螢光金奈米原子簇之合成與應用在汞離子感測之研究

Abstract

螢光金奈米原子簇是近年來備受矚目的奈米材料之一，其具有螢光性穩定、合成條件較緩和且前驅物毒性低的優點，且可經由修飾金奈米原子簇表面使其具有功能性用以抓取特定目標物，可應用於各種分析領域。本論文中嘗試使用一鍋反應以6-氮雜-2-硫代胸腺嘧啶做為還原劑合成表面包覆有6-氮雜-2-硫代胸腺嘧啶之金奈米原子簇，成功合成出具有在波長約505 nm放光之綠色螢光性質的金奈米原子簇 (激發光源波長467 nm) ，粒子直徑大小約1.96 ± 0.44 nm，實驗結果發現由於配體-金屬奈米粒子電荷轉移之效應，溶液酸鹼值會使此金奈米原子簇的表面官能基的共振結構及電子密度產生改變，而對螢光性質有顯著的影響，當此金奈米原子簇在pH 10甘胺酸緩衝液中時測得其螢光生命期為17.83 ± 0.24 ns，螢光量子產率為3.80 ± 0.24%。由於文獻指出核酸鹼基中的胸腺嘧啶 (Thymine, T) 能以氮原子與汞離子形成T-Hg-T的穩定螯合物，因此本論文進一步利用此6-氮雜-2-硫代胸腺嘧啶其類似胸腺嘧啶的結構用於汞離子的選擇性感測實驗。實驗中發現金奈米原子簇與水中的汞離子結合造成的金奈米原子簇螢光焠熄現象可對汞離子進行選擇性偵測，對鉛、鐵、鎳、鋅等其他重金屬離子雖無明顯螢光焠熄現象，但在汞離子與其他重金屬離子混合的複雜樣品中，亦會對汞離子的感測造成干擾，研究中發現使用2,6-吡啶二甲酸做為遮蔽劑則可降低偵測時的干擾。實驗結果顯示對於含汞離子標準水樣的偵測極限已可到達1 nM左右，且在擬真實水樣中也對汞離子具有感測效果，然而由於擬真實水樣之基質成分複雜，受此干擾影響使得金奈米原子簇對於稀釋十倍之擬真實水樣中汞離子的偵測極限僅為10 nM左右，因此仍必須進一步提升此方法之偵測極限方可進行實際應用。本論文中也嘗試了將金奈米原子簇與其他材料結合以開發簡易汞離子快速檢測方法，但目前此方法偵測極限僅為1 μM左右，仍有其改善之空間。

Fluorescent gold nanoclusters (AuNCs) have attracted considerable attentions lately because of their features of high stability, ease of synthesis, and low toxicity. AuNCs can be functionalized to have the capability of selectively probing specific targets. Thus, AuNCs have been applied in the development of analytical methods. In this study, we explored that 6-aza-2-thiothymine (ATT) immobilized gold nanoclusters (AuNCs@ATT) can be generated by reacting tetrachloroaurate with ATT, which plays as reducing agents, through a one-pot reaction. The generated AuNCs@ATT have a maximum emission wavelength at 505 nm (λexcitaion= 467 nm) with the diameter of 1.96 ± 0.44 nm. The fluorescence of the AuNCs is sensitive to pH changes, which may result from ligand to metal nanoparticle charge transfer involving in the generation of fluorescence of the AuNCs@ATT. When preparing the AuNCs in glycine-NaOH buffer (pH10), the fluorescence lifetime of AuNCs@ATT is 17.83 ± 0.24 ns, while the quantum yield is 3.80 ± 0.24%. It has been demonstrated that Hg2+ can selectively chelate with thymine previously. Because the structure of ATT is similar to the structure of thymine, we proposed that Hg2+ ions should be able to interact with the ATT on the surface of AuNCs@ATT, causing the change of the resulting fluorescence. In this work, it is demonstrated that AuNCs@ATT can be used to selectively bind with Hg2+, resulting the quenching of the fluorescence of the AuNCs@ATT. However, there was no obvious quenching effect occurring when mixing the AuNCs@ATT with transition metal ions including, Fe3+, Ni2+, and Zn2+. However, a slight fluorescence quenching was observed when mixing the AuNCs with Pb2+. 2, 6-Pyridine-dicarboxylic acid was successfully used as a masking agent to reduce the interference from Pb2+ when conducting the AuNCs@ATT-based sensing experiments. The limit of detection (LOD) for standard aqueous Hg2+ is as low as 1 nM, while the LOD for a simulated real sample is only ~10 nM owing to the presence of the complex matrix. It is also demonstrated that AuNCs@ATT immobilized paper strips can be readily used to sense the presence of Hg2+ from aqueous solution simply examined by naked eyes. However, more efforts should be made to further improve the sensitivity of this strip-based approach since the LOD is only as low as 1 μM so far.