One-step synthesis of amino-dextran-protected gold and silver nanoparticles and its application in biosensors

A sensitive method for the detection of the lectin protein concanavalin A (Con A) was developed using amino-dextran (AD)-protected gold (AD-Au) and silver nanoparticles (AD-Ag) as sensitive optical probes. The AD-Au and AD-Ag nanoparticles were synthesized by directly applying amino-dextran as a reductive and protective reagent. The size of the nanoparticles could be altered by changing the molar ratio of AD to the metal salt. The amino-dextran bound to Con A by forming a 4:1 Au-Con A complex at neutral pH, and the nanoparticles were induced to aggregate by Con A. The absorption intensity of the nanoparticles decreased linearly with as the Con A concentration was increased from 3.85×10^–8 to 6.15×10^–7 M. The Au-Con A complex was dissociated by the disaccharide isomaltose, which has a higher affinities for Con A than Au; this competitive strategy could also be used to detect similar types of saccharides.     

生物传感器研究及应用进展

生物传感器是由分子识别元件和信号转换器构成的分析检测仪器,具有敏感、准确、易操作等特点.本文综述了近几年国内外生物传感器研究现状,重点介绍了酶传感器、免疫传感器、DNA传感器和微生物细胞传感器的研究创新以及在医学、环境监测、食品安全、军事等领域应用的最新进展,展望了未来的研究方向.     

壳聚糖-二茂铁复合物的制备及其在电化学传感器上的应用

壳聚糖-二茂铁复合物(CHIT-Fc)由二茂铁羧酸的羧基和脱乙酰壳多糖的羟基缩合合成,并通过红外光谱检测.合成得到的壳聚糖-二茂铁复合物通过物理吸附作为固定胆固醇氧化酶(CHOx)的基体.同时,使用Nafion稀释液可以消除诸如抗坏血酸和尿酸的影响.最佳测试条件下,采用示差脉冲(DPV)研究胆固醇生物传感器的响应,在4.0×10-6mol/L～1.0×10-4 mol/L范围内,氧化峰电流与胆固醇浓度呈现良好的线性关系,线性方程为Ipa=0.0223c-0.0875(Ipa:μA,c:μmol/L,R=0.9982),检测限为5.0×10-7mol/L(S/N=3).     

电氧化异丙肾上腺素的纳米复合电催化剂：用作传感器

在金纳米粒子(AuNPs)上经苯硫酚衍生物(3,4二羟基苯基-偶氮-苯硫酚, DAT)自组装制得了一种新型纳米复合物,用于修饰玻璃碳电极(GCE/AuNP-DAT).采用循环伏安法研究了该新型电极的性质,并将其用作异丙肾上腺素(IP)电催化剂,考察了该纳米复合物的电催化活性,从而得到反应机理和催化反应速率常数.由于GCE/AuNP-DAT电极对尿酸氧化没有电催化活性,因此可将IP的氧化信号从该改进电极中分离出来,从而排除了尿酸对IP测定的干扰.该电极可作为传感器,当用于差动脉冲伏安法测定IP时,线性动态范围为1.0–1500.0μmol/L,检测极限为0.46μmol/L.     

Development of a pressure-driven nanofluidic control system and its application to an enzymatic reaction

A novel air-pressure-based nanofluidic control system was developed and its performance was examined. We found that the flow in a 100 nm scale nanochannel on a chip (called an extended nanospace channel) could be controlled within the pressure range of 0.003–0.4 MPa, flow rate range of 0.16–21.2 pL/min, and residence time range of 24 ms–32.4 s by using the developed nanofluidic control system. Furthermore, we successfully demonstrated an enzyme reaction in which the fluorogenic substrate TokyoGreen-β-galactoside (TG-β-gal) was hydrolyzed to the fluorescein derivative TokyoGreen (TG) and β-galactose by the action of β-galactosidase enzyme as a calalyst in a Y-shaped extended nanospace channel. The parameters for the reaction kinetics, such as K _m, V _max and k _cat, were estimated for the nanofluidic reaction, and these values were compared with the results of bulk and microfluidic reactions. A comparison showed that the enzyme reaction rate in the Y-shaped extended nanospace channel increased by a factor of about two compared with the rates in the bulk and micro spaces. We thought that this nanospatial property resulted from the activated protons of water molecules in the extended nanospace. This assumption was supported by the result that the pH dependence of the maximum enzyme activity in the Y-shaped extended nanospace channel was slightly different from that in the bulk and micro spaces. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Acetone extracted propolis as a novel membrane and its application in phenol biosensors: the case of catechol

A novel biosensor for catechol has been constructed by immobilizing polyphenol oxidase (PPO) into acetone-extracted propolis (AEP) composite modified with gold nanoparticles (GNPs) and attached to multiwalled carbon nanotube (MWCNTs) on a gold electrode surface. The propolis for AEP was obtained from honeybee colonies. Under the optimum conditions, this method could be successfully used for the amperometric determination of catechol within a concentration range of 1 × 10⁻⁶ to 5 × 10⁻⁴ M, with a detection limit of 8 × 10⁻⁷ M (S/N = 3). The effects of pH and operating potential are also explored to optimize the measurement conditions. The best response was obtained at pH 5, while an optimum ratio of signal-to-noise (S/N) was obtained at −20 mV (versus Ag/AgCl), which was selected as the applied potential for the amperometric measurements. All subsequent experiments were performed at pH 5. Cyclic voltammetry and electrochemical impedance spectroscopy was used to characterize the PPO/CNTs/GNPs/AEP/Au biosensor. The biosensor also exhibited good selectivity, stability, and reproducibility.

     

Acetone extracted propolis as a novel membrane and its application in phenol biosensors: the case of catechol

A novel biosensor for catechol has been constructed by immobilizing polyphenol oxidase (PPO) into acetone-extracted propolis (AEP) composite modified with gold nanoparticles (GNPs) and attached to multiwalled carbon nanotube (MWCNTs) on a gold electrode surface. The propolis for AEP was obtained from honeybee colonies. Under the optimum conditions, this method could be successfully used for the amperometric determination of catechol within a concentration range of 1 × 10^?6 to 5 × 10^?4?M, with a detection limit of 8 × 10^?7?M (S/N = 3). The effects of pH and operating potential are also explored to optimize the measurement conditions. The best response was obtained at pH?5, while an optimum ratio of signal-to-noise (S/N) was obtained at ?20?mV (versus Ag/AgCl), which was selected as the applied potential for the amperometric measurements. All subsequent experiments were performed at pH?5. Cyclic voltammetry and electrochemical impedance spectroscopy was used to characterize the PPO/CNTs/GNPs/AEP/Au biosensor. The biosensor also exhibited good selectivity, stability, and reproducibility.     

Study of carbon nanotubes-HRP modified electrode and its application for novel on-line biosensors

In this paper, multi-walled carbon nanotubes (MWCNTs) were successfully immobilized on the surface of a glassy carbon electrode by mixing with horse-radish peroxidase (HRP). The electrochemical behavior of H2O2 was also studied with the MWCNTs-HRP modified electrode as a working electrode. The MWCNTs-HRP modified electrode showed excellent response of reduction current for the determination of H2O2 at the potential of -300 mV (vs. Ag/AgCl). We assembled the MWCNTs-HRP modified electrode in a thin-layer flow cell and the H2O2 solution was continuously introduced into the cell with a syringe pump. We optimized the sensitivity of the H2O2 sensor by adjusting the working potential and the pH of the buffer solution. The peak current increased linearly with the concentration of H2O2 in the range 3.0 x 10(-7) to approximately 2.0 x 10(-4) mol L(-1). The detection limit is 1.0 x 10(-7) mol L(-1) (S/N = 3). The interferences from ascorbic acid, uric acid and other electroactive substances can be greatly excluded since the sensor can be operated at -300 mV. Stability and reproducibility of the MWCNTs-HRP chemically modified electrode were also studied in this paper. Fabricated with glucose and lactate oxidase, the MWCNTs-HRP electrode was also applied to prepare the on-line glucose and lactate biosensors because of the high sensitivity for the determination of H2O2.     

Development of a miRNA-controlled dual-sensing system and its application for targeting miR-21 signaling in tumorigenesis

MicroRNAs (miRNAs) are considered to be strong prognostic markers and key therapeutic targets in human diseases, especially cancer. A sensitive monitoring platform for cancer-associated miRNA (oncomiR) action is needed for mechanistic studies, preclinical evaluation, and inhibitor screening. In this study, we developed and systemically applied a sensitive and efficient lentivirus-based system for monitoring oncomiR actions, essentially miR-21. The specificity and sensitivity of “miRDREL” against various oncomiRs were validated by checking for tight correlations between their expression and targeting efficacy. Experiments based on the transfection of synthetic mimics and antagomir-mediated depletion of oncomiRs further confirmed the specificity of the system. Systemic application of miRDRELs to natural oncomiR targets, knockdown of key microprocessors, and physiological triggering of oncomiRs also demonstrated that the system is an effective tool for monitoring cellular oncomiR action. Importantly, molecular modeling-based screening confirmed the action of the miR-21-targeting drug ivermectin and led to the identification of a new effective derivative, GW4064, for inhibiting oncogenic DDX23-miR-21 signaling. Furthermore, proteomic-kinase inhibitor screenings identified a novel oncogenic kinome-DDX23-miR-21 axis and thus expands our understanding of miR-21 targeting therapeutics in tumorigenesis. Taken together, these data indicate that miRDREL and its versatile application have great potential in basic, preclinical studies and drug development pipelines for miRNA-related diseases, especially cancer.Subject terms: Oncogenes, Cell signalling     

Implantable application of polymer-based biosensors

Implantable sensors offer a great opportunity to extract physiological information from inside the body by real-time monitoring. With the demand for personal healthcare and point-of-care treatment, a long-term stable sensor of excellent mechanical and biological compatibility with human organs is urgently required. In contrast to rigid electronic devices using silicon or metallic materials, soft sensors are realized by flexible polymers in a simple way, endowing the implantable sensor with a tissue-mimetic structure. In this article, we systematically review the development of implantable electronic sensors based on polymer materials. The unique properties of polymers are introduced, followed by their applications in implantable device fabrication. Strategies to integrate polymers with implantable sensors, encompassing device interface, geometry, and integration, are also summarized. Furthermore, biosensing applications of polymer-based implantable devices are described, ranging from physical stimulus monitoring to biochemical analysis in vivo. Finally, we envision how advances in polymer materials may facilitate the development of intelligent sensors with broader applications in vivo.     

Conducting polymer nanostructures and their application in biosensors

Nowadays, functionalized conducting polymer nanomaterials have been received great attention in nanoscience and nanotechnology because of their large surface area. This article reviews various methods for synthesis of conducting polymer nanostructures and their applications in sensing materials, focusing on hard-template, soft-template and other methods and the formation mechanism of conducting polymer nanostructures by these methods. Conducting polymer nanostructures, such as nanotubes, nanowires, and nanoparticles, as sensing platforms for various applications are also summarized.     

Label-free biosensors based on optically responsive nanocomposite layers: sensitivity and dynamic range

Core-shell nanoparticle layers have proven to be a promising tool for the label-free detection of binding events. Upon reflection of white light, they exhibit pronounced extinction peaks in the UV/vis and NIR regime of the electromagnetic spectrum, which shift to higher wavelengths when molecules are adsorbed. Beside drastic simplification of the instrumentation and related reduction in cost, a significantly stronger response toward alkanethiol adsorption has been observed in previous experiments than in conventional surface plasmon resonance (SPR). However, as the amount of molecules deposited onto the nanoparticle films was unknown, no quantitative relationship could be established between the measured wavelength shifts and the surface mass density of the adsorbate. In order to facilitate quantitative molecule detection, self-assembled monolayers (SAMs) of simple and ethylene glycol (EG) terminated alkanethiols with various chain lengths were prepared on the nanoparticle-coated substrates. The measured red-shift of the extinction spectrum upon molecule adsorption was related to the amount of adsorbate as determined by X-ray photoelectron spectroscopy (XPS). For the whole range of film thicknesses studied, a linear relationship is found yielding a sensitivity factor of 0.027 nm/(ng/cm (2)). As proven by enzyme-linked immunosorbent assay (ELISA), such determined sensitivity factor can also be used to correctly predict the amount of surface-bound protein in immunoreactions from the measured wavelength shifts. It is concluded that the decay length of the evanescent electric field associated with the nanoparticle sensors is more than 100 nm and, thus, significantly larger than that observed for localized surface plasmons excited in small isolated metal clusters.     

Comparison of biosensors based on gold and nanocomposite electrodes for monitoring of malic acid in wine

Amperometric biosensors based on a gold planar electrode and on two types of nanocomposite electrodes consisting of multi-walled carbon nanotubes for the determination of L-malic acid designed for wine-makers were developed. The biosensors designed for wine-makers were constructed by immobilization of L-malate dehydrogenase and diaphorase within chitosan layers on the surface of the electrodes. The coenzyme NAD+ and the electrochemical mediator ferricyanide were present in the measuring solution. The current resulting from re-oxidation of produced ferrocyanide was measured at a working potential of +300 mV against an Ag/AgCl reference electrode. The biosensor based on a gold electrode showed linearity over the range 10–520 μM with a detection limit of 5.41 μM. Calibration curves for biosensors utilizing nanocomposites were obtained both with the linear range of 10 to 610 μM. The detection limits were 1.57 and 1.77 μM, respectively. The biosensors showed satisfactory operational stability (no loss of sensitivity after 30 consecutive measurements) and storage stability (90% of the initial sensitivity after one year of storage at room temperature). The results obtained from measurements of wine samples were in a good correlation with the standard HPLC method. Satisfactory biosensor sensitivity, specificity and stability allowed their successful commercialization.     

In situ spontaneous reduction synthesis of spherical Pd@Cys-C60 nanoparticles and its application in nonenzymatic glucose biosensors

Novel spherical Pd@Cys-C(60) nanoparticles were synthesized using an in situ spontaneous reduction process without any other reducing agent. A nonenzymatic electrochemical biosensor was developed for the detection of glucose based on the spherical nanoparticles film.     

Studies on the construction and operation of miniaturized potentiometric biosensors

This study aims at presenting the studies on construction and operation of solid-state miniaturized biosensor with potentiometric detection. The performance of sensors with layer which consisted of mixture of aliphatic thiols and thiols containing ferrocene terminal groups or the conductive polymer layer obtained by electrochemical polymerization of 3,4-ethylenedioxythiophene was compared. Both of the applied modifications proved to significantly affect the sensors’ performance, influencing the stability of their working parameters in time. Wherein, the greatest improvement in planar sensors’ operating parameters was achieved by applying conductive polymer layer. Subsequently, a system creating universal platform for the construction of a biosensor, dedicated to almost any analyte determination, depending on the composition of the affinity proteins used in the receptor layer, was developed. For the construction of proposed biosensor, alkaline phosphatase was chosen as a model enzyme, assuming either the role of direct component of receptor layer or a label in affinity biosensor. The affinity biosensor structure was characterized by a sandwich assay, using a highly specific interaction occurring between streptavidin and biotin. Aside from optimization of various components of the constructed sensor, the most adequate analysis conditions were designated in the course of presented research. As it turned out, the composition of buffer solution used has a significant influence on the activity of the applied enzyme as well as on the working parameters of the sensor. Tris buffer was, therefore, found as the one ensuring the best performance of sensors utilizing alkaline phosphatase.     

Preparation of a new core-shell Ag@SiO2 nanocomposite and its application for fluorescence enhancement

Ag@SiO₂ nanoparticles with different shell thicknesses were synthesized via modified Stöber method. Rhodamine B isothiocyanate was covalently bound onto the surface of Ag@SiO₂ nanoparticles to form fluorescent core-shell Ag@SiO₂ nanocomposites. Effects of shell thickness on the fluorescence enhancement were examined using the corresponding nanobubbles prepared by cyanide etching as a control. The result showed that the fluorescence enhanced as the shell thickness increased till the distance between fluorophore and metal core reached about 75 nm with the optimal enhancement factor of ∼5-folds. Further increasing of fluorophore-metal distance caused a decrease in the enhancement factor.     

Urease purification from the seeds ofCajanus Cajan and its application in a biosensor construction

Urease has been purified from the seeds of Cajanus Cajan. The purification process involves three solvent extraction steps followed by DEAE-cellulose column chromatography. The specific activity of the purified enzyme is found to be 1920 U/mg with the recovery of 8%. The application of the purified enzyme in a biosensor construction is discussed.     

Design and application of a flow cell for carbon-film based electrochemical enzyme biosensors

A flow cell has been designed for use with an electrochemical enzyme biosensor, based on low-cost carbon-film electrodes. Three types of mediators were used: cobalt and copper hexacyanoferrates and poly(neutral red) (PNR), covered with glucose oxidase (GOx) immobilised by cross-linking with glutaraldehyde in the presence of bovine serum albumin or inside a oxysilane sol–gel network. Mixtures of sol–gel precursors were made from 3-aminopropyl-triethoxysilane (APTOS) together with methyltrimethoxysilane (MTMOS), methyltriethoxysilane (MTEOS), tetraethyloxysilane (TEOS) or 3-glycidoxypropyl-trimethoxysilane (GOPMOS), and the best chosen for encapsulation. Optimisation in batch mode, using amperometric detection at fixed potential, showed the PNR-GOx modified carbon-film electrodes to be best for flow analysis for both glutaraldehyde and sol–gel enzyme immobilisation. Both types of enzyme electrode were tested under flow conditions and the reproducibility and stability of the biosensors were evaluated. The biosensors were used for fermentation monitoring of glucose in grape must and interference studies were also performed.     

Superabsorbent nanocomposite and its properties

Starch-g-poly (AM-AMPS)/illite superabsorbent nanocomposite was synthesized by grafting copolymerization reaction of starch, acrylamide(AM) and 2-acrylamido-2- methyl propane sulfonic acid (APMS) in the presence of illite micropowder in deionized aqueous solution. The influence factors on water absorbency of the superabsorbent nanocoposite was optimized by single factor experiment. The synthesized superabsorbent nanocomposite exhibited the maximum water absorbency of 1320?g H₂O/g in deionized water and 142?g H₂O/g in 0.9?wt% sodium chloride (NaCl) solution. FTIR spectra confirmed that the grafting copolymerization between -OH groups on starch and monomers generated during the reaction. XRD analysis confirmed that crystal interlayer of illite was pulled open to 3.61?nm. TEM showed that illite slice layer randomly dispersed in the matrix of superabsorbent nanocomposite. The superabsorbent nanocomposite had a better thermal stability the corresponding superabsorbent material without illite by TGA and DSC analysis. The superabsorbent nanocomposite with excellent water absorbency and water retention could be especially useful in industry, agricultural, horticultural applications.