Upconversion Luminescence Resonance Energy Transfer (LRET)‐Based Biosensor for Rapid and Ultrasensitive Detection of Avian Influenza Virus H7 Subtype

Avian influenza viruses (AIV) with good adaptation and various mutations have threatened both human and animals’ health. The H7 subtypes have the potential to cause pandemic threats to human health due to the highly pathogenic characteristics. Therefore, it is quite urgent to develop a novel biosensor for rapid and sensitive detection of H7 subtypes. In this work, a biosensor based on luminescence resonance energy transfer (LRET) from BaGdF₅:Yb/Er upconversion nanoparticles (UCNPs) to gold nanoparticles (AuNPs) has been developed for rapid and sensitive H7 subtypes detection. The amino modified capture oligonucleotide probes are covalently linked to poly(ethylenimine) (PEI) modified BaGdF₅:Yb/Er UCNPs. The thiol modified oligonucleotides with H7 hemagglutinin gene sequence are conjugated to surfaces of AuNPs. The hybridization process between complementary strands of H7 Hemagglutinin gene and its probe brings the energy donor and acceptor into close proximity, leading to the quenching of fluorescence of UCNPs. A linear response is obtained ranging from 10 pm to 10 nm and the limit of detection (LOD) is around 7 pm with detection time around 2 hours. This biosensor is expected to be a valuable diagnostic tool for rapid and sensitive detection of AIV.     

Recent Advances in Upconversion Nanoparticles‐Based Multifunctional Nanocomposites for Combined Cancer Therapy

Lanthanide‐doped upconversion nanoparticles (UCNPs) have the ability to generate ultraviolet or visible emissions under continuous‐wave near‐infrared (NIR) excitation. Utilizing this special luminescence property, UCNPs are approved as a new generation of contrast agents in optical imaging with deep tissue‐penetration ability and high signal‐to‐noise ratio. The integration of UCNPs with other functional moieties can endow them with highly enriched functionalities for imaging‐guided cancer therapy, which makes composites based on UCNPs emerge as a new class of theranostic agents in biomedicine. Here, recent progress in combined cancer therapy using functional nanocomposites based on UCNPs is reviewed. Combined therapy referring to the co‐delivery of two or more therapeutic agents or a combination of different treatments is becoming more popular in clinical treatment of cancer because it generates synergistic anti‐cancer effects, reduces individual drug‐related toxicity and suppresses multi‐drug resistance through different mechanisms of action. Here, the recent advances of combined therapy contributed by UCNPs‐based nanocomposites on two main branches are reviewed: i) photodynamic therapy and ii) chemotherapy, which are the two most widely adopted therapies of UCNPs‐based composites. The future prospects and challenges in this emerging field will be also discussed.     

Glutathione Mediated Size‐Tunable UCNPs‐Pt(IV)‐ZnFe2O4 Nanocomposite for Multiple Bioimaging Guided Synergetic Therapy

Here a multifunctional nanoplatform (upconversion nanoparticles (UCNPs)‐platinum(IV) (Pt(IV))?ZnFe₂O₄, denoted as UCPZ) is designed for collaborative cancer treatment, including photodynamic therapy (PDT), chemotherapy, and Fenton reaction. In the system, the UCNPs triggered by near‐infrared light can convert low energy photons to high energy ones, which act as the UV–vis source to simultaneously mediate the PDT effect and Fenton's reaction of ZnFe₂O₄ nanoparticles. Meanwhile, the Pt(IV) prodrugs can be reduced to high virulent Pt(II) by glutathione in the cancer cells, which can bond to DNA and inhibit the copy of DNA. The synergistic therapeutic effect is verified in vitro and in vivo results. The cleavage of Pt(IV) from UCNPs during the reduction process can shift the larger UCPZ nanoparticles (NPs) to the smaller ones, which promotes the enhanced permeability and retention (EPR) and deep tumor penetration. In addition, due to the inherent upconversion luminescence (UCL) and the doped Yb³⁺ and Fe³⁺ in UCPZ, this system can serve as a multimodality bioimaging contrast agent, covering UCL, X‐ray computed tomography, magnetic resonance imaging, and photoacoustic. A smart all‐in‐one imaging‐guided diagnosis and treatment system is realized, which should have a potential value in the treatment of tumor.     

Gold and Hairpin DNA Functionalization of Upconversion Nanocrystals for Imaging and In Vivo Drug Delivery

Although multifunctional upconversion imaging probes have recently attracted considerable interest in biomedical research, there are currently few methods for stabilizing these luminescent nanoprobes with oligonucleotides in biological systems. Herein, a method to robustly disperse upconversion nanoprobes in physiological buffers based on rational design and synthesis of nanoconjugates comprising hairpin‐DNA‐modified gold nanoparticles is presented. This approach imparts the upconversion nanoprobes with excellent biocompatibility and circumvents the problem of particle agglomeration. By combining single‐band anti‐Stokes near‐infrared emission and the photothermal effect mediated by the coupling of gold to upconversion nanoparticles, a simple, versatile nanoparticulate system for simultaneous deep‐tissue imaging and drug molecule release in vivo is demonstrated.     

Strategies for Constructing Upconversion Luminescence Nanoprobes to Improve Signal Contrast

Lanthanide‐doped upconversion nanoparticles (UCNPs) can convert two or more lower‐energy near‐infrared photons to a single photon with higher energy, which makes them particularly suitable for constructing nanoprobes with large imaging depth and minimal interference of autofluorescence and light scattering from biosamples. Furthermore, they feature excellent photostability, sharp and narrow emissions, and large anti‐Stokes shift, which confer them the capability of long‐period bioimaging and real‐time tracking. In recent years, UCNPs‐based nanoprobes (UC‐nanoprobes) have been attracting increasing interest in biological and medical research. Signal contrast, the ratio of signal intensity after and before the reaction of the probe and target, is the determinant factor of the sensitivity of all reaction‐based probes. This progress report presents the methods of constructing UC‐nanoprobes, with a focus fixed on recent strategies to improve the signal contrast, which have kept on promoting the bioapplication of this type of probe.     

Size‐Dependent Cellular Uptake of DNA Functionalized Gold Nanoparticles

The extensive use of gold nanoparticles (AuNPs) in nanomedicine, especially for intracellular imaging, photothermal therapy, and drug delivery, has necessitated the study of how functionalized AuNPs engage with living biological interfaces like the mammalian cell. Nanoparticle size, shape, surface charge, and surface functionality can affect the accumulation of functionalized AuNPs in cells. Confocal microscopy, flow cytometry, and inductively coupled plasma mass spectrometry demonstrate that CaSki cells, a human cervical cancer cell line, internalize AuNPs functionalized with hairpin, single stranded, and double stranded DNA differently. Surface charge and DNA conformation are shown to have no effect on the cell‐nanoparticle interaction. CaSki cells accumulate small DNA‐AuNPs in greater quantities than large DNA‐AuNPs, demonstrating that size is the major contributor to cellular uptake properties. These data suggest that DNA‐AuNPs can be easily tailored through modulation of size to design functional AuNPs with optimal cellular uptake properties and enhanced performance in nanomedicine applications.     

Chromophore‐Modified Highly Selective Ratiometric Upconversion Nanoprobes for Detection of ONOO−‐Related Hepatotoxicity In Vivo

Acute hepatitis is a major problem affecting public health and has attracted more and more attention. Generally, as the standard means, blood tests are taken for evaluating hepatitis. However, such tests fail to accurately reflect the level of hepatitis in vivo. Herein, two highly selective ratiometric fluorescent probes are designed to track peroxynitrite (ONOO^?) as the hepatitis indicator, and further evaluate acute liver injury in vivo through dye‐grafted upconversion nanoparticles (UCNPs). Specifically, upconversion luminescence of nanoprobes at 540 or 660 nm can be quenched by the designed and synthesized chromophore E‐CC or H‐CC, that can be destroyed by ONOO^? via energy transfer (ET) process, while the upconversion luminescence intensity at 810 nm remains the same. Thus, the developed nanoprobes can be used for ratiometric detection (I₅₄₀/I₆₆₀ or I₆₆₀/I₈₁₀) of ONOO^?. Moreover, the developed near infrared ratiometric nanoprobes can highly selectively detect ONOO^?, which can eliminate the interference of HOCl and SO₃^2?. Finally, it is demonstrated that this highly selective ratiometric nanosystem can achieve effective detection of ONOO^? in living cells and CCl₄‐induced acute liver injury models. It provides some reference value for clinical detection of hepatotoxicity.     

Anti‐Biofouling Polymer‐Decorated Lutetium‐Based Nanoparticulate Contrast Agents for In Vivo High‐Resolution Trimodal Imaging

Nanomaterials have gained considerable attention and interest in the development of novel and high‐resolution contrast agents for medical diagnosis and prognosis in clinic. A classical urea‐based homogeneous precipitation route that combines the merits of in situ thermal decomposition and surface modification is introduced to construct polyethylene glycol molecule (PEG)‐decorated hybrid lutetium oxide nanoparticles (PEG–UCNPs). By utilizing the admirable optical and magnetic properties of the yielded PEG–UCNPs, in vivo up‐conversion luminescence and T₁‐enhanced magnetic resonance imaging of small animals are conducted, revealing obvious signals after subcutaneous and intravenous injection, respectively. Due to the strong X‐ray absorption and high atomic number of lanthanide elements, X‐ray computed‐tomography imaging based on PEG–UCNPs is then designed and carried out, achieving excellent imaging outcome in animal experiments. This is the first example of the usage of hybrid lutetium oxide nanoparticles as effective nanoprobes. Furthermore, biodistribution, clearance route, as well as long‐term toxicity are investigated in detail after intravenous injection in a murine model, indicating the overall safety of PEG–UCNPs. Compared with previous lanthanide fluorides, our nanoprobes exhibit more advantages, such as facile construction process and nearly total excretion from the animal body within a month. Taken together, these results promise the use of PEG–UCNPs as a safe and efficient nanoparticulate contrast agent for potential application in multimodal imaging.     

915 nm Light‐Triggered Photodynamic Therapy and MR/CT Dual‐Modal Imaging of Tumor Based on the Nonstoichiometric Na0.52YbF3.52:Er Upconversion Nanoprobes

Lanthanide (Ln³⁺)‐doped upconversion nanoparticles (UCNPs) as a new generation of multimodal bioprobes have attracted great interest for theranostic purpose. Herein, red emitting nonstoichiometric Na_0.52YbF_3.52:Er UCNPs of high luminescence intensity and color purity are synthesized via a facile solvothermal method. The red UC emission from the present nanophosphors is three times more intense than the well‐known green emission from the ≈30 nm sized hexagonal‐phase NaYF₄:Yb,Er UCNPs. By utilizing Na_0.52YbF_3.52:Er@SrF₂ UCNPs as multifunctional nanoplatforms, highly efficient in vitro and in vivo 915 nm light‐triggered photodynamic therapies are realized for the first time, with dramatically diminished overheating yet similar therapeutic effects in comparison to those triggered by 980 nm light. Moreover, by virtue of the high transverse relaxivity (r ₂) and the strong X‐ray attenuation ability of Yb³⁺ ions, these UCNPs also demonstrate good performances as contrast agents for high contrast magnetic resonance and X‐ray computed tomography dual‐modal imaging. Our research shows the great potential of the red emitting Na_0.52YbF_3.52:Er UCNPs for multimodal imaging‐guided photodynamic therapy of tumors.     

High‐Performance Upconversion Nanoprobes for Multimodal MR Imaging of Acute Ischemic Stroke

Multimodal magnetic resonance (MR) imaging, including MR angiography (MRA) and MR perfusion (MRP), plays a critical role in the diagnosis and surveillance of acute ischemic stroke. However, these techniques are hindered by the low T₁ relaxivity, short circulation time, and high leakage rate from vessels of clinical Magnevist. To address these problems, nontoxic polyethylene glycol (PEG)ylated upconversion nanoprobes (PEG‐UCNPs) are synthesized and first adopted for excellent MRA and MRP imaging, featuring high diagnostic sensitivity toward acute ischemic stroke in high‐resolution imaging. The investigations show that the agent possesses superior advantages over clinical Magnevist, such as much higher relaxivity, longer circulation time, and lower leakage rate, which guarantee much better imaging efficiency. Remarkably, an extremely small dosage (5 mg Gd kg^?1) of PEG‐UCNPs provides high‐resolution MRA imaging with the vascular system delineated much clearer than the Magnevist with clinical dosage as high as 108 mg Gd kg^?1. On the other hand, the long circulation time of PEG‐UCNPs enables the surveillance of the progression of ischemic stroke using MRA or MRP. Once translated, these PEG‐UCNPs are expected to be a promising candidate for substituting the clinical Magnevist in MRA and MRP, which will significantly lengthen the imaging time window and improve the overall diagnostic efficiency.     

Engineering of Lanthanide‐Doped Upconversion Nanoparticles for Optical Encoding

Lanthanide‐doped upconversion nanoparticles (UCNPs) are an emerging class of luminescent materials that emit UV or visible light under near infra‐red (NIR) excitations, thereby possessing a large anti‐Stokes shift property. Due to their sharp excitation and emission bands, excellent photo‐ and chemical stability, low autofluorescence, and high tissue penetration depth of the NIR light used for excitation, UCNPs have surpassed conventional fluorophores in many bioapplications. A better understanding of the mechanism of upconversion, as well as the development of better approaches to preparing UCNPs, have provided more opportunities to explore their use for optical encoding, which has the potential for applications in multiplex detection and imaging. With the current ability to precisely control the microstructure and properties of UCNPs to produce particles of tunable emission, excitation, luminescence lifetime, and size, various strategies for optical encoding based on UCNPs can now be developed. These optical properties of UCNPs (such as emission and excitation wavelengths, ratiometric intensity, luminescence lifetime, and multicolor patterns), and the strategies employed to engineer these properties for optical encoding of UCNPs through homogeneous ion doping, heterogeneous structure fabrication and microbead encapsulation are reviewed. The challenges and potential solutions faced by UCNP optical encoding are also discussed.     

Near-infrared light activated persistent luminescence nanoparticles via upconversion

Persistent luminescence nanoparticles (PLNPs) and upconversion nanoparticles (UCNPs) are two special optical imaging nanoprobes.In this study,efficient upconverted persistent luminescence (UCPL) is realized by combining their unique features into polymethyl methacrylate,forming a film composed of both PLNPs and UCNPs.The red persistent luminescence (～640 nm) of the PLNPs (CaS∶Eu,Tm,Ce) can be activated by upconverted green emission of UCNPs (β-NaYF4∶Yb,Er@NaYF4) excited by near-infrared light (NIR).Using this strategy,both the unique optical properties of PLNPs and UCNPs can be optimally synergized,thus generating efficient upconversion,photoluminescence,and UCPL simultaneously.The UCPL system has potential applications in in vivo bioimaging by simply monitoring the biocompatible low power density of NIR-light-excited persistent luminescence.Due to its simplicity,we anticipate that this method for the preparation of UCPL composite can be easily adjusted using other available upconversion and persistent phosphor pairs for a number of biophotonic and photonic applications.     

Aptamer-conjugated upconversion nanoprobes assisted by magnetic separation for effective isolation and sensitive detection of circulating tumor cells

Detection of circulating tumor cells （CTCs） plays an important role in cancer diagnosis and prognosis. In this study, aptamer-conjugated upconversion nano- particles （UCNPs） are used for the first time as nanoprobes to recognize tumor cells, which are then enriched by attaching with magnetic nanoparticles （MNPs） and placing in the presence of a magnetic field. Owing to the autofluorescence- free nature of upconversion luminescence imaging, as well as the use of magnetic separation to further reduce background signals, our technique allows for highly sensitive detection and collection of small numbers of tumor cells spiked into healthy blood samples, and shows promise for CTC detection in medical diagnostics.     

Responsive Upconversion Nanoprobe for Background‐Free Hypochlorous Acid Detection and Bioimaging

Responsive nanoprobes play an important role in bioassay and bioimaging, early diagnosis of diseases and treatment monitoring. Herein, a upconversional nanoparticle (UCNP)‐based nanoprobe, Ru@UCNPs, for specific sensing and imaging of hypochlorous acid (HOCl) is reported. This Ru@UCNP nanoprobe consists of two functional components,, i.e., NaYF₄:Yb, Tm UCNPs that can convert near infrared light‐to‐visible light as the energy donor, and a HOCl‐responsive ruthenium(II) complex [Ru(bpy)₂(DNCH‐bpy)](PF₆)₂ (Ru‐DNPH) as the energy acceptor and also the upconversion luminescence (UCL) quencher. Within this luminescence resonance energy transfer nanoprobe system, the UCL OFF–ON emission is triggered specifically by HOCl. This triggering reaction enables the detection of HOCl in aqueous solution and biological systems. As an example of applications, the Ru@UCNPs nanoprobe is loaded onto test papers for semiquantitative HOCl detection without any interference from the background fluorescence. The application of Ru@UCNPs for background‐free detection and visualization of HOCl in cells and mice is successfully demonstrated. This research has thus shown that Ru@UCNPs is a selective HOCl‐responsive nanoprobe, providing a new way to detect HOCl and a new strategy to develop novel nanoprobes for in situ detection of various biomarkers in cells and early disgnosis of animal diseases.     

DNA‐Assembled Core‐Satellite Upconverting‐Metal–Organic Framework Nanoparticle Superstructures for Efficient Photodynamic Therapy

DNA‐mediated assembly of core–satellite structures composed of Zr(IV)‐based porphyrinic metal‐organic framework (MOF) and NaYF₄,Yb,Er upconverting nanoparticles (UCNPs) for photodynamic therapy (PDT) is reported. MOF NPs generate singlet oxygen (¹O₂) upon photoirradiation with visible light without the need for additional small molecule, diffusional photosensitizers such as porphyrins. Using DNA as a templating agent, well‐defined MOF–UCNP clusters are produced where UCNPs are spatially organized around a centrally located MOF NP. Under NIR irradiation, visible light emitted from the UCNPs is absorbed by the core MOF NP to produce ¹O₂ at significantly greater amounts than what can be produced from simply mixing UCNPs and MOF NPs. The MOF–UCNP core–satellite superstructures also induce strong cell cytotoxicity against cancer cells, which are further enhanced by attaching epidermal growth factor receptor targeting affibodies to the PDT clusters, highlighting their promise as theranostic photodynamic agents.     

Theranostic Upconversion Nanobeacons for Tumor mRNA Ratiometric Fluorescence Detection and Imaging‐Monitored Drug Delivery

Remote optical detection and imaging of specific tumor‐related biomarkers and simultaneous activation of therapy according to the expression level of the biomarkers in tumor site with theranostic probes should be an effective modality for treatment of cancers. Herein, an upconversion nanobeacon (UCNPs‐MB/Dox) is proposed as a new theranostic nanoprobe to ratiometrically detect and visualize the thymidine kinase 1 (TK1) mRNA that can simultaneously trigger the Dox release to activate the chemotherapy accordingly. UCNPs‐MB/Dox is constructed with the conjugation of a TK1 mRNA‐specific molecular beacon (MB) bearing a quencher (BHQ‐1) and an alkene handle modified upconversion nanoparticle (UCNP) through click reaction and subsequently loading with a chemotherapy drug (Dox). With this nanobeacon, quantitative ratiometric upconversion detection of the target with high sensitivity and selectivity as well as the target triggered Dox release in vitro is demonstrated. The sensitive and selective ratiometric detection and imaging of TK1 mRNA under the irradiation of near infrared light (980 nm) and the mRNA‐dependent release of Dox for chemotherapy in the tumor MCF‐7 cells and A549 cells are also shown. This work provides a smart and robust platform for gene‐related tumor theranostics.     

Hybrid Nanoparticle Pyramids for Intracellular Dual MicroRNAs Biosensing and Bioimaging

This study strategically fabricates multifunctional nanopyramids to allow the ultrasensitive quantification of dual microRNAs (miR‐203^b and miR‐21) in living cells and their responsive bioimaging in vivo. The nanopyramids, composed of Au‐Cu₉S₅ nanoparticles (NPs), upconversion NPs (UCNPs), and Ag₂S NPs, emit two luminescent signals simultaneously with excitation at 808 nm, arising from the UCNPs at 541 nm in the visible region and from the Ag₂S NPs at 1227 nm in the second window of near‐infrared (NIR‐II) region. The upconversion luminescence has a linear relationship with miR‐203^b from 0.13 to 54.54 fmol per 10 µg_RNA and a limit of detection (LOD) of 0.09 fmol per 10 µg_RNA, whereas the Ag₂S NP luminescence has a linear relationship with miR‐21 from 0.37 to 43.56 fmol per 10 µg_RNA, with a LOD of 0.23 fmol per 10 µg_RNA. Significantly, this study demonstrates that the nanopyramids can be successfully used for miRs‐responsive bioimaging in a tumor‐bearing animal model. Furthermore, taking advantage of the photothermal capabilities of pyramids, the tumors can also be eliminated completely. These nanopyramids not only overcome the obstacles in the simultaneous detection of multiple miRs at the cellular level but also provide a cancer theranostic platform in vivo.     

Phytotoxicity,Translocation, and Biotransformation of NaYF4 Upconversion Nanoparticles in a Soybean Plant

The increasing uses of rare‐earth‐doped upconversion nanoparticles (UCNPs) have obviously caused many concerns about their potential toxicology on live organisms. In addition, the UCNPs can be released into the environment, then transported into edible crop plants, and finally entered into food chain. Here, the soybean is chosen as a model plant to study the subchronic phytotoxicity, translocation, and biotransformation of NaYF₄ UCNPs. The incubation with UCNPs at a relative low concentration of 10 μg mL^?1 leads to growth promotion for the roots and stems, while concentration exceeding 50 μg mL^?1 brings concentration‐dependent inhibition. Upconversion luminescence imaging and scanning electron microscope characterization show that the UCNPs can be absorbed by roots and parts of the adsorbed UCNPs are then transported through vessels to stems and leaves. The near‐edge X‐ray absorption fine structure spectra reveal that the adsorbed NaYF₄ nanoparticles are relatively stable during a 10 d incubation. Energy‐dispersive X‐ray spectrum further indicates that a small amount of NaYF₄ is dissolved/digested and can transform into Y‐phosphate clusters in roots.