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A major constituent in the deposit of the brain in a patient with Alzheimer's disease (AD) is the aggregates/fibrils of amyloid-β (Aβ) peptides containing 39-43 amino acids. The total Aβ levels and the concentration ratio between the most abundant Aβ(1-40) peptide and the more aggregation-prone Aβ(1-42) in body fluids (e.g., cerebrospinal fluid or CSF) have been suggested as possible criteria for early diagnosis of AD. By immobilizing capture antibodies specific to the two peptides in separate fluidic channels, surface plasmon resonance (SPR) has been used to quantify Aβ(1-40) and Aβ(1-42) present in CSF samples collected from AD patients and healthy donors. With signal amplification by streptavidin conjugated to an antibody that is selective to the common N-terminus of the Aβ peptides, concentrations as low as 20 pM can be readily measured. The range of Aβ peptide concentrations measurable by this method spans 4 orders of magnitude. The ability of regenerating the sensor surface for repeated measurements not only improves the reproducibility but also enhances the sample throughput. Our data reveal that the ratio of Aβ(1-40) concentration versus Aβ(1-42) concentration in CSF samples from AD patients is almost twice as high as that from healthy persons. In contrast to the commonly used enzyme-linked immunosorbent assay (ELISA), SPR obviates the need of a more expensive and less stable enzyme conjugate and the use of carcinogenic substrate for the signal detection and allows the binding events to be monitored in real time. [ABSTRACT FROM AUTHOR]

Typical sulfur-containing amino acids, cysteine and methionine, were employed as stabilizers in place of lead(II) acetate in the electroless nickel plating (ENP) system. Each of these compounds presents a critical stabilizing concentration of ca. 10 −5mol/L, below which the ENP rate is slightly promoted with increasing concentration but above which it is significantly suppressed. Their role in stabilizing the ENP bath was found to involve inhibition of the anodic reaction of hypophosphite. The chemical adsorption of these two amino acids on active nickel sites at the Ni plating surface was studied via their adsorption on an in situ generated Ni powder. In addition, the stabilization mechanism was investigated by using potentiometry, X-ray photoelectron spectroscopy (XPS), and UV−vis/infrared spectroscopy. Finally, the bath stabilizing capabilities of these two amino acids and the change in ENP properties with time were assessed through a continuous operation comprising four metal-turnover (MTO) runs. [ABSTRACT FROM AUTHOR]