Enhancing the Maturation of Human Pluripotent Stem Cell-Derived Cardiomyocytes with an n-Type Organic Semiconductor Coating

Human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) are a promising cell source for cardiac regenerative medicine and in vitro modeling. However, hPSC-CMs exhibit immature structural and functional properties compared with adult cardiomyocytes. Various electrical, mechanical, and biochemical cues have been applied to enhance hPSC-CM maturation but with limited success. In this work, we investigated the potential application of the semiconducting polymer poly{[N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (P(NDI2OD-T2)) as a light-sensitive material to stimulate hPSC-CMs optically. Our results indicated that P(NDI2OD-T2)-mediated photostimulation caused cell damage at irradiances applied long-term above 36 μW/mm2 and did not regulate cardiac monolayer beating (after maturation) at higher intensities applied in a transient fashion. However, we discovered that the cells grown on P(NDI2OD-T2)-coated substrates showed significantly enhanced expression of cardiomyocyte maturation markers in the absence of a light exposure stimulus. A combination of techniques, such as atomic force microscopy, scanning electron microscopy, and quartz crystal microbalance with dissipation monitoring, which we applied to investigate the interface of the cell with the n-type coating, revealed that P(NDI2OD-T2) impacted the nanostructure, adsorption, and viscoelasticity of the Matrigel coating used as a cell adhesion promoter matrix. This modified cellular microenvironment promoted the expression of cardiomyocyte maturation markers related to contraction, calcium handling, metabolism, and conduction. Overall, our findings demonstrate that conjugated polymers such as P(NDI2OD-T2) can be used as passive coatings to direct stem cell fate through interfacial engineering of cell growth substrates.

SpyDirect: A Novel Biofunctionalization Method for High Stability and Longevity of Electronic Biosensors

Electronic immunosensors are indispensable tools for diagnostics, particularly in scenarios demanding immediate results. Conventionally, these sensors rely on the chemical immobilization of antibodies onto electrodes. However, globular proteins tend to adsorb and unfold on these surfaces. Therefore, self-assembled monolayers (SAMs) of thiolated alkyl molecules are commonly used for indirect gold-antibody coupling. Here, a limitation associated with SAMs is revealed, wherein they curtail the longevity of protein sensors, particularly when integrated into the state-of-the-art transducer of organic bioelectronics-the organic electrochemical transistor. The SpyDirect method is introduced, generating an ultrahigh-density array of oriented nanobody receptors stably linked to the gold electrode without any SAMs. It is accomplished by directly coupling cysteine-terminated and orientation-optimized spyTag peptides, onto which nanobody-spyCatcher fusion proteins are autocatalytically attached, yielding a dense and uniform biorecognition layer. The structure-guided design optimizes the conformation and packing of flexibly tethered nanobodies. This biolayer enhances shelf-life and reduces background noise in various complex media. SpyDirect functionalization is faster and easier than SAM-based methods and does not necessitate organic solvents, rendering the sensors eco-friendly, accessible, and amenable to scalability. SpyDirect represents a broadly applicable biofunctionalization method for enhancing the cost-effectiveness, sustainability, and longevity of electronic biosensors, all without compromising sensitivity.