Small-Molecule Two-Photon Probes for Bioimaging Applications

The achievement of high-efficient pure red emissive carbon dots (CDs) is still a great challenge as well as one of the most critical issues that hinders widespread applications of CDs. Herein, a facile approach for the preparation of high-efficient red emissive CDs (R-CDs) is reported, and they exhibit numerous unique features including pure red emission (λmax ≈ 640 nm), respectable quantum yield (22.9%), low cytotoxicity, two-photon excited fluorescence (TPEF), and high photothermal conversion efficiency (43.9% under irradiation of 671 nm laser). Moreover, the chemical composition and photophysical properties of the R-CDs are detailed characterized and analyzed, and from which their photoluminescence mechanism is proposed. Interestingly, the R-CDs are found to particularly light up RNA-rich nucleolus both in one-photon and two-photon modes as well as show excellent counterstain compatibilities with other classical subcellular dyes. The localization of the R-CDs in nucleolus is supported by ribonuclease d...

Toward High-Efficient Red Emissive Carbon Dots: Facile Preparation, Unique Properties, and Applications as Multifunctional Theranostic Agents

Lipid droplets are dynamic organelles involved in various physiological processes and their detection is thus of high importance to biomedical research. Recent reports show that AIE probes for lipid droplet imaging have the superior advantages of high brightness, large Stokes shift and excellent photostability compared to commercial dyes but suffer from the problem of having a short excitation wavelength. In this work, an AIE probe, namely TPA-BI, was rationally designed and easily prepared from triphenylamine and imidazolone building blocks for the two-photon imaging of lipid droplets. TPA-BI exhibited TICT+AIE features with a large Stokes shift of up to 202 nm and a large two-photon absorption cross-section of up to 213 GM. TPA-BI was more suitable for two-photon imaging of the lipid droplets with the merits of a higher 3D resolution, lesser photobleaching, a reduced autofluorescence and deeper penetration in tissue slices than a commercial probe based on BODIPY 493/503, providing a promising imaging tool for lipid droplet tracking and analysis in biomedical research and clinical diagnosis.

/pdf/two-photon-aie-bio-probe-with-large-stokes-shift-for-20xvci3ulw.pdf

Two-photon AIE bio-probe with large Stokes shift for specific imaging of lipid droplets.

We report on two-photon fluorescence excitation (TPE) action
cross sections for five widely used molecular
fluorophores. Measurements were performed by use of ultrashort
(∼100-fs) Ti:sapphire pulsed excitation over the range 690–960
nm. TPE spectra were obtained by comparison with a fluorescein
calibration standard. Large cross sections were found for the
cyanine reagent Cy 3 (∼140 GM) and for Rhodamine 6G (∼150
GM), both at 700 nm [1 GM = 10-50
(cm4 s)/photon]. Several fluorophores show
interesting and desirable blue shifts with respect to twice the
one-photon absorption wavelength. Fluorophore fluorescence
intensities showed no significant departure (±4%) from quadratic
illumination power dependence, indicating genuine two-photon
processes. Implications of these measurements for two-photon
laser-scanning microscopy are discussed.

Two-photon fluorescence excitation cross sections of biomolecular probes from 690 to 960 nm

S-adenosyl methionine (SAM) is a universal biological cofactor that is found in all branches of life where it plays a critical role in the transfer of methyl groups to various biomolecules, including DNA, proteins and small-molecule secondary metabolites The methylation process thus has important implications in various disease processes and applications in industrial chemical processing This methyl transfer is catalysed by SAM-dependent methyltransferases (MTases), which are by far the largest groups of SAM-dependent enzymes A significant amount is now known regarding the structural biology and enzymology of these enzymes, and, consequently, there is now significant scope for the development of new MTases and SAM analogues for applications from biomolecular imaging to biocatalytic industrial processes This review will focus on current efforts in the manipulation of class I and V SAM-dependent MTases and the use of synthetic SAM analogues, which together offer the best prospects for rational redesign towards biotechnological applications Firstly, metabolic engineering of organisms incorporating small-molecule MTases is discussed; this can be applied in a variety of areas from the industrial bioprocessing of flavourants and antibiotics to frontier research in biofuel production and bioremediation Secondly, the application of MTases in combination with SAM analogues is reviewed; this allows the tagging of proteins and oligonucleotides with moieties other than the methyl group Such tagging allows the isolation of the tagged biomolecule and aids its visualisation by a range of analytical methods The review then summarises the potential advantages of MTase-mediated chemistry and offers some future perspectives on downstream applications

S‐Adenosyl‐Methionine‐Dependent Methyltransferases: Highly Versatile Enzymes in Biocatalysis, Biosynthesis and Other Biotechnological Applications

A versatile synthetic strategy to access a set of highly fluorescent π-conjugated triphenylamines bearing a functional linker at various positions on one phenyl ring is described. These compounds were designed for large two-photon absorption (2PA) and in particular for labeling of biomolecules. The monoderivatized trisformylated or trisiodinated intermediates described herein allow introduction of a large variety of electron-withdrawing groups required for large 2PA as well as a panel of chemical functions suitable for coupling to biomolecules. The monoderivatized three-branched compounds and in particular the benzothiazole (TP-3Bz) series show remarkable linear (high extinction coefficients and high quantum yield) and nonlinear (high 2-photon cross sections) optical properties. Interestingly the presence of functional side chains does not disturb the two-photon absorption. Finally, monoderivatized two-branched derivatives also appear to be valuable candidates. Altogether the good optical properties of th...

Synthetic strategies to derivatizable triphenylamines displaying high two-photon absorption.

A series of mono-, bis- and trisvinyl-pyridinium triphenylamines (TP-py) has been synthesised and evaluated for its one- and two-photon absorption (2PA) induced-fluorescence properties under biological conditions. Interestingly, these compounds are only weakly fluorescent in water, whereas their fluorescence emissions are strongly restored (exaltation factors of 20-100) upon binding to double-stranded DNA. Additional measurements in glycerol indicate that the fluorescence increases are the result of immobilisation of the dyes in the DNA matrix, which inhibits rotational de-excitation modes. This particular feature is especially remarkable in the case of the bis and tris derivatives (TP-2 py, TP-3 py), which each display a high affinity (K(d) ~ microM) for dsDNA. TPIF measurements have shown that TP-2 py and TP-3 py each have a large 2PA cross section (delta up to 700 GM) both in glycerol and in the presence of DNA, which ranks them amongst the best 2PA biological fluorophores. Finally, one- and two-photon confocal imaging in cells revealed that these compounds perform red staining (lambda(em)=660-680 nm) of nuclear DNA with excellent contrast. The remarkable optical properties of the TP-py series, combined with their high photostability and their easy synthetic access, make these compounds extremely attractive for use in confocal and 2PA microscopy.

Vinyl-pyridinium triphenylamines: novel far-red emitters with high photostability and two-photon absorption properties for staining DNA.

Sequence-specific Methyltransferase-Induced Labelling (SMILing) of plasmid DNA for studying cell transfection.

S equence-specific M ethyltransferase- I nduced L abel ing of DNA (SMILing DNA)

A series of red emitting vinyl-triphenyamines (TP) have been synthesized and evaluated for their two photon absorption (2PA) properties. These compounds are virtually non fluorescent in the free state but exhibit a bright red fluorescence upon binding to double-stranded DNA, both in one- and two-photon absorption. This feature allows one- and two-photon confocal imaging in cells of nuclear DNA with an excellent contrast. Derivatizable analogues for covalent bioconjugation to oligonucleotides are described and variation on the structure is discussed.

/pdf/new-triarylamine-based-far-red-dna-stainers-with-high-two-3fseet97m9.pdf

New triarylamine-based far-red DNA stainers with high two-photon absorption properties.

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