Trisodium phosphate

Ascorbic acid, citric acid, disodium hydrogen phosphate, ethylenediamine, methyl blue, oxalic acid, phosphoric acid, quinine sulfate, sodium citrate, sodium dihydrogen phosphate, sodium hydroxide, trisodium phosphate, and the other metal salts used here were purchased from Sigma-Aldrich (St. Louis, MO, USA). Ultrapure water (≥18.2 MΩ cm) was used throughout all the experiments.

Hexanal, 2-methylpyrazine, 2,3-dimethylpyrazine, 2,5-dimethylpyrazine, 2-methyl-2-thiazoline, 2-pentylfuran, 2-ethyl-3,5-dimethylpyrazine, 3-hydroxy-2-methyl-4H-pyran-4-one, 2-methylphenol, 2-acetyl-2-thiazoline, (E,E)-2,4-decadienal, 2-methoxy-4-vinylphenol, 4-hydroxy-3-methoxybenzaldehyde, 4-heptanone, 2-methyl-3-heptanone, trisodium phosphate, calcium carbonate, anhydrous sodium sulfate, corn starch and sodium chloride were purchased from Sigma-Aldrich (St. Louis, MO, USA). Methanol and methylene chloride, in GC-Resolv^® grade, were purchased from Fischer Scientific (Pittsburgh, PA, USA). Maizewise™ whole grain and Innovasure™ refined maize flours were purchased from Cargill (Minneapolis, MN, USA). All the sensory reference materials, dry uncooked Bob′s Red Mill Steel Cut Oats, Bergen Unsalted Lightly Roasted Almonds, Organic Valley Whole UHT Milk, Toasted Wonder Bread™, Nilla^® Wafers, and Old Dutch Restaurante^® Style Yellow Corn Tortillas Chips, were purchased from a local grocery store.

In the present work, chelators in a completely basic form (all acidic functional groups were titrated with Na⁺) were impregnated into the macroporous silica support using their aqueous solutions (typically, 0.25–2.0 wt% chelator concentrations). For the preparation of the aqueous solutions, trisodiumphosphate (1 in Fig. 3a, Sigma Aldrich, 96%) and ethylenediaminetetraacetic acid tetrasodium salt dihydrate (4, Sigma Aldrich, 99%) were directly dissolved in deionized water. In the cases of chelators in an acidic form, such as 1-hydroxyethane 1,1-diphosphonic acid monohydrate (2, Sigma Aldrich, 95%), ethylenediamine tetramethylene phosphonic acid (3, Tokyo Chemical Industry, 98%), diethylenetriaminepentaacetic acid (5, Sigma Aldrich, 99%), and meso-2,3-dimercaptosuccinic acid (6, Sigma Aldrich, 98%), controlled amounts of NaOH were dissolved together in deionized water to completely titrate acidic H⁺ into Na⁺. After the wet impregnation of the chelators into the silica support, the samples were dried in a vacuum oven at 100 °C for 12 h. The final loading of chelators was controlled in the range of 0–4 wt% with respect to the mass of silica support.

Gold nanoparticles (AuNPs) of 13 nm diameter was prepared as reported in previous work [24 (link)]. Before conjugation, detecting probe (DP; Bio Basic Inc., Ontario, Canada; sequence: 5′-SH-C6-ATC ATC GA AGT GGC TTC A-3′) was prepared by adding 500 mM acetate buffer (pH 4.68, which consist of 1 M sodium acetate (Ajax Finechem Pty. Ltd., NSW, Australia) and 0.21 M acetic acid (Fisher Scientific) to the lyophilized DP and topped up to 100 μM with distilled water. AuNP–DP conjugates were prepared by adding 6 μL of 100 μM detecting probe (DP) to 1 mL AuNPs solution and left for 16 h for conjugation. 1% sodium dodecyl sulfate (SDS) (Sigma Aldrich) and 2 M NaCl (Merck) was then added to the solution to achieve a final concentration of 0.0% SDS and 0.16 M NaCl in the solution. The solution was then allowed to age for at least 24 h before centrifugation at 14,000 g for 25 min. Following centrifugation, the supernatant was removed while the pellet was resuspended in 67 μL eluent buffer, which comprised of 5% bovine serum albumin (w/v; AMRESCO, Solon, OH, USA), 0.25% Tween-20 (w/v; Sigma Aldrich), 10% sucrose (w/v; Ajax Finechem Pty. Ltd.) and 20 nM trisodium phosphate (Sigma Aldrich). The resulting AuNP–DP conjugate solution was kept at 4 °C for future use. We have characterized the AuNPs in our previous publication. Their average sizes are 13 nm [3 (link)].

Sodium acetate (NaAc; p.a., POCH, Poland), magnesium acetate (Mg(Ac)₂; p.a., POCH, Poland), potassium persulfate (VWR Chemicals), potassium hydroxide (POCH, Poland), trisodium phosphate (Chempur, Poland), 1× PBS buffer (pH 7.4; Sigma), absolute ethanol (99.8%; POCH, Poland), EDTA (Sigma), tris–EDTA buffer (TE; Sigma), tris(2-carboxyethyl)phosphine hydrochloride (TCEP; Sigma), 2-amino-2-(hydroxymethyl)propane-1,3-diol (Tris; Sigma), 6-mercaptohexan-1-ol (MCH; Sigma) were all of high purity, and were used as received. For all the experiments, we used distilled and deionized water with a conductivity of 0.056 μS cm⁻¹ produced by the Hydrolab system. The following oligonucleotides, purchased from MWG-Operon (Eurofins), were used:
• Capture DNA (5′ → 3′): thiol-C6-GCCTTCACAGGGTCCTTTATGT.
• Complementary target DNA (5′ → 3′): ACATAAAGGACCCTGTGAAGGC.

Analytical, HPLC, and LCMS grade chemicals were used in this study. Folin–Ciocalteu reagent, gallic acid, sodium carbonate, aluminium chloride, hydrated sodium acetate, quercetin, vanillin, sulfuric acid, l-ascorbic acid, iron(III) chloride hexahydrate (Fe(III)Cl₃∙6H₂O), 2,4,6-tripyridyl-S-triazine (TPTZ), ABTS, potassium persulfate, potassium ferrocyanide (III), trichloroacetic acid (TCA), ferric chloride, sodium phosphate dibasic heptahydrate (Na₂HPO₄∙7H₂O), sodium phosphate monobasic monohydrate (Na₂HPO₄∙H₂O), hydrochloric acid (HCl), ammonium molybdate, trisodium phosphate, ferrozine, ferrous chloride, iron(II) chloride, ethylene diamine tetraacetic acid (EDTA), iron(II) sulfate heptahydrate, and 3-hydroxybenzoic acid were purchased from Sigma Aldrich (Castle Hill, NSW, Australia). Hydrogen peroxide (30%) and sodium carbonate anhydrous were purchased from Chem-Supply Pty Ltd. (Adelaide, SA, Australia), and 98% sulfuric acid was purchased from RCI Labscan (Rongmuang, Thailand). HPLC and LC-MS grade reagents, including ethanol, methanol, acetonitrile, formic acid, and iron(III) chloride anhydrous, were purchased from Thermo Fisher Scientific Inc. (Scoresby, VIC, Australia).

Following materials have been used in this study: ʟ-aspartic acid (CAS: 56-84-8, Aldrich, ≥98%), orthophosphoric acid (CAS: 7664-38-2, Aldrich, ≥99%), dimethylformamide (CAS: 68-12-2, VWR, ≥99.9%) cystamine dihydrochloride (CAS: 56-17-7, Fluka, ≥98%), lysine methyl ester dihydrochloride (CAS: 26348-70-9, Bachem, 97%), dimethyl sulfoxide (CAS: 67-68-5, VWR, ≥99%), dibutylamine (CAS: 111-92-2, Aldrich, ≥99.5%), citric acid monohydrate (CAS: 5949-29-1, VWR, 100%, normapur), imidazole (CAS.288-32-4, Sigma-Aldrich, ≥99.5%, puriss), sodium chloride (CAS: 7647-14-5, Sigma-Aldrich, puriss), sodium hydroxide (CAS: 1310-73-2, Reanal, puriss), borax (CAS: 1303-96-4, Hungaropharma, ≥99.5%), disodium hydrogen phosphate (CAS: 7558-79-4, Sigma-Aldrich, ≥98%), trisodium phosphate (CAS: 10101-89-0, Sigma-Aldrich, ≥98%), phosphate-buffered saline (PBS) tablet (Sigma), ᴅʟ-dithiothreitol (CAS: 3483-12-3, Sigma, ≥99%).