Biomedical subjects

Erik A Johannessen

Publications and source records attributed to Erik A Johannessen.

6 recordsLinked to original sources

PubMed2006

Biocompatibility of a lab-on-a-pill sensor in artificial gastrointestinal environments.

In this paper, we present a radiotelemetry sensor, designed as a lab-in-a-pill, which incorporates a two-channel microfabricated sensor platform for real-time measurements of temperature and pH. These two parameters have potential application for use in remote biological sensing (for example they may be used as markers that reflect the physiological environment or as indicators for disease, within the gastrointestinal tract). We have investigated the effects of biofouling on these sensors, by exploring their response time and sensitivity in a model in vitro gastrointestinal system. The artificial gastric and intestinal solutions used represent a model both for fasting, as well as for the ingestion of food and subsequent digestion to gastrointestinal chyme. The results showed a decrease in pH sensitivity after exposure of the sensors for 3 h. The response time also increased from an initial measurement time of 10 s in pure GI juice, to ca. 25 s following the ingestion of food and 80 s in simulated chyme. These in vitro results indicate that changes in viscosity in our model gastrointestinal system had a pronounced effect on the unmodified sensor.

Biocompatible Materials↗

PubMed2005

Implementation of radiotelemetry in a lab-in-a-pill format.

A miniaturised lab-in-a-pill device has been produced incorporating a temperature and pH sensor with wireless communication using the 433.92 MHz ISM band. The device has been designed in order to enable real time in situ measurements in the gastrointestinal (GI) tract, and accordingly, issues concerning the resolution and accuracy of the data, and the lifetime of the device have been considered. The sensors, which will measure two key parameters reflecting the physiological environment in the GI (as indicators for disease) were both controlled by an application specific integrated circuit (ASIC). The data were sampled at 10-bit resolution prior to communication off chip as a single interleaved data stream. This incorporated a power saving serial bitstream data compression algorithm that was found to extend the service lifetime of the pill by 70%. An integrated on-off keying (OOK) radio transmitter was used to send the signal to a local receiver (base station), prior to acquisition on a computer. A permanent magnet was also incorporated in the device to enable non-visual tracking of the system. We report on the implementation of this device, together with an initial study sampling from within the porcine GI tract, showing that measurements from the lab-on-a-pill, in situ, was within 90% of literature values.

Animals↗

PubMed2005

A programmable microsystem using system-on-chip for real-time biotelemetry.

A telemetry microsystem, including multiple sensors, integrated instrumentation and a wireless interface has been implemented. We have employed a methodology akin to that for System-on-Chip microelectronics to design an integrated circuit instrument containing several "intellectual property" blocks that will enable convenient reuse of modules in future projects. The present system was optimized for low-power and included mixed-signal sensor circuits, a programmable digital system, a feedback clock control loop and RF circuits integrated on a 5 mm x 5 mm silicon chip using a 0.6 microm, 3.3 V CMOS process. Undesirable signal coupling between circuit components has been investigated and current injection into sensitive instrumentation nodes was minimized by careful floor-planning. The chip, the sensors, a magnetic induction-based transmitter and two silver oxide cells were packaged into a 36 mm x 12 mm capsule format. A base station was built in order to retrieve the data from the microsystem in real-time. The base station was designed to be adaptive and timing tolerant since the microsystem design was simplified to reduce power consumption and size. The telemetry system was found to have a packet error rate of 10(-3) using an asynchronous simplex link. Trials in animal carcasses were carried out to show that the transmitter was as effective as a conventional RF device whilst consuming less power.

Computer Systems↗

PubMed2004

Implementation of multichannel sensors for remote biomedical measurements in a microsystems format.

A novel microelectronic "pill" has been developed for in situ studies of the gastro-intestinal tract, combining microsensors and integrated circuits with system-level integration technology. The measurement parameters include real-time remote recording of temperature, pH, conductivity, and dissolved oxygen. The unit comprises an outer biocompatible capsule encasing four microsensors, a control chip, a discrete component radio transmitter, and two silver oxide cells (the latter providing an operating time of 40 h at the rated power consumption of 12.1 mW). The sensors were fabricated on two separate silicon chips located at the front end of the capsule. The robust nature of the pill makes it adaptable for use in a variety of environments related to biomedical and industrial applications.

Biomedical Engineering↗

PubMed2002

Micromachined nanocalorimetric sensor for ultra-low-volume cell-based assays.

Current strategies for cell-based screening generally focus on the development of highly specific assays, which require an understanding of the nature of the signaling molecules and cellular pathways involved. In contrast, changes in temperature of cells provides a measure of altered cellular metabolism that is not stimulus specific and hence could have widespread applications in cell-based screening of receptor agonists and antagonists, as well as in the assessment of toxicity of new lead compounds. Consequently, we have developed a micromachined nanocalorimetric biological sensor using a small number of isolated living cells integrated within a subnanoliter format, which is capable of detecting 13 nW of generated power from the cells, upon exposure to a chemical or pharmaceutical stimulus. The sensor comprises a 10-junction gold and nickel thermopile, integrated on a silicon chip which was back-etched to span a 800-nm-thick membrane of silicon nitride. The thin-film membrane, which supported the sensing junctions of the thermoelectric transducer, gave the system a temperature resolution of 0.125 mK, a low heat capacity of 1.2 nJ mK(-1), and a rapid (unfiltered) response time of 12 ms. The application of the system in ultra-low-volume cell-based assays could provide a rapid endogenous screen. It offers important additional advantages over existing methods in that it is generic in nature, it does not require the use of recombinant cell lines or of detailed assay development, and finally, it can enable the use of primary cell lines or tissue biopsies.

Adipocytes↗

PubMed2002

A suspended membrane nanocalorimeter for ultralow volume bioanalysis.

A nanocalorimetric suspended membrane sensor for pL volumes of aqueous media was fabricated by bulk silicon micromachining using anisotropic wet etching and photo and electron beam lithographic techniques. A high-temperature sensitivity of 125 microK and a rapid unfiltered time constant of 12 ms have been achieved by integrating a miniaturized reaction vessel of 0.7-nL volume on a 800-nm-thick and 300 x 300- microm2-large silicon nitride membrane, thermally insulated from the surrounding bulk silicon. The combination of a ten-junction gold and nickel thermoelectric sensor with an integrated ultralow noise preamplifier has enabled the resolution of 15-nW power in a single measurement, a result confirmed by electrical calibration. The combination of a high sensitivity and rapid response time is a consequence of miniaturization. The choice of gold and nickel as sensor material provided the maximum thermal sensitivity in the context of ease of fabrication and cost. The nanocalorimetric sensor has the potential for integration in an ultralow-volume high-density array format for the characterization of processes in which there is an exchange of heat.

Biosensing Techniques↗