A Unique Class of Near-Infrared Functional Fluorescent Dyes with Carboxylic-Acid-Modulated Fluorescence ON/OFF Switching: Rational Design, Synthesis, Optical Properties, Theoretical Calculations, and Applications for Fluorescence Imaging in Living Animals

Computational Biomaterials: Computational Simulations for Biomedicine

With the flourishing development of material simulation methods (quantum chemistry methods, molecular dynamics, Monte Carlo, phase field, etc.), extensive adoption of computing technologies (high-throughput, artificial intelligence, machine learning, etc.), and the invention of high-performance computing equipment, computational simulation tools have sparked the fundamental mechanism-level explorations to predict the diverse physicochemical properties and biological effects of biomaterials and investigate their enormous application potential for disease prevention, diagnostics, and therapeutics. Herein, the term "computational biomaterials" is proposed and the computational methods currently used to explore the inherent properties of biomaterials, such as optical, magnetic, electronic, and acoustic properties, and the elucidation of corresponding biological behaviors/effects in the biomedical field are summarized/discussed. The theoretical calculation of the physiochemical properties/biological performance of biomaterials applied in disease diagnosis, drug delivery, disease therapeutics, and specific paradigms such as biomimetic biomaterials is discussed. Additionally, the biosafety evaluation applications of theoretical simulations of biomaterials are presented. Finally, the challenges and future prospects of such computational simulations for biomaterials development are clarified. It is anticipated that these simulations would offer various methodologies for facilitating the development and future clinical translations/utilization of versatile biomaterials.

Single-atom engineering of hemicyanine and its amphiphilic derivative for optimized near infrared phototheranostics

Near-infrared (NIR) dyes are widely used in the field of in vivo phototheranostics. Hemicyanine dyes (HDs) have recently received tremendous attention due to their easy synthesis and excellent NIR features. However, HDs can easily form non-fluorescent aggregates and their potential for phototherapy still needs further exploration due to their poor ability to generate reactive oxygen species (ROS). Herein, a series of hemicyanine dyes with different chalcogen atom (O, S, Se) substitutions were constructed to achieve optimized potential for phototheranostics. By replacing O with the heavy atom Se in the xanthene skeleton, CySe-NEt₂ showed much more favourable features such as extended NIR absorption/emission wavelength, boosted ¹O₂ generation rate and higher photothermal effect. In addition, a poly(ethylene glycol) (PEG) group was introduced into the scaffold and yielded a nanotheranostic agent CySe-mPEG_5K, which easily formed nanoparticles with appealing features such as excellent photostability, effective prevention of unpleasant H-aggregation, fast/selective tumor accumulation and minimum dark toxicity. Solid tumor growth was significantly suppressed through combined photodynamic therapy (PDT) and photothermal therapy (PTT) guided by NIR fluorescence (NIRF) and photoacoustic (PA) imaging. This study not only presents the first example of selenium-substituted hemicyanine dyes, but also offers a reliable design strategy for the development of potent NIR phototheranostic agents with multi-mode imaging-guided combination therapeutic ability.

Family of hNQO1 Activatable Near-Infrared Fluoro-Photoacoustic Probes for Diagnosis of Wound Infection and Ulcerative Colitis

Bacterial infections can easily occur when patients mishandle wounds or eat moldy food. The prompt diagnosis of a bacterial infection could effectively reduce the risk of possible anatomical damage. However, non-invasive early detection of bacterial infections is difficult to achieve due to the lack of favorable tools. Here, we designed two hNQO1 fluorescent probes (RX2 and RX3) to visualize bacterial infection after deep learning on the pathogenesis of bacterial infection. RX2 and RX3 enable early detection of bacterial infection and are verified to be, respectively, suitable for fluorescence imaging (FLI) and photoacoustic imaging (PAI) by comparing the signal-to-background ratio of both probes in a mouse model of myositis caused by Escherichia coli infection. In view of the difference in penetration depth between the two imaging modalities, we further applied RX2 for FLI of E. coli-infected wounds and RX3 for PAI of E. coli-infected inflammatory bowel disease, suggesting the great potential of both probes for early diagnosis of bacterial infections.

Rational Design of Asymmetric Polymethines to Attain NIR(II) Bioimaging at >1100 nm

Organic molecules having emission in the NIR(II) region are emergent and receiving enormous attention. Unfortunately, attaining accountable organic emission intensity around the NIR(II) region is hampered by the dominant internal conversion operated by the energy gap law, where the emission energy gap and the associated internal reorganization energy λ_int play key roles. Up to the current stage, the majority of the reported organic NIR(II) emitters belong to those polymethines terminated by two symmetric chromophores. Such a design has proved to have a small λ_int that greatly suppresses the internal conversion. However, the imposition of symmetric chromophores is stringent, limiting further development of organic NIR(II) dyes in diversity and versatility. Here, we propose a new concept where as far as the emissive state of the any asymmetric polymethines contains more or less equally transition density between two terminated chromophores, λ_int can be as small as that of the symmetric polymethines. To prove the concept, we synthesize a series of new polymethines terminated by xanthen-9-yl-benzoic acid and 2,4-diphenylthiopyrylium derivatives, yielding AJBF1112 and AEBF1119 that reveal emission peak wavelength at 1112 and 1119 nm, respectively. The quantum yield is higher than all synthesized symmetric polymethines of 2,4-diphenylthiopyrylium derivatives (SC1162, 1182, 1185, and 1230) in this study. λ_int were calculated to be as small as 6.2 and 7.3 kcal/mol for AJBF1112 and AEBF1119, respectively, proving the concept. AEBF1119 was further prepared as a polymer dot to demonstrate its in vitro specific cellular imaging and in vivo tumor/bone targeting in the NIR(II) region.

A biotin-guided near-infrared fluorescent probe for imaging hydrogen sulfide and differentiating cancer cells

Imaging cancer specific biomarkers with near-infrared (NIR) fluorescent probes can help inaccurate diagnosis. Hydrogen sulfide (H₂S) has been reported to be involved in many physiological and pathological processes and is considered as one of the key gasotransmitters during the development of cancer. To achieve specific H₂S detection in cancer cells, we reported a biotin-guided NIR fluorescent sensor P1 targeting a cancer cell surface biomarker, based on the H₂S-specific thiolysis of the NBD-amine-hemicyanine conjugate. The probe showed a fast turn-on signal at 754 nm upon H₂S activation and good selectivity towards H₂S over millimolar levels of other biothiols. We successfully employed P1 to image endogenous H₂S and demonstrated its tumor-targeting ability in live cells. P1 could differentiate multiple cancer cells with various levels of H₂S from normal cells, indicating its potential for cancer imaging.

Rational design of pH-activated upconversion luminescent nanoprobes for bioimaging of tumor acidic microenvironment and the enhancement of photothermal therapy

The development of effective and safe tumor photothermal therapeutic strategies has attracted considerable attention. Herein, we synthesized tumor microenvironment (TME)-activatable self-assembling organic nanotheranostics (NRhD-PEG-X NPs (X = 1, 2, 3, and 4)) for precise tumor targeting and upconversion image-guided photothermal therapy (PTT). The amphiphilic polymer NRhD-PEG-X consisted of upconversion luminescent probes (NRhD) modified with polyethylene glycol (PEG) of various lengths. The continuous external irradiation-free photothermal NRhD-PEG-4 NPs with pKa 6.70 displayed high sensitivity and selectivity to protons, resulting in the turn-on upconversion luminescence and enhanced photothermal properties in the acidic TME without asynchronous therapy and side effects. This nanotheranostic offers acidic activatability, tumor targetability, and PTT enhancement, thus allowing autofluorescence-free upconversion luminescent imaging-guided precision PTT. Our strategy affords a paradigm to develop activatable theranostic nanoplatforms for precision medicine. STATEMENT OF SIGNIFICANCE: As a hyperthermia-based treatment, activatable photothermal therapy (PTT) is highly significant in tumor treatment. Herein, we develop acidic tumor microenvironment-activatable nanotheranostics for upconversion luminescent imaging-guided diagnosis and precision tumor-targeted PTT. PEGylation of upconversion dyes not only could self-assemble to yield organic nanoparticles in water, but it could also significantly improve biocompatibility, stability, and circulation time and tune significantly the pKa value of nanoparticles. In an acidic tumor microenvironment, NRhD-PEG-4 NPs with pKa 6.70 show high sensitivity to release NRhDH⁺-PEG-4 NPs, which exhibit good upconversion luminescence and enhanced photothermal effect. Therefore, upconversion luminescence imaging-guided precision PTT has high potential to enhance cancer diagnostic and therapeutic efficiency.

Design strategies and applications of smart optical probes in the second near-infrared window

Over the last decade, a series of synergistic advances in the synthesis chemistries and imaging instruments have largely boosted a significant revolution, in which large-scale biomedical applications are now benefiting from optical bioimaging in the second near-infrared window (NIR-II, 1000-1700 nm). The large tissue penetration and limited autofluorescence associated with long-wavelength imaging improve translational potential of NIR-II imaging over common visible-light (400-650 nm) and NIR-I (750-900 nm) imaging, with ongoing profound effects on the studies of precision medicine. Unfortunately, the majority of NIR-II probes are designed as "always-on" luminescent imaging contrasts, continuously generating unspecific signals regardless of whether they reach pathological locations. Thus, in vivo imaging by traditional NIR-II probes usually suffers from weak detect precision due to high background noise. In this context, the advances of optical imaging now enter into an era of precise control of NIR-II photophysical kinetics. Developing NIR-II optical probes that can efficiently activate their luminescent signal in response to biological targets of interest and substantially suppress the background interferences have become a highly prospective research frontier. In this review, the merits and demerits of optical imaging probes from visible-light, NIR-I to NIR-II windows are carefully discussed along with the lens of stimuli-responsive photophysical kinetics. We then highlight the latest development in engineering methods for designing smart NIR-II optical probes. Finally, to appreciate such advances, challenges and prospect in rapidly growing study of smart NIR-II probes are addressed in this review.

Evolving an Ultra-Sensitive Near-Infrared β-Galactosidase Fluorescent Probe for Breast Cancer Imaging and Surgical Resection Navigation

Early diagnosis and therapy are clinically crucial in decreasing mortality from breast carcinoma. However, the existing probes have difficulty in accurately identifying the margins and contours of breast carcinoma due to poor sensitivity and specificity. There is an urgent need to develop high-sensitive fluorescent probes for the diagnosis of breast carcinoma and for differentiating tumors from normal tissues during surgery. β-Galactosidase is a significant biomarker, whose overexpression is closely associated with the progression of breast tumors. Herein, we have constructed a β-galactosidase-activated fluorescent probe NIR-βgal-2 through rational design and molecular docking engineering simulations. The probe displayed superior sensitivity (detection limit = 2.0 × 10^-3 U/mL), great affinity (K_m = 1.84 μM), and catalytic efficiency (k_cat/K_m = 0.24 μM^-1 s^-1) for β-galactosidase. Leveraging this probe, we demonstrated the differentiation of cancer cells overexpressing β-galactosidase from normal cells and then applied the probe for intraoperative guided excision of breast tumors. Moreover, we exhibited the application of NIR-βgal-2 for the successful resection of orthotopic breast tumors by "in situ spraying" and monitored a good prognostic recovery. This work may promote the application of enzyme-activated near-infrared fluorescent probes for the development of carcinoma diagnosis and image-guided surgery.

A pyridyl functionalized rhodamine chemodosimeter for selective fluorescent detection of mercury ions and cell imaging

Rhodamines gain sustained attention owing to their great potential for probe design applications. Herein, the facile preparation of a new pyridyl functionalized rhodamine dye PR is reported, which has stable fluorescence signal in water with maximum emission peak at 594 nm and Stokes shift of 81 nm. Based on dye PR, a new fluorescent probe PRHg has been developed by modifying the spirolactone of PR with hydrazine hydrate so as to produce spirolactam recognizing group for sensing of Hg²⁺. PRHg exhibits high selectivity and sensitivity towards Hg²⁺ in water/ethanol (v/v = 4/1, pH = 7.0) by a specific Hg²⁺-binding promoted spirolactam ring opening and hydrolyzing process. And, the detection limit for Hg²⁺ is evaluated to be 8.5 nM. Besides, the probe can respond to Hg²⁺ within 40 min and over a wide pH range from 4.0 to 10.0. Moreover, PRHg (40 µM) performs low cytotoxicity to HeLa cells (over 91.0 % cell survival rate), which allows the probe to be employed for tracing intracellular Hg²⁺ by fluorescence imaging.

A quinoline-rhodamine hybrid probe for ratiometricly sensing of Hg2+ in water and cell imaging application

To develop efficient tools for monitoring toxicant Hg²⁺ in aqueous solution attracts great attention because the abnormal distribution of Hg²⁺ in environment poses great threat to human health. We here report the preparation of a novel quinoline-rhodamine hybrid fluorescent probe P7RHg for ratiometricly sensing of Hg²⁺ in water, with a spirolactam-thiosemicarbazide reaction group. Upon treatment by Hg²⁺, the ratio of fluorescence intensity (F₆₀₀/F₄₆₀) exhibits nearly 90-fold enhancement, presenting two well-resolved emission peaks (140 nm). Meanwhile, the specific Hg²⁺-induced desulfurization provides probe P7RHg an excellent selectivity to Hg²⁺, with a detection limit of 8.6 nM. Moreover, the low cytotoxicity allows P7RHg to be employed for tracing Hg²⁺ in living cells by confocal fluorescence imaging.

Solid-State Emission and Aggregate Emission of Aroyl- S,N-Ketene Acetals Are Controlled and Tuned by Their Substitution Pattern

Aroyl-S,N-ketene acetals are a novel highly diverse class of aggregation-induced emission fluorogens (AIEgens) with a plethora of interesting properties. An expanded compound library of more than 110 dyes set the stage for the first qualitative control and tuneability of all aspects of their photophysical properties. The interplay of substituents not only allows tuning and prediction of the emission color, but also of the intensity, and quantum yields both in solids and in the aggregated state; these can be rationalized by scrutinizing intermolecular interactions in the crystalline solid state.

HClO-Activated Near-Infrared Fluorogenic Aza-BODIPY-Bisferrocene Triad with High Turn-on Ratio for In Vivo Biosensing

Optically monitoring hypochlorous acid (HClO) in living body favors diagnosis and study of inflammatory diseases. However, this has been hampered by limited strategies to develop highly fluorogenic tools in the deep-penetration near-infrared spectrum. Herein, a near-infrared aza-BODIPY-bisferrocene triad Fc₂ -CBDP that unexpectedly achieves an exceptionally sensitive and selective fluorescence turn-on (>220-fold) response toward HClO through single-ferrocene oxidation and boron-alkynyl hydrolysis cascade is reported. Mechanism insight shows that Fc₂ -CBDP features "enhanced charge transfer"-caused quenching due to intramolecular bisferrocene electronic coupling, which is decoupled in the reaction with HClO. The utility of Fc₂ -CBDP for intracellular HClO imaging is evaluated and, more importantly, in vivo high-contrast deep-tissue imaging of lymphatic inflammation and colitis is realized. This work provides new insights into both HClO and ferrocene chemistry, and extends the reach of fluorogenic strategies in the near-infrared biosensing.

Bioinspired large Stokes shift small molecular dyes for biomedical fluorescence imaging

Long Stokes shift dyes that minimize cross-talk between the excitation source and fluorescent emission to improve the signal-to-background ratio are highly desired for fluorescence imaging. However, simple small molecular dyes with large Stokes shift (more than 120 nanometers) and near-infrared (NIR) emissions have been rarely reported so far. Here, inspired by the chromophore chemical structure of fluorescent proteins, we designed and synthesized a series of styrene oxazolone dyes (SODs) with simple synthetic methods, which show NIR emissions (>650 nanometers) with long Stokes shift (ranged from 136 to 198 nanometers) and small molecular weight (<450 daltons). The most promising SOD9 shows rapid renal excretion and blood-brain barrier passing properties. After functioning with the mitochondrial-targeted triphenylphosphonium (TPP) group, the resulting SOD9-TPP can be engineered for head-neck tumor imaging, fluorescence image-guided surgery, brain neuroimaging, and on-site pathologic analysis. In summary, our findings add an essential small molecular dye category to the classical dyes.

Excluding interference and detecting Microcystin-LR in the natural lakes and cells based a unique fluorescence method

Cyanobacteria blooms that cause the death of aquatic and terrestrial organisms have attracted considerable attention since the 19th century. The most typical toxin in cyanobacteria blooms is cyanobacteria toxin, particularly microcystin-LR (MC-LR). Therefore, a simple and highly efficient method for detecting MC-LR plays a role in studying the ecological toxicology of MC-LR. However, as MC-LR itself is located in a complex environment, traditional techniques present complex and false-positive defects. To address the above issues, novel technologies should be explored and discovered. Herein, we describe the development of MC-BDKZ as the first paradigm of probes that can concurrently report MC-LR in natural lakes and cells. This novel material shows large Stokes Shift and possesses good photostability and high sensitivity. Considering the properties mentioned above, MC-BDKZ not only achieves the detection of MC-LR in the lake water samples, but also completes the imaging of exogenous MC-LR in cells. Moreover, the interference of many factors in the lake and cells is excluded completely in the process of MC-LR detection. We comprehensively analyzed the response principle and potential application of MC-BDKZ in the process of MC-LR detection. Compared with the conventional MC-LR detection technologies, fluorescence probe technology shows better convenience and greatly reduces distance from the practical application in vitro and in vivo. We envisioned that the development of this visual research tool could provide crucial clues for exploring the pathogenesis of MC-LR in body.

Natural flavylium-inspired far-red to NIR-II dyes and their applications as fluorescent probes for biomedical sensing

Fluorescent probes that emit in the far-red (600-700 nm), first near-infrared (NIR-I, 700-900 nm), and second NIR (NIR-II, 900-1700 nm) regions possess unique advantages, including low photodamage and deep penetration into biological samples. Notably, NIR-II optical imaging can achieve tissue penetration as deep as 5-20 mm, which is critical for biomedical sensing and clinical applications. Much research has focused on developing far-red to NIR-II dyes to meet the needs of modern biomedicine. Flavylium compounds are natural colorants found in many flowers and fruits. Flavylium-inspired dyes are ideal platforms for constructing fluorescent probes because of their far-red to NIR emissions, high quantum yields, high molar extinction coefficients, and good water solubilities. The synthetic and structural diversities of flavylium dyes also enable NIR-II probe development, which markedly advance the field of NIR-II in vivo imaging. In the last decade, there have been huge developments in flavylium-inspired dyes and their applications as far-red to NIR fluorescent probes for biomedical applications. In this review, we highlight the optical properties of representative flavylium dyes, design strategies, sensing mechanisms, and applications as fluorescent probes for detecting and visualizing important biomedical species and events. This review will prompt further research not only on flavylium dyes, but also into all far-red to NIR fluorophores and fluorescent probes. Moreover, this interest will hopefully spillover into applications related to complex biological systems and clinical treatments, ranging in focus from the sub-organelle to whole-animal levels.

Reducing the internal reorganization energy via symmetry controlled π-electron delocalization

The magnitude of the reorganization energy is closely related to the nonradiative relaxation rate, which affects the photoemission quantum efficiency, particularly for the emission with a lower energy gap toward the near IR (NIR) region. In this study, we explore the relationship between the reorganization energy and the molecular geometry, and hence the transition density by computational methods using two popular models of NIR luminescent materials: (1) linearly conjugated cyanine dyes and (2) electron donor-acceptor (D-A) composites with various degrees of charge transfer (CT) character. We find that in some cases, reorganization energies can be significantly reduced to 50% despite slight structural modifications. Detailed analyses indicate that the reflection symmetry plays an important role in linear cyanine systems. As for electron donor-acceptor systems, both the donor strength and the substitution position affect the relative magnitude of reorganization energies. If CT is dominant and creates large spatial separation between HOMO and LUMO density distributions, the reorganization energy is effectively increased due to the large electron density variation between S0 and S1 states. Mixing a certain degree of local excitation (LE) with CT in the S1 state reduces the reorganization energy. The principles proposed in this study are also translated into various pathways of canonically equivalent π-conjugation resonances to represent intramolecular π-delocalization, the concept of which may be applicable, in a facile manner, to improve the emission efficiency especially in the NIR region.

A novel long excitation/emission wavelength fluorophore as platform utilized to construct NIR probes for bioimaging and biosensing

Near-infrared (NIR) fluorophores, especially dicyano-based fluorophores and xanthene-based hemicyanines, have beenput high expectation in bioimaging application due to their excellent optical properties. However, they suffer from inherentshortagessuch as short excitation/emission wavelength (less than 700 nm) or small Stokes shift (20-50 nm). Herein, we constructed a novel NIR dicyano-based fluorophore (DCO-HBTN). Toourknowledge, it is the first reported dicyano-based fluorophore of which the excitation/emission wavelength is more than 650 nm and Stokes shift is more than 100 nm. To demonstrate the feasibility of our efforts, we developed two NIR fluorescent probes (Probe-Cys and Probe-H₂S) based on the fluorophore, Probe-Cys displayed good selective and highly sensitive (LOD = 0.28 μM) recognition of Cys over Hcy and GSH, which was used to visualize endogenous Cys in tumor tissue. Probe-H₂S exhibited an. excellent specific and sensitive (LOD = 0.11 μM) response to H₂S, which was applied in monitoring H₂S releasing from the prodrug in vitro and in vivo.

X3Σg- → b1Σg+ Absorption Spectra of Molecular Oxygen in Liquid Organic Solvents at Atmospheric Pressure

Spectra and absorption coefficients of the forbidden 765 nm X³Σ_g^- → b¹Σ_g⁺ transition of molecular oxygen dissolved in organic solvents at atmospheric pressure were recorded over a 5 m path length using a liquid waveguide capillary cell. The results show that it is possible to investigate this weak near-infrared absorption transition in a common liquid hydrocarbon solvent without the need for a potentially dangerous high oxygen pressure. Proof-of-principle data from benzene, toluene, chlorobenzene, bromobenzene, and iodobenzene reveal a pronounced heavy atom effect on this spin-forbidden transition. For example, the absorption coefficient at the band maximum in iodobenzene, (28.9 ± 3.3) × 10^-3 M^-1 cm^-1, is approximately 21 times larger than that in benzene, (1.4 ± 0.1) × 10^-3 M^-1 cm^-1. These absorption measurements corroborate results obtained from O₂(X³Σ_g^-) → O₂(b¹Σ_g⁺) excitation spectra of O₂(a¹Δ_g) → O₂(X³Σ_g^-) phosphorescence, which depended on data from a plethora of convoluted experiments. Spectroscopic studies of molecular oxygen in liquid solvents can help evaluate aspects of the seminal Strickler-Berg approach to treat the effect of solvent on Einstein's A and B coefficients for radiative transitions. In particular, our present results are a key step toward using the O₂(X³Σ_g^-) → O₂(b¹Σ_g⁺) transition to evaluate the speculated limiting condition of applying the Strickler-Berg treatment to a highly forbidden process. This latter issue is but one example of how an arguably simple homonuclear diatomic molecule continues to aid the scientific community by providing fundamental physical insight.

A new HClO-activated "turn-off" mitochondria-targetable NIR fluorescent probe for imaging of osteoarthritis in vivo

Hypochlorous acid (HClO) as a biomarker of inflammation has been implicated in redox signaling and combating microbial infection. Therefore, it is of great significance to develop an efficient method for detection and analysis of HClO in osteoarthritis. Herein, a new"turn-off" mitochondria-targetable NIR fluorescent probe, NIR-ClO, was reported for specific analysis and imaging of osteoarthritis response-related HOCl levels in vitro and in vivo. In the presence of HClO, due to the specific HOCl-triggered C = C bond cleavage reaction, NIR-ClO obtained a high sensitive and selective fluorescence "On-Off" response toward HClO with a good limit of detection(LOD) as low as 28.3 nM, and showed a fast response time (<60 s) , which allow it to be used for detection of HClO under a simulated physiological condition. In addition, NIR-ClO was successfully used to imaging of HClO in living RAW264.7 cells and osteoarthritis model rat. The results suggest that NIR-ClO is a robust tool for future studies on diagnosis osteoarthritis.

Ratiometric afterglow luminescent nanoplatform enables reliable quantification and molecular imaging

Afterglow luminescence is an internal luminescence pathway that occurs after photo-excitation, holds great promise for non-background molecular imaging in vivo, but suffer from poor quantitative ability owing to luminescent attenuation over time. Moreover, the inert structure and insufficient reactive sites of current afterglow materials make it hard to design activatable afterglow probes for specific detection. Here, we report a ratiometric afterglow luminescent nanoplatform to customize various activatable afterglow probes for reliable quantification and molecular imaging of specific analytes, such as NO, ONOO⁻ or pH. Notably, these afterglow probes can not only address the attenuation of afterglow intensity and eliminate the interference of factors (e.g., laser power, irradiation time, and exposure time), but also significantly improve the imaging reliability in vivo and signal-to-background ratios (~1200-fold), both of which enable more reliable quantitative analysis in biological systems. Moreover, as a proof-of-concept, we successfully design an NO-responsive ratiometric afterglow nanoprobe, RAN1. This nanoprobe can monitor the fluctuations of intratumoral NO, as a biomarker of macrophage polarization, making it possible to real-time dynamically evaluate the degree cancer immunotherapy, which provides a reliable parameter to predict the immunotherapeutic effect.

Afterglow luminescence is promising for non-background molecular imaging in vivo. Here the authors report a ratiometric afterglow luminescent nanoplatform to generate activatable afterglow probes for quantification of specific analytes including NO.

Near-infrared Fluorescent Probe Based on Rhodamine Derivative for Detection of NADH in Live Cells

A near-infrared fluorescent probe was prepared for selective detection of reduced nicotinamide adenine dinucleotide (NADH) in live cells. The probe turns off the fluorescence with a closed spironolactone switch. However, reduction of the probe by NADH turns on fluorescence at 740 nm. Theoretical calculations suggest a more planar arrangement between the rhodamine and quinoline moieties with increased π-delocalization resulting from reduction.

A self-triggered radioligand therapy agent for fluorescence imaging of the treatment response in prostate cancer

PURPOSE

Radioligand therapy (RLT) targeting prostate-specific membrane antigen (PSMA) is emerging as an effective treatment option for metastatic castration-resistant prostate cancer (mCRPC). An imaging-based method to quantify early treatment responses can help to understand and optimize RLT.

METHODS

We developed a self-triggered probe 2 targeting the colocalization of PSMA and caspase-3 for fluorescence imaging of RLT-induced apoptosis.

RESULTS

The probe binds to PSMA potently with a K_i of 4.12 nM, and its fluorescence can be effectively switched on by caspase-3 with a K_m of 67.62 μM. Cellular and in vivo studies demonstrated its specificity for imaging radiation-induced caspase-3 upregulation in prostate cancer. To identify the detection limit of our method, we showed that probe 2 could achieve 1.79 times fluorescence enhancement in response to ¹⁷⁷Lu-RLT in a medium PSMA-expressing 22Rv1 xenograft model.

CONCLUSION

Probe 2 can potently bind to PSMA, and the fluorescence signal can be sensitively switched on by caspase-3 both in vitro and in vivo. This method may provide an effective tool to investigate and optimize PSMA-RLT.

Recent Progress of Cyanine Fluorophores for NIR-II Sensing and Imaging

The cyanine fluorophores, a kind of classic organic fluorophores, are famous for their high extinction coefficient, simple synthetic route, and relatively long absorption and emission wavelengths. Moreover, the excellent biocompatibility and low toxicity in biological samples make cyanine fluorophores show excellent application value in the biomedical field, especially in Near-Infrared II (NIR-II) sensing and imaging. In this review, we briefly outline the history, characteristics, and current state of development of cyanine fluorophores. In particular, we described the application of cyanine fluorophores in NIR-II sensing and imaging. We hope this review can help researchers grab the latest information in the fast-growing field of cyanine fluorophores for NIR-II sensing and imaging.

Double-site-based a smart fluorescent sensor for logical detecting of sulphides and its imaging evaluation of living organisms

Thiophenol and hydrosulphite are a group of toxic environmental pollutants, which contaminate land, water and food exhibiting a serious risk to human health. Herein, we reported a xanthene dye-based sensor (DSF) with dual well-known response sites for visual detecting PhSH and HSO₃^-. Specifically, when DSF reacted with PhSH firstly, the color of the solution changed to blue with bright red fluorescence emission. After added with HSO₃^-, the color of the solution became yellow, and emitted yellow fluorescence signal. However, DSF was first added with HSO₃^-, the color of the solution changed to purple with no-fluorescence emission, and then PhSH was added, the color of the solution changed to yellow with a bright yellow fluorescence. Notably, DSF exhibited high sensitivity and selectivity for PhSH and HSO₃^- detection with a very low detection limits of 2.27 nM and 22.91 nM, respectively. More importantly, DSF could detect PhSH and HSO₃^- in water, real-food and biological systems. Therefore, the experimental results showed DSF as a robust new logical monitoring tool for the detection of PhSH and HSO₃^- in water, real-food samples and biological systems.

Activity-based NIR fluorescent probes based on the versatile hemicyanine scaffold: design strategy, biomedical applications, and outlook

The discovery of a near-infrared (NIR, 650-900 nm) fluorescent chromophore hemicyanine dye with high structural tailorability is of great significance in the field of detection, bioimaging, and medical therapeutic applications. It exhibits many outstanding advantages including absorption and emission in the NIR region, tunable spectral properties, high photostability as well as a large Stokes shift. These properties are superior to those of conventional fluorogens, such as coumarin, fluorescein, naphthalimides, rhodamine, and cyanine. Researchers have made remarkable progress in developing activity-based multifunctional fluorescent probes based on hemicyanine skeletons for monitoring vital biomolecules in living systems through the output of fluorescence/photoacoustic signals, and integration of diagnosis and treatment of diseases using chemotherapy or photothermal/photodynamic therapy or combination therapy. These achievements prompted researchers to develop more smart fluorescent probes using a hemicyanine fluorogen as a template. In this review, we begin by describing the brief history of the discovery of hemicyanine dyes, synthetic approaches, and design strategies for activity-based functional fluorescent probes. Then, many selected hemicyanine-based probes that can detect ions, small biomolecules, overexpressed enzymes and diagnostic reagents for diseases are systematically highlighted. Finally, potential drawbacks and the outlook for future investigation and clinical medicine transformation of hemicyanine-based activatable functional probes are also discussed.

Synthesis of sialic acid conjugates of the clinical near-infrared dye as next-generation theranostics for cancer phototherapy

Cancer is a multifaceted global health problem that requires continuous action to develop next-generation cancer theranostics. Inspired by the emerging use of indocyanine green (ICG), the only clinically approved near-infrared (NIR) dye for cancer phototherapy, here we synthesized two ICG conjugate theranostics by coupling ICG to sialic acid (Sia) through the C2 and C9 positions of Sia, respectively, referred to as Sia-C2-ICG and Sia-C9-ICG. Encouragingly, Sia-C2/C9-ICGs show superior in vitro properties, including enhanced stability, reduced non-specific binding to serum proteins, and improved blood compatibility, highlighting the benefits of Sia coupling. Notably, in vivo NIR imaging shows that Sia-C9-ICG significantly promotes tumor targeting and effectively prolongs the circulation time in the body, while Sia-C2-ICG is superior to ICG but inferior to Sia-C9-ICG in targeting tumors. Furthermore, Sia-C9-ICG combined with NIR laser irradiation can lead to excellent photothermal and photodynamic therapies for cancer cells, resulting in superior solid tumor ablation. To our knowledge, this is the first report of Sia-NIR conjugates achieving significant tumor reduction in vivo. Together, these advances render Sia-C9-ICG an attractive lead as next-generation cancer theranostics that can be translated clinically to treat human patients.

Red-Shift (2-Hydroxyphenyl)-Benzothiazole Emission by Mimicking the Excited-State Intramolecular Proton Transfer Effect

Novel strategies to optimize the photophysical properties of organic fluorophores are of great significance to the design of imaging probes to interrogate biology. While the 2-(2-hydroxyphenyl)-benzothiazole (HBT) fluorophore has attracted considerable attention in the field of fluorescence imaging, its short emission in the blue region and low quantum yield restrict its wide application. Herein, by mimicking the excited-state intramolecular proton transfer (ESIPT) effect, we designed a series of 2-(2-hydroxyphenyl)-benzothiazole (HBT) derivatives by complexing the heteroatoms therein with a boron atom to enhance the chance of the tautomerized keto-like resonance form. This strategy significantly red-shifted the emission wavelengths of HBT, greatly enhanced its quantum yields, and caused little effect on molecular size. Typically, compounds 12B and 13B were observed to emit in the near-infrared region, making them among the smallest organic structures with emission above 650 nm.

A coumarin based fluorescent probe for NIR imaging guided photodynamic therapy against S. aureus-induced infection in mice models

A coumarin based and viscosity responsive fluorescent probe (HZAU800) was designed and synthesized. The probe, containing a strong electron-donating and rigid group on 7-position of coumarin, and a rhodamine derivative...

Bovine mammary alveolar MAC-T cells afford a tool for studies of bovine milk exosomes in drug delivery

Bovine milk exosomes (BMEs) have attracted attention as vehicles for delivering RNA therapeutics. BMEs originate in mammary alveolar cells. Here, we determined whether bovine mammary alveolar MAC-T cells afford a tool to assess RNA delivery by BMEs. MAC-T cells exosomes (MAC-T BMEs) and BMEs were harvested by differential ultracentrifugation. Exosome size, morphology, microRNA content and marker proteins were assessed using nanoparticle tracking analysis, transmission electron microscopy, real-time PCR and immunoblot analysis, respectively. MAC-T cells were genetically engineered to secrete MAC-T BMEs endogenously labeled with a near-infrared fluorescent protein and tissue distribution was compared to fluorophore-labeled BMEs following intravenous injection in C57BL/6 mice. Morphology and size were similar in MAC-T BMEs and BMEs (94 ± 5.8 nm and 101 ± 4.2 nm, p > 0.05). Both preparations expressed miR-320a, miR-200c and let-7a-5p (positive controls) but not miR-1 (negative control). Exosome marker proteins, CD9, CD63, CD81 and Tsg101, were detected in both MAC-T BMEs and BMEs. Distribution in mouse tissues was similar for both preparations, with liver being the primary accumulation site. Collectively, MAC-T BMEs afford a tool for BMEs-based RNA delivery studies.

Benchmarking Density Functional Approximations for Excited-State Properties of Fluorescent Dyes

This study presents an extensive analysis of the predictive power of time-dependent density functional theory in determining the excited-state properties of two groups of important fluorescent dyes, difluoroboranes and hydroxyphenylimidazo[1,2-a]pyridine derivatives. To ensure statistically meaningful results, the data set is comprised of 85 molecules manifesting diverse photophysical properties. The vertical excitation energies and dipole moments (in the electronic ground and excited states) of the aforementioned dyes were determined using the RI-CC2 method (reference) and with 18 density functional approximations (DFA). The set encompasses DFAs with varying amounts of exact exchange energy (EEX): from 0% (e.g., SVWN, BLYP), through a medium (e.g., TPSSh, B3LYP), up to a major contribution of EEX (e.g., BMK, MN15). It also includes range-separated hybrids (CAM-B3LYP, LC-BLYP). Similar error profiles of vertical energy were obtained for both dye groups, although the errors related to hydroxyphenylimidazopiridines are significantly larger. Overall, functionals including 40-55% of EEX (SOGGA11-X, BMK, M06-2X) ensure satisfactory agreement with the reference vertical excitation energies obtained using the RI-CC2 method; however, MN15 significantly outperforms them, providing a mean absolute error of merely 0.04 eV together with a very high correlation coefficient (R2 = 0.98). Within the investigated set of functionals, there is no single functional that would equally accurately determine ground- and excited-state dipole moments of difluoroboranes and hydroxyphenylimidazopiridine derivatives. Depending on the chosen set of dyes, the most accurate μGS predictions were delivered by MN15 incorporating a major EEX contribution (difluoroboranes) and by PBE0 containing a minor EEX fraction (hydroxyphenylimidazopiridines). Reverse trends are observed for μES, i.e., for difluoroboranes the best results were obtained with functionals including a minor fraction of EEX, specifically PBE0, while in the case of hydroxyphenylimidazopiridines, much more accurate predictions were provided by functionals incorporating a major EEX contribution (BMK, MN15).

The Chemistry of Organic Contrast Agents in the NIR-II Window

Optical imaging, especially fluorescence and photoacoustic imaging, possesses non-invasiveness, high spatial and temporal resolution, and high sensitivity, etc., compared to positron emission tomography (PET) or magnetic resonance imaging (MRI). Due to the merits from the second near infrared (NIR-II) window imaging, like deeper penetration depth, high signal-to-noise ratio, high resolution, and low tissue damage, researchers devote great efforts to develop contrast agents with NIR-II absorption or emission. In this review, we summarized recently developed organic luminescent and photoacoustic materials, ranging from small molecules to conjugated polymers. Then, we systematically introduced engineering strategies and their imaging performance, classified by the skeleton cores. Finally, we elucidated the challenges and prospective of these NIR-II organic dyes for potential clinical applications. We hope our summary can inspire further development of NIR-II contrast agents.

Engineering naphthalimide-cyanine integrated near-infrared dye into ROS-responsive nanohybrids for tumor PDT/PTT/chemotherapy

Photodynamic (PDT) and photothermal therapies (PTT) are emerging treatments for tumour ablation. Organic dyes such as porphyrin, chlorin, phthalocyanine, boron-dipyrromethene and cyanine are the clinically or preclinically used photosensitizer or photothermal agents. Development of structurally diverse near-infrared dyes with long absorption wavelength is of great significance for PDT and PTT. Herein, we report a novel near-infrared dye ML880 with naphthalimide modified cyanine skeleton. The introduction of naphthalimide moiety results in stronger electron delocalization and larger redshift in emission compared with IR820. Furthermore, ML880 is co-loaded with chemotherapeutic drug into ROS-responsive mesoporous organosilica (RMON) to construct nanomedicine NBD&ML@RMON, which exhibits remarkable tumor inhibition effects through PDT/PTT/chemotherapy in vivo.

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The structure of the near-infrared dye ML880 was first reported.

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ML880 showed potential to be an excellent phototherapy agent activated by NIR laser.

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ML880 and chemodrug were co-loaded into ROS-degradable mesoporous organosilica to prepare NBD&ML@RMON.

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NBD&ML@RMON showed ROS- and NIR-responsible drug release behaviors.

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The remarkably tumor inhibition was achieved by the combined PDT/PTT/chemotherapy under 880 nm laser.

Fluorescent Biosensors Based on Silicon Nanowires

Nanostructures are arising as novel biosensing platforms promising to surpass current performance in terms of sensitivity, selectivity, and affordability of standard approaches. However, for several nanosensors, the material and synthesis used make the industrial transfer of such technologies complex. Silicon nanowires (NWs) are compatible with Si-based flat architecture fabrication and arise as a hopeful solution to couple their interesting physical properties and surface-to-volume ratio to an easy commercial transfer. Among all the transduction methods, fluorescent probes and sensors emerge as some of the most used approaches thanks to their easy data interpretation, measure affordability, and real-time in situ analysis. In fluorescent sensors, Si NWs are employed as substrate and coupled with several fluorophores, NWs can be used as quenchers in stem-loop configuration, and have recently been used for direct fluorescent sensing. In this review, an overview on fluorescent sensors based on Si NWs is presented, analyzing the literature of the field and highlighting the advantages and drawbacks for each strategy.

Synthesis and fluorescence properties of red-to-near-infrared-emitting push-pull dyes based on benzodioxazole scaffolds

Fluorescence imaging with high temporal and spatial resolution has emerged as one of the most promising techniques to monitor biomolecules and biological processes in living systems. Among many kinds of small molecular fluorescent dyes, 2,1,3-benzoxadiazole (BD) derivatives have been widely applied in many chemical and biological applications due to their excellent photophysical properties. However, only a limited number of BD dyes with long emission wavelengths were reported. Herein, we have reported a new class of red-to near-infrared-emitting small molecular dyes 2a-3a based on benzodioxazole scaffolds, which are named VBDfluors. To bathochromically shift both absorption and emission, the conjugation system was extended by introducing electron-withdrawing group-substituted vinyl groups at position 7 via a Knoevenagel condensation reaction. The basic photophysical properties of VBDfluors were detected and summarized. The VBDfluors display excellent photophysical properties, including emission in the red-to-NIR region, large Stokes shifts, good stability/photostability and cell permeability. The geometry of the molecules was optimized by density functional theory (DFT) and time-dependent DFT (TDDFT) methods. Bioimaging results indicated that 2a and 3a exhibited excellent cell permeability and could be utilized for visualization of lipid droplets in living cells.

Research Progress of Small Molecule Fluorescent Probes for Detecting Hypochlorite

Hypochlorous acid (HOCl) generates from the reaction between hydrogen peroxide and chloride ions via myeloperoxidase (MPO)-mediated in vivo. As very important reactive oxygen species (ROS), hypochlorous acid (HOCl)/hypochlorite (OCl⁻) play a crucial role in a variety of physiological and pathological processes. However, excessive or misplaced production of HOCl/OCl⁻ can cause variety of tissue damage and human diseases. Therefore, rapid, sensitive, and selective detection of OCl⁻ is very important. In recent years, the fluorescent probe method for detecting hypochlorous acid has been developed rapidly due to its simple operation, low toxicity, high sensitivity, and high selectivity. In this review, the progress of recently discovered fluorescent probes for the detection of hypochlorous acid was summarized with the aim to provide useful information for further design of better fluorescent probes.

Simultaneous Absorbance and Fluorescence Measurements Using an Inlaid Microfluidic Approach

A novel microfluidic optical cell is presented that enables simultaneous measurement of both light absorbance and fluorescence on microlitre volumes of fluid. The chip design is based on an inlaid fabrication technique using clear and opaque poly(methyl methacrylate) or PMMA to create a 20.2 mm long optical cell. The inlaid approach allows fluid interrogation with minimal interference from external light over centimeter long path lengths. The performance of the optical cell is evaluated using a stable fluorescent dye: rhodamine B. Excellent linear relationships (R² > 0.99) are found for both absorbance and fluorescence over a 0.1-10 µM concentration range. Furthermore, the molar attenuation spectrum is accurately measured over the range 460-550 nm. The approach presented here is applicable to numerous colorimetric- or fluorescence-based assays and presents an important step in the development of multipurpose lab-on-chip sensors.

Sulphide activity-dependent multicolor emission dye and its applications in in vivo imaging

Reactive sulfur species (RSS) play pivotal roles in various pathological and physiological processes. There exists an intricate relevance in generation and metabolism among these substances. Although they are nucleophilic, there are still some differences in their reactivity. There are many methods to detect them by using reactive fluorescent probes, but the systematic study of their reactivity is still lacking. In our study, we designed a multiple reaction site fluorescent probe based on benzene conjugated benzopyrylium and NBD. The study revealed that besides both biothiols and hydrogen sulfide, sulfur dioxide (SO₂) can cleave the ether bond. There are two reaction forms for GSH with low reactivity: cutting the ether bond and adding the conjugated double bond of benzopyrylium. Nevertheless, Cys/Hcy with higher activity can further rearrange with NBD after cutting the ether bond. In addition, SO₂ can not only cleave the ether bond, but also continue to add the conjugated double bond of benzopyrylium. The above processes lead to multicolor emission of the probe, thus realizing the characteristic analysis of different sulfides. Thus the probe can be used for the detection of sulfide in mitochondria, and further for the imaging of sulfide in cells and zebrafish. This effective analysis method will provide a broad application prospect for practical applications.

The screening of drug-induced nephrotoxicity using gold nanocluster-based ratiometric fluorescent probes

Herbal medicines are potential candidates for the treatment of various diseases, but their medication safety remains poorly regulated. Current screening methods for the herbal medicine-induced nephrotoxic effects include histological and serological assessments, which often fail to reflect the kidney dysfunction instantly. Here we report a ratiometric fluorescence approach for the rapid and facile screening of drug-induced acute kidney injury using chromophore-modified gold nanoclusters. These gold nanoclusters are highly sensitive to reactive oxygen species (ROS), with a detection limit of 14 nM for ˙OH. After passing through the glomerular filtration barrier, the gold nanocluster-based probes can quantify the fluctuation of the ROS level in the kidneys and evaluate the risk of drug-induced nephrotoxicity. We further employed nephrotoxic triptolide as the model drug and the screening of drug-induced early renal injury was demonstrated using the nanoprobes, which is unattainable by conventional diagnostic approaches. Our fluorescent probes also allow the identification of other nephrotoxic components from herbal medicine such as aristolochine, providing a high-throughput strategy for the screening of herbal supplement-induced nephrotoxicity.