Palmsens3

We electroplated Pt black on the Pt microelectrodes to improve the quality of their recording. The Pt black plating solution contained 3% hexachloroplatinic acid hydrate (520896-5G, Sigma-Aldrich, USA), 0.025% HCl (4090-4400, DAEJUNG, South Korea), and 0.025% lead acetate (316512-5G, Sigma-Aldrich, USA) in deionized water^{17 (link)}. The tip of the neural probe was immersed in the plating solution with a reference electrode (Ag/AgCl wire) and a counter electrode (Pt wire). The Pt microelectrodes were electroplated selectively by applying the electrical potential (–0.2 V, 35 s) through a potentiostat (PalmSens3, PalmSens, Netherlands).
To measure the impedance of the Pt black microelectrodes, we immersed the tip of the neural probe in 0.1 M phosphate-buffered saline solution (21-040-CV, CORNING, USA) with the reference electrode (CHI 151, CH Instruments, Inc., Austin, TX, USA). The impedances of the 16 microelectrodes were measured by a frequency sweep mode (10 Hz–10 kHz) using an impedance analyzer (nanoZ, Neuralynx, Bozeman, Montana, USA).

The screen-printed carbon electrodes (SPCEs) utilized in this work (PalmSens B.V., Randhoeve, The Netherlands) possessed a conventional three-electrode configuration constructed on a corundum ceramic base of the dimensions 25.4 mm × 7.26 mm, with a carbon working electrode (WE), a silver reference electrode (RE), and a carbon counter electrode, which acted as the auxiliary electrode (Figure 1). CV measurements were obtained at constant room temperature with the help of a potentiostat (PalmSens3™, PalmSens B.V., Randhoeve, The Netherlands), which was operated through the PSTrace software (version 5.8), as described elsewhere [23 (link)].

Electrochemical measurements were performed either at the Solar Simulation Lab (Viterbi Faculty of Electrical Engineering, Technion) using a Zennium electrochemical workstation (Zahner Elektrik) and a solar simulator light source (Oriel Sol3A), or at the Hydrogen Lab (Grand Technion Energy Program) with an nStat multichannel potentiostat (Ivium) and a Xenon lamp solar simulator (Abet). For some measurements, we used a Palmsens3 (Palmsens) potentiostat and A1 light line (Sciencetech). All measurements were carried out in a three electrodes configuration under the illumination of one solar unit (1SU). Graphite (Graphite Store, pn#bl001230) was used as a working electrode, a Pt electrode (ALS) served as the counter electrode and a Ag/AgCl/3 M NaCl as a reference electrode (ALS). For each measurement, a sample containing 150 µg of chl a was placed on the 1.8 cm diameter graphite electrode. The sample was not stirred or replaced during the measurement. The medium was phosphate buffer (100 mM phosphate, pH 6) containing 100 mM NaCl. When indicated, 150 µM of DCMU was added. For the ΔpsbA mutant, chlorophyll amount of 50 µg was used. For the relevant electrochemical measurements, 6 mM of D-glucose in the absence or presence of 5 mM iodoacetic acid (sodium salt) were added.

Measurements were acquired on a PalmSens3 using the MUX8 multiplexer with a common reference and a common ground. For EIS, the direct-current offset (DC offset) was placed at the redox potential of the redox reporter, determined through identifying the voltage at which the impedance reached a minimum while sweeping voltage at a frequency of 100 Hz (~0.2 V vs. Ag/AgCl for ferricyanide). EIS spectra were then acquired for each channel (up to 6 channels per experiment) with an AC_RMS amplitude of 5 mV from 5000 Hz to 1 Hz. Analysis of each spectra was performed using software provided by Palmsens through fitting to a modified Randle’s cell as done previously (Figure S3) [37 (link),38 (link)]. The resistance to charge transfer (R_CT) was recorded and further analyzed for each electrode in each condition.
Square wave voltammetry (SWV), electrochemical voltammograms were acquired by sweeping potential at 10 Hz and 20 mV AC amplitude from 0.05 V to 0.3 V, with a step-size of 1 mV when using ferricyanide redox reporters (Figure S4). When methylene blue was the redox reporter, the amplitude was changed to 10 mV and the scan was changed to sample from −0.15 to 0 V. Each spectrum had the observed peak current reported.

Cyclic (CV) and square wave (SWV) voltammograms were acquired using a handheld potentiostat (PalmSens3, PalmSens BV, The Netherlands) with the supplied PSTrace 5.3 software in a three-electrode setup. The following parameters were used for all the SWV measurements: pulse amplitude of 100 mV, potential step of 5 mV, and 50 Hz of frequency. Prior to the DNA measurements by SWV, the sample reservoir was cleaned with DNA decontamination reagent (Fisher Scientific) followed by Nuclease-free ultrapure water (Fisher Scientific).

All electrochemical assays were conducted in triplicate, at room temperature (25 ± 1 °C), performed in a low temperature-synthesized gold screen-printed electrode (BT 220, DropSens, Asturias, Spain, working and auxiliary electrodes are made of gold, while reference electrode is available in silver) using the potentiostat PalmSens 3 (PalmSens, Houten, The Netherlands) with the PSTrace 5.4 software (PalmSens, Netherlands).