Figure 4: Specificity and sensitivity of the bioengineered, tetravalent bodies, towards cardiac α-actinin and titin, 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 α-actinin and titin, which were modified with chelates coordinating Eu and Tb with their unique emission spectra, 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. The htAbs are exquisitely specific to the main components of the sarcomeres revealed in the figure 2: α-actinin – appearing as the bright line of the Z-line and two bright lines parallel to the Z-line of the titin’s elastic domains. Pixel brightness compared between the specific labels and the backgrounds was accepted at the statistical significance p < 0.001. HFW: 4.8 μm.