A Strategy of NIR Dual-Excitation Upconversion for Ratiometric Intracellular Detection

Dye-sensitized lanthanide-doped upconversion nanoprobe for enhanced sensitive detection of Fe3+ in human serum and tap water

Iron ion (Fe3+) detection is crucial for human health since it plays a crucial role in many physiological activities. In this work, a novel Schiff-base functionalized cyanine derivative (CyPy) was synthesized, which was successfully assembled on the surface of upconversion nanoparticles (UCNPs) through an amphiphilic polymer encapsulation method. In the as-designed nanoprobe, CyPy, a recognizer of Fe3+, is served as energy donor and β-NaYF4:Yb,Er upconversion nanoparticles are adopted as energy acceptor. As a result, a 93-fold enhancement of upconversion luminescence is achieved. The efficient energy transfer from CyPy to β-NaYF4:Yb,Er endows the nanoprobe a high sensitivity for Fe3+ in water with a low detection limit of 0.21 μM. Moreover, the nanoprobe has been successfully applied for Fe3+ determination in human serum and tap water samples with recovery ranges of 95 %-105 % and 97 %-106 %, respectively. Moreover, their relative standard deviations are all below 3.72 %. This work provides a sensitive and efficient methodology for Fe3+ detection in clinical and environmental testing.

Assembly of Dye Molecules in Covalent Organic Frameworks for Enhanced Colorimetric Biosensing

Colorimetric assays have been extensively investigated for biosensing applications due to their advantages of visual recognizability, ease of use, and low cost. However, advancing their development is a great challenge due to the inherent limitations of colorimetric dyes. Herein, we report a strategy to assemble dyes in covalent organic frameworks (COFs) to effectively reinforce the applicability of pH-responsive dyes in colorimetric bioassays. Experimental results reveal that three-dimensional COFs can promote the assembly of dyes through hydrogen bonding, resulting in the formation of a dye-supermolecule@COF assembly. Consequently, when sensitized at increased pH levels (e.g., hydroxyl ions), disruption of hydrogen bonds may trigger a rapid transition from their insoluble fixed state within the COFs into soluble, visibly detectable dye anions. This process can also be facilitated by increased hydrophilicity and elevated electrostatic repulsion between the dye anions and COFs, leading to the substantial release of chromogenic dye anions from the COF pores into the solution, thereby amplifying the colorimetric signal output. Therefore, by employing various synthesized dye-supermolecule@COFs as signal tags, we developed a colorimetric bioassay capable of accurately identifying breast cancer cell subtypes. This study not only highlights the effectiveness of dye-supermolecule@COFs in enhancing colorimetric biosensing but also underscores the potential of employing the COF-mediated dye assembly strategy for colorimetric assays.

Understanding of Lanthanide-Doped Core-Shell Structure at the Nanoscale Level

The groundbreaking development of lanthanide-doped core-shell nanostructures have successfully achieved precise optical tuning of rare-earth nanocrystals, leading to significant improvements in energy transfer efficiency and facilitating multifunctional integration. Exploring the atomic-level structural, physical, and optical properties of rare-earth core-shell nanocrystals is essential for advancing our understanding of their fundamental principles and driving the development of emerging applications. However, our knowledge of the atomic-level structural details of rare-earth nanocrystal core-shell structures remains limited. This review provides a comprehensive discussion of synthesis strategies, characterization techniques, interfacial ion-mixing phenomena, strain effects, and spectral modulation in core-shell structures of rare-earth-doped nanocrystals. Additionally, we prospectively discuss the challenges encountered in studying the fine structures of rare-earth-doped core-shell nanocrystals, particularly the increasing demand for researchers to integrate interdisciplinary knowledge and utilize high-end precision instruments.

IR808@MnO nano-near infrared fluorescent dye's diagnostic value for malignant pleural effusion

BACKGROUND

Malignant pleural effusion is mostly a complication of advanced malignant tumors. However, the cancer markers such as carbohydrate antigen 125 (CA 125), carbohydrate antigen 15-3 (CA 15-3), carbohydrate antigen 19-9 (CA 19-9), and cytokeratin fragment 21-1 (CYFRA 21-1) have low sensitivity and organ specificity for detecting malignant pleural effusion.

RESEARCH QUESTION

Is IR808@MnO nano-near infrared fluorescent dye worthy for the diagnosis in differentiating benign and malignant pleural effusions.

STUDY DESIGN AND METHODS

This experiment was carried out to design and characterize the materials for in vitro validation of the new dye in malignant tumor cells in the A549 cell line and in patients with adenocarcinoma pleural effusion. The dye was verified to possess tumor- specific targeting capabilities. Subsequently, a prospective hospital-based observational study was conducted, enrolling 106 patients and excluding 28 patients with unknown diagnoses. All patients underwent histopathological analysis of thoracoscopic biopsies, exfoliative cytological analysis of pleural fluid, and analysis involving the new dye. Statistical analyses were performed using Microsoft Excel, GraphPad Prism, and the R language.

RESULTS

The size of IR808@MnO was 136.8 ± 2.9 nm, with peak emission at 808 nm, and it has near-infrared fluorescence properties. Notably, there was a significant difference in fluorescence values between benign and malignant cell lines (p < 0.0001). The malignant cell lines tested comprised CL1-5, A549, MDA-MB-468, U-87MG, MKN-7, and Hela, while benign cell lines were BEAS-2B, HUVEC, HSF, and VE. The most effective duration of action was identified as 30 min at a concentration of 5 μl. This optimal duration of action and concentration were consistent in patients with lung adenocarcinoma accompanied by pleural effusion and 5 μl. Of the 106 patients examined, 28 remained undiagnosed, 39 were diagnosed with malignant pleural effusions, and the remaining 39 with benign pleural effusions. Employing the new IR808@MnO staining method, the sensitivity stood at 74.4%, specificity at 79.5%, a positive predictive value of 69.2%, and a negative predictive value of 82.1%. The area under the ROC curve was recorded as 0.762 (95% CI: 0.652-0.872). The confusion matrix revealed a positive predictive value of 75.7%, a negative predictive value of 75.6%, a false positive rate of 22.5%, and a false negative rate of 26.3%.

INTERPRETATION

The IR808@MnO fluorescent probe represents an efficient, sensitive, and user-friendly diagnostic tool for detecting malignant pleural fluid, underscoring its significant potential for clinical adoption.

A new ratiometric fluorescence nanosensor based on NaYF4:3%Er@NaYF4 upconversion nanoparticles for sensitive determination of Rose Bengal in water

Rose Bengal (RB) is used as a sensitizer in ambient water due to its property of catalyzing the production of singlet oxygen (1O2). However, this property also brings phototoxicity and carcinogenicity. The NaYF4:3%Er@NaYF4 core-shell upconversion nanoparticles (UCNPs) with higher upconversion efficiency was synthesized to detect RB in ambient water. Due to fluorescence resonance energy transfer (FRET) between RB and UCNPs, the upconversion fluorescence at 538 nm emitted by UCNPs was quenched by the RB, while the emission at 566 nm of RB raised. In the best conditions, the ratiometric emission intensity F566/F538 was positively proportional to RB concentration and the linear range was 0.04-15.0 μg·mL-1 (R2 = 0.996). The detection limit (S/N = 3) of RB was 2.46 ng·mL-1. The recoveries ranged from 99.0% to 105.6% (relative standard deviation 0.97-3.24%, n = 3) in tap water and 100.3%-104.9% (relative standard deviation 0.66-1.94%, n = 3) in lake water. This proposed method exhibits lower detection limit and larger linear, which possesses practical application value to the detection of RB in water.

Dye-Triplet-Sensitized Downshifting Nanoprobes with Ratiometric Dual-NIR-IIb Emission for Accurate In Vivo Detection

Despite the emerging near-infrared-IIb (NIR-IIb, 1500-1700 nm) bioimaging significantly improving the in vivo penetration depth and resolution, quantitative detection with accuracy remains challenging due to its inhomogeneous fluorescence signal attenuation in biological tissue. Here, ratiometric dual-NIR-IIb in vivo detection with excitation wavelengths of 808 and 980 nm is presented using analyte-responsive dye-triplet-sensitized downshifting nanoprobes (DSNPs). NIR cyanine dye IR-808, a recognizer of biomarker hypochlorite (ClO-), is introduced to trigger a triplet energy transfer process from the dye to Er3+ ions of DSNPs under 808 nm excitation, facilitating the formation of an analyte-responsive 1525 nm NIR-IIb assay channel. Meanwhile, DSNPs also enable emitting intrinsic nonanalyte-dependent downshifting fluorescence at the same NIR-IIb window under 980 nm excitation, serving as a self-calibrated signal to alleviate the interference from the probe amount and depth. Due to the two detected emissions sharing identical light propagation and scattering, the ratiometric NIR-IIb signal is demonstrated to ignore the depth of penetration in biotissue. The arthritis lesions are distinguished from normal tissue using ratiometric probes, and the amount of ClO- can be accurately output by the established detection curves.

Uncovering Different Responses and Energy Mechanisms of Sensitizer and Activator in Host Manipulation for Upconversion Nanoparticles

Agile and efficient upconversion luminescence (UCL) fine-tuning strategies are the most demanded for in the frontier applications of highly doped upconversion nanoparticles (UCNPs). By doping Zn²⁺ ions into NaHoF₄ and NaGdF₄:Yb³⁺ shells using the oleate method, the separate influences of Zn²⁺ on Ho³⁺ and Yb³⁺ ions in UCL-related processes were analyzed in detail, revealing relevant UCL changes and underlying energy mechanisms from a novel but explicit perspective. Different behaviors of green and red UCL before and after Zn²⁺-ion doping were attributed to the disparities in the energy pathways and features of the sample structures. Herein, the populations of ⁵S₂/⁵F₄ and ⁵F₅ states, not the usually mentioned decay time, decided the UCL intensities of the NaHoF₄@NaYbF₄-structured highly doped UCNPs. The advantageous small sizes and intense single-band red UCL of these UCNPs were further developed by combining our previous strategies with introducing Zn²⁺ ions into the NaHoF₄ matrix. Overcoming energy loss by surface quenchers and Zn²⁺-triggered inner defects is the key factor in maximizing 4f-4f transitions. To the best of our knowledge, the current study is the first attempt to date to experimentally reveal separate impacts of the heteroions on activators and sensitizers in UCL-related processes and can deepen the theoretical investigation of Ho-based UCL for the broadened applications of NaHoF₄ UCNPs.

AIEgen-sensitized lanthanide nanocrystals as luminescent probes for intracellular Fe3+ monitoring

The abnormal Fe³⁺ level is known to cause various diseases, such as heart failure, liver damage and neurodegeneration. In situ probing Fe³⁺ in living cells or organisms is highly desired for both biological research and medical diagnostics. Herein, hybrid nanocomposites NaEuF₄@TCPP were constructed by the assembly of an aggregation-induced emission luminogen (AIEgen) TCPP and NaEuF₄ nanocrystals (NCs). The anchored TCPP on the surface of NaEuF₄ NCs can reduce rotational relaxation of the excited state and efficiently transfer the energy to the Eu³⁺ ions with minimized nonradiative energy loss. Consequently, the prepared NaEuF₄@TCPP nanoparticles (NPs) exhibited an intense red emission with a 103-fold enhancement relative to that in NaEuF₄ NCs under 365 nm excitation. A selectively quenching response to Fe³⁺ ions for the NaEuF₄@TCPP NPs makes them luminescent probes for sensitive detection of Fe³⁺ ions with a low detection limit of 340 nM. Moreover, the luminescence of NaEuF₄@TCPP NPs could be recovered by the addition of iron chelators. Benefiting from their good biocompatibility and stability in living cells, together with the characteristic of the reversible luminescence response, the lipo-coated NaEuF₄@TCPP probes were successfully applied for real-time monitoring of Fe³⁺ ions in living HeLa cells. These results are expected to motivate the exploration of AIE-based lanthanide probes for sensing and biomedical applications.

ClO- Induced Dual-Excitation Fluorescent Probes Responding to Diverse Testing Modes with Ratio Methodology

Single-excitation ratio fluorescent probes have enabled the output signal with high signal-to-noise ratio, but are still plagued with technique challenges, including signal distortion and limited application scenario. Herein, a dual-excitation near-infrared (NIR) fluorescent probe P1 of coumarin derivatives is constructed, showing high signal output ability in the visible region and high tissue penetration depth ability in the NIR region. As NIR probe P1 selectively recognizes ClO^-, the emission signal in the visible region (480 nm) of P1 is enhanced during the recognition process. Meanwhile, the NIR emission (830 nm) of the conjugated system is weakened, finally realizing that ClO^- triggered the dual-excitation (720/400 nm) ratio fluorescence signal detection and monitoring. The signal of detection in vitro has high responsiveness. Meanwhile, in the process of NIR monitoring in vivo, positive contrast imaging of fluorescence is constructed, which can accurately monitor ClO^- changes over time. The current dual-excitation fluorescence-based data calibration and/or comparison method improves the application of the traditional single-excitation ratio fluorescence strategy and provide innovative detection tools for accurate measurement of fluorescence detection, with detection/monitoring modes suitable for different physiological environments.

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.

Near-infrared-II ratiometric fluorescence probes for non-invasive detection and precise navigation surgery of metastatic sentinel lymph nodes

Sentinel lymph node (SLN) biopsy is the key diagnostic procedure to determine tumor metastasis and treatment plan. Current SLN biopsy has considerable drawbacks in that SLNs (both malignant and normal) must be removed by navigation surgery, followed by a time-consuming pathological examination. The selective, non-invasive, and real-time diagnosis of metastatic status in SLNs is becoming essential. Methods: Here, we design two lanthanide-doped nanoparticles as a pair of NIR-II ratiometric fluorescence probes, one of which is conjugated with tumor-targeting moiety, while the other is conjugated with PEG as an internal reference. The NIR-II ratiometric fluorescence signal (I_{1060 nm}/I_{1525 nm}) from two well-separated channels were used to identify the tumor-draining SLNs. The precise navigation surgery of metastatic SLNs was performed and we further evaluated their surgery outcomes. Results: The NIR-II ratiometric fluorescence facilitates an ideal fluorescence-guided surgery with only resection of tumor-positive SLNs, thereby avoiding unnecessary removal of the normal SLNs. In addition, our system has a time-saving operation procedure and can be performed under the operation light without altering the appearance of surgical settings. Conclusion: The present study enables non-invasive and real-time detection metastatic status in SLNs with high sensitivity and selectivity. Our investigations will provide a new direction for SLN biopsy and substantially improve cancer surgery outcomes.

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-.

Highly Retentive, Anti-Interference, and Covert Individual Marking Taggant with Exceptional Skin Penetration

The development of high-performance individual marking taggants is of great significance. However, the interaction between taggant and skin is not fully understood, and a standard for marking taggants has yet to be realized. To achieve a highly retentive, anti-interference, and covert individual marking fluorescent taggant, Mn²⁺ -doped NaYF₄ :Yb/Er upconversion nanoparticles (UCNPs), are surface-functionalized with polyethyleneimine (PEI) to remarkably enhance the interaction between the amino groups and skin, and thus to facilitate the surface adhesion and chemical penetration of the taggant. Electrostatic interaction between PEI₆₀₀ -UCNPs and skin as well as remarkable penetration inside the epidermis is responsible for excellent taggant retention capability, even while faced with robust washing, vigorous wiping, and rubbing for more than 100 cycles. Good anti-interference capability and reliable marking performance in real cases are ensured by an intrinsic upconversion characteristic with a distinct red luminescent emission under 980 nm excitation. The present methodology is expected to shed light on the design of high-performance individual marking taggants from the perspective of the underlying interaction between taggant and skin, and to help advance the use of fluorescent taggants for practical application, such as special character tracking.

Lanthanide/Cu2-xSe Nanoparticles for Bacteria-Activated NIR-II Fluorescence Imaging of Infection

A material system enabling specific NIR-II fluorescence imaging of Gram-positive bacteria is described. The material system is based on the electrostatic binding of Cu_2-xSe and vancomycin-modified NaGdF₄:Nd,Yb@NaGdF₄ downconversion nanoparticles (DCNPs), the fluorescence of which is weak owing to the spectral overlap of Cu_2-xSe absorption with the DCNP NIR emission. The presence of Gram-positive bacteria precisely disconnects the bond between vancomycin-modified DCNPs and Cu_2-xSe, thus enabling a strong fluorescent signal. In vivo studies show that the material system can be specifically activated at the site of Gram-positive bacterial infection but is essentially nonfluorescent in the area of Gram-negative bacterial infection.

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.

Advanced NIR ratiometric probes for intravital biomedical imaging

Near-infrared (NIR) fluorescence imaging technology (NIR-I region, 650-950 nm and NIR-II region, 1000-1700 nm), with deeper tissue penetration and less disturbance from auto-fluorescence than that in visible region (400-650 nm), is playing a more and more extensive role in the field of biomedical imaging. With the development of precise medicine, intelligent NIR fluorescent probes have been meticulously designed to provide more sensitive, specific and accurate feedback on detection. Especially, recently developed ratiometric fluorescent probes have been devoted to quantify physiological and pathological parameters with a combination of responsive fluorescence changes and self-calibration. Herein, we systemically introduced the construction strategies of NIR ratiometric fluorescent probes and their applications in biological imagingin vivo, such as molecular detection, pH and temperature measurement, drug delivery monitoring and treatment evaluation. We further summarized possible optimization on the design of ratiometric probes for quantitative analysis with NIR fluorescence, and prospected the broader optical applications of ratiometric probes in life science and clinical translation.

Background-free sensing platform for on-site detection of carbamate pesticide through upconversion nanoparticles-based hydrogel suit

On-site monitoring of carbamate pesticide in complex matrix remians as a challenge in terms of the real-time control of food safety and supervision of environmental quality. Herein, we fabricated robust upconversion nanoparticles (UCNPS)/polydopamine (PDA)-based hydrogel portable suit that precisely quantified carbaryl in complex tea samples with smartphone detector. UCNPS/PDA nanoprobe was developed by polymerization of dopamine monomers on the surface of NaErF₄: 0.5% Tm³⁺@NaYF₄ through electrostatic interaction, leading to efficient red luminescence quenching of UCNPS under near-infrared excitation, which circumvented autofluorescence and background interference in complicated environment. Such a luminescence quenching could be suppressed by thiocholine that was produced by acetylcholinesterase-mediated catalytic reaction, thus enabling carbaryl bioassay by inhibiting the activity of enzyme. Bestowed with the feasibility analysis of fluorescent output, portable platform was designed by integrating UCNPS-embedded sodium alginate hydrogel with 3D-printed smartphone device for quantitatively on-site monitoring of carbaryl in the range of 0.5-200 ng mL^-1 in tea sample, accompanied by a detection limit of 0.5 ng mL^-1. Owing to specific UCNPS signatures and hydrogel immobilization, this modular platform displayed sensitive response, portability and anti-interference capability in complex matrix analysis, thus holding great potential in point-of-care application.

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.

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.

Lanthanide-Doped Near-Infrared Nanoparticles for Biophotonics

Light in the near-infrared (NIR) spectral region is increasingly utilized in bioapplications, providing deeper penetration in biological tissues owing to the lower absorption and scattering in comparison with light in the visible range. Lanthanide-doped luminescent nanoparticles with excitation and/or emission in the NIR range have recently attracted tremendous attention as one of the prime candidates for noninvasive biological applications due to their unique optical properties, such as large Stokes shift, spectrally sharp luminescence emissions, long luminescence lifetimes, and excellent photostability. Herein, recent advances of lanthanide-doped nanoparticles with NIR upconversion or downshifting luminescence and their uses in cutting-edge biophotonic applications are presented. A set of efficient strategies for overcoming the fundamental limit of low luminescence brightness of lanthanide-doped nanoparticles is introduced. An in-depth literature review of their state-of-art biophotonics applications is also included, showing their superiority for high-resolution imaging, single-nanoparticle-level detection, and efficacy for tissue-penetrating diagnostics and therapeutics.

Near-Infrared Multipurpose Lanthanide-Imaging Nanoprobes

Optical imaging plays a growing role in modern biomedical research and clinical applications due to its high sensitivity, superb spatiotemporal resolution and minimal hazards. Lanthanide-doped nanoparticles (LDNPs), as a classical category of luminescent materials, exhibit promising photostability, near-infrared (NIR)-excited frequency up-/down-converting capabilities, emission fine-tuning and multispectral features, which have greatly promoted the endeavors of deeper and clearer diagnostics in complex living conditions. This review focuses on the recent advances of LDNP-based multipurpose imaging studies using upconversion, downshifting, lifetime, photoacoustic and multimodal nanoprobes in the NIR (650-1000 nm) and the second near-infrared window (NIR-II, 1000-1700 nm). The principle and design of various functional, activatable, multiplexing or multimodal lanthanide-imaging nanoprobes (LINPs) as well as representative biophotonic applications are summarized in detail. In addition, the future perspectives and challenges for facilitating LINPs to clinical translations are discussed.