Electronic supplementary material

A glassy carbon electrode modified with graphene and tyrosinase immobilized on platinum nanoparticles for sensing organophosphorus pesticides

Tao Liu, Minrong Xu, Huanshun Yin, Shiyun Ai*, Xiangjin Qu, Shanshan Zong

College of Chemistry and Material Science, Shandong Agricultural University, Taian, Shandong 271018, China

Fig. S1. Effects of pH (a), applied potential (b), enzyme loading (c) and inhibition time (d) on the response of Tyr/Nano-Pt/Graphene/GCE biosensor. (d): (i) chlorpyrifos, (ii) profenofos and (iii) malathion.

The activity of tyrosinase was greatly affected by pH. So the effect of pH on the response of Tyr/Nano-Pt/Graphene/GCE biosensor was investigated detailedly. The maximum current response was obtained at pH 7.5 (Fig.S1a). Therefore, pH 7.5 was chosen for the subsequent analytical experiments.

In amperometric detection, the potential applied to the working electrode directly affects the sensitivity, detection limit and stability of this method. So the effect of applied potential was also studied (Fig.S1b). It was found that the current responses achieved a maximum at about +0.06 V (versus SCE). Therefore, the applied potential of +0.06 V was selected as the most suitable detection potential.

The enzyme loading was another influence factor on the response of the biosensor. The current response increased with increasing the amount of tyrosinase and reached the maximum at 37.6 U (Fig.S1c), then decreased when the amount of tyrosinase was increased further. This phenomenon could be attributed to the increase of tyrosinase film thickness, which can enhance the electrode resistance and slow the electron transfer between substrate and electrode. Therefore, 37.6 U was chosen as the optimal enzyme concentration.

Besides, the effect of inhibition time on the response of Tyr/Nano-Pt/Graphene/GCE biosensor was investigated with chlorpyrifos, profenofos and malathion, respectively. And 20 min (Fig.S1d) was chosen as the optimal incubation time.

Fig. S2. Typical steady-state response of the biosensor. Inset: Calibration curve. Applied potential, +0.06 V; supporting electrolyte, 0.01 M phosphate buffer solution (pH 7.5).

Fig. S3. Inhibition curves for pesticides chlorpyrifos (a); profenofos (b); and malathion (c). Inset: The relationship between inhibition percentage and the concentration of pesticides. Experimental conditions: 25 μM catechol in 0.01 M phosphate buffer solution (pH 7.5).