pH‐induced morphological changes of carboxymethyl chitosan self assembled monolayer films

Self assembled monolayer (SAM) films of carboxymethyl chitosan (CM‐CHI) were prepared by immersing mica in CM‐CHI aqueous solution at pH = 1.7. The obtained films were further rinsed in baths of water at different pH. The pH induced morphological change of carboximethyl chitosan SAM films was investigated by atomic force microscope using tapping mode. The results showed that the morphology of the films was remarkably affected by the pH of rinse bath. Three obvious morphological changes were discussed and explained by the competition between electrostatic interaction and hydrogen bond. We draw attention to the “Crater” structures in the films and find that the formation and evolution of “Crater” structures have a close relationship with the pH of rinse bath. The formation mechanism of the other two special structures was also discussed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Electrochemical fabrication of self assembled monolayer using ferrocene-functionalized gold nanoparticles on glassy carbon electrode

Electrochemical (EC) quantification of 11-Mercaptoundecylferrocene (thiolated-ferrocene substrate, Fc-SH) onto gold nanoparticles (AuNPs) was carried out through cyclic voltammetric (CV) investigations in different base electrolyte aqueous media on glassy carbon (GC) electrode. The electrochemical data including peak current, peak potential values revealed the Fc-SH–AuNPs redox system to be adsorption controlled in terms of self assembled monolayers (SAMs). The electrochemically generated SAMs were found quite stable as these maintained the redox activity upto 3 months after repeated CV scans at 298 K. The overall output of this research can be utilized in two ways: application of electroactivity and stability of these SAMs in detection of biologically important molecules and also towards the development of EC biosensors.     

Towards osseointegration of bioinert ceramics: Introducing functional groups to alumina surface by tailored self assembled monolayer technique

The bioinert character of alumina implants does not promote bone bonding, thereby strongly limits possible applications for this material. Bone bonding to the implant surface is significantly dependent on its chemical composition. We hypothesized that a bioinert ceramic can be functionalized, introducing active groups onto the surface by self-assembled monolayer. The surface of alumina was coated with a silica layer using physical vapour deposition or flame pyrolysis. Subsequently SAM was attached by dint of octenyltrichlorosilane. Through further chemical treatments OH- and COOH-functional groups were created on the surface. The evidence of the functional groups was proven by X-ray photoelectron spectroscopy and contact angle measurements. Thereby for the first time functional groups were successfully coupled to an inert alumina surface using the method of SAM. In a next step of development, SAM technique could be used to couple biological agents to inert ceramic implant surfaces aiming the possible improvement of osseointegration.     

Self-assembled monolayer based impedimetric platform for food borne mycotoxin detection

A self-assembled monolayer (SAM) of 11-amino-1-undecanethiol (AUT) has been fabricated onto a gold (Au) substrate to co-immobilize anti-ochratoxin-A antibodies (AO-IgGs) and bovine serum albumin (BSA) to detect food borne mycotoxin [i.e., ochratoxin-A (OTA)]. AUT/Au electrode, AO-IgGs/AUT/Au immunoelectrode and BSA/IgGs/AUT/Au immunoelectrode have been characterized using scanning electron microscopy (SEM) and electrochemical studies such as cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). Electrochemical studies reveal that the AUT-SAM with NH2 groups provide favorable conditions to immobilize AO-IgGs with better orientation, resulting in enhanced electron transport to obtain improved sensing characteristics. The EIS response studies of the BSA/AO-IgGs/AUT/Au immunoelectrode obtained as a function of OTA concentration reveal that the value of the charge transfer resistance (RCT) increases with increased OTA concentration. The BSA/AO-IgGs/AUT/Au immunoelectrode exhibits linearity over 0.5-6.0 ng/dl, detection limit of 0.08 ng/dl using 3σb/m criteria, response time of 30 s and sensitivity of ～36.83 Ω/ng dl(-1) cm(-2) with a regression coefficient of 0.999. Attempts have been made to monitor the change in RCT of BSA/AO-IgGs/AUT/Au immunoelectrode on addition of coffee samples.     

A self tuning controller for multicomponent batch distillation with soft sensor inference based on a neural network

Multicomponent batch distillation is an operation difficult to control not only for its nonlinear and transient behaviour, but because the product quality cannot be measured rapidly and with reliability. In the present work, a computational system for direct digital control is developed for a pilot plant batch distillation column. The development of a self tuning regulator and a soft sensor of composition based on a neural network is described. Top and reboiler temperature measurements are the basis for the on-line composition inference. The computational system was experimentally tested in a computer operated pilot column. It could be seen that the neural network soft sensor is a feasible and a reliable tool to solve on-line operational problems of the control engineering systems. The developed control system permits to operate the batch distillation column efficiently and is easy to be implemented and operated.     

Urease immobilized polyethylene-g-acrylic acid membrane for urea sensor

A new type of polymer support for immobilizing urease was investigated. The starting copolymers which grafted acrylic acid onto polyethylene (PE-g-AA) were prepared via gamma ray irradiation induced grafting under controlled conditions by postirradiation procedures. The optimum conditions for coupling urease to PE-g-AA were established and the physical properties of the support affecting the immobilized enzyme activity were studied. A water soluble carbodiimide (CMC) was used as a condensing agent to immobilize urease. The activities of the resulting enzyme membranes were very high. The hydrophilicity of the support and the activity of the enzyme membrane were proportional to the degree of grafting. Its linear detecting range was 60–400 ppm.     

A polymer based fluorescent sensor for Zn detection and its application for constructing logic gates

A polymer-based fluorescent sensor was synthesized by polymerization of (S)-6,6′-dibutyl-3,3′-(di-5-salicylde-ethynyl)-2,2′-binaphthol (M-1) with (R,R)-1,2-diaminocyclohexane (M-2) via nucleophilic addition-elimination reaction. The responsive optical properties of the polymer on transition metal ions were investigated by fluorescence and UV-vis spectra. The polymer (1.0 × 10⁻⁵ mol/L in THF) could emit fluorescence at 550 nm and exhibit high selectivity for sensing Zn²⁺ with 36.1-fold fluorescence enhancement. Three logic gates were designed according to the different fluorescence responses of this polymer sensor to Zn²⁺ and Cu²⁺.     

A novel sensor platform based on aptamer-conjugated polypyrrole nanotubes for label-free electrochemical protein detection

We first present a simple yet versatile strategy for the functionalization of polymer nanotubes in a controlled fashion. Carboxylic-acid-functionalized polypyrrole (CPPy) nanotubes were fabricated by using cylindrical micelle templates in a water-in-oil emulsion system, and the functional carboxyl groups were effectively incorporated into the polymer backbone during the polymerization by using pyrrole-3-carboxylic acid (P3CA) as a co-monomer without a sophisticated functionalization process. It was noteworthy that the chemical functionality of CPPy nanotubes was readily controlled in both qualitative and quantitative aspects. On the basis of the controlled functionality of CPPy nanotubes, a field-effect transistor (FET) sensor platform was constructed to detect specific biological entities by using a buffer solution as a liquid-ion gate. The CPPy nanotubes were covalently immobilized onto the microelectrode substrate to make a good electrical contact with the metal electrodes, and thrombin aptamers were bonded to the nanotube surface via covalent linkages as the molecular recognition element. The selective recognition ability of thrombin aptamers combined with the charge transport property of CPPy nanotubes enabled the direct and label-free electrical detection of thrombin proteins. Upon exposure to thrombin, the CPPy nanotube FET sensors showed a decrease in current flow, which was probably attributed to the dipole-dipole or dipole-charge interaction between thrombin proteins and the aptamer-conjugated polymer chains. Importantly, the sensor response was tuned by adjusting the chemical functionality of CPPy nanotubes. The efficacy of CPPy nanotube FET sensors was also demonstrated in human blood serum; this suggests that they may be used for practical diagnosis applications after further optimization.     

Electrochemical sensor for bisphenol A detection based on molecularly imprinted polymers and gold nanoparticles

A novel bisphenol A (BPA) sensor based on amperometric detection has been developed by using molecularly imprinted polymers (MIPs) and gold nanoparticles. The sensitive layer was prepared by electropolymerization of 2-aminothiophenol on a gold nanoparticles-modified glassy carbon electrode in the presence of BPA as a template. Cyclic voltammetry was used to monitor the process of electropolymerization. The properties of the layer were studied in the presence of Fe(CN)₆ ³⁻/Fe(CN)₆ ⁴⁻ redox couples. The template and the non-binding molecules were removed by washing with H₂SO₄ (0.65 mol L⁻¹) solution. The linear response range of the sensor was between 8.0 × 10⁻⁶–6.0 × 10⁻² mol L⁻¹, with a detection limit of 1.38 × 10⁻⁷ mol L⁻¹ (S/N = 3). The proposed MIPs sensor exhibited good selectivity for BPA. The stability and repeatability of the MIPs senor were found to be satisfactory. The results from real sample analysis confirmed the applicability of the MIPs sensor to quantitative analysis.     

分子印迹电化学传感器检测链霉素

为实现链霉素的快速、灵敏测定,将特异性强的分子印迹技术与检测灵敏度高的电化学检测方法结合,构建链霉素分子印迹电化学传感器。以链霉素为模板分子,吡咯为功能单体,利用电化学聚合方法制备分子印迹聚合物(MIP)膜。在最优化实验条件下,以铁氰化钾为探针,利用循环伏安法(CV)对链霉素进行定量测定及传感器性能研究。结果表明:传感器线性范围为5.00×10~(-8)～8.00×10~(-5)mol/L,最低检出限(LOD)为3.45×10~(-8)mol/L,为链霉素的测定提供了高效的方法。     

Urease immobilized polyvinyl alcohol-g-butyl acrylate membrane for urea sensor

A copolymer with balanced hydrophilicity and hydrophobicity was synthesized by grafting butyl acrylate onto poly(vinyl alcohol) (PVA-g-BA). Films made from it had good urea permeability. After immobilization of the enzyme urease on the surface of it, the film was attached to the tip of an ammonia gas electrode to form an enzyme sensor. The sensor was able to detect urea in solution in the range of 6 to 600 mg/dL with a response time of about 5 min. It might be reused for over 100 times, and the reproducibility was very good. Therefore, it is very promising that this sensor may be commercialized for clinical use. The synthesis of PVA-g-BA was initiated with cerium ammonium nitrate, and the immobilization of urease was done by crosslinking with cyanuric chloride of glutaraldehyde. The former agent was proved to be more effective than the later. The amount of enzyme immobilized with the former were 26 and 13 times more than the one- and two-step methods with the latter, respectively.     

A microfluidic actuator based on thermoresponsive hydrogels

We have evaluated the potential use of thermoresponsive hydrogels based on N-isopropylacrylamide as actuators in microfluidic and lab-on-a-chip devices. This required fabrication of hydrogel actuators on the μm length scale, anisotropic swelling of the resulting materials, and control over the kinetics of the hydrogel volume phase transition. The fabrication procedure combined gel polymerization and casting techniques from the life sciences with more traditional semiconductor fabrication protocols for spin-coating, patterning, and etching. The actuator design used a PDMS membrane to separate the hydrogel actuator from the microfluidic channel and a separate reservoir for fluid to swell the actuator. As a result, the actuator could control flow for organic as well as aqueous solutions over a wide range of pH and ionic strength. The presence of a fixed substrate causes the gel swelling to be highly anisotropic, and the actuating motion is perpendicular to the substrate. The anisotropic swelling also limits the degree of swelling for the responsive hydrogel, and the total volume change is lower than the corresponding bulk materials by as much as an order of magnitude. The resulting actuators conform easily to the shape of the microfluidic channel, and the rate of the hydrogel response could be increased by using a series of semi-interpenetrating hydrogel networks. The microfluidic channels ranged in diameter from 180 to 380 μm, and the typical actuator was between 100 to 500 μm in diameter. The time scale of the actuator response was approximated by fitting with a single exponential (∼exp[−t/τ]). The time scale (τ) varied as a function of the actuator size and composition, ranging from 10 min to less than 10 s.     

基于微流控的现代生物医学检测技术概述

首先介绍了微泵和微阀等常用的微流控器件,然后介绍了利用微流控技术进行片上预处理的方法,包括细胞分离、细胞裂解和微流控富集技术。最后,对微流控在免疫检测中的应用进行了介绍。现代医学检测需要一种全自动、集成化、低成本并且易于操作的微流控系统,从这些方面考虑,给出了微流控生物芯片的一些改进方向。     

A micro sensor based on TiO2 nanorod arrays for the detection of oxygen at room temperature

A new micro gas sensor based on the TiO₂ nanorod arrays (NRAs) was developed and its response properties to oxygen (O₂) at room temperature were investigated. The micro sensor combined a pair of micro interdigitated electrodes realized by the MEMS process and sensing materials based on the TiO₂ NRAs. The TiO₂ NRAs were selectively grown on the patterned straps of Ti/Pd films through the acid vapor oxidation (AVO) process. Relationship between the morphology of the TiO₂ NRAs and reaction temperatures was analyzed with the scanning electronic microscopy (SEM) and X-ray diffraction (XRD). The results indicate that the diameters of the TiO₂ NRs enlarged as the reaction temperature increased from 140 °C to 180 °C. The TiO₂ NRAs sensors showed a good response to O₂ at room temperature (25 °C) due to the large specific surface areas of the TiO₂ NRs and the TiO₂ NR/NR junctions. The TiO₂ NRAs sensors prepared at 140 °C for 3 h exhibited better response properties to O₂ at room temperature with a fast response and recovery time. The research indicates that the TiO₂ NRAs prepared by the simple AVO process is a good choice for detecting O₂ at room temperature.     

非标记型溶菌酶荧光传感器的研究

以溴化乙锭作为信号物质,以溶菌酶适配体作为分子识别物质,构建了无需标记的在均相溶液中检测溶菌酶的荧光传感器。在优化的条件下,该方法的检出限为3×10-8mol/L,线性范围为1.0×10-7～9.0×10-7mol/L,相关系数为0.993 8。该方法不需要对适体和目标物进行标记,且具有选择性好、简单易行的特点。     

A disposable immunomagnetic electrochemical sensor based on functionalised magnetic beads on gold surface for the detection of atrazine

A disposable immunomagnetic electrochemical sensor involving magnetic particles was developed and applied for the detection of atrazine. The sensor was based on a magnetic monolayer of magnetic particles coated with streptavidin, formed on a gold electrode after application of a magnetic field. The magnetic monolayer was characterized using faradaic impedance spectroscopy, cyclic voltammetry and atomic force microscopy (AFM) techniques. The magnetic monolayer formation leads to an important change in constant phase element due to a change in thickness. AFM images show that the magnetic monolayer is formed and is very dense. The atrazine interacts with biotinyl-Fab fragment K47 and the immunoreaction was characterized by impedance spectroscopy. A decrease in electron transfer resistance was observed which could be attributed to rearrangements in the magnetic monolayer. This approach leads to a sensitive detection of atrazine, acting as an antigen, with a good linear response in the range 10-600 ng/ml.     

Enhanced NO2 gas sensor device based on supramolecularly assembled polyaniline/silver oxide/graphene oxide composites

Herein, we report a successful synthesis of supramolecularly assembled polyaniline/silver oxide/graphene oxide composite (PANI/Ag₂O/GO) for enhanced NO₂ gas sensing application. The PANI/Ag₂O/GO composite was synthesized by facile stirring followed by an ultrasonication process. The prepared material was characterized by different techniques such as x-ray diffraction, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy and Raman-scattering spectroscopy. The detailed analysis revealed that the average crystallite sizes of PANI/Ag₂O and PANI/Ag₂O/GO composites were found to be 37.37 nm and 41.55 nm, respectively. FESEM and TEM analysis showed coral-like rough-surfaced and extensively agglomerated morphology for PANI and ultrathin flexible sheet-like morphology for GO. Ag₂O nanoparticles with diameters 20–30 nm were well incorporated in the GO sheets and PANI matrix in the case of PANI/Ag₂O/GO composites. The synthesized materials were used to make resistive sensor devices that had a high response to NO₂ gas. The fabricated sensors were examined at various temperatures to obtain the optimal sensing temperature. The fabricated NO₂ gas sensor device based on PANI/Ag₂O/GO composite exhibited a highest sensitivity of 5.85 for 25 ppm at an optimized temperature (100 °C) as compared to the pure PANI (2.5) and PANI/Ag₂O composite (3.25). Further, the fabricated sensor device based on PANI/Ag₂O/GO composite was also examined at different NO₂ gas concentrations.     

A potentiometric and voltammetric sensor based on polypyrrole film with electrochemically induced recognition sites for detection of silver ion

Conducting polypyrrole membranes were deposited on glassy carbon electrodes by electropolymerizing pyrrole in the presence of Eriochrome Blue-Black B (EBB) as the counter anion. The electrodes were then subjected to several oxidation/reduction potential steps in pure silver nitrate solution for successive accumulation/stripping of silver species. This electrochemically mediated doping/templating generated selective recognition elements in the EBB/PPy film for silver ions. The resulting sensor exhibited a considerable enhancement in the potentiometric and voltammetric response characteristics: extending the linear dynamic range and lowering the detection limit. In the potentiometric mode, the sensor showed highly reproducible response with a Nernstian slope of 58.5 ± 0.3 mV per decade of Ag⁺ activity over a linear range spanning seven orders of magnitude (1 × 10⁻⁸ to 1 × 10⁻¹ M Ag⁺), with a detection limit of ∼6 × 10⁻⁹ M. The electrodes demonstrated high selectivity over a large number of cations including alkali, alkaline earth and several transition and heavy metal ions, and could be used over a wide pH range of 1-8.5. The EBB/PPy modified electrode was also used for preconcentration and differential pulse anodic stripping voltammetric (DPASV) measurements. The DPASV peak current was dependent on the concentration of Ag⁺ over the range 3 × 10⁻¹⁰ to 1 × 10⁻⁴ M. The presence of 1000-fold excess of Cd²⁺, Cu²⁺, Cr³⁺, Co²⁺, Mn²⁺, Fe²⁺, Fe³⁺, Ni²⁺ and Pb²⁺ can be tolerated in the determination of silver ion.