High throughput SECM imaging: Development and applications
Final Report Abstract
In this joint project various soft microelectrode probes for scanning electrochemical microscopy (SECM) were developed and applied to different prototypic problems. Typically, the probes are made in poly¬ethylene terephthalate sheets with carbon micro¬electrodes fabricated by UV photoablation and consecutive curing of a conductive carbon ink followed by deposition of an insulating Parylene C layer. The cross-section is exposed by mechanical razor blade or laser assisted cutting and defines the active electrode areas. Thanks to a flexibility of the thin polymeric films, the probes can touch the sample surface, bend and allow scanning of tilted, rough, curved and corrugated samples. Hard as well as soft samples like self-assembled monolayer (SAM) structures can be scanned without damaging the probe and the sample. The pressure which is exerted by the probe on the sample was determined to sinificantly less than by AFM tips. Soft linear microelectrode arrays, currently consisting of eight microelectrodes, were developed for high-throughput reactivity imaging and surface modification in order to overcome long imaging times and tilt problems in SECM imaging of large areas. A 32-channel potentiostat was integrated in the existing hardware periphery and in the in-house made software for device operation and for offline data analysis. The measured currents of the individual electrodes vary slightly due to minute differences in electrode size, geometry and working distance. In order to compensate for this variation, several calibration routines were sucessfully developed and tested. The imaging time was reduced by a factor of about six compared to conventional SECM with a single probe. High-throughput modification of an oligo(ethylene glycol) (OEG) terminated SAM on gold was performed by local electrogeneration of bromine. Individual spots, lines and complex patterns like letters, words and even a complete jpg image from a digital camera could be drawn into a SAM and later read back with SECM using soft carbon microelectrode arrays. Alternative techniques like Aerosol Jet® and Inkjet printing are alternative ways for batch production and were used for the fabrication of gold and silver microelectrodes. Deposition of thin homogenous and nanostructured Pt films allows the detection of redox active species that are difficult to detect with untreated carbon microelectrodes, such as the oxygen reduction reaction or the detection of intermediates like hydrogen peroxide. Soft probes combined with microfluidics opened the investigation of very interesting substrates and the online detection of at the substrate present or produced compounds with microchannels connected to mass spectrometers. Activity of immobilized enzymes and fingerprints contaminated with explosives were analyzed in order to demonstrate the potential of this combination. Overall the new concept of soft microelectrode arrays and soft probes combined with microfluidics was demonstrated as a powerful new concept to scan and modify large, tilted, corrugated, and curved substrates in realistic time scales in contact regime. We believe that our soft probes can be further adapted and will become are very effective tools in future projects to investigate and manipulate technical coatings, catalytically active material libraries, corrosion, organic thin films and also biological samples like single living cells or tissues.
Publications
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Soft Stylus Probes for Scanning Electrochemical Microscopy; Anal. Chem. 2009, 81, 6889-6896
F. Cortés-Salazar, M. Träuble, F. Li, J.M. Busnel, A. L. Gassner, M. Hojeij, G. Wittstock, H. H. Girault
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Fountain Pen for Scanning Electrochemical Microscopy. Anal. Meth. 2010, 2, 817-823
F. Cortés-Salazar, A. Lesch, D. Momotenko, J.-M. Busnel, G. Wittstock, H. H. Girault
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Soft Microelectrode Linear Array for Scanning Electrochemical Microscopy. Anal. Chem. 2010, 82, 10037-10044
F. Cortés-Salazar, D. Momotenko, A. Lesch, G. Wittstock, H. H. Girault
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Microfluidic Push-Pull Probe for Scanning Electrochemical Microscopy. Anal. Chem. 2011, 83, 5275-5282
D. Momotenko, F. Cortés-Salazar, A. Lesch, G. Wittstock, H. H. Girault
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Seeing Big with Scanning Electrochemical Microscopy. Anal. Chem. 2011, 83, 1493-1499
F. Cortés-Salazar, D. Momotenko, H. H. Girault, A. Lesch, G. Wittstock
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Fabrication of Soft Gold Microelectrode Arrays as Probes for Scanning Electrochemical Microscopy. J. Electroanal. Chem. 2012, 666, 52-61
A. Lesch, D. Momotenko, F. Cortés-Salazar, I. Wirth, U. M. Tefashe, F. Meiners, B. Vaske, H. H. Girault, G. Wittstock
