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New fluorescent pH sensors based on covalently linkable PET rhodamines.

ABSTRACT: A new class of rhodamines for the application as indicator dyes in fluorescent pH sensors is presented. Their pH-sensitivity derives from photoinduced electron transfer between non-protonated amino groups and the excited chromophore which results in effective fluorescence quenching at increasing pH. The new indicator class carries a pentafluorophenyl group at the 9-position of the xanthene core where other rhodamines bear 2-carboxyphenyl substituents instead. The pentafluorophenyl group is used for covalent coupling to sensor matrices by "click" reaction with mercapto groups. Photophysical properties are similar to "classical" rhodamines carrying 2'-carboxy groups. pH sensors have been prepared with two different matrix materials, silica gel and poly(2-hydroxyethylmethacrylate). Both sensors show high luminescence brightness (absolute fluorescence quantum yield ?(F)?0.6) and high pH-sensitivity at pH 5-7 which makes them suitable for monitoring biotechnological samples. To underline practical applicability, a dually lifetime referenced sensor containing Cr(III)-doped Al(2)O(3) as reference material is presented.

SUBMITTER: Aigner D

PROVIDER: S-EPMC3484401 | biostudies-literature | 2012 Sep

REPOSITORIES: biostudies-literature

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New fluorescent pH sensors based on covalently linkable PET rhodamines.

Aigner Daniel D Borisov Sergey M SM Fernández Francisco J Orriach FJ Fernández Sánchez Jorge F JF Saf Robert R Klimant Ingo I

Talanta 20120526

A new class of rhodamines for the application as indicator dyes in fluorescent pH sensors is presented. Their pH-sensitivity derives from photoinduced electron transfer between non-protonated amino groups and the excited chromophore which results in effective fluorescence quenching at increasing pH. The new indicator class carries a pentafluorophenyl group at the 9-position of the xanthene core where other rhodamines bear 2-carboxyphenyl substituents instead. The pentafluorophenyl group is used ...[more]

PMID: 22967541

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Project description:Photophysical data and orbital energy levels (from electrochemistry) were compared for molecules with the same BODIPY acceptor part (red) and perpendicularly oriented xanthene or BODIPY donor fragments (green). Transfer of energy, hence the photophysical properties of the cassettes, including the pH dependent fluorescence in the xanthene-containing molecules, correlates with the relative energies of the frontier orbitals in these systems. Intracellular sensing of protons is often achieved via sensors that switch off completely at certain pH values, but probes of this type are not easy to locate inside cells in their "off-state". A communication from these laboratories (J. Am. Chem. Soc., 2009, 131, 1642-3) described how the energy transfer cassette 1 could be used for intracellular imaging of pH. This probe is fluorescent whatever the pH, but its exact photophysical properties are governed by the protonation states of the xanthene donors. This work was undertaken to further investigate correlations between structure, photophysical properties, and pH for energy transfer cassettes. To achieve this, three other cassettes 2-4 were prepared: another one containing pH-sensitive xanthene donors (2) and two "control cassettes" that each have two BODIPY-based donors (3 and 4). Both the cassettes 1 and 2 with xanthene-based donors fluoresce red under slightly acidic conditions (pH < ?6) and green when the medium is more basic (>?7), whereas the corresponding cassettes with BODIPY donors give almost complete energy transfer regardless of pH. The cassettes that have BODIPY donors, by contrast, show no significant fluorescence from the donor parts, but the overall quantum yields of the cassettes when excited at the donor (observation of acceptor fluorescence) are high (ca. 0.6 and 0.9). Electrochemical measurements were performed to elucidate orbital energy level differences between the pH-fluorescence profiles of cassettes with xanthene donors, relative to the two with BODIPY donors. These studies confirm energy transfer in the cassettes is dramatically altered by analytes that perturb relative orbital levels. Energy transfer cassettes with distinct fluorescent donor and acceptor units provide a new, and potentially useful, approach to sensors for biomedical applications.

Project description:Orange carotenoid protein (OCP) is a photochromic carotenoprotein involved in the photoprotection of cyanobacteria. It is activated by blue-green light to a red form OCPR capable of dissipating the excess of energy of the cyanobacterial photosynthetic light-harvesting systems. Activation to OCPR can also be achieved in the dark. In the present work, activation by pH changes of two different OCPs-containing echinenone or canthaxanthin as carotenoids-is investigated in different conditions. A particular emphasis is put on OCP encapsulated in SBA-15 mesoporous silica nanoparticles. It is known that in these hybrid systems, under appropriate conditions, OCP remains photoactive. Here, we show that when immobilised in SBA-15, the OCP visible spectrum is sensitive to pH changes, but such a colorimetric response is very different from the one observed for OCP in solution. In both cases (SBA-15 matrices and solutions), pH-induced colour changes are related either by orange-to-red OCP activation, or by carotenoid loss from the denatured protein. Of particular interest is the response of OCP in SBA-15 matrices, where a sudden change in the Vis absorption spectrum and in colour is observed for pH changing from 2 to 3 (in the case of canthaxanthin-binding OCP in SBA-15: λMAX shifts from 454 to 508 nm) and for pH changing from 3 to 4 (in the case of echinenone-binding OCP in SBA-15: λMAX shifts from 445 to 505 nm). The effect of temperature on OCP absorption spectrum and colour (in SBA-15 matrices) has also been investigated and found to be highly dependent on the properties of the used mesoporous silica matrix. Finally, we also show that simultaneous encapsulation in selected surface-functionalised SBA-15 nanoparticles of appropriate fluorophores makes it possible to develop OCP-based pH-sensitive fluorescent systems. This work therefore represents a proof of principle that OCP immobilised in mesoporous silica is a promising system in the development of colorimetric and fluorometric pH and temperature sensors.

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New fluorescent pH sensors based on covalently linkable PET rhodamines.

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New fluorescent pH sensors based on covalently linkable PET rhodamines.

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