The microenvironment (local environment), including viscosity, temperature, polarity, hypoxia, and acidic-basic status (pH), plays indispensable roles in cellular processes. Significantly, organelles require an appropriate microenvironment to perform their specific physiological functions, and disruption of the microenvironmental homeostasis could lead to malfunctions of organelles, resulting in disorder and disease development. Consequently, monitoring the microenvironment within specific organelles is vital to understand organelle-related physiopathology. Over the past few years, many fluorescent probes have been developed to help reveal variations in the microenvironment within specific cellular regions. Given that a comprehensive understanding of the microenvironment in a particular cellular region is of great significance for further exploration of life events, a thorough summary of this topic is urgently required. However, there has not been a comprehensive and critical review published recently on small-molecule fluorescent chemosensors for the cellular microenvironment. With this review, we summarize the recent progress since 2015 towards small-molecule based fluorescent probes for imaging the microenvironment within specific cellular regions, including the mitochondria, lysosomes, lipid drops, endoplasmic reticulum, golgi, nucleus, cytoplasmic matrix and cell membrane. Further classifications at the suborganelle level, according to detection of microenvironmental factors by probes, including polarity, viscosity, temperature, pH and hypoxia, are presented. Notably, in each category, design principles, chemical synthesis, recognition mechanism, fluorescent signals, and bio-imaging applications are summarized and compared. In addition, the limitations of the current microenvironment-sensitive probes are analyzed and the prospects for future developments are outlined. In a nutshell, this review comprehensively summarizes and highlights recent progress towards small molecule based fluorescent probes for sensing and imaging the microenvironment within specific cellular regions since 2015. We anticipate that this summary will facilitate a deeper understanding of the topic and encourage research directed towards the development of probes for the detection of cellular microenvironments.

Small molecule based fluorescent chemosensors for imaging the microenvironment within specific cellular regions.

Near-infrared (NIR) activatable fluorescent probes have been considered to be the effective edge tools for the investigation of cell biology and disease diagnosis because of their outstanding advantages. Related genes involved in tumor genesis and progression regulate the overexpression of certain enzymes. Owing to the distinctive characteristics of quick reaction time and favorable pharmacokinetics, enzyme-reactive NIR optical probes have shown great potential in the diagnosis of tumorigenesis and in image-guided intraoperative surgeries with high signal-to-noise ratios. In this review, we mainly summarize the latest advancements in enzyme-reactive NIR fluorescent probes from design strategy to biomedical application. Specifically, some challenges and prospects in this field are presented at the end of the review, which will be beneficial to innovatively construct new multifunctional fluorescent probes and actively promote their clinical transformation in the future.

Activity‐Based NIR Enzyme Fluorescent Probes for the Diagnosis of Tumors and Image‐Guided Surgery

Nanotheranostics is one of the biggest scientific breakthroughs in nanomedicine. Most of the currently available diagnosis and therapies are invasive, time-consuming, and associated with severe toxic side effects. Nanotheranostics, on the other hand, has the potential to bridge this gap by harnessing the capabilities of nanotechnology and nanomaterials for combined therapeutics and diagnostics with markedly enhanced efficacy. However, nanomaterial applications in nanotheranostics are still in its infancy. This is due to the fact that each disease has a particular microenvironment with well-defined characteristics, which promotes deeper selection criteria of nanomaterials to meet the disease needs. In this review, we have outlined how nanomaterials are designed and tailored for nanotheranostics of cancer and other diseases such as neurodegenerative, autoimmune (particularly on rheumatoid arthritis), and cardiovascular diseases. The penetrability and retention of a nanomaterial in the biological system, the therapeutic strategy used, and the imaging mode selected are some of the aspects discussed for each disease. The specific properties of the nanomaterials in terms of feasibility, physicochemical challenges, progress in clinical trials, its toxicity, and their future application on translational medicine are addressed. Our review meticulously and critically examines the applications of nanotheranostics with various nanomaterials, including graphene, across several diseases, offering a broader perspective of this emerging field.

/pdf/nanomaterials-for-nanotheranostics-tuning-their-properties-1zx0ujzzzk.pdf

Nanomaterials for Nanotheranostics: Tuning Their Properties According to Disease Needs.

Molecular activatable probes with near-infrared (NIR) fluorescence play a critical role in in vivo imaging of biomarkers for drug screening and disease diagnosis. With structural diversity and high fluorescence quantum yields, hemicyanine dyes have emerged as a versatile scaffold for the construction of activatable optical probes. This Review presents a survey of hemicyanine-based NIR activatable probes (HNAPs) for in vivo imaging and early diagnosis of diseases. The molecular design principles of HNAPs towards activatable optical signaling against various biomarkers are discussed with a focus on their broad applications in the detection of diseases including inflammation, acute organ failure, skin diseases, intestinal diseases, and cancer. This progress not only proves the unique value of HNAPs in preclinical research but also highlights their high translational potential in clinical diagnosis.

Hemicyanine-Based Near-Infrared Activatable Probes for Imaging and Diagnosis of Diseases

It remains a considerable challenge to realize complete tumor suppression and avoid tumor regrowth by rational design of photosensitizers (PSs) to improve their photon utilization. In this Article, we provide a molecular design (Icy-NBF) based on the oxygen-content-regulated deactivation process of excited states. In the presence of overexpressed nitroreductase in hypoxic cancer cells, Icy-NBF is reduced and converted into a molecule with the same skeleton (Icy-NH2), in which the deactivation of the PS under 808 nm light irradiation proceeds via a different pathway: the excited states deactivation pathway of Icy-NBF involves radiative transition and energy transfer between Icy-NBF and O2; as for Icy-NH2, the deactivation pathway is attributed to non-radiative relaxation. By varying the O2 concentration in tumor cells, the therapeutic mechanism of Icy-NBF under 808 nm light irradiation can be switched between photodynamic and photothermal therapies, which maximizes the advantages of phototherapies with no tumor regrowth. Our study provides help in designing of smart PSs with improvement of photon utilization for efficient tumor photoablation.

Oxygen-Dependent Regulation of Excited-State Deactivation Process of Rational Photosensitizer for Smart Phototherapy.

Near-infrared off-on fluorescence probe activated by NTR for in vivo hypoxia imaging.

A novel off-on fluorescent probe, developed for imaging the hypoxic status of tumor cells by means of detecting nitroreductase (NTR), consisted of a naphthalimide fluorophore and 4-Nitrobenzyl chloroformate as exogenous hypoxia markers. The detection mechanism is based on the fact that nicotinamide adenine dinucleotide (NADH) is utilized by nitroreductase as an electron source to reduce nitroaromatics to corresponding amino derivatives. The fluorescence of probe displays distinct change from very weak fluorescence to strong green fluorescence at 550 nm after reaction with NTR. The fluorescence intensity increase of probe shows a good linearity when the concentration of NTR is in the range of 0.1–0.3 μg/mL. The probe shows significant specificity with NTR and good biocompatibility. The result of laser confocal fluorescence imaging confirmed that probe can successfully differentiate normoxic (non-fluorescent) from hypoxic conditions (strong green fluorescence) in U87 cell lines. All the results demonstrate that our probe is a promising optical imaging candidate for tumor hypoxia and can be potentially used for the detection of hypoxic-ischemic diseases.

A novel off-on fluorescent probe for imaging of hypoxia in tumor cell

Simple Summary The intraoperative navigation techniques develop rapidly, we present an update on current use and research on indocyanine green enhanced fluorescence imaging (ICG-FI) guided lymphangiography in gastric oncological surgery. ICG serves as a promising tattooed agent for lymphangiography, its application was restricted by the false negative lymph nodes and loss of specificity in targeting tumor cells. Besides, we summarized the current approaches for gain in sensitivity and specificity of ICG-FI guided lymphangiography in gastric oncological surgery. The next direction for reinforced ICG-FI was quantification of ICG intensity and detection of ICG distribution pattern, combining with intraoperative biopsy method. Abstract Huge strides have been made in the navigation of gastric cancer surgery thanks to the improvement of intraoperative techniques. For now, the use of indocyanine green (ICG) enhanced fluorescence imaging has received promising results in detecting sentinel lymph nodes (SLNs) and tracing lymphatic drainages, which make it applicable for limited and precise lymphadenectomy. Nevertheless, issues of the lack of specificity and unpredictable false-negative lymph nodes were encountered in gastric oncologic surgery practice using ICG-enhanced fluorescence imaging (ICG-FI), which restrict its application. Here, we reviewed the current application of ICG-FI and assessed potential approaches to improving ICG-FI.

/pdf/mapping-lymph-node-during-indocyanine-green-fluorescence-3atbvdoa.pdf

Mapping Lymph Node during Indocyanine Green Fluorescence-Imaging Guided Gastric Oncologic Surgery: Current Applications and Future Directions

Methionine (Met) is one of the essential amino acids of which the transport system L is overexpressed in various tumor cells. In this study, a near-infrared fluorescent dye (IR-780) and methionine were conjugated through a piperazin–polyamines linker to form Cy-Met. The successful synthesis of Cy-Met was validated by optical characterization, NMR, and MS spectra. The absorption peak of Cy-Met was at 680 nm, and the fluorescence peak was at 790 nm. The cytotoxicity assay and cell imaging studies indicated that Cy-Met had good biocompatibility and specific affinity to tumor cells. The dynamic distribution and clearance investigations showed that Cy-Met was eliminated by the liver–intestine pathway. Notably, Cy-Met displayed tumor-targeting ability in U87, H22, and EAC tumor-bearing mice with an evident long circulation time. The results implied that Cy-Met could act as a promising fluorescence probe specialized for long-term tumor monitoring.

Methionine-Decorated Near Infrared Fluorescent Probe for Prolonged Tumor Imaging.

The invention provides a photothermal tumor drug. The photothermal tumor drug takes a phase-change material as a shell and a target drug, a near-infrared probe and CuS nanoparticles are packaged in the shell. According to the photothermal tumor drug provided by the invention, a primary laser irradiation heating curve experiment proves that a photothermal material has relatively high photothermal conversion efficiency, and electron microscope and grain diameter analysis shows that the photothermal tumor drug has a driven targeting tumor property of a nano-material and can be used for chemical therapy and thermal therapy combined therapy of tumor parts.

Photothermal tumor drug as well as synthesis and application thereof to tumor treatment

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