Direct Measurement of Two-photon action cross section.

We present a simple and fast methodology for measuring the two-photon (2P) action cross section of phototriggers. The method uses a standard 2P microscopy setup for both uncaging and detection and a set of lithographically made microcuvettes in order to reduce the total excitation volume and, thus, the photolysis time. The procedure does not need a standard and can be used for any caged compounds that present different emission properties before and after uncaging. We tested the method with 2P active ruthenium-based caged serotonin and compared the obtained value with a standard measure involving fluorescein as reference.