Discerning the Chemistry in Individual Organelles with Small-Molecule Fluorescent Probes

Aggregation-Induced Fluorescence Probe for Monitoring Membrane Potential Changes in Mitochondria

Fluorescent probe 2 was designed for selectively determining mitochondria membrane potential changes. The probe selectively detects changes in the mitochondria membrane potential in a manner that is more sensitive than that of the commercially available indicator, Rodamine 123. As a result, the probe 2 is ideal for future studies designed to assess the functions of mitochondria in cells.

A Novel Colorimetric Fluorescent Probe for SO₂ and Its Application in Living Cells Imaging

A novel chromenylium-based fluorescent probe was exploited for sulphur dioxide (SO₂) detecting. The probe displayed a remarkable fluorescence turn-on response towards SO₂ based on the nucleophilic addition reaction to the carbon-carbon double bond with 105 nm Stock shift. The probe was successfully applied for the quantification of SO₂.The linear detection range was from 0-160 μM with the detection limit as low as 99.27 nM. It also exhibited high selectivity for SO₂ than other reactive species and amino acids. Furthermore, cell staining experiments indicated that the probe was cell membrane permeable and could be used for high-performance imaging of SO₂ in living cells. The superior properties of the probe made it highly promising for use in chemical and biological applications.

In Situ Construction of Protein-Based Semisynthetic Biosensors

Chemically constructed biosensors consisting of a protein scaffold and an artificial small molecule have recently been recognized as attractive analytical tools for the specific detection and real-time monitoring of various biological substances or events in cells. Conventionally, such semisynthetic biosensors have been prepared in test tubes and then introduced into cells using invasive methods. With the impressive advances seen in bioorthogonal protein conjugation methodologies, however, it is now becoming feasible to directly construct semisynthetic biosensors in living cells, providing unprecedented tools for life-science research. We discuss here recent efforts regarding the in situ construction of protein-based semisynthetic biosensors and highlight their uses in the visualization and quantification of biomolecules and events in multimolecular and crowded cellular systems.

pH-Independent two-photon fluorescent lysotrackers for real-time monitoring autophagy

Two carbazole-based two-photon fluorescent lysotrackers with different electron-donating groups (a methoxyl group for Lyso-MCO and a dimethylamino group for Lyso-NCO, respectively) have been developed from simple starting materials via an only 2-step procedure. Both of them exhibit pH-independent and specific lysosome location with a rapid staining rate, high photostability and deep issue penetration along with large two-photon absorption action cross-sections. By virtue of the better two-photon absorption properties of Lyso-NCO, it was chosen to visually monitor lysosomal tracking and autophagy. Compared with the approach of GFP-LC3 for autophagy detection, lysotracker Lyso-NCO achieved efficient and real-time visualization of the membrane fusion period in the autophagy process through detecting the level of the co-localization coefficients between Lyso-NCO and Mitotracker Red FM (MTR) in live cells.

Recent Advances in the Development of Chromophore-Based Chemosensors for Nerve Agents and Phosgene

The extreme toxicity and ready accessibility of nerve agents and phosgene has caused an increase in the demand to develop effective systems for the detection of these substances. Among the traditional platforms utilized for this purpose, chemosensors including surface acoustic wave (SAW) sensors, enzymes, carbon nanotubes, nanoparticles, and chromophore based sensors have attracted increasing attention. In this review, we describe in a comprehensive manner recent progress that has been made on the development of chromophore-based chemosensors for detecting nerve agents (mimic) and phosgene. This review comprises two sections focusing on studies of the development of chemosensors for nerve agents (mimic) and phosgene. In each of the sections, the discussion follows a format which concentrates on different reaction sites/mechanisms involved in the sensing processes. Finally, chemosensors uncovered in these efforts are compared with those based on other sensing methods and challenges facing the design of more effective chemosensors for the detection of nerve agents (mimic) and phosgene are discussed.

Intra-mitochondrial biomineralization for inducing apoptosis of cancer cells

Mitochondria targeting mineralization can form biominerals inside cancerous mitochondria through concentration dependent silicification, resulting in dysfunction of mitochondria leading to apoptosis. These results suggest potential therapeutics for cancer treatment.

The use of biomineralization that regulates cellular functions has emerged as a potential therapeutic tool. However, the lack of selectivity still limits its therapeutic efficacy. Here, we report a subcellular-targeting biomineralization system featuring a triphenylphosphonium cation (TPP) (the mitochondria-targeting moiety) and trialkoxysilane (the biomineralization moiety via silicification). The TPP-containing trialkoxysilane exhibited approximately seven times greater cellular uptake into cancer cells (SCC7) than into normal cells (HEK293T) due to the more negative mitochondrial membrane potentials of the cancer cells. In turn, its accumulation inside mitochondria (pH 8) induces specific silicification, leading to the formation of silica particles in the mitochondrial matrix and further activation of apoptosis. In vivo assessment confirmed that the biomineralization system efficiently inhibits tumor growth in a mouse xenograft cancer model. Exploiting both the subcellular specificity and the targeting strategy provides new insight into the use of intracellular biomineralization for targeted cancer therapy.

A hydrophobic organelle probe based on aggregation-induced emission: Nanosuspension preparation and direct use for endoplasmic reticulum imaging in living cells

Organic fluorophores have a wide range of biological uses and are usually needed to be prepared as water-soluble compounds or nanoparticles for applications in aqueous biosystems owing to their hydrophobic properties, which often is a complex, time-consuming and high-cost process. Here, the nanoparticle preparation of hydrophobic fluorophores and their application in cell imaging have been investigated. It was found: a) fetal bovine serum (FBS) shows an excellent dispersion effect on hydrophobic small-molecule organic compounds; b) a hydrophobic C6-unsubstituted tetrahydropyrimidine (Me-THP-Naph) can be prepared as nanosuspensions utilizing cell culture medium with 10% FBS and directly be used as a specific real-time imaging probe for the endoplasmic reticulum (ER), a dynamic organelle playing a crucial role in many cellular processes. Compared with existing ER-targeted organic fluorescent probes, Me-THP-Naph, a product of an efficient five-component reaction that we developed, has unconventional aggregation-induced emission characteristics and shows advantages of low cost, long-term staining, good photostability, high signal-to-noise ratio and excellent biocompatibility, which make it a potential specific probe for real-time ER imaging. More importantly, this work affords a simple strategy for direct application of hydrophobic organic compounds in aqueous biological systems.

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.

Imaging of lysosomal pH changes with a novel quinoline/benzothiazole probe

A fluorescent pH probe BTVQ for imaging lysosomal pH fluctuations in live cells and extreme acidity in E. coli cells.

A new GFP fluorophore-based probe for lysosome labelling and tracing lysosomal viscosity in live cells

A new GFP (green fluorescent protein) fluorophore-based probe (Lys-V) was designed and synthesized for mapping lysosomal viscosity in live cells.

A ‘turn-on’ fluorescent probe for lysosomal phosphatase: a comparative study for labeling of cancer cells

A turn-on fluorescent probe (LP1) discriminates cancer cells from normal cells based on expression of phosphatase in lysosomes.

An ESIPT fluorescent probe and a nanofiber platform for selective and sensitive detection of a nerve gas mimic

An ESIPT based fluorescent probe, containing a hydroxyphenyl-benzothiazole fluorophore and an oxime reaction site, serves as a selective probe for a nerve gas mimic, diethyl cyanophosphonate (DECP), in solutions and the gas phase.

A highly fluorescent water soluble spirobifluorene dye with a large Stokes shift: synthesis, characterization and bio-applications

The first water-soluble highly emitting spirobifluorene-based dye and its applications for live cell imaging and BSA detection are reported.

Cation–anion interaction-directed formation of functional vesicles and their biological application for nucleus-specific imaging

A strategy for the construction of counterion-induced vesicles in aqueous media has been described. Furthermore, the imidazolium salt with an AIE fluorophore exhibits highly specific nucleus imaging in the living cells.

Dual-site lysosome-targeted fluorescent probe for separate detection of endogenous biothiols and SO2 in living cells

A novel lysosome-targeted fluorescent probe was developed for the separate detection of endogenous biothiols and SO₂ in living cells.

Multiple cation-doped linear polymers toward ATP sensing and a cell imaging application

A set of multiple cation-doped linear polymers (abbreviated as OPY-1,2-BE, OPY-1,4-BB, OPY-1,8-BO, OPY-1,4-OBB) synthesized from a dipyridine derivative (OPY) and dibrominated compounds were employed as fluorescent probes for adenosine triphosphate (ATP) sensing.

Sydnone-coumarins as clickable turn-on fluorescent sensors for molecular imaging

Sydnone-coumarin compounds are interesting turn-on fluorogenic probes for protein labeling.

Conformational restraint as a strategy for navigating towards lysosomes

Using the conformational restraint strategy, we developed a hydrazonate-derived coumarin into a lysosome targeting probe for imaging native formaldehyde at the subcellular level.

A naphthalimide based fast and selective fluorescent probe for hypochlorous acid/hypochlorite and its application for bioimaging

A reversible and mitochondria targetable fluorescent probe (Nap-Se) bearing 1,8-naphthalimide and a selenomorpholine fragment was designed and synthesized.

Development of a mitochondria targetable ratiometric time-gated luminescence probe for biothiols based on lanthanide complexes

A mitochondria targetable ratiometric luminescence probe based on a mixture of Eu³⁺ and Tb³⁺ complexes has been developed for the specific recognition and ratiometric time-gated luminescence detection of biothiols in aqueous and living samples.

In vivo imaging of hepatocellular nitric oxide using a hepatocyte-targeting fluorescent sensor

A hepatocyte-targeting fluorescent NO sensor has been fabricated with good water solubility, excellent selectivity, and high sensitivity (∼1.62 nM).

Mitochondria-targeted ratiometric fluorescent detection of hydrazine with a fast response time

A fluorescent hydrazine-probe was synthesized, which exhibited high sensitivity, excellent selectivity and anti-interference ability.

A reversible frequency upconversion probe for real-time intracellular lysosome-pH detection and subcellular imaging

The probe NRH-Lyso shows an FUCL response to acidic pH and is a promising candidate for lysosome imaging in living cells.

Pyrrolopyrrole aza boron dipyrromethene based two-photon fluorescent probes for subcellular imaging

A series of two-photon-absorbing pyrrolopyrrole aza boron dipyrromethenes have been prepared which can serve as fluorescent probes for subcellular imaging.

Discovery of a fluorescent probe with HDAC6 selective inhibition

There is increasing interest in discovering HDAC6 selective inhibitors as chemical probes to elucidate the biological functions of HDAC6 and ultimately as new therapeutic agents. Small-molecular fluorescent probes are widely used to detect target protein location and function, identify protein complex composition in biological processes of interest. In the present study, structural modification of the previously reported compound 4MS leads to two novel fluorescent HDAC inhibitors, 6a and 6b. Determination of IC50 values against the panel of Zn2+ dependent HDACs (HDAC1-11) reveals that 6b is a HDAC6 selective inhibitor, which can induce hyperacetylation of tubulin but not histone H4. Importantly, fluorescent and immunofluorescent analyses of cells treated with the proteasome inhibitor MG132 demonstrates that 6b can selectively target and image HDAC6 within the inclusion body, the aggresome. These results identify 6b not only as a HDAC6 selective inhibitor but also as a fluorescent probe for imaging HDAC6 and investigating the roles of HDAC6 in various physiological and pathological contexts.

Pyrene-nucleobase conjugates: synthesis, oligonucleotide binding and confocal bioimaging studies

Fluorescent pyrene–linker–nucleobase (nucleobase = thymine, adenine) conjugates with carbonyl and hydroxy functionalities in the linker were synthesized and characterized. X-ray single-crystal structure analysis performed for the pyrene–C(O)CH₂CH₂–thymine (2) conjugate reveals dimers of molecules 2 stabilized by hydrogen bonds between the thymine moieties. The photochemical characterization showed structure-dependent fluorescence properties of the investigated compounds. The conjugates bearing a carbonyl function represent weak emitters as compared to compounds with a hydroxy function in the linker. The self-assembly properties of pyrene nucleobases were investigated in respect to their binding to single and double strand oligonucleotides in water and in buffer solution. In respect to the complementary oligothymidine T₁₀ template in water, compounds 3 and 5 both show a self-assembling behavior according to canonical base–base pairing. However, in buffer solution, derivative 5 was much more effective than 3 in binding to the T₁₀ template. Furthermore the adenine derivative 5 binds to the double-stranded (dA)₁₀–T₁₀ template with a self-assembly ratio of 112%. Such a high value of a self-assembly ratio can be rationalized by a triple-helix-like binding, intercalation, or a mixture of both. Remarkably, compound 5 also shows dual staining pattern in living HeLa cells. Confocal microscopy confirmed that 5 predominantly stains mitochondria but it also accumulates in the nucleoli of the cells.

Applications of vibrational tags in biological imaging by Raman microscopy

As a superb tool to visualize and study the spatial-temporal distribution of chemicals, Raman microscopy has made a big impact in many disciplines of science. While label-free imaging has been the prevailing strategy in Raman microscopy, recent development and applications of vibrational/Raman tags, particularly when coupled with stimulated Raman scattering (SRS) microscopy, have generated intense excitement in biomedical imaging. SRS imaging of vibrational tags has enabled researchers to study a wide range of small biomolecules with high specificity, sensitivity and multiplex capability, at a single live cell level, tissue level or even in vivo. As reviewed in this article, this platform has facilitated imaging distribution and dynamics of small molecules such as glucose, lipids, amino acids, nucleic acids, and drugs that are otherwise difficult to monitor with other means. As both the vibrational tags and Raman instrumental development progress rapidly and synergistically, we anticipate that this technique will shed light onto an even broader spectrum of biomedical problems.

Fluorescent nucleobases as tools for studying DNA and RNA

Understanding the diversity of dynamic structures and functions of DNA and RNA in biology requires tools that can selectively and intimately probe these biomolecules. Synthetic fluorescent nucleobases that can be incorporated into nucleic acids alongside their natural counterparts have emerged as a powerful class of molecular reporters of location and environment. They are enabling new basic insights into DNA and RNA, and are facilitating a broad range of new technologies with chemical, biological and biomedical applications. In this Review, we will present a brief history of the development of fluorescent nucleobases and explore their utility as tools for addressing questions in biophysics, biochemistry and biology of nucleic acids. We provide chemical insights into the two main classes of these compounds: canonical and non-canonical nucleobases. A point-by-point discussion of the advantages and disadvantages of both types of fluorescent nucleobases is made, along with a perspective into the future challenges and outlook for this burgeoning field.

Supramolecular assembly affording a ratiometric two-photon fluorescent nanoprobe for quantitative detection and bioimaging

Fluorescence quantitative analyses for vital biomolecules are in great demand in biomedical science owing to their unique detection advantages with rapid, sensitive, non-damaging and specific identification. However, available fluorescence strategies for quantitative detection are usually hard to design and achieve. Inspired by supramolecular chemistry, a two-photon-excited fluorescent supramolecular nanoplatform (TPSNP) was designed for quantitative analysis with three parts: host molecules (β-CD polymers), a guest fluorophore of sensing probes (Np-Ad) and a guest internal reference (NpRh-Ad). In this strategy, the TPSNP possesses the merits of (i) improved water-solubility and biocompatibility; (ii) increased tissue penetration depth for bioimaging by two-photon excitation; (iii) quantitative and tunable assembly of functional guest molecules to obtain optimized detection conditions; (iv) a common approach to avoid the limitation of complicated design by adjustment of sensing probes; and (v) accurate quantitative analysis by virtue of reference molecules. As a proof-of-concept, we utilized the two-photon fluorescent probe NHS-Ad-based TPSNP-1 to realize accurate quantitative analysis of hydrogen sulfide (H₂S), with high sensitivity and good selectivity in live cells, deep tissues and ex vivo-dissected organs, suggesting that the TPSNP is an ideal quantitative indicator for clinical samples. What's more, TPSNP will pave the way for designing and preparing advanced supramolecular sensors for biosensing and biomedicine.

HIDE Probes: A New Toolkit for Visualizing Organelle Dynamics, Longer and at Super-Resolution

Living cells are complex and dynamic assemblies that carefully sequester and orchestrate multiple diverse processes that enable growth, division, regulation, movement, and communication. Membrane-bound organelles such as the endoplasmic reticulum, mitochondria, plasma membrane, and others are integral to these processes, and their functions demand dynamic reorganization in both space and time. Visualizing these dynamics in live cells over long time periods demands probes that label discrete organelles specifically, at high density, and withstand long-term irradiation. Here we describe the evolution of our work on the development of a set of high-density environmentally sensitive (HIDE) membrane probes that enable long-term, live-cell nanoscopy of the dynamics of multiple organelles in live cells using single-molecule switching and stimulated emission depletion imaging modalities.

Photosensitizer-free visible light-mediated gold-catalysed cis-difunctionalization of silyl-substituted alkynes

A new photosensitizer-free visible light-mediated gold-catalysed cis-difunctionalization reaction is developed.

A new photosensitizer-free visible light-mediated gold-catalysed cis-difunctionalization reaction is developed. The reaction was chemoselective towards silyl-substituted alkynes with excellent regioselectivity and good functional group compatibility, giving a series of silyl-substituted quinolizinium derivatives as products. The newly synthesized fluorescent quinolizinium compounds, named JR-Fluor-1, possessed tunable emission properties and large Stokes shifts. With unique photophysical properties, the fluorophores have been applied in photooxidative amidations as efficient photocatalysts and cellular imaging with switchable subcellular localization properties.

Development of a Silicon-Rhodamine Based Near-Infrared Emissive Two-Photon Fluorescent Probe for Nitric Oxide

Two-photon (TP) fluorescent probes are potential candidates for near-infrared (NIR) imaging which holds great promise in biological research. However, currently, most TP probes emit at wavelength <600 nm, which impedes their practical applications. In this work, we explored the TP properties of a silicon-rhodamine (SiR) derivative and hence developed the first SiR scaffold based "NIR-to-NIR" TP probe (SiRNO) for nitric oxide (NO). SiRNO exhibited high sensitivity and specificity, as well as fast response for NO detection. It was able to track the subtle variation of intracellular NO content in live cells. Owing to the NIR excitation and emission, SiRNO enabled the detection of NO in situ in the xenograft tumor mouse model, revealing the NO generation during the tumor progression. This work indicates that SiR can be an ideal platform for the development of NIR emissive TP probe and may thus promote the advancement of NIR imaging.