Supplementary Material

A chemical approach to accurately characterize the coverage rate of gold nanoparticles

Xiaoli Zhu, Min Liu, Huihui Zhang, Haiyan Wang, and Genxi Li*

* Corresponding author at Department of Biochemistry and State Key Laboratory of Pharmaceutical Biotechnology, NanjingUniversity, Nanjing 210093, China.E-mail address: (G. Li)

1.Experimental

Reagents

Silver nitrate, ferric chloride, ferrous sulfateand graphene oxide (GO) were from Sigma-Aldrich and used as received. Chloroplatinic acid (H2PtCl6) was obtained from ShanghaiJiushan Chemicals Co., Ltd.Other chemicals were all of analytical grade.

Preparation of silver nanoparticles

Tannic acid solution (3.5 ml, 1%) and Na2CO3 solution (4 ml, 1%) were added into 91.5 mldoubly distilled water andincubated at 60 °C. Under rapid stirring, AgNO3 solution (1 ml, 3.4%)was added into the above mixture drop by drop. The color of the solution deepened gradually, from achromatic color, pale yellow, brownish red, and finally to black. After a further aging at 60 °C for 30 min and then cooling down to room temperature, silver nanoparticles (AgNPs) with an average diameter of 7.9 nm was prepared.

Preparation of platinum nanoparticles

Platinum particles (PtNPs)with a diameter of about 4 nm were prepared by citrate reduction of H2PtCl6. Briefly, 10 ml of 38.8 mM sodium citrate was quickly added to 100 ml of 1 mMH2PtCl6 refluxing solution under stirring and boiling for 30 min. During the time, the solution turned from clear to dark. The solution was stirred further for 10 min without heating. Finally, the solution was cooled down to room temperature and stored at 4 °C until use.

Preparation of magnetite nanoparticles

A 50 mlaqueous solution containingFeSO4 (80 mM) and FeCl3(160 mM) was firstly prepared. The solution was purged with nitrogen to remove oxygen andthen heated to80 °C.Under rapid stirring, NH3 solution (10 ml, 25%) was added drop by drop. Thereaction mixture was further stirred for 30 min. After that, the precipitatewas washed with water three times andisolated by magnetic decantation. The residue was finally made up to50 ml with doubly distilled water. Thus, magnetic Fe3O4 nanoparticles (MNPs) were prepared.

2.Results

Optimization of the two-step catalysis

Fig. S1 Absorption peaks at 420 nm vs. the concentration of maltose. Data points are recorded from the spectra response of the catalysis-based characterization system. 200 μM of maltose is adopted as the optimum

Fig. S2 Absorption peaks at 420 nm vs. temperature. 37°C is adopted as the optimum

Fig. S3 Absorption peaks at 420 nm vs. the concentration of AuNPs. 1 × AuNPs are adopted as the optimum. For simplicity, the prepared AuNPs (3.5 nM) is designated as 1 ×

Fig. S4 Absorption peaks at 420 nm vs. the reaction time. 0.5 h is adopted as the optimum

Fig. S5 Spectra response of the catalysis of different nanomaterials. The concentrations of the control materials are similarto or higher than that of Au (2, 0.9, 80, 8, and 1.2 mM for Ag, Pt, Fe3O4, C, and Au, respectively)

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