Capacitance Spectroscopy: A Versatile Approach To Resolving the Redox Density of States and Kinetics in Redox-Active Self-Assembled Monolayers

Redox active self-assembled monolayers inherently possess both electrochemically addressable and polarizable components. The latter will contribute, with additional parasitic terms, to the <i>iR</i> drop effects within any form of electronic analysis, potentially distorting results. A capacitive analysis of such interfaces (Electroactive Monolayer Capacitance Spectroscopy), presented here, enables a clean mapping of both the thermodynamic and kinetic faradaic characteristics in a single experimental run, with parasitic nonfaradaic contributions (polarization and resistance terms) both spectrally resolved and cleanly removed. The methodology enables a rapid and undistorted quantification of accessible redox site density of states (reported directly by redox capacitance), molecular surface coverage, electron transfer kinetics, and reorganization energies with comparatively little experimental effort. Exemplified here with electroactive copper protein and ferrocene films the approach is equally applicable to any redox active interface

Profiling cellular diversity in sponges informs animal cell type and nervous system evolution

The evolutionary origin of metazoan cell types such as neurons and muscles is not known. Using whole-body single-cell RNA sequencing in a sponge, an animal without nervous system and musculature, we identified 18 distinct cell types. These include nitric oxide–sensitive contractile pinacocytes, amoeboid phagocytes, and secretory neuroid cells that reside in close contact with digestive choanocytes that express scaffolding and receptor proteins. Visualizing neuroid cells by correlative x-ray and electron microscopy revealed secretory vesicles and cellular projections enwrapping choanocyte microvilli and cilia. Our data show a communication system that is organized around sponge digestive chambers, using conserved modules that became incorporated into the pre- and postsynapse in the nervous systems of other animals