Field effect modulated nanofluidic diode membrane based on Al2O3/W heterogeneous nanopore arrays

We developed Al2O3/W heterogeneous nanopore arrays for field effect modulated nanofluidic diodes. They are fabricated by transferring self-organized nanopores of anodic aluminium oxide into a W thin film. The nanopores are ∼20 nm in diameter and 400 nm in length. After mild oxidation, approximately 10 nm WO3 grows on the surface of W, forming a conformal and dense dielectric layer. It allows the application of an electrical field through the surrounding W electrode to modulate the ionic transport across the entire membrane. Our experimental findings have potential applications in high throughput controlled delivery and electrostatic sorting of biomolecules

Facile fabrication of nanofluidic diode membranes using anodic aluminium oxide

Active control of ion transport plays important roles in chemical and biological analytical processes. Nanofluidic systems hold the promise for such control through electrostatic interaction between ions and channel surfaces. Most existing experiments rely on planar geometry where the nanochannels are generally very long and shallow with large aspect ratios. Based on this configuration the concepts of nanofluidic gating and rectification have been successfully demonstrated. However, device minimization and throughput scaling remain significant challenges. We report here an innovative and facile realization of hetero-structured Al2O3/SiO2 (Si) nanopore array membranes by using pattern transfer of self-organized nanopore structures of anodic aluminum oxide (AAO). Thanks to the opposite surface charge states of Al2O3 (positive) and SiO2 (negative), the membrane exhibits clear rectification of ion current in electrolyte solutions with very low aspect ratios compared to previous approaches. Our hetero-structured nanopore arrays provide a valuable platform for high throughput applications such as molecular separation, chemical processors and energy conversion

Soft nanofluidics governing minority ion exclusion in charged hydrogels

We investigate ionic partition of negatively charged molecular probes into also negatively charged, covalently crosslinked alginate hydrogels. The aim is to delimit the domain of validity of the major nanoelectrostatic models, and in particular to assess the influence of hydrogel chain mobility on ionic partition. We find that the widely used Gibbs-Donnan model greatly overestimates exclusion of the co-ion probes used. For low molecular weight probes, a much better fit is obtained by taking into account the electrostatics in the nanometric gel pores by means of the Poisson-Boltzmann framework; the fit is improved slightly when taking into account alginate chain mobility. For high molecular weight probes, we find it essential to take into account local gel deformation due to electrostatic repulsion between the flexible gel strands and the probe. This is achieved by combining Poisson-Boltzmann simulations with heterogeneous pore size distribution given by the Ogston model, or more simply and precisely, by applying a semi-empirical scaling law involving the ratio between Debye length and pore size

Composite hydrogel-loaded alumina membranes for nanofluidic molecular filtration

In this paper a nanofluidic molecular filtration system based on soft alginate hydrogel fillings and a solid-state alumina support membrane is presented. The electrostatically controlled diffusion is characterized by partition coefficient of the hydrogel and the flux through the composite membrane for positively and negatively charged dye molecules. The partition coefficient of negatively charged fluorescein sodium molecules into the gel is 2 orders of magnitude lower in 1 mM KCl solution than that in 1 M KCl solution. The molecular transport properties through the hydrogel loaded alumina membrane are solely dominated by the soft nanoporous hydrogel. Such a composite membrane with alginate hydrogel of only 6 wt% shows a selectivity of 5 for the separation of bovine serum albumin (BSA) and bovine hemoglobin (BHb) in high ionic strength solution of phosphate-buffered saline (PBS). (C) 2014 Elsevier B.V. All rights reserved

Three-Dimensional Integrated Ultra-Low-Volume Passive Microfluidics with Ion-Sensitive Field-Effect Transistors for Multiparameter Wearable Sweat Analyzers

Wearable systems could offer noninvasive and real-time solutions for monitoring of biomarkers in human sweat as an alternative to blood testing. Recent studies have demonstrated that the concentration of certain biomarkers in sweat can be directly correlated to their concentrations in blood, making sweat a trusted biofluid candidate for non-invasive diagnostics. We introduce a fully on-chip integrated wearable sweat sensing system to track biochemical information at the surface of the skin in real time. This system heterogeneously integrates, on a single silicon chip, state-of-the-art ultra-thin body (UTB) fully-depleted silicon-on-insulator (FD-SOI) ISFET sensors with a biocompatible microfluidic interface, to deliver a “Lab-on-skinTM” sensing platform. A full process for the fabrication of this system is proposed in this work and demonstrated by standard semiconductor fabrication procedures. The system is capable of collecting small volumes of sweat from the skin of a human, and posteriorly passively driving the biofluid, by capillary action, to a set of functionalized ISFETs for analysis of pH level and Na+ and K+ concentrations. Drop-casted Ion Sensing Membranes (ISM) on the different sets of sensors on the same substrate enables multi-parameter analysis on the same chip, with small and controlled cross-sensitivities, while a miniaturized Quasi-Reference Electrode (QRE) sets a stable analyte potential, avoiding the use of a cumbersome external Reference Electrode (RE). The progresses on Lab-on-SkinTM technology reported here can lead to autonomous wearable systems enabling real-time continuous monitoring of the sweat composition, with applications ranging from medicine to lifestyle behavioral engineering and sports

Apparatus for non-invasive sensing of biomarkers in human sweat

Presented herein are devices for collecting and/or channeling a biofluid (e.g., sweat, tears, saliva) and detecting and/or quantifying one or more biomarkers in the biofluid. The biomarker(s) may include, for example, ions, salts thereof, hormones and/or steroids, proteins, metabolites and organic compounds. In certain embodiments, the devices described herein include a specially designed interface and a zero-energy micro pump that allow the device to be comfortably affixed directly to the skin of a user while biofluid is efficiently and non-invasively collected from the skin of the user. In certain embodiments, the device is housed on or in another wearable device, such as a wrist band or a smart watch. In certain embodiments, the devices described herein are disposable (e.g., after a certain period of use and/or wear the device can be disposed and replaced with a low- cost replacement)