A near-infrared AIEgen for specific imaging of lipid droplets.

A new near-infrared AIE luminogen (TPE-AC) with high specificity, good biocompatibility and excellent photostability is designed and synthesized for lipid droplet (LD) imaging in cells. TPE-AC can monitor the process of LD accumulation in cells, thus making it potential for the diagnosis of early-stage fat-related diseases.

A photostable AIEgen for nucleolus and mitochondria imaging with organelle-specific emission.

Dynamic visualization of the morphology of membrane-bound organelles offers useful insights for studying various intracellular activities. Fluorescent probes with superior specificity and photostability are desirable for long-term tracking of these processes. In this work, we present the design and synthesis of an α-cyanostilbene derivative, abbreviated as ASCP, with the aggregation-induced emission (AIE) characteristic, and its application in cell imaging. ASCP can simultaneously label mitochondria and nucleolus in live cells with distinct fluorescence, which is demonstrative of a single molecule with dual-colour organelle imaging.

An AIE-based bioprobe for differentiating the early and late stages of apoptosis mediated by H2O2.

A bioprobe, TPE-Zn2BDPA, with aggregation-induced emission characteristics was designed and synthesized to differentiate the early and late stages of apoptosis mediated by H2O2. TPE-Zn2BDPA does not respond to healthy cells, but it selectively lights up the membrane of apopotic cells in both stages with brighter fluorescence in the late apoptotic stage.

Using AIE Luminogen for Long-term and Low-background Three-Photon Microscopic Functional Bioimaging.

Fluorescent probes are one of the most popularly used bioimaging markers to monitor metabolic processes of living cells. However, long-term light excitation always leads to photobleaching of fluorescent probes, unavoidable autofluorescence as well as photodamage of cells. To overcome these limitations, we synthesized a type of photostable luminogen named TPE-TPP with an aggregation induced emission (AIE) characteristic, and achieved its three-photon imaging with femtosecond laser excitation of 1020 nm. By using TPE-TPP as fluorescent probes, three-photon microscopy under 1020 nm excitation showed little photo-damage, as well as low autofluorescence to HeLa cells. Due to the AIE effect, the TPE-TPP nanoaggregates uptaken by cells were resistant to photobleaching under three-photon excitation for an extended period of time. Furthermore, we demonstrated that for the present TPE-TPP AIE the three-photon microscopy (with 1020 nm excitation) had a better signal to noise ratio than the two-photon microscopy (with 810 nm excitation) in tissue imaging.

A Luminogen with Aggregation-Induced Emission Characteristics for Wash-Free Bacterial Imaging, High-Throughput Antibiotics Screening and Bacterial Susceptibility Evaluation.

A luminogen with aggregation-induced emission characteristics is reported for bacterial imaging and antibiotics screening studies. The luminogen can light up bacteria in a wash-free manner, which simplifies the imaging process and increases its accuracy in bacterial detection. It can also be applied to high-throughput screening of antibiotics and fast evaluation of bacterial susceptibility, giving reliable results in less than 5 h.

Light-enhanced bacterial killing and wash-free imaging based on AIE fluorogen.

The rapid acquisition of antibiotic resistance poses difficulties in the development of effective methods to eliminate pathogenic bacteria. New bactericides, especially those do not induce the emergence of resistance, are thus in great demand. In this work, we report an aggregation-induced emission fluorogen, TPE-Bac, for bacterial imaging and elimination. TPE-Bac can be readily dissolved in aqueous solution with weak emission. The presence of bacteria can turn on its emission, and thus no washing step is required in the imaging process. Meanwhile, TPE-Bac can be applied as a bactericide for elimination of bacteria. The amphiphilic TPE-Bac bearing two long alkyl chains and two positively charged amines can intercalate into the membrane of bacteria, increase membrane permeability and lead to dark toxicity. The efficiency of bacteria killing is greatly enhanced under light irradiation. TPE-Bac can serve as a photosensitizer to induce reactive oxygen species (ROS) generation, which ensures the efficient killing of bacteria. The TPE-Bac-containing agar plates can be continuously used for bacteria killing by applying light to induce ROS generation.

Specific imaging and tracking of mitochondria in live cells by a photostable AIE luminogen.

Tracking the dynamics of mitochondrial morphology has attracted much research interest because of its involvement in early stage apoptosis and degenerative conditions. To follow this process, highly specific and photostable fluorescent probes are in demand. Commercially available mitochondria trackers, however, suffer from poor photostability. To overcome this limitation, we have designed and synthesized a fluorescent agent, tetraphenylethene-triphenylphosphonium (TPE-TPP), for mitochondrial imaging. Inherent from the mitochondrial-targeting ability of TPP groups and the aggregation-induced emission (AIE) characteristics of the TPE core, TPE-TPP possesses high specificity to mitochondria, superior photostability, and appreciable tolerance to environmental change, allowing imaging and tracking of the mitochondrial morphological changes in a long period of time.

Biosensing by luminogens with aggregation-induced emission characteristics.

Fluorescent biosensors are powerful analytical tools for studying biological events in living systems. Luminescent materials with aggregation-induced emission (AIE) attributes have attracted much research interest and have been identified as a novel class of luminogens to develop fluorescent turn-on biosensors with superior sensitivity. In this Tutorial Review, we present an overview of the AIE phenomenon and its mechanism. We summarize the structural design and working principle of AIE biosensors developed recently. Typical examples of AIE biosensors are presented.

Highly fluorescent and photostable probe for long-term bacterial viability assay based on aggregation-induced emission.

Long-term tracking of bacterial viability is of great importance for monitoring the viability change of bacteria under storage, evaluating disinfection efficiency, as well as for studying the pharmacokinetic and pharmacodynamic properties of antibacterials. Most of the conventional viability dyes, however, suffer from high toxicity and/or poor photostability, making them unsuitable for long-term studies. In this work, an aggregation-induced emission molecule, TPE-2BA, which can differentiate dead and living bacteria and serve as a highly fluorescent and photostable probe for long-term viability assay. TPE-2BA is a cell-impermeable DNA stain that binds to the groove of double-stranded DNA. Bacteria with compromised membrane open the access for TPE-2BA to reach DNA, endowing it with strong emission. The feasibility of using TPE-2BA for screening effective bactericides is also demonstrated. Plate count experiment reveals that TPE-2BA poses negligible toxicity to bacteria, indicating that it is an excellent probe for long-term bacterial viability assay.

Superior fluorescent probe for detection of cardiolipin.

Cardiolipin (CL) is a unique phospholipid found in mitochondrial inner membrane. It is a key component for mitochondrial function in both respiration and apoptosis. The level of CL is an important parameter for investigating these intracellular events and is a critical indicator of a number of diseases associated with mitochondrial respiratory functions. 10-Nonyl acridine orange (NAO) is the only fluorescent dye currently available for CL detection. However, the performance of NAO is far from satisfactory in terms of selectivity and sensitivity. In this work, we report an aggregation-induced emission-active fluorogen, TTAPE-Me, for CL detection and quantification. With improved sensitivity and excellent selectivity to CL over other major mitochondrial membrane lipids, TTAPE-Me could serve as a valuable fluorescent sensor for CL quantification. The use of TTAPE-Me for the quantification of isolated mitochondria is also demonstrated.

Conjugated polyelectrolytes with aggregation-enhanced emission characteristics: synthesis and their biological applications.

Conjugated polyelectrolytes are promising candidates for the construction of fluorescent bioprobes. In this study, a series of water-soluble fluorescent polyelectrolytes have been designed and synthesized by means of the quaternization of their tetraphenylethene-containing polyyne precursors. The polyynes can be facilely prepared through Hay-Glaser polycoupling in high yields (up to 99%) with high molecular weights (up to 38,900). All the polymers exhibit a phenomenon of aggregation-induced or -enhanced emission. The fluorimetric titrations of biomolecules such as heparin, calf thymus DNA, RNA, bovine serum albumin, and human serum albumin to buffer solutions of the polyelectrolytes suggest that they are promising fluorescent bioprobes with high sensitivity and fast response. The emission intensity of the polyelectrolytes is enhanced by up to sevenfold upon binding with biomolecules through electrostatic and hydrophobic cooperative interactions. The polyelectrolytes can also serve as fluorescent visualizers for intracellular imaging with good biocompatibility and low autofluorescence interference.

Full-range intracellular pH sensing by an aggregation-induced emission-active two-channel ratiometric fluorogen.

Intracellular pH (pHi) is an important parameter associated with cellular behaviors and pathological conditions. Sensing pHi and monitoring its changes in live cells are essential but challenging due to the lack of effective probes. We herein report a pH-sensitive fluorogen for pHi sensing and tracking. The dye is a tetraphenylethene-cyanine adduct (TPE-Cy). It is biocompatible and cell-permeable. Upon diffusing into cells, it responds sensitively to pHi in the entire physiological range, visualizing the acidic and basic compartments with intense red and blue emissions, respectively. The ratiometric signal of the red and blue channels can thus serve as an indicator for local proton concentration. The utility of TPE-Cy in pHi imaging and monitoring is demonstrated with the use of confocal microscopy, ratiometric analysis, and flow cytometry.