Figure 4.

Fluorescence spectra of ASP+. (a) 1-photon fluorescence excitation spectrum and emission spectrum of ASP+. Maximum excitation was found at 450 nm (emission recorded at 600 nm), and maximum emission was seen at 605 nm. (b) The effect of BSA on the 1-photon fluorescence emission spectrum of ASP+. BSA induces a marked concentration-dependent increase in fluorescence (left y-axis) compared to ASP+ alone (right y-axis). In addition, BSA induces a blue shift of the emission peak from 605 to 570 nm. (c) Left: fluorescence emission from ASP+ in the absence (broken line) and presence of BSA (full line) in four wavelength intervals following excitation at 800 nm using a pulsed Ti:sapphire laser. Right: two-photon fluorescence excitation spectrum of ASP+ in the absence (broken line) and presence of BSA (full line). Maximum 2P excitation was obtained in the red channel (570–620 nm) at 920 nm and the emission from ASP+ alone was generally very low. BSA enhanced and induced a blueshift in the emitted signal.