Chi111

Mercaptohexanol (MCH), phosphate buffered saline (PBS), MgCl, Tris(2-carboxyethyl)phosphine hydrochloride (TCEP), serum, and vancomycin were purchased from Sigma-Aldrich (St. Louis, MO, USA). vancomycin aptamer, [/5ThioMC6-D/CGAGG GTACC GCAAT AGTAC TTATT GTTCG CCTAT TGTGG GTCGG/3MeBlN/] with conjugated methylene blue and thiol ends, was purchased from Integrated DNA Technologies (Coralville, IA, USA) and has been previously characterized. [18 (link)] The vancomycin aptamer is often used as a vehicle for wider aptamer research and was therefore an ideal test aptamer for proof-of-concept testing with peak-tracking software (vancomycin detection is not the focus of this paper). Controlled-temperature test enclosures (Happybuy Reptile Incubator 25L) and faradaic shields (TACKMETER WiFi Router Shield, and Electriduct ½” Tinned Copper Metal Braid) were purchased from Amazon (Seattle, CA, USA). A 2 mm gold rod (CHI101), Ag/AgCl reference (CHI111), and Pt counter electrodes (CHI115) were all purchased from CH Instruments (Austin, TX, USA). Polishing pads, and 0.3- and 0.05-micron alumina slurry (ET030) were purchased from eDAQ (Colorado Springs, CO, USA).

The surface morphology of the BDD nucleation and growth sides was studied using SEM (6610 V; JEOL Inc., Peabody, MA, USA). The surface chemistry of both sides was analyzed using Raman spectroscopy (532 nm Laser; HORIBA Scientific Inc., Kyoto, Japan). The surface resistivity of the BDD film was measured using a four-point probe. The electrochemical impedance of the electrodes was measured using EIS (CHI604; CH Instruments, Inc., Austin, TX, USA). The electrochemical properties of the BDD electrodes were characterized using CV (CHI604; CH Instruments, Inc., Austin, TX, USA) in a three-electrode configuration. During the experiments, the DA solution was prepared by dissolving DA in a 0.1 M, pH = 7.4 PBS buffer solution. The effect of AA interference on DA detection was evaluated using SWV measurements (CHI604; CH Instruments, Inc., Austin, TX, USA). Experimental solutions were prepared by serially diluting DA in a mixture of 100 µM AA and 0.1 M, pH = 7.4 PBS. For the three-electrode setup, an Ag/AgCl reference electrode (CHI 111; CH Instruments, Inc., Austin, TX, USA) was used, while a commercially available Pt wire (CHI 102; CH Instruments, Inc., Austin, TX, USA) was used as the counter electrode. Hexaammine-ruthenium (III) chloride (Ru(NH₃)₆Cl), KCl, DA, and AA were purchased from Sigma Aldrich.

Cyclic voltammetry was used for electrochemical study of diazepam. For the cyclic voltammetry, a CHI 800C potentiostat was used. A three-electrode system consisted of the glassy carbon working electrode (CH Instruments, USA, model CHI104, 3 mm in diameter), Ag/AgCl reference electrode (CH Instruments, USA; CHI111), and platinum wire as auxiliary electrode. pH measurements were performed using WTW720 pH-meter equipped with SenTix 81 pH electrode. Prior the cyclic voltammetry experiments, all solutions were purged with oxygen free nitrogen for 15 minutes.
Cleaning of glassy carbon electrodes was performed mechanically on a polishing pad using aluminium paste of different grain sizes (1, 0.3, and 0.05 µm, Buehler, USA). It was washed with distilled water between each paste, and after the finest paste, it was washed with methanol, distilled water, and then air-dried. This process was repeated each day before the start of the recording and in the case if detector response was not reproductive.

Voltammetry and impedance spectroscopy experiments were conducted using a potentiostat (SI 1287A, Solartron) equipped with an impedance analyzer system (Model 1260A, Solartron), which were configured in parallel. CorrWare and ZPlot software packages were utilized for data collection and processing. For all experiments, the positioning of counter and reference electrodes remained constant to ensure minimal deviations. EIS analyses were performed in the frequency range between 1.0 MHz and 1.0 mHz, with an amplitude of 10 mV. To fit the Nyquist plots, The ZView software package was employed to fit the Nyquist plots. For all measurements, an Ag/AgCl (3.0 M KCl) (CHI 111, CH Instruments) was utilized as the reference electrode (RE), while a custom-made Ti/Ta₂O₅-IrO₂ with a surface area of 3 × 1 cm² was used as the counter electrode (CE) for boosted stability. All recorded potentials in this study were converted to the Reversible Hydrogen Electrode (RHE) reference scale according to the following equation: $$E\left(\mathrm{vs}.\mathrm{RHE}\right)=0.197\mathrm{V}+0.059\mathrm{V}\times \mathrm{pH}+E\left(\mathrm{vs}.\mathrm{Ag}/\mathrm{AgCl}\right)$$

The interactions of gold compounds with protein have been performed in solution by electrochemical investigations Voltammetry measurements were performed with an electrochemical workstation (CHI1140A, CH Instruments Inc., Austin, TX, USA). The Ag/AgCl reference electrode (in 3M KCl, CHI111, CH Instruments Inc), Glassy carbon working electrode (CHI 112, CH Instruments Inc) and platinum wire counter electrode (CHI115, CH Instruments Inc) inserted into the 5.0 ml glass cell. Due to the poor solubility of the present compounds in water, their solutions were prepared in ethanol. The GCE was polished as a mirror like surface with alumina slurry on the synthetic cloth before every electrochemical analysis. The cyclic voltammetry (CV) and square wave voltammetry (SWV) were scanned from −0.4 to 1.0 V for various analyses for compounds 1–3 in the absence and in the presence of different concentration of lysozyme under physiological environment.