Atrazine

Multi-walled CNT samples were purchased from Wako pure chemicals, Japan (CNT-Wako: diameter, 3–20 nm; length, ∼10 μm), and from Chengdu Alpha Nano Technology Co., Chinese Academy of Sciences, China (CNT-Alpha: diameter, 30–50 nm; length, ∼20 μm). In this article, the raw materials (i.e., as-purchased CNTs) are abbreviated as CNT-Wako and CNT-Alpha, and the magnetically separated samples are denoted MCNT-Wako and MCNT-Alpha. Ethanol (Sigma-Aldrich Co., Denmark) was used in the solvation/separation step of MCNTs. A stock solution of atrazine (500 mg/L) was prepared by dissolving 50 mg of standard atrazine powder (Sigma-Aldrich Co., Japan) in 100 mL of LC/MS grade mEthanol (Sigma-Aldrich Co., Japan) and kept refrigerated (4°C). Standard solutions were prepared by diluting the stock solution in appropriate amounts of Milli-Q water.

Phosphate buffer saline with potassium chloride (10 mm) tablets at pH 7.4, glutaraldehyde (25%), flavin adenine dinucleotide, sodium chloride, perchloric acid (70%), chloroplatinic acid (8%), glyphosate, atrazine, aminomethylphosphonic acid, thiamethoxam, imidacloprid, clothianidin, paraoxon‐methyl, parathion‐methyl, malathion and chlorpyrifos were purchased from Sigma Aldrich. 2,4‐dichlorophenoxyacetic acid was purchased from Tokyo Chemical Industry, and dicamba was provided by the Iowa State University chem service. The glycine oxidase gene originates from Bacillus subtilis and gives rise to a 47 kDa protein.^[84, ^92] Glycine oxidase (40 µm) was prepared by the U.S. Naval Research Laboratory in a manner similar to that described in references.^[93, ^94]glutaraldehyde dilutions were prepared in PBS pH 7.4. flavin adenine dinucleotide dilutions were prepared in PBS in a pH range from 5.4–9.4. All pesticides were prepared in 10× PBS pH 7.4. Kapton polyimide substrate (0.125 µm thick) was purchased from McMaster‐Carr. River water samples were gathered from the South Skunk River in Iowa. Crop residues were tested on crops purchased from a local grocery market.

Metsulfuron-methyl, melamine, atrazine, and hexazinone were obtained from Sigma-Aldrich (St Louis, MO, USA). NaCl, MgCl₂, glucose, L-cysteine, and vitamin C were purchased from Aladdin Industrial Corporation (Shanghai, China). Chloroauric acid (HAuCl₄) was purchased from Sinopharm Chemical Reagent Co. Ltd. (Shanghai, China). All other reagents were analytical reagent grade.
A NanoDrop one^C spectrophotometer (Thermo Scientific, Waltham, MA, USA) was used to record UV-vis absorption spectra. A JEM-200CX transmission electron microscope (TEM, JEOL, Tokyo, Japan) was used for imaging particle aggregation. Vibrational spectra were obtained with a Fourier transform infrared spectrometer (FT-IR-8400, Shimadzu, Kyoto, Japan).

For single measurements at high concentrations of herbicide or inhibitor, the photocurrent from a freshly prepared cell was measured for a standard period of 30 s, as described above, and then 2 µL of 50 mM atrazine, terbutryn or stigmatellin, or 10 µl of 50 mM bentazon, bromoxynil, DCMU or capsaicin dissolved in ethanol was added. The cell was incubated for 1 min before measurement of a 30 s photocurrent. All herbicides and inhibitors were purchased from Sigma-Aldrich, and their structures are shown in Supplementary Fig. 2.
For titrations, the photocurrent from a freshly prepared cell was measured for 30 s before and after the addition of increasing concentrations of atrazine, terbutryn or stigmatellin prepared in 20 mM Tris (pH 8.0)/20 µM cyt c/30 µM UQ₀. After each addition the cell was equilibrated for 60 s before measuring the photocurrent, which was sufficient to allow stabilisation of the applied current required to maintain a potential of −100 mV vs SCE. Maximal photocurrents were plotted as a function of inhibitor concentration and fitted with a logistic function to determine the IC₅₀ and IC₅ (see text). These IC₅₀ values were used to estimate K_i using the Cheng–Prusoff equation (see text).

All reagents used in this study were purchased from Sigma Aldrich (Saint Quentin Fallavier) France, including, Lipase from Candida Rugosa enzyme (CRL, type VII, ≥700 unit/mg solid), Lipase from porcine pancreas (PPL, type II, 30–90 units/mg protein), bovine serum albumin (BSA), diazinon, parathion methyl, paraoxon methyl, atrazine, sevin, simazine, fenitrothion, sodium phosphate dibasic, sodium phosphate monobasic, KH₂PO₄, K₂HPO₄, glutaraldehyde (grade II, 25% aqueous solution), glycerol (≥99%), 6-methyl-5propyl-4 pyrimidinone, N-hydroxysuccinimide (NHS), 1-ethyl-3(3-(dimethyl-amino)propyl)carbodiimide (EDC), acidthiol(16mercacaptohexadecanoicacid). Sulfuric acid (96%), hydrogen peroxide (30%), ethanol (99%) was purchased from Fluka. All solutions were made up with ultrapure water (resistivity no less than 18 MΩ cm and obtained from a Millipore purification system).