2.1. Materials and Instruments

Spike protein, arbidol, chloroquine diphosphate, hydroxychloroquine sulfate, ribavirin, bromhexine, horseradish peroxidase (HRP), and bovine serum albumin (BSA) were purchased from Sigma-Aldrich (Shanghai) Trading Co, Ltd. (Shanghai, China), and Shuanghuanglian oral liquid was obtained from Harbin Pharmaceutical Group Sanjing Pharmaceutical Company Limited (Harbin, China). Sodium citrate and chloroauric acid were purchased from Tianjin Yingdaxigui Chemical Reagent Factory (Tianjin, China). NaOH and H₂O₂ were obtained from Tianjin Jindong Tianzheng Fine Chemical Reagent Factory (Tianjin, China). Thionin and glutaric dialdehyde were obtained from Shanghai yuanye Bio-Technology Company Limited (Shanghai, China). Acetic acid and chitosan were purchased from Guangzhou Haoying Chemical Technology Company (Guangzhou, China). All reagents used herein were of analytical grade, and ultrapure water was used in all experiments.

The CHI 660E electrochemical workstation and three-electrode system (glassy carbon electrodes ((GCE, Φ = 3 mm): Ag/AgCl reference electrode and platinum wire (Pt) counter electrode) were bought from Shanghai Chenhua Instrument Co., Ltd. (Shanghai, China), whereas the Millipore Milli-Q Pure Water System was provided by Shanghai Yarong Biochemical Equipment Co., Ltd. (Shanghai, China). The Tecnai G2F20 transmission electron microscopy (TEM) was purchased from Philips and was used for the characterization of gold nanoparticles using 200 KV of acceleration voltage. The Dimension 3100 atomic force microscope (AFM) from Veeco (Plainview, NY, USA) and the Quanta FEG 250 scanning electron microscopy (SEM) from FEI (Hillsboro, OR, USA) were used for the characterization of the sensor assembly process.