DNA-templated synthesis of PtAu bimetallic nanoparticle/graphene nanocomposites and their application in glucose biosensor

Abstract

In this paper, single-stranded DNA (ss-DNA) is demonstrated to functionalize graphene (GR) and to further guide the growth of PtAu bimetallic nanoparticles (PtAuNPs) on GR with high densities and dispersion. The obtained nanocomposites (PtAuNPs/ss-DNA/GR) were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectrometer (EDS), and electrochemical techniques. Then, an enzyme nanoassembly was prepared by self-assembling glucose oxidase (GOD) on PtAuNP/ss-DNA/GR nanocomposites (GOD/PtAuNPs/ss-DNA/GR). The nanocomposites provided a suitable microenvironment for GOD to retain its biological activity. The direct and reversible electron transfer process between the active site of GOD and the modified electrode was realized without any extra electron mediator. Thus, the prepared GOD/PtAuNP/ss-DNA/GR electrode was proposed as a biosensor for the quantification of glucose. The effects of pH, applied potential, and temperature on the performance of the biosensor were discussed in detail and were optimized. Under optimal conditions, the biosensor showed a linearity with glucose concentration in the range of 1.0 to 1,800 μM with a detection limit of 0.3 μM (S/N = 3). The results demonstrate that the developed approach provides a promising strategy to improve the sensitivity and enzyme activity of electrochemical biosensors.

Figure 1

The formation procedures of GOD/PtAuNP/ss-DNA/GR nanocomposites.

Figure 2

Photographic and TEM images and EDS spectra. (A) Photographic images of (a) unmodified GR and (b) ss-DNA/GR in water. TEM images of (B) ss-DNA/GR and (C) PtAuNP/ss-DNA/GR nanocomposites. (D) EDS spectra of PtAuNP/ss-DNA/GR nanocomposites.

Figure 3

Impedance spectrum of various electrodes in 5.0 mM K₃Fe(CN)₆/K₄Fe(CN)₆ (1:1) containing 0.1 M KCl. Bare electrode (curve a), ss-DNA/GR modified electrode (curve b), PtAuNP/ss-DNA/GR modified electrode (curve c), and GOD/PtAuNP/ss-DNA/GR modified electrode (curve d).

Figure 4

Cyclic voltammograms of GOD/PtAuNP/ss-DNA/GR modified electrode. They are in (curve a) N₂-saturated and O₂-saturated PBS (pH 7.0) in the (curve b) absence and (curve c) presence of 1.0 mM glucose at 100 mV s^-1.

Figure 5

Effects of (A) pH, (B) applied potential, and (C) temperature. These are effects on amperometric response of the GOD/PtAuNP/ss-DNA/GR modified electrode to 0.1 mM glucose in 0.1 M PBS (pH 7.0).

Figure 6

Amperometric responses of modified electrodes to additions of 0.1 mM glucose in 10-mL PBS at -0.2 V. GOD/ss-DNA/GR (curve a), GOD/PtNP/ss-DNA/GR (curve b), GOD/AuNP/ss-DNA/GR (curve c), and GOD/PtAuNP/ss-DNA/GR (curve d) modified electrodes. Left inset is the calibration curve of the biosensor.