Development of a visualization technique of proton concentration in extended nanospace channel using stimulated emission depletion microscopy

Ion behavior confined in extended nanospace (10¹-10³ nm) is important to develop novel miniaturized systems for biochemical analysis and further applications. The present study developed a measurement technique of ion distribution in nanochannel using stimulated emission depletion microscopy to achieve a spatial resolution of 87 nm. Fluorescein was used for ratiometric measurement of pH by two-excitation wavelengths. The proton distribution in a 2D nanochannel of 410 nm width and 405 nm depth was firstly measured at an uncertainty of pH 0.05, which was strongly related to the electric double layer. This technique will greatly contribute to establish nanofluidics and nanochemistry.