m8ta
you are not logged in, login. new entry
text: sort by
tags: modified
type: chronology
{1374}
hide / edit[3] / print
ref: -0 tags: nanoprobe transmembrane intracellular thiol gold AFM juxtacellular date: 02-06-2017 23:45 gmt revision:3 [2] [1] [0] [head]

PMID-20212151 Fusion of biomimetic stealth probes into lipid bilayer cores

  • Used e-beam evaporation of Cr/Au/Cr 10/10/10 or 10/5/10 onto a Si AFM tip.
    • Approx 200nm diameter; 1800 lipid interaction at the circumference.
  • Exposed the Au in the sandwich via FIB
  • Functionalized the Au with butanethiol or dodecanthiol; former is mobile on the surface, latter is polycrystaline.
    • Butanethiol showed higher adhesion to the synthetic membranes
  • Measured the penetration force & displacement through synthetic multi-layer lipid bilayers.
    • These were made via a custom protocol with 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC) and cholesterol

PMID-21469728 '''Molecular Structure Influences the Stability of Membrane Penetrating Biointerfaces.

  • Surprisingly, hydrophobicity is found to be a secondary factor with monolayer crystallinity the major determinate of interface strength
  • Previous studies using ellipsometry and IR spectroscopy have shown that alkanethiol self-assembled monolayers display an abrupt transition from a fluid to a crystalline phase between hexanethiol and octanethiol.
    • This suggests the weakening of the membrane stealth probe interface is due to the crystallinity of the molecular surface with fluid, disordered monolayers promoting a high strength interface regime and rigid, crystalline SAMs forming weak interfaces.

{1370}
hide / edit[7] / print
ref: -0 tags: juxtacellular recording gold mushroom cultured hippocampal neurons Spira date: 02-01-2017 02:44 gmt revision:7 [6] [5] [4] [3] [2] [1] [head]

Large-Scale Juxtacellular Recordings from Cultured Hippocampal Neurons by an Array of Gold-Mushroom Shaped Microelectrodes

  • Micrometer sized Au mushroom MEA electrodes.
  • Functionalized by poly-ethylene-imine (PEI, positively charged)/laminin (extracellular matrix protein) undergo a process to form juxtacellular junctions between the neurons and the gMµEs.
  • No figures, but:
    • Whereas substrate integrated planar MEA record FPs dominated by negative-peak or biphasic-signals with amplitudes typically ranging between 40-100 µV and a signal to noise ratio of ≤ 5,
    • The gMµE-MEA recordings were dominated by positive monophasic action potentials.
    • It is important to note that monophasic high peak amplitudes ≥ 100 µV are rarely obtained using planar electrodes arrays, whereas when using the gMµE-MEA, 34.48 % of the gMµEs recorded potentials ≥ 200 µV and 10.64 % recorded potentials in the range of 300-5,085 µV.
  • So, there is a distribution of coupling, approximately 10% "good".

PMID-27256971 Multisite electrophysiological recordings by self-assembled loose-patch-like junctions between cultured hippocampal neurons and mushroom-shaped microelectrodes.

  • Note 300uV - 1mV extracellular 'juxtacellular' action potentials from these mushroom recordings. This is 2 - 5x better than microwire extacellular in-vivo ephys; coupling is imperfect.
    • Sharp glass-insulated W electrodes, ~ 10Mohm, might achieve better SNR if driven carefully.
  • 2um mushroom cap Au electrodes, 1um diameter 1um long shaft
    • No coating, other than the rough one left by electroplating process.
    • Impedance 10 - 25 Mohm.
  • APs decline within a burst of up to 35% -- electrostatic reasons?
  • Most electrodes record more than one neuron, similar to in-vivo ephys, with less LFP coupling.

PMID-23380931 Multi-electrode array technologies for neuroscience and cardiology

  • The key to the multi-electrode-array ‘in-cell recording’ approach developed by us is the outcome of three converging cell biological principals:
    • (a) the activation of endocytotic-like mechanisms in which cultured Aplysia neurons are induced to actively engulf gold mushroom-shaped microelectrodes (gMμE) that protrude from a flat substrate,
    • (b) the generation of high Rseal between the cell’s membrane and the engulfed gMμE, and
    • (c) the increased junctional membrane conductance.
  • Functionalized the Au mushrooms with an RGD-based peptide
    • RGD is an extracellular matrix binding site on fibronectin, which mediates it's interaction with integrin, a cell surface receptor; it is thought that other elements of fibronectin regulate specificity with its receptor. PMID-2418980

{1353}
hide / edit[3] / print
ref: -0 tags: PEDOT electropolymerization electroplating gold TFB borate counterion acetonitrile date: 10-18-2016 07:49 gmt revision:3 [2] [1] [0] [head]

Electrochemical and Optical Properties of the Poly(3,4-ethylenedioxythiophene) Film Electropolymerized in an Aqueous Sodium Dodecyl Sulfate and Lithium Tetrafluoroborate Medium

  • EDOT has a higher oxidation potential than water, which makes polymers electropolymerized from water "poorly defined".
  • Addition of SDS lowers the oxidation potential to 0.76V, below that of EDOT in acetonitrile at 1.1V.
  • " The potential was first switched from open circuit potential to 0.5 V for 100 s before polarizing the electrode to the desired potential. This initial step was to allow double-layer charging of the Au electrode|solution interface, which minimizes the distortion of the polymerization current transient by double-layer capacitance charging.17,18 "
    • Huh, interesting.
  • Plated at 0.82 - 0.84V, 0.03M EDOT conc.
  • 0.1M LiBF4 anion / electrolyte; 0.07M SDS sufactant.
    • This SDS is incorporated into the film, and affects redox reactions as shown in the cyclic voltammagram (fig 4)
      • Doping level 0.36
    • BF4-, in comparison, can be driven out of the film.

Improvement of the Electrosynthesis and Physicochemical Properties of Poly(3,4-ethylenedioxythiophene) Using a Sodium Dodecyl Sulfate Micellar Aqueous Medium

  • "The oxidation potential of thiopene = 1.8V; water = 1.23V.
  • Claim: "The polymer films prepared in micellar medium [SDS] are more stable than those obtained in organic solution as demonstrated by the fact that, when submitted to a great number of redox cycles (n ≈ 50), there is no significant loss of their electroactivity (<10%). These electrochemical properties are accompanied by color changes of the film which turns from blue-black to red-purple upon reduction."
  • Estimate that there is about 21% DS- anions in the PEDOT - SDS films.
    • Cl - was at ~ 7%.
  • I'm still not sure about incorporating soap into the electroplating solution.. !

Electrochemical Synthesis of Poly(3,4-ethylenedioxythiophene) on Steel Electrodes: Properties and Characterization

  • 0.01M EDOT and 0.1M LiClO4 in acetonitrile.
  • Claim excellent adhesion & film properties to 316 SS.
  • Oxidation / electrodeposition at 1.20V; voltages higher than 1.7V resulted in flaky films.

PMID-20715789 Investigation of near ohmic behavior for poly(3,4-ethylenedioxythiophene): a model consistent with systematic variations in polymerization conditions.

  • Again use acetonitrile.
  • 1.3V vs Ag/AgCl electrode.
  • Perchlorate and tetraflouroborate both seemed the best counterions (figure 4).
  • Figure 5: Film was difficult to remove from surface.
    • They did use a polycrystaline Au layer:
    • "The plating process was allowed to run for 1 min (until approximately 100 mC had passed) at a constant potential of 0.3 V versus Ag/AgCl in 50 mM HAuCl4 prepared in 0.1 M NaCl."
  • Claim that the counterions are trapped; not in agreement with the SDS study above.
  • "Conditions for the consistent production of conducting polymer films employing potentiostatic deposition at 1.3 V for 60-90 s have been determined. The optimal concentration of the monomer is 0.0125 M, and that of the counterion is 0.05 M. "

PMID-24576579 '''Improving the performance of poly(3,4-ethylenedioxythiophene) for brain–machine interface applications"

  • Show that TFB (BF4-) is a suitable counterion for EDOT electropolymerization.
  • Comparison is between PEDOT:TFB deposited in an anhydrous acetronitrile solution, and PEDOT:PSS deposited in an aqueous solution.
    • Presumably the PSS brings the EDOT into solution (??).
  • figure 3 is compelling, but long-term, electrodes are not that much better than Au!
    • Maybe we should just palate with that.

PEDOT-modified integrated microelectrodes for the detection of ascorbic acid, dopamine and uric acid

  • Direct comparison of acetonitrile and water solvents for electropolymerization of EDOT.
  • "PEDOT adhesion is best on gold surface due to the strong interactions between gold and sulphur atoms.
  • images/1353_2.pdf
    • Au plating is essential!

{1270}
hide / edit[5] / print
ref: -0 tags: gold micrograin recording electrodes electroplating impedance date: 10-17-2016 20:28 gmt revision:5 [4] [3] [2] [1] [0] [head]

PMID-23071004 Gold nanograin microelectrodes for neuroelectronic interfaces.

  • We report a single-cell sized microelectrode, which has unique gold nanograin structures, using a simple electrochemical deposition method.
  • Fabricated microelectrode had a sunflower shape with 1-5 (um of micropetals along the circumference of the microelectrode and 500 nm nanograins at the center.
  • The nanograin electrodes had 69-fold decrease of impedance and 10-fold increase in electrical stimulation capability compared to unmodified flat gold microelectrodes.
  • images/1270_1.pdf pdf
  • The deposition was conducted with an aqueous solution containing 25 mM HAuCl (HAuCl · 3H O, Sigma-Aldrich, MO, 4 4 2USA) and 20 g/L polyvinylpyrrolidone (surfactant, stabilizing agent)

{1304}
hide / edit[1] / print
ref: -0 tags: gold carbon nanotube electroplating impedance PEG date: 10-24-2014 22:25 gmt revision:1 [0] [head]

PMID-21379404 Creating low-impedance tetrodes by electroplating with additives

  • Electroplated tetrodes to 30-70 kΩ by adding polyethylene glycol (PEG) or multi-walled carbon nanotube (MWCNT) solutions to a commercial gold-plating solution.
  • Cui and Martin [12] showed that altering the concentration of gold-plating solution and electroplating current can change the morphology of a gold-plated microelectrode coating.
  • Additionally, Keefer et al. [13] found that adding multi-walled carbon nanotubes (MWCNTs) to a gold-plating solution created microelectrode coatings with a “rice-like” texture and very low impedances.
  • Au electroplating solution made of non-cyanide, gold-plating solution (5355, SIFCO Selective Plating, Cleveland, OH).
  • A one-second, reversed-polarity pulse helped to clean the surface of the tetrode tip and lowered the impedances to 2MΩ to 3 MΩ before electroplating.
  • Electroplating pulses were one to five seconds long and were repeated until the tetrodes reached the desired impedances. After electroplating, the tetrodes were soaked in DI, air dried, and checked for shorts.

Conclusion: 75% PEG, commercial electropating solution, 0.1ua current pluses to 250K or less.

  • Though the Caswell Au plating solution will likely behave differently ..

{1299}
hide / edit[3] / print
ref: -0 tags: wirebonding finishes gold nickel palladium electroless electrolytic date: 09-21-2014 02:53 gmt revision:3 [2] [1] [0] [head]

Why palladium?


To prevent black nickel: http://tayloredge.com/reference/Electronics/PWB/BlackPad_ITRI_Round1.PD

Introduction The use of electroless nickel / immersion gold (E.Ni/I.Au) as a circuit board finish has grown significantly in the last few years. It provides a flat board finish, is very solderable, provides a precious metal contact surface and the nickel strengthens the plated holes. However, as the usage of E.Ni/I.Au increased, a problem was found on BGA (Ball Grid Array) components. An open or fractured solder joint sometimes appears after board assembly on the occasional BGA pad. The solder had wet and dissolved the gold and formed a weak intermetallic bond to the nickel. This weak bond to the nickel readily fractures under stress or shock, leaving an open circuit. The incidence of this problem appears to be very sporadic and a low ppm level problem, but it is very unpredictable. A BGA solder joint cannot be touched-up without the component being removed. After the BGA component is removed, a black pad is observed at the affected pad site. This black pad is not readily solderable, but it can be repaired.


From: http://www.smtnet.com/Forums/index.cfm?fuseaction=view_thread&Thread_ID=4430

You don't have enough gold. Your 2uin is too porous and is allowing the nickel to corrode. Prove that this by hand soldering to these pads with a more active flux, like a water soluble solder paste, than you are using.

You must have at least 3uin of immersion gold. Seriously consider >5uin.

Your nickel thickness is fine. Although if you wanted to trade costs, consider giving-up nickel to 150uin thickness, while increasing the gold thickness. Gold over electroless nickel creates brittle joints because of phosphorous in the nickel plating bath. The phosphorous migrates into the over-plating. Electrolytic nickel and gold plating should not be a problem.

If you stay with the electroless nickel, keep the phosphorous at a mid [7 - 9%] level. Just as important, don't let the immersion gold get too aggressive. The immersion gold works by corroding the nickel. If it is too aggressive it takes away the nickel and leave phosphorous behind. This makes it look like the phosphorous level is too high in the nickel bath.

Gold purity is very important for any type of wire bonding process. For aluminum wedge bonding, gold should have a purity of 99. 99% [no thalium] and the nickel becomes critical. No contaminates and the nickel wants to be plated a soft as possible. This requires good control of Ph and plating chemicals in the nickel-plating bath.

Harman "Wire Bonding In Microelectronics" McGraw-Hill is a good resource for troubleshooting wire bonding. I reviewed it in the SMTnet Newsletter a couple of months ago.


That said, electrolytic nickel + electrolytic gold does work well -- perhaps even better than ENEPIG:

{1267}
hide / edit[5] / print
ref: -0 tags: stretchable nanoparticle conductors gold polyurethane flocculation date: 12-13-2013 02:12 gmt revision:5 [4] [3] [2] [1] [0] [head]

PMID-23863931 Stretchable nanoparticle conductors with self-organized conductive pathways.

  • 13nm gold nanoparticles, citrate-stabilized colloidal solution
    • Details of fabrication procedure in methods & supp. materials.
  • Films are prepared in water and dried (like paint)
  • LBL = layer by layer. layer of polyurethane + layer of gold nanoparticles.
    • Order of magnitude higher conductivity than the
  • VAF = vacuum assisted floculation.
    • Mix Au-citrate nanoparticles + polyurethane and pass through filter paper.
    • Peel the flocculant from the filter paper & dry.
  • Conductivity of the LBL films ~ 1e4 S/cm -> 1e-6 Ohm*m (pure gold = 2 x 10-8, 50 x better)
  • VAF = 1e3 S/cm -> 1e-5 Ohm*m. Still pretty good.
    • This equates to a resistance of 1k / mm in a 10um^2 cross-sectional area wire (2um x 5 um, e.g.)
  • The material can sustain > 100% strain when thermo-laminated.
    • Laminated: 120C at 20 MPa for 1 hour.
  • See also: Preparation of highly conductive gold patterns on polyimide via shaking-assisted layer-by-layer deposition of gold nanoparticles
    • Patterned via MCP -- microcontact printing(aka rubber-stamping)
    • Bulk conductivity of annealed (150C) films near that of pure gold (?)
    • No mechanical properties, though; unlcear if these films are more flexible / ductile than evaporated film.

{1229}
hide / edit[2] / print
ref: -0 tags: parylene PDMS material properties gold compliant date: 02-08-2013 22:38 gmt revision:2 [1] [0] [head]

PMID-21240559 Highly-compliant, microcable neuroelectrodes fabricated from thin-film gold and PDMS

  • he microcable electrodes were also electromechanically tested, with measurable conductivity (220 kΩ) at an average 8% strain (n = 2) after the application of 200% strain.

{1191}
hide / edit[4] / print
ref: Wester-2009.04 tags: parylene flexible electrode gold Georgia date: 01-29-2013 03:14 gmt revision:4 [3] [2] [1] [0] [head]

PMID-19255461[0] Development and characterization of in vivo flexible electrodes compatible with large tissue displacements.

  • Device was 100um wide and 25um thick, and was stiff enough to enter directly.
    • carefully calibrated this stiffness -- good! we should do the same.
  • parylene composition.
  • brain tissue force on the order of 2mN.
  • No histology.
  • [http://www.ncbi.nlm.nih.gov/pubmed?term=LaPlaca%20MC[Author]&cauthor=true&cauthor_uid=19255461 laPlaca] has a good number of publications on shear stress in brain tissue.

____References____

[0] Wester BA, Lee RH, LaPlaca MC, Development and characterization of in vivo flexible electrodes compatible with large tissue displacements.J Neural Eng 6:2, 024002 (2009 Apr)

{1114}
hide / edit[1] / print
ref: Feingold-2012.04 tags: Feingold Graybeil electrode moveable recording date: 01-28-2013 02:13 gmt revision:1 [0] [head]

PMID-22170970[0] A system for recording neural activity chronically and simultaneously from multiple cortical and subcortical regions in non-human primates.

  • Up to 127 electrodes in 14 brain areas for up to a year at a time.

____References____

[0] Feingold J, Desrochers TM, Fujii N, Harlan R, Tierney PL, Shimazu H, Amemori K, Graybiel AM, A system for recording neural activity chronically and simultaneously from multiple cortical and subcortical regions in nonhuman primates.J Neurophysiol 107:7, 1979-95 (2012 Apr)

{1012}
hide / edit[3] / print
ref: Wise-1970.07 tags: Wise MEA silicon gold lithography date: 01-03-2012 19:05 gmt revision:3 [2] [1] [0] [head]

IEEE-4502738 (pdf) An Integrated-Circuit Approach to Extracellular Microelectrodes

  • Used lithography techniques & to make SiO2 & Au electrodes.
  • 2um tips.
    • Back then, small tips were deemed good; nowadays, we want larger, lower-impedance tips (fad?)
  • Most previous work is glass insulated metal electrodes [1][2]
    • C. Guld, a glass-covered platinum microelectrode. {1014}
  • Probes cannot exceed more than 50um from the edge of the chip carrier without cracking, which limits how close one may get to a given cell.

____References____

Wise, Kensall D. and Angell, James B. and Starr, Arnold An Integrated-Circuit Approach to Extracellular Microelectrodes Biomedical Engineering, IEEE Transactions on BME-17 3 238 -247 (1970)