In this study, we have used a direct immunoassay where the simple binding between antigen and an antibody is detected. Immunoassays were performed in a drop system, monitoring the decrease in the frequency of the quartz crystal microbalance device as the mass increases during immunoreaction. The QCM sensor was coated on both sides by gold electrodes; only one side of the crystal (liquid side) was in contact with the solution, the other side (contact side) was always dry. We tested a piezoelectric immunosensor for aflatoxin B1 (AFLA-B1), ochratoxin A (OTA), and fumonisin B1 (FB1) mycotoxin detection through the immobilization of DSP-anti-mycotoxin antibody (AFLA-B1-Ab anti-AFLAB1, OTA-Ab anti-OTA, FB1-Ab anti-FB1) on gold-coated quartz crystals (AT-cut/5 MHz). The DSP (3,3'-dithiodipropionic-acid-di-N- hydroxysuccinimide ester) was used for the covalent attachment of the proteins. The piezoelectric crystal electrodes were pretreated by DSP for 15 min, rinsed with water, and dried in a gentle flow of nitrogen gas. Then the DSP-coated crystals were installed in a sample holder and exposed to the antibody and to the analyte. Frequency and resistance shifts (Δf and ΔR) were measured simultaneously. © 2014 Springer International Publishing Switzerland.