Strategies to increase the proportion of neural stem cells that differentiate into neurons are vital for therapy of neurodegenerative disorders. In vitro, the extracellular matrix composition and topography have been found to be important factors in stem cell differentiation. We have developed a novel artificial extracellular matrix (aECM) formed by attaching gold nanocages (AuNCs) to glass coverslips. After culturing rat neural stem cells (rNSCs) on these gold nanocage-coated surfaces (AuNC-aECMs), we observed that 44.6% of rNSCs differentiated into neurons compared to only 27.9% for cells grown on laminin-coated glass coverslips. We applied laser irradiation to the AuNC-aECMs to introduce precise amounts of photothermally induced heat shock in cells. Our results showed that laser-induced thermal stimulation of AuNC-aECMs further enhanced neuronal differentiation (56%) depending on the laser intensity used. Response to these photothermal effects increased the expression of heat shock protein 27, 70, and 90α in rNSCs. Analysis of dendritic complexity showed that this thermal stimulation promoted neuronal maturation by increasing dendrite length as thermal dose was increased. In addition, we found that cells growing on AuNC-aECMs post laser irradiation exhibited action potentials and increased the expression of voltage-gated Na+ channels compared to laminin-coated glass coverslips. These results indicate that the photothermal response induced in cells growing on AuNC-aECMs can be used to produce large quantities of functional neurons, with improved electrochemical properties, that can potentially be transplanted into a damaged central nervous system to provide replacement neurons and restore lost function.

Physical agents such as low electric voltages and currents have recently gained attention for antimicrobial treatment due to their bactericidal capability. Although microampere electric currents were shown to suppress the growth of bacteria, it remains unclear to what extent the microampere currents damage bacterial membrane. Here, we investigated the membrane damage and two-way leakage caused by microampere electric currents (≤ 100 μA) in a short time (30 min). Based on MitoTracker staining, propidium iodide staining, filtration assays, and quantitative single-molecule localization microscopy, we found that microampere electric currents caused significant membrane damages and allowed two-way leakages of ions, small molecules and proteins. This study paves the way to new development and antibiotic applications of ultra-low electric voltages and currents. Statement of Significance: Previous studies showed that treating bacteria with milliampere electric currents for 72 hours led to significant damages of the bacterial membrane. However, it remains unclear to what extent membrane damages and two-way (i.e. inward and outward) leakages are caused by lower electric currents in a shorter time. In this work, we set out to answer this question. We carried out several assays on the bacteria treated by microampere electric currents of ≤ 100 μA for 30 min, including MitoTracker staining, propidium iodide staining, filtration assays, and quantitative single-molecule localization microscopy. We found and quantified that the membrane damages were caused by microampere electric currents in half an hour and allowed two-way leakages of ions, small molecules, and proteins.

The light-based nanowelding of metallic nanoparticles is of particular interest because it provides convenient and controlled means for the conversion of nanoparticles into microstructures and the fabrication of nanodevices. In this study, we investigated the wavelength dependence of laser-induced nanowelded shapes of silver nanoparticles (AgNPs). We observed that the nanowelded microstructures illuminated with only a 405 nm laser were more branched than those formed via illumination using both the 405 nm and 532 nm lasers. We quantified this observation by two compactness descriptors and examined the dependence of the power of the 532 nm laser. More importantly, to understand the experimental observations, we formulated and tested a hypothesis by calculating the wavelength-dependent electric field enhancement due to the surface plasmon resonance of the AgNPs and nanowelded microstructures when illuminated with lights at the two wavelengths. Based on the different patterns of hot spots for welding AgNPs from these calculations, numerical simulations successfully reproduced the different shapes of nanowelded microstructures, supporting our hypothesis. This work suggests the possibility of light-based control of the shapes of laser-induced nanowelded microstructures of metallic nanoparticles. This work is expected to facilitate the development of broader applications using the nanowelding of metallic nanoparticles.