Polydopamine-based plasmonic nanostructures for intracellular applications

Ph.D.Polydopamine (PDA), a bioinspired polymer derived from the self polymerization of monomeric dopamine (DA), is gaining ever growing attention as an adhesive coating material. However, the exploration of PDA as a building block for assembling plasmonic nanostructures remains limited. In this thesis, we demonstrate that PDA allows for the facile preparation of plasmonic nanostructures, namely, nanoshells and nanoworms, both of which exhibit a sharp plasmon peak in biological near infrared (NIR) windows and hold great promise in plasmon driven intracellular applications.Plasmonic nanoshells (NSs), classically comprising gold (Au) as the metallic component and silica as the dielectric material, are important for fundamental studies in nanoplasmonics. They also empower a myriad of applications, including sensing, energy harvesting, and cancer therapy. Yet, laborious preparation precludes the development of next generation NSs with structural complexity, compositional diversity, and tailorable plasmonic behaviors. We present an efficient approach to the bottom up assembly of concentric NSs. By employing PDA as the dielectric material and exploiting its intrinsic adhesiveness and pH tunable surface charge, the growth of each shell only takes 3-4 hours at room temperature. A series of PDA based concentric NSs with programmable nanogap thickness, elemental composition [Au and silver (Ag)], and geometrical configuration (number of layers) is prepared, followed by extensive structural characterization. Four of the Ag containing nanostructures are newly reported. Systematic investigations into the plasmonic properties of concentric NSs as a function of their structural parameters further reveal multiple Fano resonances and local field “hot spots”, infrequently reported plasmonic features for individual nanostructures fabricated using bottom up wet chemistry.Plasmonic nanochains, derived from the one dimensional assembly of individual plasmonic nanoparticles (NPs), remain infrequently explored in biological investigations due to their limited colloidal stability, ineffective cellular uptake, and susceptibility to intracellular disassembly. We report the synthesis of PDA coated plasmonic nanoworms (NWs) by sonicating citrate capped Au (Cit Au) NPs in a concentrated DA solution under alkaline conditions. DA mediates the assembly of Cit Au NPs into Au NWs within 1 min, and subsequent self polymerization of DA for 60 min enables the growth of an outer conformal PDA shell that imparts stability to the inner Au NW structure in solution, yielding “core shell” Au@PDA NWs with predominantly 4-5 Au cores per worm. Our method supports the preparation of monometallic Au@PDA NWs with different core sizes and bimetallic PDA coated NWs with Au and Ag cores. The protonated primary amine and catechol groups of DA, with their ability to interact with Cit anions via hydrogen bonding and electrostatic attraction, are critical to assembly. When compared to unassembled PDA coated Au NPs, our Au@PDA NWs scatter visible light and absorb NIR light more intensely and enter HeLa cancer cells more abundantly. Au@PDA NWs cross the cell membrane as intact entities primarily via macropinocytosis, mostly retain their inner NW structure and outer PDA shell inside the cell for 24 h, and do not induce noticeable cytotoxicity. We showcase three intracellular applications of Au@PDA NWs, including label free dark field scattering cell imaging, delivery of water insoluble cargos without pronounced localization in acidic compartments, and photothermal killing of cancer cells.Facilitated by PDA chemistry, we have not only established materials design rules for engineering complex plasmon based systems originating from the integration of multiple plasmonic elements into defined locations within a compact nanostructure, but also expanded the experimental toolbox available for preparing 1D plasmonic nanoassemblies to foster their utilization in biomedical engineering.聚多巴胺，是由多巴胺自聚合而成的仿生聚合物。它是一種具黏附性的塗層物料，並正受到與日俱增的關注。雖然如此，把聚多巴胺用作為組裝等離子體納米結構的研究仍然是寥寥可數的。在這論文當中，我們展示出聚多巴胺是能夠被用作為製備分別名為納米外殼以及納米蟲的等離子體納米結構，而兩種結構皆在生物性近红外窗口呈現出一個明確顯見的等離子體基元共振峰和在細胞內應用上具有極大的潛在價值。等離子體納米外殼常以金作為金屬部份和以硅作為介電材料它們在納米等離子體光學的基礎研究上是非常重要的。此外，它們亦促使了無數的應用的發展，包括檢測、能量收集和癌症治療等。可是，耗時費力的製備過程妨礙了下一代具備結構複雜性、成分多樣性和可調控等離子體性質的納米外殼之發展。我們研究出一個有效率的、從下到上的方法去組裝同心納米外殼。利用聚多巴胺作為介電材料以及其本質的黏附性和可隨酸鹼度改變的表面電荷，在室溫條件下我們生成每一層外殼只需要三到四小時。透過此方法，我們製備了一系列具備可控納米間隙厚度、元素成分(金和銀)和幾何構造(外殼層數)的納米外殼，並且對它們進行了深入的結構表徵。當中，有四種帶有銀成分的納米外殼都是未曾被刊登過的。針對著同心納米外殼的各項結構參數，我們的系統性分析揭示出它們擁有多於一項的法諾共振和局域電場熱點，此兩項等離子體特性都是不常見於由從下到上用化學方法而製成的獨立的納米結構。等離子體納米鏈是由獨立的納米顆粒經過一維性的組裝而成。基於不足的膠體穩定性、低效率的細胞吸收和對细胞内解體的易感性，把納米鏈用於生物學上的研究仍然是極不常見的。我們透過將帶有檸檬酸修飾的金納米顆粒浸泡在鹼性的多巴胺濃縮溶液中並且進行超聲，合成出聚多巴胺披覆等離子體納米蟲。在一分鐘內，多巴胺誘導帶有檸檬酸修飾的金納米顆粒組裝成金納米蟲。經過六十分鐘的多巴胺自聚合，一層形狀吻合的和具保護性的聚多巴胺外殼便能形成，產生出呈現「核–殼」結構並主要帶有四至五顆金納米顆粒的聚多巴胺披覆等離子體納米蟲。我們的方法能夠支援以不同大小的金納米顆粒所生成的單金屬聚多巴胺披覆納米蟲和以金和銀作內核的雙金屬聚多巴胺披覆納米蟲。在多巴胺上之質子化伯胺和鄰苯二酚基團具有通過氫鍵及靜電引力與檸檬酸根陰離子相互作用的能力，這對於納米蟲的組裝是至關重要的。與未组装的聚多巴胺披覆金納米顆粒相比，我們的聚多巴胺披覆納米蟲更強烈地散射可見光和吸收近红外光，以及更大量地進入海拉癌细胞。納米蟲以完整無缺的形態透過巨胞飲穿過细胞膜，二十四小時後大部分仍保持著納米蟲的內部結構和聚多巴胺外殼，以及沒有引起可見的細胞毒性。我們展示 了三種聚多巴胺披覆納米蟲的細胞內應用，包括無標記暗場散射細胞成像、運載不溶水的物質到酸性細胞區室以外的區域和以光熱效應殺死癌細胞。利用聚多巴胺的化學特性，我們不但為通過整合不同的等離子體元素於緻密納米結構的特定位置來製造出複雜的等離子體系統建立了設計依據，並且擴大了組裝一維納米結構的實驗工具箱從而促進它們在生物醫學工程的應用。Choi, Chun Kit.Thesis Ph.D. Chinese University of Hong Kong 2019.Includes bibliographical references (leaves 187-201).Abstracts also in Chinese.Title from PDF title page (viewed on 23 April, 2021)