Te100

Cyclic voltammetric and amperometric experiments were performed using the CHI 1240B electrochemical workstation (CH Instruments, Austin, TX, USA) with a conventional three electrode system. A three electrode type of SPE (TE100, CH Instruments) consisting of a Ag/AgCl reference electrode, a carbon counter electrode, and a carbon working electrode modified with MWCNT or electrochemically reduced graphene oxide (Er-GR) was used as sensing element. The surface area of the working electrode was 0.071 cm². The electrode was equilibrated in 0.1 M PBS electrolyte by performing cyclic voltammetry until the voltammogram became constant. Cyclic voltammetric characterizations were performed in the voltage range between −1 to +1 at a scan rate of 50 mV s⁻¹. Amperometric (time vs. current) measurements were done for 300 s and the stable current at 200 s was used to study the performance of the sensor. The morphological scanning electron microscope (SEM) images were obtained using a Zeiss Merlin field emission SEM (Carl Zeiss, Jena, Germany) at 2 keV.

Screen-printed electrodes were purchased from CH Instruments, Inc. (TE100, Bee Cave, TX, USA). The SPE pattern included 3 mm diameter carbon working electrode, carbon counter electrode, and Ag/AgCl reference electrode. Hydrogen tetrachloroaurate(iii) trihydrate (HAuCl₄·3H₂O), sodium citrate, hydrochloric acid (37%), and sodium hydroxide, were supplied by ACROS Organics. Arsenic trioxide (As₂O₃) was purchased from Sigma Aldrich. All other reagents were obtained either from Sigma Aldrich or Fisher Scientific with the highest grade available and were used without further purification. All solutions were prepared using deionized (DI) water with a resistivity of 18.2 MΩ cm at room temperature (Ultrapure Water System, Millipore, and Billerica, MA, USA). A 20 mM primary stock solution of As(iii) was prepared by dissolving As₂O₃ (solubility in water at 25 °C is 20 g L⁻¹) in DI water. To produce a standard calibration curve for As(iii), different concentrations (0.001 mM, 0.01 mM, and 0.1 mM) of As(iii) solutions were prepared by diluting the primary stock solution using DI water. Tap water samples were from our laboratory at the University of Wisconsin-Madison, WI, which did not contain any visible sediments so samples were not filtered prior to use.

The three electrode electrochemical workstation CHI 1240B (CH Instruments, Austin, TX, USA) was used for cyclic voltammetric and amperometric studies. Screen printed electrode (TE100, CH Instruments, Austin, TX, USA) comprising of carbon counter electrode, an Ag/AgCl reference electrode, and anti-CRP functionalized AuNPs modified working electrode were used as immunosensor strip. The working electrode surface area was 0.071 cm². Once the preparation was accomplished, the immunosensor strip was equilibrated in PBS cycling the voltammetric potential between −0.6 V and +0.6 V until the current stabilised. A scanning electron microscope (SEM) (Carl Zeiss, Jena, Germany) with an electron energy adjusted to 2 keV was used to obtain the morphological images of the samples.