Quartz crystal microbalance (QCM): useful for developing procedures for immobilization of proteins on solid surfaces

We demonstrate the combined use of liquid and air measurements with the quartz crystal microbalance (QCM) for quantitative analysis of multistep reaction procedures leading to immobilized proteins on solid surfaces. Reactions are conducted on the surfaces of QCM sensor crystals and are quantified by measurements of resonant frequency of the crystals before and after each reaction step. When reactions are conducted in the flow cell of the QCM in the presence of solvent, measurement of resonant frequency can be made in situ (liquid measurement). When reactions cannot be conducted in the flow cell because of temperatures or solvents not tolerated by the cell, frequency can be measured after evaporation of solvent (air measurement). Each reaction step can be analyzed by either liquid or air measurement so that the whole multistep procedure is addressed, no matter how diverse the chemical nature of the steps. We conducted identical multistep procedures on two different starting surfaces, gold and silica, and found comparable results.