Polyserotonin Nanoparticles as Multifunctional Materials for Biomedical Applications

Serotonin-based nanoparticles represent a class of previously unexplored multifunctional nanoplatforms with potential biomedical applications. Serotonin, under basic conditions, self-assembles into monodisperse nanoparticles <i>via</i> autoxidation of serotonin monomers. To demonstrate potential applications of polyserotonin nanoparticles for cancer therapeutics, we show that these particles are biocompatible, exhibit photothermal effects when exposed to near-infrared radiation, and load the chemotherapeutic drug doxorubicin, releasing it contextually and responsively in specific microenvironments. Quantum mechanical and molecular dynamics simulations were performed to interrogate the interactions between surface-adsorbed drug molecules and polyserotonin nanoparticles. To investigate the potential of polyserotonin nanoparticles for <i>in vivo</i> targeting, we explored their nano–bio interfaces by conducting protein corona experiments. Polyserotonin nanoparticles had reduced surface–protein interactions under biological conditions compared to polydopamine nanoparticles, a similar polymer material widely investigated for related applications. These findings suggest that serotonin-based nanoparticles have advantages as drug-delivery platforms for synergistic chemo- and photothermal therapy associated with limited nonspecific interactions

Nanoelectronic Investigation Reveals the Electrochemical Basis of Electrical Conductivity in <i>Shewanella</i> and <i>Geobacter</i>

The electrical conductivity measured in <i>Shewanella</i> and <i>Geobacter</i> spp. is an intriguing physical property that is the fundamental basis for possible extracellular electron transport (EET) pathways. There is considerable debate regarding the origins of the electrical conductivity reported in these microbial cellular structures, which is essential for deciphering the EET mechanism. Here, we report systematic on-chip nanoelectronic investigations of both <i>Shewanella</i> and <i>Geobacter</i> spp. under physiological conditions to elucidate the complex basis of electrical conductivity of both individual microbial cells and biofilms. Concurrent electrical and electrochemical measurements of living <i>Shewanella</i> at both few-cell and the biofilm levels indicate that the apparent electrical conductivity can be traced to electrochemical-based electron transfer at the cell/electrode interface. We further show that similar results and conclusions apply to the <i>Geobacter</i> spp. Taken together, our study offers important insights into previously proposed physical models regarding microbial conductivities as well as EET pathways for <i>Shewanella</i> and <i>Geobacter</i> spp

Evolution of Cell Size Homeostasis and Growth Rate Diversity during Initial Surface Colonization of <i>Shewanella oneidensis</i>

Cell size control and homeostasis are fundamental features of bacterial metabolism. Recent work suggests that cells add a constant size between birth and division (“adder” model). However, it is not known how cell size homeostasis is influenced by the existence of heterogeneous microenvironments, such as those during biofilm formation. <i>Shewanella oneidensis</i> MR-1 can use diverse energy sources on a range of surfaces <i>via</i> extracellular electron transport (EET), which can impact growth, metabolism, and size diversity. Here, we track bacterial surface communities at single-cell resolution to show that not only do bacterial motility appendages influence the transition from two- to three-dimensional biofilm growth and control postdivisional cell fates, they strongly impact cell size homeostasis. For every generation, we find that the average growth rate for cells that stay on the surface and continue to divide (nondetaching population) and that for cells that detach before their next division (detaching population) are roughly constant. However, the growth rate distribution is narrow for the nondetaching population, but broad for the detaching population in each generation. Interestingly, the appendage deletion mutants (Δ<i>pilA</i>, Δ<i>mshA-D</i>, Δ<i>flg</i>) have significantly broader growth rate distributions than that of the wild type for both detaching and nondetaching populations, which suggests that <i>Shewanella</i> appendages are important for sensing and integrating environmental inputs that contribute to size homeostasis. Moreover, our results suggest multiplexing of appendages for sensing and motility functions contributes to cell size dysregulation. These results can potentially provide a framework for generating metabolic diversity in <i>S. oneidensis</i> populations to optimize EET in heterogeneous environments