Alpha a high performance frequency analyzer

Electrochemical impedance spectroscopy (EIS) measurements were performed with a Novocontrol Technologies Alpha-A High Performance Frequency Analyzer (Novocontrol Technologies GmbH & Co. KG, Montabaur, Germany). Impedance spectra between 100 Hz and 10 MHz were recorded at 200 distinct frequencies in total, applying a sinusoidal voltage of 10 mV amplitude. For the MEA electrode characterization, EIS was performed in a three-electrode arrangement using one MEA electrode as a working electrode (WE), a platinum wire as a counter electrode (CE), and a commercial Silver/Silver-Chloride (Ag/AgCl) (Dri-Ref short, World Precision Instruments, Inc., Sarasota, FL, USA) electrode as reference electrode (RE). These measurements were carried out in Dulbecco’s phosphate buffer saline (PBS) (purchased from Sigma-Aldrich Chemie GmbH, Munich, Germany).
To identify the optimum AC frequency for the electroporation pulse, we determined the normalized impedance, which describes the contribution of the cell layer to the total impedance. Hereby, two EIS measurements were conducted: one without the cells and one after 24 h, when the cells completely adhered to the MEA. These measurements were performed in cell culture medium and all 60 electrodes of the MEA were short-circuited to reduce the total impedance of the WE.

The measurements were performed on a Concept 41 BDS system (Novocontrol Technologies GmbH, Montabaur, Germany) consisting of an Alpha-A High Performance Frequency Analyzer and a Novocool System for temperature control. The samples were mounted between two gold electrodes with a diameter of 30 mm. The measurements were carried out in a temperature range between −100 and 20 °C and in a frequency range between 0.1 and 2 × 10⁷ Hz.

The PEDOT:PSS and PEDOT:PSS/GO films were initially investigated using EIS. The electrode under test was connected to the WE while an Ag/AgCl pellet served as the CE, and an electrochemical Ag/AgCl RE was connected to the RE port. A Novocontrol Technologies Alpha-A High-Performance Frequency Analyzer (Novocontrol Technologies GmbH & Co. KG, Montabaur, Germany) was used to measure the impedance spectra. The spectra were obtained in the frequency range between 0.1 Hz and 1 MHz, with an applied voltage amplitude of 10 mV in 1× PBS (pH 7.4) as the electrolyte.

The ionic conductivity of the LLZO samples was measured by electrochemical impedance spectroscopy (EIS) before and after the Li⁺/H⁺ exchange experiment. As electrodes, 200 nm thick Au layers were deposited on the top and bottom side of the samples using a MED 020 coating system (Bal-Tec AG, Liechtenstein). For the measurements, which were performed at room temperature (25 °C), an Alpha-A high performance frequency analyzer (Novocontrol Technologies, Germany) in the frequency range from 10 Hz or 1 kHz to 10 MHz was used.

The dielectric measurements were performed with an Alpha-A High-Performance Frequency Analyzer with a Novocool cryo-system (Novocontrol Technologies, Montabaur, Germany). The isothermal frequency sweeps, between 0.1 Hz and 2 × 10⁶ Hz, were performed in a temperature range from −100 °C to 70 °C with an increment of 5 K. Specimens with a thickness from 150 µm to 250 µm were mounted between two round gold-plated electrodes in a plate-capacitor arrangement with a diameter of 30 mm.

The morphology of synthesized CDI-Cu NF was investigated using variable pressure field-effect scanning electron microscope (VP-FESEM, Model: Zeiss Supra 55 VP), 3D-Nanoprofiler (Hawk 3D Optical Surface Profiler from Pemtron Co.Ltd., South Korea), and high-power microscope (Olympus, Japan). Elemental analysis of NF and different chemically modified surfaces were carried out using EDX and mapping method. The chemically modified different LSG surfaces were analyzed elementally using field-transform infrared spectroscopy (FTIR, Model: Perkin Elmer Spectrum One). All the capacitance measurements were carried out at room ambient using a standard two-electrode system (Alpha-A High-Performance Frequency analyzer, Novocontrol Technologies, Germany) in 4 µl PBS as a working solution. The frequency range was set with 1 to 100 kHz and Vrms at 10 mV.

Electrical measurements were conducted to analyze signals transduced by the Ag-Ab binding reaction from the PSNG electrode, which were probed via the Au contact pad on the LOC (Fig A in S1 File). AC measurements were conducted using an impedance spectrometer (Alpha-A High Performance Frequency Analyzer, Novocontrol Technologies, Hundsangen, Germany). A two-wire probe station was used with the impedance spectrometer to measure capacitance (C), permittivity (ε), loss tangent (tan δ) and conductivity (σ). Measurement was started at 0.1 V with a scaling factor of 1.4 and a frequency range of (1 x 10⁰ to 1 x 10⁶ Hz). The loss tangent (tan δ) value was continuously monitored during capacitance measurement to ensure it stayed below 100, indicating that the immunosensor was behaving as a capacitor. A Kiethley 6487 Picoammeter was used to measure current-voltage DC characteristics of the PSNG electrode, from which amperometric characteristics and sensitivity of the immunosensor could be analyzed. At each step during hCG detection, the PSNG electrodes were washed with DI water to ensure that measurement data were valid.