Electrochemiluminescence: insights into the mechanisms and nanomaterial-based applications

Biomarkers are biological indicators of human health conditions. Their ultra-sensitive quantification is of paramount importance in clinical monitoring and early disease diagnosis. Biosensors are simple and easy-to-use analytical devices and, in their world, electrochemiluminescence (ECL) is one of the most promising analytical techniques that needs an ever-increasing sensitivity for improving its clinical effectiveness. Scope of this project was the investigation of the ECL generation mechanisms for enhancing the ECL intensity also through the identification of suitable nanostructures. The combination of nanotechnologies, microscopy and ECL has proved to be a very successful strategy to improve the analytical efficiency of ECL in one of its most promising bioanalytical approaches, the bead-based immunoassay. Nanosystems, such as [Ru(bpy)3]2+-dye-doped nanoparticles (DDSNPs) and Bodipy Carbon Nanodots, have been used to improve the sensitivity of ECL techniques thanks to their advantageous and tuneable properties, reaching a signal increase of 750% in DDSNPs-bead-based immunoassay system. In this thesis, an investigation of size and distance effects on the ECL mechanisms was carried out through the innovative combination of ECL microscopy and electrochemical mapping of radicals. It allowed the discovery of an unexpected and highly efficient mechanistic path for ECL generation at small distances from the electrode surface. It was exploited and enhanced through the addition of a branched amine DPIBA to the usual coreactant TPrA solution for enhancing the ECL efficiency until a maximum of 128%. Finally, a beads-based immunoassay and an immunosensor specific for cardiac Troponin I were built exploiting previous results and carbon nanotubes features. They created a conductive layer around beads enhancing the signal by 70% and activating an ECL mechanism unobserved before in such systems. In conclusion, the combination of ECL microscopy and nanotechnology and the deep understanding of the mechanisms responsible for the ECL emission led to a great enhancement in the signal.

Quantum integrability as a new method for exact results on N=2 supersymmetric gauge theories and black holes

In this thesis I show a triple new connection we found between quantum integrability, N=2 supersymmetric gauge theories and black holes perturbation theory. I use the approach of the ODE/IM correspondence between Ordinary Differential Equations (ODE) and Integrable Models (IM), first to connect basic integrability functions - the Baxter’s Q, T and Y functions - to the gauge theory periods. This fundamental identification allows several new results for both theories, for example: an exact non linear integral equation (Thermodynamic Bethe Ansatz, TBA) for the gauge periods; an interpretation of the integrability functional relations as new exact R-symmetry relations for the periods; new formulas for the local integrals of motion in terms of gauge periods. This I develop in all details at least for the SU(2) gauge theory with Nf=0,1,2 matter flavours. Still through to the ODE/IM correspondence, I connect the mathematically precise definition of quasinormal modes of black holes (having an important role in gravitational waves’ obervations) with quantization conditions on the Q, Y functions. In this way I also give a mathematical explanation of the recently found connection between quasinormal modes and N=2 supersymmetric gauge theories. Moreover, it follows a new simple and effective method to numerically compute the quasinormal modes - the TBA - which I compare with other standard methods. The spacetimes for which I show these in all details are in the simplest Nf=0 case the D3 brane in the Nf=1,2 case a generalization of extremal Reissner-Nordström (charged) black holes. Then I begin treating also the Nf=3,4 theories and argue on how our integrability-gauge-gravity correspondence can generalize to other types of black holes in either asymptotically flat (Nf=3) or Anti-de-Sitter (Nf=4) spacetime. Finally I begin to show the extension to a 4-fold correspondence with also Conformal Field Theory (CFT), through the renowned AdS/CFT correspondence.

Drive up electrochemical and electrochemiluminescence signal through biosensing mechanism optimization

Biomarkers are biological indicators of human health conditions. Their ultra-sensitive quantification is of cardinal importance in clinical monitoring and early disease diagnosis. Biosensors are some worldwide simple and easy-to-use analytical devices as a matter of fact, biosensors using electrochemiluminescence (ECL) are one of the most promising biosensors that needs an ever-increasing sensitivity for improving its clinical effectiveness. The principal aspiration of this project is the investigation of the ECL generation mechanisms for enhancing the ECL intensity and the development of an ultrasensitive sensor, the use of metal-oxide materials (Mox) and the substitution of metal-free dyes. Novel dyes such as BODIPY, TADF are used to improve the sensitivity of ECL techniques thanks to their advantageous and tunable properties, enhancing the signal and also the ECL efficiency. Additionally, the use of Mox could be beneficial for the investigation of two different ECL mechanisms, which occur simultaneously. In this thesis, the investigation of size and distance effects on electrochemical (EC) mechanisms was carried out through the innovative combination of a standard detection system using different size of micromagnetic beads (MBs). That allowed the discovery of an unexpected and highly efficient mechanistic path for electrochemical generation at small distances from the electrode’s surface. The smallest MBs (0.1μm) demostrate an enhancement of electrochemical signal than the bigger one (2.8μm) until 4 times of magnitude. Finally, a novel ultrasensitive sensor, based on the coreactant-luminophores mechanism, was developed for the determination of whole viral genome specific for cardiac HBV and COVID-19 virus. In conclusion, the ECL and the use of EC techniques (such as amperometry), improved the understanding of mechanisms responsible for the ECL/EC signal led to a great enhancement in the signal.