Layer-by-Layer Assembly of Polystyrene/Ag for a Highly Reproducible SERS Substrate and Its Use for the Detection of Food Contaminants.

Sihan Zhang,Hongtao Fan,Haiying Wang,Yibo Ma,Jiaqi Guo,Qian Yu,Zhihua Xu,Xianming Kong

doi:10.3390/polym13193270

Abstract

Polystyrene (PS) spheres were prepared through an emulsifier-free emulsion polymerization method, in which the reaction time, ionic strength, concentrations of copolymer were studied in detail. The resulting PS microspheres and Ag nanoparticles were used to construct a surface enhanced Raman scattering (SERS) substrate by a layer-by-layer assembly method. A relatively uniform distribution of PS/Ag in the films was obtained, and the multilayer substrate presented excellent SERS reproducibility and a tunable enhancement effect. The SERS substrate was used for detecting harmful pesticides (malachite green and dimetridazole) in food samples, with a limit of detection as low as 3.5 ppb. The obtained plasmonic composite has a promising future in the field of SERS sensing.

Highlights

Polystyrene (PS) materials have attracted considerable attention due to their multiple excellent properties such as strong adsorption capacity, oxygen permeability and the possibility of surface functionalization
Numerous methods have been proposed for preparing PS microspheres, such as suspension polymerization, emulsion polymerization, emulsifier-free emulsion polymerization (EFEP), seed polymerization and dispersion polymerization [6,7,8]
The PS/Ag nanocomposite was fabricated through a three-step procedure. It is well-known that uniformity is important in surface enhanced Raman scattering (SERS) measurement, and that it is challenging to reproduce the absolute SERS intensity of analytes with a colloidal PS composite as it is difficult to control the distribution of plasmonic PS composites after being dropped for Raman signal collection

Summary

Introduction

Polystyrene (PS) materials have attracted considerable attention due to their multiple excellent properties such as strong adsorption capacity, oxygen permeability and the possibility of surface functionalization. The key benefits of EFEP are that the product has excellent monodispersity, high purity, uniform particle size and the process is simple This method has become the common method for preparing polystyrene and many other functional polymer materials. In order to obtain the excellent properties of the SERS substrate base in a PS composite, it is important to improve the distribution of plasmonic NPs and PS spheres. The PS/Ag nanocomposite was fabricated through a three-step procedure It is well-known that uniformity is important in SERS measurement, and that it is challenging to reproduce the absolute SERS intensity of analytes with a colloidal PS composite as it is difficult to control the distribution of plasmonic PS composites after being dropped for Raman signal collection.

Apparatus

Synthesis of Ag Colloid and PS Spheres

Layer-by-Layer Assembly of Ag NPs and PS Spheres

The Effect of Reaction Conditions on the Diameter of PS Spheres

10—3 M 10—4 M 10—5 M 10—6 M 10—7 M