Engineering of cyanine-based nanoplatform with tunable response toward reactive species for ratiometric NIR-II fluorescent imaging in mice

Recent advances in fluorescent nanomaterials designed for biomarker detection and imaging

The highly sensitive detection and imaging of biomarkers are critical for early diagnosis, treatment, and prognosis monitoring. The unique size and structure of fluorescent nanomaterials provide key benefits such as excellent photostability, high fluorescence quantum yield, and tunable excitation and emission wavelengths. These properties have led to the widespread application of nanomaterials in fluorescent biomarkers detection and imaging. In this review, we began by introducing the composition of fluorescent probes and discussing the underlying sensing mechanisms. We then summarized recent advances in the use of fluorescent nanomaterials such as quantum dots (QDs), metal nanoclusters (MNCs), carbon dots (CDs), and metal-organic frameworks (MOFs) for biomarker detection and imaging. Additionally, we highlighted the applications of fluorescent nanomaterials in the detection and imaging of small molecules, biomacromolecules, and various biomarkers, including metal ions, bacteria, and circulating tumor cells (CTCs). The challenges and future prospects of fluorescent nanomaterials in biomarker detection and imaging were also discussed. We anticipate that fluorescent nanomaterials will have profound implications for clinical biomarker detection and imaging, with considerable application in both academic research and industrial applications.

Debut of enzyme-responsive anionic cyanine for overlap-free NIR-II-to-I dual-channel tumour imaging

Bridging the disparity between traditional surgical resection imaging and ex vivo histopathology, fluorescence imaging is considered a promising tool in disease diagnosis and imaging navigation. Nevertheless, its usefulness is undermined by the variability of single-wavelength fluorescence signals and limited penetration of NIR-I (650-900 nm) bioimaging. In this work, we present a novel NIR-II ratiometric fluorescent probe (CFC-GSH) with γ-glutamyl transpeptidase (GGT) sensitivity for multifunctional bioimaging. This probe leverages a GSH-capped anionic cyanine, with advantages of high brightness, excellent photostability, high specificity and favourable biocompatibility. CFC-GSH exhibits an intrinsically stable NIR-II signal prior to triggering, which can be utilized for in vivo systemic circulation vessel outlining and microvascular imaging. At the tumour site with GGT over expression, an intramolecular S,N-rearrangement would initiate the conversion of sulphur-substituted cyanine to amino-substituted cyanine, resulting in a significant emission shift of 270 nm. Using the dual-channel signal changes, CFC-GSH effectively differentiates between subcutaneous hepatocellular carcinoma (HCC) and normal tissue and precisely localizes metastatic HCC tumours in the abdominal cavity. These results reveal that CFC-GSH exhibits promising potential as a multiprospective candidate tool for fluorescence screening and diagnostic imaging in various biological scenarios.

Activatable Molecular Probes With Clinical Promise for NIR-II Fluorescent Imaging

The second near-infrared window (NIR-II) fluorescence imaging has been widely adopted in basic scientific research and preclinical applications due to its exceptional spatiotemporal resolution and deep tissue penetration. Among the various fluorescent agents, organic small-molecule fluorophores are considered the most promising candidates for clinical translation, owing to their well-defined chemical structures, tunable optical properties, and excellent biocompatibility. However, many currently available NIR-II fluorophores exhibit an "always-on" fluorescence signal, which leads to background noise and compromises diagnostic accuracy during disease detection. Developing NIR-II activatable organic small-molecule fluorescent probes (AOSFPs) for accurately reporting pathological changes is key to advancing NIR-II fluorescence imaging toward clinical application. This review summarizes the rational design strategies for NIR-II AOSFPs based on four core structures (cyanine, hemicyanine, xanthene, and BODIPY). These NIR-II AOSFPs hold substantial potential for clinical translation. Furthermore, the recent advances in NIR-II AOSFPs for NIR-II bioimaging are comprehensively reviewed, offering clear guidance and direction for their further development. Finally, the prospective efforts to advance NIR-II AOSFPs for clinical applications are outlined.

Rational Design of NIR-II Ratiometric Fluorescence Probes for Accurate Bioimaging and Biosensing In Vivo

Intravital fluorescence imaging in the second near-infrared window (NIR-II, 900-1700 nm) has emerged as a promising method for non-invasive diagnostics in complex biological systems due to its advantages of less background interference, high tissue penetration depth, high imaging contrast, and sensitivity. However, traditional NIR-II fluorescence imaging, which is characterized by the "always on" or "turn on" mode, lacks the ability of quantitative detection, leading to low reproducibility and reliability during bio-detection. In contrast, NIR-II ratiometric fluorescence imaging can realize quantitative and reliable analysis and detection in vivo by providing reference signals for fluorescence correction, generating new opportunities and prospects during in vivo bioimaging and biosensing. In this review, the current design strategies and sensing mechanisms of NIR-II ratiometric fluorescence probes for bioimaging and biosensing applications are systematically summarized. Further, current challenges, future perspectives and opportunities for designing NIR-II ratiometric fluorescence probes are also discussed. It is hoped that this review can provide effective guidance for the design of NIR-II ratiometric fluorescence probes and promote its adoption in reliable biological imaging and sensing in vivo.

Water-Soluble Lipophilic Near-Infrared Region II Fluorophores for High-Brightness Lipid Layer and Lipid Droplets Imaging Applications

Fluorescence imaging in the second near-infrared region (NIR-II, 1000-1700 nm) has garnered considerable attention for displaying the biological information of deep tissues. However, the lack of biocompatible contrast agents with bright NIR-II emission has hampered the precise clinical application of deep tissue imaging. Here, a lipophilic enhancement strategy employing donor-acceptor-donor (D-A-D) molecules, introducing long alkoxy chains and quaternary ammonium salts for the development of highly bright water-soluble NIR-II fluorophores (BBTD-2C-N), is described. Notably, liposome-encapsulated BBTD-2C-N nanoparticles (B-2C-N/DMPC) in aqueous solution exhibit a 1.8-fold increase in NIR-II fluorescence brightness compared to free BBTD-2C-N in methanol. Avoidance of the aggregation-caused quenching effect and enhanced NIR-II fluorescence are attributed to significantly attenuated π-π stacking interactions and maintained monodisperses in the hydrophobic liposome shell. Moreover, BBTD-2C-N demonstrates superior performance in visualizing lipid droplet-rich HeLa cells in vitro, as well as precise monitoring of adipose tissue and fatty liver in vivo. This study reveals a new avenue for the development of bright NIR-II fluorophores and precise in vivo imaging.

A tumor Microenvironment-triggered protein-binding Near-infrared-II Theranostic nanoplatform for Mild-Temperature photothermal therapy

Photothermal therapy (PTT) has gained significant attention as a non-invasive treatment in clinical oncology. However, the translation of PTT into clinical practice remains constrained by three fundamental limitations: acquired thermal tolerance in tumor cells, restricted light penetration depth in biological matrices, and insufficient therapeutic outcomes from single-modality treatment. To address these issues, a strategy for forming in situ complexes between near-infrared-II (NIR-II) photothermal agents and proteins is developed, aimed at damaging protein conformation and enhancing PTT effectiveness. We developed a nanoplatform called PCy-SF, consisting of the NIR-II photothermal polymer (PCy) and sorafenib (SF). PCy-SF responds to the tumor microenvironment (TME), specifically releasing Cy-CHO and sorafenib from the assemblies. The released Cy-CHO covalently binds to proteins, forming Cy-Protein complexes that activate NIR-II fluorescence, facilitating NIR-II imaging-guided photothermal therapy. Concurrently, the released SF intensifies microvascular damage, synergizing with PTT for enhanced therapeutic efficacy. Notably, PCy-SF induces a strong anticancer immune response, effectively suppressing tumor recurrence and metastasis. This study introduces a promising protein deactivation strategy for achieving mild-temperature PTT, offering broader applicability of PTT and insights for sensitizing tumors to photothermal therapy. Together, this innovative approach combining NIR-II photothermal agents with protein complexation and a responsive nanoplatform enhances PTT precision and efficacy, demonstrating significant potential in the field of cancer nanomedicine.

Oxidative stress levels and antioxidant defense mechanisms (Nrf2-Keap1 signaling pathway) in the Harderian glands of hibernating Daurian ground squirrels

Cyclic hibernation bouts in Daurian ground squirrels (Spermophilus dauricus) lead to repeated suppression and recovery of mitochondrial respiratory function across multiple organs, potentially impacting reactive oxygen species (ROS) dynamics. The Harderian gland (HG) plays an important role in endocrine regulation through porphyrin secretion. However, the influence of hibernation on oxidative pressure and associated antioxidant pathways in the HG remains inadequately understood. In the current study, we investigated the morphological changes, secretory activity, ROS levels, and underlying mechanisms in the HG of Daurian ground squirrels at distinct circannual stages of hibernation. Results indicated that: (1) Protoporphyrin levels in the HG increased during hibernation compared to the summer active (SA) phase, with a reduction in acinar lumen during torpor, potentially related to hibernation in a low-light environment. (2) Hydrogen peroxide (H2O2) and malondialdehyde (MDA) content during hibernation and post-hibernation (POST) did not exceed the levels observed in SA, indicating that the HG effectively mitigated oxidative pressure and lipid peroxidation during these periods. (3) Superoxide dismutase (SOD) activity increased while glutathione peroxidase (GPx) activity decreased during Inter-bout arousal (IBA) compared to both SA and torpor, although total antioxidant capacity (T-AOC) remained stable across all stages. (4) Overall fluorescent intensity of nuclear factor erythroid 2-related factor 2 (Nrf2) and Kelch-like ECH-associated protein 1 (Keap1) was significantly lower than in SA. These findings demonstrate that the HG in Daurian ground squirrels maintains a favorable oxidative status through the regulation of antioxidant enzyme activities during hibernation and even post-hibernation.

Biomass-derived carbon dots with pharmacological activity for biomedicine: Recent advances and future perspectives

Carbon dots (CDs), a type of nanoparticle with excellent optical properties, good biocompatibility, and small size, are finding increasing application across the fields of biology and biomedicine. In recent years, biomass-derived CDs with pharmacological activity (BP-CDs) derived from herbal medicines (HMs), HMs extracts and other natural products with demonstrated pharmaceutical activity have attracted particular attention. Herein, we review recent advances in the development of BP-CDs, covering the selection of biomass precursors, different methods used for the synthesis of BP-CDs from natural sources, and the purification of BP-CDs. Additionally, we summarize the many remarkable properties of BP-CDs including optical properties, biocompatibility and pharmaceutical efficacy. Moreover, the antibacterial, antiviral, anticancer, biosensing, bioimaging, and other applications of BP-CDs are reviewed. Thereafter, we discuss the advantages and disadvantages of BP-CDs and Western drug-derived CDs, highlighting the excellent performance of BP-CDs. Finally, based on the current state of research on BP-CDs, we suggest several aspects of BP-CDs that urgently need to be addressed and identify directions that should be pursued in the future. This comprehensive review on BP-CDs is expected to guide the precise design, preparation, and future development of BP-CDs, thereby advancing the application of BP-CDs in biomedicine.

In vivo targeted-imaging of mitochondrial acidification in an aristolochic acid I-induced nephrotoxicity mouse model by a fluorescent/photoacoustic bimodal probe

Aristolochic acid I (AAI), a natural compound in aristolochia type Chinese medicinal herb, is generally acknowledged to have nephrotoxicity, which may be associated with mitophagy. Mitophagy is a cellular process with important functions that drive AAI-induced renal injury. Mitochondrial pH is currently measured by fluorescent probes in cell culture, but existing probes do not allow for in situ imaging of AAI-induced mitophagy in vivo. We developed a ratiometric fluorescent/PA dual-modal probe with a silicon rhodamine fluorophore and a pH-sensitive hemicyanine dye covalently linked via a short chain to obtain a FRET type probe. The probe was used to measure AAI-mediated mitochondrial acidification in live cells and in vivo. The Förster resonance energy transfer (FRET)-mediated ratiometric and bimodal method can efficiently eliminate signal variability associated with the commonly used one-emission and single detection mode by ratiometric two channels of the donor and acceptor. The probe has good water-solubility and low molecular weight with two positively charged, facilitating its precise targeting into renal mitochondria, where the fluorescent/PA changes in response to mitochondrial acidification, enabling dynamic and semi-quantitative mapping of subtle changes in mitochondrial pH in AAI-induced nephrotoxicity mouse model for the first time. Also, the joint use of L-carnitine could mitigate the mitophagy in AAI-induced nephrotoxicity.

Enhancing lipid peroxidation via radical chain transfer reaction for MRI guided and effective cancer therapy in mice

Lipid peroxidation (LPO), the process of membrane lipid oxidation, is a potential new form of cell death for cancer treatment. However, the radical chain reaction involved in LPO is comprised of the initiation, propagation (the slowest step), and termination stages, limiting its effectiveness in vivo. To address this limitation, we introduce the radical chain transfer reaction into the LPO process to target the propagation step and overcome the sluggish rate of lipid peroxidation, thereby promoting endogenous lipid peroxidation and enhancing therapeutic outcomes. Firstly, radical chain transfer agent (CTA-1)/Fe nanoparticles (CTA-Fe NPs-1) was synthesized. Notably, CTA-1 convert low activity peroxyl radicals (ROO·) into high activity alkoxyl radicals (RO·), creating the cycle of free radical oxidation and increasing the propagation of lipid peroxidation. Additionally, CTA-1/Fe ions enhance reactive oxygen species (ROS) generation, consume glutathione (GSH), and thereby inactivate GPX-4, promoting the initiation stage and reducing termination of free radical reaction. CTA-Fe NPs-1 induce a higher level of peroxidation of polyunsaturated fatty acids in lipid membranes, leading to highly effective treatment in cancer cells. In addition, CTA-Fe NPs-1 could be enriched in tumors inducing potent tumor inhibition and exhibit activatable T1-MRI contrast of magnetic resonance imaging (MRI). In summary, CTA-Fe NPs-1 can enhance intracellular lipid peroxidation by accelerating initiation, propagation, and inhibiting termination step, promoting the cycle of free radical reaction, resulting in effective anticancer outcomes in tumor-bearing mice.