Distance-dependent Fluorescence Quenching of Tryptophan by Gold Nanoparticles within 5 nm Spaced by Polyprolines

• Main Authors: Lai, Ying-Chen, 賴盈禎
• Other Authors: Chu, Li-Kang
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/9ht2cm

碩士 === 國立清華大學 === 化學系所 === 106 === Gold nanoparticles (AuNPs) often induce the quenching of excited states of fluorophores when they are close. The quenching efficiency has been observed as a function of distance between the AuNP and the fluorophore. However, there has not been discussed about AuNP-induced quenching within 5 nm. In this work, tryptophan is served as the fluorophore to study the AuNP-induced quenching and polyprolines (PP), which form the rigid PPII structure in solution, are used as molecular rulers to separate the AuNP and Trp by tuning the numbers of the proline units within 5 nm. The surfaces of the AuNP were successfully anchored with peptides, CAPnWN which n=3, 6, 10, 13, through the terminal cysteine to form the Au-S bonding. The optical properties of AuNP-CAPnWN were characterized by UV/Visible absorption spectroscopy, fluorescence spectroscopy, ATR-FTIR and TEM. Besides the steady-state optical characterization, the temporal profiles of the tryptophan fluorescence at 355-365 nm upon 266 nm excitation were collected with the time-correlated single-photon counting. We found that the fluorescence kinetics of tryptophan in CAPnWN is slightly accelerated in comparison with the pure tryptophan. As the CAPnWN are attached onto the gold nanoparticles, the fluorescence kinetics becomes more accelerated as the separation becomes shorter. Both energy-transfer and electron-transfer processes are considered to be deactivation pathways. However, the energy transfer rate depends on the 1/d1.3 separation distance which is far from the nanosurface energy transfer mechanism. Therefore, the energy transfer from Trp to AuNP is not the major reason. Then, considering the electron transfer rate (k_ET) as an exponential function of the peptide chain length (k_ET∝e^(-βd)), and the π-stacking interaction between adjacent CAPnWN, the β could be fitted as 0.1 Å-1 same as previous studies. As a result, the fluorescence quenching of Trp by AuNP depends on their distance is attributed to the electron transfer mechanism. The polyprolines are served as stepping stones and the AuNPs are the electron acceptors. It is noteworthy that the polyproline can not only be the molecular ruler but also be the relay for electron transfer.