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ANALYTICAL CURRENTS NMR probe for proteins Multiplexed techniques for protein detection Matthew Coleman and colleagues at the University of California, Davis, and the Lawrence Livermore National Laboratory put the commercialized Luminex liquid array-based assay and protein microarrays in a head-to-head comparison. They found that although the Luminex system has several advantages over protein microarray technology, microarrays are better suited for building miniature diagnostic devices. Both the Luminex system and protein microarrays can perform multiplexed detections of proteins in high-throughput mode, and both use low sample and reagent volumes. Each technique has been compared with the standard ELISA procedure for protein detection, but this is the first time the two techniques have been directly compared. In the series of tests run by the investigators, the Luminex system had better limits of detection, dynamic range, and reproducibility than the protein microarrays. However, because microarrays require fewer accessories than the Luminex system, the investigators concluded that protein microarrays have more potential as a miniature on-site diagnostic tool. (J. Proteome Res. 2004, doi 10.1021/ pr034130t)
Thanks to a specially designed microcoil NMR probe, Wolfgang Peti and colleagues at the Scripps Research Institute, MRM Corp., and Sequoia Sciences have found a way to perform NMR spectroscopy on microgram amounts of proteins. The probe reduces the amount of protein required for NMR, and it allows for the complete assign ment of all of the amino acid side chains from a single experiment. The new probe, called the CapNMR, is commercially available from MRM Corp. Because of its solenoid coil design, the probe has excellent radio-frequency properties, according to the researchers. As a result, it provides information about aromatic amino acid side chains, including those connected to aliphatic side chains. Those data cannot be obtained using traditional 5-mm room-temperature probes or cryoprobes. The approach could speed up the assignment of aromatic side chains in proteins. (J. Am. Chem. Soc. 2004, 126, 5873–5878)
Biosensor for Alzheimer’s disease No clinical diagnostic tests are currently available for K Alzheimer’s disease. To meet this need, Richard Van Duyne and colleagues at Northwestern University have developed a localized surface plasmon resonance (LSPR) = Chelating agent = ADDL nanosensor that measures binding between a specific protein implicated in Alzheimer’s disease and its corre= Self-assembled monolayer = Antibody sponding antibody. Small, soluble oligomers, called amyloid-derived diffusible ligands (ADDLs), are thought to form brain Fabrication of the LSPR nanosensor for Alzheimer’s disease occurs in stages. plaques in patients with Alzheimer’s disease. The ADDLs The glass is covered with Cr, and the Ag nanotriangles adhere to the Cr. The generate an immune response and cause the body to pro- nanotriangles are then modified to attach ADDLs. duce antibodies to ADDLs (anti-ADDLs), which can be found in bodily fluids. Van Duyne and colleagues aimed to binding constant between ADDLs and anti-ADDLs. This was develop a sensor that could detect anti-ADDLs in bodily fluids the first measurement of the binding interaction between ADDLs and indicate whether a patient has Alzheimer’s disease. confined to a surface and anti-ADDLs. In the fabrication of the LSPR nanosensor, the investigators However, some unexpected behavior of the anti-ADDLs sputtered Cr onto a glass surface. They then deposited Ag nano- at very low concentrations led the researchers to investigate triangles onto the Cr layer by nanosphere lithography. The sources of nonspecific interactions. They studied the nanonanotriangles were modified with a self-assembled monolayer sensor surface by atomic force microscopy under various conand a coupling agent to attach ADDLs to the nanotriangles. ditions and found that the Cr layer nonspecifically interacted The ADDL-modified surface was then exposed to anti-ADDLs. with the anti-ADDLs. The investigators thus raised caution The investigators used wavelength shifts to measure antibody about using Cr, a material commonly used in fabrication, bebinding to the nanosensor surface. cause it may later affect detection sensitivities of biological Using the assay, the investigators measured a 3 107 M–1 sensors. (Nano Lett. 2004, doi 10.1021/nl049670j) 222 A
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