Han-Wen Cheng

Design of functional nanoparticles and assemblies for theranostic applications.

Nanostructured materials have found increasing applications in medical therapies and diagnostics (theranostics). The main challenge is the ability to impart the nanomaterials with structurally tailored functional properties which can effectively target biomolecules but also provide signatures for effective detection. The harnessing of functional nanoparticles and assemblies serves as a powerful strategy for the creation of the structurally tailored multifunctional properties. This article highlights some of the important design strategies in recent investigation of metals (especially gold and silver), and magnetically functionalized nanoparticles, and molecularly assembled or biomolecularly conjugated nanoparticles with tunable optical, spectroscopic, magnetic, and electrical properties for applications in several areas of potential theranostic interests. Examples include colorimetric detection of amino acids and small peptides, surface-enhanced Raman scattering detection of biomolecular recognition of proteins and DNAs, delivery in cell transfection and bacteria inactivation, and chemiresistive detection of breath biomarkers. A major emphasis is placed on understanding how the control of the nanostructures and the molecular and biomolecular interactions impact these biofunctional properties, which has important implications for bottom-up designs of theranostic materials.

An aggregative growth process for controlling size, shape and composition of metal, alloy and core–shell nanoparticles toward desired bioapplications

Metal nanoparticles, especially gold and its alloy, core-shell, or nanocomposites function as theranostic probes or vehicles with amplified optical, spectroscopic, electrical and magnetic signals, or unique bio-functional, bio-compatible properties upon the desired bio-conjugation. Exploration of these functions is inherently linked to the ability to control the size, shape, composition, and surface properties, which depends to a large degree on the understanding of the controllability of these nanostructure parameters in the synthesis and processing. Aggregative growth constitutes an important pathway for the control of size, shape and composition in synthesis and processing of nanoparticles. This article highlights recent progress in the exploration of aggregative growth for the control of size, shape, and composition of metal nanoparticles. Examples such as thermally-activated aggregative growth of gold, copper, copper sulfide, alloy nanoparticles, and core-shell nanoparticles with magnetic cores and gold shells are discussed. The focus is to highlight the significance of understanding the mechanistic aspects in establishing the controllability over size, shape, and composition for further harnessing the unique nanoscale properties toward desired bioapplications.

Synthesis of Gold Nanoparticles

Abstract Gold nanoparticles have become a focal point of interests in nanoscience and nanotechnology. This chapter describes the synthesis of gold nanoparticles in aqueous and organic phases with emphasis on understanding the growth mechanism in terms of sizes and properties and their relevance to analytical chemistry.

SERS nanoprobes for bio-application

The ability to tune the size, shape, composition and surface properties impart nanoparticles with the desired functions for bio-application. This article highlights some of the recent examples in the exploration of metal (e.g., gold and silver) nanoparticles, especially those with magnetic properties and bio-conjugated structures, as theranostic nanoprobes. Such nanoprobes exhibit tunable optical, spectroscopic, magnetic, and electrical properties for signal amplifications. Examples discussed in this article will focus on the nanoproble-enhanced colorimetric detection and surface enhanced Raman scattering (SERS) detection of biomarkers or biomolecules such as proteins and DNAs. The understanding of factors controlling the biomolecular interactions is essential for the design of SERS nanoprobes with theranostic functions.

Assessing the Role of Capping Molecules in Controlling Aggregative Growth of Gold Nanoparticles in Heated Solution

This report describes findings of an investigation of the role of capping molecules in the size growth in the aggregative growth of pre-formed small-sized gold nanoparticles capped with alkanethiolate monolayers toward monodispersed larger sizes. The size controllability depends on the thiolate chain length and concentration in the thermal solution. The size evolution in solution at different concentrations of alkanethiols is analyzed in relation to adsorption isotherms and cohesive energy. The size dependence on thiolate chain length is also analyzed by considering the cohesive energy of the capping molecules, revealing the importance of cohesive energy in the capping structure. Theoretical and experimental comparisons of the surface plasmonic resonance optical properties have also provided new insights into the mechanism, thus enabling the exploitation of size-dependent nanoscale properties.

Assessment of aggregative growth of MnZn ferrite nanoparticles

MnZn ferrite (MnZnFe2O4, MZF) nanoparticles (NPs) represent an intriguing class of magnetic NPs in terms of composition-tunable magnetic properties, but the ability to control the size and morphology is essential to exploit such properties. This report describes the findings of an investigation of the size and morphology controllability in terms of growth kinetics of the NPs in a thermochemical synthesis process. MZF NPs of different sizes were synthesized at different temperatures. In addition to shape evolution, the overall size of the as-synthesized magnetic NPs is shown to increase with the reaction temperature and reaction time, revealing that the size growth process can be described by an aggregative growth mechanism. While the apparent rate constant decreases with the reaction temperature, the growth factor remains at 1-2, consistent with a low-dimensionality growth mode. Higher temperature and longer reaction time apparently favor the formation of cubic shapes. The dependence of the overall average particle size on the reaction temperature yields a diffusional activation energy in the order of 10-20 kJ mol-1, a value slightly smaller than those reported for aggregative growth of other types of NPs in solutions. The unravelling of the kinetic parameters provides some new insights into the development of strategies for synthesizing MZF NPs with controllable sizes and shapes.

Nanoscale Lacing by Electrons

The ability to harness the optical or electrical properties of nanoscale particles depends on their assembly in terms of size and spatial characteristics which remains challenging due to lack of size focusing. Electrons provide a clean and focusing agent to initiate the assembly of nanoclusters or nanoparticles. Here an intriguing route is demonstrated to lace gold nanoclusters and nanoparticles in string assembly through electron-initiated nucleation and aggregative growth of Au(I)-thiolate motifs on a thin film substrate. This size-focused assembly is demonstrated by controlling the electron dose under transmission electron microscopic imaging conditions. The Au(I)-thiolate motifs, in combination with the molecularly mediated alignment, facilitate the interstring electrostatic and intrastring aurophilic interactions, which functions as a molecular template to aid electron-initiated 1D lacing. The findings demonstrate a hierarchical route for the 1D assemblies with size and spatial tunable catalytic, optical, sensing, and diagnostic properties.