Browsing by Author "Toh, Yon-Rui"

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Dynamic study on the transformation process of gold nanoclusters
(2014-11-07)
Ma, Xiaoqian
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Wen, Xiaoming
;
Toh, Yon-Rui
;
Huang, Kuo-Yen
;
Tang, Jau
In this paper, the transformation process from Au-8 to Au-25 nanoclusters (NCs) is investigated with steady state fluorescence spectroscopy and time-resolved fluorescence spectroscopy at various reaction temperatures and solvent diffusivities. Results demonstrate that Au-8 NCs, protected by bovine serum albumin, transform into Au-25 NCs under controlled pH values through an endothermic reaction with the activation energy of 74 kJ mol(-1). Meanwhile, the characteristic s-shaped curves describing the formation of Au-25 NCs suggest this process involves a diffusion controlled growth mechanism.
Optical properties of gold particle-cluster core-satellite nanoassemblies
(2013)
Yu, Pyng
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Wen, Xiaoming
;
Toh, Yon-Rui
;
Lee, Yu-Chieh
;
Tang, Jau
Better understanding of core-satellite nanostructures is of great interest to researchers owing to their unusual properties and is key to their promising applications. The well-developed techniques based on protein-nanoparticle interactions were adopted to produce core-satellite nanoassemblies of similar to 10 nm core of Au nanoparticles (AuNPs) covered by Au-25@BSA or Au-10@histidine nanoclusters (NCs). The photoexcited dynamics in the core-satellite nanoassemblies were studied using steady-state and time-resolved spectroscopic measurements. Fluorescence quenching in AuNP-AuNCs core-satellite nanostructures was observed and confirmed as static quenching. The AuNPs alter neither radiative decay nor nonradiative decay in both nanoclusters. This indicates that the electron/energy transfer within the NP-NCs core-satellite nanoassemblies is absent, in contrast to the results involving other larger NP-NPs core-satellite nanoassemblies.
Quantum Confined Stark Effect in Au-8 and Au-25 Nanoclusters
(2013-02-21)
Wen, Xiaoming
;
Yu, Pyng
;
Toh, Yon-Rui
;
Tang, Jau
;
光電工程學系
The quantum confined Stark effect is investigated for the first time in bovine serum albumin (BSA) protected Au-8 and Au-25 nanoclusters. We observed a red-shift of 63 meV in Au-8 nanoclusters upon an increase in pH from 2.14 to 12.0. Such behavior could be well explained in terms of the presence of a linear polar component and a quadratic polarizable component. In contrast, Au-25 nanoclusters exhibit more complicated Stark shifts due to their specific core/semiring structure. A plateau of the Stark shift was observed in both absorption and fluorescence, showing an offset of 30 meV. The lifetime measurements confirm that the plateau is due to the screening effect of the semirings in Au-25@BSA. Moreover, the dual fluorescent bands of Au-25 nanoclusters exhibit two different Stark shifts of 79 and 52 meV, respectively. The experimental data indicate that the Stark shift in both Au-8@BSA and Au-25@BSA has a significant linear polar component due to their asymmetric structure. This study suggests that gold nanoclusters can become a potentially useful candidate in probing local electric fields and also in pH-sensing in nanoscale environment of biological systems.