We demonstrate a nonlinear optical light scattering method for quantitative measurement of the cellular uptake and membrane transport rates of small/medium size molecules without the need of fluorescence tagging. In this method, we monitor the Second Harmonic Generation (SHG) from a ‘probe’ molecule with detectable hyper-polarization, in the presence of the ‘target’ molecule of interest while both molecules are crossing the cell membrane. The transport rate of the target molecule is extracted as a perturbation to that of the probe molecule. As a first example demonstrating this approach, we examine competitive transport of the strongly SHG-active cation, malachite green (MG), against the weakly SHG-active dication, propidium (Pro), across the outer-membrane protein channels in living E. coli. A one-site channel model is used to deconvolute from the MG transport kinetics the Pro transport rate. Comparison of model predicted and directly measured Pro transport rates validates the effectiveness of this method. Applications of this method to a variety of systems have enabled the study of the effects of molecular structural factors such as polarity and charge, membrane structural factors such as packing of the lipid bilayer and membrane proteins, and the composition of the electrolyte in which the cells live in, on the transport rate.

Quantifying molecular transport through cell membranes by nonlinear light scattering

251st National Meeting (2016)

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