With the rapid development of science and technology, the Internet of Things and big data have become important forces driving the progress of modern technology. The evolution of these technologies has spurred the widespread application of smart devices and services, bringing revolutionary changes to various industries. In this context, flexible sensors have become a key bridge between the physical and digital worlds because of their unique bendability and high adaptability. They not only provide real-time data collection and transmission, but also serve a crucial role in health monitoring and environmental detection due to their lightweight and flexible characteristics. As fabrication technologies continue to innovate, flexible sensors are evolving towards miniaturization, integration, and customization. Although flexible sensors based on a variety of micro- and nanostructures and innovative materials have made significant progress in recent years, challenges still exist in terms of sensor performance, integration capability, and fabrication efficiency. To address these challenges, we utilized ultraviolet (UV) laser direct writing technology to efficiently achieve the microstructure fabrication and material modification required for the sensing capabilities of flexible sensors by precisely controlling the time, space, and energy of the laser. Correspondingly, we developed innovative fabrication technologies based on UV laser direct writing for different types of flexible sensors, including pressure sensors, strain sensors, gas sensors, and temperature sensors. The application of these technologies not only improves the fabrication efficiency but also enhances the sensor performance to meet the demands for customization and miniaturization.@en

In modern High-Performance Computing (HPC) systems based on Field Programmable Gate Arrays (FPGA) accelerators, First-In, First-Out queues (FIFOs) are crucial for data buffering and balancing, particularly in demanding applications requiring high-throughput data streaming. Some prominent examples are: large scale signal processing, machine learning, and online network processing. Typically, these FIFOs are implemented using the available on-chip blocks RAM (BRAM) blocks organized as a circular structure, leveraging the reconfigurable nature of FPGAs to manage data efficiently. However, as applications have to process larger and larger data capacities, the associated area and power consumption of these BRAM based implementations consume significantly large portion of the on-chip resources, posing challenges for both performance and efficiency.

This thesis explores an alternative approach for large and efficient reconfigurable on-chip FIFOs by designing a dedicated ASIC block containing linear shift register structure. Unlike circular FIFOs, which rely on complex control units such as address pointers and decoders, the linear FIFOs simplify the implementation by directly shifting the data through the registers. This approach eliminates the need for the additional intricate control logic typically associated with FPGA circular buffers, making it a potentially more efficient solution for a large class of streaming applications.

The first phase of this work focuses on implementing various FIFO designs on a Xilinx Virtex-7 series FPGA, utilizing different on-chip memory resources: registers, lookup tables (LUTs), and BRAM blocks. These implementations are investigated across different bit widths, in the range of hundreds of bits, and FIFO depths of several thousand stages. The second phase compares these FPGA implementations with an ASIC-based linear FIFO of similar size, synthesized using the TSMC 40 nm standard cell library. The results demonstrate that while the ASIC-based linear FIFO offers over twice the performance of the FPGA-based designs, it requires six to seven times more area. This is attributed to the fact that register-based storage cells are approximately ten times larger than SRAM cells, highlighting the inherent trade-off between performance and area in such designs.

To address the above area overhead, this project further investigates the use of two ring-counters to replace the address decoders typically found in SRAM-based FIFO designs. As data storage requirements increase, the complexity of address decoders also grows. By simplifying the control logic with ring-counters, the design achieved area reductions of 50\% to 76\% for FIFO depths of 1 Kbits and 2 Kbits across various bit widths. These findings underscore the significant potential of this approach to optimize both area and performance in memory-intensive FPGA applications.

Tissue vitality monitoring is a crucial process to preserve patients’ health during post-surgical recovery or to ensure full adaptation and healing of transplanted organs. Among the many local factors for vitality assessment, tissue oxygenation gives an insight into entire tissue recovery and is directly linked to cell metabolism. To be able to assess oxygenation at the cellular level, NADH fluorescence sensing is used due to its contribution to the cellular respiratory cycle and high sensitivity to oxygen concentration. The current devices for NADH fluorescence sensing are limited to external measurements, where they are suitable for hospital use. This raises the need for a device that is implantable and bioresorbable so that it can stay in the body after the surgery and does not require secondary surgery for removal that puts the patient at risk. The goal of this master’s thesis is to introduce the design of a bioresorbable optical filter and photodetector for the measurements of oxygen through the detection of NADH fluorescence. The design consists of an absorption layer, a Fabry-Perot filter, and a wavelength-specific photodetector; where the overall response is designed to have high sensitivity to the emission wavelength of NADH (470nm) and low sensitivity to the excitation of NADH (350nm). ZnO nanoparticles are chosen to be the absorption layer due to their high absorption properties to 350nm and biodegradability, where the optical response is then tested through spectroscopy measurements. For the Fabry-Perot filter, a design with SiO2 and SiNx layers has been created with simulation and tested with optical measurements. The complete design consists of 15 layers and has a total thickness of approximately 1μm. Lastly; for the photodetector, Spectra simulations have been conducted for the determination of the optimal design properties. The choices are then adapted to a mask design for the fabrication, in which the back side etching of the silicon wafer is required for biodegradability and optical performance. The fabrication of the photodetector has not been completed due to the time frame of the project. The measurements on the combination of ZnO and Fabry-Perot filter show that the transmission of 470nm is 2.5-4 times larger than the transmission of 350nm, which is expected to increase to at least an order of magnitude when combined with the photodetector. For future experiments, it is recommended to conduct more tests on the filters and ZnO to ensure repeatability and consistency.

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.

This study presents an AlN-based Lamb wave (A0 mode) liquid sensing device designed for biomedical applications. The Lamb wave device features a 1.5 μm composite membrane consisting of a 500 nm LPCVD SiN and a 1 μm of a c-axis oriented AlN film. Additionally, an innovative 45° rotated IDT design was explored to minimize edge reflections towards the output IDT. Liquid testing experiments, involving IPA, DI water, and D-PBS, were conducted to see if the devices were able to differentiate between these liquids. Results demonstrate that the fabricated Lamb wave devices exhibit sensitivity to mass loading and can distinguish between liquids based on phase, frequency, and gain characteristics. Devices with the rotated IDT design have shown a significant increase in resonance by 15 dB, as well as enhanced sensitivity compared to those with the normal design. Furthermore, devices with the rotated design demonstrated a higher Q factor of 680, indicating superior performance over the normal design (Q factor of 450). These findings suggest that a Lamb wave device with the 45° rotated IDT design holds considerable potential for applications that demand accurate liquid characterization and detection.

This thesis report, one of a set of two reports, describes a novel way to detect incidents that could occur in the daily life of the elderly. Unlike most systems already implemented in this field, this system does not use any wearable (positioning) sensors and works off an Single Board Computer (SBC).Independent of both of these systems is a system for reassurance to alleviate distress.

In the past decades, the workload and the pressure on medical personnel has been growing to an unprecedented peak. This is partly due to the ageing population and the increasing capabilities to be independent at an older age, increasing the age people enter nursing homes. This paper focuses on a novel way to detect incidents that could occur in the daily life of the elderly. Unlike most systems already proposed by others, there will be no use of wearable positioning sensors and the system is implemented on an Single Board Computer (SBC). This thesis report is one of a set of two reports discussing the final implementation of the system.

The objective of this project was to develop a real-time restlessness detection algorithm for Rapid Eye Movement Sleep Behavior Disorder (RBD). This project was completed in collaboration with Momo Medical, a fast-growing start-up, and developer of the BedSense device. Our project aimed to design a system capable of detecting RBD episodes and bringing patients to a lighter sleep stage. To accomplish this, proprietary data and existing data from an RBD patient were collected through the BedSense device. Additionally, data was extracted using a hardware system (developed by another subgroup) from a non-RBD test subject. The collected data was utilized to design and implement a restlessness detection algorithm. Given the limited data collected for this project, a classical detection algorithm was developed instead of machine learning techniques. The software system demonstrated impressive performance, achieving a balanced accuracy of 95.94%, an average sensitivity of 100%, and an average specificity of 91.88%.
The results of this project were integrated with another project seeking to develop a sensor system that brings an RBD patient to a lighter sleep stage. This project built a sock system with embedded sensors and a vibration module to achieve this. The proof of concept of the final integrated system demonstrated a non-invasive method of detecting and preventing episodes caused by RBD.

The goal of this project was to develop a sensor system that detects Rapid Eye Movement Sleep Behaviour Disorder (RBD) episodes in an early stage and brings the patient to a lighter sleep stage at the episode onset. This project was completed in close collaboration with Momo Medical, a fast-growing start-up and developer of the BedSense - a device placed under mattresses that tracks the bed posture and restlessness of residents in nursing homes. To detect RBD episodes, the BedSense was used in combination with a sock that houses the biosensors EDA, PPG and an accelerometer. The sock also contains a vibrator module, that can bring the patient to a lighter sleep stage in case of an episode.

The outcomes of this project are promising, data has been recorded from both non-RBD test subjects and an RBD patient, and the vibration module has been tested.

The results of this project were integrated with another project seeking to develop an algorithm to detect RBD episodes in an early stage. This project used data from the Momo BedSense and from the sock that has been created in this project.

Prostate cancer is the most prevalent form of cancer among men, increasing in annual prevalence. Often, the disease progression is less intrusive then treatment. Sensitive and low-intrusive diagnosis methods exist but these are not specific. Causing the need for biopsy, an intrusive and high risk for complication procedure.

This thesis sets out to design, fabricate and test a low cost, maximum sensitivity for surface mass loading Love-mode surface acoustic wave (SAW) based sensor. The thesis goal and requirements build up to answer the research question: Can the biomarker CD9 in a liquid sample be detected by means of a Love-mode surface acoustic wave device?

SAW based sensors utilise the modulation of acoustic vibrations to detect an analyte. In this thesis, the change is caused by the immobilisation of a biomarker on a delay line between an input and output transducer. The method, more often referred to as gravimetric sensing, is based on the shift of the passband frequency by a change in surface mass density due to selective immobilisation of the biomarker. The change in passband frequency is detected by the change in phase at the fixed frequency. In this work, the fixed frequency within the passband is around 620MHz.

The Love-mode SAW is transceived by 8$\mu$m wavelength spaced interdigitated transducers on piezoelectric crystalline ST-cut quartz utilising Y propagating waves. The wave mode becomes Love-mode by capturing the wave energy using a slower shear horizontal wave speed 900nm polyimide waveguide layer.

The biomarker is the transmembrane protein CD9, present on extra cellular vesicles. These CD9 positive extracellular vesicles are well accessible as they are present in body fluids including urine. In this work, in vitro cell culture derived CD9 positive extracellular vesicles are used.

After an extensive study to the design of a Love-mode SAW based sensor and micro fabrication, using the high frequency probe station device characterisation method, it can be concluded Love-mode SAWs were excited. The devices show sensitivity for different liquids and are proven to be able to immobilise CD9 utilising covalent immobilised streptavidin and biotinylated monoclonal anti-CD9. The devices show a response to CD9 containing samples but are not proven to be sufficiently sensitive for CD9 in liquid sample detection.

It is recommended the sensor achieved sensitivity is first more systematically determined. Then a more robust measurement setup must be designed, less prone to cross sensitivity to environmental changes and experimental variations. Then a next generation sensor for better sensitivity to surface mass loading in liquid samples can be designed.

Capacitive, interdigital sensors in proximity of a PASiC thin film have been proposed as a cheap, robust alternative to existing ammonia sensing technologies. However, although prototype sensors have been manufactured, investigation into the working principles of this class of ammonia sensors is limited. This work aims to analyse the electrode and PASiC layer configuration to gain more insight into how design parameters influence the sensing capabilities of these devices.
To this end, finite element simulations and analytical simulations have been carried out to model the behaviour of the sensor configuration. The PASiC layer is modelled as a stack of layers with different permittivities, with the response to ammonia modelled as a change in the permittivity of the layers.
Using the simulation data, a lithography mask for a test-bench with varying electrode dimensions is designed to allow fabrication of devices for measuring the effects of different manufacturing parameters.
A series of prototypes created using this mask is then used to devise an etching setup to allow electrochemical etching of single chips to create the porous layer.
The results of the manufacturing process are analysed and discussed.

Power electronics are an important technology used to convert electricity from a source like a battery or high voltage DC bus to more usable forms of electricity. This has to be done efficiently, reliably and without failures which is critical in applications like electric cars or datacenters. Power MOSFETs with upcoming SiC and GaN devices are an important building block used in these converters. Hence these power MOSFET devices have to be improved continuously to get a lower on resistance (R_DSon), a better thermal dissipation and lower parasitic losses. In this thesis we will take a look at the embedding of power MOSFETs inside a PCB to obtain these improvements. This new technology needs to be evaluated in terms of reliability, failure-modes and thermal/electrical performance. By designing,
manufacturing and testing a PCB with embedded devices. During manufacturing silver sintering has been used for attaching the die to a copper coin. In the end the manufacturing has been done successfully.
Testing showed an 18% lower R_DSon and a twice as low junction to ambient thermal impedance indicating a better performance compared to regular packaging.

Over the years, care givers in nursing homes have seen their workload gradually increase. With no end of this trend in sight, the need for smart support systems increases. Especially systems which decrease the time spent on menial tasks are valued highly, because this frees more time for high quality and personal care.
To achieve this, Momo Medical is expanding on its nurse support system. This is a network of integrated smart solutions aiming at supporting care givers in nursing homes to provide better, faster and more personal care. The backbone of this nurse support system consists of the BedSenses, sensors which are placed under mattresses of each resident and can measure a variety of things.
This thesis describes the process of designing and creating a localization algorithm for this nurse support system. This algorithm can find residents by tracking the panic buttons they wear, so that in case of an emer- gency or whenever a care giver wants to know where a resident is located, they do not need to undertake a time consuming search in order to find them. These panic buttons send out an alive signal once every minute as well as a signal whenever the button is pressed. These signals are received by any nearby BedSenses. The algorithm looks at the signal strength with which each BedSense receives these signals and uses this to per- form localization.

To make open door policies easier in nursing homes, it is important to have a smart system that can check whether access is allowed for the person trying to enter some place or not. This thesis documents how an access control system has been built, for Momo Medical, to be used at a nursing home. It sheds light on hardware considerations made and the software written for the final product. All the knowledge gathered and the time spent has led to a final product that with minor tweaks can be used in the existing infrastructure of Momo Medical but also without the presence of it. There are however still improvements left to be made for the final product to be commercially appealing.

Introduction – Cardiovascular diseases are the leading cause of death in the world with one in three succumbing to the disease. The most common cardiovascular disease is coronary artery disease, caused by atherosclerosis resulting in a build-up of plaque within the arteries. This plaque can progress into a vulnerable plaque, which has been linked to an increase in major adverse cardiac events. Identification of a vulnerable plaque can lead to more precise treatment, better patient outcomes, and fewer reinterventions. A technique currently in development is intravascular photoacoustic catheter imaging combined with intravascular ultrasound, which can detect both the composition and the structure of a plaque. Current pullback devices – a device for driving the catheter – don’t exist for a clinical setting for this application and are used for research purposes only. This project is a design study looking into the different aspects that go into the development of such a product with the aim of usability, divided into two goals: Exploring the catheter connection to the pullback device that is suitable for users of the product, and the redesign of the pullback device.
Methods and Materials – The first part concerns the design of the catheter connection to the pullback device for users of the product. The users are interventional cardiologists and anyone who interacts with the device in a clinical setting. Catheter connector designs are prototyped and central to a short user experience study. The design space for current catheter connector devices is explored and four connectors are designed. A user experience study is made with the aim of obtaining feedback on different design aspects and what this user group prefers in catheter connector devices. The second part concerns the redesign of the system. A system design is proposed within the set requirements.
Results – Catheter connector designs are designed and 3D printed, assembled and placed in mock-up pullback devices as prototypes. These have been shown to users of the product during a user experience study. This study has shown that users (n=5) have clear preference for some design aspects, such as a twisting connection, relatively small connection devices, automatic signal connection parts, among others. A redesign of the system is performed within the set requirements, where design aspects and their consequences are considered. This is done through an iterative design process to enquire feedback from technicians, until a satisfactory system is proposed. This includes the signal transfer to the catheter and back, the rotation of the catheter, the pullback of the catheter, and its housing.
Discussion – Catheter connection design aspects have been explored after which a system redesign is proposed. This redesign lacks the connection between the signal connectors of the catheter and the pullback device. This connection is highly dependent on the disconnection method, which is non-trivial and infeasible to explore in this user experience study. The catheter connector could encompass a project in itself. The system redesign originally was aimed at the manufacture of the device, but was deemed infeasible for this project. Instead the project was aimed to be a design study of the development of such a device. As it stand, the current device is larger than preferred by users, which could be scaled down in collaboration with parts manufacturers. This can also downscale the motor for rotation, which is implemented to work at the devices maximum expected power requirements.
Conclusion – This thesis focused on the design study of a pullback device for intravascular photoacoustic and ultrasound catheter imaging for users of such a device. Catheter connection design aspects have been explored after which a system redesign is proposed considering the many different aspects that go into such a design. All designs have been handed over to Kaminari Medical

Recently, data breaches have been increasing in many organisations, causing a spotlight to be put on the security practices such as 2 Factor Authentication(2FA) technology and the methods used to protect cyberspace. This has resulted in an opportunity for passwordless authentication technologies. Biloq is an early stage venture which aims to develop hardware and software to provide continuous authentication without the burden of extra login steps that are present in existing technologies such as 2FA. This project aims to identify lead users for Biloq’s new product in the cybersecurity space. To answer this research question, first desk research was done to identify current trends in authentication technologies. This was followed by a stakeholder analysis to identify the people who are involved in ensuring the cybersecurity of their organisation, specifically with respect to the robustness of digital systems and how their staff perform authentication on a daily basis. After this, semi-structured interviews were conducted with the identified stakeholders to spot behavioral and preference patterns and narrow down as precisely as possible the type of persona which would most likely be interested to adopt Biloq’s new products and services. The final outcome of the project is identification of lead users for this new paradigm of authentication.

Every year, nearly five million people undergo knee, making it one of the most common orthopaedic procedures. Sport-related injuries and age-related diseases are the major causes that lead to a knee operation. To recover mobility, stability and muscle strength, the person must go through a post-surgical rehabilitation program.
The price of these physiotherapy sessions increases the already high medical cost of the treatment. Additionally, it is a long and repetitive process that might make them lose motivation and discourage them before finishing the whole program. It is also inaccessible for some people, who live far away from a hospital or rehabilitation centre or in areas where the public healthcare system is saturated. As a result, many people abandon their rehabilitation programs and never recover the pre-injury state.
In this project, we propose the use of a game controlled using Inertial Measurement Units to improve the rehabilitation process. The game would reduce the costs of the rehabilitation, make it accessible for everybody and increase the motivation of the patients.

Graphene is two-dimensional allotrope of carbon with a honeycomb-like lattice structure. It shows exceptional properties in electrical, optical, thermal, mechanical and chemical fields. And due to its excellent properties, it is being researched to be used in many applications such as, sensors, graphene transistors, opto-electronics, etc. To realize these applications in an industrial scale, reliable methods to grow and transfer graphene need to be developed. Methods such as chemical and mechanical exfoliation, chemical vapour deposition (CVD), etc. are a few methods which are used to synthesize graphene. And wet transfer, electrochemical delamination, etc, are a few methods to transfer graphene on to the required substrate. Graphene is sensitive to chemicals and processing steps, hence the properties/behaviour of graphene varies based on the fabrication and transfer technique used. Applied Nano-Layer(ANL) is a company based in Delft, that fabricates and transfers wafer-scale mono-layer graphene. Asmentioned before, the properties/behaviour of graphene changes based on the fabrication and transfer technique used. Therefore, in this thesis, the properties/behaviour of monolayer graphene provided by ANL, is analyzed. In this thesis, electrical properties like channel resistance, resistivity and mobility were analyzed. Also, the optical behaviour of graphene where pauli-blocking stops the absorption of light at dirac point, is analyzed. Few questions related to design of the process flow, working of the fabricated devices, propagation of light in the waveguides, modulation of light and effect of process flow on graphene, were answered to properly analyze the above stated properties/behaviour of graphene. First, a wafer-scale silicon waveguide was designed using COMSOL and BeamLab. The derived width of the waveguide was found to be for the values of 1 um to 4 um and the optimal cladding thickness was found to be 20 nm. Then, the designed waveguide structures were translated onto a mask that would be used in the fabrication of the electro-absorption modulators. Second, a cleanroom compatible process flow for the fabrication of Hall bars and electro-absorption optical modulators was designed and optimized. Several testing steps were performed to find the optimal parameters required in the process flow. Third, the hall bars and the optical modulators were fabricated in the clean room , Else-Kooi Lab(EKL), using the designed masks and process flows. The electrical properties were analyzed by extensively measuring the hall bars. As an example, the average channel resistance, dirac voltage, average resistivity and average mobility of a graphene hall bar with dimensions 2 um x 2 um was measured/calculated to be 6.74 k­, 75.9 V, 1.7 k­ and 1573.28 cm2/Vs respectively. Similarly, the values for 11 other dimensional devices were measured/calculated. The optical behaviour was analyzed by testing the electro-absorption optical modulator. A few waveguides were tested for propagation of light and a power of 0.8 uW wasmeasured for an input power of 0.6mW, which suggests that light successfully propagates though the waveguides. Graphene modulation was tested using back gate biasing and an average dirac voltage of 73.33 V was observed for 2 um x 2 um hall bar device on the optical modulator die. These two when done simultaneously theoretically should modulate light. Lastly, the impact of process flow on graphene/ graphene devices was checked. And a drastric fall to 30% working devices(for optical modulators) from 60% working devices (for hall bars) with increase in process flow steps concludes that the number of processing steps does affect the graphene/ graphene devices.

Patients with a Fontan circulation have a diminished life expectancy of only 30-40 years old. A mechanical circulatory assist device can potentially increase their life expectancy and quality of life. Given the complexity of the anatomy and physiology of the Fontan circulation, design of a safe and effective mechanical assist device is a challenging task. A device based on a viscous impeller pump is very attractive. Such a device is amenable for minimally invasive implantation through a catheter, given the miniaturization of its actuator is possible. The current thesis provides the first steps in designing and developing the small brushless electromagnetic motor intended to drive the viscous impeller pump. First, a list of requirements was defined for such an actuator. The essential requirements are that the actuator is 5.4 mm in diameter and 11 mm in length, has an outrunner configuration, can reach a power output of at least 0.92 Watts and that the within the motor generated temperature does not excessively heat up the surrounding blood or breaks the actuator. After that, the actuator's first concept was defined and validated on the torque output and heat generation. After that, various optimizations of the design were performed, which resulted in a potentially promising actuator concept. Although, the presented actuator concept meets the prescribed dimensions and is an outrunner BDLC motor, the predicted power and torque output of 0.632 Watts and 2446 μNm, respectively, both are above the required values. The actuator needs to be tested to conclude if the actuator can indeed provide sufficient drive resulting in required pumping power of the VIP.

Myocardial ischaemia induced by cardioplegia is the most prominent risk during open-heart surgery. To achieve adequate protection of the cardiomyocytes during surgery, the cardioplegia must arrive at all cardiomyocytes. Local obstruction can lead to regional ischaemia. For surgeons and perfusionist, the arrested heart is a black box. They know how much cardioplegia they are administering to the heart. However, they do not know if cardioplegia is reaching all cells. This work describes which parameters can be measured during cardioplegia induced cardiac arrest and compares the methods used in the literature to detect these parameters. Following this, it is the goal to create a proof-­of-­concept sensor for the detection of myocardial ischaemia. A literature review indicated that a fluorescent optochemical pH sensor has the most potential. To be able to develop a proof-­of-­concept, optical, chemical, and medical knowledge needs to be combined. This is necessary to map what is required and what is possible for optochemical in vivo sensing. First, a framework is designed and used to select the best technique and material suited for this project. In this framework, the medical requirements and the resources available are combined. As a result, this thesis work will use a dual wavelength pH­-sensitive fluorescent dye encapsulated in a biocompatible hydrogel. In preparation for the proof-­of-­conceptsensor, multiple samples are fabricated and extensively tested to achieve the optimal sensing layer. Using the optimised concentrations, a proof-­of-­conceptsensor is created using a miniature reflection probe and an USB spectrometer. This proof-­of-­conceptsensor shows that it can measure the changes in pH and can be corrected for multiple interferences. It also shows the potential to be further miniaturised and to be used during cardiac surgery. Before this can happen, chemical optimisation of the sensing layer is needed, and the consistency of the sensing layer needs to be improved. However, besides this, the work succeeded in selecting an optochemical sensing technique and material which shows the potential to be used in cardiac surgery