In this research fluorescent optochemical pH probes for the detection of ischaemia have been investigated. Myocardial ischaemia is the most prominent risk during heart surgery. During open heart surgery the heart is temporarily arrested and, since there no blood flowing, oxygen supply and removal of waste products is stopped and heart cells can be damaged. In this paper we propose a novel method to monitor the condition of the heart by placing optochemical pH sensors on several strategic places around the heart during surgery. Low cost opto-chemical pH sensors, using a HPTS (8-hydroxy-1,3,6-pyrene trisulfonic acid trisodium salt) fluorescent dye encapsulated in a thin bio-compatible hydrogel layer, were investigated for this application. Our research started with an extensive optical characterization of several types of hydrogel layers at different pH levels. Secondly a reflection probe prototype using several of these layers was designed, built and tested. Dual wavelength excitation and ratiometric detection of the fluorescent signals was used to detect the pH level. Typical output signals of 35% to 53% per pH in the range from 6.5-8.0 pH have been measured and a response time of typically 400 seconds was obtained for the prototypes. Finally based on our measurements on the HPTS layers and the reflection probe we propose an improved type of pH probe for the detection of ischaemia during open heart surgery.

This article describes the fabrication of MgF₂ and MgO thin-film-based optical filters and compares the optical transmission of the filters over UV. The MgF₂ thin-films were deposited by use of an e-beam technique and their optical properties were characterised by ellipsometry. The effect of substrate temperature on the optical properties was studied. The MgF₂ optimum refractive indices were obtained with a substrate temperature between 200 °C and 300 °C. Optical simulations were performed to compare the performance of MgF₂ and MgO in the fabrication of near-UV narrow bandpass optical filters. While MgO-based optical filters result in a higher transmittance peak intensity, especially at 350 nm, the MgF₂ optical filters are narrower, present lower values of FWHM, a mean value of 20 nm. This feature could be especially relevant for specific applications on fluorescent optical sensors. Finally, a Fabry-Perot based on a MgF₂/TiO₂ optical filter was deposited, using an e-beam technique for the MgF₂ thin-films and RF-sputtering technique for the TiO₂ thin-films. The MgF₂/TiO₂ optical filter peak transmittance is approximately 70% close to 400 nm, as expected. The results are discussed with focus on applications in fluorescent optical sensors for peaks at 350, 370, 380 and 400 nm, respectively.

The measurement of carbon-dioxide (CO2) concentration is very important in home and building automation, e.g. to control ventilation in energy-efficient buildings. This application requires compact, low-cost sensors that can measure CO₂ concentration with a resolution of <200 ppm over a 2500ppm range. Conventional optical (NDIR-based) CO₂ sensors require components that are CMOS-incompatible, difficult to miniaturize and power-hungry [1]. Due to their CMOS compatibility, thermal-conductivity-based sensors are an attractive alternative [2,3]. They exploit the fact that the thermal conductivity (TC) of CO₂ is lower than that of the other constituents of air, so that CO2 concentration can be indirectly measured via the heat loss of a hot wire to ambient. However, this approach requires the detection of very small changes in TC (0.25 ppm per ppm CO2 [3]).

This paper presents a readout circuit for a carbon dioxide (CO&#2082;) sensor that measures the CO&#x2082;-dependent thermal time constant of a hot-wire transducer. The readout circuit periodically heats up the transducer and uses a phase-domain &#x0394; &#x03A3; modulator to digitize the phase shift of the resulting temperature transients. A single resistive transducer is used both as a heater and as a temperature sensor, thus greatly simplifying its fabrication. To extract the transducer's resistance, and hence its temperature, in the presence of large heating currents, a pair of transducers is configured as a differentially driven bridge. The transducers and the readout circuit have been implemented in a standard 0.16&#x03BC;m CMOS technology, with an active area of 0.3 and 3.14 mm&#x00B2;, respectively. The sensor consumes 6.8 mW from a 1.8-V supply, of which 6.3 mW is dissipated in the transducers. A resolution of 94-ppm CO&#x2082; is achieved in a 1.8-s measurement time, which corresponds to an energy consumption of 12 mJ per measurement, &#x003E;10x less than prior CO&#x2082; sensors in CMOS technology.

A capacitive probe is generally used in a flex-fuel engine for measuring the ethanol content in biofuel. However, the water content in biofuel of high ethanol content cannot be disregarded or considered constant and the full composition measurement of ethanol, gasoline and water in biofuel is required. Electrical impedance spectroscopy with a customized capacitive probe operating in the 10 kHz to 1 MHz frequency range is combined with optical absorption spectroscopy in the UV spectral range between 230 and 300 nm for a full composition measurement. This approach is experimentally validated using actual fuels and the results demonstrate that electrical impedance spectroscopy when supplemented with optical impedance spectroscopy can be used to fully determine the composition of the biofuel and applied for a more effective engine management. A concept for a low-cost combined measurement system in the fuel line is presented.

Heart rate is a key factor in cardiovascular system monitoring and sports science. Some recent commercial applications use sensors in the ear but are faced with motion artifacts which corrupts the signal. Infrared thermography is a non-contact technique and may minimize motion effects with better user comfort and lower power consumption. We propose a novel system that uses infrared differential thermometry to detect the heart rate in the auricle. The signal analysis is performed using a continuous wavelet transform which extract frequency features of the bioheat transfer waveforms. Preliminary results taken from the neck provide proof of concept and similar results from the ear are expected.