Inkjet monitoring technique with quartz crystal microbalance (QCM) sensor for highly reproducible antibody immobilization

We demonstrate that a calibrated amount of a biomolecule can be microdeposited using a commercially available quartz crystal microbalance (QCM) and a piezoelectric inkjet head with a flattened surface surrounding the ejection hole. Covering the QCM with a stainless-steel cover perforated with a precisely-machined hole both significantly decreased background noise due to external sources such as air flow and temperature fluctuations and allowed accurate droplet ejection at a constant temperature. Anti-c reactive protein antibody solution (anti-CRP; 1.0 mg/ml) was continuously ejected onto a microchannel target using a piezoelectric injector; its microdeposition was monitored shot-by-shot using a 30 MHz QCM. The dispersion of the QCM frequency change per shot decreased from 7.87 to 1.01 Hz when a perforated stainless-steel cover was installed. The primary antibody was precisely deposited on the target with high reproducibility. The variation in luminescence measured by enzyme-linked immunosorbant assay (ELISA) decreased from 9.67% to 1.16% when calibrating the amount of primary antibody deposition with this developed technique.