Ian Ivar Suni

Impedance Biosensor for Peanut Protein Ara h 1

A reagentless electrochemical impedance biosensor for detection of peanut protein Ara h 1, one of the allergenic proteins found in peanuts, has been demonstrated using an Au substrate onto which an antibody film has been immobilized. Following initial stabilization of the self-assembled monolayer (SAM) through which the antibody is immobilized, the biosensor substrate exhibits stable impedance spectra at different stages of substrate preparation. By fitting the impedance spectra to a Randles equivalent circuit, one can demonstrate that the charge-transfer resistance (R(ct)) increases and the differential capacitance (Cd) decreases with increasing concentration of Ara h 1, although R(ct) exhibits greater sensitivity. The detection limit of this reagentless biosensor is estimated to be less than 0.3 nM. Assuming a Langmuir adsorption isotherm, the dissociation constant of the peanut protein Ara h 1 and its antibody can be calculated as 0.52 nM from the variation in differential capacitance with Ara h 1 concentration.

Electrochemical Impedance Biosensor for Glucose Detection Utilizing a Periplasmic E. coli Receptor Protein

We report the development of a reagentless electrochemical impedance biosensor for glucose that employs the D-glucose/galactose receptor from E. coli for direct glucose detection. The biological platform for this sensor is an Au surface to which the protein is immobilized through formation of an Au-S bond to a genetically engineered cysteine residue at the N-terminus. The impedance signal detects the extensive ligand-induced domain motion within the protein upon glucose binding. We show the applicability of impedance spectroscopy in conjunction with periplasmic binding proteins as a general method for detecting small molecules.

Cu planarization for ULSI processing by electrochemical methods: a review

The planned introduction of porous, low-k dielectric materials into Si-based semiconductor devices will provide substantial challenges for chemical mechanical planarization. These challenges arise primarily from the mechanical fragility of such dielectrics, which may not withstand the force applied during chemical mechanical planarization. Planarization by Cu electropolishing has many advantages, including its noncontact nature, easy endpoint detection, and minimal introduction of contamination. However, pattern sensitivity may limit application of Cu electropolishing to augmenting, rather than completely replacing, chemical mechanical planarization. Electrochemical mechanical planarization appears to have less pattern dependence, but is still an evolving technology whose potential limitations are still unclear. Alternative electrochemical methods for Cu planarization, including electropolishing and electrochemical mechanical planarization are herein reviewed and discussed.

Voltammetry and Impedance Studies of Ta in Aqueous HF

Tantalum (Ta) electrochemistry is studied in aqueous HF and NH 4 F by cyclic voltammetry and electrochemical impedance spectroscopy. The much greater hydrogen evolution current and the much lower charge-transfer resistancefor the high-frequency impedance loop in HF relative to NH 4 F demonstrate that the native Ta 2 O 5 film dissolves in HF, but not in NH 4 F. Weight loss experiments and cyclic voltammetry demonstrate that at cathodic potentials in aqueous HF, dissolution of Ta oxide allows electrochemical dissolution of the exposed surface into Ta 5 + . In addition, unusual low frequency impedance behavior is seen for Ta in HF analogous to that reported by Bojinov for several different metal surfaces at anodic potentials in concentrated acids. This suggests the presence of an ultrathin, passive film in HF and is consistent with the poor adhesion often obtained for Cu electrodeposition onto Ta. This passive film may correspond to the Ta suboxide (TaO) previously observed by X-ray photoelectron spectroscopy at the Ta/Ta 2 O 5 interface.

Impedance Biosensors: Applications to Sustainability and Remaining Technical Challenges

Due to their all-electrical nature, impedance biosensors have significant potential for use as simple and portable sensors for environmental studies and environmental monitoring. Detection of two endocrine-disrupting chemicals (EDC), norfluoxetine and BDE-47, is reported here by impedance biosensing, with a detection limit of 8.5 and 1.3 ng/mL for norfluoxetine and BDE-47, respectively. Although impedance biosensors have been widely studied in the academic literature, commercial applications have been hindered by several technical limitations, including possible limitations to small analytes, the complexity of impedance detection, susceptibility to nonspecific adsorption, and stability of biomolecule immobilization. Recent research into methods to overcome these obstacles is briefly reviewed. New results demonstrating antibody regeneration atop degenerate (highly doped) Si are also reported. Using 0.2 M KSCN and 10 mM HF for antibody regeneration, peanut protein Ara h 1 is detected daily during a 30 day trial.

Mechanistic Studies of Cu Electropolishing in Phosphoric Acid Electrolytes

Department of Chemical Engineering, Center for Advanced MaterialsProcessing, Clarkson University, Potsdam, New York 13699-5705, USAElectropolishing of Cu and Cu/Ta/Si wafer samples were studied using a rotating disk electrode in a variety of phosphoricacid-based electrolytes, including several with ethanol and other species added as diluents. Diluents allow a wide range of waterconcentrations to be accessed and also reduce the dissolution rate during Cu electropolishing, simplifying possible applications todamascene processing. The measured limiting current densities are subject to a Levich analysis, demonstrating that water is theacceptor species involved in the rate-determining step. The effective diffusion coefficient that is determined is in almost exactagreement with that previously obtained from the electrohydrodynamic impedance, which does not require knowledge of thelimiting species.© 2004 The Electrochemical Society. @DOI: 10.1149/1.1740783# All rights reserved.Manuscript submitted June 26, 2003; revised manuscript received January 5, 2004. Available electronically April 30, 2004.

Potassium Bromate as an Oxidizing Agent in a Titania-Based Ru CMP Slurry

Ru chemical mechanical planarization CMP was studied in slurries containing titania and potassium bromate at different pHvalues, showing that the Ru removal rate is enhanced at pH 2 or less. Potentiodynamic polarization studies indicate that thecorrosion current is enhanced in the presence of bromate, while the static etch rate experiments show that the etch rate is low.Potassium bromate increases Ru removal only at anodic potentials or during mechanical abrasion. Studies at different concentra-tions of abrasive and oxidizing agent reveal that the removal rate enhancement saturates at 0.75 mM bromate and 4 wt % titania.© 2010 The Electrochemical Society. DOI: 10.1149/1.3481948 All rights reserved.Manuscript submitted July 6, 2010; revised manuscript received July 27, 2010. Published August 31, 2010.

Development and Utilization of Camelid VHH Antibodies from Alpaca for 2,2′,4,4′-Tetrabrominated Diphenyl Ether Detection

An antibody-based analytical method for the detection of a chemical flame retardant using antibody fragments isolated from an alpaca has been developed. One specific chemical flame retardant congener, 2,2′,4,4′-tetrabrominated diphenyl ether (BDE-47), is often the major poly-BDE (PBDE) congener present in human and environmental samples and that which is the most frequently detected. An alpaca was immunized with a surrogate of BDE-47 covalently attached to a carrier protein. The resulting mRNA coding for the variable domain of heavy-chain antibodies (VHH) were isolated, transcribed to cDNA, and cloned into a phagemid vector for phage display library construction. Selection of VHHs recognizing BDE-47 was achieved by panning under carefully modified conditions. The assay sensitivity for detecting BDE-47 was down to the part-per-billion (microgram per liter) level. Cross-reactivity analyses confirmed that this method was highly selective for BDE-47 and selected hydroxylated metabolites. When exposed to elevated temperatures, the camelid VHH antibodies retained more reactivity than a polyclonal antibody developed to the same target analyte. The use of this VHH antibody reagent immobilized onto a Au electrode for impedance biosensing demonstrates the increased versatility of VHH antibodies.

Minimizing Nonspecific Adsorption in Protein Biosensors that Utilize Electrochemical Impedance Spectroscopy

Peanut protein Ara h 1, a common food allergen, has been previously detected at antibody-coated Au electrodes using electrochemical impedance spectroscopy (EIS) in ideal solutions, free from interfering species. Here, peanut protein Ara h 1 is detected by EIS at antibody-coated Au electrodes in canned soup that is filtered, diluted, and spiked with peanut protein Ara h 1. In this system, the combined strategy of sample dilution and blocking of unreacted surface sites on the Au electrode with bovine serum albumin is sufficient to dramatically reduce nonspecific adsorption. This is demonstrated by a quantitative comparison of the impedance change at two Au electrodes, one coated with the antibody to peanut protein Ara h 1 and the other coated with the antibody to cockroach protein Bla g 1. These results suggest that nonspecific adsorption does not in general limit the utility of biosensors based on EIS.

Microscopy of adsorbates by surface second-harmonic generation

A form of optical second-harmonic microscopy has been developed that spatially resolves concentration gradients of surface adsorbates. Surface concentration profiles at submonolayer levels are illuminated with a pulsed laser, and the reflected second-harmonic light is imaged into a photodiode array. Micrometer-scale resolution is obtainable while the surface damage and the spurious chemistry induced by more conventional electron- or ion-based techniques are avoided. We have used this microscopy to monitor the surface diffusion of Sb on Ge(111).