Cell Membranes Integrated into CNT Devices
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magnetic field enhancements associated with surface plasmon resonances over the non-enhanced Raman scattering methods. However, SERS requires the target molecule to adsorb onto a metal surface to benefit from surface plasmon resonance. Consequently, it has been difficult to detect biological molecules that have a low affinity for metal surfaces, and only a few types of molecules have been detected by SERS with single-molecule sensitivity to date. The researchers said that huge signal gain can be obtained by combining SERS and coherent anti-Stokes Raman scattering (CARS) as is done in surfaceenhanced coherent anti-Stokes Raman scattering (SECARS). The researchers further improved the sensitivity of SECARS over the earlier reported work, and achieved single-molecule detection of some biomolecules not detected earlier using this method. The researchers said that SECARS background originating from metal and water has limited the sensitivity of previous works. The research group used several methods, such as a polarizationsensitive CARS setup, minimized probe volume, and the use of aggregated colloidal silver nanoparticles instead of planar substrates, to reduce the background. The SECARS signals of biological molecules were increased by the addition of lithium chloride salts, which were found to be optimal for generating strong surface enhancements. The researchers then demonstrated the power of SECARS by detecting two DNA nucleotides, deoxyadenosine monophosphate (dAMP) and deoxyguanosine monophosphate (dGMP), and a peptide—angiotensin-I peptide. Although dAMP has been detected at the single-molecule level by SERS, the SECARS signal was approximately 1000 times stronger than the SERS signal for dAMP at single-molecule concentrations. The SECARS signal of dGMP was at least 100 times stronger than the SERS signal of dGMP. The researchers believe that this is the first reported detection of dGMP at single-molecule concentrations. The detection of the peptide shows that the SECARS technique can be applied to biological molecules other than nucleotides. According to the research group, the ultrasensitive detection of nonlabeled peptides and proteins has potential applications in pathogen detection, disease monitoring, and drug discovery. VIVEK RANJAN
Cell Membranes Integrated into CNT Devices Integrating biological systems and MRS BULLETIN • VOLUME 30 • JUNE 2005
processes with nanofabricated structures is a critical challenge for nanotechnology. In the May issue of Nano Letters, J.-C. Gabriel, G. Grüner, and their co-workers reported on their work, performed at Nanomix Inc., on the integration of the cell membrane of Halobacterium salinarum with carbon nanotube (CNT) network transistors, wherein both the biological and nanoelectronic structures preserve their functionality and are able to electronically interact with each other. The researchers fabricated nanotube network field-effect transistors, where the semiconducting channel is formed by a network of predominantly semiconducting nanotubes. A monolayer of the purple
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