*2.1. Chemicals and Reagents*

Sodium tungstate dihydrate (Na2WO4·2H2O), ammonium oxalate monohydrate ((NH4)2C2O4·H2O), ascorbic acid (AA), cadmium chloride hemi(pentahydrate) (CdCl2·2.5H2O), and 6-mercapto-1-hexanol (MCH) were obtained from Macklin (Shanghai, China). Potassium tellurite (K2TeO3), chloroauric acid (HAuCl4), 1-ethyl-3(3-dimethylamin opropyl) carbodiimide hydrochloride (EDC), ethanol, Tris (2-carboxyethyl) phosphine (TCEP), and *N*-hydroxysuccinimide (NHS) were purchased from Aladdin (Shanghai, China). Sodium borohydride (NaBH4) and thioglycolic acid (TGA) were obtained from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Tryptone, yeas<sup>t</sup> extract powder, and agar (bacteriological) were obtained from Qingdao Hope Bio-Technology Co., Ltd. (Qingdao, China). Tris HCl solution, Exonuclease I (Exo I), and phosphate-buffered saline (PBS) were purchased from Sangon Biotech Co., Ltd. (Shanghai, China). Raw chicken was

purchased from a local supermarket. *Listeria monocytogenes* (ATCC 19115), *Staphylococcus aureus*, *Escherichia coli O157:H7*, and *Salmonella typhimurium* were obtained from China General Microbiological Culture Collection Center (Beijing, China). The DNA strands used were ordered from Sangon Biotech Co., Ltd. (Shanghai, China). All DNA sequences are summarized as follows: aptamer (Ap), 5-NH2-(CH2)6-ATA CCA GCT TAT TCA ATT CCA AAA GCG CAC CCA TAT ATG TTC TAT GTC CCC CAC CTC GAG ATT GCA CTT ACT ATC T-3 [46]; and aptamer-complementary DNA (cDNA), 5-GTG CGC TTT TGG AAT TGA ATA AGC TGG TAT TTT TTT-(CH2)6-SH-3.
