Ion mobility spectrometry coupled to laser-induced fluorescence for probing the electronic structure and conformation of gas-phase ions

We report on an improved design of a differential ion mobility analyzer (DMA) coupled to laser-induced fluorescence (LIF) for the simultaneous retrieval of two-dimensional information on the electric mobility and fluorescence spectroscopy of gas-phase ions. This enhanced design includes an ion funnel inter-face at the input orifice of the DMA and a nozzle beam stage at the output of the DMA. These improvements allow the detection of fluorescence not only from pure dyes and their clusters, as was demonstrated recently, but also from fluorophore-tagged biomolecules. Complex mixtures of fluorescent compounds can be separated by the DMA and studied by LIF. This unique combination of instruments also provides a powerful platform for probing fluorescent proteins in the gas phase. The green fluorescent protein (GFP) was tested on a new setup. In contrast to high vacuum, where no GFP fluorescence was detected, the presence of a LIF signal at the output of the DMA could explain some specific fluorescent properties of GFP in the gas phase. Given that both conformation and fluorescence are key properties of biological molecules in the gas phase, we expect that our enhanced design will answer the question whether gas-phase proteins retain their liquid-phase native structure or not.