Influence of PDA Coating on the Structural, Optical and Surface Properties of ZnO Nanostructures

Abstract

Polydopamine (PDA) is a new biocompatible material, which has prospects in biomedical and sensor applications. Due to functional groups, it can host wide range of biomolecules. ZnO nanostructures are well known templates for optical sensors and biosensors. The combination of ZnO and PDA results in a change of optical properties of ZnO-PDA composites as a shift of photoluminescence (PL) peaks and PL quenching. However, to date, the effect of the PDA layer on fundamental properties of ZnO-PDA nanostructures has not been studied. The presented paper reports on optical and surface properties of novel ZnO-PDA nanocomposites. PDA layers were chemically synthesized on ZnO nanostructures from different solution concentrations of 0.3, 0.4, 0.5 and 0.7 mg/mL. Structure, electronic and optical properties were studied by SEM, Raman, FTIR, diffuse reflectance and photoluminescence methods. The Z-potential of the samples was evaluated in neutral pH (pH = 7.2). The response of the samples towards poly-l-lysine adsorption, as a model molecule, was studied by PL spectroscopy to evaluate the correlation between optical and surface properties. The role of the PDA concentration on fundamental properties was discussed.

Keywords: ZnO–polydopamine nanocomposites; fundamental properties; optical sensors.

Figure 1

(a) The SEM and (b) the TEM images of pristine ZnONR; (c) the TEM images of a separate ZnO/polydopamine (PDA) nanorod (0.5 mg/mL) and HRTEM images of ZnO/PDA nanorods (NRs) at (d) 0.3, (e) 0.5 and (f) 0.7 mg/mL.

Figure 2

Raman spectra of ZnO with different PDA concentrations. ZnO spectra multiplied by a factor of 40.

Figure 3

FTIR spectra of ZnO with 1 h PDA deposition.

Figure 4

Optical characterization of ZnO–PDA nanorods with various PDA concentrations: (a) PL spectra; (b) change of the photoluminescence (PL) peak position in the UV and visible range; (c) graph for the band gap estimation; (d) band gap vs. dopamine concentration.

Figure 5

ZnO–PDA nanorods response to poly-l-lysine (PLL): (a) PL spectra of ZnO–PDA 0.3 mg/mL; (b) PL spectra of ZnO–PDA 0.7 mg/mL; and (c) response to PLL of ZnO–PDA with different PDA concentrations.

Figure 5

ZnO–PDA nanorods response to poly-l-lysine (PLL): (a) PL spectra of ZnO–PDA 0.3 mg/mL; (b) PL spectra of ZnO–PDA 0.7 mg/mL; and (c) response to PLL of ZnO–PDA with different PDA concentrations.