Emission/excitation spectra of JC-1 monomers and aggregates reveals the potential use of 405 nm wavelength to specifically detect J-aggregates. JC-1 was dissolved in the presence of 0.1 (a), 35 (b) or 15% (c) DMSO to a final concentration of 2.5 μM. Emission spectra (a–c) at 405 (black) and 488 nm (gray), and excitation spectra (d) at 530 (black) and 595 nm (gray) were determined by Aminco Bowman Series 2 luminescence spectrometer. Excitation spectra of JC-1 at 0.1% DMSO (aggregates) and 35% DMSO (monomers) were determined separately (d). The black arrow indicates excitation at 405 nm. Also presented are the normalized emission (405 nm) and excitation (530nm) spectra for better visualization of the weaker signal (dotted line). The normalization factor for the emission spectra is the ratio between the fluorescent intensities measured at 595 nm of the 405 and the 488 nm-excited JC-1, and was determined to be 16.1 (a), 23.6 (b) and 13.3 (c). The normalization factor for the excitation spectrum of the 530 nm-emitted signal (=8.42) is the ratio between the 488 nm-excited fluorescence intensities at 530 nm and 595 nm (d).