Optimizing in Vitro Impedance and Physico‐Chemical Properties of Neural Electrodes by Electrophoretic Deposition of Pt Nanoparticles

Abstract

Neural electrodes suffer from an undesired incline in impedance when in permanent contact with human tissue. Nanostructures, induced by electrophoretic deposition (EPD) of ligand-free laser-generated nanoparticles (NPs) on the electrodes are known to stabilize impedance in vivo. Hence, Pt surfaces were systematically EPD-coated with Pt NPs and evaluated for impedance as well as surface coverage, contact angle, electrochemically active surface area (ECSA) and surface oxidation. The aim was to establish a systematic correlation between EPD process parameters and physical surface properties. The findings clearly reveal a linear decrease in impedance with increasing surface coverage, which goes along with a proportional reduction of the contact angle and an increase in ECSA and surface oxidation. EPD process parameters, prone to yield surface coatings with low impedance, are long deposition times (40-60 min), while high colloid concentrations (>250 μg mL ) and electric field strengths (>25 V cm ) should be avoided due to detrimental NP assemblage effects.

Perspective of Surfactant‐Free Colloidal Nanoparticles in Heterogeneous Catalysis

“…In contrast to surfactant‐coated particles, the authors found unsuppressed linear deposition kinetics only for laser‐generated surfactant‐free NPs which has been discussed in terms of a barrier‐free nanoparticle diffusion and deposition . LAL‐generated Pt NPs deposited on Pt electrodes caused an increase of charge (charge transfer) as measured by XPS, as well as an increased electrochemical surface area (ECSA) measured by cyclic voltammetry . During electrophoretic deposition of surfactant‐free NPs, the initial nanoparticle diameter does not change as annealing steps are being avoided .…”

“…Following the fractions of surface oxidation in Table , it is obvious that the range of surface oxidation reported for laser‐generated Au NPs and Pt NPs is very broad. With respect to the laser parameters used in each cited experiment it is noteworthy that the lower oxidation range of Au NPs (3.3–6.6 % and Pt NPs (20 %–40 % has mainly been observed when the laser ablation was performed using NIR‐Lasers (1030 nm and 1064 nm) with nanosecond pulse durations, which predominantly cause a high thermal load of the target lattice . On the other hand, the upper end of the oxidation range (shown in brackets in Table ) originates either from UV‐355 nm‐nanosecond laser ablation in case of Pt NPs (42 %–73 %) or ultrashort pulsed laser ablation using femtosecond laser pulses (800 nm) in case of Au NPs (12 %) .…”

“…Au � 1:7 3.3-6.6 [28,54,129] (12) [130] Pt � 1:2 20-40 [78,131] (42-73) [132] Pd � 0:85 71 [51] Ag � 0:8 80-84 [133] Ni � À 0:23 100 [56,134] [a] @pH = 0 j vs. NHE [128]; [b] (XPS) Reviews manganese, etc. leads to the partial or complete oxidation of the generated nanoparticles.…”

“…With respect to the laser parameters used in each cited experiment it is noteworthy that the lower oxidation range of Au NPs (3.3-6.6 % [28,54,129] and Pt NPs (20 %-40 % [78,131] has mainly been observed when the laser ablation was performed using NIR-Lasers (1030 nm and 1064 nm) with nanosecond pulse durations, which predominantly cause a high thermal load of the target lattice. [54,78,129,131] On the other hand, the upper end of the oxidation range (shown in brackets in Table 1) originates either from UV-355 nm-nanosecond laser ablation in case of Pt NPs (42 %-73 %) [132] or ultrashort pulsed laser ablation using femtosecond laser pulses (800 nm) in case of Au NPs (12 %). [130] Within both latter cases, a rather high energy deposition into the electron gas and hence higher electron temperatures are to be assumed.…”

“…[71] LAL-generated Pt NPs deposited on Pt electrodes caused an increase of charge (charge transfer) as measured by XPS, as well as an increased electrochemical surface area (ECSA) measured by cyclic voltammetry. [131] During electrophoretic deposition of surfactant-free NPs, the initial nanoparticle diameter does not change as annealing steps are being avoided. [153,236] Yet this method requires either catalyst support materials with low impedance or placement of the support material between the electrodes, forcing mass flow through the support.…”