1,721,004 research outputs found
Aptamer Conformational Dynamics Modulate Neurotransmitter Sensing in Nanopores
Full text link: Aptamers that undergo conformational changes upon small-molecule recognition have been shown to gate the ionic flux through nanopores by rearranging the charge density within the aptamer-occluded orifice. However, mechanistic insight into such systems where biomolecular interactions are confined in nanoscale spaces is limited. To understand the fundamental mechanisms that facilitate the detection of small-molecule analytes inside structure-switching aptamer-modified nanopores, we correlated experimental observations to theoretical models. We developed a dopamine aptamer-functionalized nanopore sensor with femtomolar detection limits and compared the sensing behavior with that of a serotonin sensor fabricated with the same methodology. When these two neurotransmitters with comparable mass and equal charge were detected, the sensors showed an opposite electronic behavior. This distinctive phenomenon was extensively studied using complementary experimental techniques such as quartz crystal microbalance with dissipation monitoring, in combination with theoretical assessment by the finite element method and molecular dynamic simulations. Taken together, our studies demonstrate that the sensing behavior of aptamer-modified nanopores in detecting specific small-molecule analytes correlates with the structure-switching mechanisms of individual aptamers. We believe that such investigations not only improve our understanding of the complex interactions occurring in confined nanoscale environments but will also drive further innovations in biomimetic nanopore technologies
Electrochemical Push–Pull Scanner with Mass Spectrometry Detection
Full text linkThis manuscript presents a push-pull electrochem. scanner able to image reactivity of initially dry surfaces by scanning electrochem. microscopy (SECM) and to probe mols. present or generated at the surface by mass spectrometry (MS). The proof-of-concept is demonstrated by coupling SECM with matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) for imaging latent human fingerprints, which had been in contact with picric acid used here as a model explosive. The push-pull electrochem. scanner also was coupled with electrospray ionization mass spectrometry (ESI-MS) to assay the activity of surface spotted enzymes. These exptl. studies are complemented by 3-dimensional finite element simulations solving Navier-Stokes and diffusion-convection differential equations to optimize the coupling between SECM imaging and mass spectrometry detection.LEP
High-throughput scanning electrochemical microscopy brushing of strongly tilted and curved surfaces
Full text linkThe feasibility of high-throughput scanning electrochemical microscopy (SECM) of strongly tilted (tilt angles ≤4°) and curved substrates (diameter of curvature ≥9 cm) is demonstrated by brushing them with a soft linear array of carbon microelectrodes. This probe made of thin polymeric layers operates in contact regime to follow the topography of highly unconventional SECM samples while keeping an almost constant working distance. Strong slope variations of the sample lead to a slight misalignment between the axes of the positioning system and the sliding direction of the microelectrode arrays. The resulting positional offsets can be predicted and corrected to yield a correct representation of the spatial relation on the surface of the sample. Moreover, a custom-made holder system ideally suited for precise control of the soft probe inclination angle and alignment with the substrate plane was also developed to perform high-throughput SECM imaging of a 1.2 cm2 curved metallic pin within less than 2 h.LEP
Parallel Imaging and Template-Free Patterning of Self-Assembled Monolayers with Soft Linear Microelectrode Arrays
Full text linkReagents were generated locally on an array of eight individually addressable electrodes in order to modify self-assembled monolayers. Since the array was manufactured in a soft polymer material, it can have mechanical contact with a delicate sample without inducing defects. Lengthy leveling procedures are not necessary and the scan times can be shortened.LEP
Finger Probe Array for Topography-Tolerant Scanning Electrochemical Microscopy of Extended Samples
Full text linkScanning electrochemical microscopy with soft microelectrode array probes has recently been used to enable reactivity imaging of extended areas and to compensate sample corrugation perpendicular to the scanning direction. Here, the use of a new type of microelectrode arrays is described in which each individual microelectrode can independently compensate corrugations of the sample surface. It consists of conventional Pt microelectrodes enclosed in an insulating glass sheath. The microelectrodes are individually fixed to a new holder system by magnetic forces. The concept was tested using a large 3D sample with heights up to 12 μm specially prepared by inkjet printing. The microelectrodes follow the topography in a constant working distance independently from each other while exerting low pressure on the surface.LEP
Tailored Fabrication of 3D Nanopores Made of Dielectric Oxides for Multiple Nanoscale Applications
No full text: Solid-state nanopores are a key platform for single-molecule detection and analysis that allow engineering of their properties by controlling size, shape, and chemical functionalization. However, approaches relying on polymers have limits for what concerns hardness, robustness, durability, and refractive index. Nanopores made of oxides with high dielectric constant would overcome such limits and have the potential to extend the suitability of solid-state nanopores toward optoelectronic technologies. Here, we present a versatile method to fabricate three-dimensional nanopores made of different dielectric oxides with convex, straight, and concave shapes and demonstrate their functionality in a series of technologies and applications such as ionic nanochannels, ionic current rectification, memristors, and DNA sensing. Our experimental data are supported by numerical simulations that showcase the effect of different shapes and oxide materials. This approach toward robust and tunable solid-state nanopores can be extended to other 3D shapes and a variety of dielectrics
Microfluidic Push-Pull Probe for Scanning Electrochemical Microscopy
Full text linkThis paper presents a microfluidic push-pull probe for scanning electrochemical microscopy (SECM) consisting of a working microelectrode, an integrated counter/reference electrode and two microchannels for pushing and pulling an electrolyte solution to and away from a substrate. With such a configuration, a droplet of a permanently renewed redox mediator solution is maintained just at the probe tip to carry out SECM measurements on initially dry substrates or in microenvironments. For SECM imaging purposes, the probe fabricated in a soft polymer material is used in a contact regime. SECM images of various gold-on-glass samples demonstrate the proof-of-concept of a push-pull probe for local surface activity characterization with high spatial resolution even on vertically oriented substrates. Finite element computations were performed to guide the improvement of the probe sensitivity.LEP
Soft Microelectrode Linear Array for Scanning Electrochemical Microscopy
Full text linkA 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.LEP
Seeing Big with Scanning Electrochemical Microscopy
Full text linkSpecialized microelectrode probes fabricated in a soft polymer film now make it possible to use scanning electrochemical microscopy to image the reactivity of large, corrugated, tilted, and dry surfaces.LEP
Fountain pen for scanning electrochemical microscopy
Full text linkA fountain pen probe has been developed to extend the scope of scanning electrochemical microscopy (SECM) experiments to dry surfaces. The fountain pen is fabricated by UV-photoablation of a polyethylene terephthalate (PET) film and consists on one side of one microchannel for flowing an electrolyte solution to the open tip, integrating a reference/counter electrode and on the other side a carbon track. The exposed tip of the track forms the working electrode located close to the microchannel outlet. The fountain pen can operate in a pointillist mode where a nanolitre droplet at the bottom of the probe connects it to a well-defined surface area to study locally the substrate, but can also operate in a scanning mode leaving a linear wet track of solution behind it to monitor the surface activity. The electrochemical characterization of the proposed fountain pen probe was performed by cyclic voltammetry, approach curves and lateral line scans over insulating and conductive substrates, showing that the flow rate and the probe-substrate distance have a major influence on its electrochemical behavior. An SECM image of a gold on glass EPFL logo is presented as a proof-ofconcept that fountain pen probes can be employed for the detection of surface activity when scanning in a contact regime.LEP
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