NIR Biosensing of Neurotransmitters in Stem Cell-Derived Neural Interface Using Advanced Core-Shell Upconversion Nanoparticles

Upconversion Nanoparticles Based Sensing: From Design to Point-of-Care Testing

Rare earth-doped upconversion nanoparticles (UCNPs) have achieved a wide range of applications in the sensing field due to their unique anti-Stokes luminescence property, minimized background interference, excellent biocompatibility, and stable physicochemical properties. However, UCNPs-based sensing platforms still face several challenges, including inherent limitations from UCNPs such as low quantum yields and narrow absorption cross-sections, as well as constraints related to energy transfer efficiencies in sensing systems. Therefore, the construction of high-performance UCNPs-based sensing platforms is an important cornerstone for conducting relevant research. This work begins by providing a brief overview of the upconversion luminescence mechanism in UCNPs. Subsequently, it offers a comprehensive summary of the sensors' types, design principles, and optimized design strategies for UCNPs sensing platforms. More cost-effective and promising point-of-care testing applications implemented based on UCNPs sensing systems are also summarized. Finally, this work addresses the future challenges and prospects for UCNPs-based sensing platforms.

Remotely Activated DNA Probe System for the Detection and Imaging of Dual miRNAs

Cancers remain the leading cause of mortality worldwide. It is crucial to detect cancer at an early stage for improving survival rates. Biomarkers have precise implications for cancer progression. Here, we built a straightforward DNA probe system that could be activated by near-infrared light to detect dual miRNAs with a high specificity. This probe is built on the basis of upconversion nanoparticles, which could emit ultraviolet light and activate DNA probes adsorbed on the outer layer. The DNA probe system is remotely controlled through manipulation of the near-infrared (NIR) light, enabling simultaneous detection of dual miRNAs. The DNA nanosystem could be effectively endocytosed by cancer cells and reflect expression levels of dual miRNAs. Overall, this study demonstrates a promising remote-controlled DNA nanoplatform for the simultaneous detection of dual miRNAs, which has tremendous potential for precise cancer diagnostics and therapies.

Cross Relaxation Enables Spatiotemporal Color-Switchable Upconversion in a Single Sandwich Nanoparticle for Information Security

Smart control of ionic interaction dynamics offers new possibilities for tuning and editing luminescence properties of lanthanide-based materials. However, it remains a daunting challenge to achieve the dynamic control of cross relaxation mediated photon upconversion, and in particular the involved intrinsic photophysics is still unclear. Herein, this work reports a conceptual model to realize the color-switchable upconversion of Tm3+ through spatiotemporal control of cross relaxation in the design of NaYF4 :Gd@NaYbF4 :Tm@NaYF4 sandwich nanostructure. It shows that cross relaxation plays a key role in modulating upconversion dynamics and tuning emission colors of Tm3+ . Interestingly, it is found that there is a short temporal delay for the occurrence of cross relaxation in contrast to the spontaneous emission as a result of the slight energy mismatch between relevant energy levels. This further enables a fine emission color tuning upon non-steady state excitation. Moreover, a characteristic quenching time is proposed to describe the temporal evolution of cross relaxation quantitatively. These findings present a deep insight into the physics of ionic interactions in heavy doping systems, and also show great promise in frontier applications including information security, anti-counterfeiting and nanophotonics.

A "Chase and Block" Strategy for Enhanced Cancer Therapy with Hypoxia-Promoted Photodynamic Therapy and Autophagy Inhibition Based on Upconversion Nanocomposites

The combination of hypoxia-promoted photodynamic therapy (PDT) and autophagy modulation has shown strong potential in the treatment of hypoxic tumors. Here, a novel design is put forward for synergistic PDT and autophagy inhibition to amplify the effect of cancer therapy by a "chase and block" strategy. Specifically, the organic photosensitive molecule (denoted FL) is encapsulated in a hydrophobic layer between multi-band emitted upconversion nanoparticles (UCNPs) and the amphiphilic polymer DSPE-PEG-COOH, allowing FL to fully exploit the luminescence spectrum of UCNPs under near-infrared (NIR) light irradiation. The FL is specifically activated by nitroreductase in the tumor microenvironment (TME), enabling hypoxia-promoted PDT and thus performing a "chase" strategy for cancer therapy. Additionally, the nanosystem is combined with an autophagy-inhibiting melittin pro-peptide (denoted as MEL), which could be triggered by the highly expressed legumain in tumor cells to inhibit the autophagy procedure by disrupting the lysosomal membrane, thus "blocking" the cancer cells from rescuing themselves and amplifying the killing effect of PDT. Both FL and MEL can be specifically activated by TME and the upconversion luminescence imaging of UCNPs offers a tracer function for the treatment. Therefore, UCNPs@FL-MEL might be an important reference for the design and development of future nanotherapeutic agents.

Progress in Nano-Biosensors for Non-Invasive Monitoring of Stem Cell Differentiation

Non-invasive, non-destructive, and label-free sensing techniques are required to monitor real-time stem cell differentiation. However, conventional analysis methods, such as immunocytochemistry, polymerase chain reaction, and Western blot, involve invasive processes and are complicated and time-consuming. Unlike traditional cellular sensing methods, electrochemical and optical sensing techniques allow non-invasive qualitative identification of cellular phenotypes and quantitative analysis of stem cell differentiation. In addition, various nano- and micromaterials with cell-friendly properties can greatly improve the performance of existing sensors. This review focuses on nano- and micromaterials that have been reported to improve sensing capabilities, including sensitivity and selectivity, of biosensors towards target analytes associated with specific stem cell differentiation. The information presented aims to motivate further research into nano-and micromaterials with advantageous properties for developing or improving existing nano-biosensors to achieve the practical evaluation of stem cell differentiation and efficient stem cell-based therapies.

Understanding FRET in Upconversion Nanoparticle Nucleic Acid Biosensors

Upconversion nanoparticles (UCNPs) have been frequently applied in Förster resonance energy transfer (FRET) bioanalysis. However, the understanding of how surface coatings, bioconjugation, and dye-surface distance influence FRET biosensing performance has not significantly advanced. Here, we investigated UCNP-to-dye FRET DNA-hybridization assays in H₂O and D₂O using ∼24 nm large NaYF₄:Yb³⁺,Er³⁺ UCNPs coated with thin layers of silica (SiO₂) or poly(acrylic acid) (PAA). FRET resulted in strong distance-dependent PL intensity changes. However, the PL decay times were not significantly altered because of continuous Yb³⁺-to-Er³⁺ energy migration during Er³⁺-to-dye FRET. Direct bioconjugation of DNA to the thin PAA coating combined with the closest possible dye-surface distance resulted in optimal FRET performance with minor influence from competitive quenching by H₂O. The better comprehension of UCNP-to-dye FRET was successfully translated into a microRNA (miR-20a) FRET assay with a limit of detection of 100 fmol in a 80 μL sample volume.

Hierarchy of hybrid materials. Part-II: The place of organics-on-inorganics in it, their composition and applications

Hybrid materials or hybrids incorporating organic and inorganic constituents are emerging as a very potent and promising class of materials due to the diverse but complementary nature of their properties. This complementarity leads to a perfect synergy of properties of the desired materials and products as well as to an extensive range of their application areas. Recently, we have overviewed and classified hybrid materials describing inorganics-in-organics in Part-I (Saveleva, et al., Front. Chem., 2019, 7, 179). Here, we extend that work in Part-II describing organics-on-inorganics, i.e., inorganic materials modified by organic moieties, their structure and functionalities. Inorganic constituents comprise of colloids/nanoparticles and flat surfaces/matrices comprise of metallic (noble metal, metal oxide, metal-organic framework, magnetic nanoparticles, alloy) and non-metallic (minerals, clays, carbons, and ceramics) materials; while organic additives can include molecules (polymers, fluorescence dyes, surfactants), biomolecules (proteins, carbohydtrates, antibodies and nucleic acids) and even higher-level organisms such as cells, bacteria, and microorganisms. Similarly to what was described in Part-I, we look at similar and dissimilar properties of organic-inorganic materials summarizing those bringing complementarity and composition. A broad range of applications of these hybrid materials is also presented whose development is spurred by engaging different scientific research communities.

Capture and Release of Cancer Cells Through Smart Bioelectronics

Noninvasive collection of target cells such as circulating tumor cells (CTCs) is crucial for biology and medicine research. Conventional methods of cell collection are often complex, requiring either size-dependent sorting or invasive enzymatic reactions. Here, we show the development of a functional polymer film, which combines the thermoresponsive poly(N-isopropylacrylamide) and the conducting poly(3,4-ethylenedioxythiopene)/poly(styrene sulfonate), and its use for the capture and release of CTCs. When coated onto microfabricated gold electrodes, the proposed polymer films are capable of noninvasively capturing and controllably releasing cells while, at the same time, monitoring these processes with conventional electrical measurements.

Surface plasmon resonance of Au/Ag metals for the photoluminescence enhancement of lanthanide ion Ln3+ doped upconversion nanoparticles in bioimaging

Deep tissue penetration, chemical inertness and biocompatibility give UCNPs a competitive edge over traditional fluorescent materials like organic dyes or quantum dots. However, the low quantum efficiency of UNCPs becomes an obstacle. Among extensive methods and strategies currently used to prominently solve this concerned issue, surface plasmon resonance (SPR) of noble metals is of great use due to the agreement between the SPR peak of metals and absorption band of UCNPs. A key challenge of this match is that the structures and sizes of noble metals have significant influences on the peak of SPR formants, where achieving an explicit elucidation of relationships between the physical properties of noble metals and their SPR formants is of great importance. This review aims to clarify the mechanism of the SPR effect of noble metals on the optical performance of UCNPs. Furthermore, novel research studies in which Au, Ag or Au/Ag composites in various structures and sizes are combined with UCNPs through different synthetic methods are summarized. We provide an overview of improved photoluminescence for bioimaging exhibited by different composite nanoparticles with respect to UCNPs acting as both cores and shells, taking Au@UCNPs, Ag@UCNPs and Au/Ag@UCNPs into account. Finally, there are remaining shortcomings and latent opportunities which deserve further research. This review will provide directions for the bioimaging applications of UCNPs through the introduction of the SPR effect of noble metals.

Second-phase-induced fluorescence quenching in non-equivalent substituted red phosphors

Concentration quenching, which generally originates from serious energy migrations among the uniformly distributed luminescent centers in the host matrix, is a key factor to influence the luminescence properties of materials. Different from previous reports, we demonstrate a novel fluorescence-quenching mechanism attributable to the second-phase Eu₂W₂O₉ in non-equivalent substituted SrWO₄:xEu³⁺ phosphors. The crystal structure, elemental distribution, and luminescence properties of the as-prepared SrWO₄:xEu³⁺ phosphors are systematically investigated. A second-phase Eu₂W₂O₉ is confirmed when the Eu³⁺-doping concentration exceeds 20%, which produces the new structure defects and energy-transfer paths, resulting in fluorescence quenching in this material. This finding gives a new perspective to analyze the concentration-quenching mechanism of the non-equivalent substituted phosphors and can help in the design of new, efficient luminescence materials. In addition, the as-prepared SrWO₄:xEu³⁺ phosphors exhibit a strong intrinsic excitation in the range of 355-425 nm, which is accompanied by the Commission Internationale de I'Eclairage (CIE) coordinates at (0.653, 0.347) and stable color purity of up to 94.52%. A packaged white light-emitting diode with CIE chromaticity coordinates of (0.398, 0.335), correlated color temperature of 3132 K, and color rendering index of 84.3 is fabricated by SrWO₄:20%Eu³⁺ phosphors with blue BAM:Eu²⁺ and green YAGB:Tb³⁺ phosphors in a near-ultraviolet chip.

Inner filter effect-based upconversion fluorescence sensing of sulfide ions

Upconversion nanocrystals (UCNCs) have emerged as a new type of fluorescent probe for sensing applications. Herein, we designed a 980 nm excited upconversion luminescence system, composed of core-shell-structured NaYF₄ : Yb,Er@NaYF₄ : Yb nanocrystals (csUCNCs) and the triethylenetetramine-Cu complex (complex-I), for quantitative detection of sulfide ions. Taking advantage of the specific recognition of complex-I toward S^2-, the as-formed compound (complex-II) exhibits excellent spectral overlap not only in the range of fluorescence emissions of UCNCs but also in the excitation wavelength for UCNCs; fluorescence quenching of UCNCs occurs where the complex-II acts as the energy acceptor. Due to the electrostatic repulsion between positively charged ligand-free csUCNCs and complex-I, the fluorescence quenching is based on the primary and secondary inner filter effect rather than the fluorescence resonance energy transfer process. The detection limit of S^2- for the upconversion-based system is calculated to be 2.7 μM, exhibiting higher detection sensitivity over the single complex-I compound measured by the spectrophotometric method. Moreover, no significant variation in upconversion luminescence is observed upon the addition of other interfering ions, showing the excellent selectivity of this nanoprobe toward S^2-.

Progress of advanced nanomaterials in diagnosis of neurodegenerative diseases

Neurodegenerative diseases (NDDs) encompass a wide range of clinically and pathologically diverse diseases characterized by progressive long-term cognitive decline, memory and function loss in daily life. Due to the lack of effective drugs and therapeutic strategies for preventing or delaying neurodegenerative progression, it is urgent to diagnose NDDs as early and accurately as possible. Nanomaterials, emerged as one of the most promising materials in the 21st century, have been widely applied and play a significant role in diagnosis and treatment of NDDs because of their remarkable properties including stability, prominent biocompatibility, unique structure, novel physical and chemical characteristics. In this review, we outlined general strategies for the application of different types of advanced materials in early and staged diagnosis of NDDs in vivo and in vitro. According to applied technology, in vivo research mainly involves magnetic resonance, fluorescence, and surface enhanced Raman imaging on structures of brain tissues, cerebral vessels and related distributions of biomarkers. In vitro research is focused on the detection of fluid biomarkers in cerebrospinal fluid and peripheral blood based on fluorescence, electrochemical, Raman and surface plasmon resonance techniques. Finally, we discussed the current challenges and future perspectives of biomarker-based NDDs diagnosis as well as potential applications regarding advanced nanomaterials.

Nanocomposites based on lanthanide-doped upconversion nanoparticles: diverse designs and applications

Lanthanide-doped upconversion nanoparticles (UCNPs) have aroused extraordinary interest due to the unique physical and chemical properties. Combining UCNPs with other functional materials to construct nanocomposites and achieve synergistic effect abound recently, and the resulting nanocomposites have shown great potentials in various fields based on the specific design and components. This review presents a summary of diverse designs and synthesis strategies of UCNPs-based nanocomposites, including self-assembly, in-situ growth and epitaxial growth, as well as the emerging applications in bioimaging, cancer treatments, anti-counterfeiting, and photocatalytic fields. We then discuss the challenges, opportunities, and development tendency for developing UCNPs-based nanocomposites.

Neurotransmitters-Key Factors in Neurological and Neurodegenerative Disorders of the Central Nervous System

Neurotransmitters are molecules that amplify, transmit, and convert signals in cells, having an essential role in information transmission throughout the nervous system. Hundreds of such chemicals have been discovered in the last century, continuing to be identified and studied concerning their action on brain health. These substances have been observed to influence numerous functions, including emotions, thoughts, memories, learning, and movements. Thus, disturbances in neurotransmitters’ homeostasis started being correlated with a plethora of neurological and neurodegenerative disorders. In this respect, the present paper aims to describe the most important neurotransmitters, broadly classified into canonical (e.g., amino acids, monoamines, acetylcholine, purines, soluble gases, neuropeptides) and noncanonical neurotransmitters (e.g., exosomes, steroids, D-aspartic acid), and explain their link with some of the most relevant neurological conditions. Moreover, a brief overview of the recently developed neurotransmitters’ detection methods is offered, followed by several considerations on the modulation of these substances towards restoring homeostasis.

Composition, thickness, and homogeneity of the coating of core-shell nanoparticles-possibilities, limits, and challenges of X-ray photoelectron spectroscopy

Core–shell nanoparticles have attracted much attention in recent years due to their unique properties and their increasing importance in many technological and consumer products. However, the chemistry of nanoparticles is still rarely investigated in comparison to their size and morphology. In this review, the possibilities, limits, and challenges of X-ray photoelectron spectroscopy (XPS) for obtaining more insights into the composition, thickness, and homogeneity of nanoparticle coatings are discussed with four examples: CdSe/CdS quantum dots with a thick coating and a small core; NaYF₄-based upconverting nanoparticles with a large Yb-doped core and a thin Er-doped coating; and two types of polymer nanoparticles with a poly(tetrafluoroethylene) core with either a poly(methyl methacrylate) or polystyrene coating. Different approaches for calculating the thickness of the coating are presented, like a simple numerical modelling or a more complex simulation of the photoelectron peaks. Additionally, modelling of the XPS background for the investigation of coating is discussed. Furthermore, the new possibilities to measure with varying excitation energies or with hard-energy X-ray sources (hard-energy X-ray photoelectron spectroscopy) are described. A discussion about the sources of uncertainty for the determination of the thickness of the coating completes this review.

Expanding the toolbox of photon upconversion for emerging frontier applications

Photon upconversion in lanthanide-based materials has recently shown compelling advantages in a wide range of fields due to their exceptional anti-Stokes luminescence performances and physicochemical properties. In particular, the latest breakthroughs in the optical manipulation of photon upconversion, such as the precise tuning of switchable emission profiles and lifetimes, open up new opportunities for diverse frontier applications from biological imaging to therapy, nanophotonics and three-dimensional displays. A summary and discussion on the recent progress can provide new insights into the fundamental understanding of luminescence mechanisms and also help to inspire new upconversion concepts and promote their frontier applications. Herein, we present a review on the state-of-the-art progress of lanthanide-based upconversion materials, focusing on the newly emerging approaches to the smart control of upconversion in aspects of light intensity, colors, and lifetimes, as well as new concepts. The emerging scientific and technological discoveries based on the well-designed upconversion materials are highlighted and discussed, along with the challenges and future perspectives. This review will contribute to the understanding of the fundamental research of photon upconversion and further promote the development of new classes of efficient upconversion materials towards diversities of frontier applications in the future.

Enhancement of Upconversion Luminescence by the Construction of a 3Yb-Er-Hf Sublattice Energy Cluster and Surface Defect Elimination

Nanotetragonal LiYF₄:RE (Tm,Er,Ho) is a kind of excellent upconversion luminescence (UCL) material potentially used in many fields, while the enhancement of UC emission and regulation of luminescence lifetime are still a challenge. Herein, a strategy was reported to enhance UCL performance with the aid of the construction of a 3Yb-Er-Hf sublattice energy cluster with the introduction of Hf⁴⁺ and the interception of surface defect fluorescence quenching. UCL was obviously decreased by Hf⁴⁺ doping without surface defect elimination, but after the interception of surface defect quenching, UCL was dramatically enhanced more than 300-fold with an Er³⁺/Hf⁴⁺ mole ratio of 1:1. The contribution of UCL enhancement by the construction of a 3Yb-Er-Hf sublattice energy cluster is about 1.5 times of the sample without energy cluster construction. Interestingly, the lifetime of UCL can also be regulated by this strategy. According to the results of systematical microstructure analyses and UCL performance behaviors examined by X-ray powder diffraction (XRD), small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), nuclear magnetic resonance (NMR), and fluorescence spectrophotometry (FS) methods, the possible mechanism of UCL enhancement was proposed. This work may be an inspiration for researchers to design and develop high-performance UCL nanomaterials.

Molecular Probes, Chemosensors, and Nanosensors for Optical Detection of Biorelevant Molecules and Ions in Aqueous Media and Biofluids

Synthetic molecular probes, chemosensors, and nanosensors used in combination with innovative assay protocols hold great potential for the development of robust, low-cost, and fast-responding sensors that are applicable in biofluids (urine, blood, and saliva). Particularly, the development of sensors for metabolites, neurotransmitters, drugs, and inorganic ions is highly desirable due to a lack of suitable biosensors. In addition, the monitoring and analysis of metabolic and signaling networks in cells and organisms by optical probes and chemosensors is becoming increasingly important in molecular biology and medicine. Thus, new perspectives for personalized diagnostics, theranostics, and biochemical/medical research will be unlocked when standing limitations of artificial binders and receptors are overcome. In this review, we survey synthetic sensing systems that have promising (future) application potential for the detection of small molecules, cations, and anions in aqueous media and biofluids. Special attention was given to sensing systems that provide a readily measurable optical signal through dynamic covalent chemistry, supramolecular host-guest interactions, or nanoparticles featuring plasmonic effects. This review shall also enable the reader to evaluate the current performance of molecular probes, chemosensors, and nanosensors in terms of sensitivity and selectivity with respect to practical requirement, and thereby inspiring new ideas for the development of further advanced systems.

Advances in fluorescence sensing enabled by lanthanide-doped upconversion nanophosphors

Lanthanide-doped upconversion nanoparticles (UCNPs), characterized by converting low-energy excitation to high-energy emission, have attracted considerable interest due to their inherent advantages of large anti-Stokes shifts, sharp and narrow multicolor emissions, negligible autofluorescence background interference, and excellent chemical- and photo-stability. These features make them promising luminophores for sensing applications. In this review, we give a comprehensive overview of lanthanide-doped upconversion nanophosphors including the fundamental principle for the construction of UCNPs with efficient upconversion luminescence (UCL), followed by state-of-the-art strategies for the synthesis and surface modification of UCNPs, and finally describing current advances in the sensing application of upconversion-based probes for the quantitative analysis of various analytes including pH, ions, molecules, bacteria, reactive species, temperature, and pressure. In addition, emerging sensing applications like photodetection, velocimetry, electromagnetic field, and voltage sensing are highlighted.

Rare-Earth Doping in Nanostructured Inorganic Materials

Impurity doping is a promising method to impart new properties to various materials. Due to their unique optical, magnetic, and electrical properties, rare-earth ions have been extensively explored as active dopants in inorganic crystal lattices since the 18th century. Rare-earth doping can alter the crystallographic phase, morphology, and size, leading to tunable optical responses of doped nanomaterials. Moreover, rare-earth doping can control the ultimate electronic and catalytic performance of doped nanomaterials in a tunable and scalable manner, enabling significant improvements in energy harvesting and conversion. A better understanding of the critical role of rare-earth doping is a prerequisite for the development of an extensive repertoire of functional nanomaterials for practical applications. In this review, we highlight recent advances in rare-earth doping in inorganic nanomaterials and the associated applications in many fields. This review covers the key criteria for rare-earth doping, including basic electronic structures, lattice environments, and doping strategies, as well as fundamental design principles that enhance the electrical, optical, catalytic, and magnetic properties of the material. We also discuss future research directions and challenges in controlling rare-earth doping for new applications.

In situ synthesis of a functional ZIF-8 nanocomposite for synergistic photodynamic–chemotherapy and pH and NIR-stimulated drug release

UCNP/TiO2/Cur@ZIF-8 can be used as a NIR and pH-responsive photodynamic-chemo candidate for tumor therapy.

Dynamic Ligand Screening by Magnetic Nanoassembly Modulates Stem Cell Differentiation

In native microenvironment, diverse physical barriers exist to dynamically modulate stem cell recruitment and differentiation for tissue repair. In this study, nanoassembly-based magnetic screens of various sizes are utilized, and they are elastically tethered over an RGD ligand (cell-adhesive motif)-presenting material surface to generate various nanogaps between the screens and the RGDs without modulating the RGD density. Large screens exhibiting low RGD distribution stimulate integrin clustering to facilitate focal adhesion, mechanotransduction, and differentiation of stem cells, which are not observed with small screens. Magnetic downward pulling of the large screens decreases the nanogaps, which dynamically suppress the focal adhesion, mechanotransduction, and differentiation of stem cells. Conversely, magnetic upward pulling of the small screens increases the nanogaps, which dynamically activates focal adhesion, mechanotransduction, and differentiation of stem cells. This regulation mechanism is also shown to be effective in the microenvironment in vivo. Further diversifying the geometries of the physical screens can further enable diverse modalities of multifaceted and safe unscreening of the distributed RGDs to unravel and modulate stem cell differentiation for tissue repair.

An overview of boosting lanthanide upconversion luminescence through chemical methods and physical strategies

Lanthanide-doped upconversion nanoparticles have attracted extensive research interest due to their promising applications in various fields.

Magnetic Control and Real-Time Monitoring of Stem Cell Differentiation by the Ligand Nanoassembly

Native extracellular matrix (ECM) exhibits dynamic change in the ligand position. Herein, the ECM-emulating control and real-time monitoring of stem cell differentiation are demonstrated by ligand nanoassembly. The density of gold nanoassembly presenting cell-adhesive Arg-Gly-Asp (RGD) ligand on Fe₃ O₄ (magnetite) nanoparticle in nanostructures flexibly grafted to material is changed while keeping macroscale ligand density invariant. The ligand nanoassembly on the Fe₃ O₄ can be magnetically attracted to mediate rising and falling ligand movements via linker stretching and compression, respectively. High ligand nanoassembly density stimulates integrin ligation to activate the mechanosensing-assisted stem cell differentiation, which is monitored via in situ real-time electrochemical sensing. Magnetic control of rising and falling ligand movements hinders and promotes the adhesion-mediated mechanotransduction and differentiation of stem cells, respectively. These rising and falling ligand states yield the difference in the farthest distance (≈34.6 nm) of the RGD from material surface, thereby dynamically mimicking static long and short flexible linkers, which hinder and promote cell adhesion, respectively. Design of cytocompatible ligand nanoassemblies can be made with combinations of dimensions, shapes, and biomimetic ligands for remotely regulating stem cells for offering novel methodologies to advance regenerative therapies.

Exploring the use of upconversion nanoparticles in chemical and biological sensors: from surface modifications to point-of-care devices

Upconversion nanoparticles (UCNPs) have emerged as promising luminescent nanomaterials due to their unique features that allow the overcoming of several problems associated with conventional fluorescent probes. Although UCNPs have been used in a broad range of applications, it is probably in the field of sensing where they best evidence their potential. UCNP-based sensors have been designed with high sensitivity and selectivity, for detection and quantification of multiple analytes ranging from metal ions to biomolecules. In this review, we deeply explore the use of UCNPs in sensing systems emphasizing the most relevant and recent studies on the topic and explaining how these platforms are constructed. Before diving into UCNP-based sensing platforms it is important to understand the unique characteristics of these nanoparticles, why they are attracting so much attention, and the most significant interactions occurring between UCNPs and additional probes. These points are covered over the first two sections of the article and then we explore the types of fluorescent responses, the possible analytes, and the UCNPs' integration with various material types such as gold nanostructures, quantum dots and dyes. All the topics are supported by analysis of recently reported sensors, focusing on how they are built, the materials' interactions, the involved synthesis and functionalization mechanisms, and the conjugation strategies. Finally, we explore the use of UCNPs in paper-based sensors and how these platforms are paving the way for the development of new point-of-care devices.

High-Sensitivity Sensing of Divalent Copper Ions at the Single Upconversion Nanoparticle Level

Single-nanoparticle-level sensing allows us to measure individual molecular interactions and probe environmental stimuli at nanometer-scale resolution. Despite these premises, limited success has been met hitherto due to the demanding challenge to distinguish a dimmed signal from a noisy background. Here, we describe an approach for high-sensitivity single-nanoparticle-level sensing of divalent copper (Cu²⁺) ions through near-infrared-to-visible upconversion luminescence against a near-null background. This nanosensor utilizes ytterbium- (Yb³⁺) and erbium (Er³⁺)-doped sodium yttrium fluoride (NaYF₄) upconversion nanoparticles (UCNPs) (maximal emission at 540 nm when excited at 980 nm) as an energy donor, of which the surface attaches Cu²⁺-dependent DNAzymes labeled with BHQ1 dye (Black Hole Quencher 1, maximal absorption at 548 nm) as energy acceptors. Adding a hint amount of Cu²⁺ ions resulted in the cleavage of a BHQ1-containing moiety in DNAzymes, thus turning on upconversion luminescence for sensitive detection. Indeed, this approach allows us to perform single-nanoparticle-level detection of Cu²⁺ ions with extraordinary signal-to-noise ratios (SNRs, >277) for all measured concentrations that cover 3 orders of magnitude (from sub-nM to μM). Importantly, a limit of detection of 220 pM was achieved, about sevenfold lower than the one at the ensemble level. Moreover, a stochastic particle-to-particle sensing behavior was also identified, featuring single-nanoparticle-level detection. This work untaps the usage of UCNPs for high-sensitivity single-nanoparticle-level biosensing.

Dynamic nanoassemblies for imaging and therapy of neurological disorders

The past decades have witnessed an increased incidence of neurological disorders (NDs) such as Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, ischemic stroke, and epilepsy, which significantly lower patients' life quality and increase the economic and social burden. Recently, nanomedicines composed of imaging and/or therapeutic agents have been explored to diagnose and/or treat NDs due to their enhanced bioavailability, blood-brain barrier (BBB) permeability, and targeting capacity. Intriguingly, dynamic nanoassemblies self-assembled from functional nanoparticles to simultaneously interfere with multiple pathogenic substances and pathological changes, have been regarded as one of the foremost candidates to improve the diagnostic and therapeutic efficacy of NDs. To help readers better understand this emerging field, in this review, the pathogenic mechanism of different types of NDs is briefly introduced, then the functional nanoparticles used as building blocks in the construction of dynamic nanoassemblies for NDs theranostics are summarized. Furthermore, dynamic nanoassemblies that can actively cross the BBB to target brain lesions, sensitively and efficiently diagnose or treat NDs, and effectively promote neuroregeneration are highlighted. Finally, we conclude with our perspectives on the future development in this field.

An electroactive and thermo-responsive material for the capture and release of cells

Non-invasive collection of target cells is crucial for research in biology and medicine. In this work, we combine a thermo-responsive material, poly(N-isopropylacrylamide), with an electroactive material, poly(3,4-ethylene-dioxythiopene):poly(styrene sulfonate), to generate a smart and conductive copolymer for the label-free and non-invasive detection of the capture and release of cells on gold electrodes by electrochemical impedance spectroscopy. The copolymer is functionalized with fibronectin to capture tumor cells, and undergoes a conformational change in response to temperature, causing the release of cells. Simultaneously, the copolymer acts as a sensor, monitoring the capture and release of cancer cells by electrochemical impedance spectroscopy. This platform has the potential to play a role in top-notch label-free electrical monitoring of human cells in clinical settings.

An NIR dual-emitting/absorbing inorganic compact pair: A self-calibrating LRET system for homogeneous virus detection

Many conventional optical biosensing systems use a single responsive signal in the visible light region. This limits their practical applications, as the signal can be readily perturbed by various external environmental factors. Herein, a near-infrared (NIR)-based self-calibrating luminescence resonance energy transfer (LRET) system was developed for background-free detection of analytes in homogeneous sandwich-immunoassays. The inorganic LRET pair was comprised of NIR dual-emitting lanthanide-doped nanoparticles (LnNPs) as donors and NIR-absorbing LnNPs as acceptors, which showed a narrow absorption peak (800 nm) and long-term stability, enabling stable LRET with a built-in self-calibrating signal. Screened single-chain variable fragments (scFvs) were used as target avian influenza virus (AIV)-binding antibodies to increase the LRET efficiency in sandwich-immunoassays. The compact sensor platform successfully detected AIV nucleoproteins with a 0.38 pM limit of detection in buffer solution and 64 clinical samples. Hence, inorganic LnNP pairs may be effective for self-calibrating LRET systems in the background-free NIR region.

Fast detection of E. coli with a novel fluorescent biosensor based on a FRET system between UCNPs and GO@Fe3O4 in urine specimens

Biosensors based on nanomaterials are becoming a research hotspot for the rapid detection of pathogenic bacteria. Herein, a "turn-on" fluorescent biosensor based on a FRET system was constructed for the fast detection of a representative pathogenic microorganism, namely, E. coli, which causes most urinary tract infections. This biosensor was constructed by utilizing synthesized UCNPs as fluorescent donors with stable luminescence performance in complex biological samples and GO@Fe3O4 as a receptor with both excellent adsorption ability and fluorescence quenching ability. A specific ssDNA selected as an aptamer which could recognize E. coli was immobilized on the UCNPs to form UCNP-Apt nanoprobes. The nanoprobes were adsorbed on the surface of GO@Fe3O4 through the π-stacking interactions between aptamers and GO. In the presence of E. coli, UCNP-Apt nanoprobes detached from GO@Fe3O4 due to the specific recognition of aptamers and bacteria, resulting in obvious fluorescence recovery, and the concentration of bacteria was positively correlated with the intensity of the fluorescence signal; such a "turn-on" signal output mode ensures excellent precision. In addition, the easy magnetic separation of GO@Fe3O4 simplifies the operation process, helping the sensor detect bacteria in 30 minutes with a linear range from 103 to 107 CFU mL-1 and a limit of detection of 467 CFU mL-1. Moreover, recovery test results also showed that the sensor has clinical application potential for the rapid detection of pathogenic microorganisms in complex biological samples.

Manipulation of up-conversion emission in NaYF4 core@shell nanoparticles doped by Er3+, Tm3+, or Yb3+ ions by excitation wavelength-three ions-plenty of possibilities

Nanoparticles (NPs) based on host compound NaYF₄ with core@shell structures were synthesised by the precipitation reaction in high-boiling point octadecene/oleic acid solvent. Four laser wavelengths were used (808, 975, 1208, or 1532 nm) for excitation of the obtained NPs. The resulting emission and mechanisms responsible for spectroscopic properties were studied in detail. Depending on NP compositions, i.e. type of doping ion (Er³⁺, Tm³⁺, or Yb³⁺) or presence of dopants in the same or different phases, adjustable up-conversion (UC) could be obtained with emission peaks covering the visible to near-infrared range (475 to 1625 nm). The presented results demonstrated multifunctionality of the prepared NPs. NaYF₄:2%Tm³⁺@NaYF₄ NPs exhibited emission at 700 and 1450 nm under 808 nm laser excitation or 800 and 1625 nm emission under 1208 nm laser radiation, as a result of ground- and excited-state absorption processes (GSA and ESA, respectively). However, NaYF₄:5%Er³⁺,2%Tm³⁺@NaYF₄ NPs showed the most interesting properties, as they can convert all studied laser wavelengths due to the absorption of Tm³⁺ (808, 1208 nm) or Er³⁺ ions (808, 975, 1532 nm), revealing a photon avalanche process under 1208 nm laser excitation, as well as GSA and ESA at other excitation wavelengths. The NaYF₄:2%Tm³⁺@NaYF₄:5%Er³⁺ NPs revealed the resultant emission properties, as the dopant ions were separated within core and shell phases. The NaYF₄:18%Yb³⁺,2%Tm³⁺@NaYF₄ and NaYF₄:18%Yb³⁺,2%Tm³⁺@NaYF₄:5%Er³⁺ samples showed the brightest emission, around 800 nm, under 975 nm excitation, though other laser wavelengths allowed for observation of luminescence, as well, especially in NPs with Er³⁺ in the outer shell, capable of UC under 1532 nm. The presented results highlight the unique and universal properties of lanthanide ions for designing luminescent NPs for a variety of potential applications, such as confocal microscopy.

A Versatile Strategy for Constructing Ratiometric Upconversion Luminescent Probe with Sensitized Emission of Energy Acceptor

When fabricating ratiometric optical probes using lanthanide-doped upconversion nanoparticles (UCNPs), which are promising luminescent materials that have widely been utilized in biosensing and bioimaging as energy donors, it is still a challenge to obtain the emission signal of energy acceptors with reasons unclear so far. Herein, we reveal that the energy-transfer efficiency and brightness of UCNPs as well as the aggregation-caused quenching (ACQ) of energy accepting dyes are the main factors restricting the emission of energy acceptors, and we have circumvented this problem by modulating the structure of UCNPs and the assembly manner of the energy donor-acceptor pair. On this basis, a proof-of-concept ratiometric upconversion nanoprobe was constructed for hydrogen sulfide (H₂S) detection with an elaborate dye Fl-1 as an energy acceptor. As the H₂S concentration increased, the emission intensity of Fl-1 at 525 nm increased gradually, accompanied by a decrease of upconversion luminescence at 480 nm, thus providing a ratiometric signal of F₄₈₀/F₅₂₅ dependent on the H₂S concentration. This probe was able to track H₂S in living cells and zebrafish and visualize the H₂S level of mice in physiological processes.

Exploring Heterostructured Upconversion Nanoparticles: From Rational Engineering to Diverse Applications

Upconversion nanoparticles (UCNPs) represent a class of optical nanomaterials that can convert low-energy excitation photons to high-energy fluorescence emissions. On the basis of UCNPs, heterostructured UCNPs, consisting of UCNPs and other functional counterparts (metals, semiconductors, polymers, etc.), present an intriguing system in which the physicochemical properties are largely influenced by the entire assembled particle and also by the morphology, dimension, and composition of each individual component. As multicomponent nanomaterials, heterostructured UCNPs can overcome challenges associated with a single component and exhibit bifunctional or multifunctional properties, which can further expand their applications in bioimaging, biodetection, and phototherapy. In this review, we provide a summary of recent achievements in the field of heterostructured UCNPs in the aspects of construction strategies, synthetic approaches, and types of heterostructured UCNPs. This review also summarizes the trends in biomedical applications of heterostructured UCNPs and discusses the challenges and potential solutions in this field.

Remote Control of Time-Regulated Stretching of Ligand-Presenting Nanocoils In Situ Regulates the Cyclic Adhesion and Differentiation of Stem Cells

Native extracellular matrix (ECM) can exhibit cyclic nanoscale stretching and shrinking of ligands to regulate complex cell-material interactions. Designing materials that allow cyclic control of changes in intrinsic ligand-presenting nanostructures in situ can emulate ECM dynamicity to regulate cellular adhesion. Unprecedented remote control of rapid, cyclic, and mechanical stretching ("ON") and shrinking ("OFF") of cell-adhesive RGD ligand-presenting magnetic nanocoils on a material surface in five repeated cycles are reported, thereby independently increasing and decreasing ligand pitch in nanocoils, respectively, without modulating ligand-presenting surface area per nanocoil. It is demonstrated that cyclic switching "ON" (ligand nanostretching) facilitates time-regulated integrin ligation, focal adhesion, spreading, YAP/TAZ mechanosensing, and differentiation of viable stem cells, both in vitro and in vivo. Fluorescence resonance energy transfer (FRET) imaging reveals magnetic switching "ON" (stretching) and "OFF" (shrinking) of the nanocoils inside animals. Versatile tuning of physical dimensions and elements of nanocoils by regulating electrodeposition conditions is also demonstrated. The study sheds novel insight into designing materials with connected ligand nanostructures that exhibit nanocoil-specific nano-spaced declustering, which is ineffective in nanowires, to facilitate cell adhesion. This unprecedented, independent, remote, and cytocompatible control of ligand nanopitch is promising for regulating the mechanosensing-mediated differentiation of stem cells in vivo.

Local-structure-dependent luminescence in lanthanide-doped inorganic nanocrystals for biological applications

This feature article overviews the recent advances in the local-structure-dependent luminescence in lanthanide-doped inorganic nanocrystals for various biological applications.

Detection of phospholipase A2 in serum based on LRET mechanism between upconversion nanoparticles and SYBR green I

Phospholipase A₂ (PLA₂) may be a vital biomarker for the prediction and diagnosis of some diseases. Consequently, it is of great significance to quantitatively detect PLA₂ in biologic samples. Herein, on the basis of the principle of luminescence resonance energy transfer (LRET) between upconversion nanoparticles (UCNPs) and SYBR Green I (SG), we proposed a technology for the highly sensitive detection of PLA₂ amount. Therein, as an energy receptor, SG will be quantitatively loaded into liposomes firstly. Then, due to the hydrolysis of liposomes under the catalysis of PLA₂, SG will be released and inserted into the double-stranded DNA (dsDNA) on the surface of UCNPs, which triggers the LRET because of the shortening of effective spatial distance between UCNPs and SG. Under exciting of NIR light, UCNPs emit luminescence at 476 nm, which makes SG emit fluorescence at 522 nm through LRET. Under optimal conditions, the emission intensity ratio (I_{522 nm}/I_{476 nm}) increased linearly with the PLA₂ amount in the range of 20 U/L to 400 U/L, and the limit of detection (LOD) reached 15 U/L. Here, after comparing with the clinical standard method, it is found that the biosensor is expected to provide a convenient and sensitive assay for the detection of PLA₂ in actual serum samples. Furthermore, such biosensor can also be used to test the inhibitor of PLA₂.

Recent Advances on Rare Earth Upconversion Nanomaterials for Combined Tumor Near-Infrared Photoimmunotherapy

Cancer has been threatening the safety of human life. In order to treat cancer, many methods have been developed to treat tumor, such as traditional therapies like surgery, chemotherapy, radiotherapy, as well as new strategies like photodynamic therapy, photothermal therapy, sonodynamic therapy, and other emerging therapies. Although there are so many ways to treat tumors, these methods all face the dilemma that they are incapable to cope with metastasis and recurrence of tumors. The emergence of immunotherapy has given the hope to conquer the challenge. Immunotherapy is to use the body's own immune system to stimulate and maintain a systemic immune response to form immunological memory, resist the metastasis and recurrence of tumors. At the same time, immunotherapy can combine with other treatments to exhibit excellent antitumor effects. Upconversion nanoparticles (UCNPs) can convert near-infrared (NIR) light into ultraviolet and visible light, thus have good performance in bioimaging and NIR triggered phototherapy. In this review paper, we summarize the design, fabrication, and application of UCNPs-based NIR photoimmunotherapy for combined cancer treatment, as well as put forward the prospect of future development.

Insight into the Luminescence Alternation of Sub-30 nm Upconversion Nanoparticles with a Small NaHoF4 Core and Multi-Gd3+ /Yb3+ Coexisting Shells

It is absolutely imperative for development of material science to adjust upconversion luminescence (UCL) properties of highly doped upconversion nanoparticles (UCNPs) with special optical properties and prominent application prospects. In this work, featuring NaHoF₄ @NaYbF₄ (Ho@Yb) structures, sub-30 nm core-multishell UCNPs are synthesized with a small NaHoF₄ core and varied Gd³⁺ /Yb³⁺ coexisting shells. X-ray diffraction, transmission electron microscopy, UCL spectrum, UCL lifetime, and pump power dependence are adhibited for characterization. Compared with the former work, except for a smaller total size, tunable emission in color from red to yellow to green, and intensity from low to stronger than that of traditional UCNPs is achieved for ≈10 nm NaHoF₄ core size by means of changing number of layers and Gd³⁺ /Yb³⁺ concentration ratios in different layers. Besides, simultaneously doping Ho³⁺ into the shells will result in lowered UCL intensity and lifted green/red ratio. Surface energy loss and sensitizing energy supply, which can be modulated with inert shielding of Gd³⁺ and sensitization of Yb³⁺ , are proved to be the essential determinant. More UCL properties of these peculiar Ho@Yb UCNPs are uncovered and detailedly summarized, and the findings can help to expand the application scope of NaHoF₄ into photoinduced therapy.

Independent Tuning of Nano-Ligand Frequency and Sequences Regulates the Adhesion and Differentiation of Stem Cells

The native extracellular matrix (ECM) can exhibit heterogeneous nano-sequences periodically displaying ligands to regulate complex cell-material interactions in vivo. Herein, an ECM-emulating heterogeneous barcoding system, including ligand-bearing Au and ligand-free Fe nano-segments, is developed to independently present tunable frequency and sequences in nano-segments of cell-adhesive RGD ligand. Specifically, similar exposed surface areas of total Fe and Au nano-segments are designed. Fe segments are used for substrate coupling of nanobarcodes and as ligand-free nano-segments and Au segments for ligand coating while maintaining both nanoscale (local) and macroscale (total) ligand density constant in all groups. Low nano-ligand frequency in the same sequences and terminally sequenced nano-ligands at the same frequency independently facilitate focal adhesion and mechanosensing of stem cells, which are collectively effective both in vitro and in vivo, thereby inducing stem cell differentiation. The Fe/RGD-Au nanobarcode implants exhibit high stability and no local and systemic toxicity in various tissues and organs in vivo. This work sheds novel insight into designing biomaterials with heterogeneous nano-ligand sequences at terminal sides and/or low frequency to facilitate cellular adhesion. Tuning the electrodeposition conditions can allow synthesis of unlimited combinations of ligand nano-sequences and frequencies, magnetic elements, and bioactive ligands to remotely regulate numerous host cells in vivo.

A Near-Infrared Photo-Switched MicroRNA Amplifier for Precise Photodynamic Therapy of Early-Stage Cancers

Stimuli-responsive photodynamic therapy (PDT) is a hot topic in precise medicine, but the low abundance of responsive trigger molecules in early-stage disease limits application. Here we designed an amplifier with multiple upconversion luminances to achieve a near-infrared photo-switched cascade reaction triggered by specific microRNA and precise PDT of early-stage cancers. This amplifier was composed of photo-caged DNA nanocombs and an upconversion nanoparticle (UCNP) sensitized with IRDye 800CW. The nanocomb was prepared by assembling a photozipper-protected hairpin and two kinds of hybridizable hairpin probes on a DNA skeleton. Upon 808-nm light irradiation, the produced UV light cleaved off the photozipper to induce microRNA-responsive cascade hybridization reaction, activating the photosensitizers linked to different hairpins to generate reactive oxygen species (ROS) under the simultaneously emitted blue light for efficient PDT.

Remote Control of Neural Stem Cell Fate Using NIR-Responsive Photoswitching Upconversion Nanoparticle Constructs

Light-mediated remote control of stem cell fate, such as proliferation, differentiation, and migration, can bring a significant impact on stem cell biology and regenerative medicine. Current UV/vis-mediated control approaches are limited in terms of nonspecific absorption, poor tissue penetration, and phototoxicity. Upconversion nanoparticle (UCNP)-based near-infrared (NIR)-mediated control systems have gained increasing attention for vast applications with minimal nonspecific absorption, good penetration depth, and minimal phototoxicity from NIR excitations. Specifically, 808 nm NIR-responsive upconversion nanomaterials have shown clear advantages for biomedical applications owing to diminished heating effects and better tissue penetration. Herein, a novel 808 nm NIR-mediated control method for stem cell differentiation has been developed using multishell UCNPs, which are optimized for upconverting 808 nm NIR light to UV emission. The locally generated UV emissions further toggle photoswitching polymer capping ligands to achieve spatiotemporally controlled small-molecule release. More specifically, with 808 nm NIR excitation, stem cell differentiation factors can be released to guide neural stem cell (NSC) differentiation in a highly controlled manner. Given the challenges in stem cell behavior control, the developed 808 nm NIR-responsive UCNP-based approach to control stem cell differentiation can represent a new tool for studying single-molecule roles in stem cell and developmental biology.

X (metal: Al, Cu, Sn, Ti)-functionalized tunable 2D-MoS2 nanostructure assembled biosensor arrays for qualitative and quantitative analysis of vital neurological drugs

In this work we report for the first time surface functionalization of 2D MoS2 with X (metals: Al, Cu, Sn, Ti) to develop a low-cost, ultra-selective biosensor array based Electronic Tongue (E-Tongue) for the detection of 4 vital neurological drugs in human saliva. The hydrothermally grown surface functionalized X-MoS2 was integrated onto a single 1 × 1 cm aluminium foil and contacts were defined using Cr electrodes. Detailed characterization revealed the formation of 2-H MoS2 and metal-X (Al, Cu, Sn, Ti)-functionalized MoS2 nanoflower like morphology decorated with nanoflake, nanorod, nanocube and nanostick structures, respectively. The response of the sensor array was recorded for aspirin, nicotine, caffeine and tramadol. Principal Component Analysis (PCA) was performed to reduce the dimension of numerous response data sets from all sensors and predict the likely possible response from various neurological drugs towards each sensor. Pattern-recognition analysis confirmed a definite pattern in response to respective functionalization and could efficiently differentiate neurological drugs from one another. Real-time analysis was performed using saliva samples for monitoring the therapeutic neurological drug concentration in the human body. Furthermore, the biosensor array was exposed to respective neurological drugs to study their sensitivity, selectivity, stability, reproducibility and adhesion onto the device. The strategy outlined can be used to develop lab-on-a-chip devices for the real-time detection of numerous bioanalytes in body fluids.

Nanostructures based on vanadium disulfide growing on UCNPs: simple synthesis, dual-mode imaging, and photothermal therapy

It remains a great challenge to integrate effective photothermal therapeutic materials with upconversion nanoparticles (UCNPs) into one structure with small size. Herein, a new and simple method was developed to combine the luminescent UCNPs with vanadium disulfide (VS2) heterogeneously growing on the UCNPs. VS2 was grown directly on the surface of UCNPs to obtain oil-soluble nanocomposites, UCNPs@VS2. Then polyethylene glycol (mPEG) was functionalized on the surface of the nanocomposites to improve the water solubility, resulting in the integrated nanostructure UCNPs@VS2-mPEG (with an approximate size of 25 nm) for bioimaging and photothermal therapy in vitro. Importantly, cytotoxicity test results show that the final nanostructure has good biocompatibility. Furthermore, due to the excellent photothermal effects of VS2 and the unique imaging function of UCNPs, the nanostructure shows effective photothermal therapy for HeLa cells and was successfully applied in magnetic resonance imaging and upconversion luminescence imaging in vitro. Therefore, this study demonstrates a simple yet powerful method of growing VS2 on the surface of UCNPs, which provides an effective method to establish one integrated nanostructure with a nanoscale advantage for dual-model bioimaging and treatment.

Recent Advances in Luminescence Imaging of Biological Systems Using Lanthanide(III) Luminescent Complexes

The use of luminescence in biological systems allows one to diagnose diseases and understand cellular processes. Molecular systems, particularly lanthanide(III) complexes, have emerged as an attractive system for application in cellular luminescence imaging due to their long emission lifetimes, high brightness, possibility of controlling the spectroscopic properties at the molecular level, and tailoring of the ligand structure that adds sensing and therapeutic capabilities. This review aims to provide a background in luminescence imaging and lanthanide spectroscopy and discuss selected examples from the recent literature on lanthanide(III) luminescent complexes in cellular luminescence imaging, published in the period 2016-2020. Finally, the challenges and future directions that are pointing for the development of compounds that are capable of executing multiple functions and the use of light in regions where tissues and cells have low absorption will be discussed.

Application of Zero-Dimensional Nanomaterials in Biosensing

Zero-dimensional (0D) nanomaterials, including graphene quantum dots (GQDs), carbon quantum dots (CQDs), fullerenes, inorganic quantum dots (QDs), magnetic nanoparticles (MNPs), noble metal nanoparticles, upconversion nanoparticles (UCNPs) and polymer dots (Pdots), have attracted extensive research interest in the field of biosensing in recent years. Benefiting from the ultra-small size, quantum confinement effect, excellent physical and chemical properties and good biocompatibility, 0D nanomaterials have shown great potential in ion detection, biomolecular recognition, disease diagnosis and pathogen detection. Here we first introduce the structures and properties of different 0D nanomaterials. On this basis, recent progress and application examples of 0D nanomaterials in the field of biosensing are discussed. In the last part, we summarize the research status of 0D nanomaterials in the field of biosensing and anticipate the development prospects and future challenges in this field.