Pgstat204

All electrochemical measurements were performed in an AutoLab PGSTAT204 potentiostat/galvanostat with an impedance module FRA32M managed by NOVA 2.1.4 software (Metrohm, Utrecht, Netherlands). Cyclic voltammetry (CV) measurements were performed from 0.0 to +1.2 V, at a scan rate of 50 mV s⁻¹, and chronoamperometry measurements at an applied potential of +0.55 V were used for the determination of L-cysteine. On the other hand, electrochemical impedance spectroscopy (EIS) was recorded from 100 kHz to 0.10 Hz, with an amplitude of 10 mV, and square wave voltammetry (SWV) measurements were performed with an amplitude of 80 mV, a frequency of 80 Hz, and a step potential of 10 mV. EIS and SWV were applied for the detection of the SARS-CoV-2 spike protein. For these analyses, 0.10 mol L⁻¹ KCl (pH 7.0) was used as a supporting electrolyte, and an equimolar mixture of 5.0 mmol L⁻¹ [Fe(CN)₆]^3−/4− was applied as a redox probe. The EIS measurements were calibrated by normalized impedance change (NIC%) [43 (link),44 (link)] concerning the control. The NIC% value was calculated using Equation (1), where, in this case, Zcontrol is the magnitude of charge transfer resistance (Rct) for a control sample without the antigen, and Zsample is the magnitude of Rct for each added point of concentration of the antigen.
$$NIC\%=\frac{Z_{sample}-Z_{control}}{Z_{control}}\times 100$$

The oxygen concentration in the glovebox atmosphere was less than 1% throughout the experiment. Such a low oxygen content was verified with chronoamperometric readings at potentials of −750 mV_Ag/AgCl and −850 mV_Ag/AgCl [16 (link)]. The results (Figure 2) showed that the oxygen content was negligible, for negative current density values are associated with oxygen reduction whilst values near zero are indicative of an inert atmosphere and those above zero of anodic behaviour in the steel.
Three techniques were deployed to assess specimen electrochemical behaviour: linear polarisation resistance (LPR); electrochemical impedance spectroscopy (EIS); and chronopotentiometry (CP). All three measure the open circuit corrosion potential (OCP) and polarisation resistance (Rp) values from which corrosion rate can be calculated. The EIS and CP findings can also be used to determine the resistance drop (R_Ω) value. All the readings were recorded on a Metrohm Autolab PGSTAT204 potentiostat/galvanostat. In the electrochemical cell used, saturated concrete was the medium, a steel bar the working electrode, stainless steel mesh the auxiliary electrode, and saturated Ag/AgCl solution the reference electrode. The electrochemical readings were logged over 232 days on duplicate samples.

All the reagents used in this study were of analytical grade, obtained from Fisher (Hampton, VA, USA), Dinâmica (Indaiatuba, Brazil), Sigma-Aldrich (St. Luis, MO, USA), or Fluka (Buchs, Switzerland) and the solutions were prepared using purified water Heal Force^® (resistivity ≥ 18.2 MΩ cm). The electrochemical measurements (cyclic voltammetry (CV), open circuit potential (OCP), and square wave voltammetry (SWV)) were performed, using a potentiostat/galvanostat PGSTAT204 (Metrohm Autolab, Utrecht, The Netherlands) managed by Nova 2.1.5 software (Metrohm Autolab, Utrecht, The Netherlands, available for free download). Cyclic voltammograms were achieved using a 0.1 mmol L⁻¹ ferricyanide potassium and 0.1 mol L⁻¹ KCl solution (both obtained from Sigma-Aldrich^®, St. Luis, MO, USA), as a redox probe and supporting electrolyte, respectively.

A DIW digital material depositor (DMD100
from Kellenn Technologies, FR) was used for the fabrication of bare
Gr electrodes.
The printed devices were morphologically characterized
by means of a digital microscope (AM4815ZTL from DinoLite, NE) and
a field emission-scanning electron microscope (MerlinFE-SEM from Carl
Zeiss, GE) with an energy-dispersive X-ray spectroscopy (EDX) analysis
system. Electrochemical performance was tested by using a potentiostat
μAutolab (PGSTAT204 from Metrohm Autolab BV, NE). Stock solutions
of H₂S were standardized using a commercial S^2– ion-selective electrode (Thermo Scientific Orion Star, USA) coupled
to a pH/ISE SB90M5 measurement system (SympHony, USA).
Real
samples were compared to a SULF-10 commercial H₂S gas sensor
coupled to a X-5 UNIAMP multimeter both from Unisense,
DK.