Molecular Interactions in Organic Nanoparticles for Phototheranostic Applications

Recent Progress in Light-Triggered Nanotheranostics for Cancer Treatment

Treatments of high specificity are desirable for cancer therapy. Light-triggered nanotheranostics (LTN) mediated cancer therapy could be one such treatment, as they make it possible to visualize and treat the tumor specifically in a light-controlled manner with a single injection. Because of their great potential in cancer therapy, many novel and powerful LTNs have been developed, and are mainly prepared from photosensitizers (PSs) ranging from small organic dyes such as porphyrin- and cyanine-based dyes, semiconducting polymers, to inorganic nanomaterials such as gold nanoparticles, transition metal chalcogenides, carbon nanotubes and graphene. Using LTNs and localized irradiation in combination, complete tumor ablation could be achieved in tumor-bearing animal models without causing significant toxicity. Given their great advances and promising future, we herein review LTNs that have been tested in vivo with a highlight on progress that has been made in the past a couple of years. The current challenges faced by these LTNs are also briefly discussed.

Chlorosome-Inspired Synthesis of Templated Metallochlorin-Lipid Nanoassemblies for Biomedical Applications

Chlorosomes are vesicular light-harvesting organelles found in photosynthetic green sulfur bacteria. These organisms thrive in low photon flux environments due to the most efficient light-to-chemical energy conversion, promoted by a protein-less assembly of chlorin pigments. These assemblies possess collective absorption properties and can be adapted for contrast-enhanced bioimaging applications, where maximized light absorption in the near-infrared optical window is desired. Here, we report a strategy for tuning light absorption toward the near-infrared region by engineering a chlorosome-inspired assembly of synthetic metallochlorins in a biocompatible lipid scaffold. In a series of synthesized chlorin analogues, we discovered that lipid conjugation, central coordination of a zinc metal into the chlorin ring, and a 3(1)-methoxy substitution were critical for the formation of dye assemblies in lipid nanovesicles. The substitutions result in a specific optical shift, characterized by a bathochromically shifted (72 nm) Qy absorption band, along with an increase in absorbance and circular dichroism as the ratio of dye-conjugated lipid was increased. These alterations in optical spectra are indicative of the formation of delocalized excitons states across each molecular assembly. This strategy of tuning absorption by mimicking the structures found in photosynthetic organisms may spur new opportunities in the development of biophotonic contrast agents for medical applications.

Long-Time Plasma Membrane Imaging Based on a Two-Step Synergistic Cell Surface Modification Strategy

Long-time stable plasma membrane imaging is difficult due to the fast cellular internalization of fluorescent dyes and the quick detachment of the dyes from the membrane. In this study, we developed a two-step synergistic cell surface modification and labeling strategy to realize long-time plasma membrane imaging. Initially, a multisite plasma membrane anchoring reagent, glycol chitosan-10% PEG2000 cholesterol-10% biotin (abbreviated as "GC-Chol-Biotin"), was incubated with cells to modify the plasma membranes with biotin groups with the assistance of the membrane anchoring ability of cholesterol moieties. Fluorescein isothiocyanate (FITC)-conjugated avidin was then introduced to achieve the fluorescence-labeled plasma membranes based on the supramolecular recognition between biotin and avidin. This strategy achieved stable plasma membrane imaging for up to 8 h without substantial internalization of the dyes, and avoided the quick fluorescence loss caused by the detachment of dyes from plasma membranes. We have also demonstrated that the imaging performance of our staining strategy far surpassed that of current commercial plasma membrane imaging reagents such as DiD and CellMask. Furthermore, the photodynamic damage of plasma membranes caused by a photosensitizer, Chlorin e6 (Ce6), was tracked in real time for 5 h during continuous laser irradiation. Plasma membrane behaviors including cell shrinkage, membrane blebbing, and plasma membrane vesiculation could be dynamically recorded. Therefore, the imaging strategy developed in this work may provide a novel platform to investigate plasma membrane behaviors over a relatively long time period.

“Smart” gold nanoparticles for photoacoustic imaging: an imaging contrast agent responsive to the cancer microenvironment and signal amplification via pH-induced aggregation

pH-Responsive “smart” gold nanoparticles were demonstrated as a new photoacoustic imaging agent that can selectively respond to the cancer microenvironment and show the amplified signal in vivo.

Decoration of porphyrin with tetraphenylethene: converting a fluorophore with aggregation-caused quenching to aggregation-induced emission enhancement

A new porphyrin derivative with aggregation-induced emission enhancement was synthesized via tetraphenylethene decoration and it demonstrates bright imaging ability in vitro.

SPION@Cu2−xS nanoclusters for highly sensitive MRI and targeted photothermal therapy of hepatocellular carcinoma

The diagnostic function of SPIONs and photo-thermal therapeutic function of CuS NPs have been incorporated into a single nanoplatform for biomedical applications.

Protection of densely populated excited triplet state ensembles against deactivation by molecular oxygen

Different approaches towards protection of triplet excited states against deactivation by molecular oxygen are summarized and reviewed.

Two-photon excitation nanoparticles for photodynamic therapy

Integration of the two-photon excitation (TPE) technique and nanomaterials to construct TPE nanoparticle-based photosensitizers for PDT is summarized and reviewed.