Kristi M. Singh

Bio-organic field effect transistors

This paper reports on the use of new DNA-based biopolymers as the semiconducting layer in field effect transistors. Thin-film field effect transistor (FET) structures are fabricated with two different DNA-biopolymers as semiconductor layers, and two different field effect transistor structures are studied. Current voltage characteristics of the FETs show that the devices are operating in depletion mode.

Chirality of sulforhodamine dye molecules incorporated in DNA thin films

Thin films formed from salmon sperm DNA reacted with a cationic surfactant (CTMA-Cl) included up to 25 wt % fluorescent molecule sulforhodamine (SRh). SRh effect on DNA chirality and vice versa was investigated by circular dichroism (CD) spectroscopy. The CD signals at 250–265 nm indicate that DNA chirality was maintained or enhanced. Induced CD (iCD) signal at 580–610 nm indicates that SRh is chiral in DNA/CTMA. iCD signal from both solutions and thin films generally increases with SRh concentration. The chirality induced in SRh molecules and the absence of significant DNA reduction in chirality are clear indicators of strong binding to DNA/CTMA.

The impact of culture medium on the development and physiology of biofilms of Pseudomonas fluorescens formed on polyurethane paint

Microbial biofilms cause the deterioration of polymeric coatings such as polyurethanes (PUs). In many cases, microbes have been shown to use the PU as a nutrient source. The interaction between biofilms and nutritive substrata is complex, since both the medium and the substratum can provide nutrients that affect biofilm formation and biodeterioration. Historically, studies of PU biodeterioration have monitored the planktonic cells in the medium surrounding the material, not the biofilm. This study monitored planktonic and biofilm cell counts, and biofilm morphology, in long-term growth experiments conducted with Pseudomonas fluorescens under different nutrient conditions. Nutrients affected planktonic and biofilm cell numbers differently, and neither was representative of the system as a whole. Microscopic examination of the biofilm revealed the presence of intracellular storage granules in biofilms grown in M9 but not yeast extract salts medium. These granules are indicative of nutrient limitation and/or entry into stationary phase, which may impact the biodegradative capability of the biofilm.

Deoxyribonucleic acid biotronics

Organic field-effect transistors (OFETs) currently utilize organic semiconductor materials with low electron mobilities and organic gate oxide materials with low dielectric constants. Compared to inorganic FETs, OFETs have slow operating speeds and high operating voltages. In this paper we discuss blending the conductive polymer polyethylene dioxythiophene (PEDOT) with deoxyribonucleic acid (DNA), with minimal optimization to produce a new bio-conductive polymer complex potentially suitable for OFETs. The conductivity of this new bio-conductive polymer complex is tunable, ranging from 10-10 S/cm to 10-3 S/cm at room temperature.

Bio-dielectrics based on DNA-Ceramic hybrid films for potential energy storage applications

The potential of DNA-based dielectrics for energy storage applications was explored via the incorporation of high dielectric constant (ε) ceramics such as TiO2 (rutile) and BaTiO3 in the DNA bio-polymer. The DNA-Ceramic hybrid films were fabricated from stable suspensions of the nanoparticles in aqueous DNA solutions. Dielectric characterization revealed that the incorporation of TiO2 (rutile) in DNA resulted in enhanced dielectric constant (14.3 at 1 kHz for 40 wt % TiO2) relative to that of DNA in the entire frequency range of 1 kHz-1 MHz. Variable temperature dielectric measurements, in the 20-80°C range, of both DNA-TiO2 and DNA-BaTiO3 films, revealed that the ceramic additive stabilizes DNA against large temperature-dependent variations in both ε and the dielectric loss factor tan δ. The bulk resistivity of the DNA-Ceramic hybrid films, in the case of both TiO2 and BaTiO3 additives in DNA, was measured to be two to three orders of magnitude higher than that of the control DNA films, indicating their potential for utilization as insulating dielectrics in capacitor applications. As a part of a baseline study, results based on a comparison of the temperature-dependent dielectric behavior of DNA and DNA-CTMA complex films as well as their frequency-dependent polarization behavior, are also discussed.

Bio-dielectric organic-inorganic hybrid films for potential energy storage applications

DNA-based bio-dielectrics incorporating sol-gel have been investigated for energy storage applications. Salmon DNA hybrid films blending sol-gel-ceramics with DNA-CTMA have potential for increased dielectric constants and higher environmental stability compared to DNA only films. Thin film capacitor devices were fabricated and characterized, showing stability in dielectric properties and reliability in voltage breakdown measurements, attaining values consistently at 300 V/um. Temperature-dependent dielectric properties as well as dielectric stability as a function of thermal cycling of these hybrid films are also discussed.

Inkjet Printing of DNA for Use in Bioelectronic Applications

Biopolymers have received much attention lately for use in electronic applications. Salmon DNA complexed with cetyltrimethyl ammonium chloride (DNA-CTMA) produces a material soluble in organic solvents, enhancing the ease of processing. DNA-CTMA has shown promise as an electron blocking layer in organic light emitting diodes (OLEDs) and potential as a gate insulating material in field effect transistors (FETs). To realize an all bio-based FET, we are continuing to investigate the use of DNA as the semiconducting layer. In addition to tailoring the properties of the biomaterial to increase the conductivity, we are also trying to better characterize these materials and explore different deposition techniques. Inkjet printing offers an unique ability to reproducibly deposit materials in a spatially controlled fashion, using picoliter amounts with high throughput. This paper will present how parameters such as solvent evaporation rate and substrate influence film properties. The characterization of the resulting DNA films includes atomic force microscopy (AFM) and white light interferometry.

DNA hybrid dielectric film devices for energy storage and bioelectronics applications

DNA biopolymer hybrids have been investigated for energy storage applications and also as potential high k gate dielectrics in bioelectronics applications such as BioFETs. DNA-based hybrid films incorporating sol-gel-derived ceramics have shown strong promise as insulating dielectrics for high voltage capacitor applications. Our studies of DNA-CTMA complex/sol-gel hybrid thin film devices have demonstrated reproducibility and stability in temperature-and frequency-dependent dielectric properties as well as reliability in DC voltage breakdown measurements, attaining values consistently in the 300 - 350 V/um range. We have also investigated DNA-inorganic hybrids by ex situ blending of aqueous solutions of DNA with high k ceramics such as BaTiO3 and TiO2. These systems are currently being investigated as potential gate dielectrics for BioFETs by virtue of their relatively high dielectric constant, high DC electrical resistivity, and lower leakage currents than pristine DNA. Functionally layered devices have also been designed, fabricated and characterized to determine any added benefit in dielectric applications. The electrical/dielectric characteristics of DNA and DNA-CTMA with sol-gel-derived ceramics, high k ceramic fillers, and in layered devices were examined to determine their effect on vital dielectric parameters for energy storage and bioelectronics applications.

DNA-based thin-film dielectrics for potential application as gate insulators in OFETs

In this study, highly stable aqueous solutions of blends containing Deoxyribonucleic acid (DNA) and high k ceramics (BaTiO₃ or TiO₂) nanoparticles were processed. Dielectric and electrical properties of the as-prepared nanocomposites thin films were investigated. Dielectric Constant <i>k</i> values of 14 and capacitance density of 2.5 nF/cm² were achieved for a 40 wt.% BaTiO₃ loading at 1 KHz. The current-voltage (IV) measurements revealed electrical resistivity in the order of 10¹⁴ Ohm-cm with leakage current densities of the order of 10^-9 A/cm² for electric field biases up to 50V/μm.

Optoelectronics using DNA as a template for dyes

Aside from salmon DNA, other DNA sources were explored namely, herring and onion, to prepare DNAsurfactant complex, which will be used as a template for dyes undergoing Forster Resonance Energy Transfer (FRET). Also, salmon DNA of low and high molecular weight were compared. This study aims to assess the effect of using different DNA sources and molecular weight on the efficiency of energy transfer between the dyes, coumarin 480 (Cm 480) and 4-[4-(dimethylamino)styryl]-1-docosyl-pyridinium bromide (Hemi 22 and to understand the fundamental properties of DNA-CTMA as a supporting matrix for optoelectronics applications.