Malkiat S. Johal
Associate Professor of Chemistry, Pomona College 

 

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Current Undergraduate Research Students

 

 


·       Robert Rawle (’08) My research is focused on the characterization and identification of potential uses of biofunctionalized surfaces, specifically surfaces composed of DNA or proteins adsorbed to a polyelectrolyte support.  The tool of choice which I utilize to examine these biofunctionalized surfaces is the quartz crystal microbalance with dissipation monitoring (QCM-D).  My central project, performed under the direction of Prof. Selassie and Prof. Johal, is centered on the creation of genomic mammalian DNA surfaces and the use of such surfaces in identifying the DNA-damaging abilities of phenolic compounds, specifically flavonoids.  In the past, I have successfully created both ssDNA and dsDNA surfaces and have observed DNA hybridization reactions on a polyelectrolyte surface using QCM-D.  I have also developed a QCM-D technique to detect DNA damage, and have used this technique to examine the detrimental capabilities of a variety of flavonoids, most notably quercetin.  Currently, I am in the process of using more conventional chemical and molecular biology techniques to verify this DNA damage.  In conjunction with Amanda Yang, I am also expanding our repertoire of surface chemistry techniques to characterize DNA surfaces, including ellipsometry, UV/vis spectroscopy, and ATR-FTIR.  I am also working in collaboration with Prof. Cheney and Connie Cheng to develop a method to detect weak protein-protein interactions using QCM-D.

 

·       Noah Rosenberg (’08) Nanoscale changes in the thickness of a thin film due to protein adsorption can be measured using a quartz crystal microbalance with dissipation monitoring (QCM-D) and multi-wavelength ellipsometry. These techniques provide the real-time detection of an antibody binding to an antigen adhered to the surface of a thin film.  The protective antigen of anthrax is the main component of the tripartite protein toxin secreted by anthrax and is often administered as a vaccination against anthrax. Noah is designing polyelectrolyte assemblies that will effectively bind the protective antigen.  He is using QCM-D as a biological sensor to show that anthrax antibodies in solution will bind to the antigen covered thin film.  The goal of Noah’s thesis is to be able to accurately detect the presence of anthrax antibodies in solution by measuring the change in mass of within the assembly containing the antigen.

 

·       Connie Cheng (’09) I am currently working with Prof Johal and Prof Cheney (Biology) in investigating protein-protein interactions using the QCM-D. GDI Displacement Factors (GDFs) and Rab Release Factors (RRFs) may play an important role in vesicle transport. These GDFs and RRFs are hypothesized to act as protein receptors for GDI (GDP Dissociation Inhibitor), a protein which recycles Rab GTPases (which direct vesicles to the correct targets membranes) back to their donor membranes and organelles. The interaction between GDFs/RRFs and GDI would thus mediate the extraction and release of rabs. Using the Yeast Two-Hybrid system, the Cheney Lab discovered a novel protein, Gint3, that may be a potential GDF or RRF. We have recently proven that Gint3 and GDI indeed interact specifically using the QCM-D. The QCM-D is able to detect even very weak interactions by measuring changes in frequency of oscillation as well as dissipation as proteins deposit, bind, and form a layer on the crystal. We plan to further investigate the nature of the GDI-Gint3 interaction and its relationship to rabs using the QCM-D.

 

·       Vincent Ma (’08) My research focuses on the fabrication and characterization of polymer light-emitting diodes (PLEDs). I am building upon a large body of work on PPV derivatives to show that the novel polymer “P2” can be easily and effectively incorporated into energy-efficient devices. In previous work, I showed that the polymer’s optical properties can be enhanced with the anionic surfactant SDS. In addition, I have found that this surfactant counteracts the photo-oxidation that plagues all polymer photovoltaic and electroluminescence systems. Once I succeed in building a working prototype, I will work to optimize its optical properties using SDS. My assembly methods include spin-casting, layer-by-layer adsorption, and a specially designed form of solvent casting. To characterize the device’s physical and electroluminescent properties, I am using ellipsometry, UV-visible spectroscopy, and fluorimetry. I hope that my research and results will provide a strong foundation for future electroluminescence work in Professor Johal’s lab.

 

·       Jeremy Treger (’09) explores the bulk-phase complexation of novel PPV-type polyelectrolytes with the anionic surfactant sodium dodecyl sulfate (SDS). He has demonstrated how SDS can be used to tune the emission properties, such as quantum yield and emission wavelength, of the polyelectrolytes by switching its conformation from a twisted (out-of-plane) state to highly conjugated state as a results of decreased electrostatic repulsion between the positive charges that are pendent on the benzene rings of the PPV-derivative. He is exploiting these interactions to fabricate multilayer thin-film organic photovoltaic devices using layer-by-layer electrostatic self-assembly method.

 

·       Amanda Yang (’10) was recently involved in a collaboration with Dr. Paul Davies, University of Cambridge. She spent the Summer 2007 working in the Cambridge SFG laboratory. Her work involves the deposition of NLO-active polyelectrolytes on functionalized gold surfaces, specifically on a self-assembled monolayer (SAM) of hydrophilic 11-mercaptoundecanoic acid. She has shown that the SFG spectra of the SAM exhibit strong CH2 resonances, which indicate the presence of gauche defects in the alkyl chains. Upon the deposition of a PEI/PAZO bilayer, these features disappeared due to extensive interpenetration of the polyelectrolyte film into the SAM. The SFG spectrum of the PEI/PAZO bilayer also exhibit a prominent resonance due to the C-H aromatic stretch (n2), indicating anisotropic ordering of the NLO-active chromophores within the assembly. Amanda has shown that the deposition of additional layers does not affect the strength of the n2 resonance.

 

·       Kavisha Singh (’10)  is investigating polyelectrolyte spin-assembly and the effect of electrostatic adsorption time on film growth. Kavisha constructs polyelectrolyte thin films composed of alternating layers are spin assembled by sequentially dropping an aqueous solution of a polycation and a polyanion on to a spinning substrate. Multilayer assemblies were fabricated from the polyanion poly[1-[4-(3-carboxy-4-hydroxyphenylazo) benzenesulfonamido]-1,2-ethanediyl, sodium salt] (PAZO) and the polycation poly(ethylenimine) (PEI). Kavisha is exploring the effect of adsorption time on the overall growth of the assemblies. Solutions are deposited on to the substrate for a predetermined amount of time and then spun for 1 minute at 3000 rpm. The assemblies are characterized using multi-wavelength ellipsometry and UV-visible absorption spectroscopy. She has shown that film growth is governed by a competition between steady-state electrostatic adsorption and mechanical entanglement under shear flow.

 

·       T.J. Lane (’10) I am interested in the incorporation of conductive polymers into organic, thin film-based, organic photonic devices. My past work with professor Johal has focused on the fabrication of PPV and C60 photovoltaic devices and the issues revolving around these systems, including efficiency of energy conversion, fabrication methodology, and photo-oxidation prevention. Currently I’m looking forward to working with Vincent Ma and Jeremy Treger in the lab to perfect the construction of a converse device, a PPV-based OLED. This summer I also became interested and proficient in the incorporation of metal oxides in thin film systems through the surface sol-gel method. I have been working on systems of quantum confinement using these structures to sandwich conductive polymer layers between dialectic layers of oxide to form quantum well structures. I plan on using the sol-gel method to isolate additional thin film components.

 

·       Rebecca Hamlin (’10) is working on immobilizing proteins and enzymes on polyelectrolyte surfaces. She is exploring how charge, conformation, and composition of underlying polyelectrolyte cushions effects the structure and function of immobilized enzymes within multilayer assemblies. Rebecca has recently completed a detailed analysis of how b-galactosidase functions on a polyelectrolyte surface. She is currently exploring kinetic features of the adsorption of lactate dehydrogenase on a poly(styrene sulfonate) film. She is currently involved in developing soft polyelectrolyte assemblies for hormone detection.

 

Graduated Spring 2007:

 

·       Daniel Wellman (’07) is studying the polyelectrolyte multilayer growth of the novel photoluminescent polycations P1 (below top) and P2 (below bottom). These polyelectrolytes were provided by Dr. Hsing-Lin Wang, Biosciences Division, Los Alamos National Laboratory. Both P1 and P2 are water soluble photoluminescent polyelectrolytes that exhibit unique pH-dependent optical properties. Dan’s work focuses on understanding the ultra-thin film properties of these potentially important materials. Dan uses a combination of multi-wavelength ellipsometry and QCM-D measurements to investigate the effect of pH on the single-component LbL assembly of P1 and P2, and their assembly with oppositely charged polyelectrolytes. His work demonstrated that the multilayer deposition of P1 alone can be induced by surface rearrangement after every deposition step. The rearrangement occurs after exposing the film to a hydrophobic environment. Furthermore, Dan has demonstrated that multilayer growth of P1 and P2 is strongly pH dependent.

 

·       Lewis Johnson’s (’07) work focuses on the fabrication and photocurrent characteristics of multilayer thin-film organic photovoltaic devices using layer-by-layer electrostatic self-assembly of a novel water-soluble cationic polyelectrolyte and a water-soluble anionic fullerene derivative on patterned indium tin oxide (ITO). The assemblies are constructed with cationic polyphenyenelvinylene derivative poly(2,5-bis[3-(N,N,N-triethylammonium bromide)-1-oxapropyl]-1,4-phenylenevinylene) (P2), which has tunable optical properties that can be modified by varying pH, ionic strength, and surfactant concentration. Lewis characterizes the films using quartz crystalline microbalance with energy dissipation (QCM-D), multi-wavelength ellipsometry, and UV/Visible spectroscopy. Lewis is also involved in other projects including enzyme entrapment in LbL assemblies and hydration studies of multilayer assemblies.