*2.1. Materials*

HAuCl4·3H2O (99%), β-CD (97%), BaP (96%), Pyr (98%), and Nap (99%) were purchased from Sigma-Aldrich. Na2HPO4, NaCl, acetone, methanol, and cyclohexane were obtained from Sinopharm Chemical Reagent Co., Ltd.(Shanghai, China), PTFE (pore size 0.1 μm, thickness 70 μm) film was bought from Whatman and polydimethylsiloxane (PDMS) was acquired from Anhui Zhongke Material Co., Ltd.(Hefei, China). Adhesive tape, apples, tomatoes, peaches, and cucumbers were purchased from local supermarkets. Ultrapure water (18.25 MΩ) was used in all experiments.
