Nitric oxide (NO) is involved in numerous biological processes, playing an important role in the regulation of diverse physiological and pathophysiological mechanisms of the cardiovascular, nervous and immune systems; and alterations in the intracellular NO concentrations have been linked to a large number of diseased states.1, 2 Considering the significant role that NO plays in important biological functions, the development and improvement of methods to detect and quantify intracellular NO are essential to further our understanding of the biological roles of NO.
This contribution will present different approaches to the constructions of (nano)probes sensitive to NO3-5 and their application for the intracellular detection and quantification of NO. Their potential to be NIR-excitable will be explored to utilise the advantage of the high photostability, high biological tissue penetration and minimal photodamage associated with this long-wavelength excitation. The (nano)probes are broadly applicable and are able to detect and potentially quantify NO levels in an extensive range of cellular environments including endogenous NO in RAW264.7γ NO- macrophages and THP-1 human leukemic cells, and endogenous and exogenous NO in endothelial cells. The (nano)probes accumulated in the acidic organelles of the tested cell lines showing negligible toxicity. The (nano)probes will be based on gold nanoparticles and on upconverting nanoparticles (UCNPs). For the UCNP-based example, a bilayer-based strategy for the surface modification of hydrophobic nanoparticles is introduced that leads to excellent colloidal stability in aqueous environments and good protection against disintegration, while permitting surface functionalization via simple carbodiimide chemistry.5
Based on their excellent sensitivity and stability, and outstanding versatility, the developed (nano)probes could be applied for the spatiotemporal monitoring of in vitro and in vivo NO levels.