Raphael M Franzini

Stanford University, Stanford, CA, United States

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Publications (6)34.8 Total impact

  • Source
    Raphael M Franzini, Eric T Kool
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    ABSTRACT: Templated fluorescence activation has recently emerged as a promising molecular approach to detect and differentiate nucleic acid sequences in vitro and in cells. Here, we describe the application of a reductive quencher release strategy to the taxonomic analysis of Gram-negative bacteria by targeting a single nucleotide difference in their 16S rRNA in a two-color assay. For this purpose, it was necessary to develop a release linker containing a quencher suitable for red and near-infrared fluorophores, and to improve methods for the delivery of probes into cells. A cyanine-dye labeled oligonucleotide probe containing the new quencher-release linker showed unprecedentedly low background signal and high fluorescence turn-on ratios. The combination of a fluorescein-containing and a near-IR emitting probe discriminated E. coli from S. enterica despite nearly identical ribosomal target sequences. Two-color analysis by microscopy and the first successful discrimination of bacteria by two-color flow cytometry with templated reactive probes are described.
    Bioconjugate Chemistry 08/2011; 22(9):1869-77. · 4.58 Impact Factor
  • Raphael M Franzini, Eric T Kool
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    ABSTRACT: We report a new strategy for template-mediated fluorogenic chemistry that results in enhanced performance for the fluorescence detection of nucleic acids. In this approach, two successive templated reactions are required to induce a fluorescence signal, rather than only one. These novel fluorescein-labeled oligonucleotide probes, termed 2-STAR (STAR = Staudinger-triggered α-azidoether release) probes, contain two quencher groups tethered by separate reductively cleavable linkers. When a 2-STAR quenched probe successively binds adjacent to two mono-triphenylphosphine-(TPP)-DNAs or one dual-TPP-DNA, the two quenchers are released, resulting in a fluorescence signal. Because of the requirement for two consecutive reactions, 2-STAR probes display an unprecedented level of sequence specificity for template-mediated probe designs. At the same time, background emission generated by off-template reactions or incomplete quenching is among the lowest of any fluorogenic reactive probes for the detection of DNA or RNA.
    Chemistry 02/2011; 17(7):2168-75. · 5.93 Impact Factor
  • Hao Li, Raphael M Franzini, Christopher Bruner, Eric T Kool
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    ABSTRACT: We describe the development of templated fluorogenic chemistry for detection of specific sequences of duplex DNA in solution. In this approach, two modified homopyrimidine oligodeoxynucleotide probes are designed to bind by triple-helix formation at adjacent positions on a specific purine-rich target sequence of duplex DNA. One fluorescein-labeled probe contains an α-azidoether linker to a fluorescence quencher; the second (trigger) probe carries a triarylphosphine group that is designed to reduce the azide and cleave the linker. The data showed that at pH 5.6 these probes yielded a strong fluorescence signal within minutes on addition to a complementary homopurine duplex DNA target. The signal increased by a factor of about 60, and was completely dependent on the presence of the target DNA. Replacement of cytosine in the probes with pseudoisocytosine allowed the templated chemistry to proceed readily at pH 7. Single nucleotide mismatches in the target oligonucleotide slowed the templated reaction considerably; this demonstrated high sequence selectivity. The use of templated fluorogenic chemistry for detection of duplex DNAs has not been previously reported and could allow detection of double-stranded DNA, at least for homopurine-homopyrimidine target sites, under native and nondenaturing conditions.
    ChemBioChem 10/2010; 11(15):2132-7. · 3.74 Impact Factor
  • Source
    Raphael M Franzini, Eric T Kool
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    ABSTRACT: RNA-templated fluorescence activation is a nucleic acid detection strategy that offers the possibility of direct visual detection of genetic information in living cells. Here we describe a new reaction strategy for fluorescence activation in which a phosphine on one DNA probe reduces an azide group in a linker on a second probe, resulting in linker cleavage and release of a fluorescence quenching group. These "Q-STAR" probes are shown to yield a strong fluorescence turn-on signal in approximately 20 min, with very low background and substantial amplification by turnover on the template. A green/red pair of such probes allowed the discrimination of two bacterial species by a single nucleotide difference in their 16S rRNA. The beneficial properties of the reductive quencher release design make these probes promising candidates for widespread application in the detection of nucleic acids in vitro and in cells.
    Journal of the American Chemical Society 11/2009; 131(44):16021-3. · 10.68 Impact Factor
  • Raphael M Franzini, Eric T Kool
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    ABSTRACT: Templated nucleic acid detection is an emerging bioanalytical method that makes use of the target DNA or RNA strand to initiate a fluorogenic reaction. The Staudinger reduction holds particular promise for templated sensing of nucleic acids because the involved functional groups are highly chemoselective. Here, the azidomethoxy group, which can be removed under Staudinger conditions, is used to cage 7-hydroxycoumarin fluorophores. Reduction by phosphines and subsequent loss of the azidomethoxy substituent induce a significant bathochromic shift of the major absorbance band in the near UV region. When excited at the appropriate wavelength, this change in the absorbance spectrum translates into a substantial fluorescence turn-on signal. The described profluorophores are readily conjugated to amino-modified DNAs and are rapidly uncaged by a triphenylphosphine-DNA probe under the control of a DNA template. In addition, turnover of the probes on the target strand occurs and yields substantial signal amplification.
    ChemBioChem 12/2008; 9(18):2981-8. · 3.74 Impact Factor
  • Raphael M Franzini, Eric T Kool
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    ABSTRACT: A nucleic acid detection scheme that employs DNA-mediated delivery of an organomercury activator to unmask a fluorophore is described. The approach relies on adjacent hybridization of two oligonucleotide conjugates containing organomercury and caged rhodamine functionalities. Postsynthetic conjugation of amino-modified DNAs enabled efficient preparation of these probes. Complementary DNA templates yielded fluorescence signals arising from metal-assisted rhodamine uncaging.
    Organic Letters 08/2008; 10(14):2935-8. · 6.14 Impact Factor

Publication Stats

76 Citations
15 Downloads
325 Views
34.80 Total Impact Points

Institutions

  • 2008–2011
    • Stanford University
      • Department of Chemistry
      Stanford, CA, United States