Figure 2
![Figure 2](http://media.springernature.com/full/springer-static/image/art%3A10.1186%2F1472-6750-11-125/MediaObjects/12896_2011_Article_694_Fig2_HTML.jpg)
Two-photon action cross-section of Hilyte Fluor 488 labelled Aβ40. The two-photon action cross-section (ϕfσ2p) of Hilyte Fluor 488 labelled Aβ40 is compared to that for Alexa Fluor 488 free dye. The units for ϕfσ2p are Goeppert-Mayer (GM), where 1 GM = 10-50 cm4 s photon-1.