Studies On Gold Nanorods-Based Biosensing And Cancer Photothermal Therapy

Gold nanorods (AuNRs) have been found wide applications in the fields of drug delivery, gene detection, immunoassay, biosensing, cell imaging and photothermal therapy owing to their unique shape, optical properties, and photothermal properties. However, there are still some limitations in the development of AuNRs:some assemblies of AuNRs were just patterned without further applications; among the biosensing systems, few colorimetric assays can be found; the AuNRs-based cell imaging shows low contrast; the AuNRs-based photothermal therapies supply high therapeutic outcomes but low specificity. In this thesis, to solve the above problems, the modern optical and imaging techniques were employed to develop the further applications in the fields of AuNRs to biosensing, cell imaging and cancer therapy. The obtained results supply the theoretical and experimental basis for further application of AuNRs. This thesis includes the following two parts:Part I, The application of AuNRs in detecting biological macromolecules and cell imaging, including the following three aspects:Firstly, a simple, rapid, colorimetric and selective assay for lysine was achieved by a controllable end-to-end assembly of AuNRs in the presence of Eu3+and lysine. This one-pot end-to-end assembly of11-mercaptoundecanoic acid (MUA) modified AuNRs was occurred in Britton-Robinson buffer of pH6.0, which involves in the coordination binding between Eu3+and COO" groups as well as the electrostatic interaction of the COO-groups of MUA with the-NH3+group of lysine. As monitored by absorption spectra, scanning electron microscopic (SEM) images and dynamic light scattering (DLS) measurement, the end-to-end chain assembly results in large red-shift in the longitudinal plasmon resonance absorption (LPRA), giving a red-to-blue color change of AuNRs. Importantly, the red-shift of LPRA is found to be linearly proportional to lysine concentrations in the range of5.0×10-6-1.0×10-3mol/L with the limit of detection (LOD) being1.6×10-6mol/L (3a/k). This red-shift of LPRA is highly selective to lysine, making it possible to develop a rapid, selective and visual assay for lysine in food samples.Secondly, a simple, sensitive and selective assay for adenosine was achieved by a controllable side-by-side assembly of AuNRs induced by a molecular recognition between adenosine and its aptamer, which leads aptamer to form a four-stranded tetraplex structures (G-quartet). It was found that the formed G-quartet could induce self-assembly of AuNRs owing to the electrostatic interaction between the positive charge of cetyltrimethylammonium bromide (CTAB) on AuNRs surface and the negative charge of the formed G-quartet. Furthermore, the side-by-side self-assembly of AuNRs is characterized by the enhancement of plasmon resonance light scattering (PRLS) signals and the blue-shift of AuNRs longitudinal plasmon resonance absorption (LPRA) band attributed to the plasmon resonance coupling. Then, with the enhanced PRLS signals, a simple, highly selective and sensitive detection method for adenosine could be developed in the range of4.0-80.0nmol/L with the limit of determination of2.0nmol/L, which is up to now the best sensitive optical detection method to our knowledge. This method has been successfully applied to the detection of adenosine acids in the brain of SD mouse in good agreement with high-performance liquid chromatographic (HPLC) method.Then, the structural formation and dark-field light scattering imaging of Au@Ag@AgI NRs were studied. The facile and noninjurious images of cells are of great significance since imaging offers insight into metabolic activities, clinical diagnosis, drug delivery and cancer therapy. In this contribution, Au core/Ag shell nanorods (Au@Ag NRs) were prepared and employed as contrast agents for cell imaging with a dark-field microscopy system. It was found that Au@Ag NRs, as identified by X-Ray diffraction (XRD) and X-Ray photoelectron spectroscopy (XPS), could restructure into Au@Ag@AgI NRs when exposed to iodine, leading to the red-shift of longitudinal plasmon resonance absorption (LPRA) and the enhancement of light scattering signals. With conjugation of with folate acid, a kind of receptor of cancer biomarker, Au@Ag@AgI NRs were successfully used for human cervical cancer cells (HeLa cells) imaging under a dark-field microscope. Further finding was that the formed Au@Ag@AgI NRs can enter into the cytoplasm of cells without significant cytotoxicity but certain antibacterial activities. These observations may open the possibility of scientific and medical applications.Part II, The application of AuNRs-aptamer conjugates in cancer therapy, as shown in the following three aspects: The AuNRs-aptamer conjugates were applied to killing prostate cancer stem cells. In this work, aptamers CSC1and CSC13were selected against DU145cancer cells and cancer stem cells respectively, which were modified to the surface of AuNRs and successfully for targeting and killing cancer cells by near-infrared (NIR) laser. Even though cancer stem cells represent only a small population among all cancer cells, the whole cell viability was lowered after laser irradiation, suggesting that tumorigenesis could be successfully controlled by this aptamer-based method, thus paving the way for early diagnosis and targeted therapy.Then, a DNA intra-strand replacement strategy for therapeutic activity has been successfully designed for multimodal therapy including both photothermal/photodynamic therapy (PTT/PDT). A photosensitizer molecule chlorin e6(Ce6) coupled short DNA sequence linked to the surface of AuNRs via hybridization with Sgc8, a DNA aptamer targeting leukemia T cell, was used to target cancer cells for the effective PTT/PDT. When target cancer cells were absent, Ce6was quenched and showed no PDT effect. However, when target cancer cells were present, the ASP changes structure to release Ce6to produce singlet oxygen for PDT upon light irradiation. This has greatly enhanced the therapeutic effect with high selectivity. Specifically, the Ce6photosensitizer molecules were used for PDT under light irradiation. At the same time, aptamer-AuNRs, a promising thermal agent, selectively bound target cancer cells for PTT with NIR laser irradiation. In addition, AuNRs are not only useful for photothermal therapy but also helpful for the delivery and activation of photosensitizer molecules. Importantly, by combining photosensitizer and photothermal agents, PTT/PDT dual therapy supplies a more effective therapeutic outcomes than either therapeutic modality alone. Owing to the advatages of aptamers, this method offers highly selective and specific targeting of cancer cells. It is expected that this PDT/PTT strategy has the potential to become a clinically viable and versatile method for targeting and killing cancers.Finally, an aptamer switch probe (ASP) linking chlorin e6(Ce6), a photosensitizer molecule, to the surface of AuNRs was used to target cancer cells for photothermal therapy (PTT) and photodynamic therapy (PDT). In the absence of target cancer cells, the fluorescence of Ce6of quenched and showed no PDT effect. However, in the presence of target cancer cells, the ASP changes structure to drive Ce6away from the gold surface, thereby producing singlet oxygen for PDT upon light irradiation. However, since each AuNR is composed of many ASP-Ce6molecules, the AuNR-ASP-Ce6 conjugate yields enhanced binding and therapeutic effect by the added ability to carry many photosensitizer molecules to kill target cells by heat upon light irradiation. Consequently, this multimodal AuNR-ASP-Ce6conjugate offers a remarkably improved and synergistic therapeutic effect compared to PTT or PDT alone, providing high specificity and therapeutic efficiency, which can be generalized to other types of cancer therapies.The above results showed that the rapid, label-free, visual, sensitive and selective methods for biological macromolecules detection using AuNRs as probes were found, which showed the promising potential in the futher reseach. Moreover, the functionalized AuNRs were used for the cell imaging and cancer therapy with high specificity, showing the great significance in clinic, which supply the theoretical and experimental support for further application of AuNRs.