Current Members of the Bohn Research Group
The following postdoctoral research associates and graduate students are
current members of the Bohn Research Group.

POSTDOCTORAL RESEARCH ASSOCIATES

Liqiang Chu
lchu1@nd.edu

B.S., Lanzhou University, China 1997
M.S., National University of Singapore, Singapore 2004
Ph.D., Max-Planck-Institute for Polymer Research, Germany 2007

Rapid and sensitive detection of a specific biomarker from body fluids (e.g., blood) is crucial for many biomedical applications. Considering the complexity of body fluids, a purification/separation step is generallu required to avoid the interference of other species. To address this issue, our group is to develop a nanofluidic delivery system based on andoic alumina membrane, which allows for the transport of a specific biomarker, and at the same time could reject other components, A TIRF-based sensing platform will also be integrated with the fluidic device to detect the presence of the biomarker of interest.

Aigars Piruska
apiruska@nd.edu

Despite the fact that there are a variety of bench-top methods for water quality assurance, rugged, low cost, field deployable sensing would be an extremely versatile tool for real time environmental monitoring and assessment of water quality in the developing world. Lead is one of the prominent environmental contaminants and our group is developing a lead sensing method based on a DNAzyme: a DNA complex that in the presence of lead cleaves itself and signals the occurence of lead contamination in a sample. We are interested in incorportating DNAzymes in nanopores and investigating the benefits of this nanoscale architecture for chemical sensing.

Ping Shi
pshi@nd.edu

Ph. D., Case Western Reserve University 2006

Metal nanowires are one of the most attractive materials for chemical sensing because of their unique properties. For example, the conductance of metal nanowires decreases upon adsorption of molecules due to the scattering of the conducting electrons by adsorbate-image charge interactions. The thinner the wires, the more significant this phenomenon. Our group is pursuing the fabrication of atomically thin metal wires (or atom-scale junctions, ASJs) and their application as highly sensitive nanostructured chemical sensors. With ASJs, it is possible to achieve single-molecule sensitivity.  Moreover, ASJs are compatible with micro- and nano-electronics, and also the detection method can be purely electrical, both indicating that ASJs have the potential to be engineered into economical and portable devices for chemical detection.

Zhen Wang
zwang3@nd.edu

My work is focused on studying macromolecular reactivity in confined geometries which is quite challenging and very few reports are available so far. We ar emaking nano-reactors using Focused Ion Beam (FIB) technique. The reaction in a single nano-reactor is monitored by 4pi microscope. Due to the confinement, reactions in nano-reactors show different properties from similar reaction systems in bulk solution.

GRADUATE STUDENTS

Sean Branagan
sbranaga@nd.edu

B.S., Cornell University 2006

Metallic subwavelength aperture arrays represent unique dually functional elements for chemical detection and digital manipulation of attoliter sample quantities on a microfluidic chip.  As a 2-D plasmonic lattice, the aperture array exhibits greatly enhanced optical transmission under resonant frequencies, offering precisely the confined electromagnetic field necessary for highly sensitive analyte detection.  When placed between polymer microchannels on a thin polymer substrate, the array enables electrokinetic switching between flow-past or flow-through processing modes. Our group seeks to (a) demonstrate multimodal fluidic processing through fabrication of a hybrid micro/nanofluidic structure and (b) experimentally investigate the limits of the integrated plasmonic/electrochemical sensor.

Barrett Duan
bduan@nd.edu

B.S., University of Wisconsin-Madison 2006

Gallium nitride (GaN) is a wide bandgap semiconductor that has shown great promises in optoelectonics and chemical and biochemical sensing application. We developed a novel, metal-assisted, electroless chemical etching method to produce porous GaN (PGaN). GaN surface is etched in HF/H2O2/EtOH solution under UV irradiation. Our PGaN surface exhibits a number of interesting and advantageous properties, including blue-shifted luminescence, extraordinarily high surface-to-volume ratio, enhanced photoconductivity, etc. Our current focus is to develop a chemical sensor comprised of PGaN.

Lindsay Elliott
lelliot2@nd.edu

Studies of Structural Heterogeneities in Temperature and Voltage Responsvie Hydrogels through Single Particle Tracking

Hydrogels are a class of polymers that offer myriad possibilities for fine control of sensing specificity and selectivity, fluid flow, drug delivery, and molecular gating when integrated into microfluidic and biomedical devices. This poetential stems from the special property of these soft materials which results in an expansion or contraction of the hydrogel in response to external perturbations such as changes in incident light, applied potential, ion concentration, pH, and temperature. However, further investigation of the fundamental properties of these materials is needed in order to realize nanoscale control in reproducible, robust devices.

Films composed of two of the most attractive types of hydrogels - voltage responsive and temperature responsive polymers - have been investigated separately in this project. Surface initiated pHEMA films and pNIPAAm films are grown by atom transfer radical polymerization, a well known polymer science technique. This living polymerization engenders excellent control of film thicknesses on the order of 10-100 nm and superior chain length uniformity compared to many other synthetic methods, In addition, patterning of the polymer film can be achieved by selective placement of the initiator layer.

Single particle tracking is employed to characterize a wide range of temporally and spatially heterogeneous microenvironments within the polyer films. In this method, fluorescent probes inserted in the void spaces within the polymer films are imaged. These images are then stacked chronologically and trajectory data for each molecule is extracted in a Matlab based tracking program. Different types of movement are identified and classified when the individual squared displacement of each molecule is analyzed. Populations of probe movement within a polymer film are compared before and after external perturbation in order to elucidate structural changes in the materials.

Travis King
tking4@nd.edu

B.S., Ohio Northern University 2003

Nanoscale fluidic systems have applications in areas as far-reaching as water purification, chemical sensing, and the study of enzyme-substrate interactions, among many others.  More specifically, our group utilizes nanocapillary array membranes (NCAMs), containing thousands of nanoscale pores, to create integrated 3-dimensional hybrid microfluidic/nanofluidic structures.  These structures allow digital fluidic control of attoliter sample volumes for the separation, concentration, reaction, and detection of analyte molecules.  A fundamental understanding of transport and chemical reactivity in these devices can be obtained by studying transport/reaction phenomena in systems containing a single nanopore, allowing detection one event at a time.  To this end, we have constructed an axially-opposed dual confocal microscope with single fluorophore sensitivity.  Along with sensitive electrical conductivity measurements, this constitutes an enabling capability for understanding the fundamental spatiotemporal characteristics of nanofluidic transport in systems of interest.

Rachel Masyuko
rmasyuko@nd.edu

The use of Lignocellulosic materials to feed the biorefinery of the future depends critically on the development of high efficiency, inexpensive pre – enzymatic protocols of raw plant material to render lignin separable from cellulose and hemicellulose. These protocols require a detailed knowledge of the spatial and temporal infiltration of reagents designed to remove and separate lignin from the processable sugar components. Our lab seeks to focus on a detailed chemical and structural understanding of this pre–enzymatic processing in space and time.

M. Windy McNerney

B.S., University of California-Davis 2003

Long-term potentiation (LTP) occurs when the simultaneous stimulation of two individual neurons results in an increase in their communication efficacy. This is thought to be one of the mechanisms that underlie the cellular basis for memory formation. However, the precise molecular and chemical mechanisms involved in LTP are not well understood, partially because current neuroscience methods rely on chemical blocking and measurements taken at scales much larger than individual molecular reactions. Only a limited amount of information about this sort of process can be extracted using these methods. My research thus aims to use a combination of nanotechnology and neuroscience, to develop methods for measurement of the chemical reactions during LTP on the single-molecular scale. This will be accompolished using the zero-mode waveguide, which is capable of measuring single molecules in a biological setting with sub-millisecond temporal resolution. The zero-mode waveguide will thus be used to unravel the mysteries behind the single molecular changes involved in memory.

Jing Zhao
jzhao2@nd.edu

B.S., Tsinghua University, China 2007

One of the most promising structures so far to have achieved single-molecule detection is the zero-mode waveguide. Zero-mode waveguides provide an excellent means of volume confinement for single molecule studies at high concentration. The waveguides are implemented as small holes in a thin aluminum or gold film on a fused silica substrate. Fluorescence is induced by a laser coupled to the waveguide via a confocal microscope in epi-illumination mode. Now before the physical design of the ZMW structure, we are doing finite element modeling calculations to understand how confinement of the electromagnetic field changes as a function of the diameter and depth of the ZMW structure.

UNDERGRADUATE STUDENTS

Justine Debelius
jdebel01@saintmarys.edu

Silicon nanopores and nanopore arrays have a variety of applications, in fields such as biochemistry, nanofluidics and medical technology. Currently, most nanopores are fabricated using FIB milling. However, this requires expensive equipment and substrates. My goal is to fabricate nanopores and uniform nanopore arrays in <100> silicon chips using a two-step anisotropic etching process involving basic laboratory equipment and relatively inexpensive chemicals.

Rachel Letteri
rletteri@nd.edu

My project is to measure the reaction kinetics of a DNA hybridization reaction in confined geometry. During the hybridization reaction, an oligomer is immobilized in a microfluidic channel and its complement with two mismatches is hybridized. Subsequently, the original oligomer’s complement is injected into the channel and a replacement reaction occurs. In the first phase of the project, I will run the reaction through a microfluidic channel coupled with a fused silica slide and use a home made total internal reflection fluorescence set up with a prism to acquire reaction kinetics data for an unconfined geometry. This data will be compared to literature results in which similar reactions have been considered. The total internal reflection fluorescence capability is achieved using a triangular prism to achieve the required incidence angle. The second phase of the project moves the reaction to a nanofluidic channel to acquire comparable data in a confined geometry. These results will be contrasted with the first phase results with a goal of learning about the reaction kinetics in nanoscale pores. This knowledge is an essential addition that will aid in the commercialization of nanopores in areas such as drug delivery and energy conservation.

Kevin Sallah
ksallah@nd.edu

Developing and investigating planar, interdigitated electrodes for use in electrochemical impedance sensors. The sensors are used to measure changes in impedance due to changing conditions, such as the presence of toxins in a tissue sample. Characteristics of the electrodes will be modified to examine the effects on the sensor's ability to recognize small concentrations of the target compound.

VISITING RESEARCHER

Hsin-Yu Lin
hsiftraeh07@gmail.com

Gold nanowires have been the focus of extensive research activities in recent years due to their high biocompatibility, sensitivity and selectivity. They can also be used for highly sensitive detection of gas, chemical, or biological specimen based on the resistance change. My goal is to fabricate a resistive-type sensor based on a single Au nanowire connected with electrodes by a combination of E-beam lithography and photolithography. The sensing principle is based on measuring the resistance change of a single Au nanowire caused by chemical adsorption between the nanowire and the adsorbates and increased surface scattering effects.

Group files

Group activities pictures

Past group pictures