Development of Nanofibers for Applications in the Field of Point-of-Care and Environmental Studies

This thesis focuses on the development and use of nanofibers (NFs), highlighting their benefits such as simple production by electrospinning, their large surface to volume ratio and the possibility of chemical modifications. These properties make NFs suitable for various applications, including biosensors, medical devices, and environmental uses. Point-of-care (POC) testing is an important tool in resource-limited settings aiming to meet the requirements of the WHO for being inexpensive, portable but still sensitive and reliable. Compared to common tests, nucleic acid testing (NAT) can enhance sensitivity and specificity significantly but involves multiple steps like nucleic acid (NA) extraction, amplification, and detection, necessitating new POC solutions. Therefore, different materials like particles and membranes developed for NA extraction and their integration in sample to answer (S2A) devices were reviewed. While emerging materials offer interesting solutions for example the protection of RNA or mild elution conditions, integration in S2A devices and automation especially in resource limited settings is a remaining challenge. Future work needs to address the integration of sample lysis, especially for complex matrices like whole blood, reduction of user-input and storage of on paper-based devices. With isothermal amplification methods and portable, battery-powered devices, NAT testing is expected to become a standard technique in the field of POC. In this thesis zwitterionic NFs were developed to allow the extraction of NA under mild conditions. Based on an initial material study, hydrophilic nylon NFs were electrospun and doped with one cationic and one anionic polymer. An in-depth material study revealed an influence of the chemical composition and the morphology of the NFs, which need to be controlled during production. After optimization, NAs could be successfully adsorbed at a pH of 4.5 in the presence of 0.1 % Tween20 by electrostatic interactions. Elution was then triggered by a change to pH 10 and the addition of 50 mM sodium chloride, as NAs are electrostatically repulsed from the anionic NFs. The addition of high salt concentrations or charged detergents typically needed for the elution used from cationic materials was avoided. Further research focused on the isolation form NA from biological samples like serum. A dilution of 1:150 allowed successful extraction, but further improvements are needed to enhance efficiency. Increasing the number of cationic binding sites by adjusting the doping ratio or adsorption pH showed potential for optimization. To achieve a sample-to-answer (S2A) device, NFs were integrated into a paper-based analytical device (µPAD). Within this flow through set-up a good extraction efficiency could be maintained. Finally, recombinase polymerase amplification (RPA) was tested on filter paper as an isothermal amplification method. Future studies should combine the extraction of NAs from serum samples within the µPAD design and the amplification via RPA within one-test design to achieve a S2A device. Microplastics (MPs) are present in the environment and human body, but their effects on organisms are still unknown. Current research focuses on investigating MP at the cellular level and within whole organisms and organs. However, commonly used commercial spherical particles do not represent the irregular fragments and fibrous particles found in the environment. This study aimed to produce true-to-life MP using NFs as a precursor. They have a great potential as a one-dimensional nanomaterial and the ease of introducing several types of dopants. The shape of the particles can be adjusted depending on the production techniques. With ball milling irregular particles around 4 µm were obtained, while fibrous particles shredded with an Ultraturrax resulted in a length of 20 µm and must be further optimized. As optical labels are often required in histological studies, DPA and UCNPs were successfully embedded in the NFs during electrospinning. A homogenous distribution and low leaching rates ensured the suitability of those optical labels. DPA labeled MP was then investigated with the ex vivo mouse isolated perfused kidney model, revealing a selective detection of the MPs within the tissue. As particles got stuck in smaller renal vessels and glomerular capillaries, future studies must focus on the impact of the shape of the MP. Based on those results, these systems can be further applied in biological assays, including cell, animal, or tissue studies and expanded towards different types of polymers as well.