Abstract
In this work, we describe the fabrication of self-assembled polyelectrolyte nanoparticles that provide a multicolor optical imaging modality. Poly(γ-glutamic acid)(γ-PGA) formed self-assembled nanoparticles through electrostatic interactions with two different cationic polymers: poly(L-lysine)(PLL) and chitosan. The self-assembled γ-PGA/PLL and γ-PGA/chitosan nanoparticles were crosslinked by glutaraldehyde. Crosslinking of the ionic self-assembled nanoparticles with glutaraldehyde not only stabilized the nanoparticles but also generated a strong autofluorescence signal. Fluorescent Schiff base bonds (C=N) and double bonds (C=C) were generated simultaneously by crosslinking of the amine moiety of the cationic polyelectrolytes with monomeric glutaraldehyde or with polymeric glutaraldehyde. The unique optical properties of the nanoparticles that resulted from the crosslinking by glutaraldehyde were analyzed using UV/Vis and fluorescence spectroscopy. We observed that the fluorescence intensity of the nanoparticles could be regulated by adjusting the crosslinker concentration and the reaction time. The nanoparticles also exhibited high performance in the labeling and monitoring of therapeutic immune cells (macrophages and dendritic cells). These self-assembled nanoparticles are expected to be a promising multicolor optical imaging contrast agent for the labeling, detection, and monitoring of cells.
Highlights
The design and synthesis of functional nanomaterials have attracted considerable interest in the fields of biology and medicine because of their potential applications in the diagnosis and treatment of diseases [1,2,3,4,5]
The ideal fluorophore for fluorescence imaging must function without being conjugated to any fluorescent materials and should be non-toxic because the fluorophore itself can alter the intrinsic behavior of labeling targets [14]
The synthesis of functional polyelectrolyte nanoparticles that provided optical imaging modalities was performed via electrostatic assembly and crosslinking without any fluorescent materials
Summary
The design and synthesis of functional nanomaterials have attracted considerable interest in the fields of biology and medicine because of their potential applications in the diagnosis and treatment of diseases [1,2,3,4,5]. The ideal fluorophore for fluorescence imaging must function without being conjugated to any fluorescent materials and should be non-toxic because the fluorophore itself can alter the intrinsic behavior of labeling targets [14] Based on these requirements, metal and semiconductor quantum dots are not ideal fluorescence imaging probes. Multifunctional nanoparticles that contained both fluorescence imaging probes and therapeutic drugs have been developed for theranostic applications [1,2,8,15,16] In this process, various organic solvents were used to encapsulate fluorescence optical imaging probes into the nanoparticle matrix. We describe fluorophore-free autofluorescent nanoparticles as a novel type of optical imaging nanoprobe [17,18,19] These nanoparticles are generated through the electrostatic assembly and crosslinking of biocompatible polyelectrolytes in aqueous solutions. We have shown that this novel optical imaging nanoprobe exhibited high performance in the labeling and monitoring of therapeutic immune cells both in vitro and in vivo
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