Graphene-Metal Nanocrystal Hybrid Materials for Bioapplications

The development of functional nanomaterials is crucial for advancing personalized and precision medicine. Graphene-metal nanocrystal hybrid materials not only possess the intrinsic advantages of graphene-based materials but also exhibit additional optical, magnetic, and catalytic properties of various metal nanocrystals, showing great synergies in bioapplications, including biosensing, bioimaging, and disease treatments. In this Perspective, we discuss the advantages and design principles of graphene-metal nanocrystal hybrid materials and provide an overview of their applications in biological fields. Finally, we highlight the challenges and future directions for their practical implementation.

Electronic Structure of a Neodymium(III) Tris(oxidiacetate) Complex from Luminescence Data and Ab Initio Calculations

Neodymium(III) is a near-infrared emissive and magnetic ion, which has found use in various high-technology applications. Yet, accurate predictions of the luminescent and magnetic properties of neodymium(III) based on the coordination environment remain to be done. Guidelines exist, but to build structure-property relationships for this element, more data are needed. Herein, we present a high-symmetry starting point. The tris(oxidiacetate) complex of neodymium(III) was prepared and crystallized, and access to the experimentally determined structure allowed us to quantify the symmetry of the compound and to perform calculations directly on the same structure that is investigated experimentally. The luminescent properties were determined and the electronic structure was computed using state-of-the-art ab initio methods. All electronic transitions in the range from 490 to 1400 nm were mapped experimentally. Using a Boltzmann population analysis, the combination of the excitation and emission spectra revealed the crystal field splitting of the 18 lowest-energy Kramers levels that experimentally could be unambiguously resolved. This assignment was supported by ab initio calculations, and the crystal field splitting was well reproduced. The electronic structure reported for the tris(oxidiacetate) complex was used to deduce the coordination structure in aqueous solution. Finally, the results are compared to empirical trends in the literature for the electronic structure of neodymium(III).

Preparation of rare earth-doped nano-fluorescent materials in the second near-infrared region and their application in biological imaging

Second near-infrared (NIR-II) fluorescence imaging (FLI) has gained widespread interest in the biomedical field because of its advantages of high sensitivity and high penetration depth. In particular, rare earth-doped nanoprobes (RENPs) have shown completely different physical and chemical properties from macroscopic substances owing to their unique size and structure. This paper reviews the synthesis methods and types of RENPs for NIR-II imaging, focusing on new methods to enhance the luminous intensity of RENPs and multi-band imaging and multi-mode imaging of RENPs in biological applications. This review also presents an overview of the challenges and future development prospects based on RENPs in NIR-II regional bioimaging.

Nanocrystals for Deep-Tissue In Vivo Luminescence Imaging in the Near-Infrared Region

In vivo imaging technologies have emerged as a powerful tool for both fundamental research and clinical practice. In particular, luminescence imaging in the tissue-transparent near-infrared (NIR, 700-1700 nm) region offers tremendous potential for visualizing biological architectures and pathophysiological events in living subjects with deep tissue penetration and high imaging contrast owing to the reduced light-tissue interactions of absorption, scattering, and autofluorescence. The distinctive quantum effects of nanocrystals have been harnessed to achieve exceptional photophysical properties, establishing them as a promising category of luminescent probes. In this comprehensive review, the interactions between light and biological tissues, as well as the advantages of NIR light for in vivo luminescence imaging, are initially elaborated. Subsequently, we focus on achieving deep tissue penetration and improved imaging contrast by optimizing the performance of nanocrystal fluorophores. The ingenious design strategies of NIR nanocrystal probes are discussed, along with their respective biomedical applications in versatile in vivo luminescence imaging modalities. Finally, thought-provoking reflections on the challenges and prospects for future clinical translation of nanocrystal-based in vivo luminescence imaging in the NIR region are wisely provided.

Ultrastrong Infrared Emission at 1460 nm from Lanthanide-Doped Nanoparticles with Interfacial Sensitization

Fluorescent imaging in the second near-infrared window (NIR-II; 1000-1700 nm) has recently received tremendous attention due to its excellent tissue probing depths and high resolution. Under NIR pumping, lanthanide-doped nanoparticles can emit infrared light covering a wide range of 800-3000 nm which has good potential for NIR-II imaging and detection. However, the low efficiency hinders their application. Here, we report intense infrared emission at 1460 nm from lanthanide-doped core/shell nanoparticles with efficient interfacial sensitization. The emitter Tm3+ ion and the sensitizer Yb3+ and Nd3+ ions are spatially separated in core and shells so that the efficient interfacial energy transfer is established between Tm3+ and Yb3+/Nd3+ ions, while thermal vibration spread of high concentration of Yb3+ ions and cross-relaxation among Tm3+, Yb3+, and Nd3+ ions are suppressed. As a result, the ultrastrong NIR-II emission at 1460 nm is achieved, which is more than 100-times that in classic core/shell nanoparticles doped with Tm3+ (NaYF4:20%Yb,0.5%Tm@ NaYF4).

Enhancing near-infrared fluorescence intensity and stability of PLGA-b-PEG micelles by introducing Gd-DOTA at the core boundary

Micelles have been extensively used in biomedicine as potential carriers of hydrophobic fluorescent dyes. Their small diameters can potentially enable them to evade recognition by the reticuloendothelial system, resulting in prolonged circulation. Nevertheless, their lack of stability in physiological environments limits the imaging utility of micelles. In particular, when a dye sensitive to water, such as IR-1061, is encapsulated in the micelle core, the destabilized structure leads to interactions between water and dye, degrading the fluorescence. In this study, we investigated a method to improve micelle stability utilizing the electrical effect of gadolinium (Gd3+ ) and tetraazacyclododecane tetraacetic acid (DOTA), introduced into the micelles. Three micellar structures, one containing a poly(lactic-co-glycolic acid)-block-poly(ethylene glycol) (PLGA-b-PEG) block copolymer, and two other structures, including PLGA-b-PEG with DOTA or Gd-DOTA introduced at the boundary of PLGA and PEG, were prepared with IR-1061 in the core. Structures that contained DOTA at the border of the PLGA core and PEG shell exhibited much higher fluorescence intensity than probes without DOTA. With Gd3+ ions at the DOTA center, fluorescence stability was enhanced remarkably in physiological environments. Most interesting is the finding that fluorescence is enhanced with increased Gd-DOTA concentrations. In conclusion, we found that overall fluorescence and stability are improved by introducing Gd-DOTA at the boundary of the PLGA core and PEG shell. Improving micelle stability is crucial for further biomedical applications of micellar probes such as bimodal fluorescence and magnetic resonance imaging.

Revealing the role of nitroxyl during hepatic ischemia-reperfusion injury with a NIR-II luminescent nanoprobe

Hepatic ischemia-reperfusion injury (HIRI) can severely impair liver function and has a potential relationship with reactive nitrogen species. Nitroxyl (HNO) has been discovered to be involved in some biological functions and pharmacological activities. However, till now, there has been no knowledge of the role of HNO in the HIRI process, mainly because accurately tracking its fluctuation at the molecular level in vivo is extremely difficult. Herein, we developed a responsive ratiometric near-infrared-II (NIR-II) nanoprobe with rare earth ions-doped nanoparticles (RENPs) as the luminophore and a molecular trigger that can specifically react with HNO to regulate the NIR-II emission of RENPs. With this nanoprobe, we revealed the relationship between HNO and the HIRI process and demonstrated that HNO may be a product of stress reactions during HIRI. This work not only creates a useful tool for visually tracking HNO in vivo but also provides first-hand information about its role in HIRI.

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.

Tracking tumor heterogeneity and progression with near-infrared II fluorophores

Heterogeneous cells are the main feature of tumors with unique genetic and phenotypic characteristics, which can stimulate differentially the progression, metastasis, and drug resistance. Importantly, heterogeneity is pervasive in human malignant tumors, and identification of the degree of tumor heterogeneity in individual tumors and progression is a critical task for tumor treatment. However, current medical tests cannot meet these needs; in particular, the need for noninvasive visualization of single-cell heterogeneity. Near-infrared II (NIR-II, 1000-1700 nm) imaging exhibits an exciting prospect for non-invasive monitoring due to the high temporal-spatial resolution. More importantly, NIR-II imaging displays more extended tissue penetration depths and reduced tissue backgrounds because of the significantly lower photon scattering and tissue autofluorescence than traditional the near-infrared I (NIR-I) imaging. In this review, we summarize systematically the advances made in NIR-II in tumor imaging, especially in the detection of tumor heterogeneity and progression as well as in tumor treatment. As a non-invasive visual inspection modality, NIR-II imaging shows promising prospects for understanding the differences in tumor heterogeneity and progression and is envisioned to have the potential to be used clinically.

Emerging ultrasmall luminescent nanoprobes for in vivo bioimaging

Photoluminescence (PL) imaging has become a fundamental tool in disease diagnosis, therapeutic evaluation, and surgical navigation applications. However, it remains a big challenge to engineer nanoprobes for high-efficiency in vivo imaging and clinical translation. Recent years have witnessed increasing research efforts devoted into engineering sub-10 nm ultrasmall nanoprobes for in vivo PL imaging, which offer the advantages of efficient body clearance, desired clinical translation potential, and high imaging signal-to-noise ratio. In this review, we present a comprehensive summary and contrastive discussion of emerging ultrasmall luminescent nanoprobes towards in vivo PL bioimaging of diseases. We first summarize size-dependent nano-bio interactions and imaging features, illustrating the unique attributes and advantages/disadvantages of ultrasmall nanoprobes differentiating them from molecular and large-sized probes. We also discuss general design methodologies and PL properties of emerging ultrasmall luminescent nanoprobes, which are established based on quantum dots, metal nanoclusters, lanthanide-doped nanoparticles, and silicon nanoparticles. Then, recent advances of ultrasmall luminescent nanoprobes are highlighted by surveying their latest in vivo PL imaging applications. Finally, we discuss existing challenges in this exciting field and propose some strategies to improve in vivo PL bioimaging and further propel their clinical applications.

Advances in Biosensing of Chemical Food Contaminants Based on the MOFs-Graphene Nanohybrids

Food safety issue is becoming an international challenge for human health owing to the presence of contaminants. In this context, reliable, rapid, and sensitive detecting technology is extremely demanded to establish food safety assurance systems. MOFs (Metal-organic frameworks) are a new type of porous crystalline material with particular physical and chemical characteristics presented in food safety requirements. (Bio)sensors driven MOF materials have emerged as a promising alternative and complementary analytical techniques, owing to their great specific area, high porosity, and uniform and fine-tunable pore buildings. Nevertheless, the insufficient stability and electrical conductivity of classical MOFs limit their utilization. Employing graphene-derived nanomaterials with high functional elements as patterns for the MOF materials not only improves the structural instability and poor conductivity but also impedes the restacking and aggregation between graphene layers, thus significantly extending the MOFs application. A review of MOFs-graphene-based material used in food contamination detection is urgently needed for encouraging the advance of this field. Herein, this paper systematically outlines current breakthroughs in MOF-graphene-based nanoprobes, outlines their principles, and illustrates their employments in identifying mycotoxins, heavy metal ions, pathogens, antibiotics, and pesticides, referring to their multiplexing and sensitivity ability. The challenges and limitations of applying MOF-graphene composite for precise and efficient assessment of food were also debated. This paper would maybe offer some inspired concepts for an upcoming study on MOF-based composites in the food security context.

The optical research progress of nanophosphors composed of transition elements in the fourth period of near-infrared windows I and II for deep-tissue theranostics

Research in the field of nano-optics is advancing by leaps and bounds, among which near-infrared (NIR) light optics have attracted much attention. NIR light has a longer wavelength than visible light, such that it can avoid shielding caused by biological tissues. This advantage has driven its importance and practicality in human treatment applications and has attracted significant attention from researchers in academia and industry. In the broad spectrum of infrared light wavelengths, the most noticeable ones are the NIR biological window I of 700-900 nm and window II of 1000-1700 nm. Luminescent materials can effectively cover the NIR biological window with different doping strategies. These doped elements are mostly transition elements with multielectron orbitals. Several nanomaterials based on narrow-spectrum lanthanides have been developed to correspond to biological applications of different wavelengths. However, this review explicitly introduces the absorption and reflection/luminescence interactions between NIR light and biological tissues independently. Unlike the adjustment of the wavelength of the lanthanide series, this review analyzes the NIR optical properties of the fourth-period element ions in transition elements (such as Cr³⁺ and Ni²⁺). These elements have a broadband wavelength of NIR light emission and higher quantum efficiency, corresponding to the absorption and emission spectrum and photobiological absorption of different NIR windows for therapeutic diagnosis. Finally, this review lists and explores other broadband NIR phosphors and has tried to discover the possibility of non-invasive precision medicine in the future.

Expanding the toolbox of photon upconversion for emerging frontier applications

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

Effect of Graphene vs. Reduced Graphene Oxide in Gold Nanoparticles for Optical Biosensors-A Comparative Study

Aiming to develop a nanoparticle-based optical biosensor using gold nanoparticles (AuNPs) synthesized using green methods and supported by carbon-based nanomaterials, we studied the role of carbon derivatives in promoting AuNPs localized surface plasmon resonance (LSPR), as well as their morphology, dispersion, and stability. Carbon derivatives are expected to work as immobilization platforms for AuNPs, improving their analytical performance. Gold nanoparticles (AuNPs) were prepared using an eco-friendly approach in a single step by reduction of HAuCl4·3H2O using phytochemicals (from tea) which act as both reducing and capping agents. UV-Vis spectroscopy, transmission electron microscopy (TEM), zeta potential (ζ-potential), and X-ray photoelectron spectroscopy (XPS) were used to characterize the AuNPs and nanocomposites. The addition of reduced graphene oxide (rGO) resulted in greater dispersion of AuNPs on the rGO surface compared with carbon-based nanomaterials used as a support. Differences in morphology due to the nature of the carbon support were observed and are discussed here. AuNPs/rGO seem to be the most promising candidates for the development of LSPR biosensors among the three composites we studied (AuNPs/G, AuNPs/GO, and AuNPs/rGO). Simulations based on the Mie scattering theory have been used to outline the effect of the phytochemicals on LSPR, showing that when the presence of the residuals is limited to the formation of a thin capping layer, the quality of the plasmonic resonance is not affected. A further discussion of the application framework is presented.

Near-Infrared II Gold Nanocluster Assemblies with Improved Luminescence and Biofate for In Vivo Ratiometric Imaging of H2S

Ultrasmall gold nanoclusters (AuNCs) are emerging as promising luminescent nanoprobes for bioimaging due to their fantastic photoluminescence (PL) and renal-clearable ability. However, it remains a great challenge to design them for in vivo sensitive molecular imaging in desired tissues. Herein, we have developed a strategy to tailor the PL and biofate of near-infrared II (NIR-II)-emitting AuNCs via ligand anchoring for improved bioimaging. By optimizing the ligand types in AuNCs and using Er³⁺-doped lanthanide (Ln) nanoparticles as models, core-satellite Ln@AuNCs assemblies were rationally constructed, which enabled 2.5-fold PL enhancement of AuNCs at 1100 nm and prolonged blood circulation compared to AuNCs. Significantly, Ln@AuNCs with dual intense NIR-II PL (from AuNCs and Er³⁺) can effectively accumulate in the liver for ratiometric NIR-II imaging of H₂S, facilitated by H₂S-mediated selective PL quenching of AuNCs. We have then demonstrated the real-time imaging evaluation of liver delivery efficacy and dynamics of two H₂S prodrugs. This shows a paradigm to visualize liver H₂S delivery and its prodrug screening in vivo. Note that Ln@AuNCs are body-clearable via the hepatobiliary excretion pathway, thus reducing potential long-term toxicity. Such findings may propel the engineering of AuNC nanoprobes for advancing in vivo bioimaging analysis.

Rare-Earth Doping in Nanostructured Inorganic Materials

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

Degradation of upconverting nanoparticles in simulated fluids evaluated by ratiometric luminescence

The effect of artificially simulated fluids on the optical properties of upconversion nanoparticles and the degradation mechanism was systematically studied.

Sensing and Imaging of PPi in vivo using Lanthanide-based Second Near-infrared Luminescent Probes

pathological changes. Here, we reported a luminescent nanoprobe for the detection and imaging of PPi in vivo based on a lanthanide nanoparticle with luminescence at the second near-infrared window modified...

Promising Graphene-Based Nanomaterials and Their Biomedical Applications and Potential Risks: A Comprehensive Review

Graphene-based nanomaterials (GBNs) have been the subject of research focus in the scientific community because of their excellent physical, chemical, electrical, mechanical, thermal, and optical properties. Several studies have been conducted on GBNs, and they have provided a detailed review and summary of various applications. However, comprehensive comments on biomedical applications and potential risks and strategies to reduce toxicity are limited. In this review, we systematically summarized the following aspects of GBNs in order to fill the gaps: (1) the history, synthesis methods, structural characteristics, and surface modification; (2) the latest advances in biomedical applications (including drug/gene delivery, biosensors, bioimaging, tissue engineering, phototherapy, and antibacterial activity); and (3) biocompatibility, potential risks (toxicity in vivo/vitro and effects on human health and the environment), and strategies to reduce toxicity. Moreover, we have analyzed the challenges to be overcome in order to enhance application of GBNs in the biomedical field.

Image-Guided TME-Improving Nano-Platform for Ca2+ Signal Disturbance and Enhanced Tumor PDT

Dysfunction of the calcium balancing system and disruption of calcium distribution can induce abnormal intracellular calcium overload, further causing serious damage and even cell death, which provides a potential therapeutic approach for tumor treatment. Herein, a nano-platform, which includes UCNPs-Ce6@RuR@mSiO₂ @PL-HA NPs (UCRSPH) and SA-CaO₂ nanoparticles, is prepared for improving the tumor micro-environment (TME), Ca²⁺ signal disturbance as well as enhanced photodynamic tumor therapy (PDT). UCRSPH combined with SA-CaO₂ can alter TME and relieve hypoxia of the tumor to realize self-reinforcing PDT under near-IR irradiation (980 nm). The ruthenium red (RuR) in the UCRSPH NPs can be released to the cytoplasm after endocytosis of the nanoparticles, target Ca²⁺ channel proteins on the endoplasmic reticulum and mitochondria, sarcoplasmic reticulum Ca²⁺ -ATPase (SERCA), and mitochondrial calcium uniporter (MCU). The combined participation of nanoparticles and RuR promotes Ca²⁺ imbalance and cytoplasmic calcium overload with the assistance of CaO₂ , and provides tumor cells higher sensitivity to PDT. Furthermore, the nano-platform also provides fluorescence imaging and calcification computed tomography imaging for in vivo treatment guidance. In conclusion, this image-guided nano-platform show potential for highly specific, efficient combined therapy against tumor cells with minimal side-effects to normal cells by integrating TME improvement, self-reinforcing PDT, and Ca²⁺ signal disturbance.

Dye-Sensitized Rare Earth-Doped Nanoparticles with Boosted NIR-IIb Emission for Dynamic Imaging of Vascular Network-Related Disorders

Real-time dynamic vascular network imaging can provide accurate hemodynamic and anatomical information, facilitating the diagnosis of blood circulatory system-related diseases and achieving precise evaluation of therapeutic effects. In vivo luminescence imaging in the NIR-IIb biological window (1500-1700 nm) has developed into a next generation of optical imaging method with significantly improved temporal-spatial resolution and penetration depth. Unfortunately, an imaging contrast agent capable of emitting NIR-IIb luminescence with sufficient brightness in this region is lacking. Herein, we designed and proposed a type of dye-sensitized rare earth-doped nanoparticle (RENPs@Alk-pi) with obviously boosted NIR-IIb emission and high biocompatibility, which can be used to realize the real-time NIR-IIb luminescence imaging with high temporal-spatial resolution and contrast. The dye sensitization process provides a 40-fold enhanced brightness of the NIR-IIb emission at 1525 nm of Er3+. Consequently, the RENPs@Alk-pi was not only able to depict a vascular network but also applicable in noninvasively monitoring the dynamic vascular processes and changes in the vascular anatomy of two blood circulatory system-related disorders, including hindlimbs ischemia and atherosclerosis. Our research provides a powerful tool for evaluating vascular network-related dysfunction and physiological processes.

Sensitizing the Luminescence of Lanthanide-Doped Nanoparticles over 1500 nm for High-Contrast and Deep Imaging of Brain Injury

Real-time and in situ visualization of cerebrovascular dysfunction is significant for studying brain injury, which however, is restricted by the complex brain structure and limited imaging strategies. Luminescence imaging in NIR-IIb region (1500-1700 nm) is a promising tool owing to its merits including deep penetration, high resolution, and fast data acquisition. Unfortunately, a luminescent material in this region with sufficient brightness and biocompatibility is scarce. Herein, Ag₂Se quantum dot-sensitized lanthanide-doped nanocrystals (QDs-LnNCs) with emission beyond 1500 nm were fabricated to image the cerebrovascular structure and hemodynamics in ischemic stroke and traumatic brain injury. The sensitization by QDs provided an over 100-fold enhanced brightness of LnNCs and a remarkable penetration depth of 11 mm. Dynamic information of blood perfusion and flow rates were acquired and the damage of the blood-brain barrier in the two injury models was investigated. Our results proved QDs-LnNCs as a kind of competent nanomaterial for noninvasive brain imaging.

Endogenous H2S-Activated Orthogonal Second Near-Infrared Emissive Nanoprobe for In Situ Ratiometric Fluorescence Imaging of Metformin-Induced Liver Injury

Metformin as a hypoglycemic drug for antidiabetic treatment has emerged as a multipotential drug for many disease treatments such as cognitive disorders, cancers, promoting weight loss. However, overdose uptake may upregulate the hepatic H₂S level, subsequently leading to serious liver injury and toxicity. Therefore, developing intelligent second near-infrared (NIR-II) emitting nanoprobes by using endogenous H₂S as a smart trigger for noninvasive highly specific in situ monitoring of the metformin-induced hepatotoxicity is highly desirable, which is rarely explored. Herein, an endogenous H₂S activated orthogonal NIR-II emitting myrica rubra-like nanoprobe based on NaYF₄:Gd/Yb/Er@NaYF₄:Yb@SiO₂ coated with Ag nanodots was explored for highly specific in vivo ratiometrically monitoring of hepatotoxicity. The designed nanoprobes were mainly uptaken by the liver and subsequently converted to NaYF₄:Gd/Yb/Er@NaYF₄:Yb@SiO₂@Ag₂S via in situ sulfuration reaction triggered by the overexpressed endogenous H₂S in the injured liver tissues, finally leading to a turn-on orthogonal emission centered at 1053 nm (irradiation by 808 nm laser) and 1525 nm (irradiation by 980 nm laser). The designed nanoprobe presents a high detection limit down to 0.7 nM of H₂S. More importantly, the in situ highly specific ratiometric imaging of the metformin-induced hepatotoxicity was successfully achieved by using the activatable orthogonal NIR-II emitting probe. Our results provide an NIR-II ratiometric fluorescence imaging strategy for highly sensitive/specific diagnosis of hepatotoxicity levels induced by metformin.

Recent advances in design of lanthanide-containing NIR-II luminescent nanoprobes

Luminescent biosensing in the second near-infrared window (NIR-II, 1000-1700 nm) region, which has weak tissue scattering and low autofluorescence, draws extensive attention owing to its deep tissue penetration, good spatial resolution and high signal-to-background ratio. As a new generation of NIR-II probes, lanthanide (Ln3+)-containing nanoprobes exhibit several superior properties. With the rapid development of Ln3+-containing NIR-II nanoprobes, many significant advances have been accomplished in their optical properties tuning and surface functional modification for further bioapplications. Rather than being exhaustive, this review aims to survey the recent advances in the design strategies of inorganic Ln3+-containing NIR-II luminescent nanoprobes by highlighting their optical performance optimization and surface modification approaches. Moreover, challenges and opportunities for this kind of novel NIR-II nanoprobes are envisioned.

Graphene and its Derivatives-Based Optical Sensors

Being the first successfully prepared two-dimensional material, graphene has attracted extensive attention from researchers due to its excellent properties and extremely wide range of applications. In particular, graphene and its derivatives have displayed several ideal properties, including broadband light absorption, ability to quench fluorescence, excellent biocompatibility, and strong polarization-dependent effects, thus emerging as one of the most popular platforms for optical sensors. Graphene and its derivatives-based optical sensors have numerous advantages, such as high sensitivity, low-cost, fast response time, and small dimensions. In this review, recent developments in graphene and its derivatives-based optical sensors are summarized, covering aspects related to fluorescence, graphene-based substrates for surface-enhanced Raman scattering (SERS), optical fiber biological sensors, and other kinds of graphene-based optical sensors. Various sensing applications, such as single-cell detection, cancer diagnosis, protein, and DNA sensing, are introduced and discussed systematically. Finally, a summary and roadmap of current and future trends are presented in order to provide a prospect for the development of graphene and its derivatives-based optical sensors.

Organic fluorescent nanoparticles with NIR-II emission for bioimaging and therapy

Fluorescence imaging technology in the second near-infrared bio-channel (NIR-II) has the advantages of low light scattering and weak autofluorescence. It can obtain high spatial resolution imaging in deeper biological tissues and realize accurate diagnosis in the lesion. As a new cancer treatment method, photothermal therapy has the characteristics of obvious curative effect and small side effects. However, the hydrophobicity and non-selectivity of many fluorescent materials, aggregation-induced fluorescence quenching, and other problems lead to undesirable imaging results. Here, we reviewed the structure of the NIR-II fluorescent molecules and these dyes whose fluorescence tail emission is in the NIR-II bio-channel, discussed in detail how to realize the redshift of the dye wavelength, including modifying the push-pull electron system, extending the conjugated chain, and forming J-aggregates and other methods. We also summarize some strategies to improve brightness, including responsiveness, targeting, adjustment of aggregation mode, and aggregation-induced emission effect, thereby improving the imaging performance and therapeutic effect of NIR-II fluorescent dyes.

Two-Photon Excitation-Based Imaging Postprocessing Algorithm Model for Background-Free Bioimaging

Bioimaging is a powerful strategy for studying biological activities, which is still limited by the difficulty of distinguishing obscured signals from high background. Despite the development of various new imaging materials and methods, target signals are still likely to be submerged in spontaneous fluorescence or scattering signals. Herein, a novel two-photon excitation-process-based imaging postprocessing algorithm model (2PIA) is introduced to minimize background noise, and triplet-triplet annihilation upconversion metal-organic frameworks (UCMOFs) are chosen as demonstration. Through the collection of several image stacks, the related polynomial of the luminescence intensity and excitation power was established, following splitting the desired signals from noise and obtaining the background-free images definitely. Both in vitro and in vivo experiments show that improved signal visibility is achieved through 2PIA and UCMOFs by removing the interference of scattering, bioluminescence, and other fluorescence materials. The imaging spatial resolution and tissue penetration depth were greatly enhanced. Benefiting from 2PIA, as low as 100 UCMOFs labeled cells can be identified from obscuring background easily after intravenous injection. This image postprocessing method combined with special two-photon excited luminescent materials can conduct biological imaging from complex background interference without using expensive instruments or delicate materials, which holds great promise for accurate biological imaging.

Recent advances in graphene-family nanomaterials for effective drug delivery and phototherapy

INTRODUCTION

Owing to the unique properties of graphene, including large specific surface area, excellent thermal conductivity, and optical absorption, graphene-family nanomaterials (GFNs) have attracted extensive attention in biomedical applications, particularly in drug delivery and phototherapy.

AREAS COVERED

In this review, we point out several challenges involved in the clinical application of GFNs. Then, we provide an overview of the most recent publications about GFNs in biomedical applications, including diverse strategies for improving the biocompatibility, specific targeting and stimuli-responsiveness of GFNs for drug delivery, codelivery of drug and gene, photothermal therapy, photodynamic therapy, and multimodal combination therapy.

EXPERT OPINION

Although the application of GFNs is still in the preclinical stage, rational modification of GFNs with functional elements or making full use of GFNs-based multimodal combination therapy might show great potential in biomedicine for clinical application.

Research advances in integrated theranostic probes for tumor fluorescence visualization and treatment

At present, cancer is obviously a major threat to human health worldwide. Accurate diagnosis and treatment are in great demand and have become an effective method to alleviate the development of cancer and improve the survival rate of patients. A large number of theranostic probes that combine diagnosis and treatment methods have been developed as promising tools for tumor precision medicine. Among them, fluorescent theranostic probes have developed rapidly in the frontier research field of precision medicine with their real time, low toxicity, and high-resolution merit. Therefore, this review focuses on recent advances in the development of fluorescent theranostic probes, as well as their applications for cancer diagnosis and treatment. Initially, small-molecule fluorescent theranostic probes mainly including tumor microenvironment-responsive fluorescent prodrugs and phototherapeutic probes were introduced. Subsequently, nanocomposite probes are expounded based on four types of nano-fluorescent particles combining different therapies (chemotherapy, photothermal therapy, photodynamic therapy, gene therapy, etc.). Then, the capsule-type "all in one" probes, which occupy an important position in theranostic probes, are summarized according to the surface carrier type. This review aims to present a comprehensive guide for researchers in the field of tumor-related theranostic probe design and development.

Covid-19 acute responses and possible long term consequences: What nanotoxicology can teach us

Long-term effects of Covid-19 disease are still poorly understood. However, similarities between the responses to SARS-CoV-2 and certain nanomaterials suggest fibrotic pulmonary disease as a concern for public health in the next future. Cross-talk between nanotoxicology and other relevant disciplines can help us to deploy more effective Covid-19 therapies and management strategies.

Activatable fluorescence sensors for in vivo bio-detection in the second near-infrared window

Fluorescence imaging in the second near-infrared (NIR-II, 1000–1700 nm) window has exhibited advantages of high optical resolution at deeper penetration (ca. 5–20 mm) in bio-tissues owing to the reduced photon scattering, absorption and tissue autofluorescence. However, the non-responsive and “always on” sensors lack the ability of selective imaging of lesion areas, leading to the low signal-to-background ratio (SBR) and poor sensitivity during bio-detection. In contrast, activatable sensors show signal variation in fluorescence intensity, spectral wavelength and fluorescence lifetime after responding to the micro-environment stimuli, leading to the high detection sensitivity and reliability in bio-sensing. This minireview summarizes the design and detection ability of recently reported NIR-II activatable sensors. Furthermore, the challenges, opportunities and prospects of NIR-II activatable bio-sensing are also discussed.

Fluorescence imaging in the second near-infrared (NIR-II, 1000–1700 nm) window has exhibited advantages of high optical resolution at deeper penetration (ca. 5–20 mm) in bio-tissues owing to the reduced photon scattering and tissue autofluorescence.

Graphene Oxide-Supported Lanthanide Metal-Organic Frameworks with Boosted Stabilities and Detection Sensitivities

The photoluminescent (PL) properties of lanthanide metal-organic frameworks (Ln-MOFs) are intrinsically subtle to water molecules, which remains the major challenge that severely limits their applications as fluorescent probes in aqueous samples. Herein novel composite fluorescent probes were prepared by growing Ln-MOFs (Tb-MOF, Eu-MOF, and Tb/Eu-MOF) on carboxylated porous graphene oxide (PGO-COOH). The 3D thorny composites presented significantly longer fluorescent lifetimes and higher quantum yields than that of the bare Ln-MOFs and exhibited long-term PL stabilities in aqueous samples up to 15 days. The stable and improved PL properties demonstrated that the highly hybrid composite structures protected the MOF components from the adverse effects of water. Furthermore, the unexpected antenna effect of the PGO-COOH substrate on Ln³⁺ was supposed to be another reason for the improved PL properties. The composites present ultralow detection limits as low as 5.6 nM for 2,4-dinitrotoluene and 2.3 nM for dipicolinic acid as turn-off and ratiometric fluorescent probes, respectively, which was attributed to the incoporation of PGO-COOH that dramatically enahnced inner filter effects and effectively protected the energy transfer process in the MOF components from the interference of the surrounding water. This work presents an effective strategy for creating ultrasensitive and stable fluorescent probes based on Ln-MOFs for applications in aqueous samples.