Flourescence lifetimes provide a valuable tool for distinguishing among fluorescing species where more tradition means such as intensity or spectral signature may be insufficient. In these images, a Zeiss LSM 710 microscope was used in conjunction with fluorescence lifetime imaging (FLIM) from ISS to measure lifetimes in-situ as an oligopeptides assembled in a microfluidic device. A pi-conjugated peryline-diimide (PDI) core is flanked by symmetric sequences of amino acids. These units self-assemble upon protonation at low pH. In the microfluidic device, coaxially focused flow of deionized water surrounding unassembled synthetic peptide is directed toward an opposed flow of 10 mM HCl, meeting in a cross-slot geometry. Planar extensional flow aligns oligopeptide structures as they assemble at the interface between these two flows. Assembled oligopeptide exhibits shorter lifetimes than unassembled. The lifetime image and corresponding histogram not only demonstrate the existence of distinct species, but also shows that the shorter lifetime material is indeed at the oligopeptide assembly front. The difference between the fluorescence lifetime map (top right) and intensity map (bottom right) demonstrating that fluorescence lifetime information can be used to inform the assembly process despite potentially uninformative fluorescence emission intensity data.