Preparation of functional nanomaterials for bioenvironmental applications

This thesis focuses on preparation and application of functional nanomaterials (e.g., apamer, gold, and carbon) for bioassay (e.g., heavy metal ions and bioimaging) in addition to cancer therapy. Chapter one introduces the framework and background of DNA-based nano-sensors and photoluminescent carbon nanodots (C-dots) in biomedical and environmental applications. In chapter two, fluorescence detection of Pb2+ in aqueous solution was demonstrated using a sensor composed of Amplex UltraRed (AUR) and a G-quadruplex oligonucleotide AGRO100. The sensing strategy is based on Pb2+ ions inducing increased DNAzyme activity of AGRO100 in the presence of hemin, which acts as a cofactor to catalyze H2O2-mediated oxidation of AUR. Under optimized conditions, this AGRO100-AUR sensor provided high sensitivity and specificity for Pb2+ over other metal ions in aqueous solutions with a limit of detection of 0.4 nM. The third chapter describes a simple assay employing a G-quadruplex oligonucleotide T30695 modified gold nanoparticles, and AUR (T30695–Au NPs/AUR) for the detection of Pb2+ ions. The surface density of T30695 units on Au NP surface played an important role in controlling the formation of the Au-Pb alloys and T30695–Pb2+ complexes and, therefore, the catalytic activity of the T30695–Au NPs. Under optimized conditions, the 40T30695–Au NP/AUR probe was highly sensitive (LOD = 0.05 nM) and selective toward Pb2+ ions. Chapter four describes a facile and green method to synthesize fluorescent C-dots from fresh tender ginger juice via a hydrothermal process. The as-prepared C-dots not only exhibited favorable photoluminescent (PL) properties (quantum yield~13.4%), but also provided extremely high selectivity and suppression efficiency on the growth of human hepatocellular carcinoma cells (HepG2), with low toxicity to normal cells. The C-dots generated greater amounts of reactive oxygen species (ROS, 18.2-fold increased) in the HepG2 cells, resulting in enhanced expression of p53 protein. Surface-assisted laser desorption/ionization time-of-flight mass spectrometry (SALDI-TOF MS) results revealed the existence of curcumin molecules (a highly active anti-cancer agent) on the surface of C-dots, which likely assisted in triggering the pro-apoptotic factor to promote HepG2 cell apoptosis. For the first time, C-dots have been used for significantly reducing the weight of HepG2 cells induced tumor in nude mice by about 96.4%. The final chapter describes a label-free probe based on C-dots that were prepared from cysteine through a hydrothermal process for real-time monitoring of Co2+ ions in vitamin B12 and nature water samples. The proposed strategy utilizes Co2+ ions to react with cysteine/residual sulfur-related molecules in solution and/or on the surfaces of C-dots to form cobalt sulfide (CoxSy) nanoparticles that further undergo aggregation to form large granular C-dots/CoxSy nanomaterials, leading to the PL quenching via a charge transfer-dependent dynamic quenching process. Under optimum conditions, this C-dots based PL assay allows detection of Co2+ ions with great sensitivity (down to 5 nM) and linearity (10 nM to 100 μM, R2 = 0.992).