Microfluidic Tools for Advanced Biomolecular Characterisation

Proteins – the key building blocks of life – are responsible for the majority of the processes behind biological function. To understand what role proteins play in health and disease, how they operate and interact, it is vital to have tools for biomolecular detection, quantification and fundamental physicochemical characterisation. In this thesis, I have focused on the development of new microfluidic approaches enabling quantitative analysis of biomolecules. First, I describe a microfluidic spray device, developed for a controlled deposition of analyte on surfaces. Due to the small micron-scale droplet size, the evaporation happens in a few milliseconds, thus, leaving only the solvent-free solutes. This method has been vital for depositing biomolecules on a scanning-probe microscopy-imaging substrate, enabling quantitative measurements of heterogeneous protein mixtures. Afterwards, I present the spray combination with gravimetric sensors, such as micro-cantilevers, for a label-free protein detection. I show that this technique can be used for a protein-solution concentration measurement in a quantitative manner. Currently, one of the main issues of diagnostic platforms is the analysis of heterogeneous mixtures. A number of protein-separation techniques have been developed; however, most of the characterisation requires an offline analysis which can introduce artefacts and reequilibration. In the second part of this dissertation, I bridge the gap between liquid chromatography, microfluidic characterisation and mechanical-sensor detection. Specifically, I demonstrate the serial combination between liquid chromatography and analyte deposition by a microfluidic spray nozzle. By depositing analytes onto a quartz-crystal microbalance, I perform a specific label-free analysis of protein mixtures. Furthermore, I present a fluidic interface, facilitating a combination of separation at fast liquid flow with microfluidic size and electrophoretic-mobility measurements. This method allows for a simultaneous measurement of molecule size and charge and acts as an additional chromatographic detector. I demonstrate that this method works for both label-free and labelled biomolecule characterisation and suggests ways to perform scalable mass-spectrometry analysis on a chip

Microcantilever biosensors

The cross-sensitivity of microcantilever sensors presents a major obstacle in the development of a commercially viable microcantilever biosensor for point of care testing. This thesis concerns electrothermally actuated bi-material microcantilevers with piezoresistive read out, developed for use as a blood coagulometer. Thermal properties of the sensor environment including the heat capacity and thermal conductivity affect the ‘thermal profile’ onto which the higher frequency mechanical signal is superimposed. In addition, polymer microcantilevers are known to have cross-sensitivity to relative humidity due to moisture absorption in the beam. However it is not known whether any of these cross sensitivities have a significant impact on performance of the sensor during pulsed mode operation or following immersion into liquid. When analysing patient blood samples, any change in signal that is not caused by the change in blood viscosity during clotting could lead to a false result and consequently an incorrect dose of anticoagulants may be taken by the patient. In order to address these issues three aspects of the operation of polymer bi-material strip cantilevers has been researched and investigated: relative humidity; viscosity/density, and thermal conductivity of a liquid environment. The relative humidity was not found to affect the resonant frequency of a microcantilever operated in air, or to affect the ability of the cantilever to measure clot times. However, a decrease in deflection with increasing relative humidity of the SmartStrip microcantilever beams is observed at 1.1 ± 0.4 μm per 1% RH, and is constant with temperature over the range 10 – 37 °C, which is an issue that should be considered in quality control. In this study, the SmartStrip was shown to have viscosity sensitivity of 2 cP within the range 0.7 – 15.2 cP, and it was also shown that the influence of inertial effects is negligible in comparison to the viscosity. To investigate cross-sensitivity to the thermal properties of the environment, the first demonstration of a cantilever designed specifically to observe the thermal background is presented. Characterisation experiments showed that the piezoresistive component of the signal was minimised to -0.8% ± 0.2% of the total signal by repositioning the read out tracks onto the neutral axis of the beam. Characterisations of the signal in a range of silicone oils with different thermal conductivities gave a resolution to thermal conductivity of 0.3 Wm-1K-1 and resulted in a suggestion for design improvements in the sensor: the time taken for the thermal background signal to reach a maximum can be increased by increasing the distance between the heater and sensor, thus lessening the impact of the thermal crosstalk within the cantilever beam. A preliminary investigation into thermal properties of clotting blood plasma showed that the sensor can distinguish the change between fresh and clotted plasma

Morpholino oligonucleotides in responsive hydrogels for microRNA sensing

In recent years, microRNA (miRNA) has garnered a high level of interest in the field of biosensor development. MiRNA are a class of small, circulating RNA sequences that are essential for healthy control of protein expression. The variation of levels of specific miRNAs has been linked with over 150 diseases since the turn of the millennium, including cancers, cardiovascular diseases, parasitic infections and neurological disorders. The improved prognosis from early detection is stark, but established methods of miRNA detection suffer from poor sensitivity, low throughput, and require specialised laboratory equipment and trained staff to perform the time-consuming techniques. A simple, cheap and sensitive miRNA point of care sensor would be an invaluable tool in healthcare. This thesis presents the continued optimisation of a miRNA sensing hydrogel with oligonucleotide crosslinks that are selectively cleaved in the presence of the target miRNA sequence. This selective reduction in crosslink density was transduced by a change in the swelling profile of the hydrogel and intelligent crosslink design used to control the swelling response for detecting a miRNA sequence, a short RNA (sRNA) sequence, or a small molecule using an aptamer. Morpholino oligonucleotides (MOs), an uncharged DNA analogue, were functionalised with an acrylamide moiety and used as responsive crosslinks for miRNA sequence detection in a world’s first MO crosslinked hydrogel. The MO crosslinks offered significant improvements over DNA crosslinked hydrogels through improved thermal stability, no salt requirement and 1000-fold improved sensitivity, facilitating a wider range of sensing conditions. Analysis was also achieved using a mobile phone camera and laptop, demonstrating portability. Carbon nanoparticles (CNP) were suspended in the hydrogels to act as a conductive component. As the hydrogel swells the distance between the particles is increased until there is no conductive pathway, resulting in an increase in the hydrogel’s resistance. Numerous reproducibility challenges were identified with regards to gel delamination and CNP leaching partly due to inefficient UV photoinitiation of the pigment composite pre-gel solution. SEM imaging identified inconsistent composite homogeneity with areas of higher CNP and gel density in DNA crosslinked composites, while MO crosslinked composites were homogenous and less conductive. Inkjet printing of the composite material using an electrostatic dispersion as the conductive component was made possible using MO crosslinks with no salt and ammonium persulfate with TEMED in place of UV initiation. Optimised synthesis resulted in homogenous conductive composites far more robust and reproducible than the UV initiated CNP composite. However, MO solution viscosity resulted in improper aspiration and inaccurate deposition. Potential solutions and improvements are suggested, facilitated by the improvements offered by MO crosslinks

Microscopy Conference 2017 (MC 2017) - Proceedings

Das Dokument enthält die Kurzfassungen der Beiträge aller Teilnehmer an der Mikroskopiekonferenz "MC 2017", die vom 21. bis 25.08.2017, in Lausanne stattfand

Microscopy Conference 2017 (MC 2017) - Proceedings

Das Dokument enthält die Kurzfassungen der Beiträge aller Teilnehmer an der Mikroskopiekonferenz "MC 2017", die vom 21. bis 25.08.2017, in Lausanne stattfand