Controlled Synthesis and Biosensing, Bioimaging and Therapeutic Applications of Plasmonic Nano-Bio Hybrid Probes

Abstract

Nanomaterials-based diagnostic and therapeutic platforms have offered significant advantages over conventional systems with regard to high sensitivity, selectivity and low cost. Among various nanomaterials, gold nanoparticles (AuNPs) possess a plethora of unique features such as size- and shape-dependent optical and electronic properties, a high surface area to volume ratio, and versatile surface-chemistry readily modifiable with ligands (including biomolecules) containing a variety of functional groups

and therefore such plasmonic nanostructures have established a centerstage amongst diverse scientific communities involving chemists, physicists, biologists and material scientists. Intelligent design and synthesis of plasmonic nanostructures and their hybrids is crucial to tune their localized surface plasmon resonance (LSPR)-based properties such as optical signaling, surface-enhanced-Raman scattering (SERS), photocatalysis and photothermal transduction, useful in biomedical applications. In spite of the proliferative growth of nanoscience in last two decades, potential real-life applications of biosensing/bioimaging/therapeutic plasmonic nanoprobes in biological systems suffer several design challenges to address the important issues such as biocompatibility (no toxicity), efficient nano-bio interfacing, sensitive signaling response and benign but effective therapeutic action. In the present thesis, we have designed and synthesized new plasmonic nanostructures/nanoassemblies which show tunable optical, SERS, enzymetic, photothermal and photocatalytic properties. We successfully demonstrated that our new nano-bio hybrid probes have potential to distinguish normal and cancer cells based on their sensitive, selective and quantitative monitoring/imaging of cellular oxidative and nitrosative stress in living cells (by optical and SERS based signaling), biodetection of glucose with clinical urinalysis trial (colorimetric/UV-Vis signaling), and organic photosensitizer-free bimodal photothermal and photodynamic therapeutic effect for cancer cells destruction. Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are chemically reactive intermediates naturally produced in the living systems as the consequence of complex endogenous and exogenous biochemical reactions. Overproduction of ROS/RNS, so-called the state of oxidative-stress is a hallmark for the pathogenesis of many diseases such as cardiovascular diseases, cancer, and neurodegenerative diseases. In chapter 1, we developed a straightforward, sensitive, and quantitative assay for the colorimetric and spectroscopic detection of various ROS and RNS such as H2O2, •OH, –OCl, NO, and O2– using glutathione-modified gold nanoparticles (GSH-AuNPs). A basic principle here is that the GSHs on the AuNP surface can be readily detached via the formation of glutathione disulfides upon the addition of ROS and RNS, and destabilized particles can aggregate to generate the plasmonic couplings between plasmonic AuNPs that trigger the red shift in UV–vis spectrum and solution color change. For nonradical species such as H2O2, this process can be more efficiently achieved by converting them into radical species via the Fenton reaction. Using this strategy, we were able to rapidly and quantitatively distinguish among cancerous and normal cells based on ROS and RNS production. Simultaneous and distinguishable quantitative monitoring of ROS and RNS in living cells is important for understanding their independent and interdependent biological roles

eventually useful in solving bio-signalling mechanistic puzzles. In chapter 2, we design a plasmonic core-satellite nanoassembly bioprobe for SERS-based distinguishable multiplex quantitative monitoring of H2O2 and NO in living cells. We have strategically conjugated myoglobin as the dual-responsive Raman reporter in the electromagnetic hot-zones of gold core-satellite nanoassemblies with the help of biocompatible polydopamine interface/spacer. ROS/RNS detection principle is based on the structural changes in Raman reporter heme prosthetic group of SERS bioprobe, distinctly and quantitatively monitored in living normal and cancer cells by SERS measurements upon reaction with intracellular H2O2 and NO. Metal nanostructures with highly branched morphologies are an interesting and useful new class of nanomaterials due to their plasmonically enhanced optical properties, large surface area and potential as catalytic substrates, sensing probes and building blocks for nanoscale devices. In particular, surface plasmon-derived photo-induced therapeutic effect and catalysis are highly dependent on their surface nanostructures, but the control of their branching structures is challenging. In chapter 3, we introduce a strategy for the controlled synthesis of plasmonic core-petal nanostructures (CPNs) with highly branched morphologies. The fine nanostructural engineering of CPNs was facilitated by gold chloride-induced oxidative disassembly of polydopamine corona around spherical Au nanoparticles and successive anisotropic growth of Au nanopetals. We show that CPNs can act as multifunctional nanoreactors that induce photodynamic and photothermal dual therapeutic effects and generate ROS. Near-infrared laser-activated CPNs can be used to induce the effective destruction of cancer cells via the synergistic combination of benign plasmonic hyperthermia (~42 °C) and ROS-mediated oxidative intracellular damage. It was also shown that CPNs exhibit very strong surface-enhanced Raman scattering signals, and this allows for post-mortem probing of ROS-mediated oxidative structural modifications of DNA that could be responsible for the apoptotic fate of cancer cells. Hybrid nanobiosensors working on enzyme-mimetic mechanisms are always desired to amalgamate best features of natural and synthetic systems. In chapter 4, we report a hybridized three component enzyme-mimetic glutathione-Au@Pt core-shell nanoprobe for recognition and colorimetric signaling of glucose. Unlike conventional glucose sensors based on natural enzymes, our nanoprobe is robust enough to operate in a wide pH range and even at high temperatures. In the biomimetic design, nanopockets present between Au core and porous Pt shell interfaced with glutathione ligand provide an optimal hydrophobic and hydrogen bonding environment for the efficient recognition of host sugar molecule as suggested from NMR spectroscopy and DFT calculations. GSH-Au@Pt catalyzes efficient oxidation of glucose to corresponding gluconic acids and co-produced H2O2 triggers dimerization of interfacial glutathione ligands resulting aggregation-induced plasmonic coupling between Au cores, exhibiting a visual colour change. Finally, clinical test with urine samples collected from diabetic patients were performed with very high degree of accuracy and almost no sensitivity towards common interfering urine ingredients such as ascorbic acid, proteins and cysteine.