A review of NIR dyes in cancer targeting and imaging

A NIR fluorescent probe for fatty acid amide hydrolase bioimaging and its application in development of inhibitors

Fatty acid amide hydrolase (FAAH) is primarily responsible for the inactivation of fatty acid ethanolamide (FAE) and is involved in a variety of biological functions related to diseases of the nervous system. Herein, we developed a highly selective and sensitive FAAH-activated near-infrared fluorescent probe named DAND and achieved the real-time detection and imaging of FAAH activity in complex biosystems. Moreover, a visual high-throughput screening method was established using DAND, piperine was identified as a novel inhibitor of FAAH. Based on the interaction of piperine with FAAH, a more potent FAAH inhibitor (11f) was designed and synthesized which possessed an IC₅₀ value of 0.65 μM. Furthermore, 11f could attenuate the liposaccharide (LPS)-induced activation of BV2 cells, exhibiting an excellent anti-inflammatory activity. These results indicated that DAND could be used as a promising molecular tool for exploring FAAH activity and for rapidly screening potential FAAH inhibitors. In addition, piperine and its derivatives could serve as potential candidate drugs for the treatment of neurodegenerative diseases in the future.

Photodynamic Therapy for the Treatment and Diagnosis of Cancer-A Review of the Current Clinical Status

Photodynamic therapy (PDT) has been used as an anti-tumor treatment method for a long time and photosensitizers (PS) can be used in various types of tumors. Originally, light is an effective tool that has been used in the treatment of diseases for ages. The effects of combination of specific dyes with light illumination was demonstrated at the beginning of 20th century and novel PDT approaches have been developed ever since. Main strategies of current studies are to reduce off-target effects and improve pharmacokinetic properties. Given the high interest and vast literature about the topic, approval of PDT as the first drug/device combination by the FDA should come as no surprise. PDT consists of two stages of treatment, combining light energy with a PS in order to destruct tumor cells after activation by light. In general, PDT has fewer side effects and toxicity than chemotherapy and/or radiotherapy. In addition to the purpose of treatment, several types of PSs can be used for diagnostic purposes for tumors. Such approaches are called photodynamic diagnosis (PDD). In this Review, we provide a general overview of the clinical applications of PDT in cancer, including the diagnostic and therapeutic approaches. Assessment of PDT therapeutic efficacy in the clinic will be discussed, since identifying predictors to determine the response to treatment is crucial. In addition, examples of PDT in various types of tumors will be discussed. Furthermore, combination of PDT with other therapy modalities such as chemotherapy, radiotherapy, surgery and immunotherapy will be emphasized, since such approaches seem to be promising in terms of enhancing effectiveness against tumor. The combination of PDT with other treatments may yield better results than by single treatments. Moreover, the utilization of lower doses in a combination therapy setting may cause less side effects and better results than single therapy. A better understanding of the effectiveness of PDT in a combination setting in the clinic as well as the optimization of such complex multimodal treatments may expand the clinical applications of PDT.

Biomimetic Glucan Particles with Aggregation-Induced Emission Characteristics for Noninvasive Monitoring of Transplant Immune Response

Real-time monitoring of post-transplant immune response is critical to prolong the survival of grafts. The current gold standard for assessing the immune response to graft is biopsy. However, such a method is invasive and prone to false negative results due to limited tissue size available and the heterogeneity of the rejection site. Herein, we report biomimetic glucan particles with aggregation-induced emission (AIE) characteristics (HBTTPEP/GPs) for real-time noninvasive monitoring of post-transplant immune response. We have found that the positively charged near-infrared AIEgens can effectively aggregate in the confined space of glucan particles (GPs), thereby turning on the fluorescence emission. HBTTPEP/GPs can track macrophages for 7 days without hampering the bioactivity. Oral administration of HBTTPEP/GPs can specially target macrophages by mimicking yeast, which then migrate to the transplant rejection site. The fluorescence emitted from HBTTPEP/GPs correlated well with the infiltration of macrophages and the degree of allograft rejection. Furthermore, a single oral HBTTPEP/GPs dose can dynamically evaluate the therapeutic response to immunosuppressive therapy. Consequently, the biomimetic AIE-active glucan particles can be developed as a promising probe for immune-monitoring in solid organ transplantation.

Synthesis of Silica Nanoparticles with Physical Encapsulation of Near-Infrared Fluorescent Dyes and Their Tannic Acid Coating

This study reports a novel method for the synthesis of silica nanoparticles (NPs) encapsulating near-infrared (NIR) fluorescent dyes through physical adsorption. Although a NIR cationic fluorescent dye, oxazine 725 (OXA), has no chemical bonding moiety toward silica NPs such as the triethoxysilyl group, the dyes were successfully incorporated into silica NPs without denaturation under the mild reaction conditions. Next, tannic acid (TA) molecules were coated in the presence of Fe³⁺ on the particle surface for the functionalization of silica NPs encapsulating OXA (OXA@SiO₂ NPs). The TA coating on the surface of OXA@SiO₂ NPs was confirmed by transmission electron microscopy and X-ray photoelectron spectroscopy. The TA coating significantly contributed to the resistance improvement against photobleaching and leakage of the dyes in the NPs. Furthermore, the obtained TA-coated silica NPs encapsulating OXAs (OXA@SiO₂@TA NPs) were used for the fluorescence imaging of African green monkey kidney (COS-7) cells, and it was shown that the fluorescence originated from OXA@SiO₂@TA NPs was clearly observed in the COS-7 cells.

The use of a uPAR-targeted probe for photothermal cancer therapy prolongs survival in a xenograft mouse model of glioblastoma

The development of tumor-targeted probes that can efficiently reach cancerous tissue is an important focus of preclinical research. Photothermal cancer therapy (PTT) relies on light-absorbing molecules, which are directed towards tumor tissue and irradiated with an external source of light. This light is transformed into heat, causing localized hyperthermia and tumor death. The fluorescent probe indocyanine green (ICG) is already used as an imaging agent both preclinically and in clinical settings, but its use for PTT is yet to be fully exploited due to its short retention time and non-specific tumor targeting. Therefore, increasing ICG tumor uptake is necessary to improve treatment outcome. The urokinase-type plasminogen activator receptor, uPAR, is overexpressed in multiple tumor types. ICG-Glu-Glu-AE105, consisting of the uPAR-targeting peptide AE105 conjugated to ICG, has shown great potential for fluorescence-guided surgery. In this study, ICG-Glu-Glu-AE105 was evaluated as photothermal agent in a subcutaneous mouse model of human glioblastoma. We observed that the photothermal abilities of ICG-Glu-Glu-AE105 triggered high temperatures in the tumor during PTT, leading to tumor death and prolonged survival. This confirms the potential of ICG-Glu-Glu-AE105 as photothermal agent and indicates that it could be used as an add-on to the application of the probe for fluorescence-guided surgery.

Color-tunable arylaminoanthraquinone dyes through hydrogen-bond-assisted charge transfer interaction

We prepared a series of arylaminoanthraquinone derivatives, including those with electron-accepting sulfone units and/or with electron-donating dialkylamino units. A color-tunable anthraquinone library that reached into the NIR region could be prepared through the precise control of frontier orbitals. Fine color-tuning was achieved through proper selection and positioning of the substituents. Effective intramolecular hydrogen-bond-assisted charge transfer interaction between electron-donating aniline/p-phenylenediamine and electron-accepting anthraquinone substructures induced a significant bathochromic shift of anthraquinone. The number and position of the substituents and the molecular conformation also significantly contributed to determining photophysical properties.

A color-tunable anthraquinone library based on arylaminoanthraquinone was prepared through hydrogen-bond-assisted charge transfer interaction.

Folate-targeted Pluronic-chitosan nanocapsules loaded with IR780 for near-infrared fluorescence imaging and photothermal-photodynamic therapy of ovarian cancer

Herein, we report the fabrication of a nanotherapeutic platform integrating near-infrared (NIR) imaging with combined therapeutic potential through photodynamic (PDT) and photothermal therapies (PTT) and recognition functionality against ovarian cancer. Owing to its NIR fluorescence, singlet oxygen generation and heating capacity, IR780 iodide is exploited to construct a multifunctional nanosystem for single-wavelength NIR laser imaging-assisted dual-modal phototherapy. We opted for loading IR780 into polymeric Pluronic-F127-chitosan nanoformulation in order to overcome its hydrophobicity and toxicity and to allow functionalization with folic acid. The obtained nanocapsules show temperature-dependent swelling and spectroscopic behavior with favorable size distribution for cellular uptake at physiological temperatures, improved fluorescence properties and good stability. The fabricated nanocapsules can efficiently generate singlet oxygen in solution and are able to produce considerable temperature increase (46 °C) upon NIR laser irradiation. Viability assays on NIH-OVCAR-3 cells confirm the successful biocompatibilization of IR780 by encapsulating in Pluronic and chitosan polymers. NIR fluorescence imaging assays reveal the ability of folic-acid functionalized nanocapsules to serve as intracellular contrast agents and demonstrate their active targeting capacity against folate receptor expressing ovarian cancer cells (NIH-OVCAR-3). Consequently, the targeted nanocapsules show improved NIR laser induced phototherapeutic performance against NIH-OVCAR-3 cells compared to free IR780. We anticipate that this class of nanocapsules holds great promise as theranostic agents for application in image-guided dual PDT-PTT and imaging assisted surgery of ovarian cancer.

A brief review of non-invasive brain imaging technologies and the near-infrared optical bioimaging

Brain disorders seriously affect life quality. Therefore, non-invasive neuroimaging has received attention to monitoring and early diagnosing neural disorders to prevent their progress to a severe level. This short review briefly describes the current MRI and PET/CT techniques developed for non-invasive neuroimaging and the future direction of optical imaging techniques to achieve higher resolution and specificity using the second near-infrared (NIR-II) region of wavelength with organic molecules.

Recent progress on nanomedicine-induced ferroptosis for cancer therapy

The current treatment strategies for cancer therapy have posed many problems in achieving high efficacy. Therefore, an urgent step is needed to develop innovative therapies that can win beyond satisfactory results against tumor. Ferroptosis that is a kind of non-apoptotic based programmed cell death has played a crucial role in eradicating tumors by reactive oxygen species and iron-dependent pathways. Research shows a remarkable potential of ferroptosis in eliminating aggressive malignancies resistant to traditional therapies. The combination of nanomedicine and ferroptosis has revealed a close relationship for the treatment of various cancer types with high efficacy. This review introduces the basics of nanomedicine-based ferroptosis first to emphasize the feasibility and properties of ferroptosis in cancer therapy. Then, the current research on the applications of nanomedicine for the ferroptosis-based anticancer therapy is highlighted. Finally, conclusions and future research directions in perspective of various challenges in developing nanomedicine-based ferroptosis into clinical therapeutics are discussed.

Metabolizable Near-Infrared-II Nanoprobes for Dynamic Imaging of Deep-Seated Tumor-Associated Macrophages in Pancreatic Cancer

Tumor-associated macrophages (TAMs) play a crucial part in cancer evolution. Dynamic imaging of TAMs is of great significance for treatment outcome evaluation and precision tumor therapy. Currently, most fluorescence nanoprobes tend to accumulate in the liver and are difficult to metabolize, which leads to strong background signals and inadequate imaging quality of TAMs nearby the liver such as pancreatic cancer. Herein, we aim to develop metabolizable dextran-indocyanine green (DN-ICG) nanoprobes in the second near-infrared window (NIR-II, 1 000-1 700 nm) for dynamic imaging of TAMs in pancreatic cancer. Compared to free ICG, the NIR-II fluorescence intensity of DN-ICG nanoprobes increased by 279% with significantly improved stability. We demonstrated that DN-ICG nanoprobes could specifically target TAMs through the interaction of dextran with specific ICAM-3-grabbing nonintegrin related 1 (SIGN-R1), which were highly expressed in TAMs. Subsequently, DN-ICG nanoprobes gradually metabolized in the liver yet remained in pancreatic tumor stroma in mouse models, achieving a high signal-to-background ratio (SBR = 7) in deep tissue (∼0.5 cm) NIR-II imaging of TAMs. Moreover, DN-ICG nanoprobes could detect dynamic changes of TAMs induced by low-dose radiotherapy and zoledronic acid. Therefore, the highly biocompatible and biodegradable DN-ICG nanoprobes harbor great potential for precision therapy in pancreatic cancer.

Nanophotonic biosensors harnessing van der Waals materials

Low-dimensional van der Waals (vdW) materials can harness tightly confined polaritonic waves to deliver unique advantages for nanophotonic biosensing. The reduced dimensionality of vdW materials, as in the case of two-dimensional graphene, can greatly enhance plasmonic field confinement, boosting sensitivity and efficiency compared to conventional nanophotonic devices that rely on surface plasmon resonance in metallic films. Furthermore, the reduction of dielectric screening in vdW materials enables electrostatic tunability of different polariton modes, including plasmons, excitons, and phonons. One-dimensional vdW materials, particularly single-walled carbon nanotubes, possess unique form factors with confined excitons to enable single-molecule detection as well as in vivo biosensing. We discuss basic sensing principles based on vdW materials, followed by technological challenges such as surface chemistry, integration, and toxicity. Finally, we highlight progress in harnessing vdW materials to demonstrate new sensing functionalities that are difficult to perform with conventional metal/dielectric sensors.

This review presents an overview of scenarios where van der Waals (vdW) materials provide unique advantages for nanophotonic biosensing applications. The authors discuss basic sensing principles based on vdW materials, advantages of the reduced dimensionality as well as technological challenges.

Controlled Aggregation of a Perylene-Derived Probe for Near-Infrared Fluorescence Imaging and Phototherapy

The design and synthesis of water-soluble phototherapeutic agents with near-infrared (NIR) fluorescence emission is highly desirable for cancer diagnosis and treatment. Here, we report the construction of an amphiphilic perylene-derived photosensitizer, AP. AP shows NIR emission with large Stokes shift (130 nm) and high 1O2 quantum yield (22%). It can self-assemble into nanoparticles in aqueous solution with quenched fluorescence emission due to aggregation-induced quenching. Upon membrane anchoring, AP is able to disassemble into free monomer molecules and specifically "light up" the cell membrane without the usually required washing procedures. Furthermore, AP is subsequently used for the efficient photodynamic therapy against cancer cells and solid tumors. The in vitro and in vivo experiments clearly indicate that AP is suitable for biological imaging and can serve as a promising photosensitizer for tumor suppression.

Antibacterial Activity of Porous Gold Nanocomposites via NIR Light-Triggered Photothermal and Photodynamic Effects

Phototherapeutic approaches, including photothermal therapy (PTT) and photodynamic therapy (PDT), have become a promising strategy to combat microbial pathogens and tackle the crisis brought about by antibiotic-resistant strains. Herein, porous gold nanoparticles (AuPNs) were synthesized as photothermal agents and loaded with indocyanine green (ICG), a common photosensitizer for PDT, to fabricate a nanosystem presenting near-infrared (NIR) light-triggered synchronous PTT and PDT effects. The AuPNs can not only convert NIR light into heat with a high photothermal conversion efficiency (50.6-68.5%), but also provide a porous structure to facilely load ICG molecules. The adsorption of ICG onto AuPNs was mainly driven by electrostatic and hydrophobic interactions with the surfactant layer of AuPNs, and the aggregate state of ICG significantly enhanced its generation of reactive oxygen species. Moreover, taking advantage of its synergistic PTT and PDT effect, the hybrid nanocomposites displayed a remarkable antibacterial effect to the gram-positive pathogen Staphylococcus aureus (S. aureus) upon 808 nm laser irradiation.

Meso-tetra(dioxanyl)porphyrins: Neutral, low molecular weight, and chiral porphyrins with solubility in aqueous solutions

The synthesis of the low-molecular weight, meso-tetra(dioxan-2-yl)porphyrin with considerable solubility in aqueous solution is described. The key intermediate dioxan-2-carbaldehyde is accessible in either racemic or in stereo-pure forms from commercially available starting materials in three steps. Using 4 × 1 or 2 + 2-type syntheses provide the porphyrin in modest yields. While the racemic aldehyde created an intractable mixture of diastereomers, the enantiopure aldehyde created a single enantiomer of the target porphyrin. The porphyrin was spectroscopically characterized. As its free base or zinc complex, it showed excellent solubility properties in organic and aqueous solvents, though free water-solubility was not achieved. The work expands on the availability of chiral porphyrins and neutral porphyrins with considerable solubility in aqueous solution.

The use of Indocyanine green fluorescent in patients with abdominal trauma for better intraoperative decision-making and less bowel anastomosis leak: case series

Despite technological advances in the management of blunt abdominal trauma, the rate of bowel anastomotic leakage (AL) remains high. The etiology of AL is multifactorial, but insufficient blood perfusion is considered to play a substantial role in the pathogenesis. In recent years, angiography with Indocyanine green (ICG), a fluorescent dye, has been introduced in the clinical practice to assess organ perfusion in several conditions. Given the scarcity of publications describing the use of ICG in trauma patients as a potentially useful strategy that may facilitate intraoperative decisions and limit the extent of bowel resection, we presented the utility of intraoperative ICG fluorescent in abdominal trauma patients in a level 1 trauma center. The use of ICG fluoroscopy in patients with abdominal trauma is feasible and useful; however, large prospective studies in trauma patients are warranted.

Nanobiotechnology-enabled energy utilization elevation for augmenting minimally-invasive and noninvasive oncology thermal ablation

Depending on the local or targeted treatment, independence on tumor type and minimally-invasive and noninvasive feature, various thermal ablation technologies have been established, but they still suffer from the intractable paradox between safety and efficacy. It has been extensively accepted that improving energy utilization efficiency is the primary means of decreasing thermal ablation power and shortening ablation time, which is beneficial for concurrently improving both treatment safety and treatment efficiency. Recent efforts have been made to receive a significant advance in various thermal methods including non-invasive high-intensity focused ultrasound, minimally-invasive radiofrequency and microwave, and non-invasive and minimally-invasive photothermal ablation, and so on. Especially, various nanobiotechnologies and design methodologies were employed to elevate the energy utilization efficiency for acquiring unexpected ablation outcomes accompanied with tremendously reduced power and time. More significantly, some combined technologies, for example, chemotherapy, photodynamic therapy (PDT), gaseous therapy, sonodynamic therapy (SDT), immunotherapy, chemodynamic therapy (CDT), or catalytic nanomedicine, were used to assist these ablation means to repress or completely remove tumors. We discussed and summarized the ablation principles and energy transformation pathways of the four ablation means, and reviewed and commented the progress in this field including newly developed technology or new material types with a highlight on nanobiotechnology-inspired design principles, and provided the deep insights into the existing problems and development direction. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Therapeutic Approaches and Drug Discovery > Emerging Technologies.

Self-recognizing and stimulus-responsive carrier-free metal-coordinated nanotheranostics for magnetic resonance/photoacoustic/fluorescence imaging-guided synergistic photo-chemotherapy

Carrier-free nanotheranostics directly assembled by using clinically used photosensitizers and chemotherapeutic drugs are a promising alternative to tumor theranostics. However, the weak interaction-driven assembly still suffers from low structural stability against disintegration, lack of targeting specificity, and poor stimulus-responsive property. Moreover, almost all exogenous ligands possess no therapeutic effect. Enlightened by the concept of metal-organic frameworks, we developed a novel self-recognizing metal-coordinated nanotheranostic agent by the coordination-driven co-assembly of photosensitizer indocyanine green (ICG) and chemo-drug methotrexate (MTX, also served as a specific "targeting ligand" towards folate receptors), in which ferric (FeIII) ions acted as a bridge to tightly associate ICG with MTX. Such carrier-free metal-coordinated nanotheranostics with high dual-drug payload (∼94 wt%) not only possessed excellent structural and physiological stability, but also exhibited prolonged blood circulation. In addition, the nanotheranostics could achieve the targeted on-demand drug release by both stimuli of internal lysosomal acidity and external near-infrared laser. More importantly, the nanotheranostics could self-recognize the cancer cells and selectively target the tumors, and therefore they decreased toxicity to normal tissues and organs. Consequently, the nanotheranostics showed strongly synergistic potency for tumor photo-chemotherapy under the precise guidance of magnetic resonance/photoacoustic/fluorescence imaging, thereby achieving highly effective tumor curing efficiency. Considering that ICG and bi-functional MTX are approved by the Food and Drug Administration, and FeIII ions have high biosafety, the self-recognizing and stimulus-responsive carrier-free metal-coordinated nanotheranostics may hold potential applications in tumor theranostics.

Balanced Intersystem Crossing in Iodinated Silicon-Fluoresceins Allows New Class of Red Shifted Theranostic Agents

Iodination of the silicon-fluorescein core revealed a new class of highly cytotoxic, red-shifted and water-soluble photosensitizer (SF-I) which is also fairly emissive to serve as a theranostic agent. Singlet oxygen generation capacity of SF-I was evaluated chemically, and up to 45% singlet oxygen quantum yield was reported in aqueous solutions. SF-I was further tested in triple negative breast (MDA MB-231) and colon (HCT-116) cancer cell lines, which are known to have limited chemotherapy options as well as very poor prognosis. SF-I induced efficient singlet oxygen generation and consequent photocytotoxicity in both cell lines upon light irradiation with a negligible dark toxicity while allowing cell imaging at the same time. SF-I marks the first ever example of a silicon xanthene-based photosensitizer and holds a lot of promise as a small-molecule-based theranostic scaffold.

Recent advances in near-infrared II imaging technology for biological detection

Molecular imaging technology enables us to observe the physiological or pathological processes in living tissue at the molecular level to accurately diagnose diseases at an early stage. Optical imaging can be employed to achieve the dynamic monitoring of tissue and pathological processes and has promising applications in biomedicine. The traditional first near-infrared (NIR-I) window (NIR-I, range from 700 to 900 nm) imaging technique has been available for more than two decades and has been extensively utilized in clinical diagnosis, treatment and scientific research. Compared with NIR-I, the second NIR window optical imaging (NIR-II, range from 1000 to 1700 nm) technology has low autofluorescence, a high signal-to-noise ratio, a high tissue penetration depth and a large Stokes shift. Recently, this technology has attracted significant attention and has also become a heavily researched topic in biomedicine. In this study, the optical characteristics of different fluorescence nanoprobes and the latest reports regarding the application of NIR-II nanoprobes in different biological tissues will be described. Furthermore, the existing problems and future application perspectives of NIR-II optical imaging probes will also be discussed.

Hows and Whys of Tumor-Seeking Dyes

Active targeting uses molecular fragments that bind receptors overexpressed on cell surfaces to deliver cargoes, and this selective delivery to diseased over healthy tissue is valuable in diagnostic imaging and therapy. For instance, targeted near-infrared (near-IR) dyes can mark tissue to be excised in surgery, and radiologists can use active targeting to concentrate agents for positron emission tomography (PET) in tumor tissue to monitor tumor metastases. Selective delivery to diseased tissue is also valuable in some treatments wherein therapeutic indexes (toxic/effective doses) are key determinants of efficacy. However, active targeting will only work for cells expressing the pivotal cell surface receptor that is targeted. That is a problem because tumors, even ones derived from the same organ, are not homogeneous, patient-to-patient variability is common, and heterogeneity can occur even in the same patient, so monotherapy with one actively targeted agent is unlikely to be uniformly effective. A particular category of fluorescent heptamethine cyanine-7 (Cy-7) dyes, here called tumor seeking dyes, offer a way to circumvent this problem because they selectively accumulate in any solid tumor. Furthermore, they persist in tumor tissue for several days, sometimes longer than 72 h. Consequently, tumor seeking dyes are near-IR fluorescent targeting agents that, unlike mAbs (monoclonal antibodies), accumulate in any solid lesion, thus overcoming tumor heterogeneity, and persist there for long periods, circumventing the rapid clearance problems that bedevil low molecular mass drugs. Small molecule imaging agents and drugs attached to tumor-seeking dyes have high therapeutic indices and long residence times in cancer cells and tumor tissue. All this sounds too good to be true. We believe most of this is true, but the controversy is associated with how and why these characteristics arise. Prior to our studies, the prevailing hypothesis, often repeated, was that tumor seeking dyes are uptaken by organic anion transporting polypeptides (OATPs) overexpressed on cancer cells. This Account summarizes evidence indicating tumor seeking Cy-7 dyes have exceptional accumulation and persistence properties because they covalently bind to albumin in vivo. That adduct formation provides a convenient way to form albumin-bound pharmaceuticals labeled with near-IR fluorophores which can be tracked in vivo. This understanding may facilitate more rapid developments of generally applicable actively targeted reagents.

Electron Donor-Acceptor Effect-Induced Organic/Inorganic Nanohybrids with Low Energy Gap for Highly Efficient Photothermal Therapy

For the design and optimization of near-infrared photothermal nanohybrids, tailoring the energy gap of nanohybrids plays a crucial role in attaining a satisfactory photothermal therapeutic efficacy for cancer and remains a challenge. Herein, we report an electron donor-acceptor effect-induced organic/inorganic nanohybrid with a low energy gap (denoted as ICG/Ag/LDH) by the in situ deposition of Ag nanoparticles onto the CoAl-LDH surface, followed by the coupling of ICG. A combination study verifies that the supported Ag nanoparticles as the electron donor (D) push electrons into the conjugated system of ICG by the electronic interaction between ICG and Ag, while OH groups of LDHs as the electron acceptor (A) pull electrons from the conjugated system of ICG by hydrogen bonding (N···H-O). This induces the formation of the D-A conjugated π-system and has a strong influence on the π-conjugated system of ICG, thus leading to a prominent decrease toward the energy gap and correspondingly an ultra-long redshift (∼115 nm). The resulting ICG/Ag/LDHs show an enhanced photothermal conversion efficiency (∼45.5%) at 808 nm laser exposure, which is ∼1.6 times larger than that of ICG (∼28.4%). Such a high photothermal performance is attributed to the fact that ICG/Ag/LDHs possess a D-π-A hybrid structure and a resulting lower energy gap, thus effectively promoting nonradiative transitions and leading to enhancement of the photothermal effect. Both in vitro and in vivo results confirm the good biocompatible properties and capability of the ICG/Ag/LDHs for NIR-triggered cancer treatment. This research demonstrates a successful paradigm for the rational design and preparation of new nanohybrids through the modulation of electron donor-acceptor effect, which offers a new avenue to achieve efficient phototherapeutic agent for improving the cancer therapeutic outcomes.

Studying the "Rigid-Flexible" Properties of Polymeric Micelle Core-Forming Segments with a Hydrophobic Phthalocyanine Probe Using NMR and UV Spectroscopy

The aim of the performed studies was to thoroughly examine the internal structure of self-assembled nanocarriers (i.e., polymeric micelles-PMs) by means of a hydrophobic phthalocyanine probe in order to identify the crucial features that are required to enhance the photoactive probe stability and reactivity. PMs of hydrophilic poly(ethylene glycol) and hydrophobic poly(ε-caprolactone) (PCL) or poly(d,l-lactide) (PDLLA) were fabricated and loaded with tetra tert-butyl zinc(II) phthalocyanine (ZnPc-t-but₄), a multifunctional spectroscopic probe with a profound ability to generate singlet oxygen upon irradiation. The presence of subdomains, comprising "rigid" and "flexible" regions, in the studied block copolymers' micelles as well as their interactions with the probe molecules, were assessed by various high-resolution NMR measurements [e.g., through-space magnetic interactions by the 1D NOE effect, pulsed field gradient spin-echo, and spin-lattice relaxation time (T₁) techniques]. The studies of the impact of the core-type microenvironment on the ZnPc-t-but₄ photochemical performance also included photobleaching and reactive oxygen species measurements. ZnPc-t-but₄ molecules were found to exhibit spatial proximity effects with both (PCL and PDLLA) hydrophobic polymer chains and interact with both subdomains, which are characterized by different rigidities. It was deduced that the interfaces between particular subdomains constitute an optimal host space for probe molecules, especially in the context of photochemical stability, photoactivity (i.e., for significant enhancement of singlet oxygen generation rates), and aggregation prevention. The present contribution proves that the combination of an appropriate probe, high-resolution NMR techniques, and UV-vis spectroscopy enables one to gain complex information about the subtle structure of PMs essential for their application as nanocarriers for photoactive compounds, for example, in photodynamic therapy, nanotheranostics, combination therapy, or photocatalysis, where the micelles constitute the optimal microenvironment for the desired photoreactions.

Stimuli-responsive polymer-based systems for diagnostic applications

Stimuli-responsive polymers exhibit properties that make them ideal candidates for biosensing and molecular diagnostics. Through rational design of polymer composition combined with new polymer functionalization and synthetic strategies, polymers with myriad responsivities, e.g., responses to temperature, pH, biomolecules, CO2, light, and electricity can be achieved. When these polymers are specifically designed to respond to biomarkers, stimuli-responsive devices/probes, capable of recognizing and transducing analyte signals, can be used to diagnose and treat disease. In this review, we highlight recent state-of-the-art examples of stimuli-responsive polymer-based systems for biosensing and bioimaging.

Structure-Based Design of a Selective Class I Histone Deacetylase (HDAC) Near-Infrared (NIR) Probe for Epigenetic Regulation Detection in Triple-Negative Breast Cancer (TNBC)

Abnormally high levels of class I histone deacetylases (HDACs) are associated with triple-negative breast cancer (TNBC) proliferation, malignant transformation, and poor prognosis of patients. Herein, we report a near-infrared imaging probe for TNBC detection via visualizing class I HDACs. Conjugating Cy5.5 to a cyclic depsipeptide inhibitor, we obtained the probe (20-Cy5.5) that retained desirable class I HDAC affinity and selectivity. Then, this probe could visualize epigenetic changes by class I HDACs in TNBC MDA-MB-231 cells and in xenograft tumor models in real time. Treatment with suberoylanilide hydroxamic acid (SAHA) significantly reduced the uptake of the probe in tumors, suggesting its potential use in evaluation of therapeutic responses of HDACi-mediated therapy. Moreover, 20-Cy5.5 could detect class I HDAC expression in TNBC lung metastasis. This novel NIR probe that achieves tumor class I HDAC imaging not only leads to a better understanding of epigenetic regulation in tumors but also has great potential for improving the TNBC diagnosis and treatment.

A Tumor Microenvironment Responsive Nanotheranostics Agent for Magnetic Resonance Imaging and Synergistic Photodynamic Therapy/Photothermal Therapy of Liver Cancer

Surgery is the main treatment for liver cancer in clinic owing to its low sensitivity to chemotherapy and radiotherapy, but this results in high mortality, recurrence, and metastasis rates. It is a feasible strategy to construct tumor microenvironments activated by nanotheranostics agents for the diagnosis and therapy of liver cancer. This study reports on a nanotheranostic agent (MONs@PDA-ICG) with manganese oxide nanoflowers (MONs) as core and polydopamine (PDA) as shell loading, with ICG as a photosensitizer and photothermal agent. MONs@PDA-ICG can not only produce ROS to kill cancer cells but also exhibit good photothermal performance for photothermal therapy (PTT). Importantly, O₂ generated by MONs decomposition can relieve the tumor hypoxia and further enhance the treatment effects of photodynamic therapy (PDT). In addition, the released Mn²⁺ ions make MONs@PDA-ICG serve as tumor microenvironments responsive to MRI contrast for highly sensitive and specific liver cancer diagnosis.

Near-Infrared-Responsive Photocatalysts

Broadening the absorption of light to the near-infrared (NIR) region is important in photocatalysis to achieve efficient solar-to-fuel conversion. NIR-responsive photocatalysts that can utilize diffusive solar energy are attractive for alleviating the energy crisis and environmental pollution. Over the past few years, considerable progress on the component and structural design of NIR-responsive photocatalysts have been reported. This study aims to systematically summarize recent progress toward the material design and mechanism optimization of NIR-responsive photocatalysts in this area. Depending on the main strategies for harvesting NIR photons, NIR-responsive photocatalysts can be categorized as direct NIR-light photocatalysts, indirect NIR-light photocatalysts, and photothermal photocatalysts. Furthermore, the construction and application of different NIR-responsive photocatalytic systems are summarized. Conclusions and perspectives are presented to further explore the potential of NIR-responsive photocatalysts in this field.

Safe Introduction of New Technologies and Techniques in Minimally Invasive Colorectal Surgery

In the past 20 years, colorectal surgery has experienced important advances as a result of new technologies that have increasingly transformed conventional open surgery into maximal usage of minimally invasive approaches. While many tools are being developed to change the way that operations are being performed, quality must not suffer. We describe here some of the aspects to pursue to achieve optimal and safe outcomes while utilizing minimally invasive techniques such as robotic surgery, transanal total mesorectal excision, as well as the role of immunofluorescence.

Emission Switching in the Near-Infrared by Reversible Trans-Cis Photoisomerization of Styrylbenzene-Conjugated Osmium Terpyridine Complexes

A new array of homoleptic osmium(II) complexes based on styrylbenzene-conjugated terpyridine ligands (tpy-pvp-X) were synthesized and their photophysical, electrochemical, and photoisomerization behaviors thoroughly investigated in this work. Both electron-donating and -withdrawing substituents were incorporated onto a tpy-pvp-X (X = H, Me, Cl, NO₂, and Ph) moiety to tune the optical properties and also the rate of photoisomerization behaviors in the complexes. All complexes display strong spin-allowed singlet metal-to-ligand charge-transfer bands in the visible (495-506 nm) and weak singlet ground state to triplet metal-to-ligand charge-transfer (³MLCT) broad bands within the 600-700 nm range. The complexes also exhibit strong phosphorescence emission from their ³MLCT state in the near-infrared domain (737-752 nm) at room temperature with excited-state lifetimes spanning between 107 and 165 ns. Two styrylbenzene units promote reversible trans-trans to trans-cis/cis-cis isomerization induced by light. The rate constants and quantum yields of photoisomerization were found to vary linearly with the Hammett σ_p parameters of the substituents. The rate and quantum yields were also found to decrease with increasing polarity of the solvents. Considerable modulation of the optical behavior along with luminescence switching in the complexes has been achieved upon photoisomerization. Moreover, the optical outputs as a function of two photonic stimuli inputs were used to demonstrate the binary function of a two-input IMPLICATION logic gate. In conjunction with the experimental study, computational investigations were also carried out in all three conformations of the complexes (trans-trans, trans-cis, and cis-cis) to have a perception of their electronic structures and for correct assignment of their absorption and emission spectral bands.

Applications of smartphone-based near-infrared (NIR) imaging, measurement, and spectroscopy technologies to point-of-care (POC) diagnostics

The role of point-of-care (POC) diagnostics is important in public health. With the support of smartphones, POC diagnostic technologies can be greatly improved. This opportunity has arisen from not only the large number and fast spread of cell-phones across the world but also their improved imaging/diagnostic functions. As a tool, the smartphone is regarded as part of a compact, portable, and low-cost system for real-time POC, even in areas with few resources. By combining near-infrared (NIR) imaging, measurement, and spectroscopy techniques, pathogens can be detected with high sensitivity. The whole process is rapid, accurate, and low-cost, and will set the future trend for POC diagnostics. In this review, the development of smartphone-based NIR fluorescent imaging technology was described, and the quality and potential of POC applications were discussed.

Interventional NIR Fluorescence Imaging of Cancer: Review on Next Generation of Dye-Loaded Protein-Based Nanoparticles for Real-Time Feedback During Cancer Surgery

The use of fluorescence imaging technique for visualization, resection and treatment of cancerous tissue, attained plenty of interest once the promise of whole body and deep tissue near-infrared (NIR) imaging emerged. Why is NIR so desired? Contrast agents with optical properties in the NIR spectral range offer an upgrade for the diagnosis and treatment of cancer, by dint of the deep tissue penetration of light in the NIR region of the electromagnetic spectrum, also known as the optical window in biological tissue. Thus, the development of a new generation of NIR emitting and absorbing contrast agents able to overcome the shortcomings of the basic free dye administration is absolutely essential. Several examples of nanoparticles (NPs) have been successfully implemented as carriers for NIR dye molecules to the tumour site owing to their prolonged blood circulation time and enhanced accumulation within the tumour, as well as their increased fluorescence signal relative to free fluorophore emission and active targeting of cancerous cells. Due to their versatile structure, good biocompatibility and capability to efficiently load dyes and bioconjugate with diverse cancer-targeting ligands, the research area of developing protein-based NPs encapsulated or conjugated with NIR dyes is highly promising but still in its infancy. The current review aims to provide an up-to-date overview on the biocompatibility, specific targeting and versatility offered by protein-based NPs loaded with different classes of NIR dyes as next-generation fluorescent agents. Moreover, this study brings to light the newest and most relevant advances involving the state-of-the-art NIR fluorescent agents for the real-time interventional NIR fluorescence imaging of cancer in clinical trials.

Inexpensive Near-Infrared Fluorimeters: Enabling Translation of nIR-Based Assays to the Field

The practical impact of analytical probes that transduce in the near-infrared (nIR) has been dampened by the lack of cost-effective and portable nIR fluorimeters. Herein, we demonstrate straightforward designs for an inexpensive microplate reader and a portable fluorimeter. These instruments require minimally complex machining and fabrication and operate with an open-source programming language (Python). Complete wiring diagrams, assembly diagrams, and scripts are provided. To demonstrate the utility of these two instruments, we performed high-throughput and field-side measurements of soil samples to evaluate the effect of soil management strategies on extracellular proteolytic, cellulolytic, and lignin-modifying activities. This was accomplished with fluorescent enzyme probes that utilized uniquely sensitive transducers exclusive to the nIR spectrum, single-walled carbon nanotubes. We also used the portable fluorimeter to evaluate spatial variations of proteolytic activity within individual field plots, while minimizing the effects of soil storage and handling. These demonstrations indicate the utility of these fluorimeters for translating analytical probes that operate in the nIR beyond the laboratory and into actual use.

Near-Infrared Monoamine Oxidase Inhibitor Biodistribution in a Glioma Mouse Model

PURPOSE

The biodistribution imaging kinetics of near-infrared monoamine oxidase inhibitor (NMI) are reported here.

METHODS

NMI was administered intravenously or orally to mice and detected by NIR fluorescence optical imaging within minutes and the longitudinal signal distribution was measured for up to 1 week after a single dose.

RESULTS

NMI rapidly reached 3.7-fold higher ventral and 3.2-fold higher brain region fluorescent signal intensity compared to oral route at 24 h. Similar patterns of NMI biodistribution were found in mice with or without intracranial implanted GL26 brain tumors. NMI was highly associated with tumors in contrast to adjacent non-tumor brain, confirming diagnostic utility. NMI 5 mg/kg imaging signal in brain at 48 h was optimal (tumor/non-tumor ratio > 3.5) with minimum off-target distribution. Intravenous NMI imaging signal peaked between 24 h and 48 h for lung, liver, kidney, blood, brain, and most other tissues. Clearance (signal weaker, but still present) from most tissues occurred by day 7. Intravenous low dose (0.5 mg/kg) minimally labeled tumor and other tissues, 5 mg/kg showed optimal imaging signal in glioma at a dose we previously reported as efficacious, and 50 mg/kg was tolerable but saturated the tissue signals beyond tumor specificity. Gel electrophoresis showed two major bands present in brain tumor and tissue protein lysates.

CONCLUSIONS

Intravenous 5 mg/kg was optimal dose to target brain tumor and identified off-target organs of concern: lungs, liver, and kidneys. These results demonstrate the biodistribution and optimal dose range of NMI for treatment and diagnostic monitoring of glioma.

Advances in Indocyanine Green-Based Codelivery Nanoplatforms for Combinatorial Therapy

Indocyanine green (ICG), a near-infrared (NIR) agent with an excellent imaging performance, has captivated enormous interest from researchers owing to its excellent therapeutic and imaging abilities. Although various nanoplatforms-based drug delivery systems (DDS) with the ability to overcome the clinical limitations of ICG has been reported, ICG-medicated conventional cancer diagnosis and photorelated therapies still lack in exhibiting the therapeutic efficacy, resulting in incomplete or partly tumor elimination. In the view of addressing these concerns, various DDSs have been engineered for the efficient codelivery of combined therapeutic agents with ICG, aiming to achieve promising therapeutic results due to multifunctional imaging-guided synergistic antitumor effects. In this article, we will systematically review currently available nanoplatforms based on polymers, inorganic, proteins, and metal-organic frameworks (MOFs), among others, for codelivery of ICG along with other therapeutic agents, providing a foundation for future clinical development of ICG. In addition, codelivery systems for ICG and different mechanism-based therapeutic agents will be illustrated. In summary, we conclude the review with the challenges and perspectives of ICG-based versatile nanoplatforms in detail.

Novel Multimodal, Multiscale Imaging System with Augmented Reality

A novel multimodal, multiscale imaging system with augmented reality capability were developed and characterized. The system offers 3D color reflectance imaging, 3D fluorescence imaging, and augmented reality in real time. Multiscale fluorescence imaging was enabled by developing and integrating an in vivo fiber-optic microscope. Real-time ultrasound-fluorescence multimodal imaging used optically tracked fiducial markers for registration. Tomographical data are also incorporated using optically tracked fiducial markers for registration. Furthermore, we characterized system performance and registration accuracy in a benchtop setting. The multiscale fluorescence imaging facilitated assessing the functional status of tissues, extending the minimal resolution of fluorescence imaging to ~17.5 µm. The system achieved a mean of Target Registration error of less than 2 mm for registering fluorescence images to ultrasound images and MRI-based 3D model, which is within clinically acceptable range. The low latency and high frame rate of the prototype system has shown the promise of applying the reported techniques in clinically relevant settings in the future.

Development of biotin-tagged near-infrared fluorescence probes for tumor-specific imaging

Near-infrared (NIR) probes are applicable for tumor imaging due to deep tissue penetration and low background signal. And cyanine dyes with long emission wavelength are excellent fluorophores to develop NIR probes. However, the aggregation of cyanine dyes in aqueous solution reduces the utilization of light. To solve this problem, polyethylene glycol (PEG) was introduced into the probes to reduce their aggregation. In our work, two new NIR probes G₁ and G₂ were designed and prepared by conjugating the cyanine dye G₀ with Biotin-PEG5-Azide. The conjugated biotin could enhance the target specificity of probes. And the photophysical and photochemical parameters demonstrated that G₁ and G₂ had a reduced aggregation tendency. In vitro fluorescence imaging proved that these two probes could be specifically taken up by HeLa cells, and in vivo imaging demonstrated that these two probes could specifically target tumors with large tumor-to-muscle (T/M) ratios. All these results indicated that G₁ and G₂ are promising NIR fluorescent contrast agents for tumor-specific imaging.

Dual laser activatable brominated hemicyanine as a highly efficient and photostable multimodal phototherapy agent

Dual phototherapy agents have attracted great interest in recent years as they offer enhanced cytotoxicity on cancer cells due to the synergistic effect of photodynamic and photothermal therapies (PDT/PTT). In this study, we demonstrate a brominated hemicyanine (HC-1), which is previously shown as mitochondria targeting PDT agent, can also serve as an effective photosensitizer for PTT for the first time under a single (640 nm or 808 nm) and dual laser (640 nm + 808 nm) irradiation. Generation of reactive oxygen species and photothermal conversion as a function of irradiation wavelength and power were studied. Both single wavelength irradiations caused significant phototoxicity in colon and cervical cancer cells after 5 min of irradiation. However, co-irradiation provided near-complete elimination of cancer cells due to synergistic action. This work introduces an easily accessible small molecule-based synergistic phototherapy agent, which holds a great promise towards the realization of local, rapid and highly efficient treatment modalities against cancer.

Cyanine conjugates in cancer theranostics

Cyanine is a meritorious fluorogenic core for the construction of fluorescent probes and its phototherapeutic potential has been enthusiastically explored as well. Alternatively, the covalent conjugation of cyanine with other potent therapeutic agents not only boosts its therapeutic efficacy but also broadens its therapeutic modality. Herein, we summarize miscellaneous cyanine-therapeutic agent conjugates in cancer theranostics from literature published between 2014 and 2020. The application scenarios of such theranostic cyanine conjugates covered common cancer therapeutic modalities, including chemotherapy, phototherapy and targeted therapy. Besides, cyanine conjugates that serve as nanocarriers for drug delivery are introduced as well. In an additional section, we analyze the potential of these conjugates for clinical translation. Overall, this review is aimed to stimulate research interest in exploring unattempted therapeutic agents and novel conjugation strategies and hopefully, accelerate clinical translation in this field.

Role of Sodium Taurocholate Cotransporting Polypeptide as a New Reporter and Drug-Screening Platform: Implications for Preventing Hepatitis B Virus Infections

PURPOSE

Sodium taurocholate cotransporting polypeptide (NTCP) is a transmembrane protein responsible for delivering indocyanine green (ICG), an ideal infrared fluorescent dye, from extracellular space into the cytoplasm. Additionally, NTCP located in the hepatocyte membrane is the portal for hepatitis B and D virus (HBV/HDV) infections. This study verified the feasibility of NTCP as a reporter and further established a drug-screening platform for HBV/HDV infections.

PROCEDURES

NTCP was transduced into HT-29, a colorectal cancer cell line. To examine the use of NTCP as a reporter, NTCP-expressing cells were treated with ICG and examined through flow cytometry, an in vivo imaging system (IVIS), and confocal microscopy. Furthermore, ICG was administrated to NTCP-expressing tumor-bearing nude mice and examined using the IVIS. To study the drug-screening platform, NTCP-expressing cells were treated with cyclosporin A, an NTCP inhibitor, and ICG, and examined using a multimode detection platform. Moreover, nude mice were injected with NTCP inhibitors and ICG, and subsequently, their ICG signal was examined in vivo and in the blood.

RESULTS

In the reporter study, the ICG signal was higher in NTCP-expressing cells/tumors than in control cells/tumors after ICG treatment. In the drug-screening platform study, NTCP-expressing cells had decreased ICG intensity after treatment with NTCP inhibitors and ICG. Nude mice that were administered cyclosporin A had lower ICG intensity in the liver and higher intensity in the peripheral tissue and blood.

CONCLUSIONS

NTCP and ICG form an ideal reporter system with extensive applications in cancer biology, robust drug-drug interactions, and drug screening in HBV/HDV infections.

Unique Benefits of Tumor-Specific Nanobodies for Fluorescence Guided Surgery

Tumor-specific fluorescence labeling is promising for real-time visualization of solid malignancies during surgery. There are a number of technologies to confer tumor-specific fluorescence. Antibodies have traditionally been used due to their versatility in modifications; however, their large size hampers efficient fluorophore delivery. Nanobodies are a novel class of molecules, derived from camelid heavy-chain only antibodies, that have shown promise for tumor-specific fluorescence labeling. Nanobodies are ten times smaller than standard antibodies, while maintaining antigen-binding capacity and have advantageous features, including rapidity of tumor labeling, that are reviewed in the present report. The present report reviews special considerations needed in developing nanobody probes, the status of current literature on the use of nanobody probes in fluorescence guided surgery, and potential challenges to be addressed for clinical translation.

NIR-II bioimaging of small organic molecule

In recent years, people have been actively exploring new imaging methods with high biological imaging performance because the clinical image definition and depth in vivo cannot meet the requirements of early diagnosis and prognosis. Based on the traditional near-infrared region I (NIR-I), the molecular probe of the near-infrared region II (NIR-II) is further explored and developed. In the NIR-II region due to the wavelength is longer than the NIR-I region can effectively reduce the molecular scattering, optical absorption of the organization, the organization of spontaneous fluorescence negligible, thus the NIR-II Fluorescence imaging (FI) can get deeper penetration depth, higher signal-to-background ratio (SBR) and better spatiotemporal resolution, FI in NIR-II region are an important and rapidly developing research region for future imaging. In the NIR-II fluorophore, small organic molecule fluorophore has attracted much attention because of its good biocompatibility and good pharmacokinetic properties. In this review, we briefly introduced the existing NIR-II organic small molecule fluorophores, and introduced the existing relatively mature methods for improving quantum yield and water solubility, and the small molecule dyes on FI of various improvement methods, also briefly introduces the small molecules of photoacoustic imaging (PAI), and a brief introduction of imaging-guided surgery (IGS) for some small organic molecules, finally, a reasonable prospect is made for the development of small organic molecules.

Thermo-responsive polymer encapsulated gold nanorods for single continuous wave laser-induced photodynamic/photothermal tumour therapy

Owing to strong and tunable surface plasmon resonance (SPR) effect and good biocompatibility, gold nanoparticles have been suggested to be a versatile platform for a broad range of biomedical applications. In this study, a new nanoplatform of thermo-responsive polymer encapsulated gold nanorods incorporating indocyanine green (ICG) was designed to couple the photothermal properties of gold nanorods (AuNRs) and the photodynamic properties of ICG to enhance the photodynamic/photothermal combination therapy (PDT/PTT). In addition to the significantly increased payload and enhancing photostability of ICG, the polymer shell in the nanoplatform also has thermo-responsive characteristics that can control the release of drugs at tumour sites upon the laser irradiation. On the basis of these improvements, the nanoplatform strongly increased drug aggregation at the tumour site and improved the photothermal/photodynamic therapeutic efficacy. These results suggest that this nanoplatform would be a great potential system for tumour imaging and antitumour therapy.

Optical and magnetic resonance imaging approaches for investigating the tumour microenvironment: state-of-the-art review and future trends

The tumour microenvironment (TME) strongly influences tumorigenesis and metastasis. Two of the most characterized properties of the TME are acidosis and hypoxia, both of which are considered hallmarks of tumours as well as critical factors in response to anticancer treatments. Currently, various imaging approaches exist to measure acidosis and hypoxia in the TME, including magnetic resonance imaging (MRI), positron emission tomography and optical imaging. In this review, we will focus on the latest fluorescent-based methods for optical sensing of cell metabolism and MRI as diagnostic imaging tools applied both in vitro and in vivo. The primary emphasis will be on describing the current and future uses of systems that can measure intra- and extra-cellular pH and oxygen changes at high spatial and temporal resolution. In addition, the suitability of these approaches for mapping tumour heterogeneity, and assessing response or failure to therapeutics will also be covered.

A general strategy to increase emission shift of two-photon ratiometric pH probes using a reversible intramolecular reaction of spiro-oxazolidine

Fluorescent pH probes have been served as powerful tools in biological and pathological studies in recent years due to the important roles of pH values in various physiological processes. Although plenty of pH probes have been delivered, development of two-photon ratiometric pH probes with large emission shift for detecting the variation of intracellular pH values is still a greatly challenging task. To address this concern, in this work, we have discovered a general strategy designing pH probes by means of a pH-dependent reversible intramolecular reaction of spiro-oxazolidine which can efficiently change their conjugation length and the electronic effect concurrently. To display the generality of the strategy, we have synthesized six pH probes, and all these probes exhibit short emission in basic conditions and dramatically red-shifted emission in acid environments. The emission shift of the six probes is more than 150 nm and even up to 210 nm, much larger than shift of all commercial and reported pH probes. The chemical sensing mechanism of intramolecular ring opening/closing reaction of spiro-oxazolidine has been confirmed with ¹H NMR spectra and density functional theory (DFT) calculations. Finally, we have used one of six with one- and two-photon properties to successfully image lysosomal pH changes under confocal and two-photon microscopes in a ratiometric manner. We believed that this spiro-oxazolidine strategy can serve as a general and powerful platform for the design of ideal pH probes.

ROS-responsive probes for low-background optical imaging: a review

Optical imaging is a facile tool for visualizing biological processes and disease progression, but its image quality is largely limited by light-induced autofluorescence or background signals. To overcome this issue, low-background optical-imaging techniques including chemiluminescence imaging, afterglow imaging and photoacoustic imaging have been developed, based on their unique working mechanisms, which are: the detection of light emissions from chemical reactions, the cessation of light excitation before signal collection, and the detection of ultrasonic signals instead of light signals, respectively. Stimuli-responsive probes are highly desirable for improved imaging results since they can significantly reduce surrounding interference signals. Reactive oxygen species (ROS), which are closely implicated in a series of diseases such as cancer and inflammation, are frequently employed as initiators for responsive agents to selectively change the imaging signal. Thus, ROS-responsive agents incorporated into low-background imaging techniques can achieve a more promising imaging quality. In this review, recent advances in ROS-responsive probes for low-background optical-imaging techniques are summarized. Moreover, the approaches to improving the sensitivity of probes and tissue penetration depth are discussed in detail. In particular, we highlight the reaction mechanisms between the probes and ROS, revealing the potential for low-background optical imaging.

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

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

Supramolecular cancer nanotheranostics

Among the many challenges in medicine, the treatment and cure of cancer remains an outstanding goal given the complexity and diversity of the disease. Nanotheranostics, the integration of therapy and diagnosis in nanoformulations, is the next generation of personalized medicine to meet the challenges in precise cancer diagnosis, rational management and effective therapy, aiming to significantly increase the survival rate and improve the life quality of cancer patients. Different from most conventional platforms with unsatisfactory theranostic capabilities, supramolecular cancer nanotheranostics have unparalleled advantages in early-stage diagnosis and personal therapy, showing promising potential in clinical translations and applications. In this review, we summarize the progress of supramolecular cancer nanotheranostics and provide guidance for designing new targeted supramolecular theranostic agents. Based on extensive state-of-the-art research, our review will provide the existing and new researchers a foundation from which to advance supramolecular cancer nanotheranostics and promote translationally clinical applications.

Mitochondria-Specific Agents for Photodynamic Cancer Therapy: A Key Determinant to Boost the Efficacy

Mitochondria-targeted photodynamic therapy (Mt-PDT), which enables the photogenerated cytotoxic oxygen species with fatal oxidative damage to block mitochondrial functions, has been considered as a promising method to enhance the anticancer effectiveness. Aiming at the challenges of PDT, in the past few decades, numerous mitochondria-targeting molecular agents have been developed to boost the PDT efficacy via directly destroying the mitochondria or activating mitochondria-mediated cell death pathways. Herein, a review for recent advances of Mt-PDT is highlighted including: mitochondrial targeting design principles and strategies, therapeutic performance of mitochondria-targeted agents-mediated PDT as well as the agent-free Mt-PDT. In addition, it puts together the achievements of the combinatory mitochondria-anchoring PDT and other anticancer strategies, demonstrating the advantages provided by Mt-PDT. The existing challenges are discussed and future settlements for the development of mitochondria-specific agents are also forecasted.