Understanding
the mobility of nano-objects in the eukaryotic cell
nucleus, at multiple length-scales, is essential for dissecting nuclear
structure–function relationships both in space and in time.
Here, we demonstrate, using single-molecule fluorescent correlation
spectroscopies, that motion of inert probes (proteins, polymers, or
nanoparticles) with diameters ranging from 2.6 to 150 nm is mostly
unobstructed in a nucleus. Supported by the analysis of electron tomography
images, these results advocate the ∼150 nm-wide interchromosomal
channels filled with the aqueous diluted protein solution. The nucleus
is percolated by these channels to allow various cargos to migrate
freely at the nanoscale. We determined the volume of interchromosomal
channels in the HeLa cell nucleus to 237 ± 61 fL, which constitutes
34% of the cell nucleus volume. The volume fraction of mobile proteins
in channels equals 16% ± 4%, and the concentration is 1 mM.
Simple fabrication, high power-to-weight and power-to-volume ratios, and the ability to operate in open air at low voltage make the ionic electroactive polymer actuators highly attractive for haptic applications. Whenever a direct tactile stimulation of the skin is involved, electrical and chemical insulation as well as a long-term stability of the actuator are required. Because of its inherent physicochemical properties such as high dielectric strength, resistance to solvents, and biological inactivity, Parylene C meets the requirements for making biocompatible actuators. We have studied the displacement and the generated force of Parylene-coated carbon nanotube actuators as well as the encapsulation quality. A 2 μm coating creates an effective electrical insulation of the actuators without altering the blocking force at frequencies from 50 mHz to 1 Hz. Moreover, the generated strain is preserved at higher frequencies (from 0.5 to 5 Hz). We employed a simple mechanical model to explain the relation between the key parameters-flexural stiffness, displacement, and force-for uncoated and coated actuators. In addition, we demonstrated that our Parylene-coated actuators are not damaged by rinsing in liquid media such as 2-propanol or water. In conclusion, our results indicate that Parylene C encapsulated actuators are safe to touch and can be used in contact with human skin and in biomedical applications in direct contact with tissues and physiological fluids.
Intrinsic
molecular brightness (MB) is a number of emitted photons
per second per molecule. When a substrate labeled by a fluorophore
and a second unlabeled substrate form a complex in solution, the MB
of the fluorophore changes. Here we use this change to determine the equilibrium constant (
K
) for the formation of the complex at pM concentrations.
To illustrate this method, we used a reaction of DNA hybridization,
where only one of the strands was fluorescently labeled. We determined
K
at the substrate concentrations from 80 pM to 30 nM. We
validated this method against Förster resonance energy transfer
(FRET). This method is much simpler than FRET as it requires only
one fluorophore in the complex with a very small (a f̃ew percent)
change in MB.
The efficient delivery of drugs to cells depends on their diffusion through the extracellular matrix (ECM) of tissues. Here we present a study of diffusion of nanoprobes of radius from...
The reaction kinetics between like-charged compounds in water is extremely slow due to Coulomb repulsions. Here, we demonstrate that by screening these interactions and, in consequence, increasing the local concentration of reactants, we boost the reactions by many orders of magnitude. The reaction between negatively charged Coenzyme A molecules accelerates ~5 million-fold using cationic micelles. That is ~104 faster kinetics than in 0.5 M NaCl, although the salt is ~106 more concentrated. Rate enhancements are not limited to micelles, as evidenced by significant catalytic effects (104–105-fold) of other highly charged species such as oligomers and polymers. We generalize the observed phenomenon by analogously speeding up a non-covalent complex formation—DNA hybridization. A theoretical analysis shows that the acceleration is correlated to the catalysts’ surface charge density in both experimental systems and enables predicting and controlling reaction rates of like-charged compounds with counter-charged species.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.