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Abstract Silver (Ag) in various forms have recently gained broad interest and been revisited due to their promising antimicrobial effects. Here we report our study on the morphological dynamics of live bacteria when subjected to Ag⁺ions. Using time-lapse microscopy, we observed oscillations of cell-length for a large fraction of bacteria exposed to 60μM of Ag⁺ions. In addition, we found that the responses of bacteria to Ag⁺ions were heterogeneous. We quantified the oscillations of cell-length with power spectral density, which appeared different from that of bacteria growing in the absence of Ag⁺ions. Furthermore, a model similar to the predator-prey argument was developed to understand the observed oscillations of cell-length upon exposure to Ag⁺ions. This model not only successfully produced the oscillations but also explained the observed heterogeneity in the bacterial responses to Ag⁺ions. 

Oxidation is a corrosion reaction where the corroded metal forms an oxide. Prevention of oxidation at the nanoscale is critically important to retain the physicochemical properties of metal nanoparticles. In this work, we studied the stability of polyethylene glycol (PEG) coated copper nanoparticles (PEGylated CuNPs) against oxidation. The freshly-prepared PEGylated CuNPs mainly consist of metallic Cu which are quite stable in air although their surfaces are typically covered with a few monolayers of cuprous oxide. However, they are quickly oxidized in water due to the presence of protons that facilitate oxidation of the cuprous oxide to cupric oxide. PEG with carboxylic acid terminus could slightly delay the oxidation process compared to that with thiol terminus. It was found that a solvent with reducing power such as ethanol could greatly enhance the stability of PEGylated CuNPs by preventing further oxidation of the cuprous oxide to cupric oxide and thus retain the optical properties of CuNPs. The reducing environment also assists the galvanic replacement of these PEGylated CuNPs to form hollow nanoshells; however, they consist of ultra-small particle assemblies due to the co-reduction of gold precursor during the replacement reaction. As a result, these nanoshells do not exhibit strong optical properties in the near-infrared region. This study highlights the importance of solvent effects on PEGylated nonprecious metal nanoparticles against oxidation corrosion and its applications in preserving physicochemical properties of metallic nanostructures. 

Growth curve measurements are commonly used in microbiology, while the use of microplate readers for such measurements provides better temporal resolution and higher throughput. However, evaluating bacterial growth with microplate readers has been hurdled by barriers such as multiple scattering. Here, we report our development of a method based on the time derivatives of the optical density (OD) and/or fluorescence (FL) of bacterial cultures to overcome these barriers. First, we illustrated our method using quantitative models and numerical simulations, which predicted the number of bacteria and the number of fluorescent proteins in time as well as their time derivatives. Then, we systematically investigated how the time derivatives depend on the parameters in the models/simulations, providing a framework for understanding the FL growth curves. In addition, as a demonstration, we applied our method to study the lag time elongation of bacteria subjected to treatment with silver (Ag + ) ions and found that the results from our method corroborated well with that from growth curve fitting by the Gompertz model that has been commonly used in the literature. Furthermore, this method was applied to the growth of bacteria in the presence of silver nanoparticles (AgNPs) at various concentrations, where the OD curve measurements failed. We showed that our method allowed us to successfully extract the growth behavior of the bacteria from the FL measurements and understand how the growth was affected by the AgNPs. 

The mechanical properties of DNA have enabled it to be a structural and sensory element in many nanotechnology applications. While specific base-pairing interactions and secondary structure formation have been the most widely utilized mechanism in designing DNA nanodevices and biosensors, the intrinsic mechanical rigidity and flexibility are often overlooked. In this article, we will discuss the biochemical and biophysical origin of double-stranded DNA rigidity and how environmental and intrinsic factors such as salt, temperature, sequence, and small molecules influence it. We will then take a critical look at three areas of applications of DNA bending rigidity. First, we will discuss how DNA’s bending rigidity has been utilized to create molecular springs that regulate the activities of biomolecules and cellular processes. Second, we will discuss how the nanomechanical response induced by DNA rigidity has been used to create conformational changes as sensors for molecular force, pH, metal ions, small molecules, and protein interactions. Lastly, we will discuss how DNA’s rigidity enabled its application in creating DNA-based nanostructures from DNA origami to nanomachines.