Specific two-photon imaging of live cellular and deep-tissue lipid droplets by lipophilic AIEgens at ultra-low concentration

Lipid droplets are highly associated with obesity, diabetes, inflammatory disorders and cancer. A reliable two-photon dye for specific lipid droplets imaging in live cells and live tissues at ultra-low concentration has rarely been reported. In this work, four new aggregation-induced emission luminogens (AIEgens) based on the naphthalene core were designed and synthesized for specific two-photon lipid droplets staining. The new molecules, namely NAP AIEgens, exhibit large Stokes shift (>110 nm), high solid-state fluorescence quantum yield (up to 30%), good two-photon absorption cross section (45–100 GM at 860 nm), high biocompatibility and good photostability. They could specifically stain lipid droplets at ultra-low concentration (50 nM) in a short time of 15 min. Such ultra-low concentration is the lowest value for lipid droplets staining in live cells reported so far. In vitro and ex vivo two-photon imaging of lipid droplets in live cells and live mice liver tissues were successfully demonstrated. In addition, selective visualization of lipid droplets in live mice liver tissues could be achieved at a depth of about 70 μm. These excellent properties render them as promising candidates for investigating lipid droplets-associated physiological and pathological processes in live biological samples

Aggregation-Induced Emission (AIE), Life and Health

Light has profoundly impacted modern medicine and healthcare, with numerous luminescent agents and imaging techniques currently being used to assess health and treat diseases. As an emerging concept in luminescence, aggregation-induced emission (AIE) has shown great potential in biological applications due to its advantages in terms of brightness, biocompatibility, photostability, and positive correlation with concentration. This review provides a comprehensive summary of AIE luminogens applied in imaging of biological structure and dynamic physiological processes, disease diagnosis and treatment, and detection and monitoring of specific analytes, followed by representative works. Discussions on critical issues and perspectives on future directions are also included. This review aims to stimulate the interest of researchers from different fields, including chemistry, biology, materials science, medicine, etc., thus promoting the development of AIE in the fields of life and health

Two-Photon Fluorescent Compounds for Specific Lipid Droplet Imaging in Live Cells and Deep Tissues at Ultralow Concentration

Fluorescent compounds that have aggregation-induced emission (AIE) characteristics. The compounds can be uti­lized as lipid droplet (LD)-specific bio-probes in cell imag­ing, with high photostability and brightness. For example, the compounds can be used for specific two-photon LDs staining in live cells and deep-tissues at ultralow concen­trations. The compounds exhibit a large Stokes shift (> 110 nm), high solid fluorescence quantum yields (up to 0.30), a good two-photon absorption cross-section (45-100 GM at 860 nm), high biocompatibility, and good photostability

Polarized Resonance Synchronous Spectroscopy as a Powerful Tool for Studying the Kinetics and Optical Properties of Aggregation-induced Emission

Light scattering and absorption both contribute to the UV-vis extinction quantified with a UV-vis spectrophotometer, but they differ drastically in their causes and effects. The existing optical studies have generally focused on the fluorescence and total photon extinction of the aggregation-induced-emission (AIE) materials. The effects of aggregation on the light absorption and scattering of AIE luminogens (AIEgens) are essentially unexplored. Herein, we reported a spectroscopic study of the structures and properties of AIE aggregates using the combination of UV-vis, fluorescence, and polarized resonance synchronous spectroscopy (PRS2) methods. Optical activities including the light absorption extinction, scattering extinction, and absorbance-normalized fluorescence emission have been quantified for the first time for the AIE aggregates prepared with an in-house prepared AIEgen 2-((4-(diphenylamino)biphenyl-4-yl)methylene)malononitrile (TPMN). Absorption extinction dominates the entire UV-vis extinction spectrum obtained with the dissolved TPMN. For the UV-vis spectrum acquired with TPMN aggregates, however, scattering extinction accounts for up to 35% of the peak photon extinction at 480 nm. This number rises to 100% in the wavelength region beyond 580 nm. Sample incubation increases the light scattering extinction, scattering depolarization, and fluorescence emission of the TPMN aggregates, but reduces their light absorption extinction. With its ability to provide information inaccessible with the existing techniques, this work demonstrates that PRS2 is a powerful tool for AIE materials in quantifying their optical properties and monitoring their aggregation/disaggregation processes

Recent Advances in Fluorescent Probes for Cancer Biomarker Detection

Many important biological species have been identified as cancer biomarkers and are gradually becoming reliable targets for early diagnosis and late therapeutic evaluation of cancer. However, accurate quantitative detection of cancer biomarkers remains challenging due to the complexity of biological systems and the diversity of cancer development. Fluorescent probes have been extensively utilized for identifying biological substances due to their notable benefits of being non-invasive, quickly responsive, highly sensitive and selective, allowing real-time visualization, and easily modifiable. This review critiques fluorescent probes used for detecting and imaging cancer biomarkers over the last five years. Focuses are made on the design strategies of small-molecule and nano-sized fluorescent probes, the construction methods of fluorescence sensing and imaging platforms, and their further applications in detection of multiple biomarkers, including enzymes, reactive oxygen species, reactive sulfur species, and microenvironments. This review aims to guide the design and development of excellent cancer diagnostic fluorescent probes, and promote the broad application of fluorescence analysis in early cancer diagnosis

Polarized resonance synchronous spectroscopy as a powerful tool for studying the kinetics and optical properties of aggregation-induced emission

Light scattering and absorption both contribute to the UV-vis extinction quantified with a UV-vis spectrophotometer, but they differ drastically in their causes and effects.</p

Fluorescent AIE-Active Materials for Two-Photon Bioimaging Applications

Fluorescence imaging has been widely used as a powerful tool forin situand real-time visualization of important analytes and biological events in live samples with remarkably high selectivity, sensitivity, and spatial resolution. Compared with one-photon fluorescence imaging, two-photon fluorescence imaging exhibits predominant advantages of minimal photodamage to samples, deep tissue penetration, and outstanding resolution. Recently, the aggregation-induced emission (AIE) materials have become a preferred choice in two-photon fluorescence biological imaging because of its unique bright fluorescence in solid and aggregate states and strong resistance to photobleaching. In this review, we will exclusively summarize the applications of AIE-active materials in two-photon fluorescence imaging with some representative examples from four aspects: fluorescence detection,in vitrocell imaging,ex vivotissue imaging, andin vivovascular imaging. In addition, the current challenges and future development directions of AIE-active materials for two-photon bioimaging are briefly discussed.</jats:p