Cancer is one of the most serious threats to human health, not only because of the frequency of disease but also because of the severe side effects experienced by the patience during the chemotherapy and radiotherapy treatments, such as immunosuppression and drug resistance. Surgery, as a treatment method, does circumvent some of the side effect issues; however, it is highly invasive and not always possible. In this respect, Photodynamic Therapy (PDT), which localizes the harmful effects of the sensitizer to areas exposed to radiation, has attracted considerable interest as an alternative, minimally invasive treatment, potentially offering no long-term side effects. In search for PDT agents, conjugated polymers nanoparticles (CPNs) have proven themselves to be a versatile class of materials, with many advantageous properties for biomedical applications.
Here, we report the development of CPNs with absorption and emission bands in the 1st near-infrared (NIR) biological transparency window, for combined NIR bioimaging and PDT application. We show that the synthesis procedure of the CPNs can be optimised to achieve CPNs of highest possible fluorescence quantum yield and singlet oxygen production, by varying the ratio of the conjugated polymer and stabilizing copolymer in the precursor solution, as well as changing its pH. We further demonstrate the feasibility of our CPNs for the combined NIR bioimaging/PDT applications on a range of different cancerous and normal cell lines. Furthermore, we show that by modifying our CPNs with a tumour-specific ligand, specific cancerous cell lines can be targeted.
Controlled manipulation and trapping of submicron-size particles has many applications in different research fields, including those in the general areas of biology and soft-condensed matter physics. Optical tweezers that make use of strongly focused laser beams are widely used for this purpose. However, their trapping abilities are substantially limited by diffraction and a lack of scalability. To overcome this, nanostructures made of plasmonic materials have attracted significant attention, as their ability to concentrate energy to very small dimensions can be exploited to generate optical traps capable of acting on nanometer-size objects. Furthermore, and when compared to conventional systems, these plasmonic traps also provide large field enhancements that allow for lower input powers. Despite such advantages, these techniques still lack the ability to provide the controlled manipulation of the trapped objects over long distances.
In this work we present a Brownian ratchet, based on plasmonic interactions, which can optically trap and manipulate dielectric nanometer-sized beads over long distances. For this purpose, the geometries of the plasmonic ratchets and the respective electric fields were modelled with COMSOL Multiphysics, and the optical forces experienced by the beads were calculated with COMSOL Multiphysics and processed with MATLAB®. Additionally, we experimentally demonstrate the rectification of the random thermal motion of subwavelength dielectric beads into one specific direction by periodically turning on and off a laser beam that illuminates the plasmonic nanostructure array and exploiting the asymmetries in the system.
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