Emstat3

Electrodes were mechanically characterized via the scotch tape test in order to test whether they were sufficiently adhered to the glass substrate. Additionally, electrodes were characterized by cyclic voltammetry. A commercial portable potentiostat (Emstat 3, Palmsens) controlled by PSTrace software was employed for all voltammetric studies. The planar electrodes were also imaged by scanning electron microscopy; standard imaging was performed on a JEOL JSM 6010 LA (JEOL, Japan) and high-resolution imaging on a Zeiss Auriga Cross Beam. SEM images were obtained using 3 separate electrode devices to ensure reproducibility. Samples were mounted onto metal stubs with double sided carbon tape and gold-coated with an automated sputter coater (Emtech K575X, Quorum Technologies) for 10 min prior to imaging.

The competition of hydrogen peroxide and luminol for HO^• as their oxidant was studied by electrochemiluminescence spectroscopy with a Cary Eclipse Fluorescence spectrophotometer, using a spectroelectrochemical cell from BASi (EF-1362) fitted with a platinum gauze as the working electrode, a platinum wire as the counter electrode, and an Ag/AgCl/KCl (sat.) as the reference electrode. All electrochemical measurements were performed using a potentiostat from PalmSens BV (EmStat3). All potentials are reported against the SHE. The electrochemiluminescence intensity was measured at the peak maxima (425 nm) at an applied potential of +1.2 V in a solution containing 5.0 × 10⁻² M luminol, 0.1 M sodium hydroxide, and concentrations of hydrogen peroxide ranging from 1 × 10⁻³ to 0.5 M. The platinum electrodes were cleaned after each measurement by electrochemical cycling (20 cycles at a sweep rate of 0.1 V/s) in 0.5 M aqueous nitric acid and then rinsed with Milli-Q^™ water.

The electrochemical tests were conducted by the PalmSens EmStat3 handheld potentiostat, which was operated by the PS Trace software version 5.9. The optimization of the synthesized material was conducted through the cyclic voltammetry measurements in a 10 mM ferricyanide solution. This involved applying a potential range of −0.2 to 0.9 V, with a scan rate of 100 mV s⁻¹. Subsequently, the electroanalytical characteristics of the microneedle sensor that was constructed were evaluated in a 0.1 M phosphate-buffered saline (PBS) solution at a pH of 7, as well as in an artificial ISF solution. This evaluation was conducted with square wave voltammetry and amperometry transduction techniques. In square wave voltammetry, a potential range ranging from −0.2 to 1 V was applied, employing optimum settings including a frequency of 10 Hz, a step potential of 10 mV, and an amplitude of 50 mV. Chronoamperometric measurements were conducted using an applied potential of 0.3 V relative to Ag/AgCl for a duration of 60 seconds. The stability of the sensor was assessed through chronoamperometry over an extended duration. The selectivity of the sensor was evaluated by employing the chronoamperometry technique in the presence of various common interfering compounds. The efficacy of the microneedle sensor has been shown by its application in a gel-mimicking model.

Cyclic voltammetry (CV) measurements were performed using a PalmSens EmStat 3+ potentiostat connected to a personal computer using the PSTrace 7.4 software, whereas electrochemical impedance spectroscopy (EIS) measurements were performed using an Ivium-n-Stat Multichannel Electrochemical Analyzer. For CV and EIS measurements, a three-electrode system was used with an Ag/AgCl reference electrode (CH Instruments, Inc. Austin, TX, USA), a platinum-mesh counter electrode (Sigma Aldrich, Gillingham, UK), and an ITO-coated glass slide working electrode. The electrodes were in a biomedically relevant buffer (4 mL of phosphate-buffered saline [PBS] at pH 7.4).
For CV measurements, the potential was swept between −1.0 V and +1.0 V vs. the Ag/AgCl electrode at a scan rate of 0.05 Vs⁻¹.
For EIS measurements, the PBS also contained [Fe(CN₆)]^3−/4− (5 mmol L⁻¹), and measurements were performed with an open-circuit potential of 230 mV, with an amplitude of applied potential perturbation of 10 mV in the frequency range of 0.1–105,000 Hz. The Nyquist plots were obtained to ascertain the electron-transfer resistance (R_et).

Chronoamperometric studies were completed using a PalmSens EmStat 3+ potentiostat connected to a computer and PSTrace software (v. 7.4) supplied by Alvatek; Tetbury, UK). The cell comprised a three-electrode system with an Ag/AgCl reference electrode, an Au counter electrode and a glassy carbon working electrode with the sample material on its surface in PBS (0.01 M, 4 mL). Prior to each experiment, there was ‘quiet time’ for 10 s, the initial potential was 0 V, the high potential was 0.7 V, the low potential was −0.5 V, the initial scan was positive, the current was measured at 1 mV intervals, the scan rate used for all experiments was 50 mV s⁻¹ and the stimulation lasted 62 s. After stimulation of the material, the cell was allowed to rest for 24 h to allow the released drug to equilibrate in the PBS solution. After allowing the drug to equilibrate in solution post stimulation, a 10 µL aliquot was taken from the electrolyte solution and diluted with 100 µL of PBS before being frozen prior to analysis. Passive release controls were run in parallel with the electrically stimulated samples.

The electrochemical measurements were carried out in a 10-mL electrochemical cell in ambient atmosphere and under stirring. The potentiostat was the EmStat3 (Palm Sens) and controlled by the PS Trace 4.2 software (Palm Sens). For the DPV measurements, a potential of − 1.4V for 120 s was applied to the WE followed by a DP scan (modulation amplitude, 50 mV; increment, 10 mV; pulse width, 75 ms; and pulse repeat time, 50 ms) and the DP voltammogram was recorded. The DPV peak of GLU appeared at about − 1.2 V. The cyclic voltammograms were obtained in 0.1 mol L^-1 PB (pH 4) containing GLU at a scan rate of 50 mV s^-1, after polarization of the WE − 1.4 V for 120 s. The connection of the three electrodes of the device to the potentiostat was accomplished using crocodile clips. All the potentials are referred with respect to the 3D-printed CB/PLA pseudo-reference electrode.

Cyclic voltammograms were measured
using a PalmSens EmStat3 potentiostat with PSTrace electrochemical
software. Analyte solutions with a typical concentration of 1.5 mmol
dm^–3 were prepared using dry MeCN, freshly distilled
from CaH₂. The supporting electrolyte was NⁿBu₄PF₆, being recrystallized
from EtOH and oven-dried prior to use with a typical solution concentration
of 0.2 mol dm^–3. The working electrode was a glassy
carbon disk; Pt wire was used as a counter electrode, and the reference
electrode was Ag/AgCl, being chemically isolated from the analyte
solution by an electrolyte-containing bridge tube tipped with a porous
frit. All potentials are quoted relative to the Fc⁺/Fc
couple as an internal reference.