Showing papers in "IEEE Transactions on Biomedical Circuits and Systems in 2007"

Design and Optimization of Printed Spiral Coils for Efficient Transcutaneous Inductive Power Transmission

Abstract: The next generation of implantable high-power neuroprosthetic devices such as visual prostheses and brain computer interfaces are going to be powered by transcutaneous inductive power links formed between a pair of printed spiral coils (PSC) that are batch-fabricated using micromachining technology. Optimizing the power efficiency of the wireless link is imperative to minimize the size of the external energy source, heating dissipation in the tissue, and interference with other devices. Previous design methodologies for coils made of 1-D filaments are not comprehensive and accurate enough to consider all geometrical aspects of PSCs with planar 3-D conductors as well as design constraints imposed by implantable device application and fabrication technology. We have outlined the theoretical foundation of optimal power transmission efficiency in an inductive link, and combined it with semi-empirical models to predict parasitic components in PSCs. We have used this foundation to devise an iterative PSC design methodology that starts with a set of realistic design constraints and ends with the optimal PSC pair geometries. We have executed this procedure on two design examples at 1 and 5 MHz achieving power transmission efficiencies of 41.2% and 85.8%, respectively, at 10-mm spacing. All results are verified with simulations using a commercial field solver (HFSS) as well as measurements using PSCs fabricated on printed circuit boards.

An Energy-Efficient Micropower Neural Recording Amplifier

Abstract: This paper describes an ultralow-power neural recording amplifier. The amplifier appears to be the lowest power and most energy-efficient neural recording amplifier reported to date. We describe low-noise design techniques that help the neural amplifier achieve input-referred noise that is near the theoretical limit of any amplifier using a differential pair as an input stage. Since neural amplifiers must include differential input pairs in practice to allow robust rejection of common-mode and power supply noise, our design appears to be near the optimum allowed by theory. The bandwidth of the amplifier can be adjusted for recording either neural spikes or local field potentials (LFPs). When configured for recording neural spikes, the amplifier yielded a midband gain of 40.8 dB and a -3-dB bandwidth from 45 Hz to 5.32 kHz; the amplifier's input-referred noise was measured to be 3.06 muVrms while consuming 7.56 muW of power from a 2.8-V supply corresponding to a noise efficiency factor (NEF) of 2.67 with the theoretical limit being 2.02. When configured for recording LFPs, the amplifier achieved a midband gain of 40.9 dB and a -3-dB bandwidth from 392 mHz to 295 Hz; the input-referred noise was 1.66 muVrms while consuming 2.08 muW from a 2.8-V supply corresponding to an NEF of 3.21. The amplifier was fabricated in AMI's 0.5-mum CMOS process and occupies 0.16 mm2 of chip area. We obtained successful recordings of action potentials from the robust nucleus of the arcopallium (RA) of an anesthesized zebra finch brain with the amplifier. Our experimental measurements of the amplifier's performance including its noise were in good accord with theory and circuit simulations.

Feedback Analysis and Design of RF Power Links for Low-Power Bionic Systems

Abstract: This paper presents a feedback-loop technique for analyzing and designing RF power links for transcutaneous bionic systems, i.e., between an external RF coil and an internal RF coil implanted inside the body. The feedback techniques shed geometric insight into link design and minimize algebraic manipulations. We demonstrate that when the loop transmission of the link's feedback loop is -1, the link is critically coupled, i.e., the magnitude of the voltage transfer function across the link is maximal. We also derive an optimal loading condition that maximizes the energy efficiency of the link and use it as a basis for our link design. We present an example of a bionic implant system designed for load power consumptions in the 1-10-mW range, a low-power regime not significantly explored in prior designs. Such low power levels add to the challenge of link efficiency, because the overhead associated with switching losses in power amplifiers at the link input and with rectifiers at the link output significantly degrade link efficiency. We describe a novel integrated Class-E power amplifier design that uses a simple control strategy to minimize such losses. At 10-mW load power consumption, we measure overall link efficiencies of 74% and 54% at 1- and 10-mm coil separations, respectively, in good agreement with our theoretical predictions of the link's efficiency. At 1-mW load power consumption, we measure link efficiencies of 67% and 51% at 1- and 10-mm coil separations, respectively, also in good accord with our theoretical predictions. In both cases, the link's rectified output dc voltage varied by less than 16% over link distances that ranged from 2 to 10 mm

The Advanced Health and Disaster Aid Network: A Light-Weight Wireless Medical System for Triage

Abstract: Advances in semiconductor technology have resulted in the creation of miniature medical embedded systems that can wirelessly monitor the vital signs of patients. These lightweight medical systems can aid providers in large disasters who become overwhelmed with the large number of patients, limited resources, and insufficient information. In a mass casualty incident, small embedded medical systems facilitate patient care, resource allocation, and real-time communication in the advanced health and disaster aid network (AID-N). We present the design of electronic triage tags on lightweight, embedded systems with limited memory and computational power. These electronic triage tags use noninvasive, biomedical sensors (pulse oximeter, electrocardiogram, and blood pressure cuff) to continuously monitor the vital signs of a patient and deliver pertinent information to first responders. This electronic triage system facilitates the seamless collection and dissemination of data from the incident site to key members of the distributed emergency response community. The real-time collection of data through a mesh network in a mass casualty drill was shown to approximately triple the number of times patients that were triaged compared with the traditional paper triage system.

A Low-Power Integrated Bioamplifier With Active Low-Frequency Suppression

Abstract: We present in this paper a low-power bioamplifier suitable for massive integration in dense multichannel recording devices. This bioamplifier achieves reduced-size compared to previous designs by means of active low-frequency suppression. An active integrator located in the feedback path of a low-noise amplifier is employed for placing a highpass cutoff frequency within the transfer function. A very long integrating time constant is achieved using a small integrated capacitor and a MOS-bipolar equivalent resistor. This configuration rejects unwanted low-frequency contents without the need for input RC networks or large feedback capacitors. Therefore, the bioamplifier high-input impedance and small size are preserved. The bioamplifier, implemented in a 0.18-mum CMOS process, has been designed for neural recording of action potentials, and optimised through a transconductance-ef-ficiency design methodology for micropower operation. Measured performance and results obtained from in vivo recordings are presented. The integrated bioamplifier provides a midband gain of 50 dB, and achieves an input-referred noise of 5.6 muVrms. It occupies less than 0.050 mm2 of chip area and dissipates 8.6 muW.

A Low-Power Blocking-Capacitor-Free Charge-Balanced Electrode-Stimulator Chip With Less Than 6 nA DC Error for 1-mA Full-Scale Stimulation

Abstract: Large dc blocking capacitors are a bottleneck in reducing the size and cost of neural implants. We describe an electrode-stimulator chip that removes the need for large dc blocking capacitors in neural implants by achieving precise charge-balanced stimulation with <6 nA of dc error. For cochlear implant patients, this is well below the industry's safety limit of 25 nA. Charge balance is achieved by dynamic current balancing to reduce the mismatch between the positive and negative phases of current to 0.4%, followed by a shorting phase of at least 1 ms between current pulses to further reduce the charge error. On +6 and -9 V rails in a 0.7-mum AMI high voltage process, the power consumption of a single channel of this chip is 47 muW when biasing power is shared by 16 channels.

Multichannel Reflective PPG Earpiece Sensor With Passive Motion Cancellation

Abstract: This paper addresses the design considerations of a novel earpiece photoplethymograph (PPG) sensor and its in-situ evaluation results. The device is encapsulated with multiple LEDs and photodiodes based on a reflective PPG design. A compact and low power circuitry was developed for signal control and conditioning. PPG signals with an averaged ac/dc ratio of 0.001-0.01 and 10% relative strength (compared to finger-based approach) were recorded from the superior and posterior auricular skins. The integrity of PPG signal and accuracy of heart rate detection were evaluated and the results showed that with adequate optical shielding and the proposed passive motion cancellation, the device was able to reliably detect heart rate both during rest and moderate exercise. The proposed sensor design is low power, easy to wear compared to conventional earlobe PPG devices.

VLSI Potentiostat Array With Oversampling Gain Modulation for Wide-Range Neurotransmitter Sensing

Abstract: A 16-channel current-measuring very large-scale integration (VLSI) sensor array system for highly sensitive electrochemical detection of electroactive neurotransmiters like dopamine and nitric-oxide is presented. Each channel embeds a current integrating potentiostat within a switched-capacitor first-order single-bit delta-sigma modulator implementing an incremental analog-to-digital converter. The duty-cycle modulation of current feedback in the delta-sigma loop together with variable oversampling ratio provide a programmable digital range selection of the input current spanning over six orders of magnitude from picoamperes to microamperes. The array offers 100-fA input current sensitivity at 3.4-muW power consumption per channel. The operation of the 3 mm times3 mm chip fabricated in 0.5-mum CMOS technology is demonstrated with real-time multichannel acquisition of neurotransmitter concentration

A Highly Flexible System for Microstimulation of the Visual Cortex: Design and Implementation

Abstract: This paper presents the design of a system intended to be used as a prosthesis allowing profoundly visually impaired patients to recover partial vision by means of microstimulation in the primary visual cortex area. The main component of the system is a bio-electronic device to be implanted inside the skull of the user, composed of a plurality of stimulation modules, whose actions are controlled via an interface module. Power and data are transmitted to the implant wirelessly through a bidirectional inductive link, allowing diagnosis of the stimulating device and its environment after implantation, as well as power delivery optimization. A high level of flexibility is supported in terms of stimulation parameters, but a configurable communication protocol allows the device to be used with maximum efficiency. The core of an external controller implemented in a system on a programmable chip is also presented, performing data conversion and timing management such that phosphene intensity can be modulated by any parameter defining stimulation, either at the pulse level or in the time domain. Measured performances achieved with a prototype using two types of custom ASICs implemented in a 0.18-mum CMOS process and commercial components fulfill the requirements for a complete visual prosthesis for humans. When on/off activation is used with predefined parameters, stimuli measured on an electronic test bench could attain a rate in excess of 500 k pulses/s.

Parallel Scan-Like Test and Multiple-Defect Diagnosis for Digital Microfluidic Biochips

Abstract: Dependability is an important attribute for microfluidic biochips that are used for safety-critical applications such as point-of-care health assessment, air-quality monitoring, and food-safety testing. Therefore, these devices must be adequately tested after manufacture and during bioassay operations. We propose a parallel scan-like testing methodology for digital microfluidic devices. A diagnosis method based on test outcomes is also proposed. The diagnosis technique is enhanced such that multiple defect sites can be efficiently located using parallel scan-like testing. Defect diagnosis can be used to reconfigure a digital microfluidic biochip such that faults can be avoided, thereby enhancing chip yield and defect tolerance. We evaluate the proposed method using complexity analysis as well as applying it to a fabricated biochip.

Mobile Noncontact Monitoring of Heart and Lung Activity

Abstract: This paper describes two methods for noncontact monitoring of heart and lung activity, namely magnetic bioimpedance monitoring and capacitive electrocardiogram (ECG) recording. In principle, both methods bear the potential for mobile application in a personal healthcare scenario. To illustrate their performance, prototypes for both methods have been developed and first results are presented. Finally, the fundamental drawbacks and limitations of these methods are discussed, including a detailed stability analysis of the capacitively coupled ldquoright legrdquo in capacitive ECG measurements with mismatching electrode capacities and the development of an adaptive noise canceller for magnetic bioimpedance monitoring based on a nonlinear signal coupling model.

Design, Fabrication, and Testing of a Hybrid CMOS/PDMS Microsystem for Cell Culture and Incubation

Abstract: We discuss the design, fabrication, and testing of a hybrid microsystem for stand-alone cell culture and incubation. The micro-incubator is engineered through the integration of a silicon CMOS die for the heater and temperature sensor, with multilayer silicone (PDMS) structures namely, fluidic channels and a 1.5-mm diameter 12-muL culture well. A 90-mum-thick PDMS membrane covers the top of the culture well, acting as barrier to contaminants while at the same time allowing the cells to breath and exchange gases with the ambient environment. The packaging for the microsystem includes a flexible polyimide electronic ribbon cable and four fluidic ports that provide external interfaces to electrical energy, closed-loop sensing and electronic control as well as solid and liquid supplies. The complete structure has a size of (2.5times2.5times0.6) cm3. We have employed the device to successfully culture BHK-21 cells autonomously over a three day period in ambient environment

Area-Power Efficient VLSI Implementation of Multichannel DWT for Data Compression in Implantable Neuroprosthetics

Abstract: Time-frequency domain signal processing of neural recordings, from high-density microelectrode arrays implanted in the cortex, is highly desired to ease the bandwidth bottleneck associated with data transfer to extra-cranial processing units. Because of its energy compactness features, discrete wavelet transform (DWT) has been shown to provide efficient data compression for neural records without compromising the information content. This paper describes an area-power minimized hardware implementation of the lifting scheme for multilevel, multichannel DWT with quantized filter coefficients and integer computation. Performance tradeoffs and key design decisions for implantable neuroprosthetics are presented. A 32-channel 4-level version of the circuit has been custom designed in 0.18-mum CMOS and occupies only 0.22 mm2 area and consumes 76 muW of power, making it highly suitable for implantable neural interface applications requiring wireless data transfer.

A Nanopower Bandpass Filter for Detection of an Acoustic Signal in a Wearable Breathing Detector

Abstract: This paper presents a nanopower programmable bandpass filter suitable to process biomedical signals. The filter proves to be very robust to mismatch and process variations even when it has been implemented using MOS transistors biased in the weak inversion region. The paper analyses design issues associated to matching and process variations for the chosen filter topology and constituent transconductor block. The design equations justify the choice of both when the main constraints are robustness and power. The sixth order, bandpass filter prototype consumes 70 nW of power, with a dynamic range greater than 47 dB and operates at 1-V power supply. The filter was designed as part of a wearable breathing detector but its wide programmability range makes it suitable for many other biomedical sensor interfaces that require steep low frequency rejection band as well as ultralow power and low voltage operation.

A Hybrid Microfluidic/CMOS Capacitive Sensor Dedicated to Lab-on-Chip Applications

Abstract: A hybrid microfluidic/IC capacitive sensor is presented in this paper for highly integrated lab-on-chips (LoCs). We put forward the design and implementation of a charge based capacitive sensor array in 0.18-mum CMOS process. This sensor chip is incorporated with a microfluidic channel using direct-write microfluidic fabrication process (DWFP). The design, construction and experimental results as well are demonstrated using four different chemical solutions with known dielectric constants. The proposed highly sensitive CMOS capacitive sensor (ap530 mV/fF) along with low complexity DWFP emerges as clear favorite for LoC applications.

Brain–Silicon Interface for High-Resolution in vitro Neural Recording

Abstract: A 256-channel integrated interface for simultaneous recording of distributed neural activity from acute brain slices is presented. An array of 16 times 16 Au recording electrodes are fabricated directly on the die. Each channel implements differential voltage acquisition, amplification and band-pass filtering. In-channel analog memory stores an electronic image of neural activity. A 3 mm times 4.5 mm integrated prototype fabricated in a 0.35-mum CMOS technology is experimentally validated in single-channel extracellular in vitro recordings from the hippocampus of mice and in multichannel simultaneous recordings in a controlled environment

Numerical and Experimental Evaluation of a Compact Sensor Antenna for Healthcare Devices

Abstract: The paper presents a compact planar antenna designed for wireless sensors intended for healthcare applications. Antenna performance is investigated with regards to various parameters governing the overall sensor operation. The study illustrates the importance of including full sensor details in determining and analysing the antenna performance. A globally optimized sensor antenna shows an increase in antenna gain by 2.8 dB and 29% higher radiation efficiency in comparison to a conventional printed strip antenna. The wearable sensor performance is demonstrated and effects on antenna radiated power, efficiency and front to back ratio of radiated energy are investigated both numerically and experimentally. Propagation characteristics of the body-worn sensor to on-body and off-body base units are also studied. It is demonstrated that the improved sensor antenna has an increase in transmitted and received power, consequently sensor coverage range is extended by approximately 25%.

Multimodality Sensor System for Long-Term Sleep Quality Monitoring

Abstract: Sleep monitoring is an important issue and has drawn considerable attention in medicine and healthcare. Given that traditional approaches, such as polysomnography, are usually costly, and often require subjects to stay overnight at clinics, there has been a need for a low-cost system suitable for long-term sleep monitoring. In this paper, we propose a system using low-cost multimodality sensors such as video, passive infrared, and heart-rate sensors for sleep monitoring. We apply machine learning methods to automatically infer a person's sleep state, especially differentiating sleep and wake states. This is useful information for inferring sleep latency, efficiency, and duration that are important for long-term monitoring of sleep quality in healthy individuals and in those with a sleep-related disorder diagnosis. Our experiments show that the proposed approach offers reasonable performance compared to an existing standard approach (i.e., actigraphy), and that multimodality data fusion can improve the robustness and accuracy of sleep state detection.

FPGA-Accelerated Deformable Image Registration for Improved Target-Delineation During CT-Guided Interventions

Abstract: Minimally invasive image-guided interventions (IGIs) are time and cost efficient, minimize unintended damage to healthy tissue, and lead to faster patient recovery. With the advent of multislice computed tomography (CT), many IGIs are now being performed under volumetric CT guidance. Registering pre-and intraprocedural images for improved intraprocedural target delineation is a fundamental need in the IGI workflow. Earlier approaches to meet this need primarily employed rigid body approximation, which may not be valid because of nonrigid tissue misalignment between these images. Intensity-based automatic deformable registration is a promising option to correct for this misalignment; however, the long execution times of these algorithms have prevented their use in clinical workflow. This article presents a field-programmable gate array-based architecture for accelerated implementation of mutual information (Ml)-based deformable registration. The reported implementation reduces the execution time of MI-based deformable registration from hours to a few minutes. This work also demonstrates successful registration of abdominal intraprocedural noncontrast CT (iCT) images with preprocedural contrast-enhanced CT (preCT) and positron emission tomography (PET) images using the reported solution. The registration accuracy for this application was evaluated using 5 iCT-preCT and 5 iCT-PET image pairs. The registration accuracy of the hardware implementation is comparable with that achieved using a software implementation and is on the order of a few millimeters. This registration accuracy, coupled with the execution speed and compact implementation of the reported solution, makes it suitable for integration in the IGI-workflow.

Flexible Communication and Control Protocol for Injectable Neuromuscular Interfaces

Abstract: BION2 is a system based on injectable neuromuscular implants whose main goal is to restore the functional movement of paralyzed limbs. To achieve this objective, the functional requirements of the implanted interfaces include not only stimulation but also integrated sensors in order to detect patient intention, to provide servocontrol of muscle activation and to sense posture to inform more global motor planning and coordination. The technical constraints for managing the system include the efficient use of forward and reverse telemetry channels with limited capacity, minimization of adverse consequences from errors in data transmission or intermittent loss of power to the implants, and ability to adjust stimulation rates and phases to achieve efficient fine control of muscle force while minimizing fatigue. This paper describes a communication and control architecture with several novel features that address these requirements

A Silicon Pancreatic Beta Cell for Diabetes

Abstract: The paper will consider how silicon devices such as ion-sensitive field effect transistors can be used to model metabolic functions in biology. In a first example, a biologically inspired silicon beta cell is presented to serve as the main building block of an artificial pancreas. This is to be used for real-time glucose sensing and insulin release for diabetics. This system presents the first silicon implementation of a metabolic cell capable of exhibiting variable bursting behavior upon glucose stimulation. Based on the Hodgkin and Huxley formalism, this approach achieves dynamics similar to that of biological beta cells by using devices biased in the subthreshold regime. In addition to mimicking the physiological behavior of the beta cell, the circuit achieves good power efficiency, measured to be 4.5 muW

On the Robust Circuit Design Schemes of Biochemical Networks: Steady-State Approach

Abstract: Based on the steady-state analyses of the synergism and saturation system (S-system) model, a robust control method is proposed for biochemical networks via feedback and feedforward biochemical circuits. Two robust biochemical circuit design schemes are developed. One scheme is to improve the system's structural stability so as to tolerate larger kinetic parameter variations, whereas the other is to compensate for the kinetic parameter variations to eliminate their effects. In addition, a multi-objective biochemical circuit design scheme is introduced for both the robust design against kinetic parameter variations and a desired sensitivity design to eliminate the effect of external disturbance simultaneously. The proposed robust circuit design schemes will provide a systematic method with potential applications in synthetic circuit design for biotechnological purpose and drug design purpose. Recent advances in both metabolic and genetic engineering have made the robust biochemical circuit control approach feasible through the design and implementation of synthetic biological networks amenable to mathematical modeling and quantitative analysis. Finally, several examples including the robust circuit design of the tricarboxylic acid cycle are used in silico to illustrate the design procedure and to confirm the performance of the proposed design method.

A Retinal Prosthesis Technology Based on CMOS Microelectronics and Microwire Glass Electrodes

Abstract: A very large format neural stimulator device, to be used in future retinal prosthesis experiments, has been designed, fabricated, and tested The device was designed to be positioned against a human retina for short periods in an operating room environment Demonstrating a very large format, parallel interface between a 2-D microelectronic stimulator array and neural tissue would be an important step in proving the feasibility of high resolution retinal prosthesis for the blind The architecture of the test device combines several novel components, including microwire glass, a microelectronic multiplexer, and a microcable connector The array format is 80 times 40 array pixels with approximately 20 microwire electrodes per pixel The custom assembly techniques involve indium bump bonding, ribbon bonding, and encapsulation The design, fabrication, and testing of the device has resolved several important issues regarding the feasibility of high-resolution retinal prosthesis, namely, that the combination of conventional CMOS electronics and microwire glass provides a viable approach for a high resolution retinal prosthesis device Temperature change from power dissipation within the device and maximum electrical output current levels suggest that the device is acceptable for acute human tests

An Address-Event Vision Sensor for Multiple Transient Object Detection

Abstract: We present a vision sensor chip designed to detect multiple transient objects - objects that either move or change in light intensity - and output their locations using address-event representation. The sensor uses a novel onset detector to detect transient objects and a dynamically-wired winner-takes-all circuit to group pixels and select the brightest pixel in each object. This paper describes the circuits and also presents measurements that characterize the performance of the sensor chip.

A High-Voltage SOI CMOS Exciter Chip for a Programmable Fluidic Processor System

Abstract: A high-voltage (HV) integrated circuit has been demonstrated to transport fluidic droplet samples on programmable paths across the array of driving electrodes on its hydrophobically coated surface. This exciter chip is the engine for dielectrophoresis (DEP)-based micro-fluidic lab-on-a-chip systems, creating field excitations that inject and move fluidic droplets onto and about the manipulation surface. The architecture of this chip is expandable to arrays of N X N identical HV electrode driver circuits and electrodes. The exciter chip is programmable in several senses. The routes of multiple droplets may be set arbitrarily within the bounds of the electrode array. The electrode excitation waveform voltage amplitude, phase, and frequency may be adjusted based on the system configuration and the signal required to manipulate a particular fluid droplet composition. The voltage amplitude of the electrode excitation waveform can be set from the minimum logic level up to the maximum limit of the breakdown voltage of the fabrication technology. The frequency of the electrode excitation waveform can also be set independently of its voltage, up to a maximum depending upon the type of droplets that must be driven. The exciter chip can be coated and its oxide surface used as the droplet manipulation surface or it can be used with a top-mounted, enclosed fluidic chamber consisting of a variety of materials. The HV capability of the exciter chip allows the generated DEP forces to penetrate into the enclosed chamber region and an adjustable voltage amplitude can accommodate a variety of chamber floor thicknesses. This demonstration exciter chip has a 32 x 32 array of nominally 100 V electrode drivers that are individually programmable at each time point in the procedure to either of two phases: 0deg and 180deg with respect to the reference clock. For this demonstration chip, while operating the electrodes with a 100-V peak-to-peak periodic waveform, the maximum HV electrode waveform frequency is about 200 Hz; and standard 5-V CMOS logic data communication rate is variable up to 250 kHz. This HV demonstration chip is fabricated in a 130-V 1.0-mum SOI CMOS fabrication technology, dissipates a maximum of 1.87 W, and is about 10.4 mm x 8.2 mm.

Clues From Digital Radio Regarding Biomolecular Recognition

Abstract: Frequency-offset immunosensors based on acoustic wave devices are known to provide extremely high sensitivity and selectivity where the target is detected and identified based on the amount of frequency shift. We propose a new method to further classify chemically similar molecules extrapolating on the concept of in-phase (I) and quadrature (Q) domain used for the detection of orthogonal M-ary signals in digital telecommunication systems. We performed a series of detection experiments using samples of explosives such as cyclotrimethylene trinitramine [or royal demolition explosive (RDX)] and trinitrotoluene (TNT), containing nitrous oxide (NO2) groups and chemically analogous substances (e.g., musk oil). This detection scheme involves the use of semi-orthogonal monoclonal anti-TNT and anti-RDX antibodies immobilized onto two separate sensor surfaces. The term semi-orthogonal represents the co-option of a term used heavily in digital radio for the purpose of describing chemical orthogonality. The antibody to TNT which we use has some reactivity with RDX, and other nitrous oxide compounds. This feature of an antibody is referred to in the literature as antibody promiscuity. The antibody for RDX which we use shows very little cross reactivity with other molecules and, hence, the chemical responsiveness of the two antibodies is not quite orthogonal. Their responses are then chemically semi-orthogonal. The two semi-orthogonal immunosensor responses were then monitored and the baseline frequency shifts were recorded. After remapping the measured frequency data of the analytes onto a new 2-D domain by setting the TNT-specific sensor as the (I) or real component and the RDX-specific sensor as the (Q) or imaginary component, we could observe that all the substances were detected and mapped out to distinct regions on the I-Q plot. We assert that there is a strong resemblance between digital radio system quadrature detection techniques and our I-Q mapping scheme of the semi-orthogonal immunosensor signatures

Introduction to Special Section From the BSN2007 Workshop

Abstract: The three papers presented in this special section are extended versions of papers presented at BSN 2007, held in Aachen, Germany on March 2007.