Emstat

Amperometry and cyclic voltammetry were performed by EmStat (Palmsens, Houten, The Netherlands) either in stirred beaker or in a flow-through cell of own construction. Magnetic stirrer (IKA, Staufen, Germany) was used for amperometric measurements in first part of this work. pH of solutions was determined by a pH meter (WTW inolab, Burladingen, Germany). Peristaltic pump Minipuls MP3 (Gilson, Villiers-le-Bel, France) with silicone tubes also from Gilson was used for amperometric measurements with the enzyme. Photoelectrochemical measurements were realized with different types of LEDs (green 525 nm, blue 470 nm, UV 395–400 nm and white) operated under stabilized working current. The working current for each LED was kept within the lower half of the maximum allowed operating current. The individual LED currents were adjusted using the Fiber Optic Spectrometer 2048XL (Avantes, Apeldoorn, The Netherlands) to achieve equal photon counts. The electrochemical current response signal was then measured at 500, 700 and 1200 mV applied to the ITO electrode, in plain PBS and with NADH.

Experiments were conducted under ambient conditions, using an EmStat (PalmSens), single-channel potentiostat. Cluster solution mixtures were prepared inside the anaerobic chamber. All solutions were purged with N₂ for 15 min prior to analysis, to ensure that no O₂ was trapped during the transfer from the anaerobic chamber to potentiostat. A conventional three-electrode cell composed of a glassy carbon working electrode, a Ag/AgCl reference electrode (Alvatek, RE-5B 3 M NaCl, +209 mV vs. standard hydrogen electrode (SHE)) and a platinum wire counter electrode was used for the electrochemical measurements. We did not explicitly add a supporting electrolyte, to minimize interference with cluster formation (as occurred with bicarbonate). However, ~0.01 M NaCl was present in samples through acid-base titrations. Relatively low ionic strength electrolytes, notably NaCl, have been shown to diminish coagulation of FeS nanoparticles^{91 (link)}, and NaCl is clearly of prebiotic relevance in marine environments. The working electrode was cleaned with 0.05 μm aluminium oxide slurry on a polishing cloth and thoroughly rinsed with double-distilled H₂O before each experiment. Data were recorded using PSTrace software (v5, PalmSens).