Office paper decorated with silver nanostars - an alternative cost effective platform for trace analyte detection by SERS

Maria João Oliveira,Elvira Fortunato,Eulália Pereira,Hugo Águas,Ricardo Franco,Miguel Peixoto De Almeida,Rodrigo Martins,Pedro Quaresma,Andreia Araújo

doi:10.1038/s41598-017-02484-8

Maria João Oliveira, Elvira Fortunato + Show 7 more

Open Access

https://doi.org/10.1038/s41598-017-02484-8

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Abstract

For analytical applications in portable sensors to be used in the point-of-need, low-cost SERS substrates using paper as a base, are an alternative. In this work, SERS substrates were produced on two different types of paper: a high porosity paper (Whatman no. 1); and a low porosity paper (commercially available office paper, Portucel Soporcel). Solutions containing spherical silver nanoparticles (AgNPs) and silver nanostars (AgNSs) were separately drop-casted on hydrophilic wells patterned on the papers. The porosity of the paper was found to play a determinant role on the AgNP and AgNS distribution along the paper fibres, with most of the nanoparticles being retained at the illuminated surface of the office paper substrate. The highest SERS enhancements were obtained for the office paper substrate, with deposited AgNSs. A limit of detection for rhodamine-6G as low as 11.4 ± 0.2 pg could be achieved, with an analytical enhancement factor of ≈107 for this specific analyte. The well patterning technique allowed good signal uniformity (RSD of 1.7%). Besides, these SERS substrates remained stable after 5 weeks of storage (RSD of 7.3%). Paper-induced aggregation of AgNPs was found to be a viable alternative to the classical salt-induced aggregation, to obtain a highly sensitive SERS substrates.

Highlights

Surface-enhanced Raman spectroscopy (SERS) has been intensively studied as a non-destructive and sensitive technique for applications in molecular detection, combining the specificity of vibrational Raman spectroscopy, with the increased sensitivity provided by plasmon assisted scattering, induced by metal nanostructures[1]
AgNPs used have an average diameter of ≈23 nm, and show the typical yellow colour corresponding to the plasmon band centred at around 400 nm (Fig. 2A) corresponding to the dipolar LSPRs of AgNPs which is in agreement with literature[25, 61]
As typical for the synthesis of anisometric nanoparticles, other morphologies are detected in the samples, namely irregular spheres and rods, but these consistently represent less than 10% of the total nanoparticles, as evaluated by Transmission electron microscopy (TEM) analysis

Summary

Introduction

Surface-enhanced Raman spectroscopy (SERS) has been intensively studied as a non-destructive and sensitive technique for applications in molecular detection, combining the specificity of vibrational Raman spectroscopy, with the increased sensitivity provided by plasmon assisted scattering, induced by metal nanostructures[1]. AgNPs and AgNSs colloidal solutions (10 μL) were drop-casted in the wells forming the paper SERS substrate. The performance of the paper plasmonic substrates was evaluated by SERS of R6G, using different densities of AgNPs and AgNSs on the paper-wells (from 4.2 × 108 up to 1.4 × 1010 NPs/mm[2]).

Results

Conclusion