Using Metalloporphyrin Nanosensors for In Situ Monitoring and Measurement of Nitric Oxide and Peroxynitrite in a Single Human Neural Progenitor Cell

Nitric oxide (NO) is an inorganic signaling molecule that plays a crucial role in the regulation of numerous physiological functions. An oxidation product of the cytoprotective NO is cytotoxic peroxynitrite (ONOO–). In biological systems, the concentrations of NO and ONOO– are typically transient, ranging from nanomolar to micromolar, and these increases are normally followed by a swift return to their basal levels due to their short life spans. To understand the vital physiological role of NO and ONOO– in vitro and in vivo, sensitive and selective methods are necessary for direct and continuous NO and ONOO– measurements in real time. Because electrochemical methods can be adjusted for selectivity, sensitivity, and biocompatibility in demanding biological environments, they are suitable for real-time monitoring of NO and ONOO– release. Metalloporphyrin nanosensors, described here, have been designed to measure the concentration of NO and ONOO– produced by a single human neural progenitor cell (hNPC) in real time. These nanosensors (200–300 nm in diameter) can be positioned accurately in the proximity of 4–5 ± 1 μm from an hNPC membrane. The response time of the sensors is better than a millisecond, while detection limits for NO and ONOO– are 1 × 10–9 and 3 × 10–9 mol/L, respectively, with a linear concentration response of up to about 1 μM. The application of these metalloporphyrin nanosensors for the efficient measurement of the concentrations of NO and ONOO– in hNPCs is demonstrated, providing an opportunity to observe in real time the molecular changes of the two signaling molecules in situ.