Production of stable and sensitive SERS substrate based on commercialized porous material of silanized support
Graphical abstract
Introduction
Surface-enhanced Raman spectroscopy (SERS), as a sensitive, nondestructive and rapid detection method, could offer abundant molecular vibration information and has emerged as a powerful technique in environmental monitoring, analytical chemistry and biological analysis [1], [2], [3], [4], [5]. With the two major enhancement mechanisms of electromagnetic enhancement and chemical enhancement contributing to the giant SERS signal, single molecule detection can be achieved by SERS [6], [7]. In order to obtain a tremendously boosted Raman signal, a SERS substrate with outstanding performance is always required [8], [9].
Benefiting from the development of nanoscience and nanotechnology, a great deal of research effort has been made to fabricate SERS-active substrates with controlled size and morphology. Techniques such as Langmuir-Blodgett (LB) assembly [10], [11], nanolithography and nanoimprint [12], [13] have been applied in the preparation of highly ordered and uniform SERS substrates with nanostructures having a wide diversity of shapes and geometries. However, some limitations still exist in current SERS substrates, for example, time-consuming preparation procedures, high commercialization cost, high variation between batches and hence poor reproducibility [14]. These drawbacks make it difficult to carry out field-based applications and routine laboratory analysis of chemicals can be extremely inconvenient.
In previous works of our group, SERS substrate fabrication was based on glycidyl methacrylate-ethylene dimethacrylate (GMA-EDMA) porous material, which acted as SERS scaffold to offer binding sites for metal nanoparticles. Both on-site synthesis and self-assembly methods were used to distribute Au/Ag nanoparticles on the surface of the porous material, thus sensitive, uniform, and stable SERS substrates were fabricated [15], [16]. These substrates performed well in SERS detection but involved tedious procedure of preparing GMA-EDMA monolithic column. In order to satisfy the criteria of rapid simple and batch fabrication, it would be of significant meaning to find a commercialized material as a replacement of GMA-EDMA material.
Diatomite is a kind of biogenic silica sedimentary rock, mainly composed of organic remains of ancient diatoms. Diatomaceous support is a commonly used solid support in chromatography, which shows very ornate surface nanoscale pore patterns forming an amazing range of intricate designs with hierarchical ordered dimensions that span from nanoscale to microscale [17]. Stationary phase material diatomaceous support possesses several characteristics such as large surface area, uniformly distributed pore size, good chemical inertness, moderate particle size and mechanical strength. More importantly, it can be obtained from professional company that ensures consistency of the material that result in good reproducibility of the SERS substrate. The porous inner structure and other advantageous features of diatomaceous support make it a good candidate material for SERS substrate fabrication. Residual pesticides in agricultural products affect the lives of wildlife and domestic animals and are one of the major food safety concerns around the world. Phosmet and triazophos are widely used in China, indicating their potential harm to humans through residues in food and water [18], [19].
In the present work, we used silanized diatomaceous support as scaffold to offer binding sites for metal nanoparticles. Gold colloid was synthesized and gold nanoparticles were immobilized onto the support material to create SERS-active substrate. The synthesis conditions were optimized and sensitivity, stability of this substrate was investigated. The developed SERS substrate was used to detect selected pesticides in real samples. The results demonstrated that this SERS substrate can be an ideal tool for practical analytical applications.
Section snippets
Chemicals and reagents
Chloroauric acid tetrahydrate (greater than 47.8% purity (gold)) was obtained from Sinopharm chemical reagent Co., Ltd. (Shanghai, China). Sodium citrate (greater than 99% purity), 101 white silanized diatomaceous supports (similar to Chromosorb W-HMDS, Co., Ltd. New York, America) and 201 red silanized diatomaceous supports (similar to Chromosorb PAW-HDMS, John-Manville Co., Ltd. New York, America) were purchased from Shanghai first reagent industry (Shanghai, China). 4-mercaptopyridine was
Fabrication of the SERS substrate
Both 101 white silanized diatomaceous support and 201 red silanized diatomaceous support were tested as candidate for the base of the new SERS substrate, they were mixed with aqueous solution of ammonia/ ethylenediamine for modification and were shaken with gold colloid for AuNPs decoration according to the experimental section, thus four kinds of SERS substrates in total were prepared. Afterwards, 1×10−7 M 4-Mpy was used as a probe molecule to test their SERS activity. Fig. 1 shows the SERS
Conclusion
In this work, we fabricated a SERS substrate with gold nanoparticle decorated 201 red silanized diatomaceous support. This SERS substrate has several advantages over previously used GMA-EDMA material such as easy fabrication, disposable, portable, stable over time, have good SERS activity and fast detection. The developed material was successfully used to detect triazophos and phosmet at a concentration of 0.01 mg/L. The SERS Substrate was also applied to detect triazophos in real samples of
Acknowledgements
This work was supported by Science and Technology Commission of Shanghai Municipality (14142201400).
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