## 3 Materials and Methods  
### Reagents and Materials  
The certified standards of carbendazim, thiophanate-methyl, pyrimethanil, metalaxyl, prochloraz, procymidone, dimethomorph, triadimefon, difenoconazole, d\({}_{4}\)-carbendazim, d\({}_{6}\)-thiophanate-methyl, d\({}_{5}\)-pyrimethanail, d\({}_{6}\)-metalaxyl, d\({}_{7}\)-prochloraz, d\({}_{8}\)-dimethomorph, d\({}_{4}\)-triadimefon, and d\({}_{6}\)-difenoconazole were supplied by Dr. Ehrenstorfer GmbH (Augsburg, Germany) with a purity of more than 98.0%. Analytical grade divinylbenzene (DVB), glycolidyl methacrylate (GMA), and 2, 2-azobis (2-methyl-propionitrile) (AIBN) were supplied by J&K Chemical (Beijing, China). Diethylenediamine and hydrochloric acid were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Ammonium acetate, formic acid, and acetonitrile were purchased from Merck KGaA (Darmstadt, Germany). All other chemicals were of analytical grade, unless stated otherwise. Preparation of Diethylenediamine-Functional Magnetic Core-Shell Polymer Modified Graphene Oxide (DETA-MPs-GO) Microspheres  
The preparation of DETA-MPs-GO microspheres includes the following four steps, as shown in Scheme 1: (1) Magnetic Fe\({}_{3}\)O\({}_{4}\) preparation: Magnetic Fe\({}_{3}\)O\({}_{4}\) was prepared via a solvothermal approach, with a small modification of the literature [28]. In this procedure, 3.0 g FeCl\({}_{3}\) was  
Figure 6: (**a**) Detection ratios of nine fungicides in 81 fruit samples; (**b**) detection concentrations of fungicides in 81 fruit samples. weighed into 80 g ethylene glycol (EG), the mixture was vortexed to achieve a yellow solution, and then 3.5 g NaAc and 2.0 g polyethylene glycol were added. Subsequently, the above solution was vigorously stirred for 40 min at room temperature to dissolve the residual solid and then transferred to a 150-mL autoclave, which was then reacted at 200 \({}^{\circ}\)C for 6 h. The magnetic Fe\({}_{3}\)O\({}_{4}\) particles were achieved and cleaned using methanol to remove the adsorbed EG. (2) The synthesis of Fe\({}_{3}\)O\({}_{4}\)@poly(GMA-_co_-DVB): Fe\({}_{3}\)O\({}_{4}\)@poly(GMA-_co_-DVB) was prepared as follows: 10 mL GMA and 5 mL DVB were added into 40 mL acetonitrile, then the solution was stirred for 20 min to prepare a preassembly solution. The Fe\({}_{3}\)O\({}_{4}\) microspheres (0.5 g) were then dispersed in 20 mL acetonitrile in a 150-mL round-bottomed flask and dispersed for 0.5 h under sonication. Then the preassembly solution, including GMA and DVB, was sneaked into the Fe\({}_{3}\)O\({}_{4}\) suspension. Then the polymerization was carried out with three addition of 0.04 g 2, 2-azobis (2-methyl-propionitrile) (AIBN) under stirring at 600 rpm. The reaction solution was heated to 70 \({}^{\circ}\)C and maintained at 70 \({}^{\circ}\)C for 3 h. (3) Synthesis of DETA-MPs: the DETA-functional magnetic core-shell polymers (DETA-MPs) were synthesized via a ring-opening reaction between diethylenetriamine (DETA) and epoxide-functional Fe\({}_{3}\)O\({}_{4}\)@poly(GMA-_co_-DVB). In the process, 0.5 g of the achieved Fe\({}_{3}\)O\({}_{4}\)@poly(GMA-_co_-DVB) was firstly added into 100 mL methanol with 10 mL of dissolve DETA, and the mixture was stirred at 80 \({}^{\circ}\)C for 8 h. The resulting DETA-MPs was washed three times with methanol and dried in a vacuum oven at room temperature overnight. (4) Preparation of DETA-MPs-GO: DETA-MPs-GO was prepared under ultrasound conditions by an amidation reaction. 100 mg GO power in 50 mL water (2.0 mg/mL) was firstly dispersed under ultrasound for 2 h, and then 160 mg N-hydroxysuccinimide (NHS) and 200 mg N-ethyl-N\({}^{\prime}\)-(3-(dimethylamino)propyl)carbodiimide (EDC) were weighed into the above GO dispersion. The achieved dispersion was reacted under stirring for 1 h in order to activate carboxyl groups (-COOH) on the GO sheet. Afterwards, 500 mg DETA-MPs was introduced and dispersed under ultrasound for 20 min. The following reaction was performed at 40 \({}^{\circ}\)C for 4 h under vigorous stirring.