Nucleic acid-specific photoactivation of oligodeoxyribonucleotides labeled with deuterated dihydro-N,N,N',N'-tetramethylrhodamine using green light

Facile Strategy to Output Fluorescein from Nucleic Acid Interactions

Biomolecular operations, which involve the conversion of molecular signals or interactions into specific functional outputs, are fundamental to the field of biology and serve as the important foundation for the design of diagnostic and therapeutic systems. To maximize their functionalities and broaden their applicability, it is crucial to develop novel outputs and facile chemical transformation methods. With this aim, in this study, we present a straightforward method for converting nucleic acid signals into fluorescein outputs that exhibit a wide range of functionalities. This operation is designed through a DNA-templated reaction based on riboflavin-photocatalyzed oxidation of dihydrofluorescein, which is readily prepared by simple NaBH4 reduction of the fluorescein with no complicated chemical caging steps. The templated photooxidation exhibits high efficiency (kapp = 2.7 × 10-3/s), generating a clear fluorescein output signal distinguishable from a low background, originating from the high stability of the synthesized dihydrofluorescein. This facile and efficient operation allows the nucleic acid-initiated activation of various fluorescein functions, such as fluorescence and artificial oxidase activity, which are applied in the design of novel bioanalytical systems, including fluorescent and colorimetric DNA sensors. The operation presented herein would expand the scope of biomolecular circuit systems for diagnostic and therapeutic applications.

Riboflavin-catalyzed templated reaction to translate nucleic acid cues into signals of rhodamine derivatives

We report a templated reaction for the facile translation of nucleic acid cues into signals of universal rhodamine derivatives based on the riboflavin-catalyzed oxidation of dihydrorhodamine compounds. The rhodamine-signaling operation enabled us to design a highly sequence-selective fluorescent sensor that can detect as little as 500 pM of the target nucleic acid in 90 min or to present a rhodamine antibody that can be further applied to immunoassays.

Red light-triggered photoreduction on a nucleic acid template

Conjugate Sn(iv)(pyropheophorbide a)dichloride-(peptide nucleic acid) catalyzes reduction of azobenzene derivatives in the presence of complementary nucleic acid (NA) upon irridiation with red light (660 nm). This is the first red light-induced NA-templated photoreduction. It is highly sensitive to single mismatches in the NA-template and can detect down to 5 nM NAs.

Red Light Triggered Fluorogenic Reaction with Picomolar Sensitivity Toward Nucleic Acids

We have previously reported on a red light triggered, singlet oxygen-mediated fluorogenic reaction that is templated in a highly sequence specific fashion by nucleic acids (S. Dutta, A. Fulop, A. Mokhir, Bioconjgate Chem. 2013, 24 (9), 1533-1542). Up to the present date, it has remained a single templated reaction responsive to nontoxic >650 nm light. However, it is operative only in the presence of relatively high (>2 nM) concentrations of templates that dramatically limit its applicability in nucleic acid detection. In the current work, we established that an inefficient intermolecular electron transfer involved in reduction of the 1,4-endoperoxide intermediate, formed in the rate-limiting reaction step, is responsible for inhibition of the reaction at low reagent concentrations. We suggested the solution of the problem which includes a combination of a cleavable (9-alkoxyanthracene) moiety with a two-electron donating fragment in one molecule. This approach enables the efficient intramolecular electron transfer to the endoperoxide intermediate in the critical reaction step. Due to the intramolecular character of the latter process, it is practically independent of concentration of the reagents. The reaction based on the improved cleavable moiety was found to be >200-fold more sensitive than the previously reported one. It is fast, sequence specific, and compatible with live cells. Accounting for short reactions times (<30 min), nontoxic trigger (red light), excellent sensitivity, and sequence specificity, this is presently the best reported photochemical templated reaction compatible with live cells.

DNA-Dye-Conjugates: Conformations and Spectra of Fluorescence Probes

Extensive molecular-dynamics (MD) simulations have been used to investigate DNA-dye and DNA-photosensitizer conjugates, which act as reactants in templated reactions leading to the generation of fluorescent products in the presence of specific desoxyribonucleic acid sequences (targets). Such reactions are potentially suitable for detecting target nucleic acids in live cells by fluorescence microscopy or flow cytometry. The simulations show how the attached dyes/photosensitizers influence DNA structure and reveal the relative orientations of the chromophores with respect to each other. Our results will help to optimize the reactants for the templated reactions, especially length and structure of the spacers used to link reporter dyes or photosensitizers to the oligonucleotides responsible for target recognition. Furthermore, we demonstrate that the structural ensembles obtained from the simulations can be used to calculate steady-state UV-vis absorption and emission spectra. We also show how important quantities describing the quenching of the reporter dye via fluorescence resonance energy transfer (FRET) can be calculated from the simulation data, and we compare these for different relative chromophore geometries.

The Histochemistry and Cell Biology pandect: the year 2014 in review

This review encompasses a brief synopsis of the articles published in 2014 in Histochemistry and Cell Biology. Out of the total of 12 issues published in 2014, two special issues were devoted to "Single-Molecule Super-Resolution Microscopy." The present review is divided into 11 categories, providing an easy format for readers to quickly peruse topics of particular interest to them.