Immersion/Electroless Deposition of Cu on Ta

Continuous Cu films are deposited on Ta by a two-step process; galvanic displacement of Ta by Cu from ammonium fluoride solutions and subsequent electroless Cu deposition from a formaldehyde-containing bath. The conditions necessary for good adhesion are discussed. The extent of oxide film removal in the HF pretreatment solution is studied by electrochemical impedance spectroscopy. The charge-transfer resistance of about 57 Ω-cm2 is several orders of magnitude lower than that measured for the Ta native oxide. These results are consistent with the removal of the Ta2O5 portion of the native oxide

Substrate Materials for Biomolecular Immobilization within Electrochemical Biosensors

Electrochemical biosensors have potential applications for agriculture, food safety, environmental monitoring, sports medicine, biomedicine, and other fields. One of the primary challenges in this field is the immobilization of biomolecular probes atop a solid substrate material with adequate stability, storage lifetime, and reproducibility. This review summarizes the current state of the art for covalent bonding of biomolecules onto solid substrate materials. Early research focused on the use of Au electrodes, with immobilization of biomolecules through ω-functionalized Au-thiol self-assembled monolayers (SAMs), but stability is usually inadequate due to the weak Au–S bond strength. Other noble substrates such as C, Pt, and Si have also been studied. While their nobility has the advantage of ensuring biocompatibility, it also has the disadvantage of making them relatively unreactive towards covalent bond formation. With the exception of Sn-doped In2O3 (indium tin oxide, ITO), most metal oxides are not electrically conductive enough for use within electrochemical biosensors. Recent research has focused on transition metal dichalcogenides (TMDs) such as MoS2 and on electrically conductive polymers such as polyaniline, polypyrrole, and polythiophene. In addition, the deposition of functionalized thin films from aryldiazonium cations has attracted significant attention as a substrate-independent method for biofunctionalization

Antibody regeneration on degenerate Si electrodes for calibration and reuse of impedance biosensors

Mild denaturing agents were studied for antibody regeneration atop degenerate (highly doped) Si and Au electrodes using comparable 11-carbon chain linker reagents onto which the mouse monoclonal antibody to peanut protein Ara h 1 is covalently immobilized. Of the reagents studied, only 200 mM KSCN is effective for antibody regeneration and detection of Ara h 1 atop Au electrodes, allowing 15 days of sensor usage after daily antibody unfolding and refolding, while 200 mM KSCN +10 mM HF is effective atop degenerate Si electrodes, allowing 30 days of sensor usage. The addition of HF is required for antibody regeneration atop Si electrodes, as demonstrated by cyclic voltammetry in the presence of 5.0 mM K3Fe(CN)6/K4Fe(CN)6 at pH 7.3, where the oxidation/reduction peaks can be observed only in the presence of HF. The impedance spectrum for detection of Ara h 1 gradually degrades during these multi-day regeneration trials, but calibration experiments performed within one day illustrate that sensor electrodes can be calibrated on the day of use to within about 2%