Mesoporous polyacrylic acid/calcium phosphate coated persistent luminescence nanoparticles for improved afterglow bioimaging and chemotherapy of bacterial infection

Coating mesoporous drug carriers on the surface of persistent luminescence nanoparticles (PLNPs) not only allows continuous luminous imaging without spontaneous fluorescence interference, but also provides drug release guidance. However, in most cases, the encapsulation of the drug-loaded shells significantly reduces the luminescence of PLNPs, which is unfavorable for bioimaging. In addition, conventional drug-loaded shells alone, such as silica shells, have difficulty in achieving responsive fast drug release. Herein, we report the fabrication of mesoporous polyacrylic acid (PAA)/calcium phosphate (CaP) shell-coated PLNPs (PLNPs@PAA/CaP) for improved afterglow bioimaging and drug delivery. The encapsulation of the PAA/CaP shell effectively prolonged the decay time and enhanced the sustained luminescence of PLNPs by about three times due to the passivation of the surface defects of PLNPs by the shell, and the energy transfer between the shell and PLNPs. Meanwhile, the mesoporous structure and negative charge of the PAA/CaP shells enabled the prepared PLNPs@PAA/CaP to carry the positively charged drug doxycycline hydrochloride efficiently. Under the acidic conditions of bacterial infection, the degradation of PAA/CaP shells and the ionization of PAA enabled fast drug release for effective killing of bacteria at the infection site. The excellent persistent luminescence properties, outstanding biocompatibility, and rapid responsive release feature make the prepared PLNPs@PAA/CaP a promising nanoplatform for diagnostic and therapeutic applications.

pH-Triggered Aggregation of Gold Nanoparticles for Enhanced Labeling and Long-Term CT Imaging Tracking of Stem Cells in Pulmonary Fibrosis Treatment

Gold nanoparticles (AuNPs) pose a great challenge in the development of nanotracers that can self-adaptively alter their properties in response to certain cellular environments for long-term stem cell tracking. Herein, pH-sensitive Au nanotracers (CPP-PSD@Au) are fabricated by sequential coupling of AuNPs with sulfonamide-based polymer (PSD) and cell-penetrating peptide (CPP), which can be efficiently internalized by mesenchymal stem cells (MSCs) and undergo pH-induced self-assembly in endosomes, facilitating long-term computed tomography (CT) imaging tracking MSCs in a murine model of idiopathic pulmonary fibrosis (IPF). Using the CPP-PSD@Au, the transplanted MSCs for the first time can be monitored with CT imaging for up to 35 days after transplantation into the lung of IPF mice, clearly elucidating the migration process of MSCs in vivo. Moreover, we preliminarily explored the mechanism of the CPP-PSD@Au labeled MSCs in the alleviation of IPF, including recovery of alveolar integrity, decrease of collagen deposition, as well as down-regulation of relevant cytokine level. This work facilitates our understanding of the behavior and effect of MSCs in the therapy of IPF, thereby providing an important insight into the stem cell-based treatment of lung diseases.

Synthesis and luminescence properties of a broadband near-infrared emitting non-gallate persistent luminescence Mg1.4Zn0.6SnO4:Cr3+ phosphor

A series of novel non-gallate near-infrared long-persistent phosphorescence Mg2-xZnxSnO4:Cr3+ phosphors were synthesized, and their structure and luminescence properties were investigated systematically. Under 448 nm blue light excitation, all the phosphors exhibit a broad emission band centered at 730 nm and a shoulder peak at 708 nm, which are attributed to the 4T2(4F) → 4A2 and 2E → 4A2 transitions of Cr3+, respectively. The excitation spectra of the samples clearly show the characteristic excitation of Cr3+ in the octahedral crystal field, with three obvious peaks at 324, 448 and 620 nm respectively. The phosphor with a composition of Mg1.4Zn0.6SnO4:0.03Cr3+ shows the strongest photoluminescence intensity which is 2.87 times and 3.09 times that of Mg2SnO4:0.03Cr3+ and Zn2SnO4:0.03Cr3+, respectively. Besides, all the samples show intense near-infrared long-persistent phosphorescence. For the optimized sample Mg1.4Zn0.6SnO4:0.005Cr3+, its phosphorescence can still be observed with a night vision instrument 18 h after removing the 365 nm UV light source. Finally, a feasible phosphorescence mechanism of the Mg1.4Zn0.6SnO4:Cr3+ phosphor was proposed and discussed. This study may provide a new method for developing novel near-infrared long-persistent phosphorescence phosphors through crystal structure modification.