Reto B. Schoch
Postdoctoral Associate
Department of Electrical Engineering and Computer Science

Biological Engineering Division

rschoch@mit.edu

Personal website

Reto B. Schoch received the Dipl. Masch.-Ing. degree in Mechanical Engineering from ETHZ, Zurich, Switzerland (2003), majored in micro- and nanotechnology and biomedical technology. He received his Ph.D. from EPFL, Lausanne, Switzerland (2006), in Microengineering. In 2006, he joined the Micro/ Nanofluidics BioMEMS Group at MIT as a postdoctoral associate.

Main research activity: nanofluidics

Introduction

Nanofluidics is defined as the study and application of fluid flow in and around nanometer-sized objects with at least one characteristic dimension below 100 nm. On the nanometer scale transport phenomena become possible which are not accessible at bigger length scales. Nanochannels have a big surface-to-volume ratio, leading to surface charge dominated transport and high charge-selectivity. Fluid flow in nanometer-sized apertures is laminar, and for electrokinetic transport the Debye length, zeta potential, ion mobility, and ion valence have to be considered.

Transport phenomena

The nanochannel conductance shows a conductance plateau (on a log-log scale) at low ionic strength, because of an excess of counterions in the nanometer-sized aperture which equilibrate the surface charge. Diffusion of ions with a different net charge results in an exclusion of co-ions and an enrichment of counterions in the nanochannel when the Debye length is comparable to the smallest dimension of the channel cross-section. This exclusion-enrichment effect is important to describe the permselectivity of a nanochannel, and can be used to separate biomolecules by charge. The transport obtained with an external driving force as an electric field or a pressure gradient, can be exploited to separate and preconcentrate molecules on a chip. Such charge-selective features are of interest for micro total analysis systems to achieve integrated devices for biomedical applications.

Applications

Efficient methods for separating and purifying biomolecules from a complex mixture are of the utmost importance in biology and biomedical engineering. The separation of proteins under native conditions was achieved on an anisotropic nanofilter array (ANA), leading to distinct streams of the proteins based on their size or charge. The separation mechanisms are Ogston sieving for the size-based separation, and electrostatic sieving for charge-based separation of proteins. These results hold great promise for integrated biomolecule sample preparation and analysis systems on a chip.

Research Projects

Continuous-Flow Size- or Charge-Based Separation of Proteins under Native Conditions through the ANA