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

Detection of ascorbic acid by persistent luminescent nanoparticles based on CoOOH nanosheets modification

Persistent luminescent nanomaterials (PLNPs) Zn0.8Ga2O4: Cr3+, Zr3+ with high brightness and good dispersion were prepared by hydrothermal method. The PLNPs were used as luminescent units, and CoOOH nanosheets were used as quenching agents. Based on the fluorescence internal filtering effect, the luminescence of PLNPs were effectively quenched by CoOOH modification on the surface of PLNPs. However, the introduction of ascorbic acid (AA) restored the luminescence of PLNPs and successfully achieved highly sensitive and selective detection of AA. This was due to a selective redox reaction between CoOOH and AA, in which CoOOH was reduced to Co2+. The degree of luminescence recovery of PLNPs showed a good linear relationship with AA concentration in the range 5-250 µM, with a detection limit of 0.72 µM. The recovery of actual spiked samples were 97.9-102.2%. This method is expected to provide reference for the study of other redox substances in biological systems.

Rechargeable Afterglow Nanotorches for In Vivo Tracing of Cell-Based Microrobots

As one of the self-luminescence imaging approaches that require pre-illumination instead of real-time light excitation, afterglow luminescence imaging has attracted increasing enthusiasm to circumvent tissue autofluorescence. In this work, we developed organic afterglow luminescent nanoprobe (nanotorch), which could emit persistent luminescence more than 10 days upon single light excitation. More importantly, the nanotorch could be remote charged by 660 nm light in a non-invasive manner, which showed great potential for real-time tracing the location of macrophage cell-based microrobots.

Nanocrystals for Deep-Tissue In Vivo Luminescence Imaging in the Near-Infrared Region

In vivo imaging technologies have emerged as a powerful tool for both fundamental research and clinical practice. In particular, luminescence imaging in the tissue-transparent near-infrared (NIR, 700-1700 nm) region offers tremendous potential for visualizing biological architectures and pathophysiological events in living subjects with deep tissue penetration and high imaging contrast owing to the reduced light-tissue interactions of absorption, scattering, and autofluorescence. The distinctive quantum effects of nanocrystals have been harnessed to achieve exceptional photophysical properties, establishing them as a promising category of luminescent probes. In this comprehensive review, the interactions between light and biological tissues, as well as the advantages of NIR light for in vivo luminescence imaging, are initially elaborated. Subsequently, we focus on achieving deep tissue penetration and improved imaging contrast by optimizing the performance of nanocrystal fluorophores. The ingenious design strategies of NIR nanocrystal probes are discussed, along with their respective biomedical applications in versatile in vivo luminescence imaging modalities. Finally, thought-provoking reflections on the challenges and prospects for future clinical translation of nanocrystal-based in vivo luminescence imaging in the NIR region are wisely provided.

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.

Near-Infrared Rechargeable Persistent Luminescence Nanoparticles for Biomedical Implants In Vivo Noninvasive Bioimaging

Luminescent imaging has garnered significant attention for in vivo tracking of biomedical implants during and after surgery due to its human friendliness, affordability, and high sensitivity. However, conventional fluorescent probes are susceptible to background autofluorescence interference from living tissues, often resulting in poor signal-to-noise ratios. Herein, we report a background interference-free persistent luminescent implant (PLI) with excellent persistent luminescence (PL) performance, which can be clearly and long-term detected by an optical imaging system after implantation. Rechargeable near-infrared persistent luminescence nanoparticles (PLNPs) were prepared first via a simple hydrothermal approach and then modified by PEGylation to improve their hydrophilicity, biocompatibility, and compatibility with polymer substrates. The PEGylated PLNPs were facilely complexed into a polymer matrix to fabricate the PLI. The obtained PLIs can well inherit the PL properties of PLNPs, exhibiting good PL optical imaging performance without tissue autofluorescence interference. Furthermore, both PLNPs and PLIs possess good biocompatibility, and the addition of PLNPs has no negative impact on the biocompatibility of the polymer matrix. This work fully utilizes the luminescent properties of PLNPs and adapts this PL to the field of biomedical implant imaging, which provides new insight for designing biomedical imaging systems.

Effect of the Elaboration Method on Structural and Optical Properties of Zn1.33Ga1.335Sn0.33O4:0.5%Cr3+ Persistent Luminescent Nanomaterials

Near-infrared (NIR) persistent luminescence (PersL) materials have demonstrated promising developments for applications in many advanced fields due to their unique optical properties. Both high-temperature solid-state (SS) or hydrothermal (HT) methods can successfully be used to prepare PersL materials. In this work, Zn1.33Ga1.34Sn0.33O4:0.5%Cr3+ (ZGSO:0.5%Cr3+), a newly proposed nanomaterial for bioimaging, was prepared using SS and HT methods. The results show the crystal structure, morphology and optical properties of the samples that were prepared using both methods. Briefly, the crystallite size of the ZGSO:0.5%Cr3+ prepared using the SS method is ~3 µm, and as expected, is larger than materials prepared using the HT method. However, the growth process used in the hydrothermal environment promotes the formation of ZGSO:0.5%Cr3+ with more uniform shapes and smaller sizes (less than 500 nm). Different diameter ranges of nanoparticles were obtained using HT and ball milling (BM) methods (ranging from 25-50 nm) and by using SS and BM methods (25-200 nm) as well. In addition, the SS-prepared microstructure material has stronger PersL than HT-prepared particles before they go through ball milling to create nanomaterials. On the contrary, after BM treatment, ZGSO:0.5%Cr3+ HT and BM NPs present higher PersL and photoluminescence (PL) properties than ZGSO:0.5%Cr3+ SS and BM NPs, even though both kinds of NPs present worse PersL and PL compared to the original particles before BM. To summarize: preparation methods, whether by SS or HT, with additional grinding as a second step, can have a significant impact on the morphological and luminescent features of ZGSO:0.5%Cr3+ PersL materials.

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.

Synthesis and characterization of a near-infrared persistent luminescent Cr-doped zinc gallate-calcium phosphate composite

Near-infrared (NIR)-emitting persistent luminescence (PersL) nanoparticles have attracted great attention as a novel optical probe for bioimaging and biosensing applications. These nanoparticles emit long-lasting luminescence after the removal of the excitation source, which effectively eliminates the interference from tissue autofluorescence. Cr-doped zinc gallate (ZnGa₂O₄:Cr³⁺, CZGO) is a representative NIR-emitting PersL material. On the other hand, amorphous calcium phosphate (ACP) is a widely used drug carrier due to its high biocompatibility. In this work, we present a design of an ACP-based drug carrier with PersL properties, by forming a CZGO-ACP composite. The PersL properties of CZGO were preserved by composite formation, while it is found that the Zn²⁺ could migrate from CZGO to ACP during composite formation, leading to different luminescence mechanisms between pure CZGO and the CZGO-ACP composite. The electronic structure of the composite was analyzed by synchrotron X-ray absorption spectroscopy, and a structure-luminescence correlation was proposed.

HKUST-1 nano metal-organic frameworks combined with ZnGa2O4:Cr3+ near-infrared persistent luminescence nanoparticles for in vivo imaging and tumor chemodynamic and photothermal synergic therapy

The multifunctional theranostic nanoplatform based on the combination of persistent luminescent nanoparticles (PLNPs) and metal-organic frameworks (MOFs) has both in vivo imaging and tumor therapeutic drug-loading functions, providing a new strategy for accurate and effective tumor diagnosis and treatment. Herein, the near-infrared (NIR) PLNP SiO₂@Zn_1.05Ga_1.9O₄:Cr was combined with HKUST-1 MOFs to form a core-shell structure theranostic nanoplatform which possessed the triple function of autofluorescence-free NIR PersL bioimaging, tumor chemodynamic therapy (CDT), and tumor photothermal therapy (PTT). Also, the photothermal conversion efficiency reached 58.7%, which is superior to the reported nano metal-organic framework (NMOF) photothermal reagents. We demonstrated that the nanoplatform could enter the tumors of mice within 0.5 h and could be target-activated by H₂O₂ and H₂S in the tumor cells, resulting in effective PTT and CDT synergistic treatment. Tumor-bearing mice experiments showed that the tumor could be completely cured without harming normal tissue. This theranostic nanoplatform may provide a promising strategy showing imaging, PTT, and CDT synergistic treatment tri-mode for clinical cancer therapy.

Continuous Flow Synthesis of Persistent Luminescent Chromium-Doped Zinc Gallate Nanoparticles

Near-infrared persistent luminescent (or afterglow) nanoparticles with the biologically appropriate size are promising materials for background-free imaging applications, while the conventional batch synthesis hardly allows for reproducibility in controlling particle size because of the random variations of reaction parameters. Here, highly efficient chemistry was matched with an automated continuous flow approach for directly synthesizing differently sized ZnGa₂O₄:Cr³⁺ (ZGC) nanoparticles exhibiting long persistent luminescence. The key flow factors responsible for regulating the particle formation process, especially the high pressure-temperature and varied residence time, were investigated to be able to tune the particle size from 2 to 6 nm and to improve the persistent luminescence. Upon silica shell encapsulation of the nanoparticles accompanied by an annealing process, the persistent luminescence of the resulting particles was remarkably enhanced. High-fidelity automated flow chemistry demonstrated here offers an alternative for producing ZGC nanoparticles and will be helpful for other compositionally complex metal oxide nanoparticles.

Turning-on persistent luminescence out of chromium-doped zinc aluminate nanoparticles by instilling antisite defects under mild conditions

Spinel oxide nanocrystals are appealing hosts for Cr³⁺ for forming persistent luminescent nanomaterials due to their suitable fundamental bandgaps. Benefiting from their antisite defect-tolerant nature, zinc gallate doped with Cr³⁺ ions has become the most studied near-infrared (NIR) persistent luminescent material. However, it remains challenging to achieve persistent luminescence from its inexpensive analogs, e.g., zinc aluminate (ZnAl₂O₄). Because the radius difference of the cations in the latter system is bigger, it is intrinsically unfavorable for ZnAl₂O₄ to form Zn-Al antisite defects under mild conditions. Herein, we report a wet-chemical synthetic route for preparing Cr³⁺-doped ZnAl₂O₄ nanoparticles with long NIR persistent luminescence. It was demonstrated that methanol (MeOH) as an important component of the mixed solvent played a critical role in tailoring the morphology of the resulting ZnAl₂O₄:Cr nanocrystals. It could particularly drive the formation of antisite defects in the resulting coral-like nanoparticles bearing zinc-rich cores and zinc gradient peripheries. To disclose the effects of MeOH on the formation of antisite defects as well as particle morphologies, small molecules released during the pyrolysis of metal acetylacetonate precursors were analyzed by using gas chromatography-mass spectrometry. In combination with density functional theory (DFT) calculations, it was found that MeOH can effectively catalyze the thermolysis of metal acetylacetonate precursors, in particular Zn(acac)₂. Therefore, MeOH exhibits remarkable effects on the formation of antisite defects by balancing the decomposition rates of Zn(acac)₂ and Al(acac)₃ through its volume fraction in the reaction system. This work thus constitutes a hitherto less common strategy for achieving NIR persistent luminescence from Cr³⁺-doped ZnAl₂O₄ nanoparticles by engineering the cation defects under mild conditions.

Persistent luminescence nanoparticles for cancer theranostics application

Persistent luminescence nanoparticles (PLNPs) are unique optical materials that emit afterglow luminescence after ceasing excitation. They exhibit unexpected advantages for in vivo optical imaging of tumors, such as autofluorescence-free, high sensitivity, high penetration depth, and multiple excitation sources (UV light, LED, NIR laser, X-ray, and radiopharmaceuticals). Besides, by incorporating other functional molecules, such as photosensitizers, photothermal agents, or therapeutic drugs, PLNPs are also widely used in persistent luminescence (PersL) imaging-guided tumor therapy. In this review, we first summarize the recent developments in the synthesis and surface functionalization of PLNPs, as well as their toxicity studies. We then discuss the in vivo PersL imaging and multimodal imaging from different excitation sources. Furthermore, we highlight PLNPs-based cancer theranostics applications, such as fluorescence-guided surgery, photothermal therapy, photodynamic therapy, drug/gene delivery and combined therapy. Finally, future prospects and challenges of PLNPs in the research of translational medicine are also discussed.

Synthesis, modification and bioapplications of nanoscale copper chalcogenides

Copper chalcogenides have a simple general formula, variable atomic ratios, and complicated crystal structures, which lead to their wealth of optical, electrical, and magnetic properties with great potential for wide applications ranging from energy conversion to the biomedical field. Herein, we summarize the recent advances in (1) the synthesis of size- and morphology tunable nanostructures by different methods; (2) surface modification and functionalization for different purposes; and (3) bioapplications for diagnosis and treatment of tumors by different imaging and therapy methods, as well as antibacterial applications. We also briefly discuss the future directions and challenges of copper chalcogenide nanoparticles in the biomedical field.

68Ga-Labeled Magnetic-NIR Persistent Luminescent Hybrid Mesoporous Nanoparticles for Multimodal Imaging-Guided Chemotherapy and Photodynamic Therapy

Featured with a zero-autofluorescence background, superior signal-to-noise ratio, high sensitivity, and deep penetration ability, near-infrared persistent luminescence nanoparticle (NIR-PLNP)-based multimodal nanoprobes show great potential for full-scale noninvasive cancer diagnosis. However, direct synthesis of NIR-PLNP-based multimodal nanoprobes with high drug loading capacity to meet growing cancer theranostic demands remains a challenge. In this work, multifunctional hybrid mesoporous nanoparticles (HMNPs) that integrate NIR-PLNPs (Ga2O3:Cr3+, Nd3+), magnetic nanoparticles (Gd2O3), and radionuclides (68Ga) are designed and constructed via a large-pore (mesoporous silica nanoparticle) MSN-templated strategy. The ingenious composition design endows HMNPs with rechargeable NIR-PL, superior longitudinal relaxivity, and excellent radioactivity, making these versatile nanoparticles available for long-term in vivo NIR-PL imaging, magnetic resonance imaging (MRI), and positron emission tomography (PET) imaging. More importantly, the application of large-pore MSN templates maintains the mesoporous structure of HMNPs, promising excellent drug loading capacity of these nanoparticles. As a proof-of-concept, HMNPs loaded with a high dose of DOX (chemotherapy agent) and Si-Pc (photosensitizer) are rationally designed for chemotherapy and NIR-PL-sensitized photodynamic therapy (PDT), respectively. Studies with mice tumor models demonstrate that the DOX/Si-Pc-loaded HMNPs possess excellent cancer cell killing ability and an outstanding tumor suppression effect without systemic toxicity. This work shows the great potential of HMNPs as an "all-in-one" nanotheranostic tool for multimodal NIR-PL/MR/PET imaging-guided chemotherapy and NIR-PL-sensitized photodynamic cancer therapy and provides an innovative paradigm for the development of NIR-PLNP-based nanoplatforms in cancer theranostic.

Longer and Stronger: Improving Persistent Luminescence in Size-Tuned Zinc Gallate Nanoparticles by Alcohol-Mediated Chromium Doping

Benefiting from near-infrared persistent luminescence, chromium-doped zinc gallate nanoparticles have become appealing for background-free biomedical imaging applications, where autofluorescence from adjacent tissues no longer poses a problem. Nevertheless, the synthesis of persistent luminescent nanoparticles with controllable and biologically appropriate size, high luminescence intensity, and long persistent duration remains very challenging. Herein, we report a solvothermal synthetic route for preparing differently sized ZnGa₂O₄:Cr nanoparticles with a particle size tunable from 4 to 31 nm and afterglow duration longer than 20 h. The route involves lower reaction temperatures and involves no reworking of the particles postsynthesis, providing materials that have far fewer unwanted defects and much higher luminescence yields (up to 51%). It was found that methanol played a paramount role in obtaining the Cr³⁺-doped ZnGa₂O₄ nanoparticles. The effects of methanol were discussed in combination with NMR spectroscopy studies and theoretical calculations, and the underlying alcohol-mediated growth and doping mechanisms were elucidated, which will be beneficial for developing highly persistent luminescent nanoparticles.

Optically Active Nanomaterials for Bioimaging and Targeted Therapy

Non-invasive tracking for monitoring the selective delivery and transplantation of biotargeted agents in vivo has been employed as one of the most effective tools in the field of nanomedicine. Different nanoprobes have been developed and applied to bioimaging tissues and the treatment of diseases ranging from inflammatory and cardiovascular diseases to cancer. Herein, we will review the recent advances in the development of optics-responsive nanomaterials, including organic and inorganic nanoparticles, for multimodal bioimaging and targeted therapy. The main focus is placed on nanoprobe fabrication, mechanistic illustrations, and diagnostic, or therapeutical applications. These nanomedicine strategies have promoted a better understanding of the biological events underlying diverse disease etiologies, thereby facilitating diagnosis, illness evaluation, therapeutic effect, and drug discovery.

Cholesterol-Modified Black Phosphorus Nanospheres for the First NIR-II Fluorescence Bioimaging

Black phosphorus (BP) nanostructures with unique layer-dependent properties have been extensively applied in the fields of electronic devices, energy conversion and storage, and nanomedicine. As a narrow band gap semiconductor, they are expected to show strong second near-infrared (NIR-II) fluorescence. However, there is no report on the NIR-II fluorescence of free-standing BP nanostructures, which have great potential in the NIR-II fluorescence bioimaging because of their excellent biocompatibility and biodegradability. Here, for the first time, we report that the BP nanoparticles modified with cholesterol exhibit strong NIR-II fluorescence and can be encapsulated with the PEGylated lipid to form BP@lipid-PEG nanospheres for in vitro and in vivo NIR-II imaging. The resultant BP@lipid-PEG nanospheres exhibit broad emissions from 900 to 1650 nm under excitation by an 808 nm laser and have 8% quantum yield of that of standard dye IR-26. We also show that the NIR-II fluorescence image acquired with emission beyond 1400 nm has the sharpest contrast and can be used to in situ measure the diameter of blood vessels. In addition to NIR-II fluorescence imaging, we also show the potential of BP@lipid-PEG nanospheres in photoacoustic (PA) imaging. Both the long-wavelength NIR-II fluorescence imaging and PA imaging reveal that the as-fabricated BP@lipid-PEG nanospheres can be gradually metabolized by the liver in 48 h, thus making them promising for bioapplications.

Boosting the Radiosensitizing and Photothermal Performance of Cu2- xSe Nanocrystals for Synergetic Radiophotothermal Therapy of Orthotopic Breast Cancer

The small difference between tumor and normal tissues in their responses to ionizing radiation has been a significant issue for radiotherapy of tumors. Herein, we report that dumbbell-shaped heterogeneous copper selenide-gold nanocrystals can serve as an efficient radiosensitizer for enhanced radiotherapy. The mean lethal dose of X-rays to 4T1 tumor cells can be drastically decreased about 40%, that is, decreasing from 1.81 to 1.10 Gy after culture with heterostructures. Due to the synergetic effect of heterostructures, the dose of X-rays is also much lower than those obtained from mixture of Cu_{2- x}Se + Au nanoparticles (1.78 Gy), Cu_{2- x}Se nanoparticles (1.72 Gy) and Au nanoparticles (1.50 Gy), respectively. We demonstrate that the sensitivity enhancement ratio of Cu_{2- x}Se nanoparticles was significantly improved 45% ( i. e., from 1.1 to 1.6) after the formation of heterostructures with gold. We also show that the heteronanocrystals exhibit an enhanced photothermal conversion efficiency, due to the synergetic interactions of localized surface plasmon resonance. These properties highly feature them as a multimodal imaging contrast agent (particularly for photoacoustic imaging, computed tomography imaging, and single photon emission computed tomography after labeled with radioisotopes) and as a radiosensitizer for imaging guided synergetic radiophotothermal treatment of cancer. The research provides insights for engineering low- Z nanomaterials with high- Z elements to form heteronanostructures with enhanced synergetic performance for tumor theranostics.

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.