Nanomaterials and micromotorsnovel tools for the design and development of (bio)-detection and chemical processes

Abstract

Over the last decade nanotechnology has been developed substantially allowing the discovery, synthesis and applications of new materials at the micro and nanoscale which has opened new opportunities for the development of creative research in both chemistry and analytical chemistry. In this Doctoral Thesis, different nanomaterials, such as gold nanoparticles (AuNPs) and single-walled carbon nanotubes (SWCNTs) as well as micromotors, have been employed as new tools for the development of (bio)-detection and chemical processes taking into account their unique properties and characteristics. Firstly, AuNPs exhibit a strong localized surface plasmon resonance (LSPR) which makes them an ideal tool for their use in fast and inexpensive colorimetric methods. Secondly, SWCNTs specifically enhance the electrochemical sensing because they permit to increase voltammetric currents and heterogeneous electron-transfer rates, the surface fouling of nanomaterial-based electrodes is insignificant and there is an apparent electrocatalysis towards the oxidation/reduction of a wide variety of compounds. Thus, this specific nanomaterial features allow to expect an improved analytical performance in terms of sensitivity, reproducibility and even selectivity. Thirdly, micro and nanomotors are devices in the micro and nano scales capable of converting energy into movement and forces. The energy source is closely related to the microstructure shape, actually both shape and propulsion systems are connected. A remarkable feature of these micromotors is their autonomous movement which can improve different steps of the analytical process, such as sample enrichment or (multiplexed)-detection. Another important characteristic of these micromotors is their tunable surface through different functionalization which can be used in many applications involving different kind of biomolecules, such as, enzymes or antibodies. Thus, the overall nanomaterial and micromotors features allow to expect an improved performance in the developments of (bio)-detection and chemical processes. On the other hand, microfluidic systems and lab-on-a-chip (LOC) technologies offer excellent opportunities to improve the analytical performance by reducing of the analysis time, decreasing extremely the consumption of sample and reagents with negligible waste generation, integrating multiplexing analysis, and especially portability to provide the possibility of development of point-of-care testing approach. In addition, in microfluidic-LOC systems, electrochemistry is a valuable detection mode that provides high sensitivity, allows miniaturization, and it is highly compatible with micro and nanotechnologies. Nevertheless, because of the extremely low sample volumes introduced into microfluidic-LOC systems, their sensitivity is often low and presents a drawback; however the sensitivity can be enhanced and the problem overcome by exploiting the surface characteristics of nanomaterials. As consequence, the microfluidic-LOC systems coupling to nanomaterials used as detectors become very pertinent. Also, the employment of micromotors in confined microfluidic-LOC systems offers extraordinary promises such as the development of future free-fluidic pumping LOCs and avoids their derived instrumentation (i.e. pumps or high voltage suppliers) supporting the new (bio)-sensing in the micromotor autonomous guided movement. Therefore, the creative use of nanomaterials and their related assembling structures as well as micromotors as innovative tools for sensing, biosensing and improvement of efficiency and performance of chemical and analytical processes have constituted the main motivation of this Doctoral Thesis. Accordingly, this Doctoral Thesis has two well-defined objectives: The first objective has been the synthesis and characterization of well-established nanomateriales in both 0-D (AuNPs) and 1-D (SWCNTs) for two well-separated and defined analytical applications. In the first one, AuNPs have been extensively studied as novel tools for the assessment of antioxidant activity in food samples. In order to exploit the expected advantages of the SWCNTs, in the second one, these carbon nanomaterials were exhaustively characterized and studied taking into account the influence of their purity as well as their behavior as exclusive transducers for electrochemical sensing in microfluidics-LOC systems. The second objective has been the design, synthesis, characterization and development of motors and micromotors for enhancing chemical and sensing processes: in the environmental field, to improve the efficiency in the removal of contaminants from polluted waters and treating industrial wastes and in the biosensing field, to develop a simple and rapid biodetection of protein toxins by using a multiplexed immunoassay.