Surfactant-Free Aqueous Synthesis of Novel Ba2GdF7:Yb3+, Er3+@PEG Upconversion Nanoparticles for in Vivo Trimodality Imaging

Upconversion nanoparticle-based fluorescence resonance energy transfer sensing platform for the detection of cathepsin B activity in vitro and in vivo

A simple fluorescence resonance energy transfer (FRET) sensing platform (termed as USP), comprised of upconversion nanoparticles (UCNPs) as the energy donor and Cy5 as the energy acceptor, has been synthesized for cathepsin B (CTSB) activity detection in vitro and in vivo. When Cy5-modified peptide substrate (peptide-Cy5) of CTSB is covalently linked on the surface of UCNPs, the FRET between the UCNPs (excitation: 980 nm; emission: 541 nm/655 nm) and Cy5 (excitation: 645 nm) leads to a reduction in the red upconversion luminescence (UCL) signal intensity of UCNPs. Cy5 can be liberated from UCNPs in the presence of CTSB through the cleavage of peptide-Cy5 by CTSB, leading to the recovery of the red UCL signal of UCNPs. Because the green UCL signal of UCNPs remains constant during the CTSB digestion, it can be considered as an internal reference. The findings demonstrate the ability of USP to detect CTSB with the linear detection ranges of 1 to 100 ng·mL^-1 in buffer and 2 × 10³ to 1 × 10⁵ cells in 0.2 mL cell lysates. The limits of detection (LODs) are 0.30 ng·mL^-1 in buffer and 887 cells in 0.2 mL of cell lysates (S/N = 3). The viability of USP to detect CTSB activity in tumor-bearing mice is has further been investigated using in vivo fluorescent imaging.

Recent progress in the development of upconversion nanomaterials in bioimaging and disease treatment

Multifunctional lanthanide-based upconversion nanoparticles (UCNPs), which feature efficiently convert low-energy photons into high-energy photons, have attracted considerable attention in the domain of materials science and biomedical applications. Due to their unique photophysical properties, including light-emitting stability, excellent upconversion luminescence efficiency, low autofluorescence, and high detection sensitivity, and high penetration depth in samples, UCNPs have been widely applied in biomedical applications, such as biosensing, imaging and theranostics. In this review, we briefly introduced the major components of UCNPs and the luminescence mechanism. Then, we compared several common design synthesis strategies and presented their advantages and disadvantages. Several examples of the functionalization of UCNPs were given. Next, we detailed their biological applications in bioimaging and disease treatment, particularly drug delivery and photodynamic therapy, including antibacterial photodynamic therapy. Finally, the future practical applications in materials science and biomedical fields, as well as the remaining challenges to UCNPs application, were described. This review provides useful practical information and insights for the research on and application of UCNPs in the field of cancer.

Peptide-enhanced tumor accumulation of upconversion nanoparticles for sensitive upconversion luminescence/magnetic resonance dual-mode bioimaging of colorectal tumors

Currently, it is still a great challenge to develop tumor targeting nanoparticles with high sensitivity and high resolution for improving the non-invasive detection ability of colorectal cancer (CRC) at an early stage. In this study, NaErF₄:Yb@NaGdF₄:Yb core@shell upconversion nanoparticles (UCNPs) were prepared with high upconversion luminescence (UCL) emission in red light region through adjusting the doping ratios of Er and Yb elements in the core. For biomedical applications, the carboxyl-terminated silica shell was introduced to transfer the as-prepared UCNPs from the organic phase to the aqueous phase, and allowed conjugation with peptide ligands derived from the l-SP5 peptide (i.e., l-SP5-H and l-SP5-C), respectively. Due to the tumor-targeting affinity of the PSP motif in the peptide ligands, the as-prepared peptide functionalized UCNPs (UCNP@SiO₂-l-SP5-H and UCNP@SiO₂-l-SP5-C) can be used as an active tumor targeting contrast agents for UCL/T₁-weighted magnetic resonance (MR) dual-mode imaging. Both the in vitro and in vivo experimental results demonstrated that UCNP@SiO₂-l-SP5-C has relatively high affinity for the HCT116 CRC subtype. Moreover, UCNP@SiO₂-l-SP5-C can visualize ultra-small subcutaneous xenografted HCT116 tumors (c.a. 13 mm³ in volume) by in vivo UCL imaging. STATEMENT OF SIGNIFICANCE: 1. High red emission UCNPs were synthesized for tumor-targeting dual-mode bioimaging. 2. With tumor-binding affinity peptide, UCNP@SiO₂-l-SP5-C shows high HCT116 tumor targeting ability. 3. UCNP@SiO₂-l-SP5-C successfully achieves sensitive detection of ultrasmall HCT116 tumors.

Acute hepatotoxicity of multimodal targeted imaging contrast agent NaLuF4:Gd,Yb,Er-PEG/PEI-FA in mice

In the past few decades, upconversion nanoparticles (abbreviated as UCNPs) have been more widely applied in the biomedical fields, such as in vitro and in vivo upconversion fluorescent bioimaging, photodynamic therapy, biological macromolecular detection, imaging mediated drug delivery and so on. But meanwhile, there is still not much research on the acute toxicity of upconversion nanoparticles in vivo, such as acute hepatotoxicity. In this work, we studied the in vivo biodistribution and acute hepatotoxicity of multimodal targeted contrast agent NaLuF₄:Gd,Yb,Er-PEG/PEI-FA nanoprobe, which were synthesized by the solvothermal method and modified with Polyethylene glycol (PEG), Polyetherimide (PEI), folic acid (FA) on the surface. The acute hepatotoxicity in mice was systematically assessed after tail vein injection of different concentration of UCNPs. The results showed that NaLuF₄:Gd,Yb,Er-PEG/PEI-FA nanoparticles with an average diameter of 44.5 ± 10.4 nm, and three typical upconversion fluorescence emission bands at 520 nm, 540 nm and 660 nm under the excitation of 980 nm laser. In vivo distribution experiments results demonstrated that approximately 87% of UCNPs injected through the tail vein accumulate in the liver. In the acute hepatotoxicity test, the intravenously injection dose of UCNPs was 10, 40, 70 and 100 mg/kg, respectively. The body weight, blood routine, serum biochemistry, histomorphology and liver oxidative stress were detected and observed no significant acute hepatotoxicity damage under the injection dose of 100 mg/kg. In conclusion, NaLuF₄:Gd,Yb,Er-PEG/PEI-FA nanoprobes are safe and reliable, and have potential applications in the field of tumor targeted multimodal imaging.

Fabrication of NaYF4:Yb3+,Tm3+-modified Ag nanocubes with upconversion luminescence and photothermal conversion properties

Herein, uniform Ag nanocube@NaYF₄:Yb³⁺,Tm³⁺ multifunctional nanocomposites were constructed by a facile synthetic strategy. Following the successful synthesis of Ag nanocubes, cubic phase NaYF₄:Yb³⁺,Tm³⁺ upconversion luminescent nanocrystals were modified on the surface of the Ag nanocubes, enhanced the mutual assistance of energy and versatility of the materials. Upon irradiation with a near-infrared laser, the nanocomposites exhibited excellent upconversion fluorescence and good photothermal conversion capability. Furthermore, the potential biological applications and biosafety of the Ag@NaYF₄:Yb³⁺,Tm³⁺ nanocomposites were also demonstrated; the obtained nanocomposites could achieve a good bactericidal performance and photothermal treatment of cancer cells, and they could be potentially applied in the biomedical field as a promising agent. Furthermore, this method provides a facile approach for synthesizing a multifunctional nanocomposite with different properties.

Ag nanocubes@NaYF₄:Yb³⁺,Tm³⁺ multifunctional nanocomposites with florescence and photothermal ability are fabricated by a facile strategy, which enhance the mutual assistance of energy and biological application.

An l-cysteine-mediated iodide-catalyzed reaction for the detection of I−

In this study, a highly selective and eco-friendly fluorescent sensor consisting of upconversion (UCNPs) and gold nanoparticles (AuNPs) was developed for the detection of iodide (I⁻).

Y1-receptor-ligand-functionalized ultrasmall upconversion nanoparticles for tumor-targeted trimodality imaging and photodynamic therapy with low toxicity

Achieving efficient photodynamic therapy (PDT) in deeper biological tissue is still the biggest bottleneck that limits its widespread application in clinic. Although deeper biological tissue PDT could be realized through a combination of upconversion nanoparticles with a photosensitizer, issues with particle-size-induced upconversion fluorescence (UF) reduction and the related in vivo toxicity still cannot be solved properly. In this study, we synthesized Y1Rs-ligand [Pro30, Nle31, Bpa32, Leu34]NPY(28-36) (NPY)-modified and photosensitizer MC540-loaded LiLuF4:Yb,Er@nLiGdF4@mSiO2 multifunctional nanocomposites (MNPs) with a core-multishell structure and ultrasmall size. Their in vitro and in vivo breast tumor targeting, trimodality imaging performance, PDT therapeutic efficacy, and acute toxicity were evaluated. Our results demonstrated that the core-multishell MNPs(MC540) could achieve excellent UF imaging, and that doping with Gd3+ and Lu3+ rare earth ions could enhance the MR and CT imaging performance. In addition, the mSiO2 shell provided a higher loading rate for the photosensitizer MC540, and the DSPE-PEG thin layer coating outside the MNPs(MC540) further improved the water solubility and biocompatibility, reducing the acute toxicity of the nanocomposites. Finally, the NPY modification enhanced the targetability of MNPs(MC540)/DSPE-PEG-NPY to breast tumors, improving the trimodality UF, CT, and MR imaging performance and PDT efficacy for Y1-receptor-overexpressed breast cancer. In general, our developed multifunctional nanocomposites can serve as a theranostic agent with low toxicity, providing great potential for their use in clinical breast cancer diagnosis and therapy.

A water-soluble, upconverting Sr2Yb0.3Gd0.7F7:Er3+/Tm3+@PSIoAm bio-probe for in vivo trimodality imaging

Multi-modality in vivo bioimaging has great renown for offering more comprehensive information in medical diagnosis and research. Incorporating different bioimaging capabilities into one biocompatible nanoprobe requires an elegant structural design. Considering optical and magnetic properties, X-ray absorption ability, and clinical safety, we prepared a water-soluble and upconverting PSIoAm-modified Sr2Yb0.3Gd0.7F7:Er3+/Tm3+ bio-probe that not only had high photostability and excellent cell membrane permeability, but could also distinguish the four types of cancer cells and normal cells tested within the scope of our study. What's more, it could realize the in vivo trimodality imaging of upconversion fluorescence, X-ray computed tomography and magnetic resonance. The histological analysis of visceral sections further demonstrated that the multifunctional bio-probe was highly safe, which could be applied to clinical diagnosis.

Sandwich DNA Hybridization Fluorescence Resonance Energy-Transfer Strategy for miR-122 Detection by Core-Shell Upconversion Nanoparticles

An upconversion nanoparticle (UCNP)-based fluorescence resonance energy-transfer (FRET) strategy is normally restricted by the complicated preparations, low energy-transfer efficiency, and the challenge on improving specificity. Herein, simple DNA-functionalized UCNPs were designed as energy donors for constructing a FRET-based probe to detect the liver-specific microRNA 122 (miR-122). To improve FRET efficiency, UCNPs were constructed with confined core-shell structures, in which emitting ions were precisely located in the thin shell to make them close enough to external energy acceptors. Subsequently, capture DNA was simply functionalized on the outer surface of UCNPs based on ligand exchange that contributed to shortening the energy-transfer distance without extra modification. To gain high specificity, the donor-to-acceptor distance of FRET was controlled by a sandwich DNA hybridization structure using two shorter DNAs with designed complementary sequences (capture DNA and dye-labeled report DNA) to capture the longer target of miR-122. Therefore, the sensitive detection of miR-122 was achieved based on the decreased signals of UCNPs and the increased signals of the dye labeled on reported DNA. With good biocompatibility, this method has been further applied to cancer cell imaging and in vivo imaging, which opened up a new avenue to the sensitive detection and imaging of microRNA in biological systems.

Renal-Clearable Peptide-Functionalized Ba2GdF7 Nanoparticles for Positive Tumor-Targeting Dual-Mode Bioimaging

Considering the dilemma between the effective tumor targeting and the avoidance of potential toxicity, it is desired to design nanoprobes with positive tumor-targeting and good renal clearance ability. In the present work, we developed epidermal growth factor receptor (EGFR)-targeted peptide-functionalized Ba₂GdF₇ nanoparticles (termed as pEGFR-targeted Ba₂GdF₇ NPs) for positive tumor-targeting magnetic resonance imaging and X-ray computed tomography (MRI/CT) dual-mode bioimaging. The positive tumor-targeting ability of pEGFR-targeted Ba₂GdF₇ NPs is achieved by conjugation of EGFR-targeted peptides on the 6.5 nm Ba₂GdF₇ NP surface through the formation of Gd-phosphonate coordinate bonds. The pEGFR-targeted Ba₂GdF₇ NPs display desirable cytocompatibility in the test concentration range and high binding affinity with lung cancer cells. In vivo MR and CT imaging results demonstrate that the pEGFR-targeted Ba₂GdF₇ NPs are able to be accumulated and detained within an engrafted A549 lung carcinoma, which enhances both MR and CT contrast in the tumor tissue. Systematic in vivo experimental results further demonstrate that the pEGFR-targeted Ba₂GdF₇ NPs have favorable in vivo renal clearance kinetics as well as reasonable in vivo biocompatibility.

Three-dimensional angiography fused with CT/MRI for multimodal imaging of nanoparticles based on Ba4Yb3F17:Lu3+,Gd3+

Designing nanosized multi-modality contrast agents for high-resolution imaging is challenging since most agents are only useful for single-mode imaging. In this work, we successfully synthesized biocompatible polyethylene glycol (PEG-) and l-glutamine (GLN-) modified Ba4Yb3F17:Lu3+,Gd3+ nanoparticles (LNPs@PEG@GLN) that can be employed as a multi-modality contrast agent. Fluorescence dye-modified LNPs@PEG@GLN nanoparticles can be used for computed tomography (CT), magnetic resonance imaging (MRI), and fluorescence imaging (FI). They display high X-ray absorption, outstanding T2-weighted imaging capability, and good fluorescence uptake. Furthermore, LNPs@PEG@GLN enhances contrast efficiencies for different imaging modalities in vivo. Interestingly, LNPs@PEG@GLN is a promising agent for CT angiography. These nanoparticles could be a promising contrast agent for multi-modality imaging and diagnosing vascular diseases.

A theranostic nanoplatform: magneto-gold@fluorescence polymer nanoparticles for tumor targeting T1&T2-MRI/CT/NIR fluorescence imaging and induction of genuine autophagy mediated chemotherapy

Multifunctional nanoparticles, bearing low toxicity and tumor-targeting properties, coupled with multifunctional diagnostic imaging and enhanced treatment efficacy, have drawn tremendous attention due to their enormous potential for medical applications. Herein, we report a new kind of biocompatible and tumor-targeting magneto-gold@fluorescent polymer nanoparticle (MGFs-LyP-1), which is based on ultra-small magneto-gold (Fe3O4-Au) nanoparticles and NIR emissive fluorescent polymers by a solvent-mediated method. This kind of nanoparticle could be taken up efficiently and simultaneously serve for in vivo tumor targeting T1&T2-MRI/CT/near infrared (NIR) fluorescence bioimaging. Furthermore, the nanoparticles exhibit small size, higher tumor targeting accumulation, excellent cytocompatibility for long-term tracking, and no disturbing cell proliferation and differentiation. Moreover, clear and convincing evidence proves that as-synthesized MGFs-LyP-1 could elicit genuine autophagy via inducing autophagosome formation, which offers a definite synergistic effect to enhance cancer therapy with doxorubicin (DOX) at a nontoxic concentration through enhancement of the autophagy flux. Meanwhile, the as-prepared nanoparticles could be rapidly cleared from mice without any obvious organ impairment. The results indeed reveal a promising prospect of an MGFs-LyP-1 contrast agent with low toxicity and high efficiency for promising application in biomedicine.

Surfactant-free aqueous synthesis of novel Ba3Gd2F12:Ln3+ nanocrystals with luminescence properties

Novel Ba₃Gd₂F₁₂:Ln³⁺ (Ln = Eu, Dy, Tb, Ce, Er, Tm, and Yb) nanocrystals with multicolor emissions have been prepared via a surfactant-free aqueous hydrothermal route for the first time.

Sequential growth of CaF2:Yb,Er@CaF2:Gd nanoparticles for efficient magnetic resonance angiography and tumor diagnosis

It is a significant challenge to develop nanoscale magnetic resonance imaging (MRI) contrast agents with high performance of relaxation.