A novel electrochemical sensor for determination of dopamine based on AuNPs@SiO(2) core-shell imprinted composite

A novel core-shell composite of gold nanoparticles (AuNPs) and SiO(2) molecularly imprinted polymers (AuNPs@SiO(2)-MIPs) was synthesized through sol-gel technique and applied as a molecular recognition element to construct an electrochemical sensor for determination of dopamine (DA). Compared with previous imprinting recognition, the main advantages of this strategy lie in the introduction and combination of AuNPs and biocompatible porous sol-gel material (SiO(2)). The template molecules (DA) were firstly adsorbed at the AuNPs surface due to their excellent affinity, and subsequently they were further assembled onto the polymer membrane through hydrogen bonds and π-π interactions formed between template molecules and silane monomers. Cyclic voltammetry (CV) was carried out to extract DA molecules from the imprinted membrane, and as a result, DA could be rapidly and effectively removed. The AuNPs@SiO(2)-MIPs was characterized by ultraviolet visible (UV-vis) absorbance spectroscopy, transmission electron microscope (TEM) and Fourier transform infrared spectrometer (FT-IR). The prepared AuNPs@SiO(2)-MIPs sensor exhibited not only high selectivity toward DA in comparison to other interferents, but also a wide linear range over DA concentration from 4.8×10(-8) to 5.0×10(-5)M with a detection limit of 2.0×10(-8)M (S/N=3). Moreover, the new electrochemical sensor was successfully applied to the DA detection in dopamine hydrochloride injection and human urine sample, which proved that it was a versatile sensing tool for the selective detection of DA in real samples.     

Application of a quartz crystal nanobalance to the molecularly imprinted recognition of phenylalanine in solution

A quartz crystal nanobalance (QCN) biosensor was developed for the selective determination of phenylalanine (Phe) in aqueous solutions. A Phe imprinted copolymer was synthesized using polyacrylonitrile and acrylic acid [poly(AN-co-AA)]. The copolymer was then coated on quartz crystal electrode to form complementary structures for the template recognition of Phe. The composite electrode was then used to determine Phe levels in solution. Determinations were based on frequency shifts of molecularly imprinted polymer (MIP) modified quartz crystal electrode caused by Phe adsorption. The frequency shifts were linearly dependent on Phe concentration over the range 50∼500 mgL⁻¹. The results obtained show that the imprinted poly(AN-co-AA) modified biosensor had higher sensitivity (0.5839 Hz/mgL⁻¹) than a non-molecularly imprinted copolymer (0.2724 Hz/mgL⁻¹). Furthermore, good reproducibility, R.S.D. = 1.84% (n = 7) was observed, and the detection limit was 45 mgL⁻¹. The selectivity of the imprinted poly(AN-co-AA) modified biosensor was examined using a number of analytes similar to Phe, i.e., dopamine (DA), ascorbic acid (AscA), vanillylmandelic acid (VMA), uric acid (UA), tryptophan (Trp), and tyrosine (Tyr), and the results obtained showed a size dependent selective effect.     

Electrochemical and piezoelectric monitoring of taurine via electropolymerized molecularly imprinted films

A molecularly imprinted electrochemical quartz crystal microbalance (EQCM) sensor is fabricated here for taurine, a β ‐amino acid significant for functioning of almost all vital organs. The polymeric film of l ‐methionine was electrochemically deposited on gold‐coated EQCM electrode. Experimental parameters were optimized for controlling the performance of molecularly imprinted polymer (MIP)‐modified sensor such as ratio of monomer and template, number of electropolymerization cycles, mass deposited in each cycle, and pH. Thus, fabricated MIP‐EQCM sensor was successfully applied for estimation of taurine in solutions with varying matrices, such as aqueous, human blood plasma, milk from cow, buffalo, and milk powder. Under optimized parameters, response of MIP sensor to taurine was linearly proportional to its concentration with limit of detection as 0.12μM. Hence, a highly sensitive and selective piezoelectric sensor for taurine has been reported here via imprinting approach.     

Electrochemical sensor for dopamine based on a novel graphene-molecular imprinted polymers composite recognition element

A novel composite of graphene sheets/Congo red-molecular imprinted polymers (GSCR-MIPs) was synthesized through free radical polymerization (FRP) and applied as a molecular recognition element to construct dopamine (DA) electrochemical sensor. The template molecules (DA) were firstly absorbed at the GSCR surface due to their excellent affinity, and subsequently, selective copolymerization of methacrylic acid (MAA) and ethylene glycol dimethacrylate (EGDMA) was further achieved at the GSCR surface. Potential scanning was presented to extract DA molecules from the imprinted polymers film, and as a result, DA could be rapidly and completely removed by this way. With regard to the traditional MIPs, the GSCR-MIPs not only possessed a faster desorption and adsorption dynamics, but also exhibited a higher selectivity and binding capacity toward DA molecule. As a consequence, an electrochemical sensor for highly sensitive and selective detection of DA was successfully constructed as demonstration based on the synthesized GSCR-MIPs nanocomposites. Under experimental conditions, selective detection of DA in a linear concentration range of 1.0 × 10(-7)-8.3 × 10(-4)M was obtained, which revealed a lower limit of detection and wider linear response compared to some previously reported DA electrochemical MIPs sensors. The new DA electrochemical sensor based on GSCR-MIPs composites also exhibited excellent repeatability, which expressed as relative standard deviation (RSD) was about 2.50% for 30 repeated analyses of 20 μM DA.     

A novel fluorescent sensor based on electrosynthesized benzene sulfonic acid‐doped polypyrrole for determination of Pb(II) and Cu(II)

To develop conducting organic polymers (COPs) as luminescent sensors for determination of toxic heavy metals, a new benzene sulfonic acid‐doped polypyrrole (PPy‐BSA) thin film was electrochemically prepared by cyclic voltammetry (CV) on flexible indium tin oxide (ITO) electrode in aqueous solution. PPy‐BSA film was characterized by FTIR spectrometry, X‐ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The optical properties of PPy‐BSA were investigated by ultraviolet (UV)‐visible absorption and fluorescence spectrometry in dimethylsulfoxide (DMSO) diluted solutions. PPy‐BSA fluorescence spectra were strongly quenched upon increasing copper(II) ion (Cu²⁺) and lead(II) ion (Pb²⁺) concentrations in aqueous medium, and linear Stern–Volmer relationships were obtained, which indicated the existence of a main dynamic fluorescence quenching mechanism. BSA‐PPy sensor showed a high sensitivity for detection of both metallic ions, Cu²⁺ and Pb²⁺, with very low limit of detection values of 3.1 and 18.0 nM, respectively. The proposed quenching‐fluorimetric sensor might be applied to the determination of traces of toxic heavy metallic ions in water samples.     

Surface plasmon resonance sensor using molecularly imprinted polymer for detection of sialic acid

A surface plasmon resonance (SPR) sensor using a molecularly imprinted polymer-coated sensor chip for the detection of sialic acid was developed. The thinly coated polymer was prepared by co-polymerizing N,N,N-trimethylaminoethyl methacrylate, 2-hydroxyethyl methacrylate and ethyleneglycol dimethacrylate in the presence of p-vinylbenzeneboronic acid ester with sialic acid. The sensor showed a selective response to ganglioside of which sialic acid is located at the non-reducing end and gave a linear relationship from 0.1 to 1.0 mg of ganglioside.     

Chiral determination of cinchonine using an electrochemiluminescent sensor with molecularly imprinted membrane on the surfaces of magnetic particles

A novel molecular imprinting electrochemiluminescence sensor for detecting chiral cinchonine molecules was developed with a molecularly imprinted polymer membrane on the surfaces of magnetic microspheres. Fe₃O₄@Au nanoparticles modified with 6‐mercapto‐beta‐cyclodextrin were used as a carrier, cinchonine as a template molecule, methacrylic acid as a functional monomer and N ,N ′‐methylenebisacrylamide as a cross‐linking agent. Cinchonine was specifically recognized by the 6‐mercapto‐beta‐cyclodextrin functional molecularly imprinted polymer and detected based on enhancement of the electrochemiluminescence intensity caused by the reaction of tertiary amino structures of cinchonine molecules with Ru(bpy)₃²⁺. Cinchonine concentrations of 1 × 10^?10 to 4 × 10^?7 mol/L showed a good linear relationship with changes of the electrochemiluminescence intensity, and the detection limit of the sensor was 3.13 × 10^?11 mol/L. The sensor has high sensitivity and selectivity, and is easy to renew. It was designed for detecting serum samples, with recovery rates of 98.2% to 107.6%.     

An epitope‐imprinted piezoelectric diagnostic tool for Neisseria meningitidis detection

Neisseria meningitidis, a human‐specific bacterial pathogen causes bacterial meningitis by invading the meninges (outer lining) of central nervous system. It is the polysaccharide present on the bacterial capsid that distinguishes various serogroups of N. meningitidis and can be utilized as antigens to elicit immune response. A computational approach identified candidate T‐cell epitopes from outer membrane proteins Por B of N. meningitidis (MC58): (²⁷³KGLVDDADI²⁸² in loop VII and ¹⁷⁰GRHNSESYH¹⁷⁹ in loop IV) present on the exposed surface of immunogenic loops of class 3 outer membrane proteins allele of N. meningitidis. One of them, KGLVDDADI is used here for designing a diagnostic tool via molecularly imprinted piezoelectric sensor (molecularly imprinted polymer‐quartz crystal microbalance) for N. meningitidis strain MC58. Methacrylic acid, ethylene glycol dimethacrylate and azoisobutyronitrile were used as functional monomer, cross‐linker and initiator, respectively. The epitope can be simultaneously bound to methacrylic acid and fitted into the shape‐selective cavities. On extraction of epitope sequence from thus grafted polymeric film, shape‐selective and sensitive sites were generated on electrochemical quartz crystal microbalance crystal, ie, known as epitope imprinted polymers. Imprinting was characterized by atomic force microscopy images. The epitope‐imprinted sensor was able to selectively bind N. meningitidis proteins present in blood serum of patients suffering from brain fever. Thus, fabricated sensor can be used as a diagnostic tool for meningitis disease.     

Molecularly imprinted core‐shell magnetic nanoparticles for selective extraction of triazines in soils

In this work, a propazine‐imprinted polymer was synthesized on the surface of modified magnetic nanoparticles to be used in the solid‐phase extraction of triazines in soil samples. The effect of different solvents on the selective extraction of target analytes was assessed to establish the optimum rebinding conditions. The obtained magnetic molecularly imprinted particles exhibited high selectivity for triazines and were easily collected and separated by an external magnetic field without additional centrifugation or filtration steps. Under optimum conditions, a magnetic molecularly imprinted solid‐phase extraction method was developed allowing the extraction of several triazines (desisopropylatrazine, desethylatrazine, simazine, atrazine, and propazine) from soil samples and their subsequent final determination by high‐performance liquid chromatography with diode‐array detection. Recoveries for the triazines studied were within the range 5.4% to 40.6%, with relative standard deviations lower than 7.0% (n = 3). The detection limits were within 0.1 to 3 ng g⁻¹, depending upon the triazine and the type of soil used.     

Overoxidized polypyrrole film directed single-walled carbon nanotubes immobilization on glassy carbon electrode and its sensing applications

In this paper, the films of overoxidized polypyrrole (PPyox) directed single-walled carbon nanotubes (SWNTs) have been electrochemically coated onto glassy carbon electrode (GCE). Electroactive monomer pyrrole was added into the solution containing sodium dodecyl sulfate (SDS) and SWNTs. Then, electropolymerization was proceeded at the surface of GCE, and a novel kind of conducting polymer/carbon nanotubes (CNTs) composite film with the orientation of CNTs were obtained correspondingly. Finally, this obtained polypyrrole (PPy)/SWNTs film modified GCE was oxidized at a potential of +1.8 V. It can be found that this proposed PPyox/SWNTs composite film modified GCE exhibited excellent electrocatalytic properties for some species such as nitrite, ascorbic acid (AA), dopamine (DA) and uric acid (UA), and could be used as a new sensor for practical applications. Compared with previous CNTs modified electrodes, SWNTs were oriented towards the outside of modified layer by PPyox and SDS, which made the film easily conductive. Moreover, this proposed film modified electrode was more stable, selective and applicable.     

Selective solid-phase extraction using molecularly imprinted polymer for analysis of methamidophos in water and soil samples

An analytical methodology for the analysis of methamidophos in water and soil samples incorporating a molecularly imprinted solid-phase extraction process using methamidophos-imprinted polymer was developed. Binding study demonstrated that the polymer exhibited excellent affinity and high selectivity to the methamidophos. Evidence was also found by FT-IR analysis that hydrogen bonding between the CO(2)H in the polymer cavities and the NH(2) and P=O of the template was the origin of methamidophos recognition. The use of molecularly imprinted solid-phase extraction improved the accuracy and precision of the GC method and lowered the limit of detection. The recovery of methamidophos extracted from a 10.0 g soil sample at the 100 ng/g spike level was 95.4%. The limit of detection was 3.8 ng/g. The recovery of methamidophos extracted from 100 mL tap and river water at 1 ng/mL spike level was 96.1% and 95.8%, and the limits of detection were 10 and 13 ng/L respectively. These molecularly imprinted solid-phase extraction procedures enabled selective extraction of polar methamidophos successfully from water and soil samples, demonstrating the potential of molecularly imprinted solid-phase extraction for rapid, selective, and cost-effective sample pretreatment.     

ZnO–CuxO/polypyrrole nanocomposite modified electrode for simultaneous determination of ascorbic acid,dopamine, and uric acid

Novel zinc oxide (ZnO) nanosheets and copper oxide (Cu_xO, CuO, and Cu₂O) decorated polypyrrole (PPy) nanofibers (ZnO–Cu_xO–PPy) have been successfully fabricated for the simultaneous determination of ascorbic acid (AA), dopamine (DA), and uric acid (UA). The morphology and structure of ZnO–Cu_xO–PPy nanocomposites were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy. Compared with the bare glassy carbon electrode (GCE), PPy/GCE, Cu_xO–PPy/GCE, and ZnO–PPy/GCE, ZnO–Cu_xO–PPy/GCE exhibits much higher electrocatalytic activities toward the oxidation of AA, DA, and UA with increasing peak currents and decreasing oxidation overpotentials. Cyclic voltammetry (CV) results show that AA, DA, and UA could be detected selectively and sensitively at ZnO–Cu_xO–PPy/GCE with peak-to-peak separation of 150 and 154 mV for AA–DA and DA–UA, respectively. The calibration curves for AA, DA, and UA were obtained in the ranges of 0.2 to 1.0 mM, 0.1 to 130.0 μM, and 0.5 to 70.0 μM, respectively. The lowest detection limits (signal/noise = 3) were 25.0, 0.04, and 0.2 μM for AA, DA, and UA, respectively. With good selectivity and sensitivity, the current method was applied to the determination of DA in injectable medicine and UA in urine samples.     

Determination of phenformin hydrochloride using molecular imprinting technology coupled with flow-injection chemiluminescence

A novel method was developed using molecular imprinting technology (MIT) coupled with flow‐injection chemiluminescence (FI‐CL) for highly sensitive detection of phenformin hydrochloride (PH). The phenformin imprinted polymer was synthesized with methacrylic acid (MAA) as a functional monomer and ethylene glycol dimethacrylate (EGDMA) as a cross‐linker. Newly synthesized molecularly imprinted polymer (MIP) particles were packed into a column as a selective recognition element for determination of PH. A CL method for the determination of PH was developed based on the CL reaction of PH with N‐bromosuccinimide sensitized by eosin Y in basic media. The optimization of detection conditions was investigated. The CL intensity responded linearly to the concentration of PH in the range 0.09–2.0 µg/mL, with a correlation coefficient of 0.9920. The detection limit was 0.031 µg/mL. The relative standard deviation for the determination of 1.0 µg/mL PH solution was 1.0% (n = 11). The method was applied to the determination of PH in urine samples, with satisfactory results. Copyright © 2011 John Wiley & Sons, Ltd.     

Trace-level sensing of dopamine in real samples using molecularly imprinted polymer-sensor

Induced-fit responsive dopamine (DA) imprinted polymer, poly (melamine-co-chloranil), was used as a suitable coating material for the modification of a hanging mercury drop electrode. The zwitterionic conformation of the imprinted polymer responded differential pulse, cathodic stripping voltammetric current, without any false-positive or false-negative contributions of non-specific sorptions, in aqueous environment of complex matrices. The limit of detection (3σ) of dopamine was found to be as low as 0.148 ng mL⁻¹, by the proposed sensor that could be considered a sensitive marker of dopamine depletion in Parkinson's disease (PD).     

Quartz crystal microbalance for the determination of daminozide using molecularly imprinted polymers as recognition element

As the daminozide (DM) and its metabolite have been identified to be potentially carcinogenic, rapid detection method for them is necessary for food safety. A type of piezoelectric crystal sensor has been prepared by using a molecularly imprinted polymer (MIP) as recognition element. The molecularly imprinted polymer was prepared by hot-induced precipitation polymerization, and then the polymer particles were fixed on the surface of the electrode. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were employed to evaluate the obtained imprinted polymer particles and the MIP sensitive film coated on the electrode. The results showed that a typical time-response curve of the MIP-coated crystal to the DM solution had been given, frequency shifts versus logarithm changes of DM showed good linear correlation within the concentration range of 1.0x10(-9) to 10(-6) mg/mL (y=11.38 lg x+115.45, r=0.9872) and 1.0x10(-6) to 10(-1) mg/mL (y=25.22lgx+209.44, r=0.9938), respectively. The detection limit was 5.0x10(-8) mg/mL (S/N=3), which is lower than that of conventional methods. Further, computer simulation technology was employed to investigate the interaction between methacrylic acid and DM for elucidating the recognition mechanism. The influencing factor pH has also been investigated. The injection experiments of DM structurally related compounds indicated that the obtained sensor has high sensitivity, excellent selectivity, low cost, good reproducibility, and reusable property by combining with piezoelectric crystal and molecularly imprinted polymer.     

A MIP-based impedimetric sensor for the detection of low-MW molecules

Mimicking the selectivity and sensitivity of biological systems for sensor devices is of increasing interest in biomedical, environmental and chemical analysis. Synthetic materials with imprinted nanocavities, acting as highly selective artificial receptors, are a tailor-made solution in obtaining such a sensor. Incorporation of such molecularly imprinted polymers (MIPs) in a platform suitable for electrochemical measurements, can offer high sensitivity together with device miniaturization and an electronic read-out. As a proof of principle, a MIP-based sensor for L-nicotine has been developed. To this end, the molecular structure of L-nicotine was imprinted in a polymer matrix of polymethacrylic acid (PMAA). Subsequently, microparticles of the imprinted polymer were immobilized on thin films of the conjugated polymer OC(1)C(10)-PPV. These films were incorporated in an impedimetric sensing device. Using electrochemical impedance spectroscopy, the real part of the impedance was monitored for various concentrations. This setup allows for the detection of l-nicotine from 1 to 10 nM and is insensitive for the resembling molecule L-cotinine.     

Efficient one-pot synthesis of molecularly imprinted silica nanospheres embedded carbon dots for fluorescent dopamine optosensing

A new type of eco-friendly molecularly imprinted polymer (MIP) was synthesized through an efficient one-pot room-temperature sol-gel polymerization and applied as a molecular recognition element to construct dopamine (DA) fluorescence (FL) optosensor. Highly luminescent carbon dots (CDs) were firstly synthesized via a one-step reaction in organosilane, and their surface were anchored with MIP matrix (CDs@MIP). The resulting composite of a synergetic combination of CDs with MIP showed high photostability and template selectivity. Moreover, the composite allowed a highly sensitive determination of DA via FL intensity decreasing when removal of the original templates. The new MIP-based DA sensing protocol was applied to detect DA concentration in aqueous solution, the relative FL intensity of CDs@MIP decreased linearly with the increasing DA in the concentration range of 25-500nM with a detection limit (3σ) of 1.7nM. Furthermore, the proposed method was successfully intended for the determination of trace DA in human urine samples without the interference of other molecules and ions.     

A novel reductive graphene oxide‐based magnetic molecularly imprinted poly(ethylene‐co‐vinyl alcohol) polymers for the enrichment and determination of polychlorinated biphenyls in fish samples

The novel reductive graphene oxide‐based magnetic molecularly imprinted poly(ethylene‐co‐vinyl alcohol) polymers (rGO@m‐MIPs) were successfully synthesized as adsorbents for six kinds of polychlorinated biphenyls (PCBs) in fish samples. rGO@m‐MIPs was prepared by surface molecular imprinting technique. Besides, Fe₃O₄ nanoparticles (NPs) were employed as magnetic supporters, and rGO@Fe₃O₄ was in situ synthesis. Different from functional monomer and cross‐linker in traditional molecularly imprinted polymer, here, 3,4‐dichlorobenzidine was employed as dummy molecular and poly(ethylene‐co‐vinyl alcohol) was adopted as the imprinted polymers. After morphology and inner structure of the magnetic adsorbent were characterized, the adsorbent was employed for disperse solid phase extraction toward PCBs and exhibited great selectivity and high adsorption efficiency. This material was verified by determination of PCBs in fish samples combined with gas chromatography‐mass spectrometry (GC‐MS) method. According to the detection, the low detection limits (LODs) of PCBs were 0.0035–0.0070 µg l⁻¹ and spiked recoveries ranged between 79.90 and 94.23%. The prepared adsorbent can be renewable for at least 16 times and expected to be a new material for the enrichment and determination of PCBs from contaminated fish samples. Copyright © 2015 John Wiley & Sons, Ltd.     

Molecularly imprinted polyaniline film for ascorbic acid detection

Molecularly imprinted polyaniline (PANI) film (～ 100 nm thick) has been electrochemically fabricated onto indium-tin-oxide (ITO) coated glass plate using ascorbic acid (AA) as template molecule. Fourier transform infra-red spectroscopy, scanning electron microscopy, cyclic voltammetry and differential pulse voltammetry (DPV) studies indicate the presence of AA in PANI matrix, which also acts as a dopant for PANI. Further, the AA selective molecularly imprinted PANI electrode (AA-MI-PANI/ITO) has been developed via over-oxidation of AA doped PANI electrode which leads to the removal of AA moieties from PANI film. The response studies using DPV technique have revealed that this molecularly imprinted AA-MI-PANI/ITO electrode can detect AA in the range of 0.05-0.4 mM with detection limit of 0.018 mM and sensitivity of 1.2 × 10(-5) AmM(-1). Interestingly, this AA-MI-PANI/ITO electrode shows excellent reusability, selectivity and stability.