Investigation of binding event perturbations caused by elevated QCM-D oscillation amplitude

Abstract

We report measurements with the quartz crystal microbalance with dissipation monitoring (QCM-D) technique, with focus on how the shear oscillation amplitude of the sensor surface influences biorecognition binding events. Technically, this is made as reported recently (M. Edvardsson, M. Rodahl, B. Kasemo, F. Höök, Anal. Chem., 2005, 77(15), 4918–4926) by operating the QCM in dual frequency mode; one harmonic (n = n₁) is utilized for continuous excitation of the QCM-D sensor at resonance at variable driving amplitudes (1–10 V), while the second harmonic (n ≠ n₁) is used for combined f and D measurements. By using one harmonic as a “probe” and the other one as an “actuator”, elevated amplitudes can be used to perturb – or activate – binding reactions in a controlled way, while simultaneously maintaining the possibility of probing the adsorption and/or desorption events in a non-perturbative manner using combined f and D measurements. In this work we investigate the influence of oscillation amplitude variations on the binding of NeutrAvidin-modified polystyrene beads (∅ ∼200 nm) to a planar biotin-modified lipid bilayer supported on an SiO₂-modified QCM-D sensor. These results are further compared with data on an identical system, except that the NeutrAvidin–biotin recognition was replaced by fully complementary DNA hybridization. Supported by micrographs of the binding pattern, the results demonstrate that there exists, for both systems, a unique critical oscillation amplitude, A_c, below which binding is unaffected by the oscillation, and above which binding is efficiently prevented. Associated with A_c, there is a critical crystal radius, r_c, defining the central part of the crystal where binding is prevented. From QCM-D data, A_c for the present system was estimated to be ∼6.5 nm, yielding a value of r_c of ∼3 mm – the latter number was nicely confirmed by fluorescent- and dark-field micrographs of the crystal. Furthermore, the fact that A_c is observed to be identical for the two types of biorecognition reactions suggests that it is neither the strength, nor the number of contact points, that determine the amplitude at which binding is prevented. Rather, particle size seems to be the determining parameter.