Synthesis And Function Investigation Of Biomaterial-Templated Nanoparticle Hybrids

Biomaterial-metal nanoparticle hybrids incorporate the specific recognition, transmission, and highly selective catalytic abilities of biomaterials, such as proteins/enzymes and DNA, with the unique electronic, photonic, and catalytic properties of metal nanoparticles to deliver structural versatilities and multifunctionalities. Biomaterial-metal nanohybrids have been used widely in sensing, catalysis, bio-labeling, nanocircuitry and biomedicine. Research in this thesis deals with the preparation and property investigations of biomaterial templated metal nanoparticles/nanoclusters. More details are given as follows:1. Mechanically shortened fish sperm DNA molecules were used as effective nucleation templates for the in-situ electroless deposition of Pd nanoparticles on glassy carbon electrodes. Atomic force microscopy (AFM) was employed to check the morphologies of as-deposited Pd nanoparticles on the modified electrode surface. Electrocatalytic properties of the modified electrodes toward the reductions of dissolved oxygen and hydrogen peroxide, as well as the oxidation of hydrazine were further investigated by cyclic voltammetry (CV). The DNA-assisted electroless deposition of highly dispersed Pd with remarkable electrocatalytic activities is expected to offer an easy, quick and cost-effective strategy toward applications in fuel cells as well as electrochemical sensors.2. An extremely easy, reliable, low-cost and environment-friendly method was developed to synthesize impressively stable and highly fluorescent gold nanoclusters (AuNCs) embedded in a natural eggshell membrane (ESM), during which ESM acted as both a template and a reductant. Besides ESM, there are various other protein-containing solid phase materials such as feather and silk could also been employed as matrices for the synthesis. In addition, based on the significant fluorescence quenching of the as-synthesized AuNC-ESM monolith upon interaction with Hg²⁺, a concept of an Hg²⁺ sensing paper was suggested and preliminarily demonstrated, achieving a visual detection limit of 1μM (200ppb) for Hg²⁺ under unoptimized conditions. This work is also of potential interests for applications such as"hidden"writing or anti-counterfeiting due to the highly stable fluorescence of the Au-NCs under various harsh conditions and its sensitive response toward specific metal ion. Finally and most importantly, this novel synthetic platform promises its use for low-cost and green-chemistry syntheses of various other metal-based nanomaterials (fluorescent or non-fluorescent), which, due to their existing form as a solid state membrane, will be very easy to get recycled after various uses.3. In sharp contrast to the synthesis of fluorescent gold nanoclusters that solely depended on the reducing ability of the ESM itself, more reduction choices were available to generate fluorescent silver nanoclusters. Based on these findings, the ESM system turned out to be a versatile synthetic platform in the case of silver with multimode reduction routes including UV, NaBH4 and the protein template itself at a basic pH. These results further secure a mechanistic investigation in the future on the chemical nucleation process of metal nanoclusters within a protein-based matrix, which is critically important in the development of a more efficient and rationalized synthetic strategy toward higher quantum yield and tunable fluorescence emissions. Since silver nanoclusters are appealing due to their potentials in surface enhanced Raman scattering, catalysis and bioimaging, the as-prepared Ag-ESM with red to infrared emissions might find important applications in these areas.4. A DNAzyme structure that had an effector-recognizing part appearing as a single stranded DNA linkage flanked by two split G-quadruplex halves was designed. In the presence of K⁺, the two split G-quadruplex halves would cooperatively transform into an intact G-quadruplex after capturing a hemin molecule and formed G-quadruplex/hemin complex with peroxidase-like activities for the catalytic oxidation of ABTS by H₂O₂, which could be employed to colorimetrically monitor the peroxidase activity of the complex. Hybridization of the single stranded part in the DNAzyme with a perfectly matched effector strand formed a rigid DNA duplex between the two G-quadruplex halves and thus efficiently suppressed the enzymatic activity of the G-quadruplex/hemin complex, while the mismatched effector strand was not able to regulate the peroxidase activity effectively. The split G-quadruplex is an especially useful module to design simple, low-cost and label-free sensors toward various biological or environmental targets of interest.