Ion-selective optodes (ISOs), the optical analog of ion-selective electrodes, have played an increasingly important role in chemical and biochemical analysis. Here we extend this technique to ion-selective photoacoustic optodes (ISPAOs) that serve at the same time as fluorescence-based ISOs, and apply it specifically to potassium (K+). Notably, the potassium ion is one of the most abundant cations in biological systems, involved in numerous physiological and pathological processes. Furthermore, it has been recently reported that the presence of abnormal extracellular potassium concentrations in tumors suppresses the immune responses and thus suppresses immunotherapy. However, unfortunately, sensors capable of providing potassium images in vivo are still a future proposition. Here, we prepared an ion-selective potassium nanosensor (NS) aimed at in vivo photoacoustic (PA) chemical imaging of the extracellular environment, while being also capable of fluorescence based intracellular ion-selective imaging. This potassium nanosensor (K+ NS) modulates its optical properties (absorbance and fluorescence) according to the potassium concentration. The K+ NS is capable of measuring potassium, in the range of 1 mM to 100 mM, with high sensitivity and selectivity, by ISPAO based measurements. Also, a near infrared dye surface modified K+ NS allows fluorescence-based potassium sensing in the range of 20 mM to 1 M. The K+ NS serves thus as both PA and fluorescence based nanosensor, with response across the biologically relevant K+ concentrations, from the extracellular 5 mM typical values (through PA imaging) to the intracellular 150 mM typical values (through fluorescence imaging).
metabolism. The luminescence lifetime measurement of oxygen-sensitive molecules is a very promising, non-invasive approach to determine pO2 in vivo. However, this measurement is frequently perturbed by the excited oxygen sensor's phototoxic effect. In this study, we compared two watersoluble oxygen sensors: Pd-meso-tetra(4-carboxyphenyl) porphyrin (PdTCPP) and dichlorotris(1, 10-phenanthroline)-ruthenium(II) hydrate ([Ru(Phen)3]2þ) for their phototoxicity and ability to measure oxygen consumption during hypericin induced photosensitization in vitro (single cells and isolated mitochondria) and in vivo (Chick's chorioallantoic membrane). Hypericin, a molecule with interesting spectral properties, does not perturb PdTCPP and [Ru(Phen)3]2þ lifetime measurements. The excitation of this molecule at 590 nm is spectrally ''far'' from the absorption bands of PdTCPP and [Ru(Phen)3]2þ, which allows induction of photodamages without contributions from these oxygen sensors. Since PdTCPP's stability in biological systems requires that it is bound with serum proteins, the impact of the serum albumins concentration in the system on the reliability of oxygen measurements was evaluated as well. In conclusions, we demonstrated optimal phototoxicity, serum albumin concentration-related lifetime variations, stability and oxygen sensitivity in vitro and in vivo for [Ru(Phen)3]2þ. We could not demonstrate a similar set of properties for PdTCPP.
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