Ionic current driven by a viscosity gradient.

Gradients of voltage, pressure, temperature, and salinity can transport objects in micro- and nanofluidic systems by well-known mechanisms. This paper explores the dynamics of particles in a viscosity gradient with numerical simulations. The different stochastic rules used to integrate the random motion of Brownian particles affect the steady-state distribution of particles in a diffusivity gradient. Importantly, the simulations illuminate the important role that the boundary conditions play, disallowing a steady-state flux when the boundary conditions mimic those of a closed container, but allowing flux when they mimic electrodes. These results provide an interpretation for measurements of a steady ionic current flowing between electrodes separated by a nanofluidic channel with a liquid viscosity gradient.

Prognostic marker analysis in pediatric intracranial ependymomas.

Histologic grading methods dependent upon H&E staining review have not been shown to reliably predict survival in children with intracranial ependymomas due to the subjectivity of the analytical methods. We hypothesized that the immunohistochemical detection of MIB-1, Tenascin C, CD34, VEGF, and CA IX may represent objective markers of post-operative survival (Progression Free and Overall Survival; PFS, OS) in these patients. Intracranial ependymomas from patients aged 22 years or less were studied. The original histologic grade was recorded, H&E sections were reviewed for vascular proliferation status, and immunohistochemistry was used to determine MIB-1, Tenascin C, CD34, VEGF, and CA IX status. Based upon the World Health Organization (WHO) grading system, 3 Grade I, 18 Grade II and 9 Grade III ependymomas were studied. Median follow-up time was 9.0 years; median PFS was, 6.1 years. Original WHO grade did not correlate with PFS or OS. Peri-necrotic CA IX localization correlated with PFS (Log rank = 0.0181) and OS (Log rank p = 0.0015). All patients with a CA IX ≤ 5 % total area localization were alive at last follow-up. Perinecrotic CA IX staining was also associated with vascular proliferation (p = 0.006), though not with VEGF expression score. MIB-1 labeling index (LI) correlated with OS (HR 1.06, 95 % CI 1.01, 1.12) and PFS (HR 1.08, 95 % CI 1.02, 1.14). MIB-1 LI and perinecrotic CA IX individually correlated with PFS. The effect of perinecrotic CA IX remained when grade was added to a Cox model predicting PFS. Immunodetection of CA IX and MIB-1 expression are predictive biomarkers for survival in children with posterior fossa ependymomas. These markers represent objective indicators of survival that supplement H&E grading alone.

The nanopore mass spectrometer.

We report the design of a mass spectrometer featuring an ion source that delivers ions directly into high vacuum from liquid inside a capillary with a sub-micrometer-diameter tip. The surface tension of water and formamide is sufficient to maintain a stable interface with high vacuum at the tip, and the gas load from the interface is negligible, even during electrospray. These conditions lifted the usual requirement of a differentially pumped system. The absence of a background gas also opened up the possibility of designing ion optics to collect and focus ions in order to achieve high overall transmission and detection efficiencies. We describe the operation and performance of the instrument and present mass spectra from solutions of salt ions and DNA bases in formamide and salt ions in water. The spectra show singly charged solute ions clustered with a small number of solvent molecules.