Office: PHSC 413 Phone: (405) 325-2054 Email: ivan-yip@ou.edu Full Publication List	Wai Tak Yip Associate Professor Ph.D., University of Chicago, 1996 OU Junior Faculty Research Program Recipient, 2001
Division: Physical Chemistry, Materials Science & Biophysical Chemistry Research Interests Single molecule spectroscopy of semiconducting nanocrystal/polymer composite materials; development of novel single molecule detection techniques; devising new strategies for DNA sequencing and computing by hibridization; charge transport in DNA; electroporation of lipid bilayer membranes;

Position Available in the Lab

Research Description

My research program encompasses the interdisciplinary interests of physical chemistry, biochemistry, and materials science. The main theme of my research is to apply optical spectroscopy and electrochemistry to study prototypical electronic devices derived from different kinds of materials such as organic polymers, semiconducting nanocrystals, enzymes, catalytic antibodies, and deoxyribonucleic acids (DNA). Our ultimate goal is to elucidate both the optical and electrical properties of these molecular building blocks and obtain microscopic insights into the factors that lead to their successful applications in molecular electronics.

In general, conventional techniques that rely upon ensemble measurements cannot provide sufficient microscopic information on an inhomogeneously distributed molecular property. Very often, the molecular property is statistically averaged and represented by a macroscopic observable that can be obtained in an ensemble measurement. Unfortunately, regenerating the molecular property distribution from the macroscopic observable rarely gives a unique answer. Thus, the best way to acquire microscopic information of a molecular property is to study one molecule at a time so that any existing heterogeneity in the molecular property can be unveiled. Recent advances in solid-state technology have allowed the optical detection of single molecules at room temperature. Single molecule spectroscopy is therefore particularly suitable for retrieving microscopic information from a molecular system.

We apply single molecule spectroscopy to study the optical and electrical properties of different varieties of molecular building block immobilized inside organic and inorganic matrices. The schematic of a home-built sample scanning confocal microscope used for single molecule spectroscopy is shown in Figure 1.

The incorporation of organic dyes into porous silica hosts using the "sol-gel" method has provided a valuable alternative to design new optical materials. It is well-documented that organic dyes exhibit enhanced photostability when trapped inside sol-gel matrices instead of solvent hosts. The enhanced photostability is believed to originate from more restricted intramolecular motions of encapsulated molecules, thereby reducing the number of dynamic interactions that lead to photodegradation. Surprisingly, experiments that can reveal a direct link between the mobility of a molecule and its photostability are still lacking. We will use single molecule spectroscopy to achieve simultaneous detection of the mobility and photostability of organic dyes trapped inside different sol-gel films. This will allow us to directly correlate the optical properties of a molecule with its own mobility. By performing the same experiment on sol-gel films that are characterized with different porosities, the optical characteristics of organic dyes in different microenvironments can be examined.

The sol-gel method has recently been adopted for the immobilization of biomolecules in biosensor development. To date, biomolecules including enzymes, catalytic antibodies, and nucleic acids have been successfully encapsulated. Yet very little is known about how guest-host interactions influence the biological activity of a biomolecule. To realize the full potential of sol-gel based biosensor, it is important to understand how biomolecules behave in different sol-gel environments. We will study sol-gel immobilized firefly luciferase and monitor its bioluminescence activity at the single molecule level. The ability to look into single enzymatic reactions provides an alternative approach to the study of biocatalysis. In this work, the biological activity of individual firefly luciferase molecules will be monitored and compared. The ultimate goals of this project are to provide critical information for the rational design and fabrication of novel bioanalytical devices and to improve our technology for the making of versatile molecular electronics.

In a typical single molecule spectroscopic setup, a continuous wave laser is usually employed as the source of excitation. Since the range of wavelengths provided by commercial laser systems is rather limited, only molecules that exhibit significant absorption at the available wavelengths can be studied. Moreover, due to the differences in local environment, it is believed that single molecule absorption spectra are inhomogeneously distributed. Thus, using a fixed laser wavelength for optical excitation will deposit different amount of excess internal energy to different molecules. Although at present the influence of excess internal energy on the fluorescence properties of single molecules is not clear, it is not surprising to find that the photophysical dynamics of the molecule would be altered. In this project, we would like to replace the optical excitation with an electrical excitation and explore the feasibility of performing single molecule spectroscopy by electroluminescence. Electrical excitation is a direct and precisely tunable source of excitation and it is most suitable for the study of electroluminescence in conjugated polymers. Meanwhile, electrical excitation also provides another dimension of resolution by selectively exciting molecules according to their valence band gap energies.

The increasing demand for high storage capacity devices in the foreseeable future has encouraged much research effort to encode digital information at the molecular level. Along this line, tremendous advancement in DNA chip technology has turned DNA into a potential candidate for the fabrication of ultrahigh storage capacity nanoelectronic devices. What makes DNA so promising is its ability to encode information in a quaternary format (A, T, C, G) for every single base within an oligonucleotide. As a result, for the same number of bit, the storage capacity of a DNA oligonucleotide is a power of two higher than a conventional semiconducting device that encodes information only in a binary format. In addition to the higher capability of condensing information, the physical dimension of a DNA base is much smaller than a semiconductor bit, indicating that the spatial efficiency for information storage of DNA is much better than that of a semiconductor device. The operation of retrieving information back from a DNA oligonucleotide is usually accomplished by the hybridization to a complementary strand of target DNA. In order to encode information at its highest capacity, hence, to fully utilize the quaternary format of a DNA device, DNA hybridization with the capability of discriminating single nucleotide mismatch is necessary. In this project, we will study the electrochemical response of a fluorescence dye attached to the end of a double-stranded DNA. Since a base-pair mismatch will dramatically affect the charge transport efficiency of the DNA, it is possible to achieve single nucleotide discrimination by studying the modulation of fluorescence intensity of the dye molecule when an electrical potential is applied.