Studying protein interactions is of vital importance both to fundamental biology research and to medical applications. Here, we report on the experimental proof of a universally applicable label-free homogeneous platform for rapid protein analysis. It is based on optically detecting changes in the rotational dynamics of magnetically agitated core-shell nanorods upon their specific interaction with proteins. By adjusting the excitation frequency, we are able to optimize the measurement signal for each analyte protein size. In addition, due to the locking of the optical signal to the magnetic excitation frequency, background signals are suppressed, thus allowing exclusive studies of processes at the nanoprobe surface only. We study target proteins (soluble domain of the human epidermal growth factor receptor 2 - sHER2) specifically binding to antibodies (trastuzumab) immobilized on the surface of our nanoprobes and demonstrate direct deduction of their respective sizes. Additionally, we examine the dependence of our measurement signal on the concentration of the analyte protein, and deduce a minimally detectable sHER2 concentration of 440 pM. For our homogeneous measurement platform, good dispersion stability of the applied nanoprobes under physiological conditions is of vital importance. To that end, we support our measurement data by theoretical modeling of the total particle-particle interaction energies. The successful implementation of our platform offers scope for applications in biomarker-based diagnostics as well as for answering basic biology questions.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: The authors thank Frauke Alves, Julia Bode and Fernanda Ramos Gomes from the Max-Planck-
Institute of Experimental Medicine in Göttingen for providing the trastuzumab antibody in form
of the Herceptin therapeutic drug. The figure showing the measurement principle has been created
by Darragh Crotty (www.darraghcrotty.com). Parts of this research were supported by the
European Commission FP7 NAMDIATREAM project (EU NMP4-LA-2010–246479), by the
German research foundation (DFG grant GRK 1782 to W.J.P.), and by the European Research
Council (ERC Starting Grant #335078 Colouratom). B.P. acknowledges a PostDoctoral fellowship
from the Alexander von Humboldt foundation.