Glucose sensing based on interdigitated array microelectrode.

A micro glucose sensor consisting of an interdigitated array gold microelectrode was developed. The interdigitated array structure, which has 10 microns band width and 10 microns band gap, was fabricated in a small region (2.5 x 5 mm2) on a quartz substrate. Glucose oxidase was chemically fixed onto the electrode surface through self-assembled monolayer of 11-mercaptoundecanoic acid; ferroceneacetic acid was used as electron mediator. Electrochemical properties of the glucose oxidase-immobilized microelectrode were investigated by cyclic voltammogram measurements. Results confirmed that the reductive ferroceneacetic acid generated at counter electrode diffuses through a narrow band gap (10 microns) and can reach the working electrode surface.     

Porous Cu-NiO modified glass carbon electrode enhanced nonenzymatic glucose electrochemical sensors

Porous Cu-NiO nanocomposites were successfully prepared by calcination of the Cu-Ni(OH)(2) precursor at 400 °C for 2 h. During the process of calcination, Ar was used to deaerate O(2). The structure and morphology of Cu-NiO were characterized by X-ray diffraction spectrum (XRD), energy dispersive X-ray analyses (EDX), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Using porous Cu-NiO nanocomposites, a simple non-enzymatic amperometric sensor has been fabricated (Cu-NiO/GCE) and evaluated by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and typical amperometric method. When applied to detect glucose by the amperometric method, Cu-NiO/GCE produced an ultrahigh sensitivity of 171.8 μA mM(-1), with a low detection limit of 0.5 μM (S/N = 3). What's more, interference from common co-existing species, such as UA, AA, and fructose can be avoided at the sensor. Results in this study imply that porous Cu-NiO nanocomposites are promising nanomaterials for the enzyme-free determination of glucose.     

Bulk- and surface-modified combinable PDMS capillary sensor array as an easy-to-use sensing device with enhanced sensitivity to elevated concentrations of multiple serum sample components

To enhance sensitivity and facilitate easy sample introduction into a combinable poly(dimethylsiloxane) (PDMS) capillary (CPC) sensor array, PDMS was modified in bulk and on its surface to prepare "black" PDMS coated with a silver layer and self-assembled monolayer (SAM). India ink, a traditional Japanese black ink, was added to the PDMS pre-polymer for bulk modification. The surface was modified by a silver mirror reaction followed by SAM formation using cysteine. These modifications enhanced the fluorescence signals by reflecting them from the surface and reducing background interference. A decrease in the water contact angle led to enhanced sensitivity and easy sample introduction. Furthermore, a CPC sensor array for multiplex detection of serum sample components was prepared that could quantify the analytes glucose, potassium, and alkaline phosphatase (ALP). When serum samples were introduced by capillary action, the CPC sensor array showed fluorescence responses for each analyte and successfully identified the components with elevated concentrations in the serum samples.     

Electrodeless Piezoelectric Quartz Crystal Sensor for Determination of Total Urinary Reducing Sugar

A glucose-sensing system was developed in which an electrodeless piezoelectric quartz crystal was used to measure mass changes on the surface of a quartz plate during the reduction of Ag(NH₃)⁺₂ by glucose. A satisfactory correlation was obtained between the frequency shift and the glucose concentration in the range 1.0–25 mM, and the total reducing sugar in urine was determined. Treatment with 8 M nitric acid after each measurement was effective for cleaning the quartz surface, and the electrodeless piezoelectric quartz crystal sensor possessed excellent reproducibility and reusability during repeated use over 400 times. For the determination of total reducing sugar in urine (or blood), the present method can avoid the interferences occurring in a colorimetric method such as the color and turbidity of clinical specimens.     

Validation of the mass response of a quartz crystal microbalance coated with Prussian Blue film for ac electrogravimetry

Prussian Blue (PB) films have been considerably studied for many research applications such as electrochromic material development, new material for batteries, etc. Many analytical techniques were employed for examining PB electrochemical behaviour in solution and the quartz crystal microbalance (QCM) used in the alternative regime (ac electrogravimetry) appeared as an attractive in situ mass sensor due to its low cost and its high mass sensitivity. Unfortunately, the validity of the common Sauerbrey equation was questionable with these films or in other terms if the QCM was used as a pure mass sensor. In this work PB film is examined through acoustic measurements and the response can be interpreted as a pure mass change if the thickness is around 0.15 μm. Over this limit, film viscoelastic contributions can affect drastically the mass change estimation: if the thickness is two times larger, the mass error reaches 40%.     

Quartz Crystal Microbalance Analysis of DNA-Templated Calcium Phosphate Mineralization

A quartz crystal microbalance (QCM) sensor was developed for the quantitation of calcium phosphate mineralization and the assessment of DNA as a template molecule. Inherent advantages of QCM, such as nanogram sensitivity, temporal resolution, surface-based measurements, and flow capabilities, were leveraged in the design of this sensor, and in-line fluidic mixing was used to control precursor reaction. This research shows that DNA, a highly programmable anionic polymer, is able to template and control mineralization of calcium phosphate, with nucleation occurring in less than 15 min and initial rates ranging from 4 to 8 ng/min. FT-IR measurements show mineralized material to be calcium phosphate resembling hydroxyapatite (HAP) when a DNA template is used. DNA is a promising mineralization template, and the QCM proves to be a dynamic technique for a broad range of heterogeneous mineralization experiments in complement to classic, diffusion-limited, end-point analysis techniques.     

Evaluation of the performance of sensors based on optical imaging of a chemically sensitive layer

Interest in the use of the optical properties of chemical indicators is growing steadily. Among the optical methods that can be used to capture changes in sensing layers, those producing images of large-area devices are particularly interesting for chemical sensor array development. Until now, few studies addressed the characterization of image sensors from the point of view of their chemical sensor application. In this paper, a method to evaluate such performance is proposed. It is based on the simultaneous measurement of absorption events in a metalloporphyrin layer with an image sensor and a quartz microbalance (QMB). Exploiting the well-known behaviour of QMB, comparison of signals enables estimation of the minimum amount of absorbed molecules that the image sensor can detect. Results indicate that at the single pixel level a standard image sensor (for example a webcam) can easily detect femtomoles of absorbed molecules. It should therefore be possible to design sensor arrays in which the pixels of images of large-area sensing layers are regarded as individual chemical sensors providing a ready and simple method for large sensor array development.     

Relative humidity measurement using a coated piezoelectric quartz crystal sensor

Miniature piezoelectric quartz crystals, which are manufactured cheaply by photolithographic and chemical etching techniques, have a high mass sensitivity. AT-cut 10 MHz quartz crystals have been coated with four materials and used to measure the relative humidity in various gases. The coated crystal is used as a resonator in an oscillator circuit, the frequency of which varies as a function of the change in mass. Characteristics that determine the usefulness of the coatings, such as sensitivity, response linearity, response time, selectivity, hysteresis and ageing, were evaluated. The detector has potential for use as a hygrometer, provided that the appropriate coating is chosen for a specific application.     

Commercial Copper Foam as an Effective 3D Porous Electrode for Nonenzymatic Glucose Detection

Commercially available copper foam (CF) was used as a 3D porous electrochemical sensing platform for nonenzymatic glucose detection. CF shows high electrocatalytic activity towards glucose oxidation and can be used directly for glucose electrochemical sensing without any pretreatment. The sensor exhibits high performance towards glucose in 0.1 M NaOH solution with the linear range from 1 μM to 0.5 mM, the sensitivity of 5.85 mA mM^?1 cm^?2 and the detection limit of 0.5 μM (S/N=3) simultaneously. Furthermore, the sensor shows a high selectivity for glucose against the common interferences and good reliability for glucose detection in human serum samples.     

Nanostructured NiCu LDHs/polypyrrole nanotubes composite for nonenzymatic glucose sensing in human serum

Nanostructured NiCu layered double hydroxides (NiCu LDHs) are synthesized in situ on polypyrrole nanotubes through convenient co-precipitation and hydrothermal synthesis. The nanostructured composite (NiCu LDHs/PPy) shows high electrocatalytic activities towards the glucose oxidation reaction in alkaline electrolyte so that a nonenzymatic glucose sensor is developed. It is demonstrated that the sensor offers a wide linear range from 1.5 μM to 1.0 mM with a high sensitivity of 525.8 μA mM⁻¹ cm⁻² and a low limit of detection of 66 nM (S/N = 3). The nonenzymatic sensor has been successfully applied to real blood samples for glucose monitoring with high accuracy.     

Optimising of the sensing chamber of an array of a volatile detection system

A fluid dynamic analysis was performed to optimise the positioning of sensor elements in a coated quartz crystal microbalance (QCM) based volatile detection system. The computational fluid dynamic (CFD) code used solves the Navier-Stokes equations statically and dynamically in 2D, discretised by finite elements. In the original sensor chamber, the sensor elements were positioned in a staggered pattern and at 90° to the incoming flow. The numerical analysis shows that, with the exception of the front face of the first sensor, only 45% of the flow passed over the sensors. It is shown that the response of sensor elements is strongly dependent on the sensor position. An optimised sensor chamber design was developed where the sensors are at 0° to the flow direction and a baffle plate diffuses the flow evenly over the sensor elements. The sensors are shown to receive the same flow and respond identically irrespective of position. This revised version was published online in July 2006 with corrections to the Cover Date.     

Bond rupture force measurement by means of a quartz resonator

Methods to measure the bond rupture force are considered. It is proposed to use a quartz resonator as an active element rather than simply a sensor. When the surface oscillation amplitude of an AT quartz resonator increases smoothly (rupture event scanning), a particle attached to the quartz surface is removed by inertial forces, and from their values it is easy to obtain the bond dissociation value. This procedure provides reliable measurements of the rupture force of about 10 pN. As the atomic force microscopy method, the rupture event scanning does not apply electromagnetic radiation, but has simpler instrumental set-up. The scanning requires minimum sample preparation, can be performed in various media (vacuum, air, liquid), and takes only a few minutes.     

Electrochemical Investigation of Glucose on a Highly Sensitive Nickel‐Copper Modified Pencil Graphite Electrode

Novel nickel‐copper modified pencil graphite electrode (Ni?Cu/PGE) was fabricated and used as non‐enzymatic sensor for glucose determination. Ni and copper were electrodeposited on PGE using cyclic voltammetry. Morphology and composition of the modified PGE electrode were characterized by field‐emission gun scanning electron microscopy (FEG‐SEM), energy‐dispersive X‐ray spectroscopy (EDX) and Fourier transform infrared spectroscopy (FT‐IR). Electrochemical oxidation of glucose was evaluated by cyclic voltammetry as well as by amperometry. Electrochemical measurements indicate that the Ni?Cu/PGE exhibits a high sensitivity of 2951 μA mM^?1 cm^?2, and a low detection limit of 0.99 μM which are, respectively, three times higher and twice lower than that on Ni/PGE prepared in the same conditions. Moreover, Ni?Cu/PGE exhibits a wider linear range from 1 to 10000 μM with a rapid response time within 2 s. Moreover, Ni?Cu/PGE showed a remarkable stability. The electrode was successfully applied for determination of glucose concentration in human blood without significant interference from potential endogenic interferents. The good applicability of the elaborated sensor made Ni?Cu/PGE promising for the development of effective and inexpensive non‐enzymatic glucose sensor.     

Sol–gel immobilized enzymatic glucose biosensor on gold interdigitated array (IDA) microelectrode

An enzymatic glucose biosensor with good sensitivity, selectivity and stability employing interdigitated array microelectrode (IDA μ-electrode) was reported. IDA μ-electrode was prepared by photolithography method with its surface immobilized with a layer of glucose oxidase (GOx), entrapped in a three-dimensional network composed of chitosan and tetraethyl orthosilicate sol–gel. The surface of the as-prepared IDA μ-electrode was characterized by scanning electron microscope, electron spectroscopy for chemical analysis, and atomic force microscopy. The experimental parameters for the best glucose sensing performance were optimized according to the loading of GOx, the applied voltages, the concentration of mediator, and the pH for glucose detection. The resulted biosensor exhibited a good response to glucose with a wide linear range from 0 to 35 mM and a low detection limit of 1 mM. The glucose sensor also showed a short response time (within 5 s) that the fast response was reflected by the small Michaelis–Menten constant (K_M ^app) with a value of 2.94 mM. The reported glucose biosensor exhibited good sensitivity (8.74 μA/mM.cm²), reproducibility, and stability.     

Array of Love-wave sensors based on quartz/Novolac to detect CWA simulants

An array of Love-wave sensors based on quartz and Novolac has been developed to detect chemical warfare agents (CWAs). These weapons are a risk for human health due to their efficiency and high lethality; therefore an early and clear detection is of enormous importance for the people safety. Love-wave devices realized on quartz as piezoelectric substrate and Novolac as guiding layer have been used to make up an array of six sensors, which have been coated with specific polymers by spin coating. The CWAs are very dangerous and for safety reasons their well known simulants have been used: dimethylmethyl phosphonate (DMMP), dipropyleneglycol methyl ether (DPGME), dimethylmethyl acetamide (DMA), dichloroethane (DCE), dichloromethane (DCM) and dichloropentane (DCP). The array has been exposed to these CWA simulants detecting very low concentrations, such as 25 ppb of DMMP, a simulant of nerve agent sarin. Finally, principal component analysis (PCA) as data pre-processing and discrimination technique, and probabilistic neural networks (PNN) as patterns classification technique have been applied. The performance of the sensor array has shown stability, accuracy, high sensitivity and good selectivity to these simulants.     

A large volume, portable, real-time PCR reactor

A point-of-care, diagnostic system incorporating a portable thermal cycler and a compact fluorescent detector for real-time, polymerase chain reaction (PCR) on disposable, plastic microfluidic reactors with relatively large reaction volume (ranging from 10 μL to 100 μL) is described. To maintain temperature uniformity and a relatively fast temperature ramping rate, the system utilizes double-sided heater that features a master, thermoelectric element and a thermal waveguide connected to a second thermoelectric element. The waveguide has an aperture for optical coupling between a miniature, fluorescent reader and the PCR reaction chamber. The temperature control is accomplished with a modified, feedforward, variable structural proportional-integral-derivative controller. The temperature of the liquid in the reaction chamber tracks the set-point temperature with an accuracy of ± 0.1 °C. The transition times from one temperature to another are minimized with controllable overshoots (< 2 °C) and undershoots (< 5 °C). The disposable, single-use PCR chip can be quickly inserted into a thermal cycler/reader unit for point-of-care diagnostics applications. The large reaction chamber allows convenient pre-storing of dried, paraffin-encapsulated PCR reagents (polymerase, primers, dNTPs, dyes, and buffers) in the PCR chamber. The reagents are reconstituted "just in time" by heating during the PCR process. The system was tested with viral and bacterial nucleic acid targets.     

Quartz sensor for automatic dew-point hygrometry

The frequency and amplitude of an oscillating quartz crystal are influenced by even a minimal mass load. This is used to detect a dew deposit on a Peltier-cooled quartz plate wth high sensitivity.Since the frequency but not the amplitude of specially cut quartz crystals depends strongly on the temperature, this dew-point temperature can be determined simultaneously with the same sensor element.An automatic dew-point hydrometer using this principle is described. It can be used for humidities in the range 1.6% to 100% r.h. Using saturated salt solutions in the range 12% to 76% r.h. as standards, the accuracy was better than 2% of the observed relative humidity.     

基于光波导微环谐振器的lgG非标记检测微流体分析系统

设计开发了与微环谐振器集成的微流体通道系统,不仅避免了敞开环境中由于液体挥发造成的微环谐振器表面盐分的聚结,屏蔽空气中的各种杂质,而且只需要30 μL反应溶液,减少了药品用量,大大节约了实验成本.同时,采用绝缘体硅(SOI)材料,利用光刻技术设计和制作了波导宽度为450 nm,半径为5 μm,品质因子(Q值)为20000的光波导微环谐振器.集成的微环谐振器传感系统具有低成本、免标记、能实时监测生化反应过程等特点.以不同浓度的酒精溶液为测试对象,研究了微环谐振器对均质溶液的传感性能,传感芯片对溶液折射率的探测灵敏度为76.09 nm/RIU,探测极限为5.25×10Symbolm@@_4 RIU,验证了此微环谐振器对均质溶液进行浓度检测的可行性.利用此传感系统对人免疫球蛋白IgG进行了非标记免疫检测.在测试中,采用微流体通道系统将相应抗体修饰到微环谐振器表面,利用光谱仪对修饰过程以及抗原抗体特异性结合过程中的共振谱线漂移情况进行了监测.结果表明,光波导微环谐振器可以对生物分子进行实时监测.     

Macroscopically Oriented Magnetic Core-regularized Nanomaterials for Glucose Biosensors Assisted by Self-sacrificial Label

Magnetic core-regular nanostructures composed of magnetite and regular Prussian blue was prepared by self-sacrificial macro-oriented method. Magnetic graphene oxide (MGO) was vertically oriented on the surface of home-made screen-printing electrode with the help of constant magnetic field (CMF).Then regular nanostructured Prussian blue (RPB) was realized by chemical reaction through an aerosol deposition. Finally, glucose oxidase (GOx) was immobilized by glutaraldehyde cross-linking to fabricate glucose biosensors. The linear range of CMF-RPB/MGO sensor towards glucose was 0.03∼1.35 mM, and the detection limit was 13.4 μM. The CMF-RPB/MGO sensor could apply to analyze glucose in human serum samples.     

Determination of volatile organic compounds using piezosensors modified with the Langmuir-Blodgett films of calix[4]resorcinarene

A sensor based on a piezoelectric quartz resonator modified with the Langmuir-Blodgett (LB) films of calix[4]resorcinarene is proposed for the detection of volatile organic compounds. Parameters for the formation of ordered LB films based on calix[4]resorcinarene were optimized, and the effects of the pH and metal ion content of the subphase on the behavior of the Langmuir monolayers of calix[4]resorcinarene were studied. The effects of the number of monolayers in a sensor coating, the pH of the subphase from which the monolayers were transferred, and the presence of copper ions in the subphase on the response of the resulting piezoelectric quartz sensors to the vapors of various volatile organic compounds (ethanol, benzene, toluene, ethylbenzene, ethyl acetate, acetone, hexane, and cumene) were studied. It was found that the proposed sensor was characterized by a short response time and reproducible measurements.