Engineered Poly-L-Lysine at Surfaces for Biosensing: Signal Enhancement by Density Control and Layer Architecture

Sensitive and efficient bioanalytical detection is an ongoing challenge. The possibility of physically and chemically manufacturing micro/nano features on solid supports, as well as that of precisely engineering the properties at the interface, has paved the way for a new era of surface-based biosensing devices. DNA recognition platforms have attracted growing interest due to their potential use in drug formulations, environmental monitoring and biomedical applications. The high intrinsic specificity and sensitivity of DNA biosensors can drastically improve the diagnosis and therapy efficacy of genetic diseases,. However, the characteristics of the biorecognition interface (e.g. probe density, layer architecture, surrounding environment, type of substrate) represent crucial factors for the hybridization process and the (ultra)high sensitivity of DNA biosensors. Signal amplification strategies are routinely exploited to assess reliable assays with lower limits of detection, representing opportunities for obtaining more efficient (bio)sensing platforms.
This thesis aims to develop a customizable surface strategy for biosensing applications that can finely tune the chemical environment at the biorecognition interface, by controlling the surface probe density and the physico-chemical characteristics of the substrate. This approach is based on poly-L-lysine (PLL), the functional properties of which are defined by the combination of appended groups anchored to its backbone in a preceding synthetic step, which results in a controlled functional group density at the interface upon self-assembly.
Multiple surface architectures have been developed for biosensing purposes. The strategy based on customizable modified PLL has shown the possibility of precisely tuning the antifouling and probe-binding properties of the biorecognition interface. Different substrates can directly be converted in biosensors, while controlling the type and density of the biomolecules displayed. The adaptability of the modified-PLL approach has allowed the formation of functional layer architectures on topographically structured substrates (i.e. micropillar array, gel-like multilayers, and micro/nanoparticles) to increase the sensitivity of DNA detection, envisioning the ultimate goal of single molecule quantification.