Red-Emissive Cell-Penetrating Polymer Dots Exhibiting Thermally Activated Delayed Fluorescence for Cellular Imaging

Abstract

Fluorescence imaging in living cells is key to understanding many biological processes, yet autofluorescence from the sample can lower sensitivity and hinder high-resolution imaging. Time-gated measurements using phosphorescent metal complexes can improve imaging, at the cost of potential toxicity from the use of heavy metals. Here, we describe orange/red-emitting polymer dots (Pdots) exhibiting thermally activated delayed fluorescence (TADF) for time-gated imaging. Inspired by the cell invasion mechanism of the HIV TAT protein, the Pdots were formed from block copolymers composed of a hydrophilic guanidine-rich block as a cell-penetrating peptide mimic, and a rigid organic semiconductor block to provide efficient delayed fluorescence. These all-organic polymer nanoparticles were shown to efficiently enter HeLa, CHO, and HepG2 cells within 30 min, with cell viabilities remaining high for Pdot concentrations up to 25 mg mL–1. Pdot quantum yields were as high as 0.17 in aerated water, with the Pdot structure effectively shielding the TADF emitters from quenching by oxygen. Colocalization experiments revealed that the Pdots primarily accumulate outside of lysosomes, minimizing lysosomal degradation. When used for fixed cellular imaging, Pdot-incubated cells showed high signal-to-background ratios compared to control samples with no Pdot exposure. Using time-resolved spectroscopy, the delayed emission of the TADF materials was effectively separated from that of both a biological serum and a secondary fluorescent dye.

Visible Light and Glutathione Dually Responsive Delivery of a Polymer-Conjugated Temozolomide Intermediate for Glioblastoma Chemotherapy

“…As aforementioned, disulfide bonds are highly tolerant to the low level of lysosomal GSH and pH conditions, which disfavor intracellular prodrug activation if P1NP enters cells via endocytosis, known as the most normal pathway for anionic nanomaterials without decoration of cell-penetrating ligands. − Strong reducing agent tris­(2 carboxyethyl)­phosphine hydrochloride could be more efficient in inducing disulfide bond scission, but the poor permeability to the cell membrane limited its use. Currently, how to effectively induce cleavage of disulfide bonds of nanomaterials trapped in lysosome compartments remains a big challenge frequently ignored.…”

Polymer dots and glassy organic dots using dibenzodipyridophenazine dyes as water-dispersible TADF probes for cellular imaging

“…A Pdot is a water-dispersed nanoparticle consisting of 450% organic semiconductor polymer by weight or volume, and we and others have recently shown that nanoparticles with a guanidinium-rich corona block and TADFactive core block can quickly enter mammalian cells by acting as mimics for cation-rich cell-penetrating peptides. 19,41 Here, TADF dye-loaded nanoparticles are instead prepared by encapsulating small-molecule emitters into the nanoparticle core via self-assembly. 19,42,43 Next, dyes were encapsulated into glassy organic dots (g-Odots), formed by liquefying a small-molecule organic semiconductor in the presence of TADF dye and a surfactant at high temperature under microwave irradiation.…”

TADF-based NIR-II semiconducting polymer dots for in vivo 3D bone imaging

“…Algar and Hudson's groups recently developed red-emissive TADF-grafted Pdots for time-gated cellular imaging with high contrast. 74 For NIR-II imaging, fortunately, the autofluorescence is less considered because of the significantly reduced autofluorescence in the NIR-II window.…”