Determination of adsorption-induced variation in the spring constant of a microcantilever

Although resonating microcantilevers are demonstrated to be excellent mass sensors, adsorption-induced changes in the spring constant result in errors in the calculation of adsorbed mass from shifts in resonance frequencies. However, simultaneous measurement of resonance frequency and adsorption-induced cantilever bending can be used to determine the variation in spring constant. Plotting the change in surface stress as a function of analyte concentration, the surface excess of adsorbed molecules and, therefore, the mass adsorbed can be determined. Here, we demonstrate this concept for adsorption of Na ⁺ ions on microcantilevers in NaCl solutions where a change in the spring constant was found to increase from 9.5×10^-4 to 7.5×10^-3 N/m as the NaCl concentration increased from 0.05 to 0.8 M.