Dongdong Su

Live cells imaging using a turn-on FRET-based BODIPY probe for biothiols.

We designed a red-emitting turn-on FRET-based molecular probe 1 for selective detection of cysteine and homocysteine. Probe 1 shows significant fluorescence enhancement after cleavage of the 2, 4-dinitrobenzensulfonyl (DNBS) unit from the fluorophore upon thiols treatment. The precursor of probe 1, BNM153, is a moderate quantum yield FRET dye which contributes a minimum emission leakage from its donor part. We synthesized this assembly by connecting a low quantum yield (less than 1%) BODIPY donor to a high quantum yield BODIPY acceptor via a 1, 3-triazine bridge system. It is noteworthy that the majority of the non-radiative energy loss of donor (BDN) was converted to the acceptor (BDM)s fluorescence output with minimum leaks of donor emission. The fluorescence sensing mechanism of probe 1 was illustrated by fluorescence spectroscopy, kinetic measurements, HPLC-MS analysis and DFT calculations. Probe 1 is pH-independent at the physiological pH range. Finally, live cells imaging demonstrated the utility of probe 1 as a biosensor for thiols.

A Multisite-Binding Switchable Fluorescent Probe for Monitoring Mitochondrial ATP Level Fluctuation in Live Cells

Adenosine triphosphate (ATP), commonly produced in mitochondria, is required by almost all the living organisms; thus fluorescent probes for monitoring mitochondrial ATP levels fluctuation are essential and highly desired. Herein, we report a multisite-binding switchable fluorescent probe, ATP-Red 1, which selectively and rapidly responds to intracellular concentrations of ATP. Live-cell imaging indicated that ATP-Red 1 mainly localized to mitochondria with good biocompatibility and membrane penetration. In particular, with the help of ATP-Red 1, we successfully observed not only the decreased mitochondrial ATP levels in the presence of KCN and starvation state, but also the increased mitochondrial ATP levels in the early stage of cell apoptosis. These results indicate that ATP-Red 1 is a useful tool for investigating ATP-relevant biological processes.

Chemical Fluorescent Probe for Detection of Aβ Oligomers

Aggregation of amyloid β-peptide (Aβ) is implicated in the pathology of Alzheimers disease (AD), with the soluble, Aβ oligomeric species thought to be the critical pathological species. Identification and characterization of intermediate species formed during the aggregation process is crucial to the understanding of the mechanisms by which oligomeric species mediate neuronal toxicity and following disease progression. Probing these species proved to be extremely challenging, as evident by the lack of reliable sensors, due to their heterogeneous and transient nature. We describe here an oligomer-specific fluorescent chemical probe, BoDipy-Oligomer (BD-Oligo), developed through the use of the diversity-oriented fluorescent library approach (DOFLA) and high-content, imaging-based screening. This probe enables dynamic oligomer monitoring during fibrillogenesis in vitro and shows in vivo Aβ oligomers staining possibility in the AD mice model.

Dark to light! A new strategy for large Stokes shift dyes: coupling of a dark donor with tunable high quantum yield acceptors

A new strategy for constructing large Stokes shift dyes by coupling a low quantum yield (less than 1%) BODIPY donor (BDN) with tunable high quantum yield BODIPY acceptors (BDM) has been explored to synthesize a set of novel Dark Resonance Energy Transfer (DRET) dyes, named BNM. The low quantum yield of the donor is ascribed to the intramolecular rotation of the phenyl rings, which has been proven by controlling the viscosity and temperature of the solvent. However, upon excitation of BNM compounds at the donor absorption wavelength, tunable emissions from 560 nm to 617 nm were obtained, with a high quantum yield of up to 0.75. Ultrafast dynamic studies demonstrated that the absorbed energy was transferred to the acceptor (BDM) with a high energy transfer rate, before being quenched by non-radiative intramolecular rotations. Using a dark donor makes it possible to avoid fluorescence leaks from donor emission. This is a new set of RET dyes that can be excited by a low quantum yield donor to emit a tunable wide range of high fluorescence emission.

Real-Time In Vivo Hepatotoxicity Monitoring through Chromophore-Conjugated Photon-Upconverting Nanoprobes

Drug toxicity is a long-standing concern of modern medicine. A typical anti-pain/fever drug paracetamol often causes hepatotoxicity due to peroxynitrite ONOO- . Conventional blood tests fail to offer real-time unambiguous visualization of such hepatotoxicity in vivo. Here we report a luminescent approach to evaluate acute hepatotoxicity in vivo by chromophore-conjugated upconversion nanoparticles. Upon injection, these nanoprobes mainly accumulate in the liver and the luminescence of nanoparticles remains suppressed owing to energy transfer to the chromophore. ONOO- can readily bleach the chromophore and thus recover the luminescence, the presence of ONOO- in the liver leads to fast restoring of the near-infrared emission. Taking advantages of the high tissue-penetration capability of near-infrared excitation/emission, these nanoprobes achieve real-time monitoring of hepatotoxicity in living animals, thereby providing a convenient screening strategy for assessing hepatotoxicity of synthetic drugs.

A Simple BODIPY-Based Viscosity Probe for Imaging of Cellular Viscosity in Live Cells

Intracellular viscosity is a fundamental physical parameter that indicates the functioning of cells. In this work, we developed a simple boron-dipyrromethene (BODIPY)-based probe, BTV, for cellular mitochondria viscosity imaging by coupling a simple BODIPY rotor with a mitochondria-targeting unit. The BTV exhibited a significant fluorescence intensity enhancement of more than 100-fold as the solvent viscosity increased. Also, the probe showed a direct linear relationship between the fluorescence lifetime and the media viscosity, which makes it possible to trace the change of the medium viscosity. Furthermore, it was demonstrated that BTV could achieve practical applicability in the monitoring of mitochondrial viscosity changes in live cells through fluorescence lifetime imaging microscopy (FLIM).

Boronic Acid: A Bio-Inspired Strategy To Increase the Sensitivity and Selectivity of Fluorescent NADH Probe

Fluorescent probes have emerged as an essential tool in the molecular recognition events in biological systems; however, due to the complex structures of certain biomolecules, it remains a challenge to design small-molecule fluorescent probes with high sensitivity and selectivity. Inspired by the enzyme-catalyzed reaction between biomolecule and probe, we present a novel combination-reaction two-step sensing strategy to improve sensitivity and selectivity. Based on this strategy, we successfully prepared a turn-on fluorescent reduced nicotinamide adenine dinucleotide (NADH) probe, in which boronic acid was introduced to bind with NADH and subsequently accelerate the sensing process. This probe shows remarkably improved sensitivity (detection limit: 0.084 μM) and selectivity to NADH in the absence of any enzymes. In order to improve the practicality, the boronic acid was further modified to change the measurement conditions from alkalescent (pH 9.5) to physiological environment (pH 7.4). Utilizing these probes, we not only accurately quantified the NADH weight in a health care product but also evaluated intracellular NADH levels in live cell imaging. Thus, these bio-inspired fluorescent probes offer excellent tools for elucidating the roles of NADH in biological systems as well as a practical strategy to develop future sensitive and selective probes for complicated biomolecules.

Synthesis and Systematic Evaluation of Dark Resonance Energy Transfer (DRET)-Based Library and Its Application in Cell Imaging

In this paper, we report a new strategy for constructing a dye library with large Stokes shifts. By coupling a dark donor with BODIPY acceptors of tunable high quantum yield, a novel dark resonance energy transfer (DRET)-based library, named BNM, has been synthesized. Upon excitation of the dark donor (BDN) at 490 nm, the absorbed energy is transferred to the acceptor (BDM) with high efficiency, which was tunable in a broad range from 557 nm to 716 nm, with a high quantum yield of up to 0.8. It is noteworthy to mention that the majority of the non-radiative energy loss of the donor was converted into the acceptors fluorescence output with a minimum leak of donor emission. Fluorescence imaging tested in live cells showed that the BNM compounds are cell-permeable and can also be employed for live-cell imaging. This is a new library which can be excited through a dark donor allowing for strong fluorescence emission in a wide range of wavelengths. Thus, the BNM library is well suited for high-throughput screening or multiplex experiments in biological applications by using a single laser excitation source.

Silica Nanoparticle-Enhanced Fluorescent Sensor Array for Heavy Metal Ions Detection in Colloid Solution

Sensitivity and detection limit are two vital factors that affect fluorophores-based sensing and imaging system. However, it remains a challenge to improve the sensitivity and detection limit of fluorophores, largely due to their limited response and photophysical properties. In this study, we report for the first time, a novel approach to enhance the sensitivity and detection limit of probes using silica nanoparticles, also known as silica nanoparticles-enhanced fluorescence (SiEF). SiEF can drastically improve the fluorescence intensities and detection limit of fluorophores. A SiEF-improved fluorescent sensor array for rapid and sensitive identification of different heavy metal ions is achieved, and a 3D spatial dispersion graph is obtained based on the SiEF-improved fluorescent sensor array, which provides a lower concentration dependent pattern than fluorophores alone, allowing qualitative, quantitative, and sensitive detection of heavy metal ions. Furthermore, with UV lamp irradiation of the sensor-metal ion mixtures, the output signals enable direct visual of heavy metal ions with low concentration. Thus, the SiEF approach provides a simple and practical strategy for fluorescent probes to improve their sensitivity and detection limit in analytes sensing.

A highly selective fluorescent probe for direct detection and isolation of mouse embryonic stem cells.

Graphical abstract