Lanthanide upconversion and downshifting luminescence for biomolecules detection

Luminescent Ln-MOFs for Chemical Sensing Application on Biomolecules

At present, the application of rare-earth organic frameworks (Ln-MOFs) in fluorescence sensing has entered rapid development and shown great potential in various analytical fields, such as environmental analysis, food analysis, drug analysis, and biological and clinical analysis by utilizing their internal porosity, tunable structural size, and energy transfer between rare-earth ions, ligands, and photosensitizer molecules. In addition, because the luminescence properties of rare-earth ions are highly dependent on the structural details of the coordination environment surrounding the rare-earth ions, and although their excitation lifetimes are long, they are usually not burst by oxygen and can provide an effective platform for chemical sensing. In order to further promote the development of fluorescence sensing technology based on Ln-MOFs, we summarize and review in detail the latest progress of the construction of Ln-MOF materials for fluorescence sensing applications and related sensor components, including design strategies, preparation methods, and modification considerations and initially propose the future development prospects and prospects.

Recent Advances on the Metal-Organic Frameworks-Based Biosensing Methods for Cancer Biomarkers Detection

Sensitive and selective detection of cancer biomarkers is crucial for early diagnosis and treatment of cancer, one of the most dangerous diseases in the world. Metal-organic frameworks (MOFs), a class of hybrid porous materials fabricated through the assembly of metal ions/clusters and organic ligands, have attracted increasing attention in the sensing of cancer biomarkers, due to the advantages of adjustable size, high porosity, large surface area and ease of modification. MOFs have been utilized to not only fabricate active sensing interfaces but also arouse a variety of measurable signals. Several representative analytical technologies have been applied in MOF-based biosensing strategies to ensure high detection sensitivity toward cancer biomarkers, such as fluorescence, electrochemistry, electrochemiluminescence, photochemistry and colorimetric methods. In this review, we summarized recent advances on MOFs-based biosensing strategies for the detection of cancer biomarkers in recent three years based on the categories of metal nodes, and aimed to provide valuable references for the development of innovative biosensing platform for the purpose of clinical diagnosis.

Engineering Visible to Near-Infrared Luminescence through a Selective Doping Strategy for High-Performance Temperature Sensing

Luminescence nanothermometers have garnered considerable attention due to their noncontact measurement, high spatial resolution, and rapid response. However, many nanothermometers employing single-mode measurement encounter challenges regarding their relative sensitivity. Herein, a unique class of tunable upconversion (UC) and downshifting (DS) luminescence covering the visible to near-infrared range (400-1700 nm) is reported, characterized by the superior Tm3+, Ho3+, and Er3+ emissions induced by efficient energy transfer. The outstanding negative thermal expansion characteristic of ScF3 nanocrystals has been found to guide excitation energy toward the relevant emitting states in the Yb3+-Ho3+-Tm3+-codoped system, consequently resulting in remarkable near-infrared III (NIR-III) luminescence at ∼1625 nm (Tm3+:3F4 → 3H6 transition), which in turn presents numerous opportunities for designing multimode ratiometric luminescence thermometry. Furthermore, by facilitating phonon-assisted energy transfer in Er3+-Ho3+-codoped systems, the luminescence intensity ratio (LIR) of 4I13/2 of Er3+ and 5I6 of Ho3+ in ScF3:Yb3+/Ho3+/Er3+ exhibits a strong temperature dependence, enabling NIR-II/III luminescence thermometry with superior thermal sensitivity and resolution (Sr = 0.78% K-1, δT = 0.64 K). These findings not only underscore the distinctive and ubiquitous attributes of lanthanide ion-doped nanomaterials but also hold significant implications for crafting luminescence thermometers with unparalleled sensitivity.

Sensitive detection of choline and nicotine in real samples by switching upconversion luminescence

Nicotine (3-(1-methyl-2-pyrrolidinyl)pyridine) is one of the most common addictive substances, causing the trace detection of nicotine to be very necessary. Herein, we designed and prepared a functionalized nanocomposite CS-PAA (NaYF4:19.5%Yb,0.5%Tm@NaYF4-PAA) using a simple method. The nicotine concentration was quantitatively detected through the inhibition of choline oxidase activity by nicotine and the luminescence intensity of CS-PAA being quenched by Fe3+. The mechanism of Fe3+ quenching CS-PAA emission was inferred by luminescence lifetime and UV-vis absorption spectra characterization. During the nicotine detection, both excitation (980 nm) and emission (802 nm) wavelengths of CS-PAA enable the avoidance of the interference of background fluorescence in complicated food objects, thus providing high selectivity and sensitivity with a linear range of 5-750 ng/mL and a limit of detection of 9.3 nM. The method exhibits an excellent recovery and relative standard deviation, indicating high accuracy and repeatability of the detection of nicotine.

Large enhancement of red upconversion luminescence in beta Ba2Sc0.67Yb0.3Er0.03AlO5 phosphor via Mn2+ ions doping for thermometry

Here, this study reports single-band red upconversion emission in β-Ba2ScAlO5: Yb3+/Er3+ phosphor by doping Mn2+. The optimum concentration of Mn2+ ions in β-Ba2ScAlO5: Yb3+/Er3+ phosphor was 0.20. The intensity of red and green emissions is increased by 27.4 and 19.3 times, respectively. Compared with the samples without Mn2+ ions, the red-green integral strength ratio of β-Ba2ScAlO5: Yb3+/Er3+/Mn2+ sample was significantly increased by 28.4 times, reaching 110.9. The UCL mechanism was explored by analyzing the down-conversion luminescence spectra, absorption spectra, UCL spectra, and upconversion fluorescence lifetime decay curves of Yb3+/Er3+/Mn2+ co-doped β-Ba2ScAlO5. The enhancement of upconversion red light is achieved through energy transfer between defect bands and Er3+ ions, as well as energy transfer between Mn2+ ions and Er3+ ions. In addition, the Mn2+ doped β-Ba2ScAlO5: Yb3+/Er3+ red UCL phosphors have great potential for ambient temperature sensing in the 298-523 K temperature range. The maximum sensitivity of β-Ba2ScAlO5: Yb3+/Er3+/Mn2+ phosphor as a temperature sensor at 523 K is 0.0247 K-1.

A "turn off-on" fluorescent sensor for detection of Cr(Ⅵ) based on upconversion nanoparticles and nanoporphyrin

Hexavalent chromium (Cr(Ⅵ)) is a significant environmental pollutant because of its toxic and carcinogenic properties and wide use in various industries. Hence, there is an urgent need to develop accurate and selective approaches to detect the concentration of Cr(Ⅵ) in agricultural and aquaculture products to help humans avoid potential hazards of indirectly taking in Cr(Ⅵ). In this work, we report a "turn off-on" fluorescent sensor based on citric acid coated, 808 nm-excited core-shell upconversion nanoparticles (CA-UCNPs) and self-assembled copper porphyrin nanoparticles (nano CuTPyP) for sensitive and specific detection of Cr(Ⅵ). Nano copper 5, 10, 15, 20-tetra(4-pyridyl)-21H-23H- porphine obtained by acid-base neutralization micelle-confined self-assembly method function as an effective quencher due to its excellent optical property and water solubility. Through electrostatic interactions, positively charged nano CuTPyP are attracted to the surface of negatively charged CA-UCNPs, which can almost completely quench the fluorescence emission. In the presence of Cr(Ⅵ), nano CuTPyP can discriminatively interact with Cr(Ⅵ) and form nano CuTPyP/Cr(Ⅵ) complex, which separates nano CuTPyP from CA-UCNPs and restores the fluorescence. The sensing system exhibits a good linear response to Cr(Ⅵ) concentration in the range from 0.5 to 400 µM with a detection limit of 0.36 µM. The sensing method also displays high selectivity against other common ions including trivalent chromium and is applied to the analysis of Cr(Ⅵ) in actual rice and fish samples with satisfactory results.

Highly sensitive sensing of DPA by lanthanide metal-organic frameworks and detection of fiber membranes

The detection of 2,6-pyridinecarboxylic acid (DPA), as a biomarker of Bacillus anthracis, has attracted wide attention. In previous reports of DPA detection, fluorescent probes may not have high specificity. Therefore, the rational design and development of fluorescent sensors with excellent performance is of great significance for the detection of DPA. In this study, two novel lanthanide metal-organic frameworks (Ln-MOFs) were synthesized by hydrothermal method using 3-polyfluorobiphenyl-3 ', 4,5 ' -tricarboxylic acid (H2FPTA) as ligand. Studies have shown that Ln-MOFs can detect DPA in real time, with detection limits of 0.54 μM and 0.67 μM, respectively, and have a high recovery rate (95 % -108 %) in fetal bovine serum. As a self-calibration sensor, other substances in the blood can be clearly distinguished by a two-dimensional fluorescence code diagram. After the Ln-MOFs were spun into nanofiber membranes, they responded quickly to DPA. This increases practicability and provides a promising idea for the development of simple and efficient ratio sensors.

Universal smartphone-assisted label-free CRISPR/Cas12a-DNAzyme chemiluminescence biosensing platform for on-site detection of nucleic acid and non-nucleic acid targets

The clustered regularly interspaced short palindromic repeats (CRISPR)-associated protein (Cas) (CRISPR/Cas) system enables sensitive and specific detection of biomolecules, thanks to its programmability, high fidelity, and powerful signal amplification capabilities. Herein, a universal smartphone-assisted label-free G-quadruplex (G4) DNAzyme-based chemiluminescence CRISPR/Cas12a biosensing platform (G4CLCas) is firstly described that achieves on-site, ultrasensitive visual detection of nucleic acid and non-nucleic acid targets. The G4CLCas-based sensing platform relies on Cas12a trans-cleavage activation that triggers the cleavage of the G4 DNAzyme, resulting in chemiluminescence signals off/on compared to that of the control. Chemiluminescence signals are captured as images that are quantitatively analyzed and visualized using a smartphone-assisted imaging cartridge. Under optimal conditions, G4CLCas achieves a low limit of detection (LOD) of 8.6 aM (∼5.2 copies/μL) for monkeypox virus (MPXV) DNA within the linear concentration range of 10-300 aM and can accurately quantify viral DNA in spiked samples. G4CLCas can also detect non-nucleic acid targets, whereby it achieves a low LOD value of 84.3 nM for adenosine triphosphate (ATP) within the linear concentration range of 2-2000 μM. Here, a label-free, portable, on-site CRISPR/Cas12a chemiluminescence biosensing platform based on the G4 DNAzyme substrates is proposed with potential applications in clinical detection and bioanalytical chemistry research.

Photophysics and its application in photon upconversion

Photoluminescence (PL) upconversion is a phenomenon involving light-matter interaction, where the energy of the emitted photons is higher than that of the incident photons. PL upconversion has promising applications in optoelectronic devices, displays, photovoltaics, imaging, diagnosis and treatment. In this review, we summarize the mechanism of PL upconversion and ultrafast PL physical processes. In particular, we highlight the advances in laser cooling, biological imaging, volumetric displays and photonics.

Unlabelled LRET biosensor based on double-stranded DNA for the detection of anthraquinone anticancer drugs

Based on upconversion nanoparticles (UCNPs) as energy donor and herring sperm DNA (hsDNA) as molecular recognition element, an unlabelled upconversion luminescence (UCL) affinity biosensor was constructed for the detection of anthraquinone (AQ) anticancer drugs in biological fluids. AQ anticancer drugs can insert into the double helix structure of hsDNA on the surface of UCNPs, thereby shortening the distance from UCNPs. Therefore, the luminescence resonance energy transfer (LRET) phenomenon is effectively triggered between UCNPs and AQ anticancer drugs. Hence, AQ anticancer drugs can be quantitatively detected according to the UCL quenching rate. The biosensor showed good sensitivity and stability for the detection of daunorubicin (DNR) and doxorubicin (ADM). For the detection of DNR, the linear range is 1-100 μg·mL-1 with a limit of detection (LOD) of 0.60 μg·mL-1, and for ADM, the linear range is 0.5-100 μg·mL-1 with a LOD of 0.38 μg·mL-1. The proposed biosensor provides a convenient method for monitoring AQ anticancer drugs in clinical biological fluids in the future.

Upconversion Luminescence in Mononuclear Yb/Sm Co-crystal Assemblies at Room Temperature

Metal-based upconversion luminescence transforming high-energy photons into low-energy photons is an attractive anti-Stokes shift process for fundamental research and promising applications. In this work, we developed the upconversion luminescence in co-crystal assemblies consisting of discrete mononuclear Yb and Sm complexes. The characteristic visible emissions of Sm3+ were observed under the excitation of absorption band of Yb3+ at 980 nm. A series of co-crystal assemblies were investigated based on mononuclear Yb and Sm complexes, and the strongest luminescence was obtained when the molar concentration between Yb3+ and Sm3+ is equivalent. The crystal structure was fully characterized by the single crystal X-ray diffraction and upconverting energy transfer mechanisms were verified as cooperative sensitization upconversion and energy transfer upconversion. This is the first example of Sm3+ -based upconverting luminescence in discrete lanthanide complexes which present as co-crystal assemblies at room temperature.

Nanoporous YVO4 as a luminescent host for probing molecular encapsulation

Control of phase separation of VO43- and rare earth precursors in reverse microemulsions afforded ∼35 nm YVO4 nanoparticles with functionalisable ∼7 ± 3 nm nanopores. Doping by Eu3+ allowed luminescent probing of interfacial crystallisation while xylenol orange absorption showed molecular encapsulation in particle cavities. This provides potential multifunctional systems combining UV-Vis-NIR luminescence and (photo)active molecules for optical sensing.

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.

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.

Plasmonic quenching and enhancement: metal-quantum dot nanohybrids for fluorescence biosensing

Plasmonic metal nanoparticles and semiconductor quantum dots (QDs) are two of the most widely applied nanomaterials for optical biosensing and bioimaging. While their combination for fluorescence quenching via nanosurface energy transfer (NSET) or Förster resonance energy transfer (FRET) offers powerful ways of tuning and amplifying optical signals and is relatively common, metal-QD nanohybrids for plasmon-enhanced fluorescence (PEF) have been much less prevalent. A major reason is the competition between fluorescence quenching and enhancement, which poses important challenges for optimizing distances, orientations, and spectral overlap toward maximum PEF. In this feature article, we discuss the interplay of the different quenching and enhancement mechanisms (a mixed distance dependence of quenching and enhancement - "quenchancement") to better understand the obstacles that must be overcome for the development of metal-QD nanohybrid-based PEF biosensors. The different nanomaterials, their combination within various surface and solution based design concepts, and their structural and photophysical characterization are reviewed and applications toward advanced optical biosensing and bioimaging are presented along with guidelines and future perspectives for sensitive, selective, and versatile bioanalytical research and biomolecular diagnostics with metal-QD nanohybrids.

Assembling Near-Infrared Dye on the Surface of Near-Infrared Silica-Coated Copper Sulphide Plasmonic Nanoparticles

Functionalization of colloidal nanoparticles with organic dyes, which absorb photons in complementary spectral ranges, brings a synergistic effect for harvesting additional light energy. Here, we show functionalization of near-infrared (NIR) plasmonic nanoparticles (NPs) of bare and amino-group functionalized mesoporous silica-coated copper sulphide (Cu_2-xS@MSS and Cu_2-xS@MSS-NH₂) with specific tricarbocyanine NIR dye possessing sulfonate end groups. The role of specific surface chemistry in dye assembling on the surface of NPs is demonstrated, depending on the organic polar liquids or water used as a dispersant solvent. It is shown that dye binding to the NP surfaces occurs with different efficiency, but mostly in the monomer form in polar organic solvents. Conversely, the aqueous medium leads to different scenarios according to the NP surface chemistry. Predominant formation of the disordered dye monomers occurs on the bare surface of mesoporous silica shell (MSS), whereas the amino-group functionalized MSS accepts dye predominantly in the form of dimers. It is found that the dye-NP interaction overcomes the dye-dye interaction, leading to disruption of dye J-aggregates in the presence of the NPs. The different organization of the dye molecules on the surface of silica-coated copper sulphide NPs provides tuning of their specific functional properties, such as hot-band absorption and photoluminescence.

Ratiometric upconversion luminescence nanoprobes from construction to sensing, imaging, and phototherapeutics

In terms of the combined advantages of upconversion luminescence (UCL) properties and dual-signal ratiometric outputs toward specific targets, the ratiometric UCL nanoprobes exhibit significant applications. This review summarizes and discusses the recent advances in ratiometric UCL nanoprobes, mainly including the construction of nanoprobe systems for sensing, imaging, and phototherapeutics. First, the construction strategies are introduced, involving different types of nanoprobe systems, construction methods, and ratiometric dual-signal modes. Then, the sensing applications are summarized, involving types of targets, sensing mechanisms, sensing targets, and naked-eye visual detection of UCL colors. Afterward, the phototherapeutic applications are discussed, including bio-toxicity, bio-distribution, biosensing, and bioimaging at the level of living cells and small animals, and biomedicine therapy. Particularly, each section is commented on by discussing the state-of-the-art relevant studies on ratiometric UCL nanoprobe systems. Moreover, the current status, challenges, and perspectives in the forthcoming studies are discussed. This review facilitates the exploration of functionally luminescent nanoprobes for excellent sensing, imaging, biomedicine, and multiple applications in significant fields.

Advances in upconversion luminescence nanomaterial-based biosensor for virus diagnosis

Various infectious viruses have been posing a major threat to global public health, especially SARS-CoV-2, which has already claimed more than six million lives up to now. Tremendous efforts have been made to develop effective techniques for rapid and reliable pathogen detection. The unique characteristics of upconversion nanoparticles (UCNPs) pose numerous advantages when employed in biosensors, and they are a promising candidate for virus detection. Herein, this Review will discuss the recent advancement in the UCNP-based biosensors for virus and biomarkers detection. We summarize four basic principles that guide the design of UCNP-based biosensors, which are utilized with luminescent or electric responses as output signals. These strategies under fundamental mechanisms facilitate the enhancement of the sensitivity of UCNP-based biosensors. Moreover, a detailed discussion and benefits of applying UCNP in various virus bioassays will be presented. We will also address some obstacles in these detection techniques and suggest routes for progress in the field. These progressions will undoubtedly pose UCNP-based biosensors in a prominent position for providing a convenient, alternative approach to virus detection.

Achieving Photon Upconversion in Mononuclear Lanthanide Molecular Complexes at Room Temperature

Photon upconversion luminescence at the molecule scale is a rarely observed phenomenon despite possessing colossal potential for basic research and reality applications. Here we show that the eight-coordinate erbium molecular complex composed of Er³⁺ ion, dibenzoylmethane, and 2,2'-bipyridine exhibits upconversion emission. Under direct excitation at the absorption band of Er³⁺ ion at 980 nm, the complex shows upconverted green emissions of Er³⁺ ion at 525 and 545 nm at room temperature. Noticeably, upon the introduction of fluoride ions into this complex, an additional upconverted red emission at 667 nm appears as well, and the luminescence intensities of both the green and red emissions increase by a factor of 13 at most. This study not only provides a strategy to adjust the green and red emissions in mononuclear erbium complexes but also broadens the horizons of designing lanthanide-based molecular upconversion systems.

Recent progress in upconversion nanomaterials for emerging optical biological applications

The recent advances of upconversion nanoparticles (UCNPs) have made them the ideal "partner" for a variety of biological applications. In this review, we describe the emerging biological optical applications of UCNPs, focus on their potential therapeutic advantages. Firstly, we briefly review the development and mechanisms of upconversion luminescence, including organic and inorganic UCNPs. Next, in the section on UCNPs for imaging and detection, we list the development of UCNPs in visualization, temperature sensing, and detection. In the section on therapy, recent results are described concerning optogenetics and neurotherapy. Tumor therapy is another major part of this section, including the synergistic application of phototherapy such as photoimmunotherapy. In a special section, we briefly cover the integration of UCNPs in therapeutics. Finally, we present our understanding of the limitations and prospects of applications of UCNPs in biological fields, hoping to provide a more comprehensive understanding of UCNPs and attract more attention.

Tunable fluorescence emission based on multi-layered MOF-on-MOF

Luminescent metal-organic frameworks (MOFs) have garnered considerable attention in various fields. Herein, we proposed a hierarchical confinement strategy based on MOF-on-MOF to tune luminescence emission ranging from blue to red including white light in a flexible way. The easily available ZIF-8 MOF was used as a host for the confinement of two kinds of size-matching dyes (perylene and rhodamine B) to obtain a layered ZIF-8@dye@ZIF-8@dye via in situ encapsulation and seed-mediated synthesis. ZIF-8@dye@ZIF-8@dye materials with different fluorescence emission in dispersed and solid states were both obtained by tuning the initial encapsulation concentration of dye and changing the structure of the inner and outer ZIF-8@dye layers. To our delight, ZIF-8@0.125perylene@ZIF-8@25RhB with white light emission in the dispersed state was obtained; meanwhile, ZIF-8@0.125perylene + 25RhB and mechanically mixed ZIF-8@0.125perylene + ZIF-8@25RhB could not realize white light emission under the same conditions, indicating that the proposed hierarchical confinement strategy facilitated white light regulation. Similarly, the emission of ZIF-8@dye@ZIF-8@dye in the solid state has also been investigated; ZIF-8@perylene@ZIF-8@3RhB with white light emission was obtained, while white light emission could not be achieved in ZIF-8@perylene + 3RhB and ZIF-8@perylene + ZIF-8@3RhB, which further indicated the importance of the hierarchical confinement strategy based on MOF-on-MOF. The proposed hierarchical confinement strategy may also inspire the development of other functional optical MOF materials.

Highlighting Recent Crystalline Engineering Aspects of Luminescent Coordination Polymers Based on F-Elements and Ditopic Aliphatic Ligands

Three principal factors may influence the final structure of coordination polymers (CPs): (i) the nature of the ligand, (ii) the type and coordination number of the metal center, and (iii) the reaction conditions. Further, flexible carboxylate aliphatic ligands have been widely employed as building blocks for designing and synthesizing CPs, resulting in a diverse array of materials with exciting architectures, porosities, dimensionalities, and topologies as well as an increasing number of properties and applications. These ligands show different structural features, such as torsion angles, carbon backbone number, and coordination modes, which affect the desired products and so enable the generation of polymorphs or crystalline phases. Additionally, due to their large coordination numbers, using 4f and 5f metals as coordination centers combined with aliphatic ligands increases the possibility of obtaining different crystal phases. Additionally, by varying the synthetic conditions, we may control the production of a specific solid phase by understanding the thermodynamic and kinetic factors that influence the self-assembly process. This revision highlights the relationship between the structural variety of CPs based on flexible carboxylate aliphatic ligands and f-elements (lanthanide and actinides) and their outstanding luminescent properties such as solid-state emissions, sensing, and photocatalysis. In this sense, we present a structural analysis of the CPs reported with the oxalate ligand, as the one rigid ligand of the family, and other flexible dicarboxylate linkers with –CH₂– spacers. Additionally, the nature of the luminescence properties of the 4f or 5f-CPs is analyzed, and finally, we present a novel set of CPs using a glutarate-derived ligand and samarium, with the formula [2,2′-bipyH][Sm(HFG)₂ (2,2′-bipy) (H₂O)₂]•(2,2′-bipy) (α-Sm) and [2,2′-bipyH][Sm(HFG)₂ (2,2′-bipy) (H₂O)₂] (β-Sm).

Engineering light-initiated afterglow lateral flow immunoassay for infectious disease diagnostics

The pandemic of highly contagious diseases has put forward urgent requirements for high sensitivity and adaptive capacity of point-of-care testing (POCT). Herein, for the first time, we report an aggregation-induced emission (AIE) dye-energized light-initiated afterglow nanoprobes (named LiAGNPs), implemented onto a lateral flow immunoassay (LFIA) test strip, for diagnosis of two highly contagious diseases, human immunodeficiency virus (HIV) and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) as model validation. The primary working mechanism relies on the cyclically generated singlet oxygen (¹O₂)-triggered time-resolved luminescent signals of LiAGNPs in which AIE dyes (TTMN) and chemiluminescent substrates (SO) are loaded. The designed LiAGNPs were found 2-fold and 32-fold sensitive than the currently used Eu(III)-based time-resolved fluorescent nanoparticles and gold nanoparticles in lateral flow immunoassay (LFIA), respectively. In addition, the extra optical behaviors of nude color and fluorescence of LiAGNPs enable the LFIA platform with the capability of the naked eye and fluorescent detection to satisfy the applications under varying scenarios. In short, the versatile LiAGNPs have great potential as a novel time-resolved reporter in enhancing detection sensitivity and application flexibility with LFIA platform for rapid but sensitive infectious disease diagnostics.

Cyanine-Doped Lanthanide Metal-Organic Frameworks for Near-Infrared II Bioimaging

Developing metal-organic frameworks (MOFs) with strong near-infrared II (NIR-II, 1000-1700 nm) emission is significant for biomedical research but highly challenging. So far there are no MOFs reported for NIR-II imaging in vivo due to their poor NIR-II emission efficiency. Herein, a strategy is proposed to prepare MOFs with strong NIR-II emission, by integrating NIR dye IR-3C and Ln3+ (Ln = Yb, Nd, and Er) into a same framework. IR-3C with high photon-absorption ability harvests the excitation photons and transfers energy to Ln3+ via a resonance energy transfer pathway, significantly enhancing the NIR-II emission of Ln3+ . The as-obtained Er-BTC-IR exhibits excellent NIR-IIb (1500-1700 nm) emission efficiency in aqueous phase and good biocompatibility after surface modification, which provides advanced bioimaging performance in vivo. It is able to clearly delineate the vessels, spine, and lymph of mice, and also to differentiate the vessels with acute vascular inflammation. This strategy paves the way to the preparation of NIR-II emissive MOFs and will promote their bioapplication.

Orthogonal Multiplexed NIR-II Imaging with Excitation-Selective Lanthanide-Based Nanoparticles

Multiplexed imaging in the second near-infrared (NIR-II, 1000-1700 nm) window, with much reduced tissue scattering and autofluorescence background noises, could offer comprehensive information for studying biological processes and accurate diagnosis. A critical requirement for harvesting the full potential of multiplexing is to develop fluorescent probes with emission profiles specifically tuned at distinct excitations toward their target applications. However, the lack of versatile probes with separated signals in this NIR-II window hinders the potential of in vivo multiplexed imaging. In this study, we designed three types of Nd³⁺-, Ho³⁺-, and Er³⁺-based down-shifting nanoparticles (DSNPs) with core-shell structures (csNd, csHo, and csEr). Excitation wavelengths of these nanoparticles were first screened and confirmed at 730, 915, and 655 nm. Under the new excitations, orthogonal three-color emissions in the NIR-II window (1060, 1180, and 1525 nm for csNd, csHo, and csEr, respectively) were efficiently achieved. These excitation-selective DSNPs were then demonstrated to be promising in encrypted anticounterfeiting applications with increased optical codes. By programmed administration of the DSNPs, anatomical rotation imaging can also be successfully performed to differentiate mouse bones, stomach, and blood vessels with high contrast and resolution in a fixed NIR-II channel (>1000 nm) by only switching the excitation wavelengths. This study suggests that the designed NIR-II excitation-selective DSNPs with orthogonal emissions may offer a powerful framework for spatially multiplexed imaging in biological and life sciences.

Upconversion Luminescent Humidity Sensors Based on Lanthanide-Doped MOFs

Lanthanide-doped metal-organic frameworks (Y/Yb/Er-MOF) were synthesized by a low-cost solvothermal method. The obtained Y/Yb/Er-MOF shows the cooperative upconversion luminescence of Yb3+ and upconversion luminescence of Er3+ (Yb3+-sensitized) irradiated by a continuous wave 980 nm laser. In order to explore the potential application of Y/Yb/Er-MOF in relative humidity (RH) sensors, the RH responsiveness of Y/Yb/Er-MOF was investigated by measuring the intensity changes of upconversion luminescence. The Y/Yb/Er-MOF possesses two luminescence centers, in which Yb3+ forms emission at 500 nm through the cooperative luminescence effect, and Er3+ achieves 660 nm emission through excited state absorption and successive energy transfer from Yb3+. Hence, the ratio meter luminescence sensor for RH is constructed based on Y/Yb/Er-MOF. The results show that the response of Y/Yb/Er-MOF to RH presents a linear relationship in the range of 11–95%. The cycle stability of Y/Yb/Er-MOF responses to RH was investigated with the intensity changes of upconversion luminescence, and the recovery ratio was more than 93% each time. Therefore, the Y/Yb/Er-MOF is a humidity-sensitive material with great potential for applications such as humidity sensors.

Recent Advances in Metal-Organic Framework-Based Electrochemical Biosensing Applications

In the face of complex environments, considerable effort has been made to accomplish sensitive, accurate and highly-effective detection of target analytes. Given the versatility of metal clusters and ligands, high porosity and large specific surface area, metal–organic framework (MOF) provides researchers with prospective solutions for the construction of biosensing platforms. Combined with the benefits of electrochemistry method such as fast response, low cost and simple operation, the untapped applications of MOF for biosensors are worthy to be exploited. Therefore, this review briefly summarizes the preparation methods of electroactive MOF, including synthesize with electroactive ligands/metal ions, functionalization of MOF with biomolecules and modification for MOF composites. Moreover, recent biosensing applications are highlighted in terms of small biomolecules, biomacromolecules, and pathogenic cells. We conclude with a discussion of future challenges and prospects in the field. It aims to offer researchers inspiration to address the issues appropriately in further investigations.

Versatile Types of Inorganic/Organic NIR-IIa/IIb Fluorophores: From Strategic Design toward Molecular Imaging and Theranostics

In vivo imaging in the second near-infrared window (NIR-II, 1000-1700 nm), which enables us to look deeply into living subjects, is producing marvelous opportunities for biomedical research and clinical applications. Very recently, there has been an upsurge of interdisciplinary studies focusing on developing versatile types of inorganic/organic fluorophores that can be used for noninvasive NIR-IIa/IIb imaging (NIR-IIa, 1300-1400 nm; NIR-IIb, 1500-1700 nm) with near-zero tissue autofluorescence and deeper tissue penetration. This review provides an overview of the reports published to date on the design, properties, molecular imaging, and theranostics of inorganic/organic NIR-IIa/IIb fluorophores. First, we summarize the design concepts of the up-to-date functional NIR-IIa/IIb biomaterials, in the order of single-walled carbon nanotubes (SWCNTs), quantum dots (QDs), rare-earth-doped nanoparticles (RENPs), and organic fluorophores (OFs). Then, these novel imaging modalities and versatile biomedical applications brought by these superior fluorescent properties are reviewed. Finally, challenges and perspectives for future clinical translation, aiming at boosting the clinical application progress of NIR-IIa and NIR-IIb imaging technology are highlighted.