Upconversional Nanoprobes with Highly Efficient Energy Transfer for Ultrasensitive Detection of Alkaline Phosphatase

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.

Upconversion nanoparticles anchored MnO2 nanosheets for luminescence "turn on" detecting hydrogen peroxide

The sensitively and reliably detecting hydrogen peroxide (H₂O₂) is of significant for biology and environment protection fields. Herein, we reported a high sensitive H₂O₂ nanoprobe based on upconversion nanoparticles (UCNPs) anchored MnO₂ nanosheets. In which, DNA modified NaYF₄@NaYF₄:Yb,Tm core-shell nanoparticles were anchored onto the MnO₂ nanosheets surface via π-π stacking. Owing to the luminescence resonance energy transfer, the blue luminescence of UCNPs was effectively quenched by MnO₂ nanosheets, then the luminescence could be restored by adding H₂O₂ for reducing MnO₂ to Mn²⁺, and achieving a H₂O₂ concentration-dependent luminescence change, the detection limit could reach to 0.23 nM (S/N = 3). The proposed method could detect H₂O₂ in serum, lake water and real samples. Thus, a desired upconversion luminescence sensing strategy for detection H₂O₂ in life and environmental analysis was successfully constructed. It may be provide a potential tool in disease diagnosis and environmental monitoring fields.

Fluorescence Turn-on Detection of Alkaline Phosphatase Activity and Al3+ Using Vitamin B6 Cofactor Conjugated GSH Capped Mn-doped ZnS Quantum Dots

The glutathione (GSH) functionalized Mn-doped ZnS quantum dots (GSH_Mn_ZnS QDs) was conjugated with pyridoxal 5'-phosphate (PLP). The -CHO group of vitamin B₆ cofactor PLP interacted with the -NH₂ group of GSH functionalized Mn_ZnS QDs. The conjugation of PLP quenched the fluorescence emission of GSH_Mn_ZnS QDs at 601 nm. Addition of alkaline phosphatase (ALP) catalytically dephosphorylated the PLP into pyridoxal that restored the fluorescence emission of GSH_Mn_ZnS QDs. With a sensitivity of 0.035 U/L, the PLP conjugated GSH_Mn_ZnS QDs was applied to quantify ALP activity in human serum and plasma. Further, the developed nanoprobe PLP conjugated GSH_Mn_ZnS QDs was also applied to detect Al³⁺. The complexation-induced fluorescence enhancement was observed at 492 nm upon the interaction of Al³⁺ with the PLP conjugated GSH_Mn_ZnS QDs. Without any interference from other tested metal ions, this nanoprobe can be employed to detect Al³⁺ down to 2.30 µM.

Recent advances in tumor biomarker detection by lanthanide upconversion nanoparticles

Early tumor diagnosis could reliably predict the behavior of tumors and significantly reduce their mortality. Due to the response to early cancerous changes at the molecular or cellular level, tumor biomarkers, including small molecules, proteins, nucleic acids, exosomes, and circulating tumor cells, have been employed as powerful tools for early cancer diagnosis. Therefore, exploring new approaches to detect tumor biomarkers has attracted a great deal of research interest. Lanthanide upconversion nanoparticles (UCNPs) provide numerous opportunities for bioanalytical applications. When excited by low-energy near-infrared light, UCNPs exhibit several unique properties, such as large anti-Stoke shifts, sharp emission lines, long luminescence lifetimes, resistance to photobleaching, and the absence of autofluorescence. Based on these excellent properties, UCNPs have demonstrated great sensitivity and selectivity in detecting tumor biomarkers. In this review, an overview of recent advances in tumor biomarker detection using UCNPs has been presented. The key aspects of this review include detection mechanisms, applications in vitro and in vivo, challenges, and perspectives of UCNP-based tumor biomarker detection.

The Coming of Age of Neodymium: Redefining Its Role in Rare Earth Doped Nanoparticles

Among luminescent nanostructures actively investigated in the last couple of decades, rare earth (RE³⁺) doped nanoparticles (RENPs) are some of the most reported family of materials. The development of RENPs in the biomedical framework is quickly making its transition to the ∼800 nm excitation pathway, beneficial for both in vitro and in vivo applications to eliminate heating and facilitate higher penetration in tissues. Therefore, reports and investigations on RENPs containing the neodymium ion (Nd³⁺) greatly increased in number as the focus on ∼800 nm radiation absorbing Nd³⁺ ion gained traction. In this review, we cover the basics behind the RE³⁺ luminescence, the most successful Nd³⁺-RENP architectures, and highlight application areas. Nd³⁺-RENPs, particularly Nd³⁺-sensitized RENPs, have been scrutinized by considering the division between their upconversion and downshifting emissions. Aside from their distinctive optical properties, significant attention is paid to the diverse applications of Nd³⁺-RENPs, notwithstanding the pitfalls that are still to be addressed. Overall, we aim to provide a comprehensive overview on Nd³⁺-RENPs, discussing their developmental and applicative successes as well as challenges. We also assess future research pathways and foreseeable obstacles ahead, in a field, which we believe will continue witnessing an effervescent progress in the years to come.

In-depth insight into the Yb3+ effect in NaErF4-based host sensitization upconversion: a double-edged sword

NaErF₄ is the most extensively studied host for self-sensitized upconversion (UC), and Yb³⁺ is the most commonly used energy absorber. It has been reported that the red luminescence of Er³⁺ can be enhanced by introducing Yb³⁺ into the NaErF₄ host lattice, where Yb³⁺ ions serve as trapping centers to confine the excitation energy. Also, it has been pointed out that the Yb³⁺ doping in the shell of NaErF₄-hosted core-shell nanocrystals can further improve the red emission intensity. Conversely, it can be argued that the Yb³⁺ doping in the shell always results in the luminescence quenching of the NaErF₄ core. These imply that the impact of Yb³⁺ on NaErF₄-based host-sensitized UC is rather complicated and must be probed deeply. In this study, we thoroughly discussed the effect of Yb³⁺ located in the core/shell on the NaErF₄-based host sensitization UC and afforded the related mechanism interpretations. In the NaErF₄ core nanocrystals, the green-dominated UCL presented an enhancement on increasing the concentration of the Yb³⁺ dopant owing to the promoted energy harvesting for luminescence. Furthermore, the emission properties of NaErF₄:10%Yb shelled with diverse inert layers were also investigated, and the intensity difference of these core-inert shell nanoparticles could be explained by the lattice mismatch and shell thickness. In NaErF₄:10%Yb@NaYF₄:Yb with variable Yb³⁺ doping in the shell, the red-dominated UCL was generally weakened with more Yb³⁺ localized in the shell, which was ascribed to the competition of energy pooling and energy dissipation of Yb³⁺ in the outer layer. Therefore, Yb³⁺ ions wield a two-sided influence (termed a "double-edged sword") on the UC emissions of the Er³⁺ host. Additionally, we demonstrated the application potential of such UCNPs in water sensing and high-level anti-counterfeiting. This work offers an in-depth insight into the UC mechanism of Yb³⁺-doped NaErF₄ nanocrystals and inspires the engineering of novel luminescent materials with distinguished properties.

Synthesis of stable core-shell perovskite based nano-heterostructures

Despite having exceptional optical and photoelectric properties, the application of organometal halide perovskites (OHP) is restricted due to the limited penetration depth of the UV excitation light and poor stability. Attempts have been made to make composite materials by mixing other materials such as upconversion nanoparticles (UCNP) with OHP. In contrast to linear absorption and emission of OHP, the nonlinear upconversion of UCNP offers numerous advantages such as deep penetration depth of the near-infrared (NIR) excitation light, minimal photodamage to biological tissues, and negligible background interference, which offer great potential in various applications such as multiplexed optical encoding, three-dimensional displays, super-resolution bioimaging, and effective solar spectrum conversion. However, it is challenging to synthesize hybrid OHP-UCNP nanocrystals due to the inherent difference in crystal structures of hexagonal phase UCNP and cubic phase OHP. In this work, we report OHP-UCNP heterostructured nanocrystals synthesized via growing cubic phase NaGdF₄ UCNP over cubic phase CsPbBr₃ OHP in a seed-mediated process based on a very small lattice mismatch and then converting cubic phase UCNP to hexagonal phase through heating. The juxtaposition of UCNP over OHP in a single nanocrystal facilitates efficient energy transfer from UCNP to OHP under NIR excitation and acts as a protective layer improving the stability. The stability is further enhanced by coating an inert UCNP shell on the OHP-UCNP nano-heterostructures with the same UCNP material earlier used in the heterostructures. The coating demonstrated greater stability under continuous UV exposure and in harsh environments such as high temperatures and polar solvents. These NIR excitable perovskite-UCNP nano-heterostructures with improved stability have great potential for use in new optoelectronic and biological applications.

A Self-Made Optical Tweezers Integrated Upconversion Luminescence Confocal Scanning Instrument Enables Stable and Noninvasive Long-Term In Situ Imaging a Single Suspension Cell Under Exceptionally Efficient Luminescent Resonance Energy Transfer Sensing

It is necessary to explore labeling probes with worthy optical properties and a noninvasive fluorescence imaging manner for stable long-term in situ measuring a single suspension cell. In response to these goals, we herein make a breakthrough on two fronts. On one hand, a co-sensitizer-induced efficient 808 nm near-infrared light-excited luminescence-confined upconversion nanoparticle with a low thermal effect is fabricated by employing a layer-by-layer seed growing approach to develop a sandwich structure, under which the luminescence domain is vastly restricted into an extremely thin inner shell (∼ 2.77 nm) to finally bring about a high-efficiency luminescent resonance energy transfer (LRET) sensing behavior. On the other hand, a self-made optical tweezers integrated upconversion luminescence confocal scanning instrument is applied to enhance the imaging accuracy, after which the liquid viscous force is sufficiently overcome by the resulting single beam gradient force and the analyzed suspension cell is always immobilized to the focal plane to ensure a constant luminescence excitation condition. By making use of a metal ion-dependent DNAzyme and a hairpin DNA strand to design a corresponding LRET sensing system, our nanoprobe shows satisfactory assay performance for two model biomolecules (Ca²⁺ and TK1 messenger RNA). Following the optical trapping-assisted imaging, this exceptional measurement method is capable of effectively monitoring the intracellular target changes in different physiological states, endowing a powerful toolbox for single cell analysis.

Redox-Responsive Breakup of a Nucleic Acids@CoOOH Nanocomplex Triggering Cascade Recycling Amplification for Sensitive Sensing of Alkaline Phosphatase

Alkaline phosphatase (ALP), an essential hydrolase with crucial roles in living organisms, has widely been regarded as a biomarker for various human diseases in clinical diagnoses. Herein, taking advantage of cobalt oxyhydroxide (CoOOH) nanoflakes and nonenzymatic cascade recycling amplification (CRA), a highly sensitive and label-free fluorescence biosensing strategy for the determination of ALP activity is introduced. In our design, ALP can promote the dephosphorylation of l-ascorbic acid 2-phosphate (AAP) to reduce ascorbic acid (AA), which is then able to decompose CoOOH in a nucleic acids@CoOOH nanocomplex into Co²⁺ cofactors. Further, enzyme-free CRA was rapidly initiated by integrating DNAzyme recycling amplification and catalytic hairpin assembly, resulting in the generation of an abundance of G-quadruplex structure-contained DNA duplexes. In the presence of thioflavin T (ThT), analytical target ALP was converted in an amplified and activatable fluorescence signal. The experimental results show that this method can be applied for the quantitative analysis of ALP activity with a low detection limit of 0.027 mU/mL. Moreover, this developed biosensing approach exhibits excellent specificity, and the evaluation of ALP activity in the complex human serum samples was successfully realized, indicating that it can afford a reliable, robust, and cost-effective nanoplatform for an ALP-based clinical diagnosis and for biomedical research.

Self-Assembly of Upconversion Nanoparticles Based Materials and Their Emerging Applications

In the past few decades, significant progress of the conventional upconversion nanoparticles (UCNPs) based nanoplatform has been achieved in many fields, and with the development of nanoscience and nanotechnology, more and more complex situations need a UCNPs based nanoplatform having multifunctions for specific multimodal or multiplexed applications. Through self-assembly, different UCNPs or UCNPs with other materials could be combined together within an entity. It is more like an ideal UCNPs nanoplatform, a unique system with the properties defined by its individual components as well as by the morphology of the composite. Various designs can show their different desired properties depending on the application situation. This review provides a complete summary on the optimization of the synthesis method for the recently designed UCNPs assemblies and summarizes various applications, including dual-modality cell imaging, molecular delivery, detection, and programmed control therapy. The challenges and limitations the UCNPs assembly faces and the potential solutions in this field are also presented.

Nano-octahedral bimetallic Fe/Eu-MOF preparation and dual model sensing of serum alkaline phosphatase (ALP) based on its peroxidase-like property and fluorescence

Herein a nano-scale bimetallic Fe/Eu-MOF with a regular octahedral structure was synthesized for the first time. The synthesized Fe/Eu-MOF has both peroxidase-like activity and fluorescence properties. Fe/Eu-MOF can catalyze H₂O₂ to oxidize the chromogenic substrate TMB to produce blue oxTMB, which has ultraviolet absorption at 652 nm. Unexpectedly, the generated oxTMB can effectively quench the fluorescence of the catalyst Fe/Eu-MOF at 450 nm. The quenching mechanism is mainly the internal filtration effect (IFE), accompanied by static quenching (SQE), Förster resonance energy transfer (FRET) and photoelectron transfer (PET). Fe/Eu-MOF has a high affinity for sodium pyrophosphate (PPi). PPi can be adsorbed to the surface of Fe/Eu-MOF, destroying the structure of Fe/Eu-MOF and inhibiting its catalytic activity, resulting in a decrease in UV absorbance and the decline of fluorescence quenching. In contrast, phosphoric acid (Pi) has almost no effect on the reaction system. Alkaline phosphatase (ALP) can catalyze the hydrolysis of PPi to Pi, thereby reducing the inhibitory effect of PPi. Based on this, we successfully constructed a dual-mode ALP sensor with high selectivity. The linear ranges based on the 652 nm absorption or the fluorescence detection are from 1 to 200 U/L, and the detection limits are 0.6 for the absorption method and 0.9 U/L for the fluorescence method, respectively.

Lanthanide upconversion and downshifting luminescence for biomolecules detection

Biomolecules play critical roles in biological activities and are closely related to various disease conditions. The reliable, selective and sensitive detection of biomolecules holds much promise for specific and rapid biosensing. In recent years, luminescent lanthanide probes have been widely used for monitoring the activity of biomolecules owing to their long luminescence lifetimes and line-like emission which allow time-resolved and ratiometric analyses. In this review article, we concentrate on recent advances in the detection of biomolecule activities based on lanthanide luminescent systems, including upconversion luminescent nanoparticles, lanthanide-metal organic frameworks, and lanthanide organic complexes. We also introduce the latest remarkable accomplishments of lanthanide probes in the design principles and sensing mechanisms, as well as the forthcoming challenges and perspectives for practical achievements.

Holographic Optical Tweezers and Boosting Upconversion Luminescent Resonance Energy Transfer Combined Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas12a Biosensors

Taking advantage of outstanding precision in target recognition and trans-cleavage ability, the recently discovered CRISPR/Cas12a system provides an alternative opportunity for designing fluorescence biosensors. To fully exploit the analytical potential, we introduce here some meaningful concepts. First, the collateral cleavage of CRISPR/Cas12a is efficiently activated in a functional DNA regulation manner and the bottleneck which largely applicable to nucleic acids detection is broken. After selection of a representative aptamer and DNAzyme as the transduction pathways, the sensing coverage is extended to a small organic compound (ATP) and a metal ion (Na⁺). The assay sensitivity is significantly improved by utilizing a bead-supported enrichment strategy wherein emerging holographic optical tweezers are used to enhance imaging stability and simultaneously achieve multiflux analysis. Last, a sandwich-structured energy-concentrating upconversion nanoparticle triggered boosting luminescent resonance energy transfer mode is comined to face with complicated biological samples by skillfully confining the emitters into a very limited inner shell. Following the above attempts, the developed CRISPR/Cas12a biosensors not only present an ultrasensitive assay behavior toward these model non-nucleic acid analytes but also can serve as a formidable toolbox for determining real samples including single cell lysates and human plasma, proving a good practical application capacity.

A dual-signal fluorescent probe for detection of acid phosphatase

Acid phosphatase has become a significant indicator of prognostic and medical diagnosis, and its dysfunction may lead to a series of diseases. A novel dual-signal fluorescence method for acid phosphatase detection based on europium polymer (europium-pyridine dicarboxylicacid-adenine) and pyridoxal phosphate (PLP) was proposed. PLP coordinated with europium polymer via Eu³⁺ and P-O bonds, and the fluorescence of europium polymer was quenched due to the photoinduced electron transfer (PET) effect between aldehyde and europium polymer. Upon addition of acid phosphatase, the PLP was transformed to phosphate (Pi) and pyridoxal (PL). The PL was released from the surface of europium polymer, and the blue emission was enhanced due to the formation of internal hemiacetal, while the fluorescence of europium polymer recovered. The blue (PL) and red emission (Eu³⁺) were positively correlated with acid phosphatase activity; thus the sensitive assay of acid phosphatase was effectively achieved. The two signals were applied to determine the acid phosphatase with limits of detection (LOD) of 0.04 mU/mL and 0.38 mU/mL, and the linear ranges were 0.13-5.00 mU/mL and 1.25-20.00 mU/mL, respectively. The probe can be used to trace the acid phosphatase in biological systems and holds promise for use in clinical diagnosis and early prevention.

A highly sensitive immunofluorescence sensor based on bicolor upconversion and magnetic separation for simultaneous detection of fumonisin B1 and zearalenone

Mycotoxins cause significant harm to human health, so it is imperative to develop a highly sensitive and easy-to-operate method for the detection of mycotoxins. Herein, a fluorescence-based magnetic separation immunoassay for simultaneous detection of mycotoxins fumonisin B1 and zearalenone is established. The method employed high fluorescent upconversion-nanoparticles(UCNPs) conjugated with biotinylated antigens as upconversion fluoroscent probes. Magnetic nanoparticles(MNPs) immobilized with monoclonal antibodies are used as immune-capture probes. Highly sensitive detection of FB1 and ZEN was achieved based on the luminescence properties of UCNPs and the separation effects of MNPs. The results showed a robust linear correlation between the enhanced fluorescence emission intensity and the logarithmic concentrations of FB1 and ZEN under the optimal conditions (R²(FB1) = 0.9965, R²(ZEN) = 0.9976), and the linear ranges were 0.05-5 ng mL^-1. Furthermore, the limits of detection (LOD) were 0.016 ng mL^-1 for FB1 and 0.012 ng mL^-1 for ZEN. The standard addition method was used to determine the content of FB1 and ZEN in the samples to evaluate the accuracy of the process. The average recoveries were 89.48% to 113.69% and 85.97% to 113.82%, respectively. Compared with the other five mycotoxins, this method had high selectivity. It is expected that the multi-component simultaneous detection can be further realized by using the multicolor labeling characteristics of UCNPs.

Rational Design of Dual-Emission Lanthanide Metal-Organic Framework for Visual Alkaline Phosphatase Activity Assay

The alkaline phosphatase (ALP) activity assay is very significant for disease diagnosis and biomedical research. Lanthanide metal-organic framework (Ln-MOF) based fluorescence sensors have great application potential in ALP activity assays. However, it is critical but challenging to investigate the emission law of Ln-MOFs for revealing rational design principles and selecting an appropriate MOF. Here, we describe a reasonable design strategy for dual-emission Ln-MOFs based on theoretical calculations. This strategy combines Reinhoudt empirical rule, intramolecular charge transfer theory, and aggregation/coordination-induced emission theory; reveals the luminescence law of Ln-MOFs; and provides theoretical guidance for the rational design of dual-emission Ln-MOFs. On the basis of this strategy, we create a dual-emission Tb-MOF fluorescent probe used for ALP activity assay and investigate the detection mechanism. The probe shows ultrasensitive (limit of detection 0.002 mU mL^-1) and selective response to ALP, and it suits for point-of-care visual detection coupled with a self-designed portable enzyme activity assay kit and smartphone-assisted visual device. The kit-based visual assay method can accurately quantify the activity of ALP in real serum samples (recovery >93%, and relative error is less than 6.8% compared with the results of fluorescence spectrometer-based method) and consumes only 25 μL of serum. In addition, a logical decoder based on the "dual-key unlocking strategy" is designed, providing a feasible solution for the development of intelligent ALP activity detection equipment. As far as we know, this is the first report of a theoretical calculation-guided versatile design strategy for dual-emission Ln-MOFs and a portable enzyme activity assay kit for visual detection.

A redox modulated fluorescence nanoplatform for the detection of alkaline phosphatase activity with fluorescent polydopamine nanoparticles

Herein, we simply synthesized intrinsic fluorescent polydopamine nanoparticles (PDA NPs) in sodium hydroxide solution (NaOH, pH 11), and constructed a new fluorescence nanoplatform for the detection of alkaline phosphatase (ALP) using PDA NPs as an effective signal reporter. The nanoplatform was constructed by the combination of enzymatic hydrolysis of ALP to the substrate l-ascorbic acid-2-phosphate (AA2P) and the chemical redox reaction between l-ascorbic acid (AA) and mercury ion (Hg2+). The fluorescence of PDA NPs could be effectively quenched by Hg2+ through the coordination effect between Hg2+ and the functional groups on the surface of PDA NPs. However, the quenching effect was greatly inhibited by the addition of AA into the solution. Based on this point, the activity of ALP could be monitored by hydrolysis of the substrate AA2P to AA and the fluorescence output of PDA NPs. The nanoplatform exhibited high sensitivity and desirable selectivity for ALP detection. With a wide linear range of 0 to 18 U L-1, a detection limit of 0.4 U L-1 was achieved using the developed nanosensor. The proposed method could not only be used to screen the inhibitor of ALP but also be used to detect ALP activity in human serum samples successfully. Moreover, the strategy can easily be expanded to determining other kinds of enzymes participating in AA-generation reactions.

A novel copper ion sensing fluorescent probe for fast detection of pyrophosphate and alkaline phosphatase

A Cu²⁺ sensing fluorescent probe is synthesized via a Mannich reaction and is applied in the fluorescence detection of pyrophosphate and alkaline phosphatase.

Hybrids of Upconversion Nanoparticles and Silver Nanoclusters Ensure Superior Bactericidal Capability via Combined Sterilization

It is highly desired to develop new antibacterial agents with superior bactericidal efficiency for minimizing the damage to biological cells. We developed a combined antibacterial nanohybrid exhibiting a superb bactericidal effect and excellent biocompatibility by integrating upconversion nanoparticles (UCNPs) with silver nanoclusters (AgNCs). UCNPs and methylene blue (MB) molecules were encapsulated with silica microspheres via microemulsion, with MB as the photosensitizer. Silver ions (Ag⁺) were reduced by amino groups on the surface of silica spheres, wherein silver nanoclusters (AgNCs) were formed in situ to produce the nanohybrid, UCNPs@SiO₂(MB)@AgNCs. UCNPs emit visible light at 655 nm under excitation by near-infrared radiation (NIR, 980 nm). MB absorbs the emission from UCNPs to generate toxic singlet oxygen (¹O₂), which leads to the apoptosis of bacteria cells. Meanwhile, silver ions released from AgNCs destroy the bacteria membrane structure. Upon NIR irradiation at 980 nm for 10 min, 8.33 μg mL^-1 nanohybrid results in a 100% killing rate for both Gram-positive S. aureus (+) and Gram-negative E. coli (-).

Current and Perspective Diagnostic Techniques for COVID-19

Since late December 2019, the coronavirus pandemic (COVID-19; previously known as 2019-nCoV) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been surging rapidly around the world. With more than 1,700,000 confirmed cases, the world faces an unprecedented economic, social, and health impact. The early, rapid, sensitive, and accurate diagnosis of viral infection provides rapid responses for public health surveillance, prevention, and control of contagious diffusion. More than 30% of the confirmed cases are asymptomatic, and the high false-negative rate (FNR) of a single assay requires the development of novel diagnostic techniques, combinative approaches, sampling from different locations, and consecutive detection. The recurrence of discharged patients indicates the need for long-term monitoring and tracking. Diagnostic and therapeutic methods are evolving with a deeper understanding of virus pathology and the potential for relapse. In this Review, a comprehensive summary and comparison of different SARS-CoV-2 diagnostic methods are provided for researchers and clinicians to develop appropriate strategies for the timely and effective detection of SARS-CoV-2. The survey of current biosensors and diagnostic devices for viral nucleic acids, proteins, and particles and chest tomography will provide insight into the development of novel perspective techniques for the diagnosis of COVID-19.

Organic Linkers Enable Tunable Transfer of Migrated Energy from Upconversion Nanoparticles

Energy transfer plays a pivotal role in applying lanthanide-doped upconversion nanoparticles (UCNPs) as optical probes for diverse applications, particularly in biology and medicine. However, achieving tunable energy transfer from UCNPs to different acceptors remains a daunting challenge. Here, we demonstrate that using small organic molecules as linkers, the energy transfer from UCNPs to acceptors can be modulated. Specifically, organic linkers can enable efficient energy transfer from NaGdF₄:Yb/Tm@NaGdF₄ core-shell UCNPs to different acceptors. Moreover, the organic linker-mediated energy transfer can be facilely tuned by simply changing organic linkers. Based on our mechanistic investigations, the extraction of Gd³⁺ migrated energy from UCNPs by organic linkers and the subsequent energy injection from linkers to acceptors should be the two key processes for controlling the energy transfer. The tunable energy transfer from UCNPs allows us to design novel applications, including sensors and optical waveguides, based on UCNPs. These findings may open up new ways to develop UCNP-based bioapplications and advance further fabrication of hybrid upconversion nanomaterials.

A single-component yet multifunctional tongue-mimicking sensor array for upconversion fluorescence biosensing

A novel single-component nanoprobe has been created for the pattern recognition of antioxidants in a “turn on” manner by integrating with the prevention of PDA formation with an antioxidant.