Agilent 700 series

An aliquot (∼1.5 g) of each of the powdered foods were sent to Eurofins Food Testing UK Ltd to measure the amount of total sulphur. Inductively Coupled Plasma Spectrophotometry Optical Emission Spectrometry (Agilent 700 series) was performed following an acid digestion step using nitric acid and hydrochloric acid.

In vitro measurements of pH-triggered Zn²⁺ and H₂O₂ release from NPs were carried out by immersing the NPs in different PBS solutions (pH = 7.4, 5). The solutions were centrifuged to collect the supernatants at different time points. The concentration of Zn²⁺ in the supernatant was measured by ICP–OES (Agilent 700 Series), and the amount of H₂O₂ outside the dialysis tube was detected using a hydrogen peroxide assay kit (Beyotime Biotechnology Co., Ltd., China).
Then, a portable dissolved oxygen meter (Rex, JPBJ-608, China) was employed to detect the dissolved O₂ in the aqueous solutions. The catalytic activities of the ZnC and ZnCM NPs were measured under the following four experimental conditions: a. ZnC (1 mg/mL) immersed in PBS at pH 7.4; b. ZnC (1 mg/mL) immersed in PBS at pH 5; c. ZnCM (1 mg/mL) immersed in PBS at pH 5; and d. ZnCM (1 mg/mL) immersed in PBS at pH 7.4. An oxygen electrode probe was inserted to measure the O₂ concentration.

The morphologies of as‐synthesized ICPs were examined with transmission electron microscope (TEM, JEM‐2100F) and element analysis was carried out with an energy‐dispersive X‐ray spectroscopy (XPS, Thermo Scientific K‐Alpha). X‐ray diffraction (XRD) was obtained by Rigaku Ultima IV X‐ray diffractometer. Inductively coupled plasma‐optical emission spectrometry (ICP‐OES, Agilent 700 Series, Agilent Technologies, USA) was used for the quantitative elemental analysis. FTIR spectra were conducted on a Nicolet 7000‐C spectrometer in the range of 400–4000 cm⁻¹. Brunauer–Emmett–Teller (BET) specific surface areas were measured with a surface area and porosity analyzer (Micromeritics ASAP 2460). The particle size and zeta potential were detected by Zetasizer Nano Series (Malvern, USA)

Speciation of As in the soil solution was determined using high-performance liquid chromatography (HPLC)-ICP-MS (HPLC: PerkinElmer Flexar HPLC System) within 48 h after soil solution sampling. The standard As species that were measured included arsenite [As(III)], arsenate [As(V)], monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), and arsenobetaine (AsB). In a few cases, unidentified species in small amounts were detected in soil solutions and were quantified using the standard curve for As(V). The limit of detection (LOD) was 0.28 and 0.11 μg kg⁻¹, and the limit of quantification (LOQ) was 0.94 and 0.37 μg kg⁻¹ for F-soil and A-soil, respectively. The total amount of dissolved As in soil solutions was calculated by adding the values for all species, including unidentified ones, higher than the LOD. When none of the species exceeded the LOD, the total As in the soils was fixed at 0 μg kg⁻¹ in the data analysis. The concentration of dissolved Fe was measured via inductively coupled plasma-optical emission spectrometry (Agilent 700 Series, Agilent Technologies, Santa Clara, CA, USA). LOD was 0.011 mg kg⁻¹ and LOQ was 0.036 mg kg⁻¹. Moreover, for each dissolved As species and dissolved Fe, data lower than the LOD were reported as 0 mg kg⁻¹, and those above LOD but below LOQ were reported as the calculated values. Further details are provided in the Supplementary Files.