An experimental study of nanoparticle focusing with aerodynamic lenses

High sampling efficiencies of analyte ions, molecules or particles are needed to maximize the sensitivity of mass spectrometers. “Ion funnels”, hich utilize electrodynamic focusing, have been shown to effectively focus ions with mass-to-charge ratio (m/z) ranging from ∼100 to 5000. ocusing efficiencies of ion funnels drop for higher m/z values because very high voltages are needed to overcome the particle inertia. Conventional aerodynamic lenses” utilize inertia to focus down to 25 nm in diameter (∼5 MDa); to date, Brownian diffusion has prevented the effective focusing f particles smaller than this. We recently reported a design procedure that should, in principle, extend focusing with aerodynamic lenses to particles s small as 3 nm (∼10 kDa), thereby bridging the gap between the ion funnel and the conventional aerodynamic lenses. In this paper, we report for he first time experimental results for the performance of these new “nanolenses”. Measurements were done using spherical oil droplets, proteins, nd sodium chloride particles ranging in size from 3 to 30 nm diameter. We found that particle transport efficiencies from atmospheric pressure to acuum through the aerodynamic lens system were greater than 80% for 10–30 nm particles, and greater than 50% for a∼3.8 nm protein (Lysozyme rom chicken egg white, molecular weight 14.3 kDa). Particle beam diameters were about a factor of two greater than predicted by our numerical imulations, but provide clear evidence that the nanolenses effectively focus all three particle types. 2006 Elsevier B.V. All rights reserved.