Figure 5: Specificity and sensitivity of the bioengineered, tetravalent antibodies towards cardiac myosin and actin were highlighted on the human cardiac myofibrils by multiphoton fluorescence spectroscopy (MPFS). The cardiac myofibrils were labeled with the monospecific tetravalent antibodies (htAbs) or monoclonal antibodies (mAbs) targeting myosin and actin, which were modified with chelates coordinating Eu and Tb, thus providing opportunities for double labeling. The images of the whole mounts by Zernicke’s contrast were added for the structural reference (wm). All samples were run in triplicates. The images are representative for all the patients’ samples studied. Pixel brightness compared between the specific labels and the backgrounds was accepted at the statistical significance p < 0.001. HFW: 5.1 μm.