Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01Q—SCANNING-PROBE TECHNIQUES OR APPARATUS; APPLICATIONS OF SCANNING-PROBE TECHNIQUES, e.g. SCANNING PROBE MICROSCOPY [SPM]
  • G01Q60/00—Particular types of SPM [Scanning Probe Microscopy] or microscopes; Essential components thereof
  • G01Q60/60—SECM [Scanning Electro-Chemical Microscopy] or apparatus therefor, e.g. SECM probes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23H—WORKING OF METAL BY THE ACTION OF A HIGH CONCENTRATION OF ELECTRIC CURRENT ON A WORKPIECE USING AN ELECTRODE WHICH TAKES THE PLACE OF A TOOL; SUCH WORKING COMBINED WITH OTHER FORMS OF WORKING OF METAL
  • B23H3/00—Electrochemical machining, i.e. removing metal by passing current between an electrode and a workpiece in the presence of an electrolyte
  • B23H3/04—Electrodes specially adapted therefor or their manufacture
  • B23H3/06—Electrode material

Definitions

• the present invention relates to a microelectrode, in particular a microelectrode for Scanning Electrochemical Microscopy and electroanalysis or for microchemical reactors and for so-called electrochemical micromachining (EMM), and to a manufacturing method thereof.
• a microelectrode for Scanning Electrochemical Microscopy and electroanalysis or for microchemical reactors and for so-called electrochemical micromachining (EMM), and to a manufacturing method thereof.
• EMM electrochemical micromachining
• microelectrodes introduced in the 1980s, offers the typical advantages of electrochemical analysis devices, such as high sensitivity, precision and accuracy and the possibility to record an electrical signal (potential or current difference) correlated to the activity (concentration) of the analyte in real time.
• Microelectrodes allow particularly fast response times (in the order of milliseconds), mainly due to the peculiar spatial distribution of the material transport profiles which allow very rapid diffusion of the reacting species on the surface.
• Microelectrodes can have various geometries with at least one of the dimensions comprised between 1 and 100 microns. They are typically metallic devices and can be functionalized on the surface, e.g. with enzymes. In particular cases such as microcavities, a metal microsupport can allow the study of small quantities of low/medium conductivity materials.
• the most common geometry is the metal microdisc, based on a microwire (commercially available) coated with an insulating material, a section of which is exposed.
• the problem at the basis of the present invention is to make available a microelectrode which can be made in a short time in an automated (and therefore scalable) manner and of high robustness.
• the object of the present invention is a microelectrode comprising at least one electrode element comprising an electrode wire and a contact wire, and an electrode body made of a polymer material, wherein the electrode wire and the contact wire are joined by a junction made of an at least partially conductive material and are embedded in said electrode body, and wherein the electrode wire ends at the level of a distal end of the electrode body so that only a discoid surface of the electrode wire remains exposed, and wherein the contact wire ends outside the proximal end of the electrode body.
• the microelectrode of the invention may comprise two electrode elements in the same electrode body.
• the microelectrode of the invention may comprise a longitudinal channel in the electrode body, into which an optical fiber can be inserted.
• the microelectrode of the invention may comprise, on at least part of the outer surface of the electrode body, a coating of silver or other metals with a similar function.
• a further object of the invention is a method for manufacturing the microelectrode of the invention which comprises a liquid injection phase of a polymeric hardening material into a tube mold into which said electrode element is inserted.
• Figure 1 is an enlarged side view of a microelectrode according to the invention.
• Figure 2 is an enlarged side view of a second embodiment of the microelectrode according to the invention.
• Figure 3A is an enlarged side view of a third embodiment of the microelectrode according to the invention.
• Figure 3B is an enlarged front view of the microelectrode in figure 3A;
• Figure 4A is an enlarged side view of a fourth embodiment of the microelectrode of the invention.
• Figure 4B is an enlarged front view of the microelectrode in figure 4A;
• Figure 5 is an enlarged side view of the step of manufacturing of the microelectrode according to the invention.
• the microelectrode according to the invention indicated by reference numeral 1 as a whole, comprises an electrode element 10, comprising an electrode wire 2 and a contact wire 3, and an electrode body 4 made of plastic material, wherein the electrode wire 2 and the contact wire 3 are joined by a junction 5 made of an at least partially conductive material and are embedded in said electrode body 4 and wherein the electrode wire ends at the level of a distal end 4a of the electrode body 4 and the contact wire 3 ends outside the proximal end 4b of the electrode body 4.
• Electrochemical Microscopy SECM
• the contact wire 3 It is also important for the contact wire 3 to protrude from the electrode body 4 so that it can be connected to a measuring instrument.
• the electrode wire 2 is centered in the electrode body 4 i.e. the distance of the X-X axis of the electrode wire 2 from the outer surface 4c of the electrode body 4 is substantially uniform.
• the electrode body 4 can have various shapes, according to the needs and applications to which it will be dedicated.
• Figures 1 and 2 show two possible shapes of the electrode body 4, 104 by way of example.
• the electrode body 4 in figure 1 has a substantially cylindrical shape, while the electrode body 104 in figure 2 has a cylindrically shaped portion 104c, adjacent to the proximal end 104b and a substantially conical or conical-frustum portion 104d at the distal end 104a.
• the microelectrode 201 has a double wire and comprises a first electrode element 10 and a second electrode element 10', separated by an insulating septum 6, e.g. a septum made of polymeric material, such as polyethylene terephthalate (PET).
• an insulating septum 6 e.g. a septum made of polymeric material, such as polyethylene terephthalate (PET).
• PET polyethylene terephthalate
• the electrode elements 10, 10' are formed by an electrode wire 2, a contact wire 3 and a junction 5 and are embedded in an electrode body 204.
• the shape shown, which has a tip at the distal end 204a, is only indicative because other shapes of the microelectrode 201 can be prepared according to needs and applications.
• the double wire microelectrode 201 can be used for example, for the simultaneous determination of two parameters.
• Figure 4 shows a fourth embodiment of the microelectrode of the invention, wherein an electrode element 10 is embedded in an electrode body 304 and wherein the electrode body 304 comprises a longitudinal channel 7 which connects the distal end 304a with the proximal end 304b of the electrode body 304.
• the longitudinal channel 7 may comprise an optical fiber.
• the shape of the microelectrode 301 is by way of example only.
• the microelectrode 1 comprises a coating made of silver or other metals, such as gold or platinum, on at least part of the electrode 4 body, which acts as a reference electrode or counter electrode.
• the result is a self-standing microelectrode which can be immersed in a solution for measurement without the need for other electrodes.
• the microelectrode 1 can be a microcavity microelectrode, i.e. having a discoid surface 2a on which a microcavity is made, as described below.
• Such microelectrodes can be used to house a finely subdivided material in the form of micro or nanometric particles to study their electrochemical properties or use them as an active phase in sensor technology .
• the electrode body 4, 104, 204, 304 has a diameter comprised between 0.5 mm and 1 mm, or a diameter between 0.3 mm and 0.5 mm, or may comprise a proximal portion at the distal end 4a, 104a, 204a, 304a having a diameter between 0.3 mm and 0.5 mm and a proximal portion at the proximal end 4b, 104b, 204b, 304b having a diameter between 0.5 mm and 1 mm.
• the electrode body 4, 104 the electrode body 4, 104,
• the electrode body 4, 104, 204, 304 is made of an epoxy resin, in particular a two-component epoxy resin which can be polymerized at room temperature, or it can be made of a thermosetting or UV-crosslinking polymer or of a thermo-shrinkable polymer. It is also possible to make the electrode body 4, 104, 204, 304 of a silicone polymer or silicone rubber, preferably of the two-component type that can be polymerized at room temperature. In the case of polymer which can be polymerized at room temperature, however, the curing time must be long enough to allow the microelectrode
• the electrode wire 2 has a diameter between 10 and 100 microns and a length comprised between 1 and 2 cm, but embodiments in which the diameter and length of electrode wire 2 are outside the indicated measurements cannot be excluded, as needed.
• the electrode wire 2 can be a metal wire, in particular a wire of a metal normally used for electrodes, such as, for example, gold or platinum, or it can be a carbon fiber wire.
• the contact wire 3 has a diameter comprised between 0.1 and 0.2 millimeters and a length comprised between 9 and 10 cm, but also in this case embodiments in which the diameter and length of contact wire 3 are outside the indicated measurements cannot be excluded, as needed.
• the contact wire 3 is a wire made of a conductive material chosen from those normally used for electrical contacts, e.g. a copper wire.
• the junction 5 is preferably made with an electrically conductive adhesive, i.e. an adhesive which comprises a conductive component in a percentage by weight of 20% or more.
• the conductive component is preferably chosen between silver, nickel, copper or graphite.
• An example of an electrically conductive adhesive is the silver paste (mono- or bi-component), which can contain a percentage by weight of silver varying between 30% and 60%, the remaining part being glycols and solvents.
• the microelectrode 1 according to the invention can be made, as shown in figure 5, by means of the procedure described below comprising the following steps: a) providing an electrode wire 2, a contact wire 3, a material for the junction 5 and a tube 11 made of a plastic material having a first end 11a and a second end lib and having an inner diameter substantially corresponding to the outer diameter of the electrode body 4 to be manufactured; b) joining one end of the electrode wire 2 with one end of the contact wire 3 by means of the junction 5, to form an electrode element 10; c) inserting the electrode element 10 into said tube 11 so that the contact wire 3 projects from said first end 11a of the tube 11 for a length m, and that a section of length n of the tube 11 between the discoid surface 2a of the electrode wire 2 and the second end lib of the tube 11 remains empty; d) injecting, through said first end 11a of the tube 11, a hardening polymer material to form the electrode body 4, at least up to the level of the discoid surface 2a of
• the method of the invention comprises the following steps: al) providing an electrode wire 2, a contact wire 3, a material for the junction 5 and a tube 11 made of a plastic material having a first end 11a and a second end lib and comprising a first portion having an inner diameter substantially corresponding to the outer diameter of the cylindrical portion 104c and a portion of a smaller diameter at least at the conical or conical-frustum portion 104d of the electrode body 104 to be manufactured; bl) joining one end of the electrode wire 2 with one end of the contact wire 3 by means of the junction 5, to form an electrode element 10; cl) inserting the electrode element 10 into said tube 11 so that the contact wire 3 projects from said first end 11a of the tube 11 for a length m and that a section of length n of the tube 11 between the discoid surface 2a of the electrode wire 2 and the second end lib of the tube 11 remains empty; dl) injecting, through said first step: al) providing an electrode wire 2, a contact wire 3, a material for the
• the tube 11 from the electrode body 104 starting from the second end lib; fl) if the electrode body 104 extends beyond the discoid surface 2a of the electrode wire 2, cutting the excess portion so that the discoid surface 2a of the electrode wire 2 is at the same level as the distal end 104a of the electrode body 104; gl) optionally, lapping and polishing the discoid surface 2a of the electrode wire 2 and the distal end 104a of the electrode body 104; h) forming the conical or conical-frustum portion 104d by chemical etching;
• the tube 11 is preferably made of a non-stick material, more preferably PTFE (polytetrafluoroethylene ) and has an inner diameter preferably comprised between 0.4 and 1 mm, more preferably between 0.5 and 0.7 mm, and a length preferably of about 8-12 cm.
• PTFE polytetrafluoroethylene
• the length of the tube 11 depends on the length of the electrode element 10 and in any event, it is such that, once the electrode element 11 has been inserted, a portion of length n from the second end lib is left empty and the contact wire 3 is made to protrude from the first end 11a by a sufficient length for its electrical connection to an instrument .
• the tube 11 used in step al) for making the microelectrode 101 preferably consists of two pieces of tube, a first piece with a diameter not exceeding 0.5 mm and a length preferably of 3-5 cm and a second piece with an inner diameter preferably comprised between 0.7 and 1 mm and a length preferably of 6-8 cm, in which the first piece can be inserted in the second piece, e.g. for about 1-2 mm in length, to make the tube 11.
• the tube 11 can have a section of any shape, e.g. circular (as shown in the figures), elliptical, square, rectangular, polygonal, etc. In given embodiments, the tube 11 may also be conical, spherical, ogival or have any other shape that is adaptable to various needs.
• Steps b) and bl) are preferably carried out by using an electrically conductive adhesive as defined above, more preferably silver paste, for the junction 5.
• Steps c) and cl) are carried out by threading the free end of the electrode wire 2 into the first end 11a of the tube 11 and making it advance up to a distance n from the second end lib of the tube 11, wherein such a distance n is preferably at least 1 cm.
• the injection of the polymeric hardener material according to steps d) and dl) may be by any means suited for such injection, e.g. a syringe.
• Steps g) and gl) can be carried out, e.g. by means of a lapping machine using abrasive paper and abrasive suspensions in the order of 1000 mesh, 2400 mesh, 4000 mesh and 0.3 micron alumina, for a time which ensures the disappearance of traces of polymeric material left by the previous step.
• the step h) of chemical etching preferably provides soaking the portion of the electrode body
• a sulfuric acid solution may be used, preferably in the presence of hydrogen peroxide.
• piranha solution consisting of a mixture of concentrated sulfuric acid (95-97% by weight) and hydrogen peroxide in a 2:1 ratio.
• Step h) provides soaking of the distal end 104a of the electrode body 104 perpendicularly to the surface of the solution and for a length substantially corresponding to the conical or conical-frustum portion 104d to be achieved.
• the electrode body 104 is moved vertically with soaking/removal cycles lasting 2 seconds each and for a total time preferably comprised between 3 and 5 minutes.
• Step 1) which is necessary if the preceding step blackened the treated electrode body 204, can be carried out using a bleaching agent, e.g. chosen between hydrogen peroxide and sodium hypochlorite.
• the electrode element 10 must be centered in the electrode body 4, 104.
• the method of the invention comprises, between step b), bl) and step c), cl), the following steps: i) soaking a portion of the electrode element 10 from the end of the electrode wire 2 into melted paraffin; ii) soaking for a fraction of time the portion of step i) into the hardening polymer material before hardening; iii) hardening the polymer material adhered to said portion of the electrode element 10.
• the assembly thus formed is placed in a tube 11 as defined above, which may have a diameter of up to 2 mm, and will proceed as described in steps c), d) e), f) and optionally g), h) and 1).
• the microelectrode in the embodiment in figures 4A and 4B, which comprises the longitudinal channel 7, may be obtained by the procedure used for the microelectrode 1, but by inserting a wire or tube made of a non-stick polymer, e.g. PTFE, into the tube 11, in parallel to the electrode element 10. After the hardening of the polymeric hardening material, such a wire or tube can be pulled out, so that the longitudinal channel 7 can be created inside the electrode body 204.
• a wire or tube made of a non-stick polymer e.g. PTFE
• the microelectrode with a silver outer coating can be obtained as follows. This procedure, applicable to all the cases described above, aims to obtain a homogeneous layer of Ag on the external walls of the microelectrode, to be used as a reference electrode and/or counter electrode. In this manner, the microelectrode becomes self-standing and can be soaked in the desired solution without the need to introduce other electrodes .
• the procedure comprises the following steps:
• an electrical contact can be generated using the aforementioned conductive adhesive to connect a copper wire or other metal. It is also possible to protect the deposit and contact with a protective layer, e.g. epoxy resin.
• microelectrode with discoid surface 2a with microcavity can be obtained as follows.
• r (in m) is the radius of the discoid surface 2a
• Iss (in A) the steady-state current limit
• C (in mol m -3 ) and D (in m 2 s -1 ) are respectively the concentration and the diffusion coefficient of the redox species
• n are the electron moles/reagent moles
• F the Faraday constant (96485 C/electron moles).
• the etching is carried out by applying a pulsed current between 1.5 mA cm -2 (1000 s) and -0.075 mA cm- 2 (1000 s). Among these, it is possible to add a current-free step. The current density values and their duration can be varied at will. It is also possible to apply a single anodic galvanostatic pulse. The number of cycles or the etching time depends on the desired depth.
• the cavity can be filled with any finely divided solid substance by pressing the electrode tip repeatedly (5-10 times) on a small amount of the powder.
• the powders materials finely divided into the form of micro or nanometric particles
• the powders can consist of any conductive or semiconductor material, to study its electrochemical or photoelectrochemical properties or to be used as an active material in sensor technology. It is advisable to check the correct filling under a microscope. To empty the cavity, simply soak the tip in an ultrasonic bath for a few seconds and check again under the microscope.
• microelectrodes according to the invention can be used for multiple applications.
• the microelectrode 101 with conical or conical- frustum portion 104d can be used as a tip for Scanning Electrochemical Microscopy.
• the double wire microelectrode 201 can be used for the simultaneous determination of two parameters in a solution or as conductometric cells.
• the microelectrode 301 equipped with longitudinal channel 7, into which an optical fiber can be inserted, can be used in photochemical or photoelectrochemical reactions or for reading an optical signal.
• the silver-coated microelectrode can be used as a self-standing microelectrode.
• microelectrodes of the invention can be in water analysis, as sensors for pollutants, in the food industry or other uses both in research and industrial applications, in the field of microreactors and micromachining.
• microelectrodes of the invention are low cost, as they can be prepared with an easily scalable process, can have the desired shape according to the needs and have a high resistance by virtue of the mechanical properties of the polymeric material used.
• a method for the injection of the polymeric hardening material has been described but an extrusion and 3D printing procedure can also be provided. It is apparent that only some particular embodiments of the present invention have been described, to which a person skilled in the art will be able to make all the changes necessary to adapt it to particular applications, without because of this departing from the scope of protection of the present invention.

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• 2019
  • 2019-12-17 IT IT102019000024193A patent/IT201900024193A1/it unknown
• 2020
  • 2020-11-30 WO PCT/IB2020/061266 patent/WO2021123977A1/en active Application Filing

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