Research in our group combines themes at the forefront of nanoscience, biomolecular engineering, and electrochemistry, for the development of innovative analytical tools and their application in both the physical and life sciences. Examples include the development of sensitive, nanometer scale chemical and biological sensors that will probe materials and biological systems with unprecedented temporal and spatial resolution. Researchers in the group will gain a highly interdisciplinary background electrochemistry, biochemistry, nanotechnology and biomolecular engineering pushing the frontiers of basic science while also narrowing the gap between laboratory-bound research and real-world applicability. To learn more about specific research projects we are working on, please follow the links.
Bio-Inspired Scanning Ion Conductance Microscopy
Objective: The objective of this proposal is to develop a bio-inspired, protein channel-based scanning ion conductance microscope for simultaneous surface imaging and specific molecule concentration mapping.
Scanning ion conductance microscopy (SICM) represents a powerful scanned-probe microscopy capable of providing conductance and topography mapping with high spatial resolution (nm) of a variety of biological and inorganic substrates. The technique relies on changes in a distance-dependent access resistance or changes in ionic current into a pulled-nanopipet imaging probe. While SICM is a powerful technique for imaging, particularly of biological samples (1-5), the imaging probes generally lack chemical specificity thus limiting the chemical information that can be obtained. Naturally occurring trans-membrane protein channels represent reproducible nanopores with activities that can be gated by specific molecules that can potentially impart chemically specificity to SICM (6-11). Protein channels can be incorporated into analytical devices to provide extremely specific and sensitive detection capabilities down to the single molecule level. Here, we aim to couple the promising imaging capabilities of SICM with the exquisite specific single molecule detection abilities of protein channel measurements to create a bio-inspired SICM (Fig. 1) capable of simultaneously providing surface topography information and information about specific molecular flux.
Monitoring Glial Cell Communication
Objective: The overarching goal of this project is the development of nanoscale sensors capable of monitoring single cell communication by specifically detecting ATP as it is released from astrocyte cells. The methodology we develop here should be able to transcend from single cell measurements to in vivo measurements and should be adaptable to a wide range of biomolecular targets.
Over the past decade, adenosine triphosphate (ATP) has emerged as an important signaling molecule particularly in the central nervous system providing possible functions related to information processing, memory formation, sleep homeostasis, gene expression and neurological disorders. There has been recent evidence suggesting that astrocytes – non-neuronal glial cells – play a vital role in intercellular communication in the nervous system via the release of ATP as well as glutamate and D-serine. Several questions still remain, however, about ATP signaling from astrocytes such as 1) what is the general release mechanism of ATP, 2) what activities control this release and finally, 3) what is the role of ATP signaling in vivo. Currently, there are no good methods to directly measure ATP release and furthermore the translation of these methodologies to the in vivo setting has been left unmet. As such, we set out to develop the analytical methodology to address ATP signaling from astrocytes in experimental conditions ranging from cultured single cells to conditions in the central nervous system of a living animal. Achievement of this goal provides an analytical methodology to probe the physiological role of ATP and how this changes in respond to various disease states.
Electrochemical aptamer-based (E-AB) sensors, employing oligonucleotide aptamers that bind specific targets, represent a new class of biosensor that can specifically detect a wide range of biomolecular targets regardless of their intrinsic activity. For example, E-AB sensors have been described against a number of targets including small molecules, proteins and inorganic ions. Sensor signaling is predicated on specific target binding induced changes in the conformation or flexibility of the electrode-bound, redox-tagged DNA aptamer. These changes thus change the efficiency with which electrons can transfer between the redox tag and electrode and can be measure voltammetrically. As such E-AB sensors are reagentless and reusable and are capable of detecting targets in complex sample matrices including whole blood and cellular lysates. Coupling the promising attributes of E-AB sensors with nanometer-scale electrodes, we will develop sensors that will achieve the sensitivity and resolution (both spatial and temporal) needed to specifically detect ATP release from single astrocyte cells.
Aptamer-Hydrogel Sensors for Compatible Interfacing with Biology
Objective: The overarching goal of this project is to develop a copolymer membrane in which a blend of conducting and biocompatible polymers create a anti-fouling sensing matrix for long term in vivo sensing.
Biosensors have the potential to revolutionize how we study living systems. The information we learn about the molecular basis of organism function could lead to new paradigms biology and the life sciences. Unfortunately, while examples of new biosensor platforms continue to grow, two major barriers impede utilization of devices outside the controlled laboratory setting: 1) Sensors fail to respond when challenged in complicated biological sample matrices due to “biofouling,” which masks the true biological response of interest, and/or 2) The sensor perturbs the environment and thereby elicits an unnatural response by the biological system being studied. New biosensor designs are thus needed that enable proper interfacing with the biological environment.
Our specific goals are to couple the tunable biocompatibility of hydrogel polymeric membranes with the selective and specific recognition capability of E-AB sensors to yield devices capable of interfacing directly with biological systems, and to demonstrate their broad applicability using test-bed biological environments.
Random Walk Models to Better Understand Biosensors
Objective: The goal of this research is to use single molecule random walk simulations to better understand the electrochemical response of DNA-based biosensors. With this knowledge we can rationally design and improve the analytical performance of such sensors.
We develop a random walk model to simulate the Brownian motion and the electrochemical response of a single molecule confined to an electrode surface via a flexible molecular tether. We use our simple model, which requires no prior knowledge of the physics of the molecular tether, to predict and better understand the voltammetric response of surface-confined redox molecules when
motion of the redox molecule becomes important. The single molecule is confined to a half-sphere volume with a maximum radius determined by the flexible molecular tether (5-20 nm) and is allowed to undergo true three-dimensional diffusion. Distance and potential dependent electron transfer probabilities are evaluated throughout the simulations to generate cyclic voltammograms of the model system. We then validate our model with experimental investigations of electrochemical, DNA-based sensors.