Abstract
Fluorescence-amplified far-red/near-infrared (FR/NIR) nanoparticles (NPs) are synthesized by co-encapsulation of conjugated polymer donor (poly[9,9-bis(2-(2-(2-methoxyethoxy)ethoxy)ethyl)fluorenyldivinylene]; PFV) and a fluorogen acceptor (2-(2,6-bis((E)-4-(phenyl(4'-(1,2,2-triphenylvinyl)-[1,1'-biphenyl]-4-yl)amino)styryl)-4H-pyran-4-ylidene)malononitrile; TPE-TPA-DCM) with aggregation-induced emission (AIE) characteristics using biocompatible bovine serum albumin (BSA) as the encapsulation matrix. The good spectral overlap and close proximity between PFV and TPE-TPA-DCM in BSA NPs result in a 5.3-fold amplified TPE-TPA-DCM emission signal via fluorescence resonance energy transfer (FRET). The obtained PFV/TPE-TPA-DCM co-loaded BSA NPs are spherical in shape with a large Stokes shift of ∼223 nm and low cytotoxicity. The BSA matrix allows further functionalization with arginine-glycine-aspartic acid (RGD) peptide to yield fluorescent probes for specific recognition of integrin receptor-overexpressed cancer cells. The advantage of PFV amplified FR/NIR signal from TPE-TPA-DCM is further demonstrated in cellular and in vivo imaging using HT-29 colon cancer cells and a murine hepatoma H22 tumor-bearing mouse model, respectively. The high FR/NIR fluorescence and specific cancer targeting ability by RGD surface functionalization make the PFV/TPE-TPA-DCM co-loaded BSA-RGD NPs a unique FR/NIR fluorescent probe for cellular imaging and in vivo tumor diagnosis in a high contrast and selective manner.
Highlights
Development of efficient fluorescent probes with intense far-red/near-infrared (FR/NIR) emission (>650 nm) and large Stokes shifts is of great importance in cancer research.[1]
Recent studies have revealed that conjugated polymers (CPs)-based nanoprobes show high brightness, good photostability and low cytotoxicity, which make them ideal candidates for in vitro and in vivo imaging applications.[2c,13,21] By virtue of these desirable features, a CP is selected in this study to pair with an FR/NIR aggregation-induced emission (AIE) luminogen to constitute the first signal amplified FR/NIR probe for live-animal imaging and cancer diagnosis
These results suggest that more PFV/TPE-TPA-DCM co-loaded bovine serum albumin (BSA)-RGD NPs are internalized by HT-29 cancer cells due to specific binding between RGD and integrin receptors overexpressed in HT-29 cells.[25]
Summary
Development of efficient fluorescent probes with intense far-red/near-infrared (FR/NIR) emission (>650 nm) and large Stokes shifts is of great importance in cancer research.[1]. As compared to sophisticated chemical modifications to improve the brightness of each fluorophore, fluorescence resonance energy transfer (FRET) is a powerful spectroscopic tool to enhance fluorescence signals and increase apparent Stokes shift of fluorescent probes for biological sensing and imaging.[14] It takes advantage of the light-harvesting property of the donor to enhance the acceptor fluorescence when they are within close proximity.[15] In this regard, conjugated polymers (CPs) are effective light-harvesting energy donors due to their π-conjugated backbones and large absorption coefficients,[16] which have been reported to enhance the fluorescence of various fluorescent materials, such as organic fluorophores,[17] fluorescent proteins,[18] QDs[19] and gold nanoclusters.[20] In addition, recent studies have revealed that CP-based nanoprobes show high brightness, good photostability and low cytotoxicity, which make them ideal candidates for in vitro and in vivo imaging applications.[2c,13,21] By virtue of these desirable features, a CP is selected in this study to pair with an FR/NIR AIE luminogen to constitute the first signal amplified FR/NIR probe for live-animal imaging and cancer diagnosis. This study opens up new opportunities for the development of a new generation of promising probes for the advancement of bioimaging
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