Dendritic Phosphorescent Probes for Oxygen Imaging in Biological Systems

Department of Biochemistry and Biophysics, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
ACS Applied Materials & Interfaces (Impact Factor: 6.72). 06/2009; 1(6):1292-304. DOI: 10.1021/am9001698
Source: PubMed


Oxygen levels in biological systems can be measured by the phosphorescence quenching method using probes with controllable quenching parameters and defined biodistributions. We describe a general approach to the construction of phosphorescent nanosensors with tunable spectral characteristics, variable degrees of quenching, and a high selectivity for oxygen. The probes are based on bright phosphorescent Pt and Pd complexes of porphyrins and symmetrically pi-extended porphyrins (tetrabenzoporphyrins and tetranaphthoporphyrins). pi-Extension of the core macrocycle allows tuning of the spectral parameters of the probes in order to meet the requirements of a particular imaging application (e.g., oxygen tomography versus planar microscopic imaging). Metalloporphyrins are encapsulated into poly(arylglycine) dendrimers, which fold in aqueous environments and create diffusion barriers for oxygen, making it possible to regulate the sensitivity and the dynamic range of the method. The periphery of the dendrimers is modified with poly(ethylene glycol) residues, which enhance the probe's solubility, diminish toxicity, and help prevent interactions of the probes with the biological environment. The probe's parameters were measured under physiological conditions and shown to be unaffected by the presence of biomacromolecules. The performance of the probes was demonstrated in applications, including in vivo microscopy of vascular pO(2) in the rat brain.

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Available from: Sava Sakadzic, Dec 20, 2013
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    • "2.7. Optical method for oxygen consumption measurements Oxygen partial pressure was measured by a phosphorescence quenching method, using a new oxygen-sensitive phosphorescent porphyrin-dendrimer Oxyphor G3 (palladium-tetrabenzoporphyrin, encapsulated inside gen 2 poly-arylglycine (AG) dendrimer)[38]. The periphery of the dendrimer is modified with oligoethyleneglycol residues, which makes the probe highly water soluble and biologically inert. In contrast to earlier generation oxyphors, oxyphor G3 does not bind to serum albumin in the perifusion medium. "
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    • "Extra-cellular probes are useful for the measurement of oxygen consumption rate (OCR) in small biological samples, adding them to the media and analyzing the effects of drugs, culture conditions or cell metabolic state [12]. Such probes are also used in in vivo imaging via local or systemic intravenous administration [33], designed to remain in the vasculature, have low toxicity on cells (though organ toxicity and systemic effects can occur due to high doses used) [12]. However, extra-cellular probes are not very suitable for in vitro studies with respiring objects such as 3D tissue models as they do not stain the cells within tissue. "
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    • "Thus by measuring the phosphorescence decay time τ after an excitation pulse, the absolute pO2 value can be determined based on a pre-established τ vs. pO2 calibration curve (Extended Data Fig. 2). The metalloporphyrin in PtP-C343 is protected by a dendrimer with a polyethylene glycol (PEG) overcoat (Extended Data Fig. 3) to insure biocompatibility and to prevent unwanted interactions of the probe with bio-macromolecules20,23. To enhance the two-photon excitation cross section, several coumarin-343 (C343) moieties are grafted onto the dendrimer shell as two-photon “antennas” that funnel the captured energy to the metalloporphyrin by way of intramolecular energy transfer20,21. "
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