Fast Optical pH Manipulation and Imaging

Abstract

We describe a complete system for optical pH manipulation and imaging. The system consists of a photoactive Ruthenium complex capable of inducing a change of more than 5 pH units at the nanosecond time scale. A compatible imaging system acquires microscopic pH images at 1200 fps using a nonexpensive commercial digital camera and an LED illumination system. We use the system as a superb tool to investigate flow in Flow Injection Analysis (FIA) models.

A Visible-Light-Sensitive Caged Serotonin

“…Entities that have been caged include ions, 1 acids, 2 bases, 3 neurotransmitters, 4 fluorophores, 5,6 small-molecule drugs, 7 gene inducers, 8,9 and even nucleic acids 10 and proteins. 11,12 Phototriggers are light-sensitive, and will release the caged molecule upon irradiation with light of the proper wavelength, 13 thus removing the restrictions for the caged entity to interact normally with its targets.…”

“…They present unique properties, including nanosecond photoreaction kinetics through heterolytic photocleavage with no secondary reaction products, 7,17 and sensitivity to visible light in the blue and green regions. 3,6,7,18–20 As an important advantage over other photoprotective groups, Rubipyridyl phototriggers can be used in a two-photon regime. 17,21–24 Ruthenium phototriggers can also be used for general delivery of drugs, toward application in therapy.…”

“…A caged compound, or phototrigger, is a molecule reversibly bound to or “caged within” a protecting group that restricts its interactions with cell-membrane receptors, proteins, or other molecules. Entities that have been caged include ions, acids, bases, neurotransmitters, fluorophores, , small-molecule drugs, gene inducers, , and even nucleic acids and proteins. , Phototriggers are light-sensitive, and will release the caged molecule upon irradiation with light of the proper wavelength, thus removing the restrictions for the caged entity to interact normally with its targets. As the uncaging spot size can be precisely determined by focusing a low-power laser, this technique can have very high spatial and temporal resolution, making it of great advantage in biological research, for it allows the delivery of molecules without mechanically acting on the preparation, a problem usually associated with more invasive techniques like microinjection.…”

“…As we have shown in recent years, ruthenium-bipyridyl coordination complexes yield excellent phototriggers suitable for neurophysiology studies. They present unique properties, including nanosecond photoreaction kinetics through heterolytic photocleavage with no secondary reaction products, , and sensitivity to visible light in the blue and green regions. ,,,− As an important advantage over other photoprotective groups, Ru-bipyridyl phototriggers can be used in a two-photon regime. ,− Ruthenium phototriggers can also be used for general delivery of drugs, toward application in therapy. Turro and Bonnet and their co-workers have shown the versatility of Ru­(II) polypyridines for caging nitriles and thioethers. − A similar strategy using the photoredox properties of the Ru­(II) polypyridyl chemistry was used by Ford and Santana da Silva to release nitric oxide (NO) by visible light, both directly or mediated by energy transfer processes from molecular antennas. , …”

Direct Measurement of Two-Photon Action Cross Section

“…Denk pioneered the field with the first two-photon microscope . Since then, many probes and actuators have been designed and developed for imaging − and uncaging, , mostly for biological systems, but not restricted to them. − …”