Schematic representation of the MFP head and the hydrodynamic confinement of a microjet (in green) between the blunt surface of the MFP and the substrate surface. The size of the confinement depends on the ratio of aspiration to injection flow rates, the size and separation of the apertures, and the gap. The MFP operation allows surface treatment in an immersed environment by flushing the confined stream across the surface.
A custom-made MFP holder consisting of an aluminum handle and a PMMA screw-clamp. Clamping of the PDMS/MFP piece is performed by screwing the nut that also serves for rotational alignment of the MFP apertures along the X (or Y) axis. The Si chip with the mesa is bonded to the PDMS block. The two capillaries for injection and aspiration are plugged in from the top. The transparency of the Plexiglas allows the use of transmission illumination to visualize the probe and surface underneath when using low magnification objectives.
Custom slide insert with tilt adjustment mechanism. (a) Picture of the different elements of the slide insert including a base plate and a cover plate machined in Al with a central opening, sealing rings, and four screws for clamping a glass slide between the base and cover plates. (b) Picture of the assembled plates. Three set screws on the outer edges serve as support of the slide insert on the microscope stage and allow adjusting the horizontality of the slide. The alignment is critical because when scanning over long distances, a slight misalignment could alter the gap between MFP and substrate significantly.
(a) Overview of the automated MFP station with its various components used for operating the MFP. The station integrates fluidic control using microsyringe pumps, positioning and movement control using the microscope stage, and imaging control using the CCD camera. The MFP positioning system is needed for accurate placement of the MFP over the surface. An environmental chamber was removed to allow visualizing the MFP positioning system. (b) Close-up view of the MFP positioning system. The assembly provides high-resolution x-, y-, and z-positioning of the MFP, as well as two-angle control using goniometers to ensure parallelism with the substrate. The linear motion slide acts as a shock absorber and support for the probe holder. The figure also shows the custom slide insert, MFP holder, and the illuminated MFP.
The MFP is aligned using the white light interferences. The fringes observed originate at the point of contact between the MFP and the surface, and their width correlate with the parallelism of the MFP. (a)–(c) show misalignment of the MFP around various axes. The spacing between the fringe lines is indicative of the tilting angle of the MFP. Here, we can observe that the lines on the top right figure (b) are much closer than the lines on the top left (a) or bottom left (c) figures. This implies that the misalignment angle between the MFP head and the glass slide is greater on the top right figure than on the other two. (d) Shows a MFP parallel to the surface with a dark central mesa (first interference) and brighter posts. This result is due to a curvature between the MFP head and glass slide preventing contact of all features simultaneously. This setup allows alignment of the MFP with the substrate with submicrometer accuracy.
(a) Simplified schematic of the Master-slave software architecture providing an overview of the computerized controls of the automated MFP station. (b) Screen capture of the LABVIEW software user interface. The software allows simultaneous control and monitoring of the syringe pumps, stage, camera, and microscope. Automated control of stage movement and dispensing can also be done using a script.
Patterning of fluorescein-labeled biotin on a streptavidin-coated epoxy slide. The patterns were formed by rapidly moving the MFP from spot to spot, and using the injection and aspiration flow rate of 1 and 10 nL/s, respectively, a gap of and a concentration of biotin of . The pattern was written from the bottom left side and moved up the first column, then right and down the second column and so forth. Vertical and horizontal displacement steps were 32 and per step, respectively.
Streaklines tracing simulations using finite-element analysis show the flow geometry of the reagents during operation of the MFP. (a) 3D view of the MFP and the flow. (b) and (c) Cross-sectional views along the xz and yz axes, respectively. (d) Superposition of top views of the experimental results (right most pattern from Fig. 7) and of the projection of the streakline patterns that both have similar shape. The length and width of the proteins deposited on the substrate are and respectively, and are reported in (c) and (d) for comparison.
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