Preparation And Application Of Hybrid Materials Based On Water-soluble Macrocyclic Arenes And Gold Nanoparticles

Nanomaterials have stimulated great interest in both the basic and appliedsciences because of their unique physical and chemical characteristics that aresubstantially different from bulk materials. Amongst them, in particular, goldnanoparticles (AuNPs) possess many excellent properties, including highchemical stability, facile synthesis, surface functionalization, biocompatibility,tunable optical and electronic properties and so on. Meanwhile, supramolecularmacrocycles continue to be central to supramolecular chemistry. The marriage ofAuNPs and supramolecular macrocycles can lead to the birth of novelsupramolecular hybrid nanomaterials, which combines and enhances thecharacteristics of the two components, such as the electronic, thermal, andcatalytic properties of AuNPs and molecular recognition of the macrocyclic hosts.This line of research broadens the horizon of nanomaterials, and expands theirpotential applications.In this dissertation, novel hybrid nanomaterials were fabricated based onAuNPs functionalized with three kinds of water-soluble macrocyclic arenes, i.e.,amino pillar[5]arene (AP[5]A), carboxylatopillar[5]arene (CP[5]A) andsulfonatocalix[4]arene (SC[4]A), respectively. Systematic researches have beencarried out on their preparations, supramolecular self-assemblies and applicationsin sensing and drug delivery. Firstly, AP[5]A, with five amine groups on each rim, can act as a linkerbetween different AuNPs to regulate and control their self-assembly throughligand exchange. Ultimately, we obtained different assembly forms ofAP[5]A-functionalized AuNPs. The first step, the sodium citrate-stabilized AuNPs(Ct-AuNPs) with narrow size distributions (27.52.9nm) were successfullyproduced in aqueous solutions. Then we figured out ca.1300of AP[5]Amolecules can be functionalized on the surface of each AuNP. Based on the data,we conducted a systematic research on the self-assembly process of AP[5]A andAuNPs. Different amounts of AP[5]As were added into the solutions of Ct-AuNPs.Through monitoring the Zeta potential changes of different assembly forms ofAP[5]A-functionalized AuNPs, we found the surface potential of Ct-AuNPs to benegative, and the addition of AP[5]As can cause the assembly of Ct-AuNPs withthe absolute value of Zeta potential (negative) gradually decrease to zero,resulting in coagulation. When the amount of AP[5]As continued to increase, theassembly of AuNPs happened again, which was different from the formerassembly form, that is, Zeta potential changed into positive and graduallyincreased. Finally, we obtained stable AP[5]A-functionalized AuNPs with gooddispersion. We envision that AP[5]A would endow the hybrid nanomaterials manypotential applications. For example, AP[5]A can serve as recognition sites forselectively capturing the target molecules; more importantly, due to the richhost-guest chemistry of AP[5]A, the analyte molecules are subjected to intensefield enhancement at the heart of the plasmonic hot spot to realize SERS-basedultrasensitive detection.Secondly, we adopted one-step method under the control of reductant, watersoluble CP[5]A was employed as a stabilizing ligand for in situ preparation ofAuNPs for the first time. CP[5]A-modified AuNPs with good dispersion andnarrow size distributions (3.1±0.5nm) were successfully produced in aqueoussolutions, suggesting a green synthetic pathway for the application of AuNPs inbiological systems. Then the interactions and assembly between guest moleculesand CP[5]A-modified AuNPs have also been investigated. Corresponding assembling mechanism was discussed and analyzed. We found that the assemblyof CP[5]A-modified AuNPs mediated by viologen I was a dynamic equilibriumrelying on the amount of viologen I added and incubation time; And viologen II(viologens I dimer) could bridge CP[5]A-modified AuNPs together to achieve1Dchain-like and2D network-like self-assembled architectures, rather than simplymass aggregation. All these results indicated that the AuNP-immobilized CP[5]Asstill possess good host-guest properties. Based on the supramolecularself-assembly process between viologen I (paraquat) and CP[5]A-modifiedAuNPs, we found CP[5]A-modified AuNPs can also be used as optical probes forherbicide detection.Thirdly, different from traditional ways, we introduced a layer of mesoporoussilica on the surface of gold nanorods for the post-functionalization ofmacrocyclic molecules. Thus, we constructed a novel cancer theranostic hybridplatform, based on mesoporous silica-coated gold nanorods (AuNR@MSNs)gated by SC[4]A switches, for bio-friendly near-infrared (NIR) light-triggeredcargo release in a remote and stepwise fashion. Specifically, compared toultraviolet-visible, near-infrared light stimulus enables deeper penetration and lessrisk of damage to body tissues. The advantages of supramolecular switches,mesoporous silicas, and AuNRs were combined in one drug delivery system.Mesoporous silicas coated on AuNRs guarantee a high drug payload and can beeasily post-functionalized. Significantly, the plasmonic heating from the NIRlight-stimulated AuNRs cores can decrease the ring-stalk binding affinity, leadingto the dissociation of SC[4]A rings from the stalks, thus opening the nanovalvesand releasing the cargo. The NIR light-responsive mechanized AuNR@MSNsoffers exciting prospects for non-invasive controlled drug delivery, being moreeffective and safer. Previously, NIR light-responsive supramolecular nanovalvesbased on AuNR@MSNs have never been reported.