Localized Surface Plasmonic Photothermal Nanoparticle for Biomolecular Diagnostics and Skin Antifungal Therapy

Localized surface plasmonic nanoparticle refers to nanoparticle in which free electrons inside the structure can collectively coherently oscillate under the excitation of external electromagnetic waves. Under the resonant excitation, the plasmonic nanoparticles exhibit large scattering and absorption cross section, the nonradiative energy decay endows the nanoparticles great potential as nanoheater. Among diverse plasmonic nanomaterials, gold (Au) has been widely employed in different fields because of its superior stability, biocompatibility, easy modification and the wide resonance wavelength region. However, there are still some disadvantages of Au which limits its application. For example, an obvious quenching effect of fluorophore will be observed when it contacts directly with Au nanoparticles, which hinders the application of Au nanoparticle in the field of fluorescence detection. In this thesis, Au-based plasmonic nanoparticles with different structures, compositions and modifications are prepared and their applications in biomolecular diagnostics and skin antifungal therapy are investigated.

Polymerase chain reaction (PCR) is the gold standard for highly sensitive molecular diagnostics of target nucleic acids. Compared with conventional PCR which is limited by sophisticated equipment and lengthy detection time, plasmonic photothermal (PPT)- PCR has been considered as the next-generation PCR technology, which benefits from the ultrafast thermocycling and low cost. However, it still has some disadvantages, like 1) the limit of detection (LOD) will be limited by the quenching effect between the plasmonic materials and the fluorophore used for subsequent analysis. 2) Most PPT- PCR platform can only support for one target detection, while the detection of several targets at the same time is needed in the reality. Herein, a plasmonic magnetic nanocomposite composed by Fe₃O₄ core and Au shell (PMN) is constructed for detecting 4 different targets simultaneously through multiplex PPT-PCR. Photothermal property contributes for rapid thermocycling of PCR, and magnetic property contributes for easy separation of PMN to decrease the quenching effect. This molecular diagnostic platform achieves the detection of 4 kinds of target simultaneously, which is beneficial for the rapid multiple clinical diagnostics.

On the other hand, the threat to human health caused by fungal infections cannot be ignored. Candida albicans is one of the most common fungi which can cause skin infection, and quite stubborn, not easy to eradicate. Due to the special structure of fungal cells, skin cells are much more fragile than the fungal cells, thus it is quite challengeable that keeping the safety of normal skin when operating the antifungal treatments. Herein, a specific modified gold nanoheater (AuNR) is designed to link with C. albicans directly, and the C. albicans on skin can be killed effectively under the irradiation of a commercial near-infrared (NIR) lamp. This study provides a promising strategy for the localized photothermal sterilization of skin fungal infection.