Dropsens

Cyclic voltammetry scans were run for PAN fibers and PAN:PEDOT:PSS fibers using working and auxiliary carbon screen printed electrodes (SPEs) and an Ag|AgCl reference electrode (Metrohm DropSens, Herisau, Switzerland), connected to a potentiostat (400B Electrochemical Analyzer, CH Instruments, Austin, TX, USA). Fiber samples were deposited on the working electrode surface. The electrodes were dipped in 2.5 mL of degassed PBS 0.01 M, pH 7.4, as electrolytic medium. Cycles were run in a potential window of −0.7 V to +0.7 V, with scan rates ranging from 0.01 V s⁻¹ to 0.2 V s⁻¹.

In order to study the optical properties of the produced graphene films, graphene from solution was deposited onto glass substrates with dimensions of ca. 2 cm × 1 cm (Figure 2a). Although a great number of different types of substrate materials have been used, such as silica [37 (link)], chromium [38 (link)], tin [39 (link)], silver [40 (link)], or platinum [41 (link)], glass substrates were used in this paper. Glass is generally a popular choice, not just because glass slides are inexpensive and widely available, but also because the optical characteristics of deposited films can be subsequently examined [42 (link)]. For measuring the electrical resistance, the film was deposited onto Metrohm DropSens substrates with a pair of interdigitated electrodes (G-IDEPT10, Oviedo, Spain, Figure 2b). Using an automated pipette, the entire specific volume of the graphene dispersion in NMP was vertically dripped onto the surface of deionized water. Because the volumes ranged from 250 to 1000 µL, while the amount of graphene in that volume was kept fixed, the concentration of graphene was varied. As the film of graphene formed on the surface of the water, the LB method was used to deposit the film onto the target substrate [32 (link)].

Polyethyleneimine (PEI) and graphene oxide (GO), utilized for the preparation of thin films, were purchased from Sigma-Aldrich. Standards of acetone (C₃H₆O; 58.08 gmol⁻¹; 99.0%) and isopropanol (C₃H₈O; 60.10 gmol⁻¹; 98.0%) were purchased from Laborspirit-Labchem. Standards of ethanol (C₂H₆O; 46.07 gmol⁻¹; 99.8%) and methanol (CH₄O; 32.04 gmol⁻¹; 99.8%) were obtained from Honeywell. Standard of acetic acid (C₂H₄O₂; 60.05 gmol⁻¹; 99.8%) was purchased from Fisher Scientific. The ceramic-based sensor supports with deposited gold interdigitated electrodes (IDE) were acquired from Metrohm DropSens (length: 22.8 mm; width: 7.6 mm; thickness: 1 mm; electrodes width: 200 μm; distance between electrodes: 200 μm).

All blood cultures were tested after the blood culture flagged positive as recommended by the manufacturer. For aerobic blood culture, a 40 μL sample was mixed with 40 μL of reagent and incubated 1 h at 37 ± 2°C. For anaerobic blood culture, a pre-analysis was needed: a 500 μL sample was centrifuged one time 2 min at 6,000 g; the pellet was re-suspended into 500 μL of NaCl solution (0.9%) and re-centrifuged 2 min at 6,000 g; this second pellet was suspended into 40 μL of buffer and 40 μL of reagent; the mix was incubated 1 h at 37 ± 2°C. After this incubation, 20 μL of the mix was placed on the ceramic electrode and after in the sensor. The reagent includes a “false” 3GC substrate which is hydrolysed when there is a 3GC β-lactamase, this frees an electro-conductive product. The intensity of the electrochemical signal [measured by DropSens (Metrohm, Villebon Courtaboeuf, France)] is posted in nanoAmpere (nA). The threshold of positivity is 80 nA for blood culture.

An electrochemical analyzer Autolab/PGSTAT302N (Metrohm Autolab, Utrecht, Netherlands) controlled by the Nova 2.1. software was used for constant potential amperometry experiments. The electrochemical (EC) behavior of maraviroc was investigated on platinum (Pt), gold (Au) and glassy carbon (GC) SPE working electrodes (respectively 550, 220BT and 110; Metrohm DropSens) in which Ag-serves as a pseudo-reference electrode with platinum, gold and carbon electrodes as auxiliary electrodes, respectively. Measurements were carried out by applying a potential 1400 mV for 5 min, with a scan rate 100 mV s⁻¹ and interval time 0.5 s. A solution of phosphate buffer at pH 7.4, and acetonitrile 50:50 (v/v) was used as a supporting electrolyte, in which a stock solution of maraviroc (2 mg mL⁻¹) was diluted to prepare a working solution (0.01 mg mL⁻¹). All the experiments were carried out at room temperature, by placing an 80 µL drop of solution on the surface of the SPE to cover all three electrodes.

We manually
applied 10 × 10 mm pieces of the solid polymer electrolyte to
cover the working, auxiliary and pseudoreference electrodes of commercial
screen-printed PEDOT and carbon electrodes reference P10 and DRP-110,
respectively (DropSens, ES). A SPELEC UV–vis spectroelectrochemistry
apparatus (Metrohm-Dropsens, ES; DropView SPELEC software) was used
for the spectroelectrochemical experiments. The transmission cell
(TRANSCELL; DropSens, ES) was used in the experiments. Unless otherwise
stated, all potentials are reported versus Ag. In all cases, the open
circuit potential (OCP) was determined first to ensure that all subsequent
experiments started at a zero-current level.

A customized SPELEC instrument (Metrohm-DropSens), controlled by DropView SPELEC software (Metrohm-DropSens), was used to perform SEC experiments. Our group in collaboration with Metrohm-DropSens has developed this instrument. Matlab R2018a and R x64 3.6.2 were used to carry out the data processing.