Hydrazine monohydrate

N-hexane (95%), THF (99.9%), and dichloromethane were purchased from Th. Geyer (Renningen, Germany); methanol and acetonitrile (HPLC-grade) were purchased from VWR (Darmstadt, Germany)); N,N-dimethylformamide (DMF, 99%) was purchased from Acros Organics (Geel, Belgium); anhydrous 1,2-dichlorobenzene (DCB, 99%), methanol (HPLC-grade), cobalt carbonyl (Co₂(CO)₈) containing 1%–5% n-hexane as stabilizer, hydrazine monohydrate (N₂H₂ 64%–65%), 2,2′-bipyridyl (99%), styrene (99%), α,α′-dichloro-p-xylene (98%), 18-crown-16 (99%), phthalimide potassium salt (99%), copper(I) chloride (97%), and alumina (activated, neutral, Brockmann Activity I) were purchased from Sigma Aldrich (Steinheim, Germany) and used as received without further purification. copper(I) chloride was purified by stirring in glacial acetic acid overnight, washed with ethanol and dried under vacuum. Co₂(CO)₈ was kept in the fridge of a glovebox, and n-hexane evaporated in the glovebox before use. styrene was passed through a short column of neutral alumina to remove inhibitors and deoxygenated by bubbling with N₂ before starting a polymerization.

Toluene (99.8%), methyl alcohol (99.9%), and nitric acid (68.0–70.0%) were purchased from Samchun. Tetrahydrofuran (THF) was obtained from Duksan. Hydrochloric acid (36.5–38.0%) was ordered from J.T.Baker. Silk fibroin (5% solution) was purchased from Advanced BioMatrix. Sodium nitrite, 6-bromo-1-hexene, chloroplatinic acid hexahydrate (H₂PtCl₆ ∙ 6H₂O), decanoic acid, hydrazine monohydrate, silver acetate, dodecylamine (DDA), lead(II) bromide, methylammonium bromide (MABr), 4-methoxyaniline, sodium hydride, and tetrabutylammonium borohydride (TBAB) were obtained from Sigma-Aldrich. AZ-5214E was used as photoresist (PR). Sodium hydroxide, phenol, and petroleum ether were ordered from Daejung. N,N-dimethylformamide (DMF) was purchased from Honeywell. Silicone elastomer base and silicone elastomer curing agent (Sylgard 184) were obtained from Dow Corning.

To quantify the concentration of lactate in biological samples, JEG-3 cell culture supernatants were incubated for 90 min in a 96-well plate with the following buffer solution: NAD+ (Roche Diagnostics; 0.75 mM), Hydrazine monohydrate (Sigma Aldrich, Henri Desbruères, France; 0.4 M), Glycine (EUROMEDEX, Souffelweyersheim, France; 0.4 M) and L-LDH enzyme (Roche, Meylan, France; 40 Units/well). In each well, lactate was converted back into pyruvate via the reduction of NAD+ into NADH and H+ (stoichiometry 1:1) by L-LDH. The absorbance of NADH was measured at 340 nm using a microplate reader before and after the addition of the enzyme L-LDH (40 units/well). Lactate concentration was calculated from NADH absorbance value using the Beer–Lambert law, considering the dilution factor and stoichiometry.

Propanoic acid hydrazide (≥90%), O-ethylhydroxylamine hydrochloride (97%), adipic acid dihydrazide (≥98%,), O,O′-1,3-propanediylbishydroxylamine dihydrochloride (98%), propyl isocyanate, hexamethylenediisocyanate, hydrazine monohydrate, activated charcoal (Norit), sodium periodate (NaIO₄) and ethylene glycol were purchased from Sigma-Aldrich. Propyl semicarbazide and N,N′-(hexane-1,6-diyl)bis(hydrazinecarboxamide) (HDCA) (¹H NMR structures shown in Figures S1 and S2 in Supplementary Information) were synthesized according to literature [38 (link)]. Sodium alginate was purchased from FMC (Manugel GMB, Lot No. G9402001, Dialysis membrane (Spectra/Por^®) with molecular weight cut off (MWCO) 3500 Dalton (Da) from VWR, Netherlands.
Dulbecco’s modified Eagle’s medium (DMEM, high glucose and supplemented with GlutaMAX™ and Sodium Pyruvate), DEME-F12 (low glucose), Dulbecco’s phosphate buffer saline (PBS), fetal bovine serum (FBS), penicillin/streptomycin (P/S), calcein AM, ethidium homodimer, Alexa Fluor^® 488 Phalloidin, DAPI and PrestoBlue™ cell viability reagent were purchased from Thermo Fisher Scientific.

Butylamine (99 +%), pentylamine (99%), and hexylamine (99%) were purchased from Acros Organics (Morris Plains, NJ, USA). 3,5-dinitrobenzoyl chloride (DNBC) (96.5%), propylamine (98%), tert-Butylamine (99.5%), 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) (99%), anhydrous N,N-dimethylacetamide (DMAc) (99.8%), triethylamine (TEA) (99.5%), hydrazine monohydrate (80%), anhydrous pyridine (99.8%), and Pd/C (10%) were purchased from Sigma-Aldrich (Milwaukee, WI, USA). All other reagents and solvents were purchased commercially as analytical grade and used without further purification.

Fifty milliliters of D.I. water, 100 mg PDDA-G, 131.1 mg H₂AuCl₄ (Sigma-Aldrich, Ltd), and 8 mL hydrazine monohydrate (98 %, Sigma-Aldrich, Ltd) were added and then the mixture was sonicated for 30 min before the mixture was transferred into a 100-mL Teflon-lined autoclave apparatus and heated at 90 °C for 24 h. The composite of Au nanoparticles on PDDA-modified graphene (Au/PDDA-G) as a solution was centrifuged three times with D.I. water followed with removal of supernatants. The residuals were dried under vacuum at 90 °C for 24 h and then collected.
The composite of bimetallic PtAu nanoparticles on PDDA-modified graphene (PtAu/PDDA-G) was obtained in a similar way by mixing 99 mg PDDA-modified graphene, 215.3 mg K₂PtCl₆ (~0.456 mmol), and 133 mg H₂AuCl₄ (~0.456 mmol) with 50 mL D.I. water and sonificated for 30 min, followed by addition of 10 mL hydrazine monohydrate (80 %) and sonificated further for 10 min. After that, the mixture was transferred to a 100-mL Teflon-lined autoclave apparatus and heated at 90 °C for 24 h. The collected PtAu/PDDA-G solutions were centrifuged three times with D.I. water followed with removal of supernatants. The residuals were dried under vacuum at 90 °C for 24 h and then collected. The cubic Pt/G was synthesized in the previous method [33 ].