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.