Project Descriptions:

The Human-on-a-Chip Initiative

Swiss 3T3 fibroblasts arrayed on a chemically textured surface such as might be used in a microfluidic environment for toxin sensing.

Typical sensor research focuses on new methods to characterize a sample for chemical components of interest.  However, people required to perform work in hazardous environments usually do not care what compound is present; they only care if an unknown, unseen chemical threat is potentially toxic or not.  This project seeks to create a sensor that instantly alerts personnel to toxic threats in water.  The sensor will accomplish this by realizing the challenging goal of integrating human physiology into a microfluidic chip.  The capacity to mimic human physiologic response on a chip will support intriguing applications ranging from rapid in vivo-like bioassays to molecule-blind sensing of toxins in the environment.  For example, injecting an aqueous sample onto the sensor device could trigger passage through a number of organ-mimic regions informing a human toxicity decision tree.  Microfluidic channels - functioning as artificial vasculature - carries samples through a 3D integrated fluidic device capable of sample splitting and transporting individual aliquots to disparate sensing modalities, each representing a specific physiological function.  Sequential or simultaneous probes of effects on nerve cells, kidney enzymes, mucosa membranes or cardiac myocytes all could take place - each step providing a signal notifying the user of a potential toxin - all without regard to its chemical identity, thereby assessing exposure to environmental toxins on a personalized basis.  This interdisciplinary multi-university project is being carried out in collaboration with colleagues at the US Army Engineering Research and Development Center, Colorado State, Columbia, Cornell, Harvard and MIT.
Professor Paul Bohn

Electronic Detection of Single Molecules at Atomic Junctions

Electrical resistance change upon adsorption of a single molecular layer of cysteine comprised of ~1000 total molecules. Photomicrograph of a gold atomic junction construct

Atomic junctions in metal nanowires show unique properties that make them attractive for chemical and biological sensing.  Due to their extremely small size (ideally a single atom wide), the electronic resistance of these structures is very sensitive to the presence of airborne and waterborne contaminants such as environmental pollutants chem/bio warfare agents.  We are working to incorporate gold atom-scale junctions in microfluidic architectures to create portable sensors with high selectivity and sensitivity.  Creating gold wires that are a single atom wide starts with patterning techniques that are carried out in the particulate-free environment of a microelectronics cleanroom.  Electrochemical methods are then employed to control the size of the junction and fabricate the final devices.  Detection is based on the measurement of changes in electrical resistance as molecules interact with the surface of the wire. In addition, these small metal junctions can be made to respond specifically to certain molecules by chemically modifying the surface. In the data shown here an ultrasmall window is opened by ion beam milling directly over a gold atomic junction which is then exposed to the amino acid, cysteine.  The entire structure is only large enough to support ~1000 molecules, and the resistance fluctuations at long times correspond to equivalent surface populations variations of ±20 molecules.
Professor Paul Bohn