Molecular Fluorophores for Deep-Tissue Bioimaging

Tracking the Fate of Therapeutic Proteins Using Ratiometric Imaging of Responsive Shortwave Infrared Probes

Monoclonal antibodies (mAbs) are essential agents for cancer treatment and diagnosis. Advanced optical imaging strategies have the potential to address specific questions regarding their complex in vivo life cycle. This study presents responsive shortwave infrared (SWIR) probes and an associated imaging scheme to assess mAb biodistribution, cellular uptake, and proteolysis. Specifically, we identify a Pegylated benzo-fused norcyanine derivative (Benz-NorCy7) that is activated in acidic environments and can be appended to mAbs without significant changes in optical properties. As a mAb conjugate, this agent shows high tumor specificity in a longitudinal imaging study in a murine model. To enable independent tracking of mAb uptake and lysosomal uptake and retention, a two-color ratiometric imaging strategy was employed using an "always-ON" heptamethine cyanine dye (λex = 785 nm) and the pH-responsive Benz-NorCy7 (λex = 890 nm). To assess proteolytic catabolism, we append a cleavable carbamate to Benz-NorCy7 to create turn-ON probes. These agents facilitate the comparison of two common peptide linkers and provide insights into their in vivo properties. Overall, these studies provide a strategy to assess the fate of protein-based therapeutics using optical imaging.

The latest developments of near-infrared fluorescent probes from NIR-I to NIR-II for bioimaging

Near-infrared I (NIR-I: 650-950 nm) fluorescence imaging is a powerful tool for deep-tissue biological imaging, addressing the limitations of photon penetration depth in the visible-light region. Over the past decade, NIR imaging has extended to the near-infrared II (NIR-II: 1000-1700 nm) region, offering high-resolution and low background imaging by suppressing light scattering, and autofluorescence of tissues. Near-infrared fluorescent probes from NIR-I to NIR-II, with diverse functionalities, are increasingly utilized across biological fields to meet various detection needs and to explore physiological events in real time and spatial dimensions. This review discusses recent advancements in small-molecule NIR fluorescent dyes and probes, particularly those based on cyanine and rhodamine scaffolds, highlighting examples of their applications in bioimaging.

Phenazinium- and Malachite Green-Based Pd(II) Cages: Chiroptical Discrimination of Nucleoside Triphosphates

Organic chromophores have been successfully implemented into supramolecular systems to bestow them with distinct photophysical properties for various applications, ranging from solar energy conversion, photochemical reactions or as receptors for guest molecules with optical readout. We had previously introduced first members of the large family of coal-tar dyes (methylene blue, crystal violet and rhodamine) as integral components of coordination cages. Here, we add two new chromophores, malachite green (MGP) and a purple phenazinium dye (PHP), serving as backbones of bis-monodentate banana-shaped ligands with pyridine donors. We show the formation of corresponding green and purple coloured Pd2L4 coordination cages and investigate their interaction with chiral guest molecules via UV-Vis and CD spectroscopy. The PHP cage can be used to recognize nucleoside triphosphates, based on chirality transfer from the guests to the structurally flexible helicate. In combination with the already known methylene blue cage MBP we could further differentiate between all four canonical NTPs through characteristic changes in the observed CD signatures.

Two-photon brightness of NIR-emitting, atomically precise DNA-stabilized silver nanoclusters

Near-infrared (NIR) emitters with high two-photon absorption (2PA) cross-sections are of interest to enable in vivo imaging in the tissue transparency windows. This study explores the potential of DNA-stabilized silver nanoclusters (Ag N -DNAs) as water-soluble two-photon absorbers. We investigate 2PA of four different atomically precise Ag N -DNA species with far-red to NIR emission and varying nanocluster and ligand compositions. 2PA cross-sections, σ 2, were determined by two-photon excited luminescence (2PEL) technique for a wide wavelength range from 810 to 1400 nm. The Ag N -DNAs exhibited reversed strength of corresponding transitions in the two-photon regime, as compared to one-photon, which further demonstrates the complex photophysics of these emitters. Maximal 2PA cross-section value (∼582 GM) was observed for (DNA)3[Ag21]15+, which is stabilized by 3 DNA oligomers. (DNA)2[Ag16Cl2]8+ presented distinct 2PA behavior from the Ag N -DNAs without chlorido ligands, with a high 2PA of 176 GM at 1050 nm. Our findings support the potential of Ag N -DNAs as NIR-to-NIR two-photon probes that are both excited and emit in the NIR. Their high σ 2 and fluorescence quantum yield values result in superior two-photon brightness on the order of ∼102 GM, significantly higher than water-soluble organic fluorophores.

Aggregation-Induced Emission Luminogens Realizing High-Contrast Bioimaging

A revolutionary transformation in biomedical imaging is unfolding with the advent of aggregation-induced emission luminogens (AIEgens). These cutting-edge molecules not only overcome the limitations of traditional fluorescent probes but also improve the boundaries of high-contrast imaging. Unlike conventional fluorophores suffering from aggregation-caused quenching, AIEgens exhibit enhanced luminescence when aggregated, enabling superior imaging performance. This review delves into the molecular mechanisms of aggregation-induced emission (AIE), demonstrating how strategic molecular design unlocks exceptional luminescence and superior imaging contrast, which is crucial for distinguishing healthy and diseased tissues. This review also highlights key applications of AIEgens, such as time-resolved imaging, second near-infrared window (NIR-II), and the advancement of AIEgens in sensitivity to physical and biochemical cue-responsive imaging. The development of AIE technology promises to transform healthcare from early disease detection to targeted therapies, potentially reshaping personalized medicine. This paradigm shift in biophotonics offers efficient tools to decode the complexities of biological systems at the molecular level, bringing us closer to a future where the invisible becomes visible and the incurable becomes treatable.

Roadmap for Designing Donor-π-Acceptor Fluorophores in UV-Vis and NIR Regions: Synthesis, Optical Properties and Applications

Donor acceptor (D-π-A) fluorophores containing a donor unit and an acceptor moiety at each end connected by a conjugated linker gained attention in the last decade due to their conjugated system and ease of tunability. These features make them good candidates for various applications such as bioimaging, photovoltaic devices and nonlinear optical materials. Upon excitation of the D-π-A fluorophore, intramolecular charge transfer (ICT) occurs, and it polarizes the molecule resulting in the 'push-pull' system. The emission wavelengths of fluorophores can be altered from UV-vis to NIR region by modifying the donor unit, acceptor moiety and the π linker between them. The NIR emitting fluorophores with restricted molecular rotations are used in aggregation-induced emission (AIE). D-π-A fluorophores with carboxylic acid and cyano groups are preferred in photovoltaic applications, and fluorophores with large surface area are used for two photon absorbing applications. Herein, we report the synthesis, optical properties, and applications of various D-π-A fluorophores in UV-vis and NIR region.

As Aggregation-Induced Emission Meets with Noncovalent Conformational Locks: Subtly Regulating NIR-II Molecules for Multimodal Imaging-Navigated Synergistic Therapies

Phototheranostics is growing into a sparking frontier in disease treatment. Developing single molecular species synchronously featured by powerful absorption capacity, superior second near-infrared (NIR-II) fluorescence and prominent photothermal conversion ability is highly desirable for phototheranostics, yet remains formidably challenging. In this work, we propose a molecular design philosophy that the integration of noncovalent conformational locks (NoCLs) with aggregation-induced emission (AIE) in a single formulation is able to boost multiple photophysical properties for efficient phototheranostics. The introduction of NoCLs skeleton with conformation-locking feature in the center of molecular architecture indeed elevates the structural planarity and rigidity, which simultaneously promotes the absorption capacity and bathochromic-shifts the emission wavelength centered in NIR-II region. Meanwhile, the AIE tendency mainly originated from flexibly propeller-like geometry at the ends of molecular architecture eventually endows the molecule with satisfactory emission intensity and photothermal conversion in aggregates. Consequently, by utilizing the optimized molecule, unprecedented performance on NIR-II fluorescence-photoacoustic-photothermal trimodal imaging-guided photothermal-chemo synergistic therapy is demonstrated by the precise tumor diagnosis and complete tumor ablation.

Brightness Strategies toward NIR-II Emissive Conjugated Materials: Molecular Design, Application, and Future Prospects

Recent advances have been made in second near-infrared (NIR-II) fluorescence bioimaging and many related applications because of its advantages of deep penetration, high resolution, minimal invasiveness, and good dynamic visualization. To achieve high-performance NIR-II fluorescence bioimaging, various materials and probes with bright NIR-II emission have been extensively explored in the past few years. Among these NIR-II emissive materials, conjugated polymers and conjugated small molecules have attracted wide interest due to their native biosafety and tunable optical performance. This review summarizes the brightness strategies available for NIR-II emissive conjugated materials and highlights the recent developments in NIR-II fluorescence bioimaging. A concise, detailed overview of the molecular design and regulatory approaches is provided in terms of their high brightness, long wavelengths, and superior imaging performance. Then, various typical cases in which bright conjugated materials are used as NIR-II probes are introduced by providing step-by-step examples. Finally, the current problems and challenges associated with accessing NIR-II emissive conjugated materials for bright NIR-II fluorescence bioimaging are briefly discussed, and the significance and future prospects of these materials are proposed to offer helpful guidance for the development of NIR-II emissive materials.

Light/X-ray/ultrasound activated delayed photon emission of organic molecular probes for optical imaging: mechanisms, design strategies, and biomedical applications

Conventional optical imaging, particularly fluorescence imaging, often encounters significant background noise due to tissue autofluorescence under real-time light excitation. To address this issue, a novel optical imaging strategy that captures optical signals after light excitation has been developed. This approach relies on molecular probes designed to store photoenergy and release it gradually as photons, resulting in delayed photon emission that minimizes background noise during signal acquisition. These molecular probes undergo various photophysical processes to facilitate delayed photon emission, including (1) charge separation and recombination, (2) generation, stabilization, and conversion of the triplet excitons, and (3) generation and decomposition of chemical traps. Another challenge in optical imaging is the limited tissue penetration depth of light, which severely restricts the efficiency of energy delivery, leading to a reduced penetration depth for delayed photon emission. In contrast, X-ray and ultrasound serve as deep-tissue energy sources that facilitate the conversion of high-energy photons or mechanical waves into the potential energy of excitons or the chemical energy of intermediates. This review highlights recent advancements in organic molecular probes designed for delayed photon emission using various energy sources. We discuss distinct mechanisms, and molecular design strategies, and offer insights into the future development of organic molecular probes for enhanced delayed photon emission.

Computational chemistry facilitates the development of second near-infrared xanthene-based dyes

CONTEXT

The dyes in the second near-infrared (NIR-II) region play a crucial role in advancing imaging technology. However, developing small-molecule dyes in NIR-II poses a significant bottleneck to meet the substantial demands in biological fields, which may be attributed to the lack of a rational design strategy. Herein, we designed a series of rhodamine analogs with more red-shifted emission by replacing the oxygen-bridge atom in xanthene-based dyes with -C(CH3)2, -Si(CH3)2, -SO2, and -P(O)Ph. We investigated the frontier molecular orbital, electrostatic potential surfaces, the interaction region indicator, electron-hole distribution, and absorption and emission spectrum of xanthene-based dyes using (time-dependent) density functional theory. Our results demonstrated that these designed small molecular dyes exhibit long emission wavelengths covering 1377-1809 nm. We expected these findings to enable the targeted design of long-wavelength rhodamines.

METHOD

Geometry optimization of dyes in the ground and excited states was carried out at ω-B97XD/Def2SVP level using Gaussian 16 A03. The absorption and emission wavelengths were evaluated using 13 functional, including TPSSH, O3LYP, B3LYP*, B3LYP, PBE0, MPW1B95, PBE-1/3, PBE38, MPWB1K, MN15, BHandHLYP, ω-B97XD, and CAM-B3LYP.

Reengineering of Donor-Acceptor-Donor Structured Near-Infrared II Aggregation-Induced Emission Luminogens for Starving-Photothermal Antitumor and Inhibition of Lung Metastasis

Electron acceptor possessing strong electron-withdrawing ability and exceptional stability is crucial for developing donor-acceptor-donor (D-A-D) structured aggregation-induced emission luminogens (AIEgens) with second near-infrared (NIR-II) emission. Although 6,7-diphenyl-[1,2,5] thiadiazolo [3,4-g] quinoxaline (PTQ) and benzobisthiadiazole (BBT) are widely employed as NIR-II building blocks, they still suffer from limited electron-withdrawing capacity or inadequate chemo-stability under alkaline conditions. Herein, a boron difluoride formazanate (BFF) acceptor is utilized to construct NIR-II AIEgen, which exhibits a better overall performance in terms of NIR-II emission and chemo-stability compared to the PTQ- and BBT-derived fluorophores. With finely tuned intramolecular motions and strong D-A interaction strength, TPE-BFF simultaneously exhibits high molar extinction coefficient (ε= 4.31 × 104 M-1cm-1), strong NIR-II emission (Φ = 0.49%) and photothermal effect (η = 58.5%), as well as high stability. Thanks to these merits, the thermosensitive nanoparticles constructed by integrating TPE-BFF and the antiglycolytic agent 2-deoxy-d-glucose (2DG) are successfully utilized for imaging-guided photothermal antitumor lung metastasis by regulating glycolysis and reducing ATP-dependent heat shock proteins. Combining experimental results and theoretical calculations, BFF proves to be an outstanding electron acceptor for the design of versatile NIR-II AIEgens. Overall, this study offers a promising alternative for developing multifunctional NIR-II AIEgens in biomedical applications.

Recent Advances in the Synthesis and Optical Applications of Acridine-based Hybrid Fluorescent Dyes

Acridine-based hybrid fluorescent dyes represent a category of dyes that integrate the acridine chromophore with other functional groups or materials to enhance their fluorescence properties. These dyes have garnered substantial attention across various domains, encompassing bioimaging, sensing, and optoelectronics. In recent years, researchers have directed their efforts toward fabricating acridine-based hybrid fluorescent dyes with improved water solubility, biocompatibility, and targeting capabilities. These advancements have facilitated their utilization in biological imaging applications, such as monitoring cellular processes, investigating protein-protein interactions, and detecting specific biomolecules. This review delineates the recent progress in synthesizing acridine-based hybrid fluorescent dyes and their applications in optical properties over the past decade. This review is anticipated to catalyze the development of innovative fluorescent materials featuring heightened properties and functionalities.

Visible and near-infrared light-induced photoclick reactions

Photoclick reactions combine the advantages offered by light-driven processes, that is, non-invasive and high spatiotemporal control, with classical click chemistry and have found applications ranging from surface functionalization, polymer conjugation, photocrosslinking, protein labelling and bioimaging. Despite these advances, most photoclick reactions typically require near-ultraviolet (UV) and mid-UV light to proceed. UV light can trigger undesirable responses, including cellular apoptosis, and therefore, visible and near-infrared light-induced photoclick reaction systems are highly desirable. Shifting to a longer wavelength can also reduce degradation of the photoclick reagents and products. Several strategies have been used to induce a bathochromic shift in the wavelength of irradiation-initiating photoclick reactions. For instance, the extension of the conjugated π-system, triplet-triplet energy transfer, multi-photon excitation, upconversion technology, photocatalytic and photoinitiation approaches, and designs involving photocages have all been used to achieve this goal. Current design strategies, recent advances and the outlook for long wavelength-driven photoclick reactions are presented.

Preparation of NIR-II Polymer Nanoprobe Through Twisted Intramolecular Charge Transfer and Förster Resonance Energy Transfer of NIR-I Dye

Near-infrared-II (NIR-II) fluorescence imaging is pivotal in biomedical research. Organic probes exhibit high potential in clinical translation, due to advantages such as precise structure design, low toxicity, and post-modifications convenience. In related preparation, enhancement of NIR-II tail emission from NIR-I dyes is an efficient method. In particular, the promotion of twisted intramolecular charge transfer (TICT) of relevant NIR-I dyes is a convenient protocol. However, present TICT-type probes still show disadvantages in relatively low emission, large particle sizes, or limited choice of NIR-I dyes, etc. Herein, the synthesis of stable small-sized polymer NIR-II fluoroprobes (e.g., 7.2 nm), integrating TICT and Förster resonance energy transfer process to synergistically enhance the NIR-II emission is reported. Strong enhanced emissions can be obtained from various NIR-I dyes and lanthanide elements (e.g., twelvefold at 1250 nm from Nd-DTPA/IR-808 sample). The fluorophore provides high-resolution angiography, with high-contrast imaging on middle cerebral artery occlusion model mice for distinguishing occlusion. The fluorophore can be rapidly excreted from the kidney (urine ≈65% within 4 h) in normal mice and exhibits long-term renal retention on acute kidney injury mice, showing potential applications in the prognosis of kidney diseases. This development provides an effective strategy to design and synthesize effective NIR-II fluoroprobes.

BF2-Bridged Azafulvene Dimer-Based 1064 nm Laser-Driven Superior Photothermal Agent for Deep-Seated Tumor Therapy

Small organic photothermal agents (PTAs) with absorption bands located in the second near-infrared (NIR-II, 1000-1700 nm) window are highly desirable for effectively combating deep-seated tumors. However, the rarely reported NIR-II absorbing PTAs still suffer from a low molar extinction coefficient (MEC, ϵ), inadequate chemostability and photostability, as well as the high light power density required during the therapeutic process. Herein, we developed a series of boron difluoride bridged azafulvene dimer acceptor-integrated small organic PTAs. The B-N coordination bonds in the π-conjugated azafulvene dimer backbone endow it the strong electron-withdrawing ability, facilitating the vigorous donor-acceptor-donor (D-A-D) structure PTAs with NIR-II absorption. Notably, the PTA namely OTTBF shows high MEC (7.21×104 M-1 cm-1), ultrahigh chemo- and photo-stability. After encapsulated into water-dispersible nanoparticles, OTTBF NPs can achieve remarkable photothermal conversion effect under 1064 nm irradiation with a light density as low as 0.7 W cm-2, which is the lowest reported NIR-II light power used in PTT process as we know. Furthermore, OTTBF NPs have been successfully applied for in vitro and in vivo deep-seated cancer treatments under 1064 nm laser. This study provides an insight into the future exploration of versatile D-A-D structured NIR-II absorption organic PTAs for biomedical applications.

Bioluminescent Systems for Theranostic Applications

Bioluminescence, the light produced by biochemical reactions involving luciferases in living organisms, has been extensively investigated for various applications. It has attracted particular interest as an internal light source for theranostic applications due to its safe and efficient characteristics that overcome the limited penetration of conventional external light sources. Recent advancements in protein engineering technologies and protein delivery platforms have expanded the application of bioluminescence to a wide range of theranostic areas, including bioimaging, biosensing, photodynamic therapy, and optogenetics. This comprehensive review presents the fundamental concepts of bioluminescence and explores its recent applications across diverse fields. Moreover, it discusses future research directions based on the current status of bioluminescent systems for further expansion of their potential.

Exploring flavylium-based SWIR emitters: Design, synthesis and optical characterization of dyes derivatized with polar moieties

Imaging in the shortwave infrared (SWIR, 1000-1700 nm) region is gaining traction for biomedical applications, leading to an in-depth search for fluorophores emitting at these wavelengths. The development of SWIR emitters, to be used in vivo in biological media, is mostly hampered by the considerable lipophilicity of the structures, resulting from the highly conjugated scaffold required to shift the emission to this region, that limit their aqueous solubility. In this work, we have modulated a known SWIR emitter, named Flav7, by adding hydrophilic moieties to the flavylium scaffold and we developed a new series of Flav7-derivatives, which proved to be indeed more polar than the parent compound, but still not freely water-soluble. Optical characterization of these derivatives allowed us to select FlavMorpho, a new compound with improved emission properties compared to Flav7. Encapsulation of the two compounds in micelles resulted in water-soluble SWIR emitters, with FlavMorpho micelles being twice as emissive as Flav7 micelles. The SWIR emission extent of FlavMorpho micelles proved also superior to the tail-emission of Indocyanine Green (ICG), the FDA-approved reference cyanine, in the same region, by exciting the probes at their respective absorption maxima in phosphate buffered saline (PBS) solution. The availability of optical imaging devices equipped with lasers able to excite these dyes at their maximum of absorption in the SWIR region, could pave the way for implemented SWIR imaging results.

Julolidinyl aza-BODIPYs as NIR-II fluorophores for the bioimaging of nanocarriers

The aggregation-caused quenching (ACQ) rationale has been employed to improve the fluorescence imaging accuracy of nanocarriers by precluding free probe-derived interferences. However, its usefulness is undermined by limited penetration and low spatiotemporal resolution of NIR-I (700-900 nm) bioimaging owing to absorption and diffraction by biological tissues and tissue-derived autofluorescence. This study aimed to develop ACQ-based NIR-II (1000-1700 nm) probes to further improve the imaging resolution and accuracy. The strategy employed is to install highly planar and electron-rich julolidine into the 3,5-position of aza-BODIPY based on the larger substituent effects. The newly developed probes displayed remarkable photophysical properties, with intense absorption centered at approximately 850 nm and bright emission in the 950-1300 nm region. Compared with the NIR-I counterpart P2, the NIR-II probes demonstrated superior water sensitivity and quenching stability. ACQ1 and ACQ6 exhibited more promising ACQ effects with absolute fluorescence quenching at water fractions above 40% and higher quenching stability with less than 2.0% fluorescence reillumination in plasma after 24 h of incubation. Theoretical calculations verified that molecular planarity is more important than hydrophobicity for ACQ properties. Additionally, in vivo and ex vivo reillumination studies revealed less than 2.5% signal interference from prequenched ACQ1, in contrast to 15% for P2.

Photophysics of fluorescent nanoparticles based on organic dyes - challenges and design principles

Fluorescent nanoparticles have become attractive for bioanalysis and imaging, due to their high brightness and photostability. Many different optical materials have been applied in fluorescent nanoparticles with a broad range of properties and characteristics. One appealing approach is the incorporation of molecular organic fluorophores in nanoparticles with the intention of transferring their known attractive solution-state properties directly to the nanoparticles. However, as molecular dyes are packed closely together in the nanoparticles their interactions most often result in fluorescence quenching and change in spectral properties making this approach challenging. In this perspective we will first discuss the origins of quenching and spectral shifts observed in dye based nanoparticles. On this background, we will then describe various designs of dye based NPs and how they address the challenges of dye-dye interactions and quenching. Our aim is to provide a general framework for understanding the supramolecular mechanisms that determine the photophysics of dye based nanoparticles. This framework of molecular photophysics and its relation to the internal structure of dye based nanoparticles can hopefully serve to assist rational design and optimization of new and improved dye based nanoparticles.

Hypoxic environment of wounds and photosynthesis-based oxygen therapy

The hypoxic environment is among the most important factors that complicates the healing of chronic wounds, such as venous leg ulcers, pressure injuries and diabetic foot ulcers, which seriously affects the quality of life of patients. Various oxygen supply treatments are used in clinical practice to improve the hypoxic environment at the wound site. However, problems still occur, such as insufficient oxygen supply, short oxygen infusion time and potential biosafety risks. In recent years, artificial photosynthetic systems have become a research hotspot in the fields of materials and energy. Photosynthesis is expected to improve the oxygen level at wound sites and promote wound healing because the method provides a continuous oxygen supply and has good biosafety. In this paper, oxygen treatment methods for wounds are reviewed, and the oxygen supply principle and construction of artificial photosynthesis systems are described. Finally, research progress on the photosynthetic oxygen production system to promote wound healing is summarized.

NIR-II light in clinical oncology: opportunities and challenges

Novel strategies utilizing light in the second near-infrared region (NIR-II; 900-1,880 nm wavelengths) offer the potential to visualize and treat solid tumours with enhanced precision. Over the past few decades, numerous techniques leveraging NIR-II light have been developed with the aim of precisely eliminating tumours while maximally preserving organ function. During cancer surgery, NIR-II optical imaging enables the visualization of clinically occult lesions and surrounding vital structures with increased sensitivity and resolution, thereby enhancing surgical quality and improving patient prognosis. Furthermore, the use of NIR-II light promises to improve cancer phototherapy by enabling the selective delivery of increased therapeutic energy to tissues at greater depths. Initial clinical studies of NIR-II-based imaging and phototherapy have indicated impressive potential to decrease cancer recurrence, reduce complications and prolong survival. Despite the encouraging results achieved, clinical translation of innovative NIR-II techniques remains challenging and inefficient; multidisciplinary cooperation is necessary to bridge the gap between preclinical research and clinical practice, and thus accelerate the translation of technical advances into clinical benefits. In this Review, we summarize the available clinical data on NIR-II-based imaging and phototherapy, demonstrating the feasibility and utility of integrating these technologies into the treatment of cancer. We also introduce emerging NIR-II-based approaches with substantial potential to further enhance patient outcomes, while also highlighting the challenges associated with imminent clinical studies of these modalities.

DNA Walker-Driven Mass Nanotag Assembly System for Simultaneously Profiling Dual Markers of Oxidative Stress at Different Cellular Locations

Simultaneous profiling of redox-regulated markers at different cellular sublocations is of great significance for unraveling the upstream and downstream molecular mechanisms of oxidative stress in living cells. Herein, by synchronizing dual target-triggered DNA machineries in one nanoentity, we engineered a DNA walker-driven mass nanotag (MNT) assembly system (w-MNT-AS) that can be sequentially activated by oxidative stress-associated mucin 1 (MUC1) and apurinic/apyrimidinic endonuclease 1 (APE1) from plasma membrane to cytoplasm and induce recycled assembly of MNTs for multiplex detection of the two markers by matrix-assisted laser desorption ionization mass spectrometry (MALDI MS). In the working cascade, the sensing process governs the separate activation of w-MNT-AS by MUC1 and APE1 in diverse locations, while the assembly process contributes to the parallel amplification of the ion signal of the characteristic mass tags. In this manner, the differences between MCF-7, HeLa, HepG2, and L02 cells in membrane MUC1 expression and cytoplasmic APE1 activation were fully characterized. Furthermore, the oxidative stress level and dynamics caused by exogenous H2O2, doxorubicin, and simvastatin were comprehensively demonstrated by tracking the fate of the two markers across different cellular locations. The proposed w-MNT-AS coupled MS method provides an effective route to probe multiple functional molecules that lie at different locations while participating in the same cellular event, facilitating the mechanistic studies on cellular response to oxidative stress and other disease-related cellular processes.

Experimental and theoretical comprehension of ESIPT fluorophores based on a 2-(2'-hydroxyphenyl)-3,3'-dimethylindole (HDMI) scaffold

Excited-State Intramolecular Proton Transfer (ESIPT) emission is associated with intense single or multiple fluorescence in the solid-state, along with enhanced photostability and sensitivity to the close environment. As a result, ESIPT probes are attractive candidates for ratiometric sensing of a variety of substrates. A new family of ESIPT fluorophores is described herein, inspired by the well-known 2-(2'hydroxyphenyl)benzazole (HBX) organic scaffold. The connection of 3,3'-dimethylindole (or 3H-indole) derivatives with phenol rings triggers the formation of novel 2-(2'-hydroxyphenyl)-3,3'-dimethylindole (HDMI) fluorophores, capable of stimuli-responsive ESIPT emission. This brand new family of dyes displays redshifted emission, as compared to HBX, along with an unprecedented acid/base-mediated stabilization of different rotamers, owing to supramolecular interactions with methyl groups. These compounds are therefore highly sensitive to external stimuli, such as the presence of acid or base, where protonated and deprotonated species have specific optical signatures. Moreover, a new pyridine-functionalized HDMI dye displays acid-sensitive AIE properties. The photophysical properties of all compounds have also been studied using ab initio calculations to support experiments in deciphering the nature of the various radiative transitions observed and the related excited rotameric species.

Aptasensor-encapsulating semi-permeable proteinosomes for direct target detection in non-treated biofluids

Detecting biomarkers in biofluids directly without sample treatments makes molecular diagnostics faster and more efficient. Aptasensors, the nucleic acid-based molecular biosensors, can detect a wide range of target molecules, but their susceptibility to degradation and aggregation by nucleases and charged proteins, respectively, limits their direct use in clinical samples. In this work, we demonstrate that when aptasensors are encapsulated in proteinosomes, the protein-based liposome mimics, clinically important small molecules can be sensitively and selectively detected in non-treated specimens, such as 100 % unpurified serum. As serum albumin is used to form the membrane, the nanomeshed proteinosomes become semi-permeable and antifouling, which enables exclusive admission of small molecules while blocking unwanted large proteins. Consequently, the enclosed aptasensors can maintain close-to-optimal performance for target binding, and nucleolytic degradation and electrostatic aggregation are effectively suppressed. Three different structure-switching aptamers specific for estradiol, dopamine, and cocaine, respectively, are demonstrated to fully conserve their high affinities and specificities inside the microcapsules. The shielding effect of proteinosomes is indeed exceptional; the enclosed DNA aptasensors remain completely intact over 18 h in serum and even in an extremely concentrated DNase solution (1 mg/ml, ∼300,000× the serum level). Moreover, the proteinosome-mediated compartmentalization enables independent operation of multiple aptasensors in the same mixture. Hence, simultaneous real-time sensing of two different targets is demonstrated with different operation modes, 'recording' target appearance and 'reporting' target concentration changes. This work is the first demonstration of small-molecule-specific aptasensors operating with optimal performance in serum environments and will find promising applications in molecular diagnostics.

Amplifying dual-visible-light photoswitching in aqueous media via confinement promoted triplet-triplet energy transfer

Achieving visible-light photochromism is a long-term goal of chemists keen to exploit the opportunities of molecular photoswitches in multi-disciplinary research studies. Triplet-sensitization offers a flexible approach to building diverse visible-light photoswitches using existing photochromic scaffolds, circumventing the need for sophisticated molecular design and synthesis. Unfortunately, distance-dependence and environment-sensitivity of triplet-excited species remain as key challenges that severely impair sensitization efficiency and limit their practical availability. We present herein a nature-inspired nanoconfinement strategy in which a triplet-sensitized visible-light photoswitch/sensitizer system is assembled into nanoconfined micelles (d ∼ 40 nm). A ca. 10-fold efficiency increase of triplet-triplet energy transfer for photochromism as well as an amplified fluorescence on/off contrast upon bi-directional visible-light excitation (470/560 nm) was achieved in full aqueous media. By virtue of this, the hybrid photoswitchable system is successfully applied for both flash information encryption and multiple dynamic cell imaging assays, further proving its versatility in materials and life science.

2X-Rhodamine: A Bright and Fluorogenic Scaffold for Developing Near-Infrared Chemigenetic Indicators

Chemigenetic fusion of synthetic dyes with genetically encoded protein tags presents a promising avenue for in vivo imaging. However, its full potential has been hindered by the lack of bright and fluorogenic dyes operating in the "tissue transparency" near-infrared window (NIR, 700-1700 nm). Here, we report 2X-rhodamine (2XR), a novel bright scaffold that allows for the development of live-cell-compatible, NIR-excited variants with strong fluorogenicity beyond 1000 nm. 2XR utilizes a rigidified π-skeleton featuring dual atomic bridges and functions via a spiro-based fluorogenic mechanism. This design affords longer wavelengths, higher quantum yield (ΦF = 0.11), and enhanced fluorogenicity in water when compared to the phosphine oxide-cored, or sulfone-cored rhodamine, the NIR fluorogenic benchmarks currently used. We showcase their bright performance in video-rate dynamic imaging and targeted deep-tissue molecular imaging in vivo. Notably, we develop a 2XR variant, 2XR715-HTL, an NIR fluorogenic ligand for the HaloTag protein, enabling NIR genetically encoded calcium sensing and the first demonstration of in vivo chemigenetic labeling beyond 1000 nm. Our work expands the library of NIR fluorogenic tools, paving the way for in vivo imaging and sensing with the chemigenetic approach.

Biomimetic NIR-II fluorescent proteins created from chemogenic protein-seeking dyes for multicolor deep-tissue bioimaging

Near-infrared-I/II fluorescent proteins (NIR-I/II FPs) are crucial for in vivo imaging, yet the current NIR-I/II FPs face challenges including scarcity, the requirement for chromophore maturation, and limited emission wavelengths (typically < 800 nm). Here, we utilize synthetic protein-seeking NIR-II dyes as chromophores, which covalently bind to tag proteins (e.g., human serum albumin, HSA) through a site-specific nucleophilic substitution reaction, thereby creating proof-of-concept biomimetic NIR-II FPs. This chemogenic protein-seeking strategy can be accomplished under gentle physiological conditions without catalysis. Proteomics analysis identifies specific binding site (Cys 477 on DIII). NIR-II FPs significantly enhance chromophore brightness and photostability, while improving biocompatibility, allowing for high-performance NIR-II lymphography and angiography. This strategy is universal and applicable in creating a wide range of spectrally separated NIR-I/II FPs for real-time visualization of multiple biological events. Overall, this straightforward biomimetic approach holds the potential to transform fluorescent protein-based bioimaging and enables in-situ albumin targeting to create NIR-I/II FPs for deep-tissue imaging in live organisms.

Novel nanoparticle AuNCs conjugated with Desmoglein-3 antibody for FL/CT dual-mode targeted imaging and precise treatment of lung squamous cell carcinoma

Due to lack of effective, early and non-invasive diagnostic as well as treatment tools, the surgical treatment opportunities for lung squamous cell carcinoma (SCC) are limited, resulting in high mortality rates. Therefore, the combination of targeted recognition and precise treatment of lung SCC is of great significance. In this study, a multifunctional nanoparticle is designed and synthesized, which specifically identifies lung SCC cells for target imaging and therapy. Desmoglein-3 (Dsg-3), a transmembrane glycoprotein found in desmosomes, is highly expressed in lung SCC cells. Gold nanoclusters (AuNCs) conjugated with Dsg-3 antibodies to form Au-Dsg-3 through coupling reaction. The results showed that the fluorescence imaging (FI) intensity and computed tomography (CT) signal of Au-Dsg-3 significantly increased within 6 h in vitro and in vivo, achieving dual-modal imaging to detect lung SCC effectively. Besides, Au-Dsg-3 even integrates targeted photothermal therapy (PTT) characteristics in a single nanoparticle. When exposed to near-infrared radiation (NIR), the temperature of the tumor site increased rapidly and reached a high temperature of 53.3 °C after 600 s, causing tumor ablation and growth inhibition. In summary, Au-Dsg-3 provides a key platform for targeted biological imaging and collaborative PTT, which demonstrates good performance on lung SCC.

NIR-II emissive donor-acceptor-donor fluorophores for dual fluorescence bioimaging and photothermal therapy applications

Fluorescence bioimaging with near-infrared II (NIR-II) emissive organic fluorophores has proven to be a viable noninvasive diagnostic technique. However, there is still the need for the development of fluorophores that possess increased stability as well as functionalities that impart stimuli responsiveness. Through strategic design, we can synthesize fluorophores that possess not only NIR-II optical profiles but also pH-sensitivity and the ability to generate heat upon irradiation. In this work, we employ a donor-acceptor-donor (D-A-D) design to synthesize a series of NIR-II fluorophores. Here we use thienothiadiazole (TTD) as the acceptor, 3-hexylthiophene (HexT) as the π-spacer and vary the alkyl amine donor units: N,N-dimethylaniline (DMA), phenylpiperidine (Pip), and phenylmorpholine (Morp). Spectroscopic analysis shows that all three derivatives exhibit emission in the NIR-II region with λemimax ranging from 1030 to 1075 nm. Upon irradiation, the fluorophores exhibited noticeable heat generation through non-radiative processes. The ability to generate heat indicates that these fluorophores will act as theranostic (combination therapeutic and diagnostic) agents in which simultaneous visualization and treatment can be performed. Additionally, biosensing capabilities were supported by changes in the absorbance properties while under acidic conditions as a result of protonation of the alkyl amine donor units. The fluorophores also show minimal toxicity in a human mammary cell line and with murine red blood cells. Overall, initial results indicate viable NIR-II materials for multiple biomedical applications.

Ytterbium 10-carboxyperylene-3,4,9-tricarboxylates for targeted NIR luminescent bioimaging

Two new ytterbium coordination compounds Yb(HPTC)(H2O)2 (Yb1) and Yb(HPTC)(Phen) (Yb2) were obtained using 10-carboxyperylene-3,4,9-tricarboxylate ion (HPTC3-) as a sensitizer. Both coordination compounds exhibited intense NIR-II luminescence upon excitation in the visible range and formed stable suspensions with nanoparticles of 50-70 nm in size in an aqueous solution of sodium alginate. Both complexes demonstrated non-toxicity up to at least 25 mg L-1 in two cell cultures: cancer cells MCF7 and embryonic cells HEK293T - making them suitable for bioimaging. For both complexes, the accumulation in cells was directly measured and it was shown that the accumulation of Yb2 was the same for both cell types (0.51-0.52 πg per cell), while Yb1 demonstrated selective accumulation in cancer cells (0.04 πg per cell for HEK293T and 7.00 πg per cell for MCF7). Thus, Yb1 can also be proposed as a selective vis-excited NIR emitting bioprobe.

Molecular Engineering of Bright NIR-I/NIR-II Nanofluorophores for High-Resolution Bioimaging and Tumor Detection in Vivo

A comprehensive approach for the construction of NIR-I/NIR-II nanofluorophores with exceptional brightness and excellent chemo- and photostability has been developed. This study first confirmed that the amphiphilic molecules with stronger hydrophobic moieties and weaker hydrophilic moieties are superior candidates for constructing brighter nanofluorophores, which are attributed to its higher efficiency in suppressing the intramolecular charge transfer/aggregation-caused fluorescence quenching of donor-acceptor-donor type fluorophores. The prepared nanofluorophore demonstrates a fluorescence quantum yield exceeding 4.5% in aqueous solution and exhibits a strong NIR-II tail emission up to 1300 nm. The superior performance of the nanofluorophore enabled the achievement of high-resolution whole-body vessel imaging and brain vessel imaging, as well as high-contrast fluorescence imaging of the lymphatic system in vivo. Furthermore, their potential for highly sensitive fluorescence detection of tiny tumors in vivo has been successfully confirmed, thus supporting their future applications in precise fluorescence imaging-guided surgery in the early stages of cancer.

A flavonol-labelled cellulose fluorescent probe combined with composite fluorescent film imaging and smartphone technology for the detection of Fe3

Fe3+ is one of the most widely distributed and abundant elements on earth. Realizing efficient and real-time monitoring of Fe3+ is of great significance for the natural environment and the health of living organisms. In this paper, a flavonol-labelled cellulose-based fluorescent probe (ACHM) was synthesized by using dialdehyde cellulose (DAC) as the backbone and combining with flavonol derivatives (AHM - 1). The mechanism of recognizing Fe3+ was verified by characterizing the structure of ACHM by NMR, HRMS (High Resolution Mass Spectrometry), FTIR (Fourier Transform Infrared Spectroscopy), XRD (X-ray Diffraction), TG (Thermogravimetry) and SEM (Scanning Electron Microscopy). The H2O solution of the probe ACHM showed good fluorescence properties. It has quenching fluorescence properties for Fe3+, with a low limit of detection (LOD) of 0.10 μM and a fast response time of only 20 s. In addition, in order to expand the application range of the probe, ACHM was prepared as a fluorescent composite film with an average tensile strength of 32.9 MPa and an average elongation at break of 3.39 %. It shows its superiority in mechanical properties. The probe also demonstrated its practical application value for detecting Fe3+ in smartphone imaging applications.

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.

A Mitochondria-Targeted NIR-II Molecule Fluorophore for Precise Cancer Phototheranostics

Subcellular organelle mitochondria are becoming a key player and a driver of cancer. Mitochondrial targeting phototheranostics has attracted increasing attention for precise cancer therapy. However, those phototheranostic systems still face great challenges, including complex and multiple components, light scattering, and insufficient therapeutic efficacy. Herein, a molecular fluorophore IR-TPP-1100 was tactfully designed by molecular engineering for mitochondria-targeted fluorescence imaging-guided phototherapy in the second near-infrared window (NIR-II). IR-TPP-1100 not only exhibited prominent photophysical properties and high photothermal conversion efficiency but also achieved excellent mitochondria-targeting ability. The mitochondria-targeting IR-TPP-1100 enabled NIR-II fluorescence and photoacoustic dual-modality imaging of mitochondria at the organism level. Moreover, it integrated photothermal and photodynamic therapy, obtaining remarkable tumor therapeutic efficacy by inducing mitochondrial apoptosis. These results indicate that IR-TPP-1100 has great potential for precise cancer therapy and provides a promising strategy for developing mitochondria-targeting NIR-II phototheranostic agents.

NIR-II organic small molecule probe for labeling lymph nodes and guiding tumor imaging

Organic small molecule fluorescent groups have injected new material support into the field of medical imaging due to their unique luminescence mechanism and easy tuning of structure. The great potential of NIR-II window imaging forces us to continuously optimize the structure of organic fluorophores to design better fluorescent molecules for fluorescence imaging-guided surgery. An ideal organic small molecule fluorescent group: it can penetrate into the inside of the organism, clearly present the internal structure and the edge contour of different tissues, so as to perfectly achieve internal imaging and accurately guide external surgery. In vivo, fluorescent groups do not damage normal tissues and organs. However, problems such as low quantum yield and poor biocompatibility greatly limit the clinical transformation of NIR-II fluorescent small molecules. To avoid the shortcomings of NIR-II fluorescent probes as much as possible and better realize image-guided surgery, in this experiment, the biplane donor unit was incorporated into the twisted D-π-A-π-D structure to expand the conjugated structure of the fluorescent group, which not only realized NIR-II emission, but also had high quantum yield and biosafety.

HSA-ZW800-PEG for Enhanced Optophysical Stability and Tumor Targeting

Small molecule fluorophores often face challenges such as short blood half-life, limited physicochemical and optical stability, and poor pharmacokinetics. To overcome these limitations, we conjugated the zwitterionic near-infrared fluorophore ZW800-PEG to human serum albumin (HSA), creating HSA-ZW800-PEG. This conjugation notably improves chemical, physical, and optical stability under physiological conditions, addressing issues commonly encountered with small molecules in biological applications. Additionally, the high molecular weight and extinction coefficient of HSA-ZW800-PEG enhances biodistribution and tumor targeting through the enhanced permeability and retention effect. The unique distribution and elimination dynamics, along with the significantly extended blood half-life of HSA-ZW800-PEG, contribute to improved tumor targetability in both subcutaneous and orthotopic xenograft tumor-bearing animal models. This modification not only influences the pharmacokinetic profile, affecting retention time and clearance patterns, but also enhances bioavailability for targeting tissues. Our study guides further development and optimization of targeted imaging agents and drug-delivery systems.

Deep-red photoluminescent mechanoresponsive polymers with dynamic CuI-arylamide mechanophores

We demonstrate the use of copper arylamide complexes as efficient photoluminescent mechanophores to design deep-red/near-IR emissive polymers showing reversible changes in photoluminescence intensity in the red/near-IR region in response to mechanical stretching. The mechanoresponse was repeatable over 30 cycles, showing a measurable increase of photoluminescence intensity even at a small applied stress of ca. 0.01 MPa. We demonstrate the potential of using conformationally dynamic copper amide complexes as sensitive and reversible mechanophores for near-IR imaging; systematic control over the emission range was achieved using amide modification.

An Extended NIR-II Superior Imaging Window from 1500 to 1900 nm for High-Resolution In Vivo Multiplexed Imaging Based on Lanthanide Nanocrystals

High-resolution in vivo optical multiplexing in second near-infrared window (NIR-II, 1000-1700 nm) is vital to biomedical research. Presently, limited by bio-tissue scattering, only luminescent probes located at NIR-IIb (1500-1700 nm) window can provide high-resolution in vivo multiplexed imaging. However, the number of available luminescent probes in this narrow NIR-IIb region is limited, which hampers the available multiplexed channels of in vivo imaging. To overcome the above challenges, through theoretical simulation we expanded the conventional NIR-IIb window to NIR-II long-wavelength (NIR-II-L, 1500-1900 nm) window on the basis of photon-scattering and water-absorption. We developed a series of novel lanthanide luminescent nanoprobes with emission wavelengths from 1852 nm to 2842 nm. NIR-II-L nanoprobes enabled high-resolution in vivo dynamic multiplexed imaging on blood vessels and intestines, and provided multi-channels imaging on lymph tubes, tumors and intestines. The proposed NIR-II-L probes without mutual interference are powerful tools for high-contrast in vivo multiplexed detection, which holds promise for revealing physiological process in living body.

Near-Infrared II Hemicyanine Dye with Large Stokes Shift Designed by TICT Regulation for Boosting Imaging-Guided Photothermal Therapy

The serious threat that cancer poses to human health highlights the significance of early detection and effective treatment. The integration of fluorescence diagnosis and photothermal therapy in NIR-II has gained attention due to its high sensitivity, fast response, and noninvasiveness. Fluorescence, produced by the radiative relaxation process of electrons in a molecule, and photothermal, generated by the nonradiative relaxation process of electrons in a molecule, are competing photophysical processes. Hence, it is a challenge for the molecule to balance between the properties of fluorescence and photothermal. In this study, a NIR-II hemicyanine with TICT character is designed to obtain molecules with both better fluorescence and photothermal properties, utilizing positively charged pyridine salt and triphenylamine as electron acceptor and donor, respectively, and oxole as the conjugated π-bridge. HCY-995, one of the synthesized compounds, has a quantum yield of 0.09%, photothermal conversion efficiency of 54.90%, and a significant Stoke shift of 232 nm, which makes it appropriate for the integration of photothermal therapy and high-resolution imaging. This study provides new insights into the development of NIR-II molecules with fluorescent and photothermal integrated properties.

Ultra-Bright Heptamethine Dye Clusters Based on a Self-Adaptive Co-Assembly Strategy for NIR-IIb Biomedical Imaging

Despite the wide range of applications of bright NIR-II polymethine scaffolds in biomedical imaging, their solvatochromism and aggregation-caused quenching (ACQ) effects in aqueous solutions limit their inherent brightness using traditional encapsulation methods, and effective hydrophilization strategies are still scarce. Here, a new set of Flav dyes is synthesized and PEGylated, followed by manufacturing DSPE@FlavP2000 nanoparticles using a self-adaptive co-assembly strategy to overcome these limitations. FlavP2000 can autonomously adjust its conformation when co-assembled with DSPE-PEG2000 , resulting in high-efficiency luminescence (≈44.9% fluorescence of Flav in DMSO). DSPE@FlavP2000 enables NIR-IIb (>1500 nm) angiography with high signal-to-noise ratios. Notably, this co-assembly can occur in situ between FlavP2000 with proteins in the living body based on a novel mechanism of brightness activation induced by disassembly (BAD), achieving consistent brightness as DSPE@FlavP2000 in blood or serum. The self-adaptive co-assembly strategy can be enhanced by incorporating an IPA moiety, which dynamically binds to albumin to prolong the dye's blood circulation time. Thus, the "enhanced" BAD is successfully applied to long-term vascular imaging and sciatic nerve imaging. Both the self-adaptive co-assembly strategy and BAD phenomenon improve the selectivity and availability of the hydrophilization methods, paving the way for efficient biological applications of polymethine dyes.

Comprehensive advances in the synthesis, fluorescence mechanism and multifunctional applications of red-emitting carbon nanomaterials

Red emitting fluorescent carbon nanomaterials have drawn significant scientific interest in recent years due to their high quantum yield, water-dispersibility, photostability, biocompatibility, ease of surface functionalization, low cost and eco-friendliness. The red emissive characteristics of fluorescent carbon nanomaterials generally depend on the carbon source, reaction time, synthetic approach/methodology, surface functional groups, average size, and other reaction environments, which directly or indirectly help to achieve red emission. The importance of several factors to achieve red fluorescent carbon nanomaterials is highlighted in this review. Numerous plausible theories have been explained in detail to understand the origin of red fluorescence and tunable emission in these carbon-based nanostructures. The above advantages and fluorescence in the red region make them a potential candidate for multifunctional applications in various current fields. Therefore, this review focused on the recent advances in the synthesis approach, mechanism of fluorescence, and electronic and optical properties of red-emitting fluorescent carbon nanomaterials. This review also explains the several innovative applications of red-emitting fluorescent carbon nanomaterials such as biomedicine, light-emitting devices, sensing, photocatalysis, energy, anticounterfeiting, fluorescent silk, artificial photosynthesis, etc. It is hoped that by choosing appropriate methods, the present review can inspire and guide future research on the design of red emissive fluorescent carbon nanomaterials for potential advancements in multifunctional applications.

Advancement of Near Infrared-II Organic Dyes in Bioimaging

In recent decades, small organic compounds having absorption and fluorescence emission in the second near-infrared (NIR-II, 1000-1700 nm) bio-window have attracted a lot of interest. Fluorescence bioimaging may be used by researchers and surgeons to genomically focus an array of biological areas and functions. The near-infrared-II (NIR-II) dye which has fluorescent imaging, bypasses the visible imaging striking barrier, making it a valuable tool for cancer early detection and very sensitive tumor resection. It can generate sub-cellular density scanning data directly and has been applied to biological and medical detection and therapy. This paper discusses the history and current state of theranostics and biosensing uses of NIR-II tiny organic producers depending on multiple skeletons. For biological imaging, organic dyes are extensively used as markers for near-infrared (NIR) fluorescent though the issue lies in instability and hydrophobicity for bio environment which is a major restriction for its utilization. Various conjugation with the probes is also adopted in order to increase the biosensing power and efficiency and to deduct their level of cytotoxicity. Some of these combinations are discussed in the paper including supramolecule usage, combining the probes with quantum dots, and an alloy of gold selenium. NIR-II fluorescence devices are also used in combination with confocal microscopy to study the cytological interaction of proteins. Several research papers stated using cell membrane enhancement units empowered with oxazolepyridine and coumarin compounds. As the need for bioimaging increases decade by decade these cons of using organic dyes alone are getting overlapped by compounding these dyes with materials that help in better penetration, bioavailability, and reduction in areas of toxicity.

"Dual-Key-and-Lock" NIR-II NSCyanines Enable High-Contrast Activatable Phototheranostics in Extrahepatic Diseases

Conventional cyanine dyes with a symmetric structure are "always-on", which can easily accumulate in the liver and display high liver background fluorescence, inevitably interfering the accurate diagnosis and therapy in extrahepatic diseases. We herein report a platform of NIR-II non-symmetric cyanine (NSCyanine) dyes by harnessing a non-symmetric strategy, which are extremely sensitive to pH/viscosity and can be activated via a "dual-key-and-lock" strategy. These NSCyanine dyes with a low pKa (<4.0) only show weak fluorescence at lysosome pH (key1), however, the fluorescence can be completely switched on and significantly enhanced by intracellular viscosity (key2) in disease tissues, exhibiting high target-to-liver ratios up to 19.5/1. Notably, high-contrast phototheranostics in extrahepatic diseases are achieved, including intestinal metastasis-imaging, acute gastritis-imaging, bacteria infected wound healing, and tumor ablation via targeted combined photothermal therapy and chemotherapy.

Delineation and detection of breast cancer using novel label-free fluorescence

BACKGROUND

Accurate diagnosis of breast cancer (BC) plays a crucial role in clinical pathology analysis and ensuring precise surgical margins to prevent recurrence.

METHODS

Laser-induced fluorescence (LIF) technology offers high sensitivity to tissue biochemistry, making it a potential tool for noninvasive BC identification. In this study, we utilized hyperspectral (HS) imaging data of stimulated BC specimens to detect malignancies based on altered fluorescence characteristics compared to normal tissue. Initially, we employed a HS camera and broadband spectrum light to assess the absorbance of BC samples. Notably, significant absorbance differences were observed in the 440-460 nm wavelength range. Subsequently, we developed a specialized LIF system for BC detection, utilizing a low-power blue laser source at 450 nm wavelength for ten BC samples.

RESULTS

Our findings revealed that the fluorescence distribution of breast specimens, which carries molecular-scale structural information, serves as an effective marker for identifying breast tumors. Specifically, the emission at 561 nm exhibited the greatest variation in fluorescence signal intensity for both tumor and normal tissue, serving as an optical predictive biomarker. To enhance BC identification, we propose an advanced image classification technique that combines image segmentation using contour mapping and K-means clustering (K-mc, K = 8) for HS emission image data analysis.

CONCLUSIONS

This exploratory work presents a potential avenue for improving "in-vivo" disease characterization using optical technology, specifically our LIF technique combined with the advanced K-mc approach, facilitating early tumor diagnosis in BC.

NIR-II Nanoprobes: A Review of Components-Based Approaches to Next-Generation Bioimaging Probes

Fluorescence and photoacoustic imaging techniques offer valuable insights into cell- and tissue-level processes. However, these optical imaging modalities are limited by scattering and absorption in tissue, resulting in the low-depth penetration of imaging. Contrast-enhanced imaging in the near-infrared window improves imaging penetration by taking advantage of reduced autofluorescence and scattering effects. Current contrast agents for fluorescence and photoacoustic imaging face several limitations from photostability and targeting specificity, highlighting the need for a novel imaging probe development. This review covers a broad range of near-infrared fluorescent and photoacoustic contrast agents, including organic dyes, polymers, and metallic nanostructures, focusing on their optical properties and applications in cellular and animal imaging. Similarly, we explore encapsulation and functionalization technologies toward building targeted, nanoscale imaging probes. Bioimaging applications such as angiography, tumor imaging, and the tracking of specific cell types are discussed. This review sheds light on recent advancements in fluorescent and photoacoustic nanoprobes in the near-infrared window. It serves as a valuable resource for researchers working in fields of biomedical imaging and nanotechnology, facilitating the development of innovative nanoprobes for improved diagnostic approaches in preclinical healthcare.

Synthesis and Characterization of Novel Thienothiadiazole-Based D-π-A-π-D Fluorophores as Potential NIR Imaging Agents

As fluorescence bioimaging has increased in popularity, there have been numerous reports on designing organic fluorophores with desirable properties amenable to perform this task, specifically fluorophores with emission in the near-infrared II (NIR-II) region. One such strategy is to utilize the donor-π-acceptor-π-donor approach (D-π-A-π-D), as this allows for control of the photophysical properties of the resulting fluorophores through modulation of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels. Herein, we illustrate the properties of thienothiadiazole (TTD) as an effective acceptor moiety in the design of NIR emissive fluorophores. TTD is a well-known electron-deficient species, but its use as an acceptor in D-π-A-π-D systems has not been extensively studied. We employed TTD as an acceptor unit in a series of two fluorophores and characterized the photophysical properties through experimental and computational studies. Both fluorophores exhibited emission maxima in the NIR-I that extends into the NIR-II. We also utilized electron paramagnetic resonance (EPR) spectroscopy to rationalize differences in the measured quantum yield values and demonstrated, to our knowledge, the first experimental evidence of radical species on a TTD-based small-molecule fluorophore. Encapsulation of the fluorophores using a surfactant formed polymeric nanoparticles, which were studied by photophysical and morphological techniques. The results of this work illustrate the potential of TTD as an acceptor in the design of NIR-II emissive fluorophores for fluorescence bioimaging applications.

Extended BODIPYs as Red-NIR Laser Radiation Sources with Emission from 610 nm to 750 nm

Herein, we report the synthetic access to a set of π-extended BODIPYs featuring a penta-arylated (phenyl and/or thiophene) dipyrrin framework. We take advantage of the full chemoselective control of 8-methylthio-2,3,5,6-tetrabromoBODIPY when we conduct the Liebeskind-Srogl cross-coupling (LSCC) to functionalize exclusively the meso-position, followed by the tetra-Suzuki reaction to arylate the halogenated sites. All these laser dyes display absorption and emission bands in the red edge of the visible spectrum reaching the near-infrared with thiophene functionalization. The emission efficiency, both fluorescence and laser, of the polyphenylBODIPYs can be enhanced upon decoration of the peripheral phenyls with electron donor/acceptor groups at para positions. Alternatively, the polythiopheneBODIPYs show an astonishing laser performance despite the charge transfer character of the emitting state. Therefore, these BODIPYs are suitable as a palette of stable and bright laser sources covering the spectral region from 610 nm to 750 nm.

A biodegradable, flexible photonic patch for in vivo phototherapy

Diagnostic and therapeutic illumination on internal organs and tissues with high controllability and adaptability in terms of spectrum, area, depth, and intensity remains a major challenge. Here, we present a flexible, biodegradable photonic device called iCarP with a micrometer scale air gap between a refractive polyester patch and the embedded removable tapered optical fiber. ICarP combines the advantages of light diffraction by the tapered optical fiber, dual refractions in the air gap, and reflection inside the patch to obtain a bulb-like illumination, guiding light towards target tissue. We show that iCarP achieves large area, high intensity, wide spectrum, continuous or pulsatile, deeply penetrating illumination without puncturing the target tissues and demonstrate that it supports phototherapies with different photosensitizers. We find that the photonic device is compatible with thoracoscopy-based minimally invasive implantation onto beating hearts. These initial results show that iCarP could be a safe, precise and widely applicable device suitable for internal organs and tissue illumination and associated diagnosis and therapy.

Molecular-Based FRET Nanosensor with Dynamic Ratiometric NIR-IIb Fluorescence for Real-Time In Vivo Imaging and Sensing

Real-time fluorescence sensing can provide insight into biodynamics. However, few fluorescent tools are available to overcome the tissue scattering and autofluorescence interference for high-contrast in vivo sensing with high spatiotemporal resolution. Here, we develop a molecular-based FRET nanosensor (MFN) capable of producing a dynamic ratiometric NIR-IIb (1500-1700 nm) fluorescence signal under a frequency-modulated dual-wavelength excitation bioimaging system. The MFN provides reliable signals in highly scattering tissues and enables in vivo real-time imaging at micrometer-scale spatial resolution and millisecond-scale temporal resolution. As a proof of concept, a physiological pH-responsive nanosensor (MFN_pH) was designed as a nanoreporter for intravital real-time monitoring of the endocytosis dynamics of nanoparticles in the tumor microenvironment. We also show that MFN_pH allows the accurate quantification of pH changes in a solid tumor through video-rate ratiometric imaging. Our study offers a powerful approach for noninvasive imaging and sensing of biodynamics with micrometer-scale spatial resolution and millisecond-scale temporal resolution.

Dual Behavior Regulation: Tether-Free Deep-Brain Stimulation by Photothermal and Upconversion Hybrid Nanoparticles

Optogenetics has been plagued by invasive brain implants and thermal effects during photo-modulation. Here, two upconversion hybrid nanoparticles modified with photothermal agents, named PT-UCNP-B/G, which can modulate neuronal activities via photostimulation and thermo-stimulation under near-infrared laser irradiation at 980 nm and 808 nm, respectively, are demonstrated. PT-UCNP-B/G emits visible light (410-500 nm or 500-570 nm) through the upconversion process at 980 nm, while they exhibit efficient photothermal effect at 808 nm with no visible emission and tissue damage. Intriguingly, PT-UCNP-B significantly activates extracellular sodium currents in neuro2a cells expressing light-gated channelrhodopsin-2 (ChR2) ion channels under 980-nm irradiation, and inhibits potassium currents in human embryonic kidney 293 cells expressing the voltage-gated potassium channels (KCNQ1) under 808-nm irradiation in vitro. Furthermore, deep-brain bidirectional modulation of feeding behavior is achieved under tether-free 980 or 808-nm illumination (0.8 W cm^-2 ) in mice stereotactically injected with PT-UCNP-B in the ChR2-expressing lateral hypothalamus region. Thus, PT-UCNP-B/G creates new possibility of utilizing both light and heat to modulate neural activities and provides a viable strategy to overcome the limits of optogenetics.