Heart failure remains a leading cause of morbidity and mortality worldwide, highlighting the need for reliable tools to assess cardiac function. Myocardial oxygenation is one of the most direct indicators of tissue health, yet current methods lack compact, implantable solutions for continuous monitoring. This work presents an implantable optical sensor that exploits the ultraviolet-excited fluorescence of NADH as a marker of oxygenation. To overcome the limited penetration of ultraviolet light, near-infrared photons are externally delivered and converted into ultraviolet emission by lanthanide-based upconverting nanoparticles(UCNPs), enabling localized excitation without implanted power sources. A Fabry–Perot filter was incorporated to suppress blue emission that overlaps with NADH fluorescence while maintaining high ultraviolet transmittance. The filter design was optimized through multilayer simulations, and deposition conditions were tuned to improve film quality. Upconverting nanoparticles were drop-cast onto the filter surface, and material characterization confirmed the presence of significant nanoparticle coverage. An optical testing platform was further established using both a xenon-based source and a laser diode, which enabled validation of up-conversion performance and filter function. Collectively, these results demonstrate the feasibility of a compact, externally powered light emitter for implantable cardiac oxygen monitoring and establish a foundation for future development of minimally invasive biosensors.

A common method of diabetes treatment is monitoring of blood glucose using a continuous glucose monitor(CGM). These monitors come in different forms, but are often uncomfortable because they penetrate the skin with needles. For this project, an alternative, smaller sensor is explored for which the design process is centred. This sensor is inserted into the dermis layer of the skin, measuring interstitial fluid glucose and should be less invasive and more comfortable to the user.
The project is divided into two parts, one discussing the sensor reading circuit, and the other the digital processing of sensor information. This report is on the digital processing, and will convert sensor data into blood glucose concentration estimates. To achieve this, various mathematical models and filter techniques are implemented and evaluated. The subsequent system is subdivided into modules, each performing a task in the total process line. The report gives a general introduction to the broad topic and eventually outlines the structure and motivation behind these models.
In the end a Kalman filter and biophysical blood-interstitial fluid dynamics model are shown to improve performance over a linear model in an in silico test environment.
This work represents a step towards a working glucose sensor which can be used in CGM solutions, with the potential application in both clinical and at-home diabetes management.

The global prevalence of diabetes mellitus is rising rapidly, increasing the demand for reliable and accessible care. Current glucose monitoring solutions are often expensive, invasive, and uncomfortable, limiting their accessibility, especially in middle and low-income countries. This thesis presents the design of a compact, low-power, and continuous glucose monitoring (CGM) system with Bluetooth and separate electronics and sensor. The design integrates a potentiostat with a custom analogue pre-processing circuit, implemented on a printed circuit board (PCB).

The system supports Bluetooth Low Energy (BLE) communication for low-power wireless data transmission and is powered by a dual-coin-cell battery system designed for two weeks of operation. Furthermore, emphasis is placed on noise minimization and analogue-domain preprocessing to reduce power consumption, reduce measurement latency, and improve measurement accuracy. This was done with a trans-impedance amplifier, a non-inverting amplifier, and an integrator for signal conditioning.
A classical potentiostat architecture was selected over more complex ASIC-based approaches for feasibility within the scope of the thesis.

Prototypes were tested using gold electrodes and phosphate-buffered saline with known analyte concentrations. Even though there were limitations barring full-system validation, the design demonstrates at least partial functioning and serves as a foundation for future refinement and integration. This work intends to contribute to the development of accessible CGM devices that balance clinical accuracy with real-world usability.

Early-stage post-surgical infection monitoring is crucial for preserving patients' health and reducing public healthcare costs. Among various parameters and symptoms, local pH shifts can provide valuable insight into the development of infections. An implantable pH sensor can be employed to monitor localised pH changes. The Ion-Sensitive Field-Effect Transistor (ISFET) is a precise pH sensing device that is compact in size and can be integrated with standard CMOS technology. Due to its small size, the ISFET is promising as an implantable sensor for in vivo pH sensing. To avoid a second surgery for sensor removal after its functional lifespan, biodegradable sensors offer an alternative, as they can degrade and be absorbed by the human body after completing their function.

The aim of this project was to design and fabricate the first fully biodegradable ISFET pH sensor, addressing the challenges of accurate real-time monitoring for post-surgical infection, specifically in hip implantation surgery. This project successfully led to the design and fabrication of an 8-mask ISFET/MOSFET device using fully biodegradable materials and incorporating two rounds of ion implantation. Chip thinning via TMAH wet etching was also explored. Several alternatives were studied to overcome challenges with Molybdenum and Mo-Si contact in having suitable interconnections and Ohmic contact between Molybdenum and Silicon.

Wearable and implantable biosensors are emerging as promising devices for the continuous monitoring of individuals in the context of sports and health. The successful development and deployment of these devices could yield tremendous health benefits to the general population. Biosensors have to perform in complex biological environments that contain a wide variety of biomolecules that can interact with the biosensor in an undesirable way, affecting the biosensor performance and lifetime. Among these interactions, the blockage of bioreceptors by biomolecules (biofouling) and the non-specific adsorption of biomolecules to the sensor are two major processes that limit the successful deployment of biosensors.
This thesis presents a novel cytomorphic double network hydrogel (CDNH) structure to address biofouling and the non-specific adsorption of biomolecules. The CDNH mimics the functioning of a cell, the best biosensor ever created in nature. Cells have a membrane that separates the interior and outer world. The cell membrane selectively allows specific molecules to pass to the interior, where the biorecognition and metabolic processes happen. The CDHN comprises a structural hydrogel hemisphere to mimic the inner cell cytoskeleton and an outer network to mimic the cell membrane. The inner network is a poly (ethylene glycol) diacrylate (PEGDA) hydrogel with a large pore size. With the open structure of the inner network, the aim is to improve the diffusion of the target molecules to the bioreceptors (aptamers). Furthermore, the aim is to reduce steric hindrance for the binding of the target molecules to the bioreceptors. The outer network is a polyacrylamide hydrogel with a very dense mesh (nanopores). The outer network aims to function as a size exclusion filter, selectively allowing only small biomarkers to access the sensing site. By separating the dense outer network from the open structured inner network, the CDNH aims to reduce biofouling and ANSM while still ensuring adequate diffusion of the target biomarkers to the receptors and binding of the target biomarkers to the receptors.
Integration of the CDNH with a relatively simple 2-electrode sensor was achieved which enabled the electrical characterization (EIS) of the CDNH, providing crucial insights into the electrical behaviour of the CDNH in an electrochemical solution.
Overall, this work presents the foundation for a novel structure that is expected to improve biosensing drastically, contributing to the realization of continuous sports and health monitoring.

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.

Thermoelectric generators (TEGs) are critical in environments where alternative energy harvesting methods are necessary, such as space exploration. This thesis investigates using a two-dimensional hole gas (2DHG) as a p-type material within a Gallium Nitride (GaN) based TEG. This study focuses on determining the thermoelectric performance of the 2DHG by measuring the Seebeck coefficient, electrical conductivity, and power factor for extremely cold environments.

This work introduces a novel simulation method used to evaluate different structures to find the optimal hole densities for maximizing the power factor (PF) of the 2DHG. A structure was realized, and its thermoelectric properties were experimentally assessed. Key results, including a Seebeck coefficient of 100 − 200 μV /∆K, a sheet resistance of 70 − 120 kΩ , and a resulting Power Factor (PF) of 60 − 100 μW m−1K−2, are measured over an extremely low-temperature range of 50 - 300 Kelvin and discussed for future applications.

These results demonstrate that GaN-based TEGs can significantly broaden the temperature range and improve the performance of TEGs in extreme conditions. These findings pave the way for more efficient thermoelectric systems, with potential applications in aerospace, deep-space missions, and other challenging environments.

Purpose
The main purpose of this report is to find out whether the OpenBCI "Ultracortex Mark IV" Electroencephalogram (EEG) headset is capable of differentiating EEG-signals of motor execution from neutral state with recorded data and to find out whether it can differ motor executions between left and right hand. Next to that, it is to be determined whether the OpenBCI headset was the optimal one for this purpose.

Method
First, the specifications of different headsets were compared. Afterwards, a montage of the electrodes was designed to detect motor execution and motor imagery, mainly centered around the locations C3, Cz and C4, on the top of the scalp. The software "Openvibe" was used to extract data from the headset during experiments and to record it in a csv file. A subject was asked to follow a video with a sound cue followed by a visual cue instructing to move either its left hand or right hand.


Result
Merging the left and right hand trial data together, the result is that the headset shows in the alpha band (7-12 Hz) mostly a decrease (ERD) in magnitude around the visual cue, sometimes followed by a bigger increase in magnitude (ERS). Looking at the extremes after the cue, it is seen that mostly the difference in magnitude is around a factor 1.5 compared to the average magnitude of before the visual cue. Splitting the trial data between left and right hand, similar results can be seen, but one hand produces slightly more ERD or ERS than the other hand depending on the position of the electrode on the left or right hemisphere of the brain.

Conclusion
The OpenBCI headset can in fact detect a difference between movement of the hands and the neutral state. Differentiating between the movements of left and right hands seems possible from the results, but the difference in the signal of left and right hand is minimal. It is recommended to repeat the experiment with more trials and different subjects to get a more solid conclusion.