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Upconverting nanophosphors (UCNPs) absorb two or more photons at 980nm and emit a higher energy photon in the visible range. UCNPs provide distinct advantages as biological imaging agents in that they have no autofluorescence, don’t photobleach, are capable of deep tissue imaging, exhibit no blinking, and are physically robust. Through surface modifications with an amphiphilic polymer, we can not only functionalize UCNPs for targeted imaging, but also tether them to plasmonic nanoparticles such as gold nanorods (AuNRs) for enhanced upconversion and multifunctionality.
We developed a process to construct UCNP-AuNR nanoclusters using polyethylene glycol. The UCNP-AuNR nanocluster is further modified with an anti-epidermal growth factor receptor (aEGFR), allowing specific binding to bladder cancer cells that highly express epidermal growth factor receptor. Once the nanoclusters bind to the cell membrane we can (1) perform targeted and high contrast imaging of the bladder cancer cells and (2) utilize localized surface plasmon of AuNRs to selectively kill the cells in situ upon detection by UCNP fluorescence.
Successful conjugation and integrity of the UCNP-AuNR nanoclusters were confirmed via electron microscopy. Then, through a combination of brighftield, confocal upconversion fluorescence, and infrared darkfield microscopy we demonstrate selective binding and high-contrast upconversion imaging of the bladder cancer cells. Finally, through a series of in vitro studies, we demonstrate two different methods of cell killing. First, with a continuous wave laser, we demonstrate effective thermal ablation of cells. Second, with a femtosecond pulse laser, we demonstrate optoporation of the cell membrane that allows increased uptake of drugs.
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