Carcinoembryonic antigen admittance biosensor based on Au and ZnO nanoparticles using FFT admittance voltammetry

In this work, a highly sensitive carcinoembryonic antigen fast Fourier transform admittance biosensor is introduced. The proposed biosensor is based on bilayer films of ZnO/Au nanoparticles as an immobilization matrix. These layers are prepared by self-assembly and deposition method on a gold electrode surface, respectively. Carcinoembryonic antibody (anti-CEA) was immobilized on gold nanoparticles and positively charged horseradish peroxidase (HRP) was used to block sites against nonspecific binding. The admittance biosensor was developed based on fast Fourier transform continuous square wave voltammetry, which produces a sensitive, fast (less than 20 s) and reliable response for determination of carcinoembryonic antigen. The technique was applied as a detector in a flow injection system. The admittances reduction current of the biosensor decreases linearly in two concentrations ranges of CEA from 0.1 to 70 ng/mL and from 70 to 200 ng/mL with a detection limit of 0.01 ng/mL in presence of 0.5 mM H(2)O(2) as an eluent solution.     

铁氰化物掺杂聚苯胺复合材料的制备和表征

以ITO导电玻璃为工作电极,在三电极系统中,采用循环伏安法制得聚苯胺薄膜,聚苯胺/铁氰化铜(CuHCF),聚苯胺/铁氰化钴(CoHCF),聚苯胺/铁氰化铈(CeHCF)复合材料。通过利用C-V、SEM、EDS、XRD、FT-IR等方法对导电复合物进行表征和性能研究。实验结果表明,制备复合物的最佳电解液浓度为0.02mol/L苯胺+0.002mol/L金属离子+0.01mol/L铁氰化钾+0.5mol/L H2SO4;聚苯胺与铁氰化物很好地键合在一起,聚苯胺/铁氰化钴复合材料的电化学性有进一步的提高,具有纳米粒子特性和独特的片状粒子结构;而聚苯胺/铁氰化铜和聚苯胺/铁氰化铈的电化学性能高于聚苯胺本体,粒子间有较大的空穴现象。     

A novel silicon nitride biosensor for specific antibody–antigen interaction

We herein report the fabrication and characterisation of a novel impedimetric immunosensor based on an electrolyte–insulator–semiconductor (EIS) structure. It is a silicon nitride/aminosilane/glutaraldehyde/antibody biosensor specifically designed for the detection of antigens. This immunosensor was fabricated following the Self-Assembled Monolayers (SAMs) method, followed by glutaraldehyde cross linker and anti-rabbit IgG immobilization. The high coverage area of the silane monolayer on silicon nitride surface was estimated with impedance spectroscopy technique and the molecular structure with Fourier-transform infrared (FTIR) technique. The binding between antibody and antigen (Rabbit IgG) was monitored by measuring the resistance variation of the grafted layer. The developed immunosensor has a limit detection of 50 ng/ml of antigen.     

Electrochemical fabrication of polyaniline films containing gold nanoparticles deposited on titanium electrode for electro-oxidation of ascorbic acid

Polyaniline films prepared on titanium were employed as substrate for the electrodeposition of gold. The modified electrode was used as anode for the electro-oxidation of ascorbic acid. The electrochemical behavior and electro-catalytic activity of Au/PAni/Ti electrode were characterized by cyclic voltammetry. The morphology of the polyaniline film and gold coating on PAni/Ti electrode were characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) techniques, respectively. Results indicated that gold nanoparticles were homogeneously dispersed on the surface of polyaniline film. The electro-oxidation of ascorbic acid is found to proceed more facile on Au/PAni/Ti electrode than on bare gold electrode. The irreversible oxidation current of ascorbic acid exhibits a linear dependence on the ascorbic acid concentration in the range of 1–5 mM.     

Response to cardiac markers in human serum analyzed by guided-mode resonance biosensor

Cardiac markers in human serum with concentrations less than 0.1 ng/mL were analyzed by use of a guided-mode resonance (GMR) biosensor. Cardiac troponin I (cTnI), creatine kinase MB (CK-MB), and myoglobin (MYO) were monitored in the serum of both patients and healthy controls. Dose-response curves ranging from 0.05 to 10 ng/mL for cTnI, from 0.1 to 10 ng/mL for CK-MB, and from 0.03 to 1.7 μg/mL for MYO were obtained. The limits of detection (LOD) for cTnI, CK-MB, and MYO were less than 0.05, 0.1, and 35 ng/mL, respectively. Analysis time was 30 min, which is short enough to meet clinical requirements. Antibody immobilization and the hydrophilic properties of the guided-mode resonance filter (GMRF) surface were investigated by X-ray photoelectron spectroscopy (XPS) and by monitoring the peak wavelength shift and water contact angle (CA). Both assays used to evaluate the surface density of the immobilized antibodies, a sandwich enzyme-linked immunosorbent assay (ELISA) and a sandwich immunogold assay, showed that the antibodies were successfully immobilized and sufficiently aligned to detect the low concentration of biomarkers. Our results show that the GMR biosensor will be very useful in developing low-cost portable biosensors that can screen for cardiac diseases.     

Development of trypsin biosensor based on ion sensitive field-effect transistors for proteins determination

This new biosensor for protein determination is based on a possibility of translation of either a proton or hydroxyl ion arising during protein hydrolysis in the presence of trypsin by means of ion selective field effect transistor (ISFET). The conditions of trypsin immobilization and main biosensor characteristics were optimized using hydrolysis reaction of nalpha-benzoyl-l-arginine ethyl ester hydrochloride (BAEE). The trypsin was immobilized on the ISFET surface using a co-reticulation process between the enzyme and BSA (4% trypsin, 6% BSA) in saturated glutaraldehyde vapour. The limit of detection of BAEE with this biosensor is 0.5 mM with a linear dynamics range from 0.5 to 5 mM, and sensitivity is about 6 mV/mM. The time of biosensor response was 5–7 min.The possibility of the application of developed biosensor for detection of small penta-peptide, which is used in some cosmetic products, has been demonstrated.     

Oriented immobilization of immunoglobulin G onto the cuvette surface of the resonant mirror biosensor through layer-by-layer assembly of multilayer films

A new method for oriented immobilization of immunoglobulin G (IgG) onto the cuvette surface of the resonant mirror biosensor through layer-by-layer (LBL) assembly of multilayer films composed of avidin/gold nanoparticles (GNp)/protein A/IgG was developed. First, avidin was added in the biotin cuvette, and then injected GNp, followed by the injection of protein A for oriented immobilization of IgG. The rinsing with PBS was applied at the end of each assembly deposition for dissociating the weak adsorption. Second, IgG was added in the protein A-coated cuvette, and regenerated by incubation with 0.1 M glycine–HCL buffer. Third, different concentrations of IgG were measured by repeating the second process. Film assembling and properties of the interaction between protein A and IgG were studied by resonant mirror biosensor and electrochemical measurements. Results confirmed that IgG was successfully oriented on the protein A-coated cuvette surface by LBL assembly of multilayer films. The interaction response was dose-dependent which showed a linear range of 0.1 – 1.6 g L^− 1 IgG, with a detection limit of 8.7 mg L^− 1 estimated at a signal-to-noise ratio of 3. Moreover, the assay for oriented immobilization of IgG exhibited a good reproducibility and a favorable reusability. This method can provide a promising platform for fabricating immunoassay and immunosensor systems, protein reactors or protein-modified substrates, and affinity probes.     

Fabrication of self-assembled polyaniline films by doping-induced deposition

The ultrathin films of polyaniline (PAni)/poly (styrenesulfonic acid)(PSSA) were fabricated via a novel self-assembling process by alternately immersing the substrates into dilute PAni solution in N-methylpyrrolidinone (NMP) and the aqueous solution of PSSA. The process was characterized by UV–Vis absorption spectroscopy. It was found that the oxidation state of polyaniline in single monolayers was dependent on the thickness of the film. The self-assembling mechanism was based on the acid-base reaction between PAni and PSSA. The thickness of the films can be easily manipulated at nanometer scale by controlling the solution chemistry and recycling times. The resulting films are uniform and adhere strongly to the substrates.     

Silver nanoparticles dispersed in polyaniline matrixes coated on titanium substrate as a novel electrode for electro-oxidation of hydrazine

Silver nanoparticles dispersed in polyaniline matrixes coated on titanium substrate, as a novel electrode, was easily synthesized by electro-polymerization of aniline on titanium and then electrodeposited silver nanoparticles on PAni electrode. The electrochemical behavior and electro-catalytic activity of silver nanoparticles/PAni/Ti electrodes were characterized by cyclic voltammetry. The morphology of silver nanoparticles on PAni/Ti electrodes were characterized by scanning electron microscopy and energy-dispersive X-ray techniques, respectively. Results indicated that silver nanoparticles with a diameter of about 40–70 nm were homogeneously dispersed on the surface of polyaniline film. The silver nanoparticles/PAni/Ti electrodes were examined for electro-catalytic activity toward oxidation of hydrazine. The results show that these modified electrodes are highly active for electro-catalytic oxidation of hydrazine.     

Electrochemical preparation and characterisation of Poly(Luminol-Aniline) films

Electrochemical polymerisation of luminol (Lum) with aniline (Ani) is carried out potentiodynamically from acidic medium with different monomers concentration ratios. Aniline units incorporation in the polymer structure is observable in the current density/potential profiles of the polymerisation and characterisation, in acidic medium, by the development of two polyaniline (PAni) like redox switching processes with increasing aniline concentration. Poly(Luminol-Aniline) (P(Lum-Ani)) films characterised in acidic medium show electroactive and stable behaviour, in which the redox process ascribed as polyluminol (PLum) type is overlaid with that of PAni displaying pH sensitivity. Unlike PAni films, the P(Lum-Ani) polymer is electroactive and stable in basic medium and a single redox switching process is observed; its redox charge is enhanced with the increase of aniline concentration in the polymerisation solution.     

Structure and properties of melt-processed PVDF/PMMA/polyaniline blends

Ternary blends composed of the matrix polymer poly(vinylidene fluoride) (PVDF) and poly(methyl methacrylate) (PMMA) with different proportions of thermally doped polyaniline (PAni) using an alkylated dopant (dodecylbenzenesulfonic acid) (DBSA) were prepared by melt mixing. The effectiveness of these blends was compared with the corresponding binary blends of PVDF or PMMA with PAni–DBSA complex. Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) measurements, thermal analysis by differential scanning calorimetry (DSC) and morphological studies by optical microscopy and scanning electron microscopy (SEM) were carried out to characterize the blends in light of the interactions between their components and on the resulting electrical conductivity. Though a notable dispersion of PAni–DBSA in the PMMA matrix was incurred along with better conductivity with respect to PVDF/PAni–DBSA and PVDF/PMMA/PAni–DBSA blends, the thin films based on PMMA/PAni–DBSA were found to be fragile in nature. However, the presence of PMMA in the ternary blends of PVDF/PMMA/PAni–DBSA provided improved dispersion of PAni–DBSA in the PVDF/PMMA host matrix as compared to PVDF/PAni–DBSA binary blends. An enhancement in the conductivity by about two orders of magnitude at >5 wt% PAni–DBSA was witnessed in the ternary blends than that of PVDF/PAni–DBSA binary blends. Thin films made of ternary blends of PVDF/PMMA/PAni–DBSA also offered superior mechanical properties and flexibility than that of PMMA/PAni–DBSA binary blends due to the contribution of PVDF in the blend.     

A comparative study of enzyme immobilization strategies for multi-walled carbon nanotube glucose biosensors

This work addresses the comparison of different strategies for improving biosensor performance using nanomaterials. Glucose biosensors based on commonly applied enzyme immobilization approaches, including sol-gel encapsulation approaches and glutaraldehyde cross-linking strategies, were studied in the presence and absence of multi-walled carbon nanotubes (MWNTs). Although direct comparison of design parameters such as linear range and sensitivity is intuitive, this comparison alone is not an accurate indicator of biosensor efficacy, due to the wide range of electrodes and nanomaterials available for use in current biosensor designs. We proposed a comparative protocol which considers both the active area available for transduction following nanomaterial deposition and the sensitivity. Based on the protocol, when no nanomaterials were involved, TEOS/GOx biosensors exhibited the highest efficacy, followed by BSA/GA/GOx and TMOS/GOx biosensors. A novel biosensor containing carboxylated MWNTs modified with glucose oxidase and an overlying TMOS layer demonstrated optimum efficacy in terms of enhanced current density (18.3 ± 0.5 μA mM(-1) cm(-2)), linear range (0.0037-12 mM), detection limit (3.7 μM), coefficient of variation (2%), response time (less than 8 s), and stability/selectivity/reproducibility. H(2)O(2) response tests demonstrated that the most possible reason for the performance enhancement was an increased enzyme loading. This design is an excellent platform for versatile biosensing applications.     

Gold nanoparticle-polyaniline composite films for glucose sensing

Gold nanoparticles (AuNPs) have been self-assembled onto electrochemically deposited polyaniline (PANI) films on indium-tin-oxide (ITO) coated glass plates to fabricate glucose biosensor. The covalent immobilization of glucose oxidase (GOx) in the near vicinity of gold nanoparticles has been obtained using N-ethyl-N'-(3-dimethylaminopropyl) carbodiimide (EDC)/N-hydroxysuccinimide (NHS), chemistry between amino groups of PANI and COOH groups of GOx. These AuNPs-PANI/ ITO and GOx/AuNPs-PANI/ITO composite films have been characterized using Fourier transform infra red (FTIR) and cyclic voltammetry (CV) techniques, respectively. The fast electron transfer from the modified PANI surface to electrode is indicated by the observed increase in amperometric response current of these GOx/AuNPs-PANI/ITO bioelectrodes. These GOx/AuNPs-PANI/ITO bioelectrodes exhibit response time of 10 s, linearity from 50 to 300 mg/dl and show value of apparent Michaelis-Menten constant (Km(app)) of 2.2 mM.     

Assessment of specific binding proteins suitable for the detection of paralytic shellfish poisons using optical biosensor technology

Paralytic shellfish poisoning (PSP) toxin monitoring in shellfish is currently performed using the internationally accredited AOAC mouse bioassay. Due to ethical and performance-related issues associated with this bioassay, the European Commission has recently published directives extending procedures that may be used for official PSP control. The feasibility of using a surface plasmon resonance optical biosensor to detect PSP toxins in shellfish tissue below regulatory levels was examined. Three different PSP toxin protein binders were investigated: a sodium channel receptor (SCR) preparation derived from rat brains, a monoclonal antibody (GT13-A) raised to gonyautoxin 2/3, and a rabbit polyclonal antibody (R895) raised to saxitoxin (STX). Inhibition assay formats were used throughout. Immobilization of STX to the biosensor chip surface was achieved via amino-coupling. Specific binding and inhibition of binding to this surface was achieved using all proteins tested. For STX calibration curves, 0-1000 ng/mL, IC50 values for each binder were as follows: SCR 8.11 ng/mL; GT13-A 5.77 ng/mL; and R895 1.56 ng/mL. Each binder demonstrated a different cross-reactivity profile against a range of STX analogues. R895 delivered a profile that was most likely to detect the widest range of PSP toxins at or below the internationally adopted regulatory limits.     

Electrochemical Behavior of CoSb3-based Electrodes Using Binary PAni/PVDF Binder

The polyaniline （PAni）/polyvinylidene fluoride （PVDF） hybrid was served as a novel binder for CoSb3-based alloy electrode. The effect of PAni content on the electrochemical performances of the alloy electrode was investigated. It was found that the CoSb3 electrode using the binary PAni/PVDF binder exhibits higher reversible capacity than that using the single PVDF binder, especially in the initial cycles. As a result, the PAni/PVDF hybrid could be a promising binder for the alloy electrode.     

DC magnetron sputtered polyaniline-HCl thin films for chemical sensing applications

Thin films of conducting polymers exhibit unique chemical and physical properties that render them integral parts in microelectronics, energy storage devices, and chemical sensors. Overall, polyaniline (PAni) doped in acidic media has shown metal-like electronic conductivity, though exact physical and chemical properties are dependent on the polymer structure and dopant type. Difficulties arising from poor processability render production of doped PAni thin films particularly challenging. In this contribution, DC magnetron sputtering, a physical vapor deposition technique, is applied to the preparation of conductive thin films of PAni doped with hydrochloric acid (PAni-HCl) in an effort to circumvent issues associated with conventional thin film preparation methods. Samples manufactured by the sputtering method are analyzed along with samples prepared by conventional drop-casting. Physical characterization (atomic force microscopy, AFM) confirm the presence of PAni-HCl and show that films exhibit a reduced roughness and potentially pinhole-free coverage of the substrate. Spectroscopic evidence (UV-vis, FT-IR, and X-ray photoelectron spectroscopy (XPS)) suggests that structural changes and loss of conductivity, not uncommon during PAni processing, does occur during the preparation process. Finally, the applicability of sputtered films to gas-phase sensing of NH(3) was investigated with surface plasmon resonance (SPR) spectroscopy and compared to previous contributions. In summary, sputtered PAni-HCl films exhibit quantifiable, reversible behavior upon exposure to NH(3) with a calculated LOD (by method) approaching 0.4 ppm NH(3) in dry air.     

导电聚苯胺纤维的制备与性能表征

以一种新型的双子表面活性剂6,6′-(丁基-1,4-二基双氧)双(3-壬基苯磺酸)(9BA-4-9BA)作为掺杂剂制备聚苯胺导电纤维,并与用2-丙烯酰胺基-2-甲基丙磺酸(AMPSA)掺杂的聚苯胺纤维的性能进行比较,探讨了聚苯胺分子量、纺丝原液的浓度、掺杂剂种类、凝固浴、牵伸工艺对纤维形貌和导电性能的影响。研究表明,质量分数为14%的AMPSA掺杂聚苯胺的二氯乙酸溶液在丙酮凝固浴中得到的初生纤维的电导率达到1.77S/cm,而质量分数为14%9BA-4-9BA掺杂聚苯胺的二氯乙酸溶液在9BA-4-9BA/丙酮凝固浴中得到的初生纤维及1倍牵伸纤维的表面形貌光滑规整,电导率分别为0.39 S/cm和1.14 S/cm。     

Highly sensitive protein sensor based on thermally-reduced graphene oxide field-effect transistor

We report the fabrication of a highly sensitive field-effect transistor (FET) biosensor using thermally-reduced graphene oxide (TRGO) sheets functionalized with gold nanoparticle (NP)-antibody conjugates. Probe antibody was labeled on the surface of TRGO sheets through Au NPs and electrical detection of protein binding (Immunoglobulin G/IgG and anti-Immunoglobulin G/anti-IgG) was accomplished by FET and direct current (dc) measurements. The protein binding events induced significant changes in the resistance of the TRGO sheet, which is referred to as the sensor response. The dependence of the sensor response on the TRGO base resistance in the sensor and the antibody areal density on the TRGO sheet was systematically studied, from which a correlation of the sensor response with sensor parameters was found: the sensor response was more significant with larger TRGO base resistance and higher antibody areal density. The detection limit of the novel biosensor was around the 0.2 ng/mL level, which is among the best of reported carbon nanomaterial-based protein sensors and can be further optimized by tuning the sensor structure.      

Effects of the surface treatment on the properties of polyaniline coated carbon nanotubes/epoxy composites

The effects of a surface treatment of carbon nanotubes (CNTs) on the electrical conductivity and the hydrophilicity of a polyaniline (PAni) coated CNTs (PAni-CNTs)/epoxy (EP) composites were examined. The surface of the CNTs was treated with various chemicals, such as acid mixtures (HNO₃:H₂SO₄), potassium persulfate (KPS) and sodium dodecyl sulfate (SDS), to improve their dispersion and reactivity with PAni. The electrical conductivity and hydrophilicity of PAni-CNTs and their EP composites were strongly affected by the surface treatment of the CNTs. The surface-treating materials remained on the surface of the CNTs affected the reactivity of the CNTs surface to PAni, and thus resulted in different PAni amounts in the PAni-CNTs. The electrical conductivity of the PAni-CNTs/EP composites decreased, but the hydrophilicity increased, with increasing the amount of PAni coating on the CNTs surface.     

Highly sensitive photoelectrochemical immunoassay with enhanced amplification using horseradish peroxidase induced biocatalytic precipitation on a CdS quantum dots multilayer electrode

Herein we demonstrate the protocol of a biocatalytic precipitation (BCP)-based sandwich photoelectrochemical (PEC) horseradish peroxidase (HRP)-linked immunoassay on the basis of their synergy effect for the ultrasensitive detection of mouse IgG (antigen, Ag) as a model protein. The hybrid film consisting of oppositely charged polyelectrolytes and CdS quantum dots (QDs) is developed by the classic layer by layer (LbL) method and then employed as the photoactive antibody (Ab) immobilization matrix for the subsequent sandwich-type Ab-Ag affinity interactions. Improved sensitivity is achieved through using the bioconjugates of HRP-secondary antibodies (Ab(2)). In addition to the much enhanced steric hindrance compared with the original one, the presence of HRP would further stimulate the BCP onto the electrode surface for signal amplification, concomitant to a competitive nonproductive absorption that lowers the photocurrent intensity. As a result of the multisignal amplification in this HRP catalyzed BCP-based PEC immunoassay, it possesses excellent analytical performance. The antigen could be detected from 0.5 pg/mL to 5.0 ng/mL with a detection limit of 0.5 pg/mL.