Current Issue : July - September Volume : 2011 Issue Number : 3 Articles : 9 Articles
An amperometric electrochemical biosensor has been developed for ammonium (NH4+) ion detection by immobilising alanine dehydrogenase (AlaDH) enzyme in a photocurable methacrylic membrane made up of poly(2-hydroxyethyl methacrylate) (pHEMA) on a screen-printed carbon paste electrode (SPE). The current detected was based on the electrocatalytic oxidation of nicotinamide adenine dinucleotide reduced (NADH) that is proportional to the consumption of NH4+ ion whilst enzymatic amination of AlaDH and pyruvate is taking place. The biosensor was operated amperometrically at a potential of +0.6?V and optimum pH 7. The NH4+ biosensor demonstrated linear response to NH4+ ion concentration in the range of 0.03ââ?¬â??1.02?mg/L with a limit of detection (LOD) of 8.52?Ã?µg/L. The proposed method has been successfully applied to the determination of NH4+ ion in river water samples without any pretreatment. The levels of possible interferents in the waters were negligible to cause any interference on the proposed method. The analytical performance of the biosensor was comparable to the colorimetric method using Nesslerisation but with much lower detection limit and linear response range at ppb level....
A dark signal temperature dependence correction method for miniature spectrometer modules is described in this paper. It is based on laboratory measurements of dark signal temperature dependence at few different integration times. A set of parameters are calculated which make it possible to estimate dark signal at any temperature and integration time within reasonable range. In field conditions, it is not always possible to take frequent dark signal readings during spectral measurements. If temperature is recorded during the measurement, this method can be used for estimating dark signal for every single spectral measurement. The method is validated on two different miniature spectrometers....
The circuitry of a capacitive nanometer displacement sensor using the ring oscillator has been analyzed and characterized. We focus on the sensitivity of the sensor to detect the nanometer displacement or strain. The displaced target object must be conductive and the medium around the target object must be an insulator or a vacuum. The sensitivity in the range of L < 1?�µm is enhanced with decreases in the size of the sensor electrode, and using a higher free-running oscillation frequency can increase sensitivity. The proposed sensor, which converts the displacement of the target object to the oscillation frequency, was fabricated with CMOS 350?nm technology, and the sensitivity was estimated at 8.16?kHz/nm. The results of our study indicated that the presented sensor has enough sensitivity to detect the nanometer displacement of the target object at a distance within 1?�µm from the surface of the sensor electrode....
The detection of radicals on a chip is demonstrated. The proposed method is based on electron spin resonance (ESR) spectroscopy and the measurement of high-frequency impedance of the microinductor fabricated on the chip. The measurement was by using a frequency sweep of approximately 100?MHz. The ESR spectra of di(phenyl)-(2,4,6-trinitrophenyl)iminoazanium (DPPH) dropped on the microinductor which is fabricated with CMOS 350-nm technology were observed at room temperature. The volume of the DPPH ethanol solution was 2?�µL, and the number of spins on the micro-inductor was estimated at about 1014. The sensitivity is not higher than that of the standard ESR spectrometers. However, the result indicates the feasibility of a near field radical sensor in which the microinductor as a probe head and ESR signal processing circuit are integrated....
A poly(3,4-ethylenedioxythiophene) (PEDOT) conducting ink is presented as a new electroactive material to be incorporated in acetylcholinesterase-(AChE-) based screen printed biosensors, acting not only as a conducting template but also as an electrochemical mediator for thiocholine oxidation. Two different strategies have been studied for the chemical synthesis of PEDOT: (a) a classical oxidative polymerisation and (b) a more innovative enzymatic polymerisation, giving a water-soluble PEDOT. The use of this water-soluble conducting polymer as mediator in screen-printed biosensors enables its deposition by printing like the rest of the layers. Highly sensitive acetylcholinesterase-(AChE-) based screen-printed biosensors have been constructed using both classical and enzymatic PEDOT, in combination with genetically modified AChE. These electrodes allow the measurement of thiocholine oxidation at potentials of 100?mV versus Ag/AgCl reference electrode through the mediation of PEDOT. Inhibition of thiocholine production in presence of CPO allow for detection of this pesticide in concentrations as low as 1�·10-10?M....
Noninvasive blood glucose sensors are still under development stage considering that they are far from being suitable for use in anartificial pancreas. The latter has three main parts: the blood glucose sensor, the insulin pump and the controller. However, for the biosensor analyzed here, some common failures such as signal shifts and unreal picks were found. They must be taken into account, for computing the correct insulin dosage for diabetic persons. Hence, a fault detection system based on discrete wavelets transform (DWT) is applied here. The main idea is, when the fault occurs, to do a proper measurement compensation for sending the corrected value to the predictive functional controller (PFC) algorithm. The study is done by reproducing the fault on the blood glucose measurements. They are obtained from a mathematical model of the endocrine system of an adult diabetic patient. This model was approved by the FDA in 2008. Then, the simulation environment includes faulty blood glucose measurements and a fault diagnosis and identification (FDI) system based on DWT. The FDI system gives to the PFC algorithm the correct information to turn it into a fault-tolerant controller (FTC). The main goal is to deliver the correct insulin dosage to the patient....
This paper describes IMU (Inertial Measurement Unit) platforms and their main target applications with a special focus on the 10-degree-of-freedom (10-DOF) inertial platform iNEMO and its technical features and performances. The iNEMO module is equipped with a 3-axis MEMS accelerometer, a 3-axis MEMS gyroscope, a 3-axis MEMS magnetometer, a pressure sensor, and a temperature sensor. Furthermore, the Microcontroller Unit (MCU) collects measurements by the sensors and computes the orientation through a customized Extended Kalman Filter (EKF) for sensor fusion....
The present paper deals with the design and the realization of a new thermoelectric sensor (Seebeck), sensitive to the infrared radiations emitted by different sources. The function mechanism utilizes radiative absorption phenomena, heat transfer, and thermoelectric effects. The sensor includes two printed circuits, the first is a planar thermoelectric circuit constituted of many plated differential thermocouples, and the second is constituted of a resistive constantan track and placed at the top of the first circuit so that the constantan track is placed on the top of the even thermocouple junctions. The constantan track, covered with a resin of great absorptivity, collects the infra-red radiations and generates temperature gradients between the junction points of the first circuit. Then the resulting temperature differences between the junction points are directly converted into a proportional Seebeck voltage. As an application, the sensor is adapted in order to realize a device for detecting infrared radiations, and the results are very encouraging....
Multiple sensor electrodes, a supplementary electrode, a reference electrode, and signal-processing circuits were integrated on a single chip to develop a chip-shaped electrochemical sensing system. L-lactate and glucose were measured using on-chip working electrodes modified by polyion complex to immobilize lactate oxidase and glucose oxidase, respectively. Cyclic voltammetry measurements were conducted using an on-chip potentiostat. Selective and quantitative detection of glucose and L-lactate and the interference behavior were studied. Hydrogen peroxide generated by enzymatic reactions was detected by an increase in anodic oxidation current. Reaction currents at +0.7?V versus Ag/AgCl were used to obtain calibration plots. The measured dynamic ranges for L-lactate and glucose were 0.2ââ?¬â??1.0?mM and 2.0ââ?¬â??8.0?mM, respectively. The sensitivities were 65?nA/mM and 15?nA/mM, respectively, using a working electrode of 0.5?mm2. The 3s detection limit was 0.19?mM and 1.1?mM, respectively. We have achieved multiple biomaterial detections on a circuit-equipped single chip. This integrated electrochemical sensor chip could be the best candidate for realizing point-of-care testing due to its portability and potential for mass production....
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