Grafting of phosphonate groups on the silica surface for the elaboration of ion-sensitive field-effect transistors

Ion-sensitive field-effect transistors (ISFETs) sensitive to Ca(2+) ions could be elaborated by means of a new grafting process of the phosphonate group at the surface of the silica gate of FETs. A grafting process involving only one chemical reaction step at the surface afforded a significant improvement of the ISFET properties. The sensitivity of the ISFET towards Ca(2+) ions at pH 10 was quasi-linear in the concentration range from 10(-1) to 10(-3) M, and the slope was 10 mV pCa(-1). The site-binding model works well in predicting the experimental data, giving the complexation constant of 10(2.7) and a low value of the grafting density. The origin of the poor response of ISFETs sensitized by means of a multistep grafting process was investigated on silica powders of high specific area: the cleavage of the organic grafts at the SiOSi bonds occurring at each step could be disclosed by means of elemental analyses, infrared, and cross-polarization and magic angle spinning nuclear magnetic resonance of the grafts.     

Quantitative real-time measurements of DNA hybridization with alkylated nonoxidized silicon nanowires in electrolyte solution

The quantitative, real-time detection of single-stranded oligonucleotides with silicon nanowires (SiNWs) in physiologically relevant electrolyte solution is demonstrated. Debye screening of the hybridization event is circumvented by utilizing electrostatically adsorbed primary DNA on an amine-terminated NW surface. Two surface functionalization chemistries are compared: an amine-terminated siloxane monolayer on the native SiO2 surface of the SiNW, and an amine-terminated alkyl monolayer grown directly on a hydrogen-terminated SiNW surface. The SiNWs without the native oxide exhibit improved solution-gated field-effect transistor characteristics and a significantly enhanced sensitivity to single-stranded DNA detection, with an accompanying 2 orders of magnitude improvement in the dynamic range of sensing. A model for the detection of analyte by SiNW sensors is developed and utilized to extract DNA-binding kinetic parameters. Those values are directly compared with values obtained by the standard method of surface plasmon resonance (SPR) and demonstrated to be similar. The nanowires, however, are characterized by higher detection sensitivity. The implication is that SiNWs can be utilized to quantitate the solution-phase concentration of biomolecules at low concentrations. This work also demonstrates the importance of surface chemistry for optimizing biomolecular sensing with silicon nanowires.     

A planar microfabricated nanoelectrospray emitter tip based on a capillary slot

We report on the fabrication and testing of planar nib-like structures for nanoelectrospray ionization-mass spectrometry (nanoESI-MS) applications. The micro-nib structures were fabricated on silicon substrates using the negative photoresist SU-8; they include capillary slots with widths of 8 and 16 microm. A suitable wafer cleaving step made the nib-like structures overhang the edge of a silicon substrate to provide a robust interface for nanoESI-MS applications; this freeing of the nib tip from the wafer surface created a point-like structure that is essential to establish an electrospray. The micro-nib sources were successfully tested on an LCQ Deca XP+ ion trap mass spectrometer using peptide samples at concentrations down to 1 microM. The high voltage was applied using a platinum wire inserted in the sample reservoir upstream to the capillary slot. A Taylor cone was clearly seen at the nib tip. The micro-nibs performed well at voltages as low as 0.8 kV; such performances are state-of-the-art with respect to current micromachined ESI-MS interfaces and are conditions comparable to those used for standard emitter tips. In addition, we clearly observed the influence of the micro-nib slot width on the ionization performances: the narrower the slot, the better the performances.     

放射标记法研究壳聚糖与牛血清白蛋白的自组装超薄膜

基片在两种带有相反电荷的聚电解质溶液中交替吸附 ,其表面形成致密有序的超薄膜的自组装 (ＥＳＡ ｅｌｅｃｔｒｏｓｔａｔｉｃｓｅｌｆ ａｓｓｅｍｂｌｙ)技术是由Ｄｅｃｈｅｒ及其合作者在 1 991年提出[1] ,由于简单易行 ,从一出现就受到了广大研究者的极大兴趣[2～ 4 ] .对生物材料来说 ,这无疑是一项非常重要且方便的表面改性手段 .因为生物材料在生物体内种植时 ,是否会被机体视为异物 ,关键在于机体与材料表面的相互作用 ,而与材料的本体性质基本无关[5] .因此利用这种技术 ,可对生物材料 ,特别是对那些生物相容性不好的材料表面进行…     

Monodispersed Gold Nanoparticles Decorated Carbon Nanotubes as an Enhanced Sensing Platform for Nanomolar Detection of Tramadol

A promising composite‐modified glassy carbon electrode is fabricated by electrodeposition of mono‐dispersed gold nanoparticles onto carbon nanotubes (AuNPs/CNTs/GCE). The electroanalysis of Tramadol (TRA) was achieved by different electrochemical techniques. The effect of different parameters including pH, concentration and potential scan on the oxidation current signal of TRA was investigated. Large excess of ascorbic acid (AA) and uric acid (UA) with a maximum molar ratio of 1/1000 and 1/100, respectively, did not interfere with the response of TRA. The detection limit with high sensitivity is 68 nM. TRA was successfully determined in pharmaceutical dosage forms, without any pretreatment of the samples.     

A microfabricated microconcentrator for sensors and gas chromatography

The key component in trace analysis is the concentration step where the analytes are accumulated before the analysis. This paper presents the development of a micromachined microconcentrator that can be used to enhance the sensitivity of microsensors. Another application demonstrated here is a concentrator-injector for a gas chromatograph. The microconcentrators were fabricated on a 6-in. silicon substrate using standard photolithographic techniques (1 in.= 2.54 cm). The channels were lined with a resistive layer, through which an electric current could be passed to cause ohmic heating. The preconcentration was done on a thin-film polymeric layer deposited above the heater in the channel. Rapid heating of the resistive layer caused the "desorption pulse" to be injected into the sensor, or onto a GC column. Due to their small size, the microconcentrators could be fabricated 20 to 50 (depending upon the size) at a time on a 6-in. silicon wafer. This paper presents the development and characterization of the microconcentrator. It was found that the microconcentrator performed well as a concentrator, and as an injector for GC. A 14-fold enrichment factor was achieved. The microconcentrator exhibited long-term stability in response, with typical relative standard deviation of between 3 and 5%.     

Photocurable ISFET for anionic surfactants. Monitoring of photodegradation processes

The preparation of a new ion-selective field-effect transistor (ISFET) based on a photocurable membrane sensitive to anionic surfactants is described. The membrane is formed by an urethane-acrylate matrix with 2-cyanophenyl octyl ether as the plasticiser. When compared to conventional ion-selective electrodes, the prepared ISFETs do not show significant differences in sensitivity and reproducibility (P=0.05). When calibrating with dodecylbenzenesulfonate (DBS(-)) the prepared ISFETs show a nernstian behaviour, with a slope of 57.5 mV per decade. The linear working range is 1.0x10(-3) to 3.0x10(-6) M DBS(-) and the detection limit is 1.2x10(-6) M. The response times were below 0.7 min in all cases (95% of the step change). As the application, photodegradation processes using titanium dioxide dispersions, were monitored for two common anionic surfactants: DBS(-), being aromatic, and the more alkylic dodecylsulfate, DS(-). The determination of surfactant concentration was performed following a standard addition methodology, using ISFETs as the sensors, and without any previous separation stages. The degradation kinetics in both cases are first-order processes, with half-life times (t(0.5)) of 31.5 min for DBS(-) and 52.0 min for DS(-).     

重氮树脂与牛血清白蛋白共价结合自组装膜及其表面细胞培养

细胞支架作为组织工程的组成部分为细胞生长提供了最佳微环境 ,并对细胞生长与功能进行控制 .由于细胞对支架表面的生物识别是细胞附着、生长和增殖的基本前提 ,所以对材料表面的功能化是一个重要的课题 [1,2 ] . Shoichet等 [3 ] 通过化学反应或等离子体处理的方法 ,将蛋白质引入到材料表面而使其功能化 .基片在两种带有相反电荷的聚电解质溶液中交替吸附 ,其表面形成致密有序的超薄自组装膜 ,这种层 -层自组装技术不仅制备方法简单 ,无需特殊的设备 ,而且对膜组成和厚度能随意调控 ,以水为介质 ,对环境友好 [4～ 6] ,无疑是一项重要的表…     

Effect of fluoroethylene carbonate (FEC) on the performance and surface chemistry of Si-nanowire Li-ion battery anodes

The effect of FEC as a co-solvent on the electrochemical performance and surface chemistry of silicon nanowire (SiNW) anodes was thoroughly investigated. Enhanced electrochemical performance was observed for SiNW anodes in alkyl carbonates electrolyte solutions containing fluoroethylene carbonate (FEC). Reduced irreversible capacity losses accompanied by enhanced and stable reversible capacities over prolonged cycling were achieved with FEC-containing electrolyte solutions. TEM studies provided evidence for the complete and incomplete lithiation of SiNW's in FEC-containing and FEC-free electrolyte solutions, respectively. Scanning electron microscopy (SEM) results proved the formation of much thinner and compact surface films on SiNW's in FEC-containing solutions. However, thicker surface films were identified for SiNW electrodes cycled in FEC-free solutions. SiNW electrodes develop lower impedance in electrolyte solutions containing FEC in contrast to standard (FEC-free) solutions. The surface chemistry of SiNW electrodes cycled in FEC-modified and standard electrolytes were investigated using X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy. The impact of FEC as a co-solvent on the electrochemical behavior of SiNW electrodes is discussed herein in light of the spectroscopic and microscopic studies.     

Abrasive properties of nano silica particles prepared by a sol–gel method for polishing silicon wafers

Abrasive properties of cocoon shaped silica particles fabricated by a sol–gel method have been studied. Since silicon wafers are polished with slurry by the mechanism of Chemical Mechanical Polishing, polishing rates may depend on various chemical and mechanical factors, such as particle concentration in slurry, slurry pH and kinds of basic compounds for controlling the slurry pH. The silicon wafer was polished by slurry continuously fed on a pad, and the polishing rate was estimated as a weight loss of the wafer. For studying the effects of the various factors on the rate, the slurries were prepared by adding the silica particles, basic compounds or salts, and the polishing rates of the slurry were measured. The effects of the various factors were made clear as follows: For the effect of particle concentration, the rates increased with increasing of the concentrations up to 1.0 wt.%. And for the effect of the slurry pH, slurries added basic compounds, such as KOH, NaOH, ammonia, were tested, and it was found that increasing of the slurry pH brought increases of the polishing rates. KOH-containing slurry of pH 13.2 had the fastest rate, 3.6 times as fast as the standard slurry with pH 9.4. For the effect of the adding of salts, it was indicated that the salts, such as KCl, NaCl, NH₄Cl, NaNO₃ and K₂SO₄ increased the polishing rates, and that KCl-containing slurry of 0.36 mol/l had the highest polishing rate, 3.4 times as fast as that of the standard slurry containing no salts.     

In vivo pH MEASUREMENT AND IMAGING OF TUMOR TISSUE USING A pH-SENSITIVE FLUORESCENT PROBE (5,6–CARBOXYFLUORESCEIN): INSTRUMENTAL AND EXPERIMENTAL STUDIES

Abstract This study evaluated the effectiveness of dual-wavelength ratio fluorescence imaging using a pH-dependent indicator (5,6–carboxyfluorescein, 5,6–CF) for in vivo pH mapping of tissue. A prototype version of a highly sensitive fluorescence imaging device consisting of a modified xenon lamp, an image-intensified camera and a digital imageprocessing system has been developed. 5,6–Carboxyfluorescein was used because its fluorescence emission increases as a function of pH in the physiological (6.0–7.4) pH range. The ratio of fluorescence intensities obtained with the imaging system has been calibrated using aqueous 5,6–CF standards at various pH values. Because the pH of interstitial fluid of malignant tumors tends to be lower than that of normal tissue and can be depressed by glucose administration, experiments were performed on 10 CDF mice bearing lymphoid leukemia P388 grafted subcutaneously. The range of linearity of the calibration curve was obtained between 5.3 and 6.7 with a measured pK, value of 5.93. Consequently the maximum sensitivity was observed in this range. The calculated pH from ratio images was 6.21 ± 0.12 in tumorous tissue. This value was equivalent to those obtained at the same time using microelectrodes (6.2 ± 0.3).
These experiments showed that a dose of 5 mg/kg 5,6–CF and an excitation power density of 2.5 mW/cm² are sufficient to give a fluorescent pH image of tumors. The limitation of 5,6–CF for the in vivo mapping of tissue results from its low pK_a and consequent range of sensitivity. The advantages of this imaging technique compared to microelectrodes are that it (1) is noninvasive, (2) displays a two-dimensional pH image with high resolution (profile distribution of pH in tissue) and (3) can be used to monitor pH over a few hours.     

Nanoband electrode for high-performance in-channel amperometric detection in dual-channel microchip capillary electrophoresis

A nanoband electrode detector integrated with a dual-channel polydimethylsiloxane microchip is proposed for in-channel amperometric detection in microchip capillary electrophoresis. Gold nanoband electrodes, which were fabricated on SU-8 substrates with a 100-nm-width gold layer, were introduced into the dual-channel microchip to be an electrochemical detector. Due to the nano-sized width of the detector, the noise of the amperometric detection was significantly reduced, and a high separation resolution was achieved for monitoring the analytes. The detection sensitivity of the system was improved by high signal-to-noise ratio, and a low detection limit on microchip was obtained for p-aminophenol (2.09 nM). Because of the high resolution in measuring half-peak width, the plate number that is used to evaluate the separation efficiency was 1.5-fold higher than that using 50-μm-width electrochemical detector. The effect of sample injection time and data acquisition time on separation efficiency was investigated, and an attractive separation efficiency was achieved with a plate number up to 17,500.     

An open design microfabricated nib-like nanoelectrospray emitter tip on a conducting silicon substrate for the application of the ionization voltage

This paper describes a novel emitter tip having the shape of a nib and based on an open structure for nano-electrospray ionization mass spectrometry (nanoESI-MS). The nib structure is fabricated with standard lithography techniques using SU-8, an epoxy-based negative photoresist. The tip is comprised of a reservoir, a capillary slot and a point-like feature, and is fabricated on a silicon wafer. We present here a novel scheme for interfacing such nib tips to MS by applying the ionization voltage directly onto the semi-conductor support. The silicon support is in direct contact with the liquid to be analyzed at the reservoir and microchannel level, thus allowing easy use in ESI-MS. This scheme is especially advantageous for automated analysis as the manual step of positioning a metallic wire into the reservoir is avoided. In addition, the analysis performance was enhanced compared with the former scheme, as demonstrated by the tests of standard peptides (gramicidin S, Glu-fibrinopeptide B). The limit of detection was determined to be lower than 10(-2) microM. Due to their enhanced performance, these microfabricated sources might be of great interest for analysis requiring very high sensitivity, such as proteomics analysis using nanoESI-MS.     

Two-dimensional microfabricated sources for nanoelectrospray

The idea of a novel two-dimensional (2D) nanoelectrospray ionization emitter tip with the shape of a nib is explored here. This novel planar design is studied as an alternative to the needle-like standard emitter tips that suffer from a lack of reproducibility and robustness and from an inherent incompatibility with high-throughput analysis. The composition of the micro-nib sources is analogous to the working of a simple fountain pen, with a liquid reservoir linked to a micro-nib tip from which the sample is electrosprayed via a capillary slot. The micro-nib prototypes described here were fabricated using microtechnology techniques and using the epoxy-based negative photoresist SU-8. The resulting free-standing micro-nib structure was supported by a silicon wafer. We present here two series of such micro-nib sources, the latter series exhibiting improved characteristics such as a 8 micro m source width of the nib tip. They were tested in mass spectrometry experiments on an ion trap mass spectrometer (LCQ Deca XP+, Thermo Finnigan) using standard peptide samples having concentrations down to 1 micro M and with a high voltage (HV) supply around 1 kV for the second series of micro-nib sources. In addition to the stability of the spray, the obtained mass spectra showed the reliability of these sources for peptide analysis; the signal of the spectra was as intense and the signal-to-noise ratio (S/N) as high as that obtained with the use of standard emitter tips.     

Graphene/poly(ethylene‐co‐vinyl acetate) composite electrode fabricated by melt compounding for capillary electrophoretic determination of flavones in Cacumen platycladi

In this report, a graphene/poly(ethylene‐co‐vinyl acetate) composite electrode was fabricated by melt compounding for the amperometric detection of capillary electrophoresis. The composite electrode was fabricated by packing a mixture of graphene and melted poly(ethylene‐co‐vinyl acetate) in a piece of fused silica capillary under heat. The structure of the composite was investigated by scanning electron microscopy and Fourier transform infrared spectroscopy. The results indicated that graphene sheets were well dispersed in the composite to form an interconnected conducting network. The performance of this unique graphene‐based detector has been demonstrated by separating and detecting rutin, quercitrin, kaempferol, and quercetin in Cacumen platycladi in combination with capillary electrophoresis. The four flavones have been well separated within 9 min in a 50‐cm‐long capillary at a separation voltage of 12 kV using a 50 mM sodium borate buffer (pH 9.2). The graphene‐based detector offered significantly lower operating potentials, substantially enhanced signal‐to‐noise characteristics, lower expense of operation, high resistance to surface fouling, and enhanced stability. It showed long‐term stability and repeatability with relative standard deviations of <5% for the peak current (n = 15).     

Microelectrodes for the measurement of cellular metabolism

The study of metabolism of cellular cultures is of great interest. Although some papers reports the monitoring of parameters such as pH, potassium, dissolved oxygen and temperature in cellular cultures using different kind of sensors, no definitive solution has been found to get reproducible and feasible results. The advantage of using sensors fabricated with microelectronic technology is focused on their small size, rapid response and the possibility of having an integrated array of microelectrodes, which favors the measurement of small volumes and fast cell metabolism changes. In this work, the viability of using a multisensor platform of microelectrodes, such as potassium and pH ISFETs, amperometric microelectrodes for dissolved O₂ and pseudo-reference microelectrodes for the study of metabolism of cellular cultures is described. Preliminary results of pH ISFETS’ response in neuronal cultures is reported.     

Fabrication and electrochemical behaviour of vertically aligned boron-doped diamond nanorod forest electrodes

Vertically aligned boron-doped diamond nanorod forests (BDDNF) were successfully fabricated by depositing a diamond film onto silicon nanowires (SiNWs) using hot filament chemical vapor deposition (HFCVD). The boron-doped diamond nanorods were characterized by Raman spectroscopy and scanning electron microscopy (SEM). The BDDNF obtained from the SiNWs on the silicon wafer could be directly used as an electrode and its electrochemical behaviour is discussed here. Compared to a flat boron-doped diamond (BDD) electrode, the BDDNF electrode showed high sensitivity in the amperometric detection of adenine.     

A flow‐through column electrolytic cell for supercritical fluid chromatography*

A novel flow‐through column electrolytic cell was proposed as a detector to obtain current signals for supercritical fluid chromatography. The electrochemical cell consisted of two electrodes and its holder, and a working and a counter electrode were fabricated from 192 carbon strings, which were composed of 400 carbon fibers of 10 μm in diameter filled into a heat‐shrinkable tube. These electrodes were placed in the center of a holder made from polyether ether ketone blocks and they were separated by polytetrafluoroethylene membrane filters. To evaluate the sensitivity of this cell, a standard solution of ferrocene was injected into the supercritical fluid chromatography system connected to the electrolytic cell. The ferrocene was eluted through a silica gel column using a mixture of a mobile phase of supercritical CO₂ and a modifier of methanol containing ammonium acetate. The current peak area of ferrocene correlated to the ferrocene concentration in the range of 10–400 μmol/L (r  = 0.999). Moreover, the limit of detection on the column estimated from a signal‐to‐noise ratio of 3 was 9.8  × 10⁻¹³ mol.     

Amperometric Glucose Biosensor Based on Ultrafine Platinum Nanoparticles

Abstract

In the present paper the ultrafine and highly dispersed platinum nanoparticles (average size 3 nm) were used for the construction of a glucose biosensor in a simple method. An excellent response to glucose has been obtained with a high sensitivity (137.7 µA mM^?1 cm^?2) and fast response time (5 s). The biosensor showed a detection limit of 5 µM (at the ratio of signal to noise, S/N=3) and a linear range form 0.2 to 3.2 mM with a correlation coefficient r=0.999. The apparent Michaelis–Menten constant (k _m) and the maximum current were estimated to be 9.36 and 1.507 mA mM^?1 cm^?2, respectively. In addition, effects of pH value, applied potential and the interferents on the amperometric response of the sensor were investigated and discussed.