Photo-stimulation of persistent luminescence nanoparticles enhances cancer cells death

Persistent luminescent nanophosphors for applications in cancer theranostics, biomedical, imaging and security

The extraordinary and unique properties of persistent luminescent (PerLum) nanostructures like storage of charge carriers, extended afterglow, and some other fascinating characteristics like no need for in-situ excitation, and rechargeable luminescence make such materials a primary candidate in the fields of bio-imaging and therapeutics. Apart from this, due to their extraordinary properties they have also found their place in the fields of anti-counterfeiting, latent fingerprinting (LPF), luminescent markings, photocatalysis, solid-state lighting devices, glow-in-dark toys, etc. Over the past few years, persistent luminescent nanoparticles (PLNPs) have been extensively used for targeted drug delivery, bio-imaging guided photodynamic and photo-thermal therapy, biosensing for cancer detection and subsequent treatment, latent fingerprinting, and anti-counterfeiting owing to their enhanced charge storage ability, in-vitro excitation, increased duration of time between excitation and emission, low tissue absorption, high signal-to-noise ratio, etc. In this review, we have focused on most of the key aspects related to PLNPs, including the different mechanisms leading to such phenomena, key fabrication techniques, properties of hosts and different activators, emission, and excitation characteristics, and important properties of trap states. This review article focuses on recent advances in cancer theranostics with the help of PLNPs. Recent advances in using PLNPs for anti-counterfeiting and latent fingerprinting are also discussed in this review.

Persistent luminescent metal-organic framework nanocomposite enables autofluorescence-free dual modal imaging-guided drug delivery

Molecular imaging-guided therapy was essential for realizing precise cancer intervention, while designing an imaging platform to achieve autofluorescence-free imaging for dual modal imaging-guided drug delivery remains a challenge. Near-infrared persistent luminescence nanoparticles (NIR PLNPs) were promising for tumor imaging due to no background interference from the tissue. Herein, a persistent luminescent metal-organic framework (PLNPs@MIL-100(Fe)) is prepared via a layer-by-layer method for dual-modal imaging-guided drug delivery. The PLNPs@MIL-100(Fe) exhibit NIR persistent luminescence emitting and T₂-weighted signal, achieving precise in vivo dual-modal imaging of tumor-bearing mice by providing high spatial resolution MR imaging and autofluorescence-free NIR imaging. The porous MIL-100(Fe) shell provides PLNPs@MIL-100(Fe) with up to 87.1% drug loading capacity and acid-triggered drug release for drug delivery. We envision that the proposed PLNPs@MIL-100(Fe) platform would provide an effective approach for precise tumor imaging and versatile drug delivery.

Fate and biological impact of persistent luminescence nanoparticles after injection in mice: a one-year follow-up

Persistent luminescence nanoparticles (PLNPs) are attracting growing interest for non-invasive optical imaging of tissues with a high signal to noise ratio. PLNPs can emit a persistent luminescence signal through the tissue transparency window for several minutes, after UV light excitation before systemic administration or directly in vivo through visible irradiation, allowing us to get rid of the autofluorescence signal of tissues. PLNPs constitute a promising alternative to the commercially available optical near infrared probes thanks to their versatile functionalization capabilities for improvement of the circulation time in the blood stream. Nevertheless, while biodistribution for a short time is well known, the long-term fate and toxicity of the PLNP's inorganic core after injection have not been dealt with in depth. Here we extend the current knowledge on ZnGa_1.995O₄Cr_0.005 NPs (or ZGO) with a one-year follow-up of their fate after a single systemic administration in mice. We investigated the organ tissue uptake of ZGO with two different coatings and determined their intracellular processing up to one year after injection. The biopersistence of ZGO was assessed, with a long-term retention, quantified by ICP-MS, mostly in the liver and spleen, parallel with a loss of their luminescence properties. The analysis of the toxicity related to combining an animal's weight, key hematological and metabolic markers, histological observations of liver tissues and quantification of the expression of 31 genes linked to different metabolic reactions did not reveal any signs of noxiousness, from the macro scale to the molecular level. Therefore, the ZGO imaging probe has been proven to be a safe and relevant candidate for preclinical studies, allowing its long term use without any in vivo disturbance of the general metabolism.

Persistent Production of Reactive Oxygen Species with Zn2GeO4:Cu Nanorod-Loaded Microneedles for Methicillin-Resistant Staphylococcus Aureus Infectious Wound Healing

Skin wound infection caused by methicillin-resistant Staphylococcus aureus (MRSA) is an urgent concern. Photodynamic therapy has emerged as a promising means of combating bacterial infection. However, continuous or repeated in situ light excitation is required for photosensitizers to produce reactive oxygen species (ROS), and most photosensitizers need sufficient oxygen to produce singlet oxygen (¹O₂), which greatly limits their clinical application. In this work, we report the preparation of Zn₂GeO₄:Cu²⁺ (ZGC) persistent luminescence nanorods with excellent ability for persistent ROS production after stopping excitation for MRSA infectious wound healing. The prepared ZGC nanorods were loaded into dissolvable microneedles (MNs) (ZGC@MNs) to penetrate biofilms and treat MRSA-infected wounds in a minimally invasive manner. ZGC showed a long-persistent photocatalytic effect to constantly produce multiple ROS (¹O₂, hydroxyl radical, and superoxide radical) accompanied by persistent luminescence after a pre-illumination. The MN tips of ZGC@MNs were rapidly dissolved to release ZGC for the continuous production of multiple ROS for at least 48 h with no need for in situ excitation and no special requirement on the amount of oxygen for eliminating MRSA biofilms. The developed ZGC@MN patches exhibited excellent antibacterial activity and biocompatibility for effectively reducing inflammation and promoting wound healing in vivo.

Recent advances in phase change material based nanoplatforms for cancer therapy

Cancer has become a severe threat to human life due to its high mortality and metastatic rate. Effective inhibition and killing of cancer cells using chemotherapeutic drugs have been a promising means in clinical cancer therapy. However, the low selectivity, drug-resistance, uncontrollability and serious side effects of chemotherapy significantly limit its further development. There is an urgent need for new treatment strategies to compensate for deficiencies inherent in chemotherapy alone. A growing body of research shows that combined treatment strategies have the potential to overcome this dilemma by achieving significantly enhanced synergistic effects and reduced side effects. Emerging phase change materials (PCMs) create an ideal nanoplatform for cancer combination therapy due to their universal loading properties, stable and temperature-responsive phase transition capability, and excellent natural biocompatibility/biodegradability. The release of therapeutic agents can be precisely controlled through external, non-intrusive stimuli (such as NIR light and ultrasound), avoiding systemic toxicity associated with conventional chemotherapy. Herein, the construction methods and design principles of PCM-based nanoplatforms serving as strict gatekeeper and smart payload delivery systems are discussed in detail. Moreover, the advantages and disadvantages of these nanoplatforms are provided. A suitable discussion and perspective of the remaining challenges and future opportunities for PCM-based nanoplatforms in cancer treatment are also given in conclusion.

Turning solid into gel for high-efficient persistent luminescence-sensitized photodynamic therapy

Bioavailable persistent luminescence material is an ideal internal light source for long-term photodynamic therapy, but inevitably suffers from low utilization efficiency and weak persistent luminescence due to corrosion and screening processes. Herein, we show a facile and smart "turning solid into gel" strategy to fabricate persistent luminescence hydrogel for high-efficient persistent luminescence-sensitized photodynamic therapy. The homogeneous persistent luminescence hydrogel was synthesized via dispersing high-temperature calcined persistent luminescence material without corrosion and screening into a biocompatible alginate-Ca²⁺ hydrogel. The simple synthesis strategy allows 100% of utilization efficiency and intact persistent luminescence of persistent luminescence material. The persistent luminescence hydrogel possesses favorable biocompatibility, bright persistent luminescence, red light renewability, good syringeability, and strong fixing ability in tumors. The persistent luminescence hydrogel can be easily injected in vivo as a powerful localized light source for superior persistent luminescence-sensitized photodynamic therapy of tumors. The "turning solid into gel" strategy enables taking full advantages of persistent luminescence for biological applications, and shows great potential in utilizing diverse theranostic agents regardless of hydrophilicity and hydrophobicity.

Controlling trapping states on selective theranostic core@shell (NaYF4:Yb,Tm@TiO2-ZrO2) nanocomplexes for enhanced NIR-activated photodynamic therapy against breast cancer cells

Photodynamic and immune therapies are innovative medical strategies against cancer, and their integration with upconversion nanoparticles (UCNPs) can improve the diagnosis and treatment of the disease. The UCNPs convert the deep penetrating near-infrared (NIR) light into higher energy emissions, allowing the imaging and detection of malignant cells and the simultaneous energy transfer for activation of the photosensitizers. In this work, the UCNPs were coated with a photocatalytic TiO₂/ZrO₂ shell and an increase of oxygen defects (V_O) was observed as a result of the partial substitution of Ti⁴⁺ by Zr⁴⁺ ions in the crystalline lattice of TiO₂. Such defects act as trapping states improving charge separation and then reducing the recombination rate of the electron-hole pairs (e^-/h⁺) generated upon resonant energy transfer from the donor (UCNPs) to acceptors (shell). The overall results are the enhancement of both ROS production and the emission band centered at 801 nm which is useful for tracking cells at the deep tissue level. However, an excess of those defects produces deleterious effects on both processes as a result of charge migration. The specificity against HER2 positive breast cancer was provided by bioconjugation with the monoclonal antibody trastuzumab. After administration of the synthesized NaYF₄:Yb,Tm@TiO₂/ZrO₂-trastuzumab theranostic nanocomplex doped with an optimal ZrO₂ molar concentration (25%) and subsequent exposure to 975 nm light (0.71 W cm^-2) during 5 minutes, HER2-positive SKBr3 breast cancer cells were suppressed with 88% drop of the cell viability, 28% higher than UCNPs decorated with a pure TiO₂ shell.

Imaging and therapeutic applications of persistent luminescence nanomaterials

The development of probes for biomolecular imaging and diagnostics is a very active research area. Among the different imaging modalities, optics emerged since it is a noninvasive and cheap imaging technique allowing real time imaging. In vitro, this technique is very useful however in vivo, fluorescence suffers from low signal-to-noise ratio due to tissue autofluorescence under constant excitation. To address this limitation, novel types of optical nanoprobes are actually being developed and among them, persistent luminescence nanoparticles (PLNPs), with long lasting near-infrared (NIR) luminescence capability, allows doing optical imaging without constant excitation and so without autofluorescence. This review will begin by introducing the physical phenomenon associated to the long luminescence decay of such nanoprobes, from minutes to hours after ceasing the excitation. Then we will show how this property can be used to develop in vivo imaging probes and also more recently nanotheranostic agents. Finally, preliminary data on their biocompatibility will be mentioned and we will conclude by envisioning on the future applications and improvements of such nanomaterials.

Long-term in vivo biodistribution and toxicity study of functionalized near-infrared persistent luminescence nanoparticles

Near-infrared (NIR) persistent luminescence nanoparticles (NPLNPs) have become one of the most promising candidates for bioimaging. Different from the other fluorescence nanoprobes, the NIR persistent luminescence of NPLNPs can last for a long time after excitation, double exposure that is nanoparticles and light exist during the long-term bioimaging. However, to date, the potential risk of nanoparticles and NIR persistent luminescence of NPLNPs is still unknown. In this study, Cr3 + -doped zinc gallate, Zn1.1Ga1.8Sn0.1O4:Cr3+ (ZGO), the most promising NPLNPs in bioimaging, was chosen as a representative for potential risk assessment. We evaluated the potential risk of nanoparticles and NIR persistent luminescence of ZGO for a long period of time. In vitro study showed that the ZGO possessed a low cytotoxicity. In vivo biodistribution results showed that the ZGO mainly accumulated in the reticuloendothelial system after intravenous injection and could be gradually cleared from the body by digestive system. In addition, the ZGO did not exhibit appreciable toxicity in mice over a period of 60 days. It's also worth mentioning that long-term NIR persistent luminescence of ZGO did not exhibit obvious toxicities both in vitro and in vivo. Our results provide important information with regards to the risk of NPLNPs in long-term bioimaging.

Engineering Persistent Luminescence Nanoparticles for Biological Applications: From Biosensing/Bioimaging to Theranostics

Persistent luminescence nanoparticles (PLNPs) are unique optical materials emitting long-lasting luminescence after ceasing excitation. Such a unique optical feature allows luminescence detection without constant external illumination to avoid the interferences of autofluorescence and scattering light from biological fluids and tissues. Besides, near-infrared (NIR) PLNPs have advantages of deep penetration and the reactivation of the persistent luminescence (PL) by red or NIR light. These features make the application of NIR-emitting PLNPs in long-term bioimaging no longer limited by the lifetime of PL. To take full advantage of PLNPs for biological applications, the versatile strategies for bridging PLNPs and biological system become increasingly significant for the design of PLNPs-based nanoprobes. In this Account, we summarize our systematic achievements in the biological applications of PLNPs from biosensing/bioimaging to theranostics with emphasizing the engineering strategies for fabricating specific PLNPs-based nanoprobes. We take surface engineering and manipulating energy transfer as the major principles to design various PLNPs-based nanoprobes based on the nature of interactions between nanoprobes and targets. We have developed target-induced formation or interruption of fluorescence resonance energy transfer systems for autofluorescence-free biosensing and imaging of cancer biomarkers. We have decorated single or dual targeting ligands on PLNPs for tumor-targeted imaging, and integrated other modal imaging agents into PLNPs for multimodal imaging. We have also employed specific functionalization for various biomedical applications including chemotherapy, photodynamic therapy, photothermal therapy, stem cells tracking and PL imaging-guided gene therapy. Besides, we have modified PLNPs with multiple functional units to achieve challenging metastatic tumor theranostics. The proposed design principle and comprehensive strategies show great potential in guiding the design of PLNPs nanoprobes and promoting further development of PLNPs in the fields of biological science and medicine. We conclude this Account by outlining the future directions to further promote the practical application of PLNPs. The novel protocols for the synthesis of small-size, monodisperse, and water-soluble PLNPs with high NIR PL intensity and superlong afterglow are the vibrant directions for the biomedical applications of PLNPs. In-depth theories and evidence on luminescence mechanism of PLNPs are highly desired for further improvement of their luminescence performance. Furthermore, other irradiations without tissue penetrating depth limit, such as X-ray, are encouraged for use in energy storage and re-excitation of PLNPs, enabling imaging in deep tissue in vivo and integrating other X-ray sensitized theranostic techniques such as computed tomography imaging and radiotherapy. Last but not least, PLNPs-based nanoprobes and the brand new hybrids of PLNPs with other nanomaterials show a bright prospect for accurate diagnosis and efficient treatment of diseases besides tumors.

Oral administration of highly bright Cr3+ doped ZnGa2O4 nanocrystals for in vivo targeted imaging of orthotopic breast cancer

Near-infrared (NIR) long lasting persistent luminescence nanoparticles (PLNPs) have attracted considerable attention in the area of in vivo bioimaging, due to their background-free luminescence characteristics and deep tissue penetration. However, the low fluorescence quantum yield and short afterglow of the currently available PLNPs limit their applications. Here, water-soluble Cr³⁺-doped ZnGa₂O₄ PLNPs with the highest quantum yield (η = 20%) ever reported, bright NIR emission, and excellent colloidal stability were successfully prepared by a one-step hydrothermal method. The afterglow of the resultant nanocrystals lasted for more than 5 days and could be repeatedly reactivated by the light (λ = 657 nm) of a portable light emitting diode lamp after decay. These nanocrystals were functionalized with α,ω-dicarboxyl-terminated poly(ethylene glycol) and poly(acrylic acid) to improve their stability and biocompatibility, so that they could be conjugated with a c(RGDyK) peptide and labeled with ^99mTc for targeted imaging of orthotopic breast cancer by afterglow luminescence imaging and single-photon emission computed tomography imaging. Our NIR-PLNP probes can effectively avoid tissue auto-fluorescence and the light scattering caused by continuous excitation during the diagnosis of cancer.