Measurement of microcantilever spring constants for probing receptor‐ligand bonding

Abstract

The force dependence of receptor–ligand bonding has been extensively studied in biophysics. Microcantilevers are a type of spring‐based force sensor and their spring constants were characterized using different methods to check that the measurements were consistent. Microcantilevers made from E‐glass fibers with a nominal diameter of 4 μm and lengths from 3–7 mm were mounted in viewing chambers and imaged under a microscope with a 100× oil immersion lens. Multiple sets of images for each microcantilever were captured at 50–800 frames per second and analyzed using custom LabVIEW IMAQ image processing program. The microcantilever intensity profile was used to find the edges (represented by two intensity troughs). The equipartition theorem was used to find spring constant values from displacements of the edges in the time domain. These were found to decrease with increasing cantilever length as expected from elastic theory. Fluctuations were also studied in frequency domain. The Power Spectral Density of the microcantilever displacements was fitted to a Lorentzian. The spring constants calculated from the Lorentzian parameters were consistent with the results from the equipartition theorem. This work was supported with funding from the Ohio University Biomimetic Nanoscience and NanoTechnology Program.