Opportunities for Persistent Luminescent Nanoparticles in Luminescence Imaging of Biological Systems and Photodynamic Therapy

Current Developments in Emerging Lanthanide-Doped Persistent Luminescent Scintillators and Their Applications

Lanthanide-doped scintillators have the ability to convert the absorbed X-ray irradiation into ultraviolet (UV), visible (Vis), or near-infrared (NIR) light. Lanthanide-doped scintillators with excellent persistent luminescence (PersL) are emerging as a new class of PersL materials recently. They have attracted great attention due to their unique "self-luminescence" characteristic and potential applications. In this review, we comb through and focus on current developments of lanthanide-doped persistent luminescent scintillators (PersLSs), including their PersL mechanism, synthetic methods, tuning of PersL properties (e. g. emission wavelength, intensity, and duration time), as well as their promising applications (e. g. information storage, encryption, anti-counterfeiting, bio-imaging, and photodynamic therapy). We hope this review will provide valuable guidance for the future development of PersLSs.

Bacterial outer membrane vesicles as drug delivery carrier for photodynamic anticancer therapy

Photodynamic Therapy (PDT) is an effective tumor treatment strategy that not only induces photocytotoxicity to kill tumor cells directly but also activates the immune system in the body to generate tumor-specific immunity, preventing cancer metastasis and recurrence. However, some limitations of PDT limit the therapeutic efficacy in deep tumors. Previous studies have used different types of nanoparticles (NPs) as drug carriers of photosensitizers (PSs) to overcome the shortcomings of PDT and improve therapeutic efficacy. Among them, bacterial outer membrane vesicles (OMVs) have natural advantages as carriers for PS delivery. In addition to the targeted delivery of PSs into tumor cells, their unique immunogenicity helps them to serve as immune adjuvants to enhance the PDT-induced immune effect, providing new ideas for photodynamic anticancer therapy. Therefore, in this review, we will introduce the biogenesis and anticancer functions of OMVs and the research on them as drug delivery carriers in PDT. Finally, we also discuss the challenges and prospects of OMVs as a versatile drug delivery carrier for photodynamic anticancer therapy.

Advanced techniques for performing photodynamic therapy in deep-seated tissues

Photodynamic therapy (PDT) is a promising localized cancer treatment modality. It has been used successfully to treat a range of dermatological conditions with comparable efficacy to conventional treatments. However, some drawbacks limit the clinical utility of PDT in treating deep-seated tumors. Notably, the penetration limitation of UV and visible light, commonly applied to activate photosensitizers, makes PDT incompetent in treating deep-seated tumors. Development in light delivery technologies, especially fiber optics, led to improved clinical strategies for accessing deep tissues for irradiation. However, PDT efficacy issues remained partly due to light penetration limitations. In this review, we first summarized the current PDT applications for deep-seated tumor treatment. Then, the most recent progress in advanced techniques to overcome the light penetration limitation in PDT, including using functional nanomaterials that can either self-illuminate or be activated by near-infrared (NIR) light and X-rays as transducers, and implantable light delivery devices were discussed. Finally, current challenges and future opportunities of these technologies were discussed, which we hope may inspire the development of more effective techniques to enhance PDT efficacy against deep-seated tumors.

Tuning the persistent luminescence property of a Y3Al2Ga3O12:Ce3+,Yb3+ phosphor by controlling the intrinsic oxygen vacancy concentration

Oxygen vacancies (V_O), acting as electron traps, have a significant impact on the persistent luminescence (PersL) property of persistent phosphors. However, the effect of V_O on PersL remains still unclear enough to limit the development of PersL materials. In this study, the V_O concentration of the Y_2.978Ce_0.018Yb_0.004Al₂Ga₃O₁₂ phosphor is accurately controlled by annealing in air and 10%H₂/90%Ar atmospheres at various temperatures. The results show as the annealing temperature increases during the air annealing the V_O concentration, the PersL durations, and the thermoluminescence (TL) intensity constantly decreases, and the three data coincide well with each other, indicating the PersL property of the Y_2.978Ce_0.018Yb_0.004Al₂Ga₃O₁₂ is successfully tuned. Besides, the trap structure of the Y_2.978Ce_0.018Yb_0.004Al₂Ga₃O₁₂ and the charge compensation effect of Yb ions on V_O defects are also discussed. By deconvoluting the TL curves, the Yb trap with a depth of 0.58 eV has been distinctly separated from the V_O traps with a quasi-continuous and broad distribution of depths ranging from 0.58 to 1.21 eV. Our work demonstrates a better understanding of the relationship between V_O and PersL is of great significance to design a high-performance phosphor.

Flexible translucent persistent luminescent films based on Sr2MgSi2O7:Eu2+,Dy3+ cellulose ether composites

Persistent luminescent materials are present in several recent studies on new applications and novel properties. In this work, we demonstrate, for the first time, the production of translucent flexible persistent composites based on Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ (SMSO) into cellulose ether matrix film. The composite was successfully prepared through a new optimized route of co-precipitation and microwave-assisted annealing followed by (3-aminopropyl)triethoxysilane (APTES) coating and dispersion in hydroxypropyl methylcellulose (HPMC). The SMSO@APTES/HPMC films show persistent luminescence emission at 475 nm (blue) and high transmittance in the visible range. To understand the fine distribution of the nanoparticles in the matrix, we have investigated their structure and dispersion by using Synchrotron Radiation X-ray fluorescence mapping and Scanning Transmission X-ray Microscopy. This innovative composite could bring new perspectives for the class of persistent luminescence materials, enhancing technologies in progress throwing light on new applications never perceived.

Photoluminescence and afterglow of Dy3+ doped CaAl2O4 derived via sol–gel combustion

A systematic investigation into the photoluminescence and afterglow mechanisms of trivalent Dy ion doped CaAl2O4.

Effect of Oxygen Vacancies on the Persistent Luminescence of Y3Al2Ga3O12:Ce3+,Yb3+ Phosphors

The effect of oxygen vacancies (V_O) and the atmosphere influence on persistent luminescence (PersL) in Y₃Al₂Ga₃O₁₂ (YAGG):Ce³⁺,Yb³⁺ are investigated by heating it in CO₂, air, and 10% H₂/90% Ar atmospheres. The V_O-rich YAGG phosphors with outstanding PersL are successfully obtained by the common contribution of the reducing atmosphere and the incorporated Yb³⁺ ions, and the concentration of oxygen vacancies in the phosphors is characterized by X-ray photoelectron spectroscopy and electron paramagnetic resonance measurements. Compared to the best sample prepared in neutral CO₂, the reduced sample shows an increase of 30% in initial intensity and 100% in duration time, while the oxidized sample decreases drastically and shows a faint and undetectable PersL. The enhancement is mainly caused by the abundant formation of V_O, which is achieved by the pairing of V_O with Yb²⁺ ions. The newly created V_O by the reducing calcination is inferred to be adjacent to the Yb site and forms a compensation-type defect cluster due to the charge compensation effect. These findings reveal that understanding the effect and formation of V_O is of great significance to design a high-performance phosphor.

Design of doxorubicin encapsulated pH-/thermo-responsive and cationic shell-crosslinked magnetic drug delivery system

The upsurge in cancer cases, such as liver cancer, has claimed millions of lives globally and has prompted the development of novel nanodrug delivery systems. These systems allow cancer drugs to be encapsulated in nanocarriers and delivered to tumor sites, and accordingly, help reduce side effects of the current chemotherapeutic treatments. Herein, we prepared nanocarriers comprising magnetic iron oxide (MIO) nanoparticles that were surface modified with crosslinked Pluronic F127 (PF127) and branched polyethylenimine (bPEI) to form MIOpoly nanocarriers. These nanocarriers were then loaded with doxorubicin (DOX) anticancer drug to form the MIOpoly-DOX complex. The nanocarriers were magnetite and possessed superparamagnetic properties. Small-angle neutron scattering (SANS) analysis indicated that the nanocarriers were thermoresponsive and spherically structured. The characteristic peaks at 1285, 1619, 2844, 2919, 2900, 2840, and 3426 cm^-1, corresponding to those of CN, -NH₂, -CH₂, and OH-, confirmed the successful crosslinking, coating of PF127-bPEI polymers on the surface of MIO nanoparticles and DOX conjugation. The bioavailability of the nanocarriers indicated a more than 85% cell viability when using HepG2 liver cancer cells. A pH (54.8% release in 48 h; pH = 5.4) and temperature (51.0% release in 48 h; 42 °C)-dependent release of DOX was observed, displaying a Korsmeyer-Peppas kinetics model at low pH and Weibull model at high temperatures. The high DOX fluorescence observed for MIOpoly-DOX indicated a high cellular uptake enhanced by alternating magnetic field. These results suggest that MIOpoly synthesized using a combined approach of surface crosslinking and grafted with PF127-bPEI appear to offer promising properties as drug delivery system. Therefore, the nanocarriers developed in the study possess a great potential for targeted delivery and thereby circumventing the limitations of conventional chemotherapy.

Recent Developments in Lanthanide-Doped Alkaline Earth Aluminate Phosphors with Enhanced and Long-Persistent Luminescence

Lanthanide-activated alkaline earth aluminate phosphors are excellent luminescent materials that are designed to overcome the limitations of conventional sulfide-based phosphors. The increasing research attention on these phosphors over the past decade has led to a drastic improvement in their phosphorescence efficiencies and resulted in a wide variety of phosphorescence colors, which can facilitate applications in various areas. This review article discusses the development of lanthanide-activated alkaline earth aluminate phosphors with a focus on the various synthesis methods, persistent luminescence mechanisms, activator and coactivator effects, and the effects of compositions. Particular attention has been devoted to alkaline earth aluminate phosphors that are extensively used, such as strontium-, calcium-, and barium-based aluminates. The role of lanthanide ions as activators and coactivators in phosphorescence emissions was also emphasized. Finally, we address recent techniques involving nanomaterial engineering that have also produced lanthanide-activated alkaline earth aluminate phosphors with long-persistent luminescence.