Innovative nanomaterials as building blocks of (Bio)sensors

In the last couple of years, the science of nanomaterials and nanotechnology has seen a significant development towards nanoscale biosensing with very low limits of detection, high versatility and the ability to detect different biophysical signals that can be associated with the presence of health or pollution markers. This capability of detecting molecules that can be associated with the presence of a disease or level of contamination represents an essential tool that impacts the general population's well-being by increasing life quality and expectancy. Even though science has improved so much over the last decades in this direction, the general analysis methods are still using expensive lab equipment, long-lasting procedures and a high number of operations that can be performed only by specialized people. Devices that can be used in situ by untrained people, that have a lower cost of production and short analysis time while preserving good analytical performances are highly preferred. However, their development is much more complex, and some challenges like the lack of selectivity, reproducibility and sensibility must be overcome. The development of electrochemical sensors is a good alternative to the traditional methods. The modification of electrodes with different nanomaterials has been extensively studied as they can generate platforms with many applications and reduce the disadvantages of unmodified electrochemical cells. Nanomaterials like metallic particles, polymers or carbon nanotubes can be used to increase the electrochemical area of the electrode and, therefore, offer higher electric signals that enable the detection of lower levels of target analytes. At the same time, an optimised deposition procedure will increase the signal to noise ratio and decrease the variations in the signal acquisition, leading to better reproducibility of the sensor. The lack of selectivity can be overcome by the immobilisation of biomolecules (peptides, enzymes, proteins, antibodies, aptamers) that can selectively recognise and bind the target analyte. These molecules are called bioreceptors, and the electrochemical sensor is called a biosensor. Besides selecting the best bioreceptor to bind the analyte, its immobilisation at the electrode surface is an important step that one must achieve. For this, nanomaterials with specific reactive groups (-COOH, -NH2) or a very reactive surface (gold, platinum) that can form bonds with the bioreceptor can be used as immobilisation platforms. The main objective of this thesis research was to develop various electrochemical platforms suitable for electroanalytical applications using different designs and strategies. For this, several nanomaterials were used as building blocks to increase the analytical performances, like conductive polymers, noble MNPs, or metallic wires. Their syntheses represent one of the most important parts of the research. Different shapes and sizes of MNPs and polymers were synthesised and optimised in order to offer the best analytical performances possible and characterised by electrochemical and different surface characterisation tools. The applicability of the developed platforms was proven in bioanalytical sensing. Target analytes with important roles in the medical and environmental fields were chosen to be detected from complex matrixes, simulating the in-situ conditions. To establish a good selectivity, bioreceptors like aptamers were immobilised on the nanostructured platforms prior to the interaction with some of the targets (tetracycline, lysozyme, ara H1 allergen). In contrast, for the targets such as glucose, folic acid, and arsenic, optimal electrochemical testing conditions were chosen in order to increase the platform selectivity toward the analytes.