Multiphoton excitation as a probe for biological fractionations

In this review of our work, we describe the application of multiphoton-excited fluorescence as a detection strategy for biological molecules fractionated in micrometer-diameter electrophoresis channels. By tightly focusing a modelocked titanium:sapphire laser beam at the outlet of such channels, spectroscopically similar components can be differentiated in analysis times that range from milliseconds to minutes. Moreover, the ability to excite different chromophores through the combined energies of different numbers of photons (e.g., two and three near-infrared quanta) provides a means to analyze species that are spectroscopically diverse. Finally, we demonstrate that multiphoton photochemistry can be used as a rapid 'photoderivatization' technique for hydroxyindoles and potentially other biological species, in some cases significantly improving the mass detectability of these analytes.