The use of heavy labels is another strategy of QCM signal amplification. In this approach, the mass of an analyte is additionally increased by attaching such bulky or heavy labels as Au, ferrite, and silica nanoparticles. This is mainly based on the sandwich format. For immunosensors, secondary Ab conjugates with colloidal gold are bonded to the primary Ag–Ab complex on the transducer surface. In the DNA sensors, the ODN sequences partially complemented to the DNA probe and target sequence form triple complexes bearing the label. The efficiency of labeling for mass sensitive transducers can be additionally increased by the accumulation of some auxiliary species after the biorecognition effect. Thus, the mass of Au nanoparticles can be additionally increased by the selective cathodic deposition of silver. The DNA adsorbs heavy metal ions. In some sensors, the polymerization of aniline adsorbed in the biochemical components on the transducer was initiated. The summary of some common amplification protocols is outlined in Fig. 3.43