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Despite the broad use of enzymes in electroanalytical biosensors, the influence of enzyme kinetics on the function of prototype sensors is often overlooked or neglected. In the present study, we employ amperometry as an alternative or complementary method to study the kinetics of tyrosinase, whose catalytic activity results in o-quinone products. We further compare our results for four monophenolic substrates with those obtained from ultraviolet-visible spectrophotometry and show that the results from both assays are in good agreement. We also observe large variations in the enzyme kinetics for different monophenolic substrates depending on the R-group at the para position. To further study this effect, we investigate the stability of quinone products in the enzymatic assay. This information can in principle be utilized to discriminate between different phenolic species by monitoring the reaction rate. [ABSTRACT FROM AUTHOR]

Amperometric detection is ideally suited for integration into micro- and nanofluidic systems as it directly yields an electrical signal and does not necessitate optical components. However, the range of systems to which it can be applied is constrained by the limited sensitivity and specificity of the method. These limitations can be partially alleviated through the use of redox cycling, in which multiple electrodes are employed to repeatedly reduce and oxidize analyte molecules and thereby amplify the detected signal. We have developed an interdigitated electrode device that is encased in a nanofluidic channel to provide a hundred-fold amplification of the amperometric signal from paracetamol. Due to the nanochannel design, the sensor is resistant to interference from molecules undergoing irreversible redox reactions. We demonstrate this selectivity by detecting paracetamol in the presence of excess ascorbic acid. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Despite gel electrophoresis being one of the main workhorses of molecular biology, the physics of polyelectrolyte electrophoresis in a strongly confined environment remains poorly understood. Theory indicates that forces in electrophoresis result from interplay between ionic screening and hydrodynamics, but these ideas could so far be addressed only indirectly by experiments based on macroscopic porous gels. Here, we provide a first direct experimental test by measuring the electrophoretic force on a single DNA molecule threading through a solid-state nanopore as a function of pore size. The stall force gradually decreases on increasing the nanopore diameter from 6 to 90 nm, inconsistent with expectations from simple electrostatics and strikingly demonstrating the influence of the hydrodynamic environment. We model this process by applying the coupled Poisson–Boltzmann and Stokes equations in the nanopore geometry and find good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

Among the variety of roles for nanopores in biology, an important one is enabling polymer transport, for example in gene transfer between bacteria and transport of RNA through the nuclear membrane. Recently, this has inspired the use of protein and solid-state nanopores as single-molecule sensors for the detection and structural analysis of DNA and RNA by voltage-driven translocation. The magnitude of the force involved is of fundamental importance in understanding and exploiting this translocation mechanism, yet so far it has remained unknown. Here, we demonstrate the first measurements of the force on a single DNA molecule in a solid-state nanopore by combining optical tweezers with ionic-current detection. The opposing force exerted by the optical tweezers can be used to slow down and even arrest the translocation of the DNA molecules. We obtain a value of 0.24±0.02 pN mV−1 for the force on a single DNA molecule, independent of salt concentration from 0.02 to 1 M KCl. This force corresponds to an effective charge of 0.50±0.05 electrons per base pair equivalent to a 75% reduction of the bare DNA charge. [ABSTRACT FROM AUTHOR]

Presents information on a study that presented scanning tunnelling spectroscopy measurements of the two-dimensional structure of individual wavefunctions in metallic single-walled carbon nanotubes. Research methods; Results and discussion on the study.

Intestinal epithelial cells are critical for gastrointestinal homeostasis. However, their function declines during aging. The aging-related loss of organ performance is largely driven by the increase in senescent cells. To date, the hallmarks and molecular mechanisms related to cellular senescence are not fully understood. Microtubules control epithelial functions, and we identified microtubule stabilization as a phenotypic marker of senescent intestinal epithelial cells. The senescence inducer determined the pathway to microtubule stabilization. Specifically, enhanced microtubule stability was associated with α-tubulin hyperacetylation or increased abundance of the microtubule-binding protein tau. We show further that overexpression of MAPT, which encodes tau, augmented microtubule stability in intestinal epithelial cells. Notably, pharmacological microtubule stabilization was sufficient to induce cellular senescence. Taken together, this study provides new insights into the molecular mechanisms that control epithelial cell homeostasis. Our results support the concept that microtubule stability serves as a critical cue to trigger intestinal epithelial cell senescence., (© 2022. The Author(s).)