical determination of L-phenylalanine at polyaniline modified carbon electrode based on β-cyclodextrin incorporated carbon nanotube composite material and imprinted sol-gel film

A sensitive and selective electrochemical sensor based on a polyaniline modified carbon electrode for the determination of l-phenylalanine has been proposed by utilizing β-cyclodextrin (β-CD) incorporated multi-walled carbon nanotube (MWNT) and imprinted sol-gel film. The electrochemical behavior of the sensor towards l-phenylalanine was investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and amperometric i-t curve. The surface morphologies of layer-by-layer assembly electrodes were displayed by scanning electron microscope (SEM). The response mechanism of the imprinted sensor for l-phenylalanine was based on the inclusion interaction of β-CD and molecular recognition capacity of the imprinted film for l-phenylalanine. A linear calibration plot was obtained covering the concentration range from 5.0 × 10⁻⁷ to 1.0 × 10⁻⁴ mol L⁻¹ with a detection limit of 1.0 × 10⁻⁹ mol L⁻¹. With excellent sensitivity, selectivity, stability, reproducibility and recovery, the electrochemical imprinted sensor was used to detect l-phenylalanine in blood plasma samples successfully.     

An optical sensor for the determination of digoxin in serum samples based on a molecularly imprinted polymer membrane

This paper reports the synthesis and testing of a molecularly imprinted polymer membrane for digoxin analysis. Digoxin-specific bulk polymer was obtained by the UV initiated co-polymerisation of methacrylic acid and ethylene glycol dimethacrylate in acetonitrile as porogen. After extracting the template analyte, the ground polymer particles were mixed with plasticizer polyvinyl chloride to form a MIP membrane. A reference polymer membrane was prepared from the same mixture of monomers but with no template. The resultant membrane morphologies were examined by scanning electron microscopy. The imprinted membrane was tested as the recognition element in a digoxin-sensitive fluorescence sensor; sensor response was measured using standard solutions of digoxin at concentrations of up to 4 × 10⁻³ mg L⁻¹. The detection limit was 3.17 × 10⁻⁵ mg L⁻¹. Within- and between-day relative standard deviations RSD (n = 5) were in the range 4.5-5.5% and 5.5-6.5% respectively for 0 and 1 × 10⁻³ mg L⁻¹ digoxin concentrations. A selectivity study showed that compounds of similar structure to digoxin did not significantly interfere with detection for interferent concentrations at 10, 30 and 100 times higher than the digoxin concentration. This simply manufactured MIP membrane showed good recognition characteristics, a high affinity for digoxin, and provided satisfactory results in analyses of this analyte in human serum.     

A Biomimetic Potentiometric Sensor Using Molecularly Imprinted Polymer for the Cetirizine Assay in Tablets and Biological Fluids

Despite the increasing number of applications of molecularly imprinted polymers (MIPs) in analytical chemistry, the construction of a biomimetic potentiometric sensor remains still challenging. In this work, a biomimetic potentiometric sensor, based on a non‐covalent imprinted polymer was fabricated for the recognition and determination of cetirizine. The MIP was synthesized by precipitation polymerization, using cetirizine dihydrochloride as a template molecule, methacrylic acid (MAA) as a functional monomer and ethylene glycol dimethacrylate (EGDMA) as a cross linking agent. The sensor showed high selectivity and a sensitive response to the template in aqueous system. The MIP‐modified electrode exhibited Nernstian response (28.0±0.9 mV/decade) in a wide concentration range of 1.0×10^?6 to 1.0×10^?2 M with a lower detection limit of 7.0×10^?7 M. The electrode has response time of ca. 20 s, high performance, high sensitivity, and good long term stability (more than 5 months). The method was satisfactory and used to the cetirizine assay in tablets and biological fluids.     

Development of a sensitive and selective kojic acid sensor based on molecularly imprinted polymer modified electrode in the lab-on-valve system

In this work, a kojic acid electrochemical sensor, based on a non-covalent molecularly imprinted polymer (MIP) modified electrode, had been fabricated in the lab-on-valve system. The sensitive layer was synthesized by cyclic voltammetry using o-phenylenediamine as the functional monomer and kojic acid as the template. The template molecules were then removed from the modified electrode surface by washing with NaOH solution. Differential pulse voltammetry method using ferricyanide as probe was applied as the analytical technique, after extraction of kojic acid on the electrode. Chemical and flow parameters associated with the extraction process were investigated. The response recorded with the imprinted sensor exhibited a response in a range of 0.01-0.2 μmol L⁻¹ with a detection limit of 3 nmol L⁻¹. The interference studies showed that the MIP modified electrode had excellent selectivity. Furthermore, the proposed MIP electrode exhibited good sensitivity and low sample/reagent consumption, and the sensor could be applied to the determination kojic acid in cosmetics samples.     

Construction of a novel molecularly imprinted sensor for the determination of O,O-dimethyl-(2,4-dichlorophenoxyacetoxyl)(3′-nitrophenyl)methinephosphonate

A novel voltammetric sensor for O,O-dimethyl-(2,4-dichlorophenoxyacetoxyl)(3′-nitrophenyl)methinephosphonate (Phi-NO₂) based on molecularly imprinted polymer (MIP) film electrode is constructed by using sol-gel technology. The sensor responds linearly to Phi-NO₂ over the concentration range of 2.0 × 10⁻⁵ to 1.0 × 10⁻⁸ mol L⁻¹ and the detection limit is 1.0 × 10⁻⁹ mol L⁻¹ (S/N = 3). This sensor provides an efficient way for eliminating interferences from coexisting substances in the solution. The high sensitivity, selectivity and stability of the sensor demonstrates its practical application for a simple and rapid determination of Phi-NO₂ in cabbage samples.     

Synthesis of nano-sized arsenic-imprinted polymer and its use as As selective ionophore in a potentiometric membrane electrode: Part 1

In this study, a new strategy was proposed for the preparation of As (III)-imprinted polymer by using arsenic (methacrylate)₃ as template. Precipitation polymerization was utilized to synthesize nano-sized As (III)-imprinted polymer. Methacrylic acid and ethylene glycol dimethacrylate were used as the functional monomer and cross-linking agent, respectively. In order to assembly functional monomers around As (III) ion, sodium arsenite and methacrylic acid were heated in the presence of hydroquinone, leading to arsenic (methacrylate)₃. The nano-sized As (III) selective polymer was characterized by FT-IR and scanning electron microscopy techniques (SEM). It was demonstrated that arsenic was recognized as As³⁺ by the selective cavities of the synthesized IIP. Based on the prepared polymer, the first arsenic cation selective membrane electrode was introduced. Membrane electrode was constructed by dispersion of As (III)-imprinted polymer nanoparticles in poly(vinyl chloride), plasticized with di-nonylphthalate. The IIP-modified electrode exhibited a Nernstian response (20.4 ± 0.5 mV decade⁻¹) to arsenic ion over a wide concentration range (7.0 × 10⁻⁷ to 1.0 × 10⁻¹ mol L⁻¹) with a lower detection limit of 5.0 × 10⁻⁷ mol L⁻¹. Unlike this, the non-imprinted polymer (NIP)-based membrane electrode was not sensitive to arsenic in aqueous solution. The selectivity of the developed sensor to As (III) was shown to be satisfactory. The sensor was used for arsenic determination in some real samples.     

Molecularly imprinted polyaniline-polyvinyl sulphonic acid composite based sensor for para-nitrophenol detection

We report results of the studies relating to the fabrication and characterization of a conducting polymer based molecularly imprinted para-nitrophenol (PNP) sensor. A water pollutant, para-nitrophenol is electrochemically imprinted with polyvinyl sulphonic acid (PVSA) doped polyaniline onto indium tin oxide (ITO) glass substrate. This PNP imprinted electrode (PNPI-PANI-PVSA/ITO) prepared via chronopotentiometric polymerization and over-oxidation is characterized by Fourier transform infra-red spectroscopy (FT-IR), UV–visible (UV–vis) spectroscopy, contact angle (CA), scanning electron microscopy (SEM), cyclic voltammetry (CV) and differential pulse voltammetry (DPV) studies. The response studies of PNPI-PANI-PVSA/ITO electrode carried out using DPV reveal a lower detection limit of 1 × 10⁻³ mM, improved sensitivity as 1.5 × 10⁻³ A mM⁻¹ and stability of 45 days. The PNPI-PANI-PVSA/ITO electrode shows good precision with relative standard deviation of 2.1% and good reproducibility with standard deviation of 3.78%.     

Molecularly imprinted conducting polymer based electrochemical sensor for detection of atrazine

An original electrochemical sensor based on molecularly imprinted conducting polymer (MICP) is developed, which enables the recognition of a small pesticide target molecule, atrazine. The conjugated MICP, poly(3,4-ethylenedioxythiophene-co-thiophene-acetic acid), has been electrochemically synthesized onto a platinum electrode following two steps: (i) polymerization of comonomers in the presence of atrazine, already associated to the acetic acid substituent through hydrogen bonding, and (ii) removal of atrazine from the resulting polymer, which leaves the acetic acid substituents open for association with atrazine. The obtained sensing MICP is highly specific towards newly added atrazine and the recognition can be quantitatively analyzed by the variation of the cyclic voltammogram of MICP. The developed sensor shows remarkable properties: selectivity towards triazinic family, large range of detection (10⁻⁹ mol L⁻¹ to 1.5 × 10⁻² mol L⁻¹ in atrazine) and low detection threshold (10⁻⁷ mol L⁻¹).     

A strategy for improving the sensitivity of molecularly imprinted electrochemical sensors based on catalytic copper deposition

A novel method to improve the sensitivity of molecularly imprinted polymer sensors was developed. Oxytetracycline (OTC), which was selected as the template molecule, was first rebound to the imprinted cavities. Gold nanoparticles were then labeled with the amino groups of OTC molecules via electrostatic adsorption and non-covalent interactions. Copper ions were catalytically reduced by the gold nanoparticles, and copper was deposited onto the electrode. The deposited copper was electrochemically dissolved, and its oxidative currents were recorded by differential pulse voltammetry (DPV). OTC could be determined indirectly within the concentration range of 3.0 × 10⁻¹⁰ to 1.5 × 10⁻⁷ mol L⁻¹ with a detection limit of 6.8 × 10⁻¹¹ mol L⁻¹.     

Application of an Hg selective imprinted polymer as a new modifying agent for the preparation of a novel highly selective and sensitive electrochemical sensor for the determination of ultratrace mercury ions

A simple and very selective electrode, based on a mercury ion imprinted polymer (IIP), and its application for the determination of Hg²⁺ ions in the real samples is introduced. Mercury ion selective cavities were created in the vinyl pyridine based cross-linked polymer. In order to fabricate the sensor carbon particles and polymer powder were mixed with melted n-eicosane. An explicit difference was observed between the responses of the electrodes modified with IIP and non imprinted polymer (NIP), indicating proper performance of the recognition sites of the IIP. Various factors, known to affect the response behavior of selective electrode, were investigated and optimized. The interference of different ionic species with the response of the electrode was also studied. The results revealed that, compared to previously developed mercury selective sensors, the proposed sensor was more selective, regarding the common potential interferer. This sensor showed a linear response range of 2.5 × 10⁻⁹–5.0 × 10⁻⁷ M and lower detection limit of 5.2 × 10⁻¹⁰ M (S/N). The sensor was successfully applied to the determination of mercury in real samples.     

A novel amperometric sensor for the detection of difenidol hydrochloride based on the modification of Ru(bpy)3 on a glassy carbon electrode

An amperometric sensor for the detection of difenidol, a tertiary amine-containing analyte, was proposed. Ruthenium(II) tris(bipyridine)/multi-walled carbon nanotubes/Nafion composite film was suggested to modify the glassy carbon electrode. The modified electrode was shown to be an excellent amperometric sensor for the detection of difenidol hydrochloride. The linear range is from 1.0 × 10⁻⁶ to 3.3 × 10⁻⁵ M with a correlation coefficient of 0.998. The limit of detection was 5 × 10⁻⁷ M, which was obtained through experimental determination based on a signal-to-noise ratio of three. The sensor was employed to the determination of the active ingredients in the tablets containing difenidol hydrochloride.     

Sensitive voltammetric determination of baicalein at DNA Langmuir-Blodgett film modified glassy carbon electrode

The present paper describes to modify a double stranded DNA-octadecylamine (ODA) Langmuir-Blodgett film on a glassy carbon electrode (GCE) surface to develop a voltammetric sensor for the detection of trace amounts of baicalein. The electrode was characterized by atomic force microscopy (AFM) and cyclic voltammetry (CV). Electrochemical behaviour of baicalein at the modified electrode had been investigated in pH 2.87 Britton-Robinson buffer solutions by CV and square wave voltammetry (SWV). Compared with bare GCE, the electrode presented an electrocatalytic redox for baicalein. Under the optimum conditions, the modified electrode showed a linear voltammetric response for the baicalein within a concentration range of 1.0 × 10⁻⁸-2.0 × 10⁻⁶ mol L⁻¹, and a value of 6.0 × 10⁻⁹ mol L⁻¹ was calculated for the detection limit. And the modified electrode exhibited an excellent immunity from epinephrine, dopamine, glucose and ascorbic acid interference. The method was also applied successfully to detect baicalein in the medicinal tablets and spiked human blood serum samples with satisfactory results.     

Highly selective and sensitive thiocyanate membrane electrode based on nickel(II)-1,4,8,11,15,18,22,25-octabutoxyphthalocyanine

A highly selective membrane electrode based on nickel(II)-1,4,8,11,15,18,22,25-octabutoxyphthalocyanine (NOBP) is presented. The proposed electrode shows very good selectivity for thiocyanate ions over a wide variety of common inorganic and organic anions. The sensor displays a near Nernstian slope of −58.7 ± 0.6 mV per decade. The working concentration range of the electrode is 1.0 × 10⁻⁶ to −1.0 × 10⁻¹ M with a detection limit of 5.7 × 10⁻⁷ M (33.06 ng/mL). The response time of the sensor in whole concentration ranges is very short (<10 s). The response of the sensor is independent on the pH range of 4.3-9.8. The best performance was obtained with a membrane composition of 30% PVC, 65% dibutyl phthalate, 3% NOBP and 2% hexadecyltrimethylammonium bromide. It was successfully applied to direct determination of thiocyanate in biological samples, and as an indicator electrode for titration of thiocyanate ions with AgNO₃ solution.     

Molecularly imprinted TiO(2) thin film using stable ground-state complex as template as applied to selective electrochemical determination of mercury

Molecular recognition sites for mercury ions were imprinted in TiO₂ film using stable ground-state complex of 1-amino-8-naphtol-3,6-disodium sulfonate (ANDS) and mercury ions as template. The complex ratio between mercury ions and ANDS was estimated to be 2:1. Compared with the controlled and pure TiO₂ electrodes, the imprinted electrode revealed selectivity towards the imprinted ions. Linear calibration plots for mercury ions were obtained and the regression equation was I_p (μA) = 4.29 × 10⁻⁷ + 19.40 [Hg²⁺] with a detection limit of 3.06 × 10⁻⁹ mol/l. The imprinted electrode could be used for more than 1 month. Recoveries were calculated at both high and low concentrations, with a mean recovery of 99.6%.     

Synthesis of Cu-mediated nano-sized salbutamol-imprinted polymer and its use for indirect recognition of ultra-trace levels of salbutamol

Cu²⁺-mediated salbutamol-imprinted polymer nanoparticles, synthesized by precipitation polymerization, were mixed with graphite powder and n-eicosane in order to fabricate a modified carbon paste electrode. This electrode was then applied for indirect differential pulse voltammetry determination of salbutamol. In the presence of Cu²⁺ ions, the formed Cu²⁺–salbutamol complex was adsorbed in to the pre-designed cavities of the MIP particles, situated on the electrode surface. Since the electrochemical signal of salbutamol was intrinsically small, the oxidation peak of the participant Cu²⁺, after reduction step, was recorded and used as an indication of salbutamol amount, adsorbed in the electrode. Different variables influencing the sensor performance were studied and the best conditions were chosen for the determination purpose. Correlation between the sensor response to salbutamol and its concentration was linear in the range of 1.0 × 10⁻⁹–5.5 × 10⁻⁸ M. Detection limit was calculated equal to 6.0 × 10⁻¹⁰ M (S/N). Five replicated determination of salbutamol (1 × 10⁻⁸ M) resulted in standard error of 3.28%, meaning a satisfactory precision of the determination method. The prepared sensor was applied for real sample analysis. In order to minimize the interference effect, the synthesized polymer was successfully used as a solid phase sorbent for salbutamol extraction, before analysis of real samples by the developed sensor.     

Flow injection chemiluminescence sensor based on core–shell magnetic molecularly imprinted nanoparticles for determination of sulfadiazine

A novel flow injection chemiluminescence (FI-CL) sensor for determination of sulfadiazine (SDZ) using core–shell magnetic molecularly imprinted polymers (MMIPs) as recognition element is developed. Briefly, a hydrophilic MMIPs layer was produced at the surface of Fe₃O₄@SiO₂ magnetic nanoparticles (MNPs) via combination of molecular imprinting and reversible stimuli responsive hydrogel. And it provided the MMIPs with excellent adsorption capacity and rapid adsorption rate due to the imprinted sites mostly situated on the surface of MMIPs. Then the prepared SDZ-MMIPs were packed into flow cell to establish a novel FI-CL sensor. The sensor provided a wide linear range for SDZ of 4.0 × 10⁻⁷ to 1.0 × 10⁻⁴ mol L⁻¹ with a detection limit of 1.54 × 10⁻⁷ mol L⁻¹. And the relative standard deviation (RSD) for the determination of 1.0 × 10⁻⁶ mol L⁻¹ SDZ was 2.56% (n = 11). The proposed method was applied to determine SDZ in urine samples and satisfactory results were obtained.