The growing demand for scalable biomedical solutions calls for precise, programmable, and cost-effective manipulation techniques at the microscale. While mechanical and magnetic methods have been explored, they often face limitations in flexibility, biocompatibility, or scalability. Optical tweezers offer high precision, but suffer from thermal side effects and complex, expensive setups. Optoelectronic tweezers (OET), by contrast, utilize patterned light to induce dielectrophoretic forces, enabling flexible, energy-efficient, and scalable control of microscopic particles using relatively simple hardware.

To support advanced biomedical research at Delft University of Technology, a fully functional OET platform was developed from the ground up. It integrates a custom transparent photoconductive microfluidic chip with a DMD-based optical system for real-time, reconfigurable actuation. Custom-fabricated PDMS microgear robots were successfully manipulated under varying electrical and optical conditions. Using precise motion tracking and calibration, the generated dielectrophoretic forces were quantified, with peak values approaching 500 pN, and benchmarked against theoretical models and literature estimates.

This research demonstrates that complex-shaped microbots can be effectively actuated within a custom-built OET system, paving the way for future applications in automated diagnostics, single-cell manipulation, and intelligent lab-on-a-chip platforms. By combining hardware innovation with theoretical insight, this work lays a robust foundation for microscale robotics in next-generation biomedical technologies.

Large scale, highly sensitive and specific diagnostic tools are needed to eliminate the transmission of schistosomiasis. This report expands upon the novel approach from M. Hoeboer and P.M. Nijman. Their Smart Optical Diagnostic Of Schistosomiasis device (SODOS), combining the principles of flow cytometry and digital holography, was able to detect schistosomiasis haematobium eggs in a 10 ml urine sample. However the mechanical complexity made it difficult to control the flow and more than 650 frames needed to be processed for each sample. The reason for this was the small flow cell volume examined within each frame. This report shows it is possible to increase the volume while maintaining the required resolution for accurate diagnosis. The size of the volume is limited by the sensor’s pixel pitch, the sensor area, the shutter time of the sensor, the thickness of the volume, the density of particles and to a lesser extent the distance of the volume to the sensor and the wavelength of the source. The density of particles in combination with the thickness of the volume proved to be
the main limiting factors. With to many particles the scattered light causes a cloudy, speckle pattern on the sensor, which does not give the desired resolution upon reconstruction. By using a 24MP APS­C CMOS colour sensor, present in the Canon EOS M50 camera, in combination with a larger volume it was possible to reconstruct eggs throughout 1.5 ml of urine using a single frame, decreasing the total required number of frames to 7. The volume thickness was 5 mm. Increasing the thickness to analyse the required 10 ml of urine in a single frame was not feasible due to scattering. However when
immersing the eggs in a Phosphate­buffered saline solution a 14 ml volume, with a thickness of 43 mm, could be analysed successfully, showing the possibilities of implementing the technique in other fields as well. The Fraunhofer particle field holography theory proved to be a valid model when making predictions regarding the resolution throughout the volume as well as providing information on the axial position of the particles.

The quality of rigid endoscopes deteriorates during clinical use due to the sterilization process, mechanical forces and wear and tear during regular use. Regulations and standards on ensuring the quality of these instruments are currently non-existent or contain only qualitative measures, resulting in subjective examinations . Defective rigid endoscopes still reach the operating room, resulting in direct and indirect patient risks. An experimental test set-up has been developed to quantify the sharpness, contrast, distortion, light transmission, vignetting and colour correctness of the optical system
of rigid endoscopes. Results are given for 85 measurements performed on 33 endoscopes, including 7 high quality endoscopes and 26 low quality endoscopes. 37 measurements have been performed on a reference rigid endoscope. The results for sharpness, contrast and distortion provide valuable insights but the current design of the test set-up proved not stable enough to draw significant conclusions. The results for light transmission, vignetting and colour correctness produce stable results and display the expected values for damaged lens systems such as loose or broken lenses. Although the current design requires significant optimization, this study has both given an account of the need for an objective method to evaluate the quality of rigid endoscopes as well as provided a promising step towards this new method and greatly encourages further research.

This work determines whether the amount of frequency components present in the data can be reduced, whilst still retaining image quality, whereas most efforts in seismological research are done in reducing spatial sampling. It is shown using a PCA on the frequency spectra of several data sets that indeed a large redundancy in frequency content is present in onshore seismic data, and an attempt is made to generate a distribution of frequencies in order of importance. Given this redundancy in the frequency spectrum of onshore seismic data, it has been attempted to reconstruct the missing frequencies by applying the Fourier transformation iteratively to the data. However, this transform does not take spatial sampling into account, which is aimed at to compensate for the missing frequencies. Therefore it has been elected to use a linear Radon transformation instead, which keeps components which are connected in space-time connected in the transform domain. A CGNE scheme has been set up to reconstruct the data, which performs very well along the almost linear asymptots in the shot records, up to a reduction of 70% of frequency components. This scheme iteratively applies the linear Radon transform to a shot record, weighing the data in the transform domain with an amplitude based norm. The energy that was spread out due to aliasing because of the missing frequencies is refocused to the main reflectors, especially along the asymptots of the reflection hyperbola. Missing frequencies are reconstructed, up to a scaling factor, and band gaps of up to 6Hz get filled in very well. Next, it is attempted in this work to give quantitative quality metrics, to make comparison between seismic images easier and based on data, rather than subjective visual inspection. Treating migration as a black box, several quality metrics have been devised for the migrated sections: correlation to the ground truth, contrast within an image, average length of found lines, and local SNR. Contrast is not a very good metric to compare between images as its average across an image is almost constant with reduction percentage. The other parameters are good metrics and show a clear trend that the fewer frequency components present in the shot records, the worse the quality of the final image. An increase in deterioration of image quality is observed around 70% reduction, which is in correspondence with the earlier found value for the shot records.

A limiting factor with regard to resolution in OPT is the limited depth of field (DoF) due to light detection with a Gaussian beam profile. The further a source in the sample is removed from the centre of rotation in the focal plane, the more distorted the image is in tangential direction due to the limited DoF. The goal of this research is to extend the depth of field in Optical Projection Tomography. The DoF limitations due to diffraction are mainly caused by the Gaussian beam shape and its inherent limitations such as a small high intensity spot and a small region of focus. An alternative to Gaussian beams is found sporadically in the literature in the form of non-diffracting beams. Non-diffracting beams are beams that propagate without diffraction and show regenerative properties after obstruction. The Bessel beam is a non-diffracting beam that is rotationally symmetric and displays a transversal high-intensity core. It can be generated without energy loss with a lens shaped like a rotationally symmetric prism, called an axicon.
A propagation simulation of the axicon generated Bessel beam, using the Hankel transform as a rotationally symmetric alternative to the 2D Fourier transform, is performed and used to verify the analytic description of the axicon generated Bessel beam. A numerical OPT simulation shows that OPT reconstructions of point sources show virtually no blurring, but do show concentric rings due to the intensity distribution of the Bessel beam. These rings can be removed by deconvolution of the projection or deconvolution of the reconstruction of simulated OPT results with the imaging point spread function (PSF) of the axicon-generated Bessel beam. The PSF describes the response of the imaging system to a point source.
Practical work is presented with the imaging set-up of an axicon with an objective lens as described earlier. The resolution of the PSF is analysed over paraxial distance from the objective lens for both coherent and incoherent illumination. The same is done for a resolution target in transmission. Comparison of the Bessel system with Gaussian models show that the DoF increase shown by the Bessel system is significant in all cases. It is found that for sources with spatially narrow intensity distributions (near-point source) the PSF resolution matches theoretical predictions. However, as the spatial light source distribution increases slightly, Bessel distributions overlap spatially. This creates artefacts and deteriorates the resolution
It is concluded that extended depth of field in OPT can be achieved with non-diffracting axicon generated Bessel beams. However, for objects larger than point sources the resolution deteriorates. Furthermore, the means of illumination are a major influence on the resulting images when using an axicon.
Further research on the optimization of illumination is recommended. Additionally, recommendations for further research on the significance of self-regeneration are made. Recommended applications for use of Bessel beams in optical imaging are those where a large DoF is desired and high resolution is less of a priority, or imaging and OPT of very sparse but large samples.

The goal of the research is to find out whether it is possible to measure a wavefront qualitatively and quantitatively with Janssen’s recently developed analytical algorithm. The spot displacements given by the wavefront sensor are used to relate the derivatives of the wavefront with respect to x and y with the Zernike coefficients of the wavefront itself. The results are compared with some conventional and commercially used methods: an iterative integration method of the SHS, which have been implemented in a Matlab script. Moreover, some of them are compared with the reconstructed wavefront obtained through interferometry. Janssen's method turns out to be a reliable and fast (regarding computation time) wavefront reconstruction method to qualify which aberrations are present.