Rapid synthesis and decoration of reduced graphene oxide with gold nanoparticles by thermostable peptides for memory device and photothermal applications

Abstract

This article presents novel, rapid, and environmentally benign synthesis method for one-step reduction and decoration of graphene oxide with gold nanoparticles (NAuNPs) by using thermostable antimicrobial nisin peptides to form a gold-nanoparticles-reduced graphene oxide (NAu-rGO) nanocomposite. The formed composite material was characterized by UV/Vis spectroscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and high-resolution transmission electron microscopy (HR-TEM). HR-TEM analysis revealed the formation of spherical AuNPs of 5-30 nm in size on reduced graphene oxide (rGO) nanosheets. A non-volatile-memory device was prepared based on a solution-processed ZnO thin-film transistor fabricated by inserting the NAu-rGO nanocomposite in the gate dielectric stack as a charge trapping medium. The transfer characteristic of the ZnO thin-film transistor memory device showed large clockwise hysteresis behaviour because of charge carrier trapping in the NAu-rGO nanocomposite. Under positive and negative bias conditions, clear positive and negative threshold voltage shifts occurred, which were attributed to charge carrier trapping and de-trapping in the ZnO/NAu-rGO/SiO₂ structure. Also, the photothermal effect of the NAu-rGO nanocomposites on MCF7 breast cancer cells caused inhibition of ~80% cells after irradiation with infrared light (0.5 W cm^-2) for 5 min.

Figure 1

Schematics for the one-pot synthesis of NAu-rGO nanocomposite using thermostable nisin peptides and its application in TFT-based memory devices.

Figure 2

Characterization of the GO, rGO, and NAu-rGO nanocomposite. (a) UV–Vis spectra of GO (blue), rGO (red), and NAu-rGO nanocomposite (black). (b) XRD patterns of rGO (black), NAu-rGO(red) (Inset: XRD patterns of GO) (c) Raman spectra of GO (black) and NAu-rGO nanocomposite (red).

Figure 3

High resolution XPS Spectra of GO, rGO, and NAu-rGO nanocomposite. (a) XPS survey scan of GO and NAu-rGO nanocomposite. (b) High-resolution XPS spectrum of Au 4 f pattern for NAu–rGO nanocomposite. High-resolution spectra of C 1 s of (c) GO and (d) NAu-rGO nanocomposite.

Figure 4

Electron microscopy studies of rGO and NAu-rGO nanocomposite. FE-SEM micrograph of (a) rGO and (b) NAu-rGO nanocomposite. Inset: right-top corner of (b) showing magnified FE-SEM image of NAuNPs formed in the rGO. High-resolution TEM (HR-TEM) micrograph of (c) and (d) NAu-rGO nanocomposite. Inset: right-top corner of (d) showing HR-TEM image of NAuNPs formed in the graphene sheets.

Figure 5

Construction and characteristics of NAu-rGO based TFT. (a) Schematic of the ZnO TFT memory device. (b) Transfer characteristics of the ZnO TFT memory device embedded with rGO at ZnO and SiO₂ interface. (c) Transfer characteristics of the ZnO TFT memory device embedded with NAu-rGO nanocomposite at ZnO and SiO₂ interface with varying drain voltage (V_DS). (d) Transfer characteristics of ZnO TFT embedded without NAu-rGO nanocomposite. (e) Output characteristics of ZnO TFT embedded with NAu-rGO nanocomposite at ZnO and SiO₂ interface.

Figure 6

Transfer characteristics of ZnO-TFT embedded with NAu-rGO nanocomposite with respect to programming time. (a) Writing characteristics and (b) erasing characteristics. (c) Schematic diagram band gap diagram of ZnO-TFT-based non-volatile memory device embedded with NAu-rGO nanocomposite without applying electric field. (d) Programming state. (e) Erasing state.

Figure 7

Cytotoxicity studies of NAu-rGO nanocomposite. (a) HeLa cell line, (b) L929 cell lines for 24 and 48 h using MTT assay.

Figure 8

Photothermal response of the NAu-rGO nanocomposite to NIR exposure. (a) Temperature increase of medium containing GO, NAuNPs, and NAu-rGO nanocomposite. MTT assay for quantifying the percent survival of MCF7 breast cancer cells after photothermal therapy for 5 min with 10 μg/mL concentrations of GO, NAuNPs, and NAu-rGO nanocomposite for (b) 2 h and (c) 24 h post-treatment for different exposure times.

Figure 9

Confocal microscopy images of MCF7 cells. (a–d) in absence of GO and NAuNPs, NAu-rGO nanocomposite in presence of (e–h) GO, (i–l) NAuNPs, and (m–p) NAu-rGO nanocomposite, which were irradiated with an 800-nm laser with a power density of 0.5 W cm² for 5 min and stained with DAPI, PI, and FDA after 24 h incubation (scale: 20 μM).