Figure 7: Specificity and sensitivity of the bioengineered, bispecific tetravalent antibodies towards cardiac α-actinin and myosin was highlighted on the cryosections by multiphoton fluorescence spectroscopy (MPFS). Immediately after the surgery, the cardiac muscles were cryoimmobilized and cryosectioned. Thereafter, the cryosections were labeled with the bioengineered tetravalent antibodies targeting α-actinin and myosin (a) or mixtures of the monoclonal antibodies against α-actinin and myosin (mAbs) both tagged with the same chelates as fluorochromes. The patterns A-bands (A) and Z-lines (Z) are clearly highlighted in both approaches. Stability of the sarcomeres was tested by incubation at 37°C for different durations. The sarcomeres were labeled with the htAbs after (c) and before the 24h incubation (d). Without stabilization of the sarcomeres with the aid of the htAbs, outlines of the A-band and Z-line start to diffuse, as the signs of deterioration (c). Presence of cross-linking htAbs assures preservation of the sarcomeric architecture (d). This result reinforces the concept of using the myocardial infarction sarcomeres as the anchoring scaffold for the hiPSCs. However, the prolonged incubation leads to the gradual deterioration of the sarcomeric architecture (e, f). Pixel brightness compared between the specific labels and the backgrounds were accepted at the statistical significance p < 0.001. HFW: 9 μm.