Fabrication of polydimethylsiloxane (PDMS)-Based Flexible Surface-Enhanced Raman Scattering (SERS) Substrate for Ultrasensitive Detection

Summary

This protocol describes a fabrication method for a flexible substrate for surface-enhanced Raman scattering. This method has been used in the successful detection of low concentrations of R6G and Thiram.

Abstract

This article presents a fabrication method for a flexible substrate designed for Surface-Enhanced Raman Scattering (SERS). Silver nanoparticles (AgNPs) were synthesized through a complexation reaction involving silver nitrate (AgNO₃) and ammonia, followed by reduction using glucose. The resulting AgNPs exhibited a uniform size distribution ranging from 20 nm to 50 nm. Subsequently, 3-aminopropyl triethoxysilane (APTES) was employed to modify a PDMS substrate that had been surface-treated with oxygen plasma. This process facilitated the self-assembly of AgNPs onto the substrate. A systematic evaluation of the impact of various experimental conditions on substrate performance led to the development of a SERS substrate with excellent performance and an Enhanced Factor (EF). Utilizing this substrate, impressive detection limits of 10^-10 M for R6G (Rhodamine 6G) and 10^-8 M for Thiram were achieved. The substrate was successfully employed for detecting pesticide residues on apples, yielding highly satisfactory results. The flexible SERS substrate demonstrates great potential for real-world applications, including detection in complex scenarios.

Introduction

Surface-Enhanced Raman Scattering (SERS), as a type of Raman scattering, offers the advantages of high sensitivity and gentle detection conditions, and can even achieve single molecule detection^1,2,3,4. Metal nanostructures, such as gold and silver, are typically used as SERS substrates to enable substance detection^5,6. Electromagnetic coupling enhancement on nanostructured surfaces plays a significant role in SERS applications. Metallic nanostructures with varying sizes, shapes, int....

Protocol

1. Synthesis of nanoparticles

1. Preparation of Silver nitrate solution
   1. Using a precision weighing balance, measure 0.0017 g of AR-grade silver nitrate (AgNO₃, see Table of Materials) and add it to 10 mL of deionized (DI) water. Stir the mixture to create a 10^-3 mol/L AgNO₃ solution.
2. Preparation of the silver-ammonia complex
   1. Take 1 mL of AR-grade ammonia water (NH₃.H₂O, see Table of Materials) using a syringe, and add it drop by drop into the silver nitrate solution while stirring. Stop the dropwise addition....

Results

In this study, a flexible SERS substrate composed of synthetic AgNPs wrapped in glucose and self-assembled on PDMS using APTES was developed, achieving excellent detection performance for practical pesticide detection applications. The detection limits for R6G and Thiram were both reached at 10^-10 M and 10^-8 M, respectively, with an Enhancement Factor (EF) of 1 x 10⁵. Furthermore, the substrate demonstrated uniformity.

The AgNPs wrapped in glucose were synthesi.......

Discussion

In this study, a flexible SERS substrate was introduced, which bonded AgNPs to PDMS through chemical modification and achieved excellent performance. During particle synthesis, specifically in the silver ammonia complex synthesis (step 1.2), the color of the solution plays a crucial role. Adding too much ammonia water dropwise can adversely affect AgNPs synthesis quality, potentially leading to unsuccessful detection results. Attention should be paid to substrate modification (step 2.2) during the synthesis process; othe.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Ammonia (NH3.H2O, 25%)	Beijing Chemical Works
APTES (98%)	Beyotime	ST1087
BD-20AC Laboratory Chrona Treater	Electro-Technic Products Inc.	12051A
D-glucose	Beijing Chemical Works
Environmental Scanning electron microscope (ESEM)	FEI	QUANTA 250
Raman microscope	Horiba JY	LabRAM HR Evolution
Rhodamine 6G	Beijing Chemical Works
Silicone Elastomer Base and Silicone Elastomer Curing Agent	Dow Corning Corporation	SYLGARD 184
Silver nitrate	Beijing Chemical Works
Thiram (C6H12N2S2, 99.9%)	Beijing Chemical Works