Kathy L. Rowlen

Plasmon-enhanced solar energy conversion in organic bulk heterojunction photovoltaics

Plasmon-active silver nanoparticle layers were included in solution-processed bulk-heterojunction solar cells. Nanoparticle layers were fabricated using vapor-phase deposition on indium tin oxide electrodes. Owing to the increase in optical electrical field inside the photoactive layer, the inclusion of such particle films lead to increased optical absorption and consequently increased photoconversion at solar-conversion relevant wavelengths. The resulting solar energy conversion efficiency for a bulk heterojunction photovoltaic device of poly(3-hexylthiophene)/[6,6]-phenyl C61 butyric acid methyl ester was found to increase from 1.3%±0.2% to 2.2%±0.1% for devices employing thin plasmon-active layers. Based on six measurements, the improvement factor of 1.7 was demonstrated to be statistically significant.

Surface-plasmon enhanced transparent electrodes in organic photovoltaics

Random silver nanohole films were created through colloidal lithography techniques and metal vapor deposition. The transparent electrodes were characterized by uv-visible spectroscopy and incorporated into an organic solar cell. The test cells were evaluated for solar power-conversion efficiency and incident photon-to-current conversion efficiency. The incident photon-to-current conversion efficiency spectra displayed evidence that a nanohole film with 92nm diameter holes induces surface-plasmon-enhanced photoconversion. The nanohole silver films demonstrate a promising route to removing the indium tin oxide transparent electrode that is ubiquitous in organic optoelectronics.

Experimental Evaluation of the FluChip Diagnostic Microarray for Influenza Virus Surveillance

ABSTRACT Global surveillance of influenza is critical for improvements in disease management and is especially important for early detection, rapid intervention, and a possible reduction of the impact of an influenza pandemic. Enhanced surveillance requires rapid, robust, and inexpensive analytical techniques capable of providing a detailed analysis of influenza virus strains. Low-density oligonucleotide microarrays with highly multiplexed “signatures” for influenza viruses offer many of the desired characteristics. However, the high mutability of the influenza virus represents a design challenge. In order for an influenza virus microarray to be of utility, it must provide information for a wide range of viral strains and lineages. The design and characterization of an influenza microarray, the FluChip-55 microarray, for the relatively rapid identification of influenza A virus subtypes H1N1, H3N2, and H5N1 are described here. In this work, a small set of sequences was carefully selected to exhibit broad coverage for the influenza A and B viruses currently circulating in the human population as well as the avian A/H5N1 virus that has become enzootic in poultry in Southeast Asia and that has recently spread to Europe. A complete assay involving extraction and amplification of the viral RNA was developed and tested. In a blind study of 72 influenza virus isolates, RNA from a wide range of influenza A and B viruses was amplified, hybridized, labeled with a fluorophore, and imaged. The entire analysis time was less than 12 h. The combined results for two assays provided the absolutely correct types and subtypes for an average of 72% of the isolates, the correct type and partially correct subtype information for 13% of the isolates, the correct type only for 10% of the isolates, false-negative signals for 4% of the isolates, and false-positive signals for 1% of the isolates. In the overwhelming majority of cases in which incomplete subtyping was observed, the failure was due to the nucleic acid amplification step rather than limitations in the microarray.

Quantitative Comparison of Five SERS Substrates: Sensitivity and Limit of Detection

Five surface-enhanced Raman scattering (SERS) substrates were quantitatively compared for ease of preparation, sensitivity, limit of detection (LOD), reproducibility, and stability. Specifically, vapor-deposited Ag films, electrochemically roughened Ag electrodes, nitric acid-etched Ag foil, Tollens-produced Ag films, and photore-duced Ag films on TiO2 were examined. Of these substrates, post-deposition-annealed Ag films exhibited the greatest sensitivity and lowest LOD, with 152 ± 1 counts per femtomole and an LOD of 0.36 ± 0.02 femtomoles of trans-1,2-bis(4-pyridyl)ethene (BPE). The substrate demonstrating the poorest sensitivity and highest LOD was Ag deposited from the Tollens reaction, with 0.38 ± 0.01 counts per femtomole and an LOD of 270 ± 20 femtomoles of BPE. The easiest substrate to prepare, nitric acid-etched Ag foils, exhibited a sensitivity of 0.485 ± 0.008 counts per femtomole and an LOD of 200 ± 10 femtomoles of BPE.

Comparison of the MChip to Viral Culture, Reverse Transcription-PCR, and the QuickVue Influenza A+B Test for Rapid Diagnosis of Influenza

ABSTRACT The performance of a diagnostic microarray (the MChip assay) for influenza was compared in a blind study to that of viral culture, reverse transcription (RT)-PCR, and the QuickVue Influenza A+B test. The patient sample data set was composed of 102 respiratory secretion specimens collected between 29 December 2005 and 2 February 2006 at Scott & White Hospital and Clinic in Temple, Texas. Samples were collected from a wide range of age groups by using direct collection, nasal/nasopharyngeal swabs, or nasopharyngeal aspiration. Viral culture and the QuickVue assay were performed at the Texas site at the time of collection. Aliquots for each sample, identified only by study numbers, were provided to the University of Colorado and Vanderbilt University teams for blinded analysis. When referenced to viral culture, the MChip exhibited a clinical sensitivity of 98% and a clinical specificity of 98%. When referenced to RT-PCR, the MChip assay exhibited a clinical sensitivity of 92% and a clinical specificity of 98%. While the MChip assay currently requires 7 to 8 h to complete the analysis, a significant advantage of the test for influenza virus-positive samples is simultaneous detection and full subtype identification for the two subtypes currently circulating in humans (A/H3N2 and A/H1N1) and avian (A/H5N1) viruses.

Surface Roughness by Contact versus Tapping Mode Atomic Force Microscopy

To evaluate and compare tapping mode and contact mode AFM measurements of surface roughness, images of quartz and mica were acquired by both methods and the height distributions and variance correlation functions analyzed. Significant deviation from the expected Gaussian profiles for the height distributions were observed for contact mode images of quartz but not for tapping mode images. Additionally, variance correlation functions were found to be highly scan size dependent for contact mode images and scan size invariant for tapping mode images. One possible explanation for the observed differences is that the scan speed limit is exceeded in contact mode for linear scan velocities as low as 0.5 μm/s.

Robust Sequence Selection Method Used To Develop the FluChip Diagnostic Microarray for Influenza Virus

ABSTRACT DNA microarrays have proven to be powerful tools for gene expression analyses and are becoming increasingly attractive for diagnostic applications, e.g., for virus identification and subtyping. The selection of appropriate sequences for use on a microarray poses a challenge, particularly for highly mutable organisms such as influenza viruses, human immunodeficiency viruses, and hepatitis C viruses. The goal of this work was to develop an efficient method for mining large databases in order to identify regions of conservation in the influenza virus genome. From these regions of conservation, capture and label sequences capable of discriminating between different viral types and subtypes were selected. The salient features of the method were the use of phylogenetic trees for data reduction and the selection of a relatively small number of capture and label sequences capable of identifying a broad spectrum of influenza viruses. A detailed experimental evaluation of the selected sequences is described in a companion paper. The software is freely available under the General Public License at http://www.colorado.edu/chemistry/RGHP/software/ .

Design and characterization of a compact dual channel virus counter.

Although there is a growing need in the field of biotechnology to rapidly and accurately quantify viruses, time‐consuming techniques such as the plaque titer method remain the “gold standard.” Flow cytometric methods for virus quantification offer the advantages of rapid analysis and statistical treatment. The technique presented in this work represents the first demonstration of a flow cytometric determination of a viral count that is directly related to the count obtained by plaque titer.

Sers-Active Ag Films from Photoreduction of Ag+ on TiO2

Because of the tremendous information content, single-molecule detection with a vibrational spectroscopic technique is a goal well worth pursuing. The vibrational technique most suitable for single-molecule detection is surface-enhanced Raman spectroscopy (SERS). For example, Kneipp et al. recently demonstrated detection of 100 molecules of rhodamine 6G using surface-enhanced resonance Raman. Van Duyne and co-workers have recently detected just 10 molecules of pyridine using SERS and Raman microscopy. The key to sensitive detection using SERS lies in optimization of the enhancing surface. For excitation with easily accessible wavelengths, as well as ease of preparation and nearly ideal surface characteristics, Ag is often the metal of choice. SERS-active Ag has been prepared in a variety of ways, such as Ag colloids, vapor-deposited thin films, electrochemically roughened electrodes, nitric-acid-etched foils, thin films from the Tollens reaction, lithographically produced islands on Si posts, and, recently, vapor-deposition of Ag over a monolayer (or double layer) of nanospheres, followed by removal of the nanospheres. Each of the methods mentioned for the generation of SERS-active surfaces has advantages and limitations; i.e., there is still room for improvement and optimization of SERS-active surfaces.

Controlling the Optical Properties of Plasmonic Disordered Nanohole Silver Films

Disordered nanohole arrays were formed in silver films by colloidal lithography techniques and characterized for their surface-plasmon activity. Careful control of the reagent concentration, deposition solution ionic strength, and assembly time allowed generation of a wide variety of nanohole densities. The fractional coverage of the nanospheres across the surface was varied from 0.05-0.36. Electrical sheet resistance measurements as a function of nanohole coverage fit well to percolation theory indicating that the electrical behavior of the films is determined by bulk silver characteristics. The transmission and reflection spectra were measured as a function of coverage and the results indicate that the optical behavior of the films is dominated by surface plasmon phenomena. Angle-resolved transmission and reflection spectra were measured, yielding insight into the nature of the excitations taking place on the metal films. The tunability of the colloidal lithography assembly method holds much promise as a means to generate customized transparent electrodes with high surface plasmon activity throughout the visible and NIR spectrum over large surface areas.