製備高產率金奈米雙三角錐及其選擇性二氧化矽包覆之研究

金奈米雙三角錐(Gold Nanobipyramids, AuNBPs)具有比金奈米棒(Gold Nanorods, AuNRs)更佳的光學性質，其兩端的尖點擁有比金奈米棒的兩端點更強的電場，因此有利於應用在光學及奈米醫學方面上。本實驗成功合成出不同波長的金奈米雙三角錐，但由於利用晶核成長法(seed-mediated growth method)所合成出的奈米粒子，其中金奈米雙三角錐的產率不到50%，因此利用benzyldimethylhexadecylammonium chloride (BDAC)進行純化的步驟，使金奈米雙三角錐的產率提高至90%以上，不僅如此，還另外測試出另一純化方法：將未純化的金奈米雙三角錐的溶液過度生長，使金奈米雙三角錐變成有銀包覆在外的銀棒，金奈米顆粒變成有銀包覆的銀顆粒，再利用顆粒大小不同使其分離，最後再利用氨水及雙氧水蝕刻掉銀的部分，兩種方法都能得到高產率的金奈米雙三角錐。接著，將金奈米雙三角錐以及另外合成出的金奈米棒在兩端分別修飾上8-arm PEG-LA，再包覆二氧化矽在其邊上，形成像大亨堡的形狀，以及在金奈米雙三角錐和金奈米棒四周包覆上二氧化矽。由於侷域化表面電漿共振的現象，金奈米棒及金奈米雙三角錐的端點可以提供較強的電場環境，這些電場被高度增強的熱點(Hot Spot)處如果修飾上螢光分子，可以放出較強的螢光，抑或是曝露於相對應波長的雷射探討其光熱轉換效率。由於二氧化矽選擇性包覆在金奈米顆粒上，可以使得未來在修飾上螢光分子上能集中在端點，又金奈米雙三角錐的尖端電場比金奈米棒的端點電場還強，可以被預期金奈米雙三角錐的螢光增強倍率會大於金奈米棒。

關鍵字

金奈米雙三角錐；金奈米棒；表面電漿共振

並列摘要

Gold nanobipyramids (AuNBPs) possess better optical properties than gold nanorods (AuNRs), and the sharp tips at both ends have a stronger electric field than the ends of the AuNRs. Therefore, this feature has made AuNBPs favorable for an enormous number of potential applications in areas including optics and nanomedicine. In this study, we successfully synthesized AuNBPs with different longitudinal plasmon resonance wavelengths (LPRWs). Due to the seed-mediated growth method we use to synthesis AuNBPs, the yield of AuNBPs is less than 50. %. Thus, benzyldimethylhexadecylammonium chloride (BDAC) was chosen for the purification. It made the yield of AuNBPs raise up more than 90%. Additionally, we also tested another method for AuNBPs purification. To address the problem of AuNBPs purification, we execute Ag overgrowth to obtain bimetallic Au/Ag nanocrystals by adding AgNO3 in the presence of cetyltrimethylammonium chloride (CTAC). Ag overgrowth on the NBPs and spherical Au nanoparticles form Au/Ag heteronanorods and (Au core)@(Ag shell), respectively. And then we depend on the size of nanoparticles to separate. Finally, the Ag segments are etched away using ammonia solution and hydrogen peroxide. Both of method can get high yield of AuNBPs. Next, AuNBPs and additionally synthesized AuNRs are respectively modified on the two ends with 8-arm PEG-LA, and then coated with silicon dioxide on their sides to form a shape like “hot dog”. Another shape is synthesized which is coated with silicon dioxide around AuNBPs and AuNRs to form ellipse. Due to the phenomenon of localized surface plasmon resonance (LSPR), the ends of AuNRs and AuNBPs can provide a strong electric field environment. The hot pots where electric fields are highly enhanced are modified with fluorescent molecules, the ends of them can enhance the intensity of the fluorescent light. We can also discuss photothermal effect while they exposed to lasers with corresponding wavelengths. Since silica dioxide is selectively coated on the side of gold nanoparticles, the fluorescent molecules can be concentrated at the end points, and the electric field of tips of AuNBPs is stronger than the end of AuNRs. We can expect that the fluorescent enhancement of AuNBPs will be greater than AuNRs.