Article

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

ABSTRACT 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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    • "Emission originating either directly ( phosphorescence) or indirectly (delayed fluorescence ) from the long-lived first excited triplet state can also be used for monitoring ( Jovin & Vaz 1989; Cioni & Strambini 2002) and has been exploited for microscopic imaging (Marriott et al. 1991). However, coupled to the long-lived emission is also the susceptibility of the triplet state to dynamic quenching by oxygen and trace impurities, which can be circumvented only after elaborate and careful sample preparation, or by creating oxygen diffusion barrier shields around the phosphorescent probes (Lebedev et al. 2009). This quenching not only shortens the triplet lifetime but also makes the luminescence practically undetectable. "
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