Computational modeling of optical properties in aluminum nanolayers inserted in ZnO for solar cell electrodes.

Numerical simulations were used to study the transmittances (Ts) of ZnO/Al/ZnO (ZAZ) films with Al thicknesses between ∼1 and 40 nm. The simulations are validated using previously reported experimental results. Multilayers with Al thicknesses between ∼1 and 10 nm are shown to have average Ts between ∼75% and 90%, which decreased farther to ∼63 and 41% for the Al layer thicknesses of 20 and 40 nm, respectively. Variations in the ZnO thickness between ∼10 and 100 nm are shown to have little effect on the optical properties of the model multilayers for a given Al thickness. The reliability of the numerical simulations is tested by comparing them with experimental measurements on films produced using similar interlayer thicknesses. These are also shown to be comparable to the performance characteristics of indium tin oxide (ITO) anodes that are used currently in organic solar cells (OSCs) and organic light emitting diodes (OLEDs).

Fabrication of periodic silicon nanopillars in a two-dimensional hexagonal array with enhanced control on structural dimension and period.

We present a method to fabricate well-controlled periodic silicon nanopillars (Si NPs) in hexagonal arrays using silica nanosphere (SNS) lithography (SNL) combined with metal-assisted chemical etching (MaCE). The period of the Si NPs is easily changed by using our silica nanosphere (SNS) spin-coating process, which provides excellent monolayer uniformity and coverage (>95%) over large surface areas. The size of the deposited SNS is adjusted by reactive ion etching (RIE) to produce a target diameter at a fixed period for control of the surface pattern size after a gold metal mask layer deposition. The Si NPs are etched with the MaCE technique following introduction of a Ni interfacial layer between the Si and Au catalyst layer for adhesion and improved lithographical accuracy. The result is a fast, convenient, and large-area applicable Si surface nanolithography technique for accurate and reproducible Si NP fabrication.

Solvent-controlled spin-coating method for large-scale area deposition of two-dimensional silica nanosphere assembled layers.

In this article, we show that introducing a N,N-dimethyl-formamide (DMF) solvent for silica nanosphere (SNS) monolayer spin-coating can offer a low-cost and simple spin-coating approach for SNS monolayer deposition even on large-area silicon surfaces. From our method, more than 95% monolayer coverage for a 2 in round Si surface was achieved, which is one of the highest reported coverage by a spin-coating method. We prove that DMF offers highly enhanced wettability and slow solvent evaporation rate compared to a conventional solvent, water, in addition to excellent SNS dispersibility in solution preventing SNS cluster deposition on the surface and consequently produces a close-packed SNS monolayer with good uniformity over the surface. In addition, the benefits of DMF are retained as the deposition area increases indicating its high tolerance to spin-coating area. Better than 90% SNS monolayer coverage on a 4 in Si substrate was achieved with the DMF spin-coating method. Moreover, DMF has the advantage that SNS spin-coating can be done under common ambient laboratory conditions with 100% pure DMF unlike previous approaches which require humidity and temperature controls or additional surfactant additions to the solution.

A cytokine immunosensor for Multiple Sclerosis detection based upon label-free electrochemical impedance spectroscopy using electroplated printed circuit board electrodes.

A biosensor for the serum cytokine, Interleukin-12 (IL-12), based upon a label-free electrochemical impedance spectroscopy (EIS) monitoring approach is described. Overexpression of IL-12 has been correlated to the diagnosis of Multiple Sclerosis (MS). An immunosensor has been fabricated by electroplating gold onto a disposable printed circuit board (PCB) electrode and immobilizing anti-IL-12 monoclonal antibodies (MAb) onto the surface of the electrode. This approach yields a robust sensor that facilitates reproducible mass fabrication and easy alteration of the electrode shape. Results indicate that this novel PCB sensor can detect IL-12 at physiological levels, <100 fM with f-values of 0.05 (typically <0.0001) in a label-free and rapid manner. A linear (with respect to log concentration) detectable range was achieved. Detection in a complex biological solution is also explored; however, significant loss of dynamic range is noted in the 100% complex solution. The cost effective approach described here can be used potentially for diagnosis of diseases (like MS) with known biomarkers in body fluids and for monitoring physiological levels of biomolecules with healthcare, food, and environmental relevance.

A methodology for rapid detection of Salmonella typhimurium using label-free electrochemical impedance spectroscopy.

A pathogen detection methodology based on Bayesian decision theory has been developed for rapid and reliable detection of Salmonella typhimurium. The methodology exploits principles from statistical signal processing along with impedance spectroscopy in order to analytically determine the existence of pathogens in the target solution. The proposed technique is validated using a cost-effective and portable immunosensor. This device uses label-free, electrochemical impedance spectroscopy for pathogen detection and has been demonstrated to reliably detect pre-infectious levels of pathogen in sample solutions. The detection process does not entail any pathogen enrichment procedures. The results using the proposed technique indicate a detection time of approximately 6min (5min for data acquisition, 1min for analysis) for pathogen concentrations in the order of 500CFU/ml. The detection methodology presented here has demonstrated high accuracy and can be generalized for the detection of other pathogens with healthcare, food, and environmental implications. Furthermore, the technique has a low computational complexity and uses a minimal data-set (only 30 data-samples) for data analysis. Hence, it is ideal for use in hand-held pathogen detectors.

A cytokine immunosensor for multiple sclerosis detection based upon label-free electrochemical impedance spectroscopy.

A biosensor for the serum cytokine, interleukin-12 (IL-12), based upon a label-free electrochemical impedance spectroscopy monitoring is described. Overexpression of IL-12 has been correlated to the diagnosis of multiple sclerosis (MS). The prototype biosensor was fabricated on a disposable gold-coated silver ribbon electrode by immobilizing anti-IL-12 monoclonal antibodies (mAbs) onto the surface of the electrode. This technique was advantageous as the silver electrodes provided a more rigid and conductive substrate than thin gold foil electrodes and helped in obtaining more reproducible data when used with the electrode holder. Results indicate that IL-12 can be detected at physiological levels, <100 fM with p<0.05 in a label-free and real-time manner. The cost-effective approach described here can be used for diagnosis of diseases (like MS) with known biomarkers in body fluids and for monitoring physiological levels of biomolecules with healthcare, food, and environmental relevance.

Potentiation of antitumor activity of irinotecan by chemically modified oligonucleotides.

Co-administration of synthetic chemically modified oligonucleotides with irinotecan, a selective topoisomerase I inhibitor, provided a significant enhancement in the antitumor activity of irinotecan. The enhancement of antitumor activity of irinotecan with co-administration of chemically modified oligonucleotides was observed in several tumor models--pancreatic cancer (Panc-1), colon cancer (HCT-116) and melanoma (A375). Inhibition of tumor growth in all three models required the co-administration of irinotecan and chemically modified oligonucleotides, but was independent of the nucleotide sequence of the oligonucleotides. The potentiation of antitumor activity was dependent on the dose of irinotecan and chemically modified oligonucleotides administered. The enhancement of antitumor activity of irinotecan was also observed by co-administration of a phosphorothioate oligonucleotide, however, to a lesser extent than did chemically modified oligonucleotides, suggesting that metabolic stability of the oligonucleotide contributes to the enhancement of antitumor activity seen with irinotecan. The co-administration of dextran sulfate sodium with irinotecan showed insignificant potentiation of antitumor activity of irinotecan, suggesting that the enhancement of antitumor activity of irinotecan observed was not a result of polyanionic characteristic of oligonucleotides. Co-administration of irinotecan and chemically modified oligonucleotides did not result in increased toxicity in the tumor models studied. Potentiation of antitumor activity of irinotecan observed with co-administration of oligonucleotides suggests that the oligonucleotides affect the pharmacokinetics and/or metabolism of irinotecan. The use of chemically modified oligonucleotides together with irinotecan may increase the therapeutic index of irinotecan in cancer patients and continued development of such agents should be considered.

Crystallization kinetics of sol-gel derived hydroxyapatite thin films.

The crystallization kinetics of sol-gel derived hydroxyapatite (HA) and tricalcium phosphate (TCP) thin films were studied to determine whether viscous sintering could be used for densification. The films were approximately 900 nm thick, and were synthesized and processed on silicon substrates. The films were fired in air in a rapid thermal annealer (RTA) for various times and the degree of crystallinity was determined by measuring the intensity of characteristic X-ray diffraction lines. The growth kinetics of HA and TCP were measured between 420 and 550 degrees C, and between 840 and 920 degrees C, respectively. Films that were subjected to an accelerated aging step before firing, exhibited a significantly lower crystallization growth rate when compared to unaged films. The aged films also became harder, as measured by nanoindentation. At temperatures above 840 degrees C, HA transformed into both alpha-and beta-TCP, with the beta form being dominant at lower temperatures. The activation energies for both transformations (amorphous film to HA, and HA to TCP) were determined, as were the constants for the Avrami equation. Based on the rapid crystallization kinetics observed for the amorphous film to HA transformation, densification through viscous sintering is essentially precluded in this system.

The application of ion beam analysis to calcium phosphate-based biomaterials.

Ion beam technology may be applied in a straightforward fashion to the analysis and modification of biomaterials. For analytical purposes, characterization using megaelectron-volt He2+ ions provides a standardless, nondestructive means for accurately quantifying the composition of material surfaces and the thickness of thin films. In this study, three complementary ion backscattering techniques were utilized to characterize hydroxyapatite (HA) films: Rutherford backscattering spectrometry (RBS) can determine composition and amounts of elements heavier than He; forward recoil elastic spectrometry (FRES) can determine hydrogen content; resonance-enhanced RBS can quantify small amounts of light elements, e.g. carbon, by choosing a particular incident beam energy resulting in excitation of the light element nucleus. At this resonance energy, the scattering cross section greatly increases, improving elemental sensitivity. Sol-gel chemistry was used to synthesize HA films by spin coating and annealing in a rapid thermal processor. Using these techniques, the chemical composition of unfired films was Ca1.63O5.4H1.8C0.24P with a thickness of 3.01 x 10(18) atoms/cm2 and after firing at 800 degrees C as Ca1.66O4.0H0.26C0.09P with a thickness of 2.11 x 10(18) atoms/cm2. This compares favorably to stoichiometric HA, which has a composition of Ca1.67O4.33H0.33P.