During most cardiac surgeries, a Cardiopulmonary bypass (CPD) is used. This is a machine which takes over the respiration and circulation functions of the heart during surgery. However, the blood supply to the heart and thus the supply of oxygen and nutrients, will be cut off when this occurs. This is also known as myocardial ischemia, which can lead to damage to the heart tissue and could even be fatal. Therefore, it is of paramount importance to detect ischemia before it causes irreversible damage.

There are several parameters that can indicate ischemia, including pH, oxygen and lactate. This work focuses on measuring the pH level of the heart tissue, since this could be measured noninvasively and is relatively simple. In order to get a clear picture of the consequences of ischemia throughout the heart, the pH level should be measured at different locations. To achieve this an optical fluorescence sensor is designed. This sensor consists of a sensor layer, two LEDs and an optical fibre connected to a spectrometer.

The fluorescent indicator dye used in the sensor layer is 8-Hydroxypyrene-1,3,6-trisulfonic acid
trisodium salt (HPTS). This fluorescent dye has two excitation peaks, one at 405nm and one at 470nm and two emission peaks one at 440nm and one at 515nm. These different excitation and emission bands enable ratiometric sensing which improves accuracy and sensitivity. This is due to the fact that the intensity of the fluorescent emission at 515nm is directly proportional with the pH level, where the intensity of the fluorescent emission at 440nm is inversely proportional to the pH level. By taking the ratios of these measured intensities the pH can be determined.

The indicator dye is immobilized in a hydrogel which is thereafter deposited on a thin glass slide. This slide is placed above two LEDs which are matched with the excitation peaks of HPTS. Adjacent to the LEDs an optical fibre is placed to capture the fluorescent emission and direct it to the spectrometer which is connected to a computer. The designed sensor system shows a 5 fold increase in ratio of intensities over a pH range of 6.2-8.2, with a significant improvement in response time compared to other HPTS and hydrogel based pH sensors reported in literature.

In this research a sensor patch for newborns is proposed. This sensor patch is a device which would be attached to the skin of a newborn in order to monitor vital health signs such as: temperature, heart rate, respiration rate and oxygen saturation. Furthermore, a bilirubin sensor will be included to check the newborn for jaundice. Thereafter, the measured data should be communicated wirelessly to a base station. What happens with the data after the base station is beyond the scope of this research. One of the main challenges is energy efficiency since the patch should be small enough to fit on a newborn whichmeans the battery should be small as well. Additionally the sensor patch should be able to operate for 3 days continuously. The overall design is divided into three subsystems: the battery control system, the microcontroller and communication and the sensors. This report focuses on the sensor part of the total system. After analysis of different kind of sensors, the SI7051 is chosen for the temperature sensor since it is themost accurate and energy efficient. In order to measure the respiration rate an acceleration sensor was chosen to be the most suitable within the system requirements. For the acceleration sensor the IIS2DLPC was selected. In order to measure the heart rate and oxygen saturation a PPG sensor is designed. Finally, the bilirubin sensor is designed which uses PPG as well. However, the designed sensors still need calibration by empirical experiments in order to obtain accurate results