Whereas the study of interfaces and thin films with the quartz crystal microbalance (QCM) is well established, biofilms have proven to be a difficult subject for the QCM. The main problem is that the shear wave emanating from the resonator surface does not usually reach to the top of the sample. This problem can be solved with torsional resonators. These have a resonance frequency in the range of tens of kHz, which is much below the frequency of the thickness-shear QCMs. The depth of penetration of the shear wave is correspondingly larger. Data acquisition and data analysis can proceed in analogy to the conventional thickness-shear QCM. Torsional resonators may also be operated as electrochemical QCMs (EQCMs), meaning that a DC electrical potential may be applied to the active electrode and that shifts of frequency and bandwidth may be acquired in parallel to the electrical current. Here we report on the formation of mixed-culture biofilms dominated by the microorganism Geobacter anodireducens. The viscoelastic analysis evidences an increase in rigidity as the films grows. Potential sweeps on electroactive biofilms reveal a softening under negative potentials, that is, under conditions, where the layer's metabolism was slowed down by insufficient oxidative activity of the substrate. For comparison, biofilms were monitored in parallel with a conventional thickness-shear QCM.

尽管对石英晶体微天平（QCM）的界面和薄膜的研究已经很成熟，但生物膜已被证明是QCM的难题。主要问题是从谐振腔表面发出的剪切波通常不会到达样品的顶部。扭转谐振器可以解决这个问题。它们的谐振频率在几十kHz范围内，远低于厚度剪切QCM的频率。剪切波的穿透深度相应地更大。数据采集​​和数据分析可以类似于常规的厚度剪切QCM进行。扭转谐振器也可以用作电化学QCM（EQCM），这意味着可以将直流电势施加到有源电极，并且可以平行于电流获取频率和带宽的偏移。在这里，我们报道了以微生物为主的混合培养生物膜的形成厌氧土杆菌。粘弹性分析表明，随着膜的生长，刚性增加。电活性生物膜上的电势扫描显示，在负电势下，即在底物的氧化活性不足而导致层的新陈代谢减慢的条件下，软化了。为了进行比较，与常规的厚度剪切QCM并行监测生物膜。