Biosensors and Biomimetic Membrane Technology Gets Boost From NIST

Many U.S. biotech firms are working to develop new medical diagnostics, pharmaceuticals and sensors based on DNA, genetically engineered proteins and other products of biotechnology, and scientists at the National Institute of Standards and Technologyare supplying them with the essential information on the fundamental nature of these materials.

A symposium focusing on thin molecular films will be part of the 214th American Chemical Society National Meeting in Las Vegas, Nev., Sept. 7-11. Organized by NIST scientists, the symposium, "Self-Assembling Thin Film Materials," begins Sept. 8. Six NIST researchers will be presenting recent research results, including work on model DNA biosensors and biomimetic membrane systems.

DNA Chip Technology Could Lead to Fast New Sensors

DNA chips have the potential to revolutionize sequencing of DNA, diagnosis of genetic diseases, detection of pathogens in food and water, and forensics and personal identification to name but a few applications. The NIST DNA chip is made of one layer of single-stranded DNA molecules which self-assemble on gold, forming a well organized monolayer. The surface-tethered DNA can then bind complementary small fragments of single-stranded DNA from solution.

Such sensors could be used to analyze DNA present in a sample of blood or urine from a patient, or in water or food. In theory, sensors could be developed to check for many bacteria and viruses at the same time.

The development of such DNA chips benefits from accurate measurements of the fundamental properties of their building blocks. NIST researchers have been studying the characteristics of the thin film monolayers and their binding to complementary strands, in addition to other issues of monolayer and bilayer self-assembly mechanism and phenomena. The ACS Symposium on Self-Assembling Thin Film Materials will present results of NIST research as well as those representing universities, government laboratories and industry from around the world. Talks and poster presentations by NIST researchers will cover the following findings:

• NIST researcher Greg Poirier will show a time-lapse movie of molecular monolayers forming on a gold surface. He has studied the mechanisms of molecular self-assembly using scanning tunneling microscopy. He will discuss the stages and mechanisms of molecular monolayer formation on Monday, Sept. 8, 1:30 p.m., Room N119, Level 1, Las Vegas Convention Center.
• Researchers have determined how to obtain optimal coverage single-stranded DNA strands on gold so the DNA molecules are neither too dense nor too sparse to bind with complementary DNA from solution. NIST scientists Tonya Herne and Michael Tarlov devised a method for characterizing the conformation of surface-immobilized, single-stranded DNA. Herne will present a paper on this work on Thursday, Sept. 11, 3 p.m., Room N119, Level 1, Las Vegas Convention Center.
• Researchers have pursued the characterization of the structure of surface-tethered DNA. Rastislav Levicky has used two techniques to gain insights on how the DNA attaches to gold. Using infrared spectroscopy, he can monitor the extent of the contact between the DNA and gold, and how it changes with the surface density of the probe chains. He also has initiated neutron reflectivity studies that hold promise in obtaining the DNA concentration profiles in the vicinity of the surface. Levicky will present some of these results at a poster session on Wednesday, Sept. 10, 7-10 p.m., Las Vegas Hilton, Pavilion 1, Level 1.
• Using various electrochemical methods to measure surface traits of thin film monolayers is a convenient way to monitor the attachment of DNA. NIST researcher Adam Steel will explain how he uses capacitance and voltammetry measurements to characterize the DNA-containing film and other methods to quantify the amount of DNA binding. His presentation will be during the Wednesday evening poster session.

Rugged Biological Membrane Mimics Aid Protein Structure Studies

Understanding the structure and function of proteins is essential for using them in biosensing, bioremediation and bioprocessing. Many such proteins are naturally associated with the membranes of living cells. These proteins lose their structure and their activity if removed from the membrane. NIST researchers are studying novel cell membrane-like materials that will make the use of such proteins possible. These biomimetic membranes are lipid bilayers which contain some of the natural greasy molecules that are found in real membranes and some molecules that are not usually found in the body. These membranes stick tightly to metal surfaces, and this makes them rugged enough that they can provide a good home for membrane proteins even in industrial applications. NIST presentations in this area will cover the following:

• Various monolayer materials can be used to synthesize bilayer membranes that mimic living cell membranes. Building rugged self-assembling synthetic cell membrane models aids in understanding the complex structure and function of cell membranes in our bodies. NIST researcher Anne Plant will describe some of the kinetics and thermodynamics of forming tethered bilayer membranes on Thursday, Sept. 11, 8:15 a.m., Room N119, Level 1, Las Vegas Convention Center.
• Living cell membranes perform many complex tasks such as transporting nutrients into the cell and communicating with other cells. In order to better understand these functions, scientists need information about the structure and function of membrane proteins. This is easier said than done, as the natural membrane proteins tend to fall apart or denature outside of natural cell membranes. NIST researcher David Vanderah has been synthesizing new compounds that may be more suitable for incorporating natural cell membrane proteins into biometric model membranes. He will present his work during the Wednesday evening poster session.
• Because membrane proteins are not usually soluble in water, NIST is developing new techniques for studying membrane protein structures. Teresa Petralli-Mallow, a National Research Council post-doctoral researcher, uses light created at interfaces to probe proteins bound to rugged biomimetic lipid membranes by non-linear optical spectroscopy. She will present her work at the Wednesday poster session.

The technical sessions in the symposium will include 65 papers presented over four days. The Wednesday poster session will include approximately 100 presentations. The purpose of the symposium is to examine the current state of the art in molecular self-assembly for the fabrication of technologically useful materials.

As a non-regulatory agency of the U.S. Department of Commerce's Technology Administration, NIST promotes economic growth by working with industry to develop and apply technology, measurements and standards.