The majority of organic near-infrared emitters utilized in diagnostic and therapeutic imaging exhibit low quantum yields when optically excited. In an effort to reduce the background noise and to localize the emission, it is advantageous to “activate” the emission only in regions of interest. To this end, a colloidal nanoparticle platform was developed that can facilitate the transfer of quenched NIR fluorophores to the interior of cells and only within the cells is the emission permitted. This platform is demonstrated with sub-100 nm poly(propargyl acrylate) (PA) nanoparticles that have been surface modified with an azide modified bovine serum albumin (azBSA). The azBSA was covalently attached to the particles through a copper catalyzed azide alkyne Huisgen cycloaddition (i.e. “click” transformation). To the azBSA, alkyne modified silicon phthalocyanine (akSiPc) fluorophores were attached through a click reaction. As a free molecule in phosphate-buffered saline (PBS), the akSiPc exhibited a 780 nm emission with a 630 nm excitation, though once attached to the PA particles via the azBSA, the emission was quenched. The emission of the akSiPc could be recovered with the incubation of the PA/BSA/akSiPc particles with trypsin, a protease which cleaves peptide chains. The trypsin digested the azBSA and “freed” the quenched akSiPc. The PA/BSA/akSiPc particles were incubated with human non-small cell lung cancer cells (A549) and live cell scanning confocal microscopy at varying time points was employed to study the particles uptake into the cells and subsequent emission activation. It was speculated that particles localized in the lysosomes of the cells where the azBSA was digested, releasing the fluorophores.

Reducing background noise in near-infrared medical imaging: Routes to activated fluorescing through surface modification of colloidal particles

251st National Meeting (2016)

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