The effects of lanthanide-doped upconverting nanoparticles on cancer cell biomarkers

3D-printed aerogels as theranostic implants monitored by fluorescence bioimaging

Aerogel scaffolds are nanostructured materials with beneficial properties for tissue engineering applications. The tracing of the state of the aerogels after their implantation is challenging due to their variable biodegradation rate and the lack of suitable strategies capable of in vivo monitoring the scaffolds. Upconversion nanoparticles (UCNPs) have emerged as advanced tools for in vitro bioimaging because of their fluorescence properties. In this work, highly fluorescent UCNPs were loaded into aerogels to obtain theranostic implants for tissue engineering and bioimaging applications. 3D-printed alginate-hydroxyapatite aerogels labeled with UCNPs were manufactured by 3D-printing and supercritical CO2 drying to generate personalize-to-patient aerogels. The physicochemical performance of the resulting structures was evaluated by printing fidelity measurements, nitrogen adsorption-desorption analysis, and different microscopies (confocal, transmission and scanning electron microscopies). Stability of the aerogels in terms of physicochemical properties was also tested after 3 years of storage. Biocompatibility was evaluated in vitro by different cell and hemocompatibility assays, in ovo and in vivo by safety and bioimaging studies using different murine models. Cytokines profile, tissue index and histological evaluations of the main organs unveiled an in vivo downregulation of the inflammation after implantation of the scaffolds. UCNPs-decorated aerogels were first-time manufactured and long-term traceable by fluorescence-based bioimaging until 3 weeks post-implantation, thereby endorsing their suitability as tissue engineering and theranostic nanodevices (i.e. bifunctional implants).

Silica-coated LiYF4:Yb3+, Tm3+ upconverting nanoparticles are non-toxic and activate minor stress responses in mammalian cells

Lanthanide-doped upconverting nanoparticles (UCNPs) are ideal candidates for use in biomedicine. The interaction of nanomaterials with biological systems determines whether they are suitable for use in living cells. In-depth knowledge of the nano-bio interactions is therefore a pre-requisite for the development of biomedical applications. The current study evaluates fundamental aspects of the NP-cell interface for square bipyramidal UCNPs containing a LiYF4:Yb3+, Tm3+ core and two different silica surface coatings. Given their importance for mammalian physiology, fibroblast and renal proximal tubule epithelial cells were selected as cellular model systems. We have assessed the toxicity of the UCNPs and measured their impact on the homeostasis of living non-malignant cells. Rigorous analyses were conducted to identify possible toxic and sub-lethal effects of the UCNPs. To this end, we examined biomarkers that reveal if UCNPs induce cell killing or stress. Quantitative measurements demonstrate that short-term exposure to the UCNPs had no profound effects on cell viability, cell size or morphology. Indicators of oxidative, endoplasmic reticulum, or nucleolar stress, and the production of molecular chaperones varied with the surface modification of the UCNPs and the cell type analyzed. These differences emphasize the importance of evaluating cells of diverse origin that are relevant to the intended use of the nanomaterials. Taken together, we established that short-term, our square bipyramidal UCNPs are not toxic to non-malignant fibroblast and proximal renal epithelial cells. Compared with established inducers of cellular stress, these UCNPs have minor effects on cellular homeostasis. Our results build the foundation to explore square bipyramidal UCNPs for future in vivo applications.

Combining Pr3+-Doped Nanoradiosensitizers and Endogenous Protoporphyrin IX for X-ray-Mediated Photodynamic Therapy of Glioblastoma Cells

Glioblastoma multiforme is an aggressive type of brain cancer with high recurrence rates due to the presence of radioresistant cells remaining after tumor resection. Here, we report the development of an X-ray-mediated photodynamic therapy (X-PDT) system using NaLuF₄:25% Pr³⁺ radioluminescent nanoparticles in conjunction with protoporphyrin IX (PPIX), an endogenous photosensitizer that accumulates selectively in cancer cells. Conveniently, 5-aminolevulinic acid (5-ALA), the prodrug that is administered for PDT, is the only drug approved for fluorescence-guided resection of glioblastoma, enabling dual detection and treatment of malignant cells. NaLuF₄:Pr³⁺ nanoparticles were synthesized and spectroscopically evaluated at a range of Pr³⁺ concentrations. This generated radioluminescent nanoparticles with strong emissions from the ¹S₀ excited state of Pr³⁺, which overlaps with the Soret band of PPIX to perform photodynamic therapy. The spectral overlap between the nanoparticles and PPIX improved treatment outcomes for U251 cells, which were used as a model for the thin tumor margin. In addition to sensitizing PPIX to induce X-PDT, our nanoparticles exhibit strong radiosensitizing properties through a radiation dose-enhancement effect. We evaluate the effects of the nanoparticles alone and in combination with PPIX on viability, death, stress, senescence, and proliferation. Collectively, our results demonstrate this as a strong proof of concept for nanomedicine.

Luminescence Tunable Europium and Samarium Complexes: Reversible On/Off Switching and White-Light Emission

Single-molecule functional materials with luminescence tunable by external stimuli are of increasing interest due to their application in sensors, display devices, biomarkers, and switches. Herein, new europium and samarium complexes with ligands having triphenylamine (TPA) groups as the redox center and 2,2'-bipyridine (bpy) as the coordinating groups and diketonate (tta) as the second ligand have been constructed. The complexes show white-light emission in selected solvents for proper mixtures of the emission from Ln³⁺ ions and the ligands. Meanwhile, they exhibit reversible luminescence switching on/off properties by controlling the external potential owing to intramolecular energy transfer from the Ln³⁺ ions to the electrochemically generated radical cation of TPA^•+. Time-dependent density functional theory (TD-DFT) calculations have been performed to study the electronic spectra. The proposed intramolecular energy transfer processes have been verified by density functional theory (DFT) studies.

Ionic aggregation-induced emission dye with bulky counterions for preparation of bright near-infrared polymeric nanoparticles

Dyes exhibiting aggregation-induced emission (AIE) are attractive building blocks for the preparation of bright fluorescent nanomaterials. AIEgens are especially efficient in pure dye aggregates, whereas they are much less explored as dopants in NPs built of hydrophobic polymers. Here, we describe an approach that combines cationic AIEgens with bulky hydrophobic counterions (fluorinated tetraphenylborates) that enables preparation of small and bright AIEgen-loaded polymeric NPs. To this end, we synthesised a cationic tetraphenylethylene (TPE) derivative and studied its salts with counterions of different sizes and hydrophobicities. In organic solvent/water mixtures, all these salts exhibited typical AIE behaviour, whereas only salts with bulky hydrophobic counterions exhibited strongly red-shifted emission in the near-infrared (NIR) region. Encapsulation of these salts into poly(methyl methacrylate-co-methacrylic acid) (PMMA-MA) NPs revealed that bulky counterions ensure (i) formation of small (∼50 nm) AIEgen-loaded polymeric NPs; (ii) good fluorescence quantum yield (up to 30%); and (iii) NIR emission reaching 700 nm. By contrast, AIEgens with small inorganic anions (perchlorate and hexafluorophosphate) blended with PMMA-MA produced large aggregates with emission in the far-red region. Single-particle microscopy revealed that our 50 nm AIEgen-loaded PMMA-MA NPs were 6-fold brighter than the NIR emitting quantum dots (QD705). These NPs feature low cytotoxicity and compatibility with live cell imaging, in contrast to large aggregates of AIEgens with small inorganic counterions that failed to internalize into the cells. The present work shows that combination of cationic AIEgens with bulky counterions opens new routes for the preparation of bright polymer-based nanomaterials.

Emerging applications of upconverting nanoparticles in intestinal infection and colorectal cancer

Colorectal cancer is the abnormal growth of cells in colon or rectum. Recent findings have acknowledged the role of bacterial infection and chronic inflammation in colorectal cancer initiation and progression. In order to detect and treat precancerous lesions, new tools are required, which may help to prevent or identify colorectal cancer at an early stage. To date, several different screening tests are available, including endoscopy, stool-based blood tests, and radiology-based tests. However, these analyses either lack sensitivity or are of an invasive nature. The use of fluorescently labeled probes can increase the detection sensitivity. However, autofluorescence, photobleaching, and photodamage are commonly encountered problems with fluorescence imaging. Upconverting nanoparticles (UCNPs) are recently developed lanthanide-doped nanocrystals that can be used as light-triggered luminescent probes and in drug delivery systems. In this review, we comprehensively summarize the recent developments and address future prospects of UCNP-based applications for diagnostics and therapeutic approaches associated with intestinal infection and colorectal cancer.