In this paper, we report, for the first time, experimental evidence of multiphoton photolysis of a caged proton compound, 2-nitrobenzaldehyde (o-NBA), using a new sensor system that utilizes fluorescent-labeled nanocapsules, i.e., a fluorescent nanostructured shell of micrometric size and nanometric thickness. The photolabile compound undergoes one-photon absorption in the UV range (200−380 nm), and the mechanism that leads to proton release is based on the well-known 2-nitrobenzyl photochemistry, which has been used for many photoactivatable-caged compounds. Because the use of UV excitation can cause biological damage, we changed our focus to multiphoton absorption−uncaging processes. The induced pH decrease was monitored by imaging changes in the pH-dependent emission of fluorescein isothiocyanate that was embedded in a nanostructured system (so-called “nanocapsules”). The nanocapsules with covalently bound dyes allow improved stability in fluorescence monitoring. Moreover, an original image processing method is introduced to quantify the uncaging. Using a femtosecond Ti:sapphire laser that was operating at 720 nm, with a pulse width of 200 fs at the sample, delivered through an adapted confocal laser scanning head and a 1-min exposure time with high power (45−50 mW), we obtained appreciable photolysis of 2-nitrobenzaldehyde. So far, we demonstrated that fluorescent-labeled nanocapsules are a suitable system as fluorescence sensors.
Two-photon photolysis of 2-nitrobenzaldehyde monitored by fluorescent labeled nanocapsules / A., Diaspro; F., Federici; Viappiani, Cristiano; S., Krol; M., Pisciotta; G., Chirico; F., Cannone; A., Gliozzi. - In: JOURNAL OF PHYSICAL CHEMISTRY. B, CONDENSED MATTER, MATERIALS, SURFACES, INTERFACES & BIOPHYSICAL. - ISSN 1520-6106. - 107(2003), pp. 11008-11012. [10.1021/jp034921i]
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