Lanthanide-doped luminescent nano-bioprobes for the detection of tumor markers

Recent advances of lanthanide nanomaterials in Tumor NIR fluorescence detection and treatment

Lanthanide nanomaterials have garnered significant attention from researchers among the main near-infrared (NIR) fluorescent nanomaterials due to their excellent chemical and fluorescence stability, narrow emission band, adjustable luminescence color, and long lifetime. In recent years, with the preparation, functional modification, and fluorescence improvement of lanthanide materials, great progress has been made in their application in the biomedical field. This review focuses on the latest progress of lanthanide nanomaterials in tumor diagnosis and treatment, as well as the interaction mechanism between fluorescence and biological tissues. We introduce a set of efficient strategies for improving the fluorescence properties of lanthanide nanomaterials and discuss some representative in-depth research work in detail, showcasing their superiority in early detection of ultra-small tumors, phototherapy, and real-time guidance for surgical resection. However, lanthanide nanomaterials have only realized a portion of their potential in tumor applications so far. Therefore, we discuss promising methods for further improving the performance of lanthanide nanomaterials and their future development directions.

Platinum Drug-Incorporating Polymeric Nanosystems for Precise Cancer Therapy

Platinum (Pt) drugs are widely used in clinic for cancer therapy, but their therapeutic outcomes are significantly compromised by severe side effects and acquired drug resistance. With the emerging immunotherapy and imaging-guided cancer therapy, precise delivery and release of Pt drugs have drawn great attention these days. The targeting delivery of Pt drugs can greatly increase the accumulation at tumor sites, which ultimately enhances antitumor efficacy. Further, with the combination of Pt drugs and other theranostic agents into one nanosystem, it not only possesses excellent synergistic efficacy but also achieves real-time monitoring. In this review, after the introduction of Pt drugs and their characteristics, the recent progress of polymeric nanosystems for efficient delivery of Pt drugs is summarized with an emphasis on multi-modal synergistic therapy and imaging-guided Pt-based cancer treatment. In the end, the conclusions and future perspectives of Pt-encapsulated nanosystems are given.

Effect of Cr3+ doping on structural and optical properties of Eu3+ doped LaVO4 phosphor

In this work, the Eu³⁺, Cr³⁺ doped and co-doped LaVO₄ phosphors have been prepared through a high temperature solid-state reaction method. The powder XRD patterns of phosphors are very sharp and intense, which reflects a highly crystalline nature of phosphors. The XRD data were also refined by a Rietveld refinement method. The particle size of the phosphor samples lies in the sub-micron to micron range. The existence of La, Eu, Cr, V and O elements was verified by EDS spectra. The FTIR spectra show various absorption bands due to different vibrating groups. The optical band gap of the phosphor decreases on increasing concentration of Cr³⁺ ion. The photoluminescence excitation spectra of Eu³⁺, Cr³⁺ co-doped LaVO₄ phosphor exhibit bands due to Eu³⁺ and Cr³⁺ ions. The Eu³⁺ doped LaVO₄ phosphor exciting at 393 and 316 nm wavelengths gives intense red color at 614 nm due to the ⁵D₀ → ⁷F₂ transition of the Eu³⁺ ion. When the Cr³⁺ ion is co-doped in the Eu³⁺ doped LaVO₄ phosphor the emission spectra contain emission bands due to Eu³⁺ and Cr³⁺ ions. The emission intensity of Eu³⁺ doped phosphor reduces due to energy transfer from Eu³⁺ to Cr³⁺ ions in presence of Cr³⁺ ions upon 393 and 386 nm excitations. The lifetime of the ⁵D₀ level of Eu³⁺ ions decreases in the Eu³⁺, Cr³⁺ co-doped LaVO₄ phosphor, which also reflects the energy transfer. The Eu³⁺, Cr³⁺ co-doped LaVO₄ phosphor also produces a large amount of heat upon 980 nm excitation. Thus, the Eu³⁺, Cr³⁺ co-doped LaVO₄ phosphors may be used for LEDs, solid state lighting and heat generating devices.

Lanthanide-Doped Upconversion Nanoparticles: Exploring A Treasure Trove of NIR-Mediated Emerging Applications

Lanthanide-doped upconversion nanoparticles (UCNPs) possess the remarkable ability to convert multiple near-infrared (NIR) photons into higher energy ultraviolet-visible (UV-vis) photons, making them a prime candidate for several advanced applications within the realm of nanotechnology. Compared to traditional organic fluorophores and quantum dots (QDs), UCNPs possess narrower emission bands (fwhm of 10-50 nm), large anti-Stokes shifts, low toxicity, high chemical stability, and resistance to photobleaching and blinking. In addition, unlike UV-vis excitation, NIR excitation is nondestructive at lower power intensities and has high tissue penetration depths (up to 2 mm) with low autofluorescence and scattering. Together, these properties make UCNPs exceedingly favored for advanced bioanalytical and theranostic applications, where these systems have been well-explored. UCNPs are also well-suited for bioimaging, optically modulating chemistries, forensic science, and other state-of-the-art research applications. In this review, an up-to-date account of emerging applications in UCNP research, beyond bioanalytical and theranostics, are presented including optogenetics, super-resolution imaging, encoded barcodes, fingerprinting, NIR vision, UCNP-assisted photochemical manipulations, optical tweezers, 3D printing, lasing, NIR-II imaging, UCNP-molecule nanohybrids, and UCNP-based persistent luminescent nanocrystals.

Review on Metal-Based Theranostic Nanoparticles for Cancer Therapy and Imaging

Theranostic agents are promising due to their ability to diagnose, treat and monitor different types of cancer using a variety of imaging modalities. The advantage specifically of nanoparticles is that they can accumulate easily at the tumor site due to the large gaps in blood vessels near tumors. Such high concentration of theranostic agents at the target site can lead to enhancement in both imaging and therapy. This article provides an overview of nanoparticles that have been used for cancer theranostics, and the different imaging, treatment options and signaling pathways that are important when using nanoparticles for cancer theranostics. In particular, nanoparticles made of metal elements are emphasized due to their wide applications in cancer theranostics. One important aspect discussed is the ability to combine different types of metals in one nanoplatform for use as multimodal imaging and therapeutic agents for cancer.

Nanotechnology-based approaches for effective detection of tumor markers: A comprehensive state-of-the-art review

As well-appreciated biomarkers, tumor markers have been spotlighted as reliable tools for predicting the behavior of different tumors and helping clinicians ascertain the type of molecular mechanism of tumorigenesis. The sensitivity and specificity of these markers have made them an object of even broader interest for sensitive detection and staging of various cancers. Enzyme-linked immunosorbent assay (ELISA), fluorescence-based, mass-based, and electrochemical-based detections are current techniques for sensing tumor markers. Although some of these techniques provide good selectivity, certain obstacles, including a low sample concentration or difficulty carrying out the measurement, limit their application. With the advent of nanotechnology, many studies have been carried out to synthesize and employ nanomaterials (NMs) in sensing techniques to determine these tumor markers at low concentrations. The fabrication, sensitivity, design, and multiplexing of sensing techniques have been uplifted due to the attractive features of NMs. Various NMs, such as magnetic and metal nanoparticles, up-conversion NPs, carbon nanotubes (CNTs), carbon-based NMs, quantum dots (QDs), and graphene-based nanosensors, hyperbranched polymers, optical nanosensors, piezoelectric biosensors, paper-based biosensors, microfluidic-based lab-on-chip sensors, and hybrid NMs have proven effective in detecting tumor markers with great sensitivity and selectivity. This review summarizes various categories of NMs for detecting these valuable markers, such as prostate-specific antigen (PSA), human carcinoembryonic antigen (CEA), alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), human epidermal growth factor receptor-2 (HER2), cancer antigen 125 (CA125), cancer antigen 15-3 (CA15-3, MUC1), and cancer antigen 19-9 (CA19-9), and highlights recent nanotechnology-based advancements in detection of these prognostic biomarkers.

A near-infrared light triggered fluormetric biosensor for sensitive detection of acetylcholinesterase activity based on NaErF4: 0.5 % Ho3+@NaYF4 upconversion nano-probe

Acetylcholinesterase (AChE), as an important neurotransmitter, is widely present in the peripheral and central nervous systems. The aberrant expression of AChE could cause diverse neurodegenerative diseases. Herein, we developed a facile and interference-free fluorimetric biosensing platform for highly sensitive AChE activity determination based on a NaErF₄: 0.5 % Ho³⁺@NaYF₄ nano-probe. This nano-probe exhibits a unique property of emitting bright monochromic red (650 nm) upconversion (UC) emission under multiband (~808, ~980, and ~1530 nm) near-infrared (NIR) excitations. The principle of this detection relies on the quenching of the strong monochromic red UC emission by oxidization products of 3,3',5,5'-tetramethylbenzidine generated through AChE-modulated cascade reactions. This system shows a great sensing performance with a detection limit (LOD) of 0.0019 mU mL^{- 1} for AChE, as well as good specificity and stability. Furthermore, we validated the potential of the nano-probe in biological samples by determination of AChE in whole blood with a LOD of 0.0027 mU mL^-1, indicating the potential application of our proposed platform for monitoring the progression of AChE-related disease.

Real-Time Tracking of Highly Luminescent Mesoporous Silica Particles Modified with Europium β-Diketone Chelates in Living Cells

Highly luminescent europium complexes modified mesoporous silica particles (MSP) were synthesized as an imaging probes for both in-vitro diagnostic and in-vivo cellular tracking agents. Europium β-diketone chelates (4,4,4-trifluoro-l-(2-thienyl)-l,3-butanedione) trioctylphosphine europium (III) (Eu(TTA)₃(P(Oct)₃)₃) were incorporated inside the nanocavities that existed in hierarchical MSP (Eu@MSP). The MSP and Eu@MSP on mouse bone marrow-derived macrophages (BMDMs) did not show any toxic effect. The MSP and Eu@MSP in the BMDMs were found at cytoplasm without any degradation and immunogenicity. However, both pro- and anti-inflammatory cytokines of macrophages were significantly increased when lipopolysaccharide and a high concentration (100 μg/mL) of MSP and Eu@MSP were treated simultaneously.

Amphiphilic ligand modified gold nanocarriers to amplify lanthanide loading for ultrasensitive DELFIA detection ofCronobacter

Thiolated ethylenediaminetetraacetic acid and thiolated acylhydrazine-terminated ligands modified gold nanoflowers as amplified nanocarriers to increase the Ln³⁺labeling ratio for improving the sensitivity of traditional DELFIA.

A fluorescent molecularly imprinted device for the on-line analysis of AFP in human serum

MIT is a promising strategy in antibody free analysis for tumour markers. Conventional nanosized MIPs with off-line analysis are beset by tedious operation and unsatisfactory analysis performance. In this work, an on-line analytical device to directly detect AFP, which is a typical tumour marker in cancer screening, was prepared for the first time. A microscope slide was chosen to be the basis of the device. APBA-PA, a polymerizable fluorescent boronic acid monomer, was synthesised and grafted on the surface of the microscope slide to act as the signal transduction pathway between the templates and the device. Along with the hydrolysis of TEOS and the elution of the templates, a portable, stable, easy to operate and low-cost analysis device for AFP with excellent repeatability was successfully prepared. Owing to the excellent selectivity and highly sensitive fluorescence response ability of the device towards the templates, the on-line detection of AFP in human serum was realized. A series of characterizations were applied to the device, and its analysis performance and possible detection mechanism were carefully studied. Furthermore, the device exhibited appropriate application prospects by comparing its analysis results with those of the commercially available ELISA. In our perception, this work is an important step towards MIPs for clinical applications.

Synthesis, functionalization and properties of uniform europium-doped sodium lanthanum tungstate and molybdate (NaLa(XO4)2, X = Mo,W) probes for luminescent and X-ray computed tomography bioimaging

A one-pot simple procedure for the synthesis of uniform, ellipsoidal Eu³⁺-doped sodium lanthanum tungstate and molybdate (NaLa(XO₄)₂, X  = W, Mo) nanophosphors, functionalized with carboxylate groups, is described. The method is based on a homogeneous precipitation process at 120 °C from appropriate Na⁺, Ln³⁺ and tungstate or molybdate precursors dissolved in ethylene glycol/water mixtures containing polyacrylic acid. A comparative study of the luminescent properties of both luminescent materials as a function of the Eu³⁺ doping level has been performed to find the optimum nanophosphor, whose efficiency as X-ray computed tomography contrast agent is also evaluated and compared with that of a commercial probe. Finally, the cell viability and colloidal stability in physiological pH medium of the optimum samples have also been studied to assess their suitability for biomedical applications.

Mixed Lanthanide Oxide Nanoparticles Coated with Alginate-Polydopamine as Multifunctional Nanovehicles for Dual Modality: Targeted Imaging and Chemotherapy

Integrating anticancer drugs and diagnostic agents in a polymer nanosystem is an emerging and promising strategy for improving cancer treatment. However, the development of multifunctional nanoparticles (NPs) for an "all-in-one" platform characterized by specific targeting, therapeutic efficiency, and imaging feedback remains an unmet clinical need. In this study, pH-responsive mixed-lanthanide-based multifunctional NPs were fabricated based on simple metal-ligand interactions for simultaneous cancer cell imaging and drug delivery. We investigated two new systems of alginate-polydopamine complexed with either terbium/europium or dysprosium/erbium oxide NPs (Tb/Eu@AlgPDA or Dy/Er@AlgPDA NPs). Tb/Eu@AlgPDA NPs were then functionalized with the tumor-targeting ligand folic acid (FA) and loaded with the anticancer drug doxorubicin (DOX) to form FA-Tb/Eu@AlgPDA-DOX NPs. Using such systems, the mussel-inspired property of PDA was introduced to improve tumor targetability and penetration, in addition to active targeting (via FA-folate receptor interactions). Determining the photoluminescence efficiency showed that the Tb/Eu@AlgPDA system was superior to the Dy/Er@AlgPDA system, presenting intense and sharp emission peaks on the fluorescence spectra. In addition, compared to Dy/Er@AlgPDA NPs (82.4%), Tb/Eu@AlgPDA NPs exhibited negligible cytotoxicity with >93.3% HeLa cell viability found in MTT assays at NP concentrations of up to 0.50 mg/mL and high biocompatibility when incubated with zebrafish (Danio rerio) embryos and larvae. The FA-Tb/Eu@AlgPDA-DOX system exhibited a pH-responsive and sustained drug-release pattern. In a spheroid model of HeLa cells, the FA-Tb/Eu@AlgPDA-DOX system showed a better penetration efficiency and spheroid growth-inhibitory effect than free DOX. After incubation with zebrafish embryos, the FA-Tb/Eu@AlgPDA-DOX system also showed improved antitumor efficacies versus the other experimental groups in HeLa tumor cell xenografted zebrafish. Therefore, our results suggested that FA-Tb/Eu@AlgPDA-DOX NPs are promising multifunctional nanocarriers with therapeutic capacity for tumor targeting and penetration.

X-ray Nanocrystal Scintillator-Based Aptasensor for Autofluorescence-Free Detection

Optical biosensors that enable highly sensitive detection of biomolecules are useful for applications in early disease diagnosis. However, the presence of UV-vis-induced background fluorescence in biological samples is still challenging. Thanks to the weak scattering and nearly no absorption of biological chromophores under X-ray excitation, we describe the development of an X-ray nanocrystal scintillator-based aptasensor that is able to achieve sensitive and homogeneous detection of target biomolecules. In this work, aptamer-labeled lanthanide-doped nanocrystal scintillators was designed to rapidly and sensitively detect lysozyme via fluorescence resonance energy transfer (FRET) in human serum samples. Benefiting from the use of low-dose X-ray as an excitation source and high-efficiency luminescence of heavy atoms-contained nanocrystals, the proposed X-ray nanocrystal scintillator-based aptasensor can readily detect lysozyme with a high sensitivity up to 0.94 nM, as well as an excellent specificity and sample recoveries. Thus, our technique suggests that the X-ray scintillating aptasensor can create a new generation of autofluorescence-free high-sensitivity strategy for biomarker sensing in biomedical applications.

Interface-Dependent Radiative Lifetimes of Yb3+, Er3+ Co-doped Single NaYF4 Upconversion Nanowires

The development of upconversion nanomaterials for many photonic applications requires a detailed understanding of their radiative lifetimes that in turn depend critically on local environmental conditions. In this work, hexagonal (β-phase) sodium-yttrium-fluoride (NaYF₄) nanowires (NWs) were synthesized and substitutionally co-doped with a luminescent solid solution of trivalent erbium and ytterbium ions. A single-beam laser trapping instrument was used in tandem with a piezo-controlled, variable-temperature stage to precisely vary the nanowire's distance from the substrate. The spontaneous photoluminescence lifetime of the ⁴S_3/2 → ⁴I_15/2 transition from Er³⁺ ions was observed to change by >60% depending on the ions' separation distance from a planar (water/glass) dielectric interface. The ⁴S_3/2 state lifetime is observed to increase by a factor of 1.62 ± 0.01 as the distance from the quartz coverslip increases from ∼0 nm to ∼40 μm. Less significant changes in the luminescence lifetime (≤10%) were observed over a temperature range between 25 and 50 °C. The distance dependence of the lifetime is interpreted quantitatively in the context of classical electromagnetic coupling between Er³⁺ ions within the nanowire and the adjacent dielectric interface. We also demonstrate potential applications of the NaYF₄ NWs for both controlling and probing temperatures at nanometer scales by integrating them within a poly(dimethylsiloxane) composite matrix.

Near-Infrared Upconversion Luminescence and Bioimaging In Vivo Based on Quantum Dots

Recently, upconversion luminescence (UCL) has been widely applied in bioimaging due to its low autofluorescence and high contrast. However, a relatively high power density is still needed in conventional UCL bioimaging. In the present study, an ultralow power density light, as low as 0.06 mW cm-2, is applied as an excitation source for UCL bioimaging with PbS/CdS/ZnS quantum dots (UCL-QDs) as probes. The speculated UCL mechanism is a phonon-assisted single-photon process, and the relative quantum yield is up to 4.6%. As determined by continuous irradiation with a 980 nm laser, the UCL-QDs show excellent photostability. Furthermore, UCL-QDs-based probe is applied in tumor, blood vessel, and lymph node bioimaging excited with an eye-safe low-power light-emitting diode light in a nude mouse with few heat effects.

Nitrogen doped carbon dots: mechanism investigation and their application for label free CA125 analysis

Nitrogen-doped CDs (N-CDs) were firstly prepared by using pear juice as the carbon source and ethanediamine as a nitrogen doping precursor with a microwave assisted pyrolysis technique. Based on the fluorescence recovery induced by competitive adsorption and desorption, a label-free “turn on” fluorescence assay with high sensitivity and selectivity was proposed for the analysis of CA125.

Lanthanide-doped mesoporous MCM-41 nanoparticles as a novel optical–magnetic multifunctional nanobioprobe

To research and develop potential multifunctional nanoprobes for biological application, lanthanide-doped MCM-41 (Ln-MCM-41, Ln = Gd/Eu) silica nanoparticles with excellent pore structure and optical–magnetic properties were synthesized via a facile and economical sol–gel method. The microstructure and pore distribution of Ln-MCM-41 nanoparticles were obviously affected by the Ln-doping. As the Ln/Si mole ratio increased, the specific surface area and total pore volume of Ln-MCM-41 nanoparticles rapidly decreased. However, the Ln-MCM-41 nanoparticles still retained the typical well-ordered mesoporous structure, and exhibited excellent drug release behavior. Moreover, the drug release rate of Ln-MCM-41 was remarkably pH-dependent and increased gradually upon decreasing pH. Additionally, these nanoparticles also exhibit considerable photoluminescence properties, living cells photoluminescence imaging in vitro, and paramagnetism behavior at room temperature due to the Ln³⁺-ions doping. Our research shows the possibility of our Ln-MCM-41 nanoparticles as multifunctional nanoprobes for application in bioseparation, bioimaging, and drug delivery.

Mesoporous Ln-MCM-41 nanoparticles with optical–magnetic dual-modal properties can be used as a multifunctional nanoprobe for application in bioseparation, optical–magnetic bioimaging, and drug delivery.

Advances in the application of upconversion nanoparticles for detecting and treating cancers

The detection and treatment of cancer cells at an early stage are crucial for prolonging the survival time and improving the quality of life of patients. Upconversion nanoparticles (UCNPs) have unique physical and chemical advantages and likely provide a platform for detecting and treating cancer cells at an early stage. In this paper, the principle of UCNPs as chemical sensors based on fluorescence resonance energy transfer (FRET) has been briefly introduced. Research progress in such chemical sensors for detecting and analyzing bioactive substances and heavy metal ions at the subcellular level has been summarized. The principle of UCNP-based nanoprobe-targeting of cancer cells has been described. The research progress in using nanocomposites for cancer cell detection, namely cancer cell targeted imaging and tissue staining, has been discussed. In the field of cancer treatment, the principles and research progress of UCNPs in photodynamic therapy and photothermal therapy of cancer cells are systematically discussed. Finally, the prospects for UCNPs and remaining challenges to UCNP application in the field of cancer diagnosis and treatment are briefly described. This review provides powerful theoretical guidance and useful practical information for the research and application of UCNPs in the field of cancer.

Impact of Lanthanide Nanomaterials on Photonic Devices and Smart Applications

Half a century after its initial emergence, lanthanide photonics is facing a profound remodeling induced by the upsurge of nanomaterials. Lanthanide-doped nanomaterials hold promise for bioapplications and photonic devices because they ally the unmatched advantages of lanthanide photophysical properties with those arising from large surface-to-volume ratios and quantum confinement that are typical of nanoobjects. Cutting-edge technologies and devices have recently arisen from this association and are in turn promoting nanophotonic materials as essential tools for a deeper understanding of biological mechanisms and related medical diagnosis and therapy, and as crucial building blocks for next-generation photonic devices. Here, the recent progress in the development of nanomaterials, nanotechnologies, and nanodevices for clinical uses and commercial exploitation is reviewed. The candidate nanomaterials with mature synthesis protocols and compelling optical uniqueness are surveyed. The specific fields that are directly driven by lanthanide doped nanomaterials are emphasized, spanning from in vivo imaging and theranostics, micro-/nanoscopic techniques, point-of-care medical testing, forensic fingerprints detection, to micro-LED devices.

808 nm excited energy migration upconversion nanoparticles driven by a Nd3+-Trinity system with color-tunability and superior luminescence properties

We have developed energy migration upconversion (EMU) nanoparticles (UCNPs) with optimal Nd³⁺-sensitization under excitation of an 808 nm laser to avoid over-heating effects caused by a 980 nm laser while maximizing the excitation efficiency. To realize efficient 808 nm sensitization, a "Nd³⁺-Trinity system" was implemented in the energy migration upconversion (EMU) cores (NaGdF₄:Yb,Tm@NaGdF₄:Yb,X, X = Eu/Tb), resulting in a core-multishell structure of EMU cores (accumulation layer@activation layer)@transition layer@harvest layer@activation layer. The spatially separated dopants and optimized Yb³⁺/Nd³⁺ content effectively prevented severe quenching events in the UCNPs and their Nd³⁺-sensitized EMU-based photoluminescence mechanism was studied under 808 nm excitation. These Nd³⁺-Trinity EMU system UCNPs presented enhanced upconversion luminescence and prolonged lifetime compared to the 980 nm excited UCNPs of the EMU system. It is proposed that 975 nm and 1056 nm NIR photons induced from the Nd³⁺ → Yb³⁺ energy transfer facilitate the Tm³⁺ accumulation process due to the matched energy gaps, which contributes to the extended lifetimes. More importantly, the synthesized UCNPs had a small average size of sub-15 nm and they not only exhibited color-tunability via Eu³⁺/Tb³⁺ activators, but also released a larger portion of Tm³⁺ red emission at 647 nm and had better penetration ability in water under 808 nm excitation, which are favorable for bioimaging applications.

Phenanthriplatin(iv) conjugated multifunctional up-converting nanoparticles for drug delivery and biomedical imaging

Platinum-based drugs cisplatin, carboplatin, and oxaliplatin are widely used in the clinical treatment of cancer.

Shaping Luminescent Properties of Yb3+ and Ho3+ Co-Doped Upconverting Core-Shell β-NaYF4 Nanoparticles by Dopant Distribution and Spacing

At the core of luminescence color and lifetime tuning of rare earth doped upconverting nanoparticles (UCNPs), is the understanding of the impact of the particle architecture for commonly used sensitizer (S) and activator (A) ions. In this respect, a series of core@shell NaYF₄ UCNPs doped with Yb³⁺ and Ho³⁺ ions are presented here, where the same dopant concentrations are distributed in different particle architectures following the scheme: YbHo core and YbHo@…, …@YbHo, Yb@Ho, Ho@Yb, YbHo@Yb, and Yb@YbHo core-shell NPs. As revealed by quantitative steady-state and time-resolved luminescence studies, the relative spatial distribution of the A and S ions in the UCNPs and their protection from surface quenching has a critical impact on their luminescence characteristics. Although the increased amount of Yb³⁺ ions boosts UCNP performance by amplifying the absorption, the Yb³⁺ ions can also efficiently dissipate the energy stored in the material through energy migration to the surface, thereby reducing the overall energy transfer efficiency to the activator ions. The results provide yet another proof that UC phosphor chemistry combined with materials engineering through intentional core@shell structures may help to fine-tune the luminescence features of UCNPs for their specific future applications in biosensing, bioimaging, photovoltaics, and display technologies.

A novel upconversion luminescence derived photoelectrochemical immunoassay: ultrasensitive detection to alpha-fetoprotein

Fabrication of near-infrared light-triggered photoelectrochemical (PEC) sensors based on the upconversion nanophosphors (UCNPs) is a novel approach, which exhibits the advantages of low background signal and non-damage to the biological substance as well as high sensitivity and improved electric detection in PEC sensors. Herein we demonstrate the preparation of novel and high-quality ZnO inverse opal photonic crystals (IOPCs)/Ag/NaYF₄:Yb,Tm hybrid films by different advanced film techniques, including colloidal self-assembling, vapor phase deposition and pulsed laser deposition and its application to sensitive detection of alpha-fetoprotein (AFP). In the complex device, ZnO IOPCs and surface plasmon resonance (SPR) of silver had ability to largely enhance local excitation electromagnetic field of NaYF₄:Yb,Tm, resulting in efficient near-infrared to visible/ultraviolet upconversion luminescence (UCL). The ultraviolet light emitted by NaYF₄:Yb,Tm could b further reabsorbed by ZnO, generating PEC responses. Furthermore, because of the high specific surface area of ZnO IOPCs and the conductivity of Ag films, ZnO IOPCs/Ag/NaYF₄:Yb,Tm hybrid films based near-infrared light-triggered PEC sensors showed ultrasensitive detection of AFP with a linear range from 0.05 ng mL^-1 to 100 ng mL^-1 and a low detection limit of ∼0.04 ng mL^-1 (40 pg mL^-1). Such an advanced device also shows promise in detection of other cancer markers in clinical and biological analysis.

Minimizing the Heat Effect of Photodynamic Therapy Based on Inorganic Nanocomposites Mediated by 808 nm Near-Infrared Light

Photodynamic therapy (PDT) based on photosensitizers (PSs) constructed with nanomaterials has become popular in cancer treatment, especially oral carcinoma cell. This therapy is characterized by improved PS accumulation in tumor regions and generation of reactive oxygen species (ROS) for PDT under specific excitation. In the selection of near-infrared (NIR) window, 808 nm NIR light because it can avoid the absorption of water is particularly suitable for the application in PDT. Hence, multiband emissions under a single 808 nm near-infrared excitation of Nd³⁺ -sensitized upconversion nanoparticles (808 nm UCNPs) have been applied for the PDT effect. 808 nm UCNPs serve as light converter to emit UV light to excite inorganic PS, graphitic carbon nitride quantum dots (CNQDs), thereby generating ROS. In this study, a nanocomposite consisting UCNPs conjugated with poly-l-lysine (PLL) to improve binding with CNQDs is fabricated. According to the research results, NIR-triggered nanocomposites of 808 nm UCNP-PLL@CNs have been verified by significant improvement in ROS generation. Consequently, 808 nm UCNP-PLL@CNs exhibit high capability for ROS production and efficient PDT in vitro and in vivo. Moreover, the mechanism of PDT treatment by 808 nm UCNP-PLL@CNs is evaluated using the cell apoptosis pathway.

An amplified comparative fluorescence resonance energy transfer immunosensing of CA125 tumor marker and ovarian cancer cells using green and economic carbon dots for bio-applications in labeling, imaging and sensing

CA125, is a marker in the clinical diagnosis of several cancers and currently is the best serum-based tumor marker for ovarian cancer. Here, we developed an ultrasensitive antibody-ssDNA aptamer sandwich-type fluorescence immunosensor for CA125 detection. Based on a novel signal amplification strategy the carbon dots (CDs) functionalized with aptamer (CD-aptamer) used as detection probe and PAMAM-Dendrimers/AuNPs was used for covalent attachment of CA125-antibody and completing the sandwich assay method. By measuring of fluorescence resonance energy transfer (FRET) signals between CDs and AuNPs as nanoquenchers, the fluorescence signal quenched during sandwich complex formed between anti-CA125, CA125 and CDs-Aptamer and decreasing of fluorescence response signal is related to CA125 concentrations. Under optimal conditions, the immunosensor exhibited an extremely low calculated detection limit of 0.5fg/mL with wide linear range 1.0fg/mL to 1.0ng/mL of CA 125. The application of the immunosensor for CA125 detection in serum samples and measuring of ovarian-cancer cells was also investigated. The immunosensor revealed good sensitivity and specificity with ovarian cell concentrations from 2.5×10³ to 2×10⁴cells/mL with correlation coefficient of 0.9937 and detection limit of 400cells/mL (4 cell in 10μL), indicating potential application of immunosensor in clinical monitoring of tumor biomarkers. Furthermore, the cell viability was not changed upon treatment with CDs probe during 24h, showing the low cytotoxicity of the probe. More importantly, CDs-antibody hybrid was achieved in selective imaging of the cancer cells over the OVCAR-3 line cells, implying its potential applications in biosensing, as well as in cancer diagnosis.

Highly Emissive Dye-Sensitized Upconversion Nanostructure for Dual-Photosensitizer Photodynamic Therapy and Bioimaging

Rare-earth-based upconversion nanotechnology has recently shown great promise for photodynamic therapy (PDT). However, the NIR-induced PDT is greatly restricted by overheating issues on normal bodies and low yields of reactive oxygen species (ROS, ¹O₂). Here, IR-808-sensitized upconversion nanoparticles (NaGdF₄:Yb,Er@NaGdF₄:Nd,Yb) were combined with mesoporous silica, which has Ce6 (red-light-excited photosensitizer) and MC540 (green-light-excited photosensitizer) loaded inside through covalent bond and electrostatic interaction, respectively. When irradiated by tissue-penetrable 808 nm light, the IR-808 greatly absorb 808 nm photons and then emit a broadband peak which overlaps perfectly with the absorption of Nd³⁺ and Yb³⁺. Thereafter, the Nd³⁺/Yb³⁺ incorporated shell synergistically captures the emitted NIR photons to illuminate NaGdF₄:Yb,Er zone and then radiate ultrabright green and red emissions. The visible emissions simultaneously activate the dual-photosensitizer to produce a large amount of ROS and, importantly, low heating effects. The in vitro and in vivo experiments indicate that the dual-photosensitizer nanostructure has trimodal (UCL/CT/MRI) imaging functions and high anticancer effectiveness, suggesting its potential clinical application as an imaging-guided PDT technique.

Epigenetic assays for chemical biology and drug discovery

The implication of epigenetic abnormalities in many diseases and the approval of a number of compounds that modulate specific epigenetic targets in a therapeutically relevant manner in cancer specifically confirms that some of these targets are druggable by small molecules. Furthermore, a number of compounds are currently in clinical trials for other diseases including cardiovascular, neurological and metabolic disorders. Despite these advances, the approved treatments for cancer only extend progression-free survival for a relatively short time and being associated with significant side effects. The current clinical trials involving the next generation of epigenetic drugs may address the disadvantages of the currently approved epigenetic drugs.

The identification of chemical starting points of many drugs often makes use of screening in vitro assays against libraries of synthetic or natural products. These assays can be biochemical (using purified protein) or cell-based (using for example, genetically modified, cancer cell lines or primary cells) and performed in microtiter plates, thus enabling a large number of samples to be tested. A considerable number of such assays are available to monitor epigenetic target activity, and this review provides an overview of drug discovery and chemical biology and describes assays that monitor activities of histone deacetylase, lysine-specific demethylase, histone methyltransferase, histone acetyltransferase and bromodomain. It is of critical importance that an appropriate assay is developed and comprehensively validated for a given drug target prior to screening in order to improve the probability of the compound progressing in the drug discovery value chain.

Charge convertibility and near infrared photon co-enhanced cisplatin chemotherapy based on upconversion nanoplatform

Optimal nano-sized drug carrier requires long blood circulation, selective extravasation, and efficient cell uptake. Here we develop a charge-convertible nanoplatform based on Pt(IV) prodrug loaded NaYF₄:Yb,Tm upconversion nanoparticles (UCNs), followed by coating a layer of PEG-PAH-DMMA polymer (UCNs-Pt(IV)@PEG-PAH-DMMA). The polymer endows the platform with high biocompatibility, initial nano-size for prolonged blood circulation and selective extravasation. Especially, the anionic polymer can response to the mild acidic stimulus (pH ∼6.5) of tumor extracellular microenvironment and experience charge-shifting to a cationic polymer, resulting in electrostatic repulsion and releases of positive UCNs-Pt(IV). The positive UCNs-Pt(IV) nanoparticles have high affinity to negative cell membrane, leading to efficacious cell internalization. Simultaneously, the ultraviolet (UV) light emitted from UCNs upon near-infrared (NIR) light irradiation, together with the reductive glutathione (GSH) in cancer cells efficiently activate the Pt(IV) prodrug to highly cytotoxic Pt(II), realizing NIR photon improved chemotherapy. The experimental results reveal the charge convertibility, low adverse effect and markedly enhanced tumor ablation efficacy upon NIR laser irradiation of this smart nanoplatform. Moreover, combining the inherent upconversion luminescence (UCL) and computed tomography (CT) imaging capabilities, an alliance of cancer diagnosis and therapy has been achieved.

Resonance Energy Transfer in Upconversion Nanoplatforms for Selective Biodetection

Resonance energy transfer (RET) describes the process that energy is transferred from an excited donor to an acceptor molecule, leading to a reduction in the fluorescence emission intensity of the donor and an increase in that of the acceptor. By this technique, measurements with the good sensitivity can be made about distance within 1 to 10 nm under physiological conditions. For this reason, the RET technique has been widely used in polymer science, biochemistry, and structural biology. Recently, a number of RET systems incorporated with nanoparticles, such as quantum dots, gold nanoparticles, and upconversion nanoparticles, have been developed. These nanocrystals retain their optical superiority and can act as either a donor or a quencher, thereby enhancing the performance of RET systems and providing more opportunities in excitation wavelength selection. Notably, lanthanide-doped upconversion nanophosphors (UCNPs) have attracted considerable attention due to their inherent advantages of large anti-Stoke shifts, long luminescence lifetimes, and absence of autofluorescence under low energy near-infrared (NIR) light excitation. These nanoparticles are promising for the biodetection of various types of analytes. Undoubtedly, the developments of those applications usually rely on resonance energy transfer, which could be regarded as a flexible technology to mediate energy transfer from upconversion phosphor to acceptor for the design of luminescent functional nanoplatforms. Currently, researchers have developed many RET-based upconversion nanosystems (RET-UCNP) that respond to specific changes in the biological environments. Specifically, small organic molecules, biological molecules, metal-organic complexes, or inorganic nanoparticles were carefully selected and bound to the surface of upconversion nanoparticles for the preparation of RET-UCNP nanosystems. Benefiting from the advantage and versatility offered by this technology, the research of RET-based upconversion nanomaterials should have significant implications for advanced biomedical applications. It should be noted that energy transfer in a UCNP based nanosystem is most often related to resonance energy transfer but that reabsorption (and maybe other energy transfer processes) may also play an important role and that more studies regarding the fundamental aspects for energy transfer with UCNPs is necessary. In this Account, we present an overview of recent advances in RET-based upconversion nanocomposites for biodetection with a particular focus on our own work. We have designed a series of upconversion nanoplatforms with remarkably high versatility for different applications. The experience gained from our strategic design and experimental investigations will allow for the construction of next-generation luminescent nanoplatform with marked improvements in their performance. The key aspects of this Account include fundamental principles, design and preparation strategies, biodetection in vitro and in vivo, future opportunities, and challenges of RET-UCNP nanosystems.

Markedly enhanced up-conversion luminescence by combining IR-808 dye sensitization and core–shell–shell structures

The up-conversion emission of core–shell–shell structured nanoparticles has been greatly enhanced by IR-808 dye sensitization of 808 nm photons.

Hexagonal β-Na(Y,Yb)F4 based core/shell nanorods: epitaxial growth, enhanced and tailored up-conversion emission

Rare earth ions-doped hexagonal β-Na(Y,Yb)F₄ nanorods can be coated perfectly with either optically active or inert shells to improve and/or tailor the upconversion emission through a one-step epitaxial growth method from α-phased nanoparticles.

Up-conversion luminescence of rare earth-doped KGd(WO4)2 phosphors for tunable multicolour light generation

A series of novel KGd(WO₄)₂ crystalline powders doped with Yb³⁺/Tm³⁺, Yb³⁺/Er³⁺ and Yb³⁺/Ho³⁺ were synthesized using a modified Pechini method.