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Background: The objective of this work was to determine the clinical accuracy of GlucoMen®Day, a new microdialysis-based continuous glucose monitoring system (CGMS) from A. Menarini Diagnostics (Florence, Italy). Accuracy evaluation was performed using continuous glucose-error grid analysis (CG-EGA), as recommended by the Performance Metrics for Continuous Interstitial Glucose Monitoring; Approved Guideline (POCT05-A)., Methods: Two independent clinical trials were carried out on patients with types 1 and 2 diabetes mellitus, the glycemic levels of whom were monitored in an in-home setting for 100-hour periods. A new multiparametric algorithm was developed and used to compensate in real-time the GlucoMen®Day signal. The time lag between continuous glucose monitoring (CGM) and reference data was first estimated using the Poincaré plot method. The entire set of CGM/reference data pairs was then evaluated following the CG-EGA criteria, which allowed an estimation of the combined point and rate accuracy stratified by glycemic ranges., Results: With an estimated time lag of 11 minutes, the linear regression analysis of the CGM/reference glucose values yielded r = 0.92. The mean absolute error (MAE) was 11.4 mg/dl. The calculated mean absolute rate deviation (MARD) was 0.63 mg/dl/min. The data points falling within the A+B zones of CG-EGA were 100% in hypoglycemia, 95.7% in euglycemia, and 95.2% in hyperglycemia., Conclusions: The GlucoMen®Day system provided reliable, real-time measurement of subcutaneous glucose levels in patients with diabetes for up to 100 hours. The device showed the ability to follow rapid glycemic excursions and detect severe hypoglycemic events accurately. Its accuracy parameters fitted the criteria of the state-of-the-art consensus guideline for CGMS, with highly consistent results from two independent studies., (© 2010 Diabetes Technology Society.)

In this issue of Journal of Diabetes Science and Technology, Valgimigli and colleagues present promising data on the clinical accuracy of the new microdialysis-based continuous glucose monitoring device GlucoMen®Day. In this analysis, two issues are addressed: first, the established way data analyses may obscure interindividual variability in terms of a glucose monitoring system's accuracy; and second, to fully appreciate the future merits of the new system, data on accuracy, while a clearly necessary prerequisite, are not sufficient and need to be augmented by patient-reported outcome data as highlighted by recent U.S. Food and Drug Administration guidelines., (© 2010 Diabetes Technology Society.)

A novel multiwall carbon nanotube (MWCNT) electrode functionalized with oxygen plasma treatment was prepared and characterized, and its DNA sensing ability for Legionella pneumophila (L. pneumophila) detection was examined using electrochemical measurement. A well-patterned MWCNT working electrode (WE) on a Pt track was fabricated using photolithography, transfer methods and an etching technique. The MWCNT WE was functionalized by oxygen plasma treatment prior to applying for DNA sensor. The surface morphology of the plasma-functionalized MWCNT (pf-MWCNT) WEs were observed by scanning electron microscope (SEM) and the change of chemical composition was characterized by X-ray photoelectron spectroscopy (XPS), and electrochemical measurements were performed using CV with ferricyanide/ferrocyanide redox couple. Effective areas of working electrodes were calculated to be 0.00453 cm(2) for pristine MWCNT electrode and 0.00747-0.00874 cm(2) for pf-MWCNT electrodes with different plasma treatment times. Differential pulse voltammetry (DPV) was carried out in methylene blue solution for DNA sensing. The pf-MWCNT based DNA sensor was successfully operated in a target concentration range of 10 pM to 100 nM and had a lower detection limit than a pristine MWCNT based DNA sensor., (Copyright 2010 Elsevier B.V. All rights reserved.)

Physiological stresses are fundamental to biomechanical testing, mechanobiological analyses, implant design, and tissue engineering. The purpose of this study was to design, fabricate, and evaluate compressive stress sensors packaged for extended, in vivo implantation in the annulus of the intervertebral disc. A commercial microelectromechanical systems (MEMS) pressure sensor die was selected as the active element for a custom stress sensor. The sensor die was modified and packaged to protect the electrical system from the biochemical and biomechanical environment. Completed sensors were calibrated under hydrostatic pressure and solid contact compression. Calibrations were performed before and after 8 weeks of in vivo implantation in a porcine disc. For the two reported sensors, stress and voltage were linearly correlated over a range of 0-1.8 MPa with less than 5% change in sensitivity. Sensitivity to solid contact stress was within 10% of that from hydrostatic pressure. In contrast to most previous studies, in which disc pressure was measured in the fluidic nucleus pulposus, these sensors may be used to measure in vivo dynamic compressive stresses in the annulus at magnitudes typical of the musculoskeletal system in a large animal over a relatively long post-operative time., (Copyright 2010 Elsevier Ltd. All rights reserved.)

Thin, pliant transducers with grid arrays of sensing elements (sensels) have been widely used for transient measurements of intra-articular contact stresses. Conventional calibration procedures for this class of sensors are based upon spatially uniform scaling of sensel output values so as to recover two known fiducial loads, physically applied with the sensor either compressed between platens or mounted in situ. Because of the nonlinearities involved, it is desirable to have the highest of those two calibration loadings be such that all individual sensels are engaged at/near the peak of their expected functional range. However, for many situations of practical interest, impracticably large total calibration forces would be required. We report development of a novel pneumatically actuated wringer-like calibration device, and companion iterative post-processing software, that bypasses this longstanding difficulty. Sensors passed through the rollers of this device experience constant-distribution traveling fiducial loads propagating across their surface, thus allowing efficient calibration of all sensels individually to contact stress levels that would be impracticably high to simultaneously apply to all sensels. Sensel-specific calibration curves are rapidly and easily generated using this new approach and compare favorably to those obtained with less expeditious conventional platen-based protocols., (Copyright 2010 Elsevier Ltd. All rights reserved.)

Background: We present a prototype handheld device based on a newly developed optomagnetic technology for the sensitive detection of cardiac troponin I (cTnI) in a finger-prick blood sample with a turnaround time of 5 min., Methods: The test was completed in a compact plastic disposable with on-board dry reagents and superparamagnetic nanoparticles. In our one-step assay, all reaction processes were precisely controlled using electromagnets positioned above and below the disposable. Nanoparticle labels (500 nm) bound to the sensor surface via a sandwich immunoassay were detected using the optical technique of frustrated total internal reflection., Results: A calibration function measured in plasma demonstrates a limit of detection (mean of blank plus 3-fold the standard deviation) of 0.03 ng/mL cTnI. A linear regression analysis of the region 0.03-6.5 ng/mL yields a slope of 37+/-4, and a linear correlation coefficient of R2=0.98. The measuring range could be extended substantially to 100 ng/mL by simultaneously imaging a second spot with a lower antibody concentration., Conclusions: The combination of magnetic particles and their fine actuation with electromagnets permits the rapid and sensitive detection of cTnI. Because of the potential high analytical performance and ease-of-use of the test, it is well suited for demanding point-of-care diagnostic applications., (Copyright 2010 Elsevier B.V. All rights reserved.)

The level at which implanted sensors and sampling devices maintain their calibration is an important research area. In this work, microdialysis probes with identical geometry and different membranes, polycarbonate/polyether (PC) or polyethersulfone (PES), were used with internal standards (Vitamin B(12) (MW 1355), antipyrine (MW 188) and 2-deoxyglucose (2-DG, MW 164)) and endogenous glucose to investigate changes in their long-term calibration after implantation into the subcutaneous space of Sprague-Dawley rats. Histological analysis confirmed an inflammatory response to the microdialysis probes and the presence of a collagen capsule. The membrane extraction efficiency (percentage delivered to the tissue space) for antipyrine and 2-DG was not altered throughout the implant lifetime for either PC- or PES membranes. Yet, Vitamin B(12) extraction efficiency and collected glucose concentrations decreased during the implant lifetime. Antipyrine was administered i.v. and its concentrations obtained in both PC- and PES-membrane probes were significantly reduced between the implant day and seven (PC) or 10 (PES) days post-implantation suggesting that solute supply is critical for in vivo extraction efficiency. For the low molecular weight solutes such as antipyrine and glucose, localized delivery is not affected by the foreign body reaction, but recovery is significantly reduced. For Vitamin B(12), a larger solute, the fibrotic capsule formed around the probe significantly restricts diffusion from the implanted microdialysis probes., (Copyright (c) 2010 Elsevier Ltd. All rights reserved.)

A thionine-modified carbon paste electrode for catechol and Bisphenol A (BPA) detection is presented. Graphite powder was modified by adsorbing thionine as electrochemical mediator. The electrochemical response of the modified carbon paste electrode (CPE) was determined before electrode modification with tyrosinase. Then, tyrosinase was added in order to assemble a biosensor. Once established the best operative conditions, an interelectrode reproducibility around 7% was obtained and the resulting biosensor showed improved sensitivities and (S=139.6+/-1.1 nA/microM for catechol and S=85.4+/-1.5 nA/microM for BPA) in comparison with the biosensor constructed without thionine (S=104.4+/-0.5 nA/microM for catechol and S=51.1+/-0.6 nA/microM for BPA) and low detection limits (0.15 microM for both the electrodes and analytes). Also the comparison with the results reported in the literature showed higher sensitivity and lower detection limit for our biosensor. Moreover the functioning of the thionine-tyrosinase CPE was validated following a biodegradation process of water polluted by BPA and comparing the time changes of BPA concentration inferred by the biosensor calibration curve and those determined by means of HPLC measurements., (2010 Elsevier B.V. All rights reserved.)

There is increased interest in the investigation and implementation of rapid screening methods for detection of pesticide residues. This study reports development of an immunostrip test for thiabendazole detection based on indirect competitive principle using carbon particles as a label. Nitrocellulose membrane strip was coated with a thiabendazole-protein conjugate in the defined test zone. In flow of an antibody-carbon complex and thiabendazole along the strip, the intensity of black colour formed in the test line reflected the thiabendazole concentration and semi-quantitative estimation could be carried out visually. The optimized test was accomplished within 10 min and the visual detection limit was achieved 0.25 ng mL(-1) of standard sample. Moreover, immunostrip was evaluated quantitatively using scanning densitometry. Based on standard curve, the detection limit of the proposed test was as low as 0.08+/-0.03 ng mL(-1) with an IC(50) value of 0.60+/-0.08 ng mL(-1) and a linear working range of 0.11-4.13 ng mL(-1). Results of testing precision, stability, and specificity demonstrated that the assay provided a reliable performance. This immunostrip was applied to analysis of spiked fruit juices in range of 0.05-5 mg L(-1). Matrix interferences were avoided by simple dilution of samples. Both visual and instrumental evaluations indicated a good agreement with results obtained by ELISA. Recoveries from juices were from 81.9 to 123.6% and relative standard deviations ranged from 9.9 to 19.3%. The developed strip offers potential as a useful rapid and simple method for screening of thiabendazole in fruit juices at levels far below the maximum residue limits., (2010 Elsevier B.V. All rights reserved.)

Preparation and analysis of standard VOC (volatile organic compound) gases are needed when developing and evaluating the performance of analytical methods or instruments to detect VOCs. In this study, we designed and developed a simple system for the analysis of VOCs based on their decomposition into CO(2) by a combustion catalyst and their subsequent detection using a solid electrolyte CO(2) sensor. In this sensor, NASICON (Na(3)Si(2)Zr(2)PO(4); Na(+) conductor) and binary carbonate (Li(2)CO(3)-BaCO(3)) were used as the solid electrolyte and the sensing layer, respectively. This developed system proved to be effective in determining the concentrations of standard gases, including VOCs (ethanol, formaldehyde, and toluene), CO, and hydrocarbons in parts per million concentrations (10-500 ppm). The system also could continuously monitor the variations in ethanol vapors prepared by a diffusion method where liquid ethanol was heated at 25 and 50 degrees C. The advantages and limitations of our developed analytical system are also discussed.

Aims: To compare the accuracy of two marketed subcutaneous glucose monitoring devices (Guardian RT, GRT; GlucoDay S, GDS) and standard microdialysis (CMA60; MD) in Type 1 diabetic patients., Methods: Seven male Type diabetic patients were investigated over a period of 26 h simulating real-life meal glucose excursions. Catheters of the three systems were inserted into subcutaneous adipose tissue of the abdominal region. For MD, interstitial fluid was sampled at 30- to 60-min intervals for offline glucose determination. Reference samples were taken at 15- to 60-min intervals. All three systems were prospectively calibrated to reference. Median differences, median absolute relative differences (MARD), median absolute differences (MAD), Bland-Altman plot and Clark Error Grid were used to determine accuracy., Results: Bland-Altman analysis indicated a mean glucose difference (2 standard deviations) between reference and interstitial glucose of -10.5 (41.8) % for GRT, 20.2 (55.9) % for GDS and 6.5 (35.2) % for MD, respectively. Overall MAD (interquartile range) was 1.07 (0.39; 2.04) mmol/l for GRT, 1.59 (0.54; 3.08) mmol/l for GDS and 0.76 (0.26; 1.58) mmol/l for MD. Overall MARD was 15.0 (5.6; 23.4) % (GRT), 19.7 (6.1; 37.6) % (GDS) and 8.7 (4.1; 18.3) % (MD), respectively. Total sensor failure occurred in two subjects using GRT and one subject using GDS., Conclusions: The three investigated technologies had comparable performance. Whereas GRT underestimated actual blood glucose, GDS and MD overestimated blood glucose. Considerable deviations during daily life meal glucose excursions from reference glucose were observed for all three investigated technologies. Present technologies may require further improvement until individual data can lead to direct and automated generation of therapeutic advice in diabetes management.

Recent progress in sensor technology has led to the development and application of electronic taste sensing systems. Especially taste prediction of pharmaceutical formulations is a matter of particular interest and is increasingly performed using electronic tongues. Several studies have dealt with electronic tongues before, but an analytical approach describing successfully conducted qualification has not been reported yet. Performance qualification of the taste sensing system SA402B (Insent Inc., Atsugi-chi, Japan) equipped with seven lipid membrane sensors was undertaken with special regard to bitter taste assessment. These sensors represent the gustatory stimuli bitterness, umami, saltiness, sourness, and the nociceptive sensation astringency. Specificity, linearity, range, accuracy, precision, detection and quantitation limit as well as robustness were established for each sensor type referring to ICH guideline Q2 (R1). Some items mentioned in the guideline were applicable whereas others had to be modified due to differences of the system to other commonly used analytical techniques. Quinine hydrochloride being one of the bitterest drugs served as model substance. A large range of linearity (0.01-100mM) with corresponding precision (RSD<4%) was found for most sensors. One sensor had a lower detection threshold (0.0025mM) for quinine hydrochloride than humans typically have. Different methods for determination of detection and quantitation limits were implemented and discussed with respect to rationality and feasibility. Therefore the approach based on visual evaluation was found as most adequate. An adapted guidance following ICH guideline Q2 was developed serving qualification of taste sensing systems in the future.

A new modified glassy carbon electrode (GCE) based on a synthesized N-(2-aminoethyl)-4,4'-bipyridine (ABP) was developed for the determination of Ag(I) by differential pulse voltammetry (DPV). ABP was covalently immobilized on GC electrodes surface using 4-nitrobenzendiazonium (4-NBD) and glutaraldehyde (GA). The Ag(I) ions were preconcentrated by chemical interaction with bipyridine under a negative potential (-0.6 V); then the reduced ions were oxidized by differential pulse voltammetry and a peak was observed at 0.34 V. The calibration curve was linear in the concentration range from 0.05 μM to 1 μM Ag(I) with a detection limit of 0.025 μM and RSD=3.6%, for 0.4 μM Ag(I). The presence of several common ions in more than 125-fold excess had no effect on the determination of Ag(I). The developed sensor was applied to the determination of Ag(I) in water samples using a standard addition method.

Background: Studies have shown that controlling blood glucose can reduce the onset and progression of the long-term microvascular and neuropathic complications associated with the chronic course of diabetes mellitus. Improved glycemic control can be achieved by frequent testing combined with changes in medication, exercise, and diet. Technological advancements have enabled improvements in analytical accuracy of meters, and this paper explores two such parameters to which that accuracy can be attributed., Methods: Four blood glucose monitoring systems (with or without dynamic electrochemistry algorithms, codeless or requiring coding prior to testing) were evaluated and compared with respect to their accuracy., Results: Altogether, 108 blood glucose values were obtained for each system from 54 study participants and compared with the reference values. The analysis depicted in the International Organization for Standardization table format indicates that the devices with dynamic electrochemistry and the codeless feature had the highest proportion of acceptable results overall (System A, 101/103). Results were significant when compared at the 10% bias level with meters that were codeless and utilized static electrochemistry (p = .017) or systems that had static electrochemistry but needed coding (p = .008)., Conclusions: Analytical performance of these blood glucose meters differed significantly depending on their technologic features. Meters that utilized dynamic electrochemistry and did not require coding were more accurate than meters that used static electrochemistry or required coding., (2010 Diabetes Technology Society.)

A calibration model was developed for a noninvasive blood glucose sensor, to determine how the blood glucose data measured by this sensor is related to blood glucose data measured with laboratory capillary finger sticks and to corrupting noise. The variability of calibration models for different patients was analyzed as well as the dynamics of the non-invasive blood glucose sensor according to reference blood glucose measurements and corrupting noise.

Background: Through minimally invasive sensor-based continuous glucose monitoring (CGM), individuals can manage their blood glucose (BG) levels more aggressively, thereby improving their hemoglobin A1c level, while reducing the risk of hypoglycemia. Tighter glycemic control through CGM, however, requires an accurate glucose sensor and calibration algorithm with increased performance at lower BG levels., Methods: Sensor and BG measurements for 72 adult and adolescent subjects were obtained during the course of a 26-week multicenter study evaluating the efficacy of the Paradigm REAL-Time (PRT) sensor-augmented pump system (Medtronic Diabetes, Northridge, CA) in an outpatient setting. Subjects in the study arm performed at least four daily finger stick measurements. A retrospective analysis of the data set was performed to evaluate a new calibration algorithm utilized in the Paradigm Veo insulin pump (Medtronic Diabetes) and to compare these results to performance metrics calculated for the PRT., Results: A total of N = 7193 PRT sensor downloads for 3 days of use, as well as 90,472 temporally and nonuniformly paired data points (sensor and meter values), were evaluated, with 5841 hypoglycemic and 15,851 hyperglycemic events detected through finger stick measurements. The Veo calibration algorithm decreased the overall mean absolute relative difference by greater than 0.25 to 15.89%, with hypoglycemia sensitivity increased from 54.9% in the PRT to 82.3% in the Veo (90.5% with predictive alerts); however, hyperglycemia sensitivity was decreased only marginally from 86% in the PRT to 81.7% in the Veo., Conclusions: The Veo calibration algorithm, with sensor error reduced significantly in the 40- to 120-mg/dl range, improves hypoglycemia detection, while retaining accuracy at high glucose levels., (2010 Diabetes Technology Society.)

Amperometric glucose sensors have advanced the care of patients with diabetes and are being studied to control insulin delivery in the research setting. However, at times, currently available sensors demonstrate suboptimal accuracy, which can result from calibration error, sensor drift, or lag. Inaccuracy can be particularly problematic in a closed-loop glycemic control system. In such a system, the use of two sensors allows selection of the more accurate sensor as the input to the controller. In our studies in subjects with type 1 diabetes, the accuracy of the better of two sensors significantly exceeded the accuracy of a single, randomly selected sensor. If an array with three or more sensors were available, it would likely allow even better accuracy with the use of voting., (2010 Diabetes Technology Society.)

Background: Knowing the statistical properties of continuous glucose monitoring (CGM) sensor errors can be important in several practical applications, e.g., in both open- and closed-loop control algorithms. Unfortunately, modeling the accuracy of CGM sensors is very difficult for both experimental and methodological reasons. It has been suggested that the time series of CGM sensor errors can be described as realization of the output of an autoregressive (AR) model of first order driven by a white noise process. The AR model was identified exploiting several reference blood glucose (BG) samples (collected frequently in parallel to the CGM signal), a procedure to recalibrate CGM data, and a linear time-invariant model of blood-to-interstitium glucose (BG-to-IG) kinetics. By resorting to simulation, this work shows that some assumptions made in the Breton and Kovatchev modeling approach may significantly affect the estimated sensor error and its statistical properties., Method: Three simulation studies were performed. The first simulation was devoted to assessing the influence of CGM data recalibration, whereas the second and third simulations examined the role of the BG-to-IG kinetic model. Analysis was performed by comparing the "original" (synthetically generated) time series of sensor errors vs its "reconstructed" version in both time and frequency domains., Results: Even small errors either in CGM data recalibration or in the description of BG-to-IG dynamics can severely affect the possibility of correctly reconstructing the statistical properties of sensor error. In particular, even if CGM sensor error is a white noise process, a spurious correlation among its samples originates from suboptimal recalibration or from imperfect knowledge of the BG-to-IG kinetics., Conclusions: Modeling the statistical properties of CGM sensor errors from data collected in vivo is difficult because it requires perfect calibration and perfect knowledge of BG-to-IG dynamics. Results suggest that correct characterization of CGM sensor error is still an open issue and requires further development upon the pioneering contribution of Breton and Kovatchev., (2010 Diabetes Technology Society.)

Current trends in healthcare technology include mobile-based applications. Relevant advances in the integration of vital signs monitoring devices with mobile platforms are widely reported nowadays. In this context, conceiving and designing an interoperable application is essential due to the growing necessity of integrating a huge and heterogeneous amount of biomedical data, coming from a wide range of devices and sensors. In this paper the key research issues associated with such integration are presented as well as a specific proposal to solve these problems. It is based on a middleware architecture for the integration of biomedical sensors with mobile devices, derived from the ISO/IEEE 11073 standards family. The application has been developed in the framework of an EU-funded R&D project called METABO.

In order to improve rapid on-line moisture sensing of seedcotton in cotton gins, a means by which to establish a reliable low-cost wide-band electronic calibration is critically needed. This calibration is needed to center the circuit due to changes in the internal signal delays and attenuation drift caused by temperature changes in the various system components and circuit elements. This research examines a hardware technique for use in conjunction with microwave reflective sensing probes having an extended bandwidth from 500 MHz through 2.5 GHz. This new technique was validated experimentally against known electrical propagation delay standards. Results of the measured propagation delay with this type of automatic electronic calibration method was found to agree with results using a vector network analyzer with a traditional S11 single port error correction calibration methodology to within 4% of the measurement, 95% confidence, with a standard error of +/-18.6 ps for the delay measurements. At this level of performance, the proposed low-cost technique exhibits superior performance, over the typical geosciences time-domain reflectometer "TDR", instruments in common use in soil moisture testing and is suitable for use in cotton gin moisture sensing.

Ion sensitive field-effect transistor (ISFET) based urease biosensors with solid state reference systems for single-ended and two-ended differential readout electronics were investigated. The sensing membranes of the biosensors were fabricated with urease immobilized in a conducting polymer-based matrix. The responses of 12.9∼198.1 mV for the urea concentrations of 8∼240 mg/dL reveal that the activity of the enzyme was not significantly decreased. Biosensors combined with solid state reference systems were fabricated, and the evaluation results demonstrated the feasibility of miniaturization. For the differential system, the optimal transconductance match for biosensor and reference field-effect transistors (REFET) pair was determined through the modification of the membranes of the REFETs and enzyme field-effect transistors (EnFETs). The results show that the transconductance curve of polymer based REFET can match with that of the EnFET by adjusting the photoresist/Nafion™ ratio. The match of the transconductance curves for the differential pairs provides a wide dynamic operating measurement range. Accordingly, the miniaturized quasi-reference electrode (QRE)/REFET/EnFET combination with differential arrangement achieved similar urea response curves as those measured by a conventional large sized discrete sensor.

A 1.8-mW, 18.5-mm(2) 64-channel current readout ASIC was implemented in 0.18-µm CMOS together with a new calibration scheme for silicon nanowire biosensor arrays. The ASIC consists of 64 channels of dedicated readout and conditioning circuits which incorporate correlated double sampling scheme to reduce the effect of 1/f noise and offset from the analog front-end. The ASIC provides a 10-bit digital output with a sampling rate of 300 S/s whilst achieving a minimum resolution of 7 pA(rms). A new electrical calibration method was introduced to mitigate the issue of large variations in the nano-scale sensor device parameters and optimize the sensor sensitivity. The experimental results show that the proposed calibration technique improved the sensitivity by 2 to 10 times and reduced the variation between dataset by 9 times.

Nanowire/nanotube biosensors have stimulated significant interest; however, the inevitable device-to-device variation in the biosensor performance remains a great challenge. We have developed an analytical method to calibrate nanowire biosensor responses that can suppress the device-to-device variation in sensing response significantly. The method is based on our discovery of a strong correlation between the biosensor gate dependence (dI(ds)/dV(g)) and the absolute response (absolute change in current, DeltaI). In(2)O(3) nanowire-based biosensors for streptavidin detection were used as the model system. Studying the liquid gate effect and ionic concentration dependence of strepavidin sensing indicates that electrostatic interaction is the dominant mechanism for sensing response. Based on this sensing mechanism and transistor physics, a linear correlation between the absolute sensor response (DeltaI) and the gate dependence (dI(ds)/dV(g)) is predicted and confirmed experimentally. Using this correlation, a calibration method was developed where the absolute response is divided by dI(ds)/dV(g) for each device, and the calibrated responses from different devices behaved almost identically. Compared to the common normalization method (normalization of the conductance/resistance/current by the initial value), this calibration method was proven advantageous using a conventional transistor model. The method presented here substantially suppresses device-to-device variation, allowing the use of nanosensors in large arrays.

In this paper we discuss the fabrication and characterization of miniaturized triglyceride biosensors on crystalline silicon and porous silicon (PS) substrates. The sensors are miniaturized Electrolyte Insulator Semiconductor Capacitors (mini-EISCAPs), which primarily sense the pH variation of the electrolyte used. The lipase enzyme, which catalyses the hydrolysis of triglycerides, was immobilized on the sensor surface. Triglyceride solutions introduced into the enzyme immobilized sensor produced butyric acid which causes the change in pH of the electrolyte. Miniaturized EISCAP sensors were fabricated using bulk micromachining technique and have silicon nitride as the pH sensitive dielectric layer. The sensors are cubical pits of dimensions 1,500 microm x 1,500 microm x 100 microm which can hold an electrolyte volume of 0.1 microl. The pH changes in the solution can be sensed through the EISCAP sensors by monitoring the flatband voltage shift in the Capacitance-Voltage (C-V) characteristics taken during the course of the reaction. The reaction rate is found to be quite high in the miniature cells when compared to the sensors of bigger dimensions.

Mitochondria are one of the major sources of reactive oxygen species (ROS) in mammalian cells. The generation of ROS underlies many physiological and pathophysiological processes that occur within cellular systems. Superoxide ([image omitted] ) is the proximal ROS generated during electron 'leakage' from the mitochondrial electron transport chain (mETC) and is known to be released at mitochondrial complex I and complex III. Monitoring mitochondrial [image omitted] production directly and in real-time offers the potential to improve understanding of the complex mechanisms involved during mitochondrial [image omitted] generation. This study reports the novel application of a cytochrome c functionalized amperometric sensor for monitoring [image omitted] generation in isolated mitochondrial fractions. The non-invasive sensor system described allowed a comparison of [image omitted] production following specific inhibition of complex I and complex III of the mETC to be made directly and in real-time.

A simple and label-free electrochemical sensor for recognition of the DNA sensor event was prepared by electrochemical polymerization of 4-hydroxyphenyl thiophene-3-carboxylate. Poly(4-hydroxyphenyl thiophene-3-carboxylate) (PHPT) was synthesized electrochemically onto glassy carbon electrode and characterized by cyclic voltammetry, FTIR and AFM measurements. An ODN-probe was physisorbed onto PHPT film and tested on hybridization with complementary ODN segments. A biological recognition can be monitored by comparison with electrochemical signal (cyclic voltammogram) of single and double strand state oligonucleotide. The oxidation current of double strand state oligonucleotide is lower than that of single strand, that is corresponding to the decrease of electroactivity of PHPT with the increase of stiffness of polymer structure. Physisorbed ODN-probe and its hybridization were observed morphologically onto ITO electrodes using AFM. The sensitivity of the electrochemical sensor is 0.02 microA/nmol, detection limit is 1.49 nmol and it has good selectivity.

Amperometric acetylcholinesterase (AChE) biosensors have been developed to resolve mixtures of chlorpyrifos oxon (CPO) and chlorfenvinfos (CFV) pesticides. Three different biosensors were built using the wild type from electric eel (EE), the genetically modified Drosophila melanogaster AChE B394 and B394 co-immobilized with a phosphotriesterase (PTE). Artificial Neural Networks (ANNs) were used to model the combined response of the two pesticides. Specifically two different ANNs were constructed. The first one was used to model the combined response of B394+PTE and EE biosensors and was applied when the concentration of CPO was high and the other, modelling the combined response of B394+PTE and B394 biosensors, was applied with low concentrations of CPO. In both cases, good prediction ability was obtained with correlation coefficients better than 0.986 when the obtained values were compared with those expected for a set of six external test samples not used for training.

We report on a novel amperometric biosensor for detecting phenolic compounds based on the co-immobilization of horseradish-peroxidase (HRP) and methylene blue (MB) with chitosan on Au-modified TiO2 nanotube arrays. The titania nanotube arrays were directly grown on a Ti substrate using anodic oxidation first; a gold thin film was then coated onto the TiO2 nanotubes by an argon plasma technique. The morphology and composition of the fabricated Au-modified TiO2 nanotube arrays were characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Cyclic voltammetry and amperometry were used to study the proposed electrochemical biosensor. The effect of pH, applied electrode potential and the concentration of H(2)O(2) on the sensitivity of the biosensor have been systemically investigated. The performance of the proposed biosensor was tested using seven different phenolic compounds, showing very high sensitivity; in particular, the linearity of the biosensor for the detection of 3-nitrophenol was observed from 3 x 10(-7) to 1.2 x 10(-4)M with a detection limit of 9 x 10(-8)M (based on the S/N=3).

In this article, the poly-calcon carboxylic acid (poly-CCA) film modified electrode was prepared by cyclic voltammetry (CV). Then, an electrochemical DNA biosensor was developed for detection of PML/RARA fusion gene in acute promyelocytic leukemia (APL) by using 18-mer single-stranded deoxyribonucleic acid as the capture probe. The capture probe was covalently attached through free amines on the DNA bases using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydrosulfosuccinimide (NHS) cross-linking reaction on a carboxylate-terminated poly-CCA monolayer modified glassy carbon electrode (GCE). The covalent immobilized capture probe could selectively hybridize with its target DNA to form double-stranded DNA (dsDNA) on GCE surface. The aim of this work is to provide a well-defined recognition interface for the detection of DNA. Differential pulse voltammetry (DPV) was used to monitor the hybridization reaction on the capture probe electrode. The decrease of the peak current of methylene blue (MB), an electroactive indicator, was observed upon hybridization of the probe with the target DNA. The results indicated that in pH 7.0 phosphate buffer solution (PBS), the oxidation peak current was linear with the concentration of complementary strand in the range of 1.0 x 10(-12) to 1.0 x 10(-11)M with a detection limit of 6.7 x 10(-13)M. This new method demonstrates its excellent specificity for single-base mismatch and complementary sequence (dsDNA) after hybridization, and it would be proposed to use in real sample.

An amperometric biosensor was fabricated for the quantitative determination of urea in aqueous medium using hematein, a pH-sensitive natural dye. The urease (Urs) was covalently immobilized onto an electrode made of gold nanoparticles functionalized with hyperbranched polyester-Boltron H40 (H40-Au) coated onto an indium-tin oxide (ITO) covered glass substrate. The covalent linkage between the Urs enzyme and H40-Au nanoparticles provided the resulting enzyme electrode (Urs/H40-Au/ITO) with a high level of enzyme immobilization and excellent lifetime stability. The response studies were carried out as a function of urea concentration with amperometric and photometric measurements. The biosensor based on Urs/H40-Au/ITO as the working electrode showed a linear current response to the urea concentration ranging from 0.01 to 35 mM. The urea biosensor exhibited a sensitivity of 7.48 nA/mM with a response time of 3s. The Michaelis-Menten constant for the Urs/H40-Au/ITO biosensor was calculated to be 0.96 mM, indicating the Urs enzyme immobilized on the electrode surface had a high affinity to urea.

A label-free and highly sensitive impedimetric aptasensor based on a polyamidoamine dendrimer modified gold electrode was developed for the determination of thrombin. Amino-terminated polyamidoamine dendrimer was firstly covalently attached to the cysteine functionalized gold electrode through glutaraldehyde coupling. Subsequently, the dendrimer was activated with glutaraldehyde, and amino-modified thrombin aptamer probe was immobilized onto the activated dendrimer monolayer film. The layer-by-layer assembly process was traced by surface plasmon resonance and electrochemical impedance spectroscopy. After electrode preparation, the detection of thrombin was investigated in the presence of the reversible [Fe(CN)6](3-/4-) redox couple using impedance technique. The results showed that the charge-transfer resistance (Rct) value had a linear relationship with the concentrations of thrombin in the range of 1-50 nM, and the detection limit (S/N=3) as low as 0.01 nM was obtained. The covalent immobilization of dendrimer on the electrode surface not only improved the immobilization capacity of probe molecules but also magnified the response signal. The aptasensor exhibited favorable regeneration ability, selectivity and stability. It also showed the detectability in biological fluid.

The report is on an electrochemical biosensor with remarkably improved sensitivity toward nitrite. In this strategy, positively charged gold nanoparticle (PCNA) is used in combination with multiwall carbon nanotubes (MWCNT) by electrostatic adsorption for fabricating PCNA/MWCNT films. Then hemoglobin (Hb) biocatalyst will easily be attached to the surface of the combination films aforementioned. After that, the Hb/PCNA films are immobilized onto the Hb/PCNA/MWCNT films through layer-by-layer assembly technique. The (Hb/PCNA)(2)/MWNT/GC electrode thus prepared exhibits enhanced electrocatalytic behavior to the reduction of nitrite at -0.10 V versus SCE in 0.05 M H(2)SO(4) solution. On condition of the low detecting potential and low pH, interference caused by direct electrochemical oxidation or oxidizable substances can be prevented. Therefore, the modified electrode shows fast response time, very high sensitivity, good selectivity and stability. The current response of the sensor increases linearly with nitrite concentration from a range of 3.6 x 10(-6) to 3.0 x 10(-3) M with a detection limit(S /N = 3) of 9.6 x 10(-7) M.

This paper reports the fabrication of highly-sensitive cholesterol biosensor based on cholesterol oxidase (ChOx) immobilization on well-crystallized flower-shaped ZnO structures composed of perfectly hexagonal-shaped ZnO nanorods grown by low-temperature simple solution process. The fabricated cholesterol biosensors reported a very high and reproducible sensitivity of 61.7 microA microM(-1)cm(-2) with a response time less than 5s and detection limit (based on S/N ratio) of 0.012 microM. The biosensor exhibited a linear dynamic range from 1.0-15.0 microM and correlation coefficient of R=0.9979. A lower value of apparent Michaelis-Menten constant (K(m)(app)), of 2.57 mM, exhibited a high affinity between the cholesterol and ChOx immobilized on flower-shaped ZnO structures. Moreover, the effect of pH on ChOx activity on the ZnO modified electrode has also been studied in the range of 5.0-9.0 which exhibited a best enzymatic activity at the pH range of 6.8-7.6. To the best of our knowledge, this is the first report in which such a very high-sensitivity and low detection limit has been achieved for the cholesterol biosensor by using ZnO nanostructures modified electrodes.

Based on well-known silver mirror reaction the Ag film was formed on Au film modified by self-assembled monolayer (SAM) of 1,6-hexanedithiol (HDT). The sensitivity of the biosensor based on this Ag/Au film is enhanced compared to that based on Au film. When the surface plasmon resonance (SPR) biosensor based on this Ag/Au film was used to determine human IgG, the range of concentrations of human IgG that could be determined is 0.30-40.00 microg mL(-1). The lowest concentration (0.30 microg mL(-1)) that could be detected was about 8 times lower than that obtained by the biosensor without modification by Ag film (2.50 microg mL(-1)), which demonstrated that the biosensor based on Ag/Au film could make the resonant wavelength move to longer wavelength following with the sensitivity enhancement of the SPR biosensor.

This work is related to the development of phase-sensitive methodologies in Surface Plasmon Resonance (SPR) biosensing. We take advantage of a specific angular dependence of phase of light, reflected under SPR geometry, on parameters of the SPR-supporting metal, and propose a polarimetry-based methodology to easily determine the optimal calibration zero point, corresponding to the maximal phase sensitivity. The proposed methodology can significantly facilitate the calibration of the system in field and multi-channel sensing, broaden the dynamic range, as well as contribute to the development of feedback loops.

A new amperometric cholesterol biosensor was prepared by immobilizing cholesterol oxidase by a glutaraldehyde crosslinking procedure on polypyrrole-polyaniline (ppy-pani) composite film on the surface of a platinum electrode. In order to prepare a biosensor for the determination of cholesterol, electropolymerization of pyrrole and aniline on Pt surface was performed with an electrochemical cell containing pyrrole and aniline in sulphuric acid by cyclic voltammetry between 0.0 and 0,7 V (vs.Ag/AgCl) at a scan rate of 50 mV upon Pt electrode. The amperometric determination is based on the electrochemical detection of H(2)O(2), which is generated in enzymatic reaction of cholesterol. The cholesterol determined by the oxidation of enzymatically generated H(2)O(2) at 0.7 V vs. Ag/AgCl. The optimized cholesterol oxidase biosensor displayed linear working range and a response time of 300 s. The effects of pH and temperature were investigated and optimum parameters were found to be 7.0, 25 degrees C, respectively. In addition to this, the stability and reproducibility of biosensor were tried. Operational stability of the proposed cholesterol biosensor was obtained by periodical measurements of the biosensor response. Biosensor at optimum activity conditions was used in 30 activity assays in one day to determine the operational stability. The results show that 82% of the response current was retained after 30 activity assays. The electrode was stored in a refrigerator at 4 degrees C after the measurements. The storage stability of the biosensor was determined by performing activity assays within 23 days. The results demonstrate that 60% of the response current was retained after 23 days. Preparing biosensor is used for the analysis of cholesterol in serum.

The feasibility of developing an immobilised protein phosphatase (PP) biosensor was tested by immobilising PP onto CNBr-activated Sepharose beads placed in Millipore microfilter plate wells. Under optimised immobilised enzyme assay conditions, okadaic acid (OA) and microcystin LR (MC-LR) inhibited Upstate Biotechnology PP (PP-2A), with IC50 values of 12.5 and 11nM respectively. Similarly, immobilised recombinant PP type 1 (rec PP-1) was inhibited by MC-LR and OA, with IC50 values of 150 and >1000nM respectively. The IC50 values for free PP-2A against OA and MC-LR were 2.5 and 3.5nM, and 0.7nM and 200nM for rec PP-1 against the same substrates respectively. For free and immobilised Neptunea arthritic PP (PP-2Ana) against OA the IC50 values were 0.45 and >1000nM respectively. Of the three immobilised enzyme systems, PP-2A showed greatest sensitivity to OA and MC-LR followed by rec PP-1 and PP-2Ana. In assessments for re-usability (determined by removal of > or =70% OA or MC-LR inhibition of PP-2A by washing), <50% of the original activity remained after 20 washings. Including 1M NaCl in the wash buffer did not increase enzyme activity with wash frequency, but rather "salted in" the inhibitor. The LoD of immobilised PP-2A to MC-LR meets the WHO guideline of 1microgl(-1) for drinking water, and the sensitivity to OA (3.5microgl(-1)) would allow detection of DSP during the peak of some phytoplankton blooms.

A carbon paper electrode was modified with the conducting copolymer of 3-methylthiopene and thiophene-3-acetic acid prepared electrochemically on the electrode, and an enzyme electrode was fabricated by covalent immobilization of glucose oxidase on the modified electrode. The modification with the conducting copolymer increased the surface area of the electrode and the amount of the immobilized enzyme. As a result, the enzyme electrode showed a high catalytic activity. Moreover, it was found that the increased surface area led to a high rate of electron transfer reaction between the electrode and p-benzoquinone employed as an electron mediator. The enzyme electrode fabricated with the modified carbon paper gave a larger glucose oxidation current than that fabricated with the bare one. In addition, the glucose oxidation current was found to increase with increasing content of the conducting copolymer in the modified carbon paper. Corresponding to the large glucose oxidation current, high performance was confirmed for the glucose fuel cell constructed with the enzyme electrode based on the modified carbon paper.

An electrochemical biosensor for the detection of bar gene coding phosphinothricin herbicide resistance is presented. The detection was based on hybridization reaction between the specific to bar gene 19-mer probe immobilized on the electrode surface and complementary DNA in a sample. Single-stranded DNA probe specific to bar gene was covalently attached by 5'-phosphate end to the surface of carbon paste electrode. Outer layer of a conventional CPE was provided with carboxyl groups of stearic acid. ssDNA was coupled to the electrode through ethylenediamine with the use of water-soluble 1-ethyl-3(3'-dimethylaminopropyl)-carbodiimide and N-hydroxy-sulfosuccinimide as activating reagents. Hybridization reaction at the electrode surface was detected via Co(bpy)(3)(3+), which possess a much higher affinity to the resulting DNA duplex compared to ssDNA probe. Detection limit of the sensor was 0.1 microM of target DNA fragments and its response was linear from 5 to 20 microM. Hybridization event was also detected by measuring guanine peak but this approach presented distinctly higher detection limit (1 muM) and lower reproducibility. Complete time of one measurement with the use of the biosensor including covalent attachment of ethylenediamine (linker) and ssDNA probe to the electrode, hybridization with target and interaction with electroactive indicator was about 70 min.

Alpha-zirconium phosphate nanosheets (ZrPNS) derived via the delamination of layered alpha-zirconium phosphate (alpha-ZrP) have been proven to be efficient support matrixes for the immobilization of horseradish peroxidase (HRP). X-ray powder diffraction (XRD) results revealed that ZrPNS in HRP-ZrPNS film remained unorderly structured for the effect of HRP. Fourier transform infrared (FTIR) spectra results revealed that HRP remained the secondary structure in HRP-ZrPNS film. The direct electrochemistry of HRP was realized in HRP-ZrPNS film on a glassy carbon electrode (GCE), showing a pair of well-defined, nearly reversible cyclic voltammetry (CV) peaks for the HRP heme Fe(III)/Fe(II) redox couple. The average surface concentration (Gamma(*)) of electroactive HRP in HRP-ZrPNS film was estimated to be 1.35x10(-10) mol cm(-2), which indicated a high loading of enzyme molecules in HRP-ZrPNS film. Based on these, a third generation reagentless biosensor was constructed for the determination of hydrogen peroxide (H(2)O(2)). The response time of the biosensor was less than 3 s, and the linear response range of the biosensor for H(2)O(2) was from 1.3x10(-6) to 1.6x10(-2) M with a correlation coefficient of 0.9997.

Staphylococcal enterotoxins (SEs) are a major cause of food-borne diseases, traditionally SEs assayed immunologically with ELISA. Carbon nanotubes' (CNT) unique mechanical and electronic properties combined with a large specific surface area make them attractive for biosensing. To investigate whether CNT could improve the sensitivity of ELISA assays, we developed an optical CNT immunosensor for the detection of Staphylococcal Enterotoxin B (SEB) in food. Anti-SEB antibodies were immobilized onto a CNT surface through electrostatic adsorption and then the antibody-nanotube mixture was bound onto a polycarbonate film. SEB was then detected by a "sandwich-type" ELISA assay on the polycarbonate film. The use of CNT increased the sensitivity of the immunosensor by at least 6-fold, lowering the detection limit of SEB. The CNT immunosensor was also able to detect SEB various foods, suggesting the utility of CNT for this and other optical-based immunological detection methods.

The focus of this study was to demonstrate that, in the luminescent sensors, the signal transduction may possibly be the most important part in the sensing process. Rational design of fluorescent sensor arrays for cations utilizing extended conjugated chromophores attached to 8-hydroxyquinoline is reported. All of the optical sensors utilized in the arrays comprise the same 8-hydroxyquinoline (8-HQ) receptor and various conjugated chromophores to yield a different response to various metal cations. This is because the conjugated chromophores attached to the receptor are partially quenched in their resting state, and upon the cation coordination by the 8-HQ, the resulting metalloquinolinolate complex displays a change in fluorescence. A delicate balance of conjugation, fluorescence enhancement, energy transfer, and a heavy metal quenching effect results in a fingerprint-like pattern of responses for each sensor-cation complex. Principal component analysis (PCA) and linear discriminant analysis (LDA) are used to demonstrate the contribution of individual sensors within the array, information that may be used to design sensor arrays with the smallest number of sensor elements. This approach allows discriminating between 10 cations by as few as two or even one sensor element. Examples of arrays comprising various numbers of sensor elements and their utility in qualitative identification of Ca(2+), Mg(2+), Cd(2+), Hg(2+), Co(2+), Zn(2+), Cu(2+), Ni(2+), Al(3+), and Ga(3+) ions are presented. A two-member array was found to identify 11 analytes with 100% accuracy. Also the best two of the sensors were tested alone and both were found to be able to discriminate among the samples with 99% and 96% accuracy, respectively. To illustrate the utility of this approach to a real-world application, identification of enhanced soft drinks based on their Ca(2+), Mg(2+), and Zn(2+) cation content was performed. The same approach to reducing array elements was used to construct three- and two-member arrays capable of identifying these complex analytes with 100% accuracy.

Electrochemical impedance spectroscopy is used to detect the binding of a 148.2 kDa antibody to a "covalent virus layer" (CVL) immobilized on a gold electrode. The CVL consisted of M13 phage particles covalently anchored to a 3 mm diameter gold disk electrode. The ability of the CVL to distinguish this antibody ("p-Ab") from a second, nonbinding antibody ("n-Ab") was evaluated as a function of the frequency and phase of the measured current relative to the applied voltage. The binding of p-Ab to the CVL was correlated with a change in the resistance, reducing it at low frequency (1-40 Hz) while increasing it at high frequency (2-140 kHz). The capacitance of the CVL was virtually uncorrelated with p-Ab binding. At both low and high frequency, the electrode resistance was linearly dependent on the p-Ab concentration from 20 to 266 nM but noise compromised the reproducibility of the p-Ab measurement at frequencies below 40 Hz. A "signal-to-noise" ratio for antibody detection was computed based upon the ratio between the measured resistance change upon p-Ab binding and the standard deviation of this change obtained from multiple measurements. In spite of the fact that the impedance change upon p-Ab binding in the low frequency domain was more than 100 times larger than that measured at high frequency, the S/N ratio at high frequency was higher and virtually independent of frequency from 4 to 140 kHz. Attempts to release p-Ab from the CVL using 0.05 M HCl, as previously described for mass-based detection, caused a loss of sensitivity that may be associated with a transition of these phage particles within the CVL from a linear to a coiled conformation at low pH.

In this paper, we have critically evaluated the electrochemical behavior of the products of seven substrates of the enzyme label, alkaline phosphate, commonly used in electrochemical immunosensors. These products (and the corresponding substrates) include indigo carmine (3-indoyl phosphate), hydroquinone (hydroquinone diphosphate), 4-nitrophenol (4-nitrophenol phosphate), 4-aminophenol (p-aminophenyl phosphate), 1-naphthol (1-naphthyl phosphate), phenol (phenyl phosphate), and L-ascorbic acid (2-phospho-L-ascorbic acid). Cyclic voltammetry and amperometry of these products were carried out at glassy carbon (GC), screen-printed carbon (SPC) and gold (Au) electrodes, respectively. Among the products, L-ascorbic acid showed the most sensitive (24.8 microA cm(-2), 12.0 microA cm(-2), and 48.0 microA cm(-2) of 100 microM ascorbic acid at GC, SPC, and Au electrodes, respectively) and well-defined amperometric response at all electrodes used, making 2-phospho-l-ascorbic acid the best substrate in electrochemical detection involving an alkaline phosphatase (ALP) enzyme label. The 2-phospho-L-ascorbic acid is also commercially available and inexpensive. Therefore, it was the best choice for electrochemical detection using ALP as label. Using mouse IgG as a model, an ALP enzyme-amplified sandwich-type amperometric immunosensor was constructed. The immunosensor was designed by electropolymerization of o-aminobenzoic acid (o-ABA) conductive polymer on the surface of GC, SPC, and Au electrodes. The anti-mouse IgG was subsequently attached on the electrode surface through covalent bonding between IgG antibody and the carboxyl groups from poly(o-ABA). Using 2-phospho-L-ascorbic acid as a substrate, the poly(o-ABA)/Au immunosensor produced the best signal (about 297 times of current density response ratio between 1000 ng mL(-1) and 0 ng mL(-1) of mouse IgG), demonstrating that amperometric immunosensors based on a conducting polymer electrode system were sensitive to concentrations of the mouse IgG down to 1 ng mL(-1), with a linear range of 3-200 ng mL(-1) (S.D.<2; n=3), and very low non-specific adsorption.

Bioassays with bioreporter bacteria are usually calibrated with analyte solutions of known concentrations that are analysed along with the samples of interest. This is done as bioreporter output (the intensity of light, fluorescence or colour) does not only depend on the target concentration, but also on the incubation time and physiological activity of the cells in the assay. Comparing the bioreporter output with standardized colour tables in the field seems rather difficult and error-prone. A new approach to control assay variations and improve application ease could be an internal calibration based on the use of multiple bioreporter cell lines with drastically different reporter protein outputs at a given analyte concentration. To test this concept, different Escherichia coli-based bioreporter strains expressing either cytochrome c peroxidase (CCP, or CCP mutants) or β-galactosidase upon induction with arsenite were constructed. The reporter strains differed either in the catalytic activity of the reporter protein (for CCP) or in the rates of reporter protein synthesis (for β-galactosidase), which, indeed, resulted in output signals with different intensities at the same arsenite concentration. Hence, it was possible to use combinations of these cell lines to define arsenite concentration ranges at which none, one or more cell lines gave qualitative (yes/no) visible signals that were relatively independent of incubation time or bioreporter activity. The discriminated concentration ranges would fit very well with the current permissive (e.g. World Health Organization) levels of arsenite in drinking water (10 µg l(-1))., (© 2007 The Authors.)

Ascorbate oxidase (ASOD) bound to polymaleimidostyrene (PMS) forms stable ASOD micelle structure in polystyrene (PS) membrane. The oxygen permeable hydrophobic ASOD micelle membrane were coated on both aminated glassy carbon electrode (AGCE) and gold electrode (AuE) for the amperometric detections of l-ascorbic acid (AsA) based on the consumption of oxygen. These AsA sensors have good sensitivities with short response time (within 1min.). A good linear relationship was observed in the concentration range of 5muM to 0.4mM when AGCE was used and the applied potential was -0.5V vs. Ag/AgCl. Interferences from the reducing agents can be avoided because the detections were conducted at cathodic potential.

Pt nanoparticles were deposited on mesoporous carbon material CMK-3. Glucose oxidase (GOx) was immobilized in the resulting Pt nanoparticles/mesoporous carbon (Pt/CMK-3) matrix, and then the mixture was cast on a glassy carbon electrode (GCE) using gelatin as a binder. The glucose biosensor exhibited excellent current response to glucose after cross-linking with glutaraldehyde. At 0.6V (vs. SCE) the response current was linear to glucose concentration in the range of 0.04-12.2mM. The response time (time for achieving 95% of the maximum current) was 15s and the detection limit (S/N=3) was 1 microM. The Michaelis-Menten constant (K(m)(app)) and the maximum current density (i(max)) were 10.8 mM and 908 microAcm(-2), respectively. The activation energy of the enzymatic reaction was estimated to be 22.54 kJ mol(-1). The biosensor showed good stability. It achieved the maximum response current at about 52 degrees C and retained 95.1% of its initial response current after being stored for 30 days. In addition, some fabrication and operation parameters for the biosensor were optimized in this work. The biosensor was used to monitor the glucose levels of serum samples after being covered with an extra Nafion film to improve its anti-interferent ability and satisfied results were obtained.

In this study, we present a new, simple and rapid impedance method to detect bacterial cells by making use of the impedance properties of bacterial cell suspensions using interdigitated microelectrodes. It was found that bacterial cell suspensions in deionized (DI) water with different cell concentrations could generate different electrical impedance spectral responses, whereas cell suspensions in phosphate buffered saline (PBS) solution could not produce any significant differences in impedance spectra in response to different cell concentrations. In DI water suspensions, impedance at 1 kHz decreased with the increasing cell concentrations in the suspensions. The impedance of cell suspensions in DI water was discussed and found that it was resulted from the cell wall charges and the release of ions or other osmolytes from the cells. A linear relationship between the impedance and the logarithmic value of the cell concentration was found in the cell concentration range from 10(6) to 10(10)cfu/ml, which can be expressed by a regression equation of Z(k Omega)=-2.06 logC (cells/20 microl)+5.23 with R(2)=0.98. The detection limit was calculated to be 3.45 x 10(6)cfu/ml, which is comparable with many label-free immunosensors for detection of pathogenic bacteria reported in the literature. To achieve the selectivity of this method, we also demonstrated the feasibility of integrating magnetic separation to this impedance method. This study has demonstrated that bacterial cell concentration can be inferred by measuring the impedance of cell suspensions in DI water. This new detection mechanism could be an alternative to current impedance methods that have been reported for the detection of bacterial cells, e.g. impedance microbiology and electrical/electrochemical impedance biosensors.

The safety of our food supply is always a major concern to consumers, food producers, and regulatory agencies. A safer food supply improves consumer confidence and brings economic stability. The safety of foods from farm-to-fork through the supply chain continuum must be established to protect consumers from debilitating, sometimes fatal episodes of pathogen outbreaks. The implementation of preventive strategies like hazard analysis critical control points (HACCP) assures safety but its full utility will not be realized unless supportive tools are fully developed. Rapid, sensitive, and accurate detection methods are such essential tools that, when integrated with HACCP, will improve safety of products. Traditional microbiological methods are powerful, error-proof, and dependable but these lengthy, cumbersome methods are often ineffective because they are not compatible with the speed at which the products are manufactured and the short shelf life of products. Automation in detection methods is highly desirable, but is not achievable with traditional methods. Therefore, biosensor-based tools offer the most promising solutions and address some of the modern-day needs for fast and sensitive detection of pathogens in real time or near real time. The application of several biosensor tools belonging to the categories of optical, electrochemical, and mass-based tools for detection of foodborne pathogens is reviewed in this chapter. Ironically, geometric growth in biosensor technology is fueled by the imminent threat of bioterrorism through food, water, and air and by the funding through various governmental agencies.

Objective: To determine, in a multicentre prospective study, the accuracy of the tissue-resonance interaction method (TRIMprob, new technology developed for the noninvasive analysis of electromagnetic anisotropy in biological tissues) in the diagnosis of prostate cancer., Patients and Methods: Two hundred patients (mean age 67.4 years) scheduled to have prostatic biopsies (because of a prostate-specific, PSA, antigen level of >/=4 ng/mL or a suspicious digital rectal examination, DRE) were preliminarily examined while unaware of their clinical details using TRIMprob in five different centres. The final diagnosis obtained with TRIMprob was compared with the final histological diagnosis after extended biopsies., Results: Of the 188 evaluable patients (mean PSA level 9.3 ng/mL, sd 8.8; mean prostate volume 62.0 mL, sd 32.4), 61 (32.4%) had a positive biopsy for adenocarcinoma of the prostate. The overall sensitivity, specificity, positive predictive value, negative predictive value (NPV) and accuracy of TRIMprob were 80%, 51%, 44%, 84% and 60%, respectively. The prostate cancer detection rate after biopsy was significantly higher in patients with a positive examination (49/111, 44%) than in patients with a negative TRIMprob (12/77, 15%; P < 0.001). When TRIMprob results were combined with DRE findings the sensitivity and NPV both increased to 92%., Conclusion: TRIMprob seems to be a useful tool in the diagnosis of prostate cancer and can increase the accuracy of PSA or DRE results. The high NPV suggests that this new technology might be useful to reduce the indications for prostatic biopsy or repeated series of biopsies in patients suspected of having prostate cancer.