Electrophysiology of Biological Systems

Molecules can Mimic Functions of a Solid-State Device:  Solid-State Functions in a Molecular Based Device:  

Diodes:  One of the goals of the molecular electronics is to prove that these devices can compete with traditional solid-state devices.  To demonstrate molecular devices as a viable option for future electronic we use an atomic force microscope we can identify signatures from molecules that mimic traditional solid-state devices such a diode.  Diodes can control the follow of current or electric charge in one direction.  These devices are useful to tune television receivers, protect electronics from voltage surges, and produce light emitting diodes (LEDs). 

We investigate films and monolayers of porphyrin molecules that exhibit diode behavior.  By controlling the film thickness and deposition time of the porphyrin onto a thin film of gold we may be able identify what conditions allow the devices to be most stable for applications for electronic devices.  

Molecular Devices & Switches:  One reason we as experimentalists are obsessed with single molecules or manipulating a few of them is that we ultimately want to control what task they perform and when they perform that task.  That task could be as simple as controlling which electronic state the molecule uses to store information.  If we are able to determine inherent characteristics in the molecules, such as chemical groups connected to the molecules, that allow one to control the tasks that can be performed, then we can integrate these molecules into electronic circuits.To investigate how one can manipulate these molecules, we use a technique that allows us to correlate the electrical response, such as molecular switching to vibrational states of the molecules.   The technique we use is called inelastic electron tunneling spectroscopy (IETS), which requires measurements to be performed at cryogenic temperatures.

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Tracking Cell Differentiation of Adult Stem Cells:  We are striving to identify and establish a technique to track cell differentiation of adult stem cells for regenerative medicine.  The goal is to study the electrical properties of a heterogeneous population of adult stem cells using scanning probe microscopy.  For example, tracking the differentiation of stem cells will allow us to identify cell types and enable us to target cells that can be used to regenerate specific human body tissues or organs.  In particular, regenerative medicine can be used to replace damaged tissue or organs to restore or establish normal function in the human body.  

Binding and Electrical Characterization of DU145 Prostate Tumor Cells:  The ability to track cell differentiation of cancer cells could lead to early detection of pre-cancerous cells.  We are investigating one of the three “classical” cell lines of prostatic cancer, DU145.  We are examining the binding of metastatic DU145 prostate cancer cells to different types of silicon carbide, a substrate utilized in biomedical applications.  We are interested in studying the binding and electrical properties of the cancer cells using scanning probe microscopy techniques. 

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Hybrid Electronics and

Characterization Lab

Nanotechnology:  Building Molecular & Nanoscale Devices

Manipulation of Single Molecules:  Imagine when your electronic devices are controlled by a single molecule that transports electric charge to perform a specific task in your smart phone.  We investigate methods and techniques to make that happen in the future.  We exploit molecules called porphyrins. Due to their strong absorption in the visible region, these molecules are typically of interest for dye-sensitized solar cells.  

We can characterize the electronic properties of these molecules for such applications by investigating individual porphyrin molecules.  We use a technique called a scanning tunneling microscope (STM) molecular break junction (MBJ).  This technique allows us to probe the conductance (an electrical property) of an individual molecule.  Based on the plots of the conductance we can identify molecular switching behavior, i.e. the molecular conductance changes from a high conductance to a low conductance.  These signatures can be manipulated by an applied voltage.   One of our goals is to understand how to control molecular switching to be exploited in electronic devices. 

Prof. Kim Michelle Lewis:

Associate Dean of Research & Professor of Physics (Howard University) 


HECL has recently moved to Howard University Department of Physics and Astronomy​ (Thirkield Hall) 2355 6th Street NW Washington, DC  20059