Fluorescent Probes For Bioimaging Research Articles

Aqueous synthesis and biostabilization of CdS@ZnS quantum dots for bioimaging applications

Bionanohybrids, combining biocompatible natural polymers with inorganic materials, have aroused interest because of their structural, functional, and environmental advantages. In this work, we report on the stabilization of CdS@ZnS core–shell quantum dots (QDs) using carboxylated cellulose nanocrytals (CNCs) as nanocarrieers in aqueous phase. The high colloidal stability was achieved with sufficient negative charge on CNC surface and the coordination of Cd2+ to carboxylate groups. This coordination allows the in-situ nucleation and growth of QDs on CNC surface. The influences of QD to CNC ratio, pH and ZnS coating on colloidal stability and photoluminescence property of CNC/QD nanohybirds were also studied. The results showed that products obtained at pH 8 with a CdS to CNC weight ratio of 0.19 and a ZnS/CdS molar ratio of 1.5 possessed excellent colloidal stability and highest photoluminescence intensity. By anchoring QDs on rigid bionanotemplates, CNC/CdS@ZnS exhibited long-term colloidal and optical stability. Using biocompatible CNC as nanocarriers, the products have been demonstrated to exhibit low cytotoxicity towards HeLa cells and can serve as promising red-emitting fluorescent bioimaging probes.

ChemInform Abstract: Development of Fluorescent Probes Based on Protection—Deprotection of the Key Functional Groups for Biological Imaging

AbstractReview: 50 refs.

How do nitrogen-doped carbon dots generate from molecular precursors? An investigation of the formation mechanism and a solution-based large-scale synthesis.

A bottom-up method, using monoethanolamine (MEA) as both a passivation agent and a solvent, has been developed for rapid and massive synthesis of nitrogen-doped carbon dots (N-C-dots) from citric acid under heating conditions. This method requires a relatively mild temperature (170 °C) without special equipment, and affords one-pot large-scale production (39.96 g) of high-quality N-C-dots (quantum yield of 40.3%) in a few minutes (10 minutes). Significantly, an interesting formation process of N-C-dots, for the first time, has been monitored by transmission electron microscopy, ultraviolet-visible absorbance spectroscopy, photoluminescence spectroscopy, Fourier transformed infrared spectroscopy, and thermogravimetric analysis, and a corresponding formation mechanism, including polymerization, aromatization, nucleation, and growth, is proposed. It is important that the MEA-based synthesis of N-C-dots can be extended to various precursors, such as glucose, ascorbic acid, cysteine, and glutathione, which show general universality. Furthermore, the N-C-dots with strong fluorescence, excellent optical stability, and low cytotoxicity are successfully applied as fluorescent probes for bioimaging.

Facile preparation and multifunctional applications of boron nitride quantum dots

Boron nitride quantum dots are obtained by a facile sonication-solvothermal technique. They are proven to be promising fluorescent bioimaging probes for bioimaging with remarkably low cytotoxicity and easily integrated into high-performance proton exchange membranes. This work will probably trigger research interest in BN and its new applications in a variety of fields.

Toward a selective, sensitive, fast-responsive, and biocompatible two-photon probe for hydrogen sulfide in live cells.

Hydrogen sulfide has emerged as an exciting endogenous gasotransmitter in addition to nitric oxide and carbon dioxide. Noninvasive detection methods for hydrogen sulfide thus become indispensable tools for studying its diverse roles in biological systems. Accordingly, fluorescent probes for hydrogen sulfide have received great attention in recent years. A practically useful fluorescent probe for bioimaging of hydrogen sulfide should be selective, sensitive, fast-responsive, biocompatible, observable in the biological optical window, and capable of deep-tissue imaging. These sensing properties, however, are extremely difficult to achieve at the same time. Disclosed here is the two-photon fluorescent probe that meets all of these criteria. The probe belongs to a Michael acceptor system, which raised a serious selectivity issue over the competing biothiols such as cysteine and glutathione. We have addressed the selectivity issue by optimizing the electronic and steric interactions between biothiols and the probe, in addition to achieving very high sensitivity, fast-response, and biocompatibility. Also, the sensing mechanism suggested in the literature was revised. The probe thus enables us to image the endogenously produced hydrogen sulfide with negligible interference from other biothiols in live cells. The excellent sensing properties of the probe combined with its capability of bioimaging thus make it a practically useful tool for further studying biological roles of hydrogen sulfide.

Highly Sensitive Low-Background Fluorescent Probes for Imaging of Nitric Oxide in Cells and Tissues

Small-molecule fluorescent probes in combination with fluorescent microscopy can be a powerful tool to provide real-time detection and high spatiotemporal resolution of transient molecules in cells and bodies. For the design of fluorescent probes for transient molecule imaging, high detection sensitivity is crucial. In this report, two new fluorescent probes, 8-(3,4-diaminophenyl)-4,4-difluoro-4-bora-3a,4a-diaza-di(1,2-dihydro)naphtho[b,g]-s-indacene (DANPBO-H) and 8-(3,4-diaminophenyl)-1,7-dimethyl-4,4-difluoro-4-bora-3a,4a-diaza-di(1,2-dihydro)naphtho[b,g]-s-indacene (DANPBO-M), have been developed for nitric oxide (NO) imaging. The detection sensitivity has been efficiently improved by use of these probes through increasing NO detection signals and decreasing background fluorescence. Fluorescence in the far-red region is enhanced by 400- and 550-fold after reaction with NO is achieved and remains stable for at least 24 h under the irradiation of xenon lamp. Excitation and emission wavelengths longer than 600 nm and excellent intracellular retention of these probes and their NO products create dark background inside and outside cells and tissues. What is more, the excellent intracellular retention of these compounds is obtained by their strong lipophilicity, which is a novel design concept diametrically opposite to the traditional approaches. The high sensitivity and dark background make DANPBO-H and DANPBO-M competitive for NO imaging in cells and tissues. The lipophilicity-based intracellular retention mechanism as a design strategy has great potential in the development of fluorescent probes for bioimaging.

A new route towards fluorescent organic nanoparticles with red-shifted emission and increased colloidal stability

Suzuki–Miyaura cross-coupling reaction with a new boron reagent has been used to conveniently and efficiently synthetize a dipolar chromophore having an elongated π-conjugated system (i.e., bithiophene based), which displays a red-shifted emission while maintaining fluorescence. Bright orange emitting FONs made from this ‘naked’ dipole have been easily prepared and studied. Very interestingly, these FONs with red-shifted emission combine markedly enhanced colloidal and structural stability in water with giant one- and two-photon brightness. As such, they hold promises as fluorescent probes for bioimaging.

Recent development of two-photon fluorescent probes for bioimaging

Fluorescent probes are essential tools for studying biological systems. The last decade has witnessed particular interest in the development of two-photon excitable probes, owing to their advantageous features in tissue imaging compared to the corresponding one-photon probes. This review summarizes various types of two-photon probes that have been applied to bioimaging, categorized by the principles in the probe design and the target analytes, which would provide a basis for the future development of novel two-photon probes for tackling important biological issues.

Small-molecule fluorophores and fluorescent probes for bioimaging

Fluorescent compounds based on synthetic small molecules are powerful tools to visualize biological events in living cells and organisms. Ever since the discovery of organic fluorescent compounds in the late nineteenth century, efforts have been made to "see" the behaviors of specific biomolecules in living systems by using these dyes as labels. Also, following the development of fluorescent Ca(2+) indicators in the 1980s, many fluorescent probes or biosensors, which are defined as molecules that show a change in fluorescence properties in the presence of their target molecule, have been reported and applied in biological research. Today, a variety of probes are available that target metal ions, pH, enzyme activities, and signaling molecules. In this review, we first consider the history of organic fluorescent molecules and discuss their utility for labeling biomolecules and staining cells. Then, we review recent progress in small-molecule fluorescent probes for metal ions and reactive oxygen species, focusing on representative work in each category. Finally, we briefly discuss attempts to create novel kinds of probes, including hybrids of small molecules and genetically encoded proteins, with the potential to overcome some of the limitations of current probes.

A near-infrared fluorophore for live-cell super-resolution microscopy of cellular proteins

The ideal fluorescent probe for bioimaging is bright, absorbs at long wavelengths and can be implemented flexibly in living cells and in vivo. However, the design of synthetic fluorophores that combine all of these properties has proved to be extremely difficult. Here, we introduce a biocompatible near-infrared silicon-rhodamine probe that can be coupled specifically to proteins using different labelling techniques. Importantly, its high permeability and fluorogenic character permit the imaging of proteins in living cells and tissues, and its brightness and photostability make it ideally suited for live-cell super-resolution microscopy. The excellent spectroscopic properties of the probe combined with its ease of use in live-cell applications make it a powerful new tool for bioimaging.

Fluorescence and two-photon absorption of push—pull aryl(bi)thiophenes: structure—property relationships

Photophysical and TPA properties of series of push-pull aryl(bi)thiophene chromophores bearing electron-donating (D) and electron-withdrawing (A) end-groups of increasing strength are presented. All compounds show an intense intramolecular charge transfer (ICT) absorption band in the visible region. Increasing the D and/or A strength as well as the length of the conjugated path induces bathochromic and hyperchromic shifts of the absorption band as reported for analogous push-pull polyenes. Yet, in contrast with corresponding push-pull polyenes, a significant increase in fluorescence is observed. In particular, chromophores built from a phenyl-bithienyl conjugated path and bearing strong D and A end-groups were found to combine very large one and two-photon brightness as well as strong emission in the red/NIR region. These molecules hold promise as biphotonic fluorescent probes for bioimaging.

Dehydrogenative Heck coupling of biologically relevant N-heteroarenes with alkenes: discovery of fluorescent core frameworks

A Pd/Cu-catalyzed dehydrogenative Heck coupling is established that allows direct alkenylation of various biologically relevant N-heteroarenes with alkenes. The resulting π-extended alkenylated N-heteroarenes exhibit interesting fluorescent properties and have proven to be potentially useful fluorescent probes for bioimaging.

Aggregation-induced red-NIR emission organic nanoparticles as effective and photostable fluorescent probes for bioimaging

Organic fluorescent probes are widely used in bioimaging and bioassays, but the notorious photobleaching hampers their applications. Encapsulation of organic dyes into nanoparticles (NPs) is an effective strategy to minimize photobleaching, but classical organic dye molecules tend to have their fluorescence quenched in aggregate states, which is termed aggregation-caused quenching (ACQ). Here we demonstrate our attempt to tackle this problem through the aggregation-induced emission (AIE) strategy. 3,4:9,10-Tetracarboxylic perylene bisimide (PBI) is a well-known organic dye with a serious ACQ problem. By attaching two tetraphenylethene (TPE) moieties to the 1,7-positions, the ACQ-characteristic PBI-derivative was converted to an AIE-characteristic molecule. The obtained PBI derivative (BTPEPBI) exhibits several advantages over classical PBI derivatives, including pronounced fluorescence enhancement in aggregate state, red to near infrared emission, and facile fabrication into uniform NPs. Studies on the staining of MCF-7 breast cancer cells and in vivo imaging of a tumor-bearing mouse model with BTPEPBI-containing NPs reveal that they are effective fluorescent probes for cancer cell and in vivo tumor diagnosis with high specificity, high photostability and good fluorescence contrast.

Beyond fluorescence

Nanoparticles that generate light through a mechanism known as second harmonic generation have been used to image live tissue. The particles overcome many problems associated with fluorescent probes for bioimaging.

Bimodal magnetic–fluorescent probes for bioimaging

Fluorescent optical probes have been intensively used in the area of bio-imaging. In this review article, we describe the recent advancements in the synthesis and application of bimodal magnetic-fluorescent probes for bioimaging. The bimodal probes consist of fluorescent [semiconducting quantum dots (e.g., CdSe/ZnS) or rare-earth doped (e.g., NaYF(4) :Yb,Er)] nanoparticles (NPs) and magnetic (iron oxide or gadolinium based) NPs for optical and magnetic resonance (MR) imaging.

Rational Design of Fluorescent Bioimaging Probes by Controlling the Aggregation Behavior of Squaraines: A Special Effect of Ionic Liquid Pendants

We herein present an effective strategy to create water-soluble fluorescent bioimaging dyes by introducing the imidazolium-based ionic liquid (IL) pendants into a fluorescent skeleton. A new type of water-soluble imidazolium-anchored squaraine dye was synthesized accordingly. The relationship between the aggregate of squaraines and their fluorescent cell imaging application was elucidated in detail. Firstly, the aggregation behavior of squaraines in water solutions could be suppressed by varying the alkyl chain attached to the imidazolium unit. Secondly, the capability of cellular uptake and staining of dyes was also dramatically enhanced upon increasing the length of the paraffinic chain. These squaraine dyes displayed an excellent photostability that could permit real-time fluorescence bioimaging experiments to be monitored over a long time period with constant sample irradiation. Additionally, we designed for the first time an Fe(II)-ion probe on the basis of an attack of the hydroxyl radical to the four-membered ring of squaraine. The results demonstrated that the imidazolium-anchored squaraines could perform "naked-eye" detection of the Fe(2+) ion over a wide range of other interfering metals in aqueous media. More surprisingly, this process showed a fluorescence "turn-off" and "-on" response through the regeneration of squaraines in cells.

細胞膜模倣ポリマーマテリアルのナノバイオ機能

Preparation and characterization of the cell membrane-inspired polymer materials, which contain 2-methacryloyloxyethyl phosphorylcholine (MPC) unit, are reviewed. The MPC polymer can provide the biointerface to suppress completely the interactions with proteins and cells. Also, on the surface, the biomolecules are immobilized without significant reduction of the their biological activity. Polymer nanoparticles covered with the biointerface and contained quantum dot (QD) s is prepared as the novel bioimaging devices. The kinetic behavior in cytoplasm of the polymer nanopartcles is discussed. Although this nanoparticles can avoid the nonselective cellular uptake from mammalian cells, when bioactive molecules are immobilized, the nanoparticles can provide the various information about the specific interaction between biomolecules and cells. From these findings, it is concluded that the nanoparticles are candidates for the role of stable and highly sensitive fluorescent bioimaging probes in the fields of nanomedicine. Controlling interactions with cells is receiving considerable importance in biomedical fields, including nanobioengineering and cell and tissue engineering. The biointerface described here are a promising design for revealing a universal platform that integrates polymer chemistry; material science; and engineering, biochemistry, cell biology, and nanofabrication.

Scalable and concise synthesis of dichlorofluorescein derivatives displaying tissue permeation in live zebrafish embryos.

Don't be so negative. We have synthesized new dichlorofluorescein derivatives that are less negatively charged than fluorescein. The synthesis is concise and scalable, and the compounds are conjugation-ready. In addition, these compounds permeate zebrafish embryos; this suggests that they might be useful fluorescent probes for bioimaging. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2268/2008/z700565_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Nanogel-quantum dot hybrid nanoparticles for live cell imaging

We report here a novel carrier of quantum dots (QDs) for intracellular labeling. Monodisperse hybrid nanoparticles (38 nm in diameter) of QDs were prepared by simple mixing with nanogels of cholesterol-bearing pullulan (CHP) modified with amino groups (CHPNH 2). The CHPNH 2–QD nanoparticles were effectively internalized into the various human cells examined. The efficiency of cellular uptake was much higher than that of a conventional carrier, cationic liposome. These hybrid nanoparticles could be a promising fluorescent probe for bioimaging.