Soft Microelectrode Linear Array for Scanning Electrochemical Microscopy

Abstract

A linear array of eight individual addressable microelectrodes has been developed in order to perform highthroughput scanning electrochemical microscopy (SECM) imaging of large sample areas in contact regime. Similar to previous reports, the soft microelectrode array was fabricated by ablating microchannels on a polyethylene terephthalate (PET) film and filling them with carbon ink. Improvements have been achieved by using a 5 µm thick Parylene coating that allows for smaller working distances, as the probe was mounted with the Parylene coating facing the sample surface. Additionally, the application of a SECM holder allows scanning in contact regime with a tilted probe, reducing the topographic effects and assuring the probe bending direction. The main advantage of the soft microelectrode array is the considerable decrease in the experimental time needed for imaging large sample areas. Additionally, soft microelectrode arrays are very stable and can be used several times, since the electrode surface can be regenerated by blade cutting. Cyclic voltammograms and approach curves were recorded in order to assess the electrochemical properties of the device. An SECM image of a gold on glass chip was obtained with high resolution and sensitivity, proving the feasibility of soft microelectrode arrays to detect localized surface activity. Finite element method (FEM) simulations were performed in order to establish the effect of diffusion layer overlapping between neighboring electrodes on the respective approach curves.Scanning electrochemical microscopy (SECM) is a scanning probe microscope technique that is being extensively employed for the spatial characterization of chemical reactivity at different interfaces (i.e., liquid/solid, liquid/liquid, and liquid/gas) with a high resolution and high sensitivity. [1][2][3][4] Instrumentally, SECM comprises a (bi)potentiostat for recording the current generated at a microelectrode, which is horizontally (x, y) and vertically (z) scanned over a substrate by using a fine positioning system. For surface reactivity imaging, the microelectrode is biased at a potential where diffusion-limited electrolysis of a redox mediator occurs and the changes on the steady-state current at the scanning microelectrode are associated with local reaction sites on the specimen surface. In addition, quantitative kinetic information can be extracted, by comparing experimental data with numerical simulations of coupled heterogeneous kinetics and mass transport phenomena. [5][6][7][8][9][10][11][12] As a consequence, SECM has found several applications on diverse fields ranging from the study of living cells, 13,14 localized corrosion, 15,16 imaging human fingerprints, 17 screening electrocatalysts, 18 patterning surfaces, 19 and investigating kinetics of very fast heterogeneous reactions. 20,21 For a rather long time, instrumental developments have aimed at increasing the lateral resolution and providing complementary information such as topography and local reactivity from complex samples. For i...

Parallel Imaging and Template‐Free Patterning of Self‐Assembled Monolayers with Soft Linear Microelectrode Arrays

“…These probes were introduced earlier for the imaging of metal-on-glass structures, human fingerprints, and enzyme activity. [28][29][30] The probe production starts with the formation of parallel microchannels with well-defined midpoint-to-midpoint distances (e.g. 250 mm or 500 mm) in a 100 mm thick polyethylene terephthalate (PET) film by laser ablation, filling the channels with a carbon ink, curing, and covering the entire probe with a 3 mm thick coating of Parylene C (see the Supporting Information for chemicals used (SI-1) and details of the probe fabrication (SI-2)).…”

“…For imaging areas larger than the width of the electrode array, several image frames can be tiled by the control software (SI-4). [29] The pressure exerted by the probe on the sample is in the range of 10 3 N m À2 . [32] Although this value is not very precise because of difficulties in estimating the contact area between the probe and the substrate, it is around four orders of magnitude smaller than the pressure in standard SFM experiments.…”

Seeing Big with Scanning Electrochemical Microscopy

“…[19][20][21] The new probes are made by classical microfabrication techniques and are appropriate for a wide range of samples, thereby broadening the applicability of SECM to new areas.…”

“…Thus, the same microfabrication methods employed for fabricating soft stylus probes have produced linear arrays of microelectrodes. 21 As a consequence, all the advantages provided by performing SECM in a contact regime are combined with a multiplexed probe array.…”

“…Finite element method simulations have predicted that even soft microelectrode arrays presenting quartermoon shape electrodes (i.e., 40 μm width and 20 μm depth) with 500 μm electrode-to-electrode distance will develop an overlapping of the diffusion layers. 21 However, for such interelectrode spacing, insignificant current differences are recorded at the inner and outer electrodes, allowing qualitative SECM imaging.…”