Portable mercury sensor for tap water using surface plasmon resonance of immobilized gold nanorods

doi:10.1016/j.talanta.2012.05.037

Talanta

Volume 99, 15 September 2012, Pages 180-185

https://doi.org/10.1016/j.talanta.2012.05.037 Get rights and content

Abstract

The surface plasmon resonance of surface immobilized gold nanorods (Au NRs) was used to quantify mercury in tap water. Glass substrates were chemically functionalized with (3-mercaptopropyl)trimethoxysilane, which chemically bound the nanorods to produce a portable and sensitive mercury sensor. The analytical capabilities of the sensor were measured using micromolar mercury concentrations. Since the analytical response was dependent upon number of nanorods present, the limit of detection was 2.28×10⁻¹⁹ M mercury per nanorod. The possibility to using glass substrates with immobilized Au NRs is a significant step towards the analysis of mercury in tap water flows at this low concentration level.

Highlights

► The surface plasmon resonance of immobilized gold nanorods was used to quantify mercury in tap water. ► Glass slides were functionalized with MPTMS and chemically bound to nanorods. ► The immobilization on the surface improves the sensitivity of nanorods for mercury. ► The immobilization on the surface improves the limits of mercury detection.

Introduction

The utility of noble metal nanorods (NR) in sensing devices has been demonstrated in a variety applications, including the monitoring of biomolecular binding, [1], [2] elucidation of molecular motion, [3], [4] and enhancement of fluorescence [5], [6] and Raman scattering [7]. The design of these nano-scale sensors frequently exploit the localized surface plasmon resonance (LSPR) that arises from the resonant oscillation of electrons, which is sensitive to the refractive index of the surrounding medium, the composition of the NR, as well as their dimensions (see Mayer et al. for a recent review) [8]. Recent work in developing myriad facile NR immobilization strategies [9], [10], [11], [12] and characterizing [2], [3], [13] the resulting surfaces has advanced the possibility of utilizing immobilized NR sensors in routine analysis.

Herein, we describe an application of a well-studied immobilization strategy to create gold (Au) NR-based sensors that are sensitive to quantity, and selective for the presence of mercury. A known environmental pollutant, mercury can damage brain, heart, kidney and lungs; portable and robust methods for detecting mercury may have important utility. While several means for accurate and sensitive quantification of mercury exist, including atomic absorbance [14] and fluorescence spectroscopy, [15] voltammetric electrochemical methods, [16] and peizo-electric quartz crystals, [17] a platform for practical, portable on-site analysis could prove useful.

Previously, the sensitivity of Au NR to metallic mercury was demonstrated by Rex et al. [18] wherein the dual SPR peaks, related to the axial and longitudinal dimensions of the NR, indicated the concentration of mercury due to the Au-mercury interaction. In that case, the known affinity for Au and metallic mercury causes in amalgam formation, resulting an alterations to the structure of the NR that can be monitored by recording the absorption spectra of colloidal NRs. That work is extended here with the use of silica substrates that are chemically functionalized with (3-mercaptopropyl)trimethoxysilane (MPTMS). The thiol group on the MPTMS provides a capture surface for the Au NRs. The shifting of the LSPR peak maximum in the absorption spectra was observed when the longitudinal:axial aspect ratio changed linearly with respect to the mercury concentration in the presence of the NRs. The analytical figures of merit (AFOM) for the detection and quantification of mercury using the sensors are described, including characterization of the sensing substrate.

Section snippets

Chemicals and reagents

All experiments used analytical-reagent grade chemicals. Hydrogen peroxide (30%), hexadecyltrimethylammonium bromide (CTAB) and (3-mercaptopropyl)trimethoxysilane (MPTMS) were purchased at Sigma-Aldrich. Au NR with peak LSPR wavelengths 615 nm (6.29×10¹¹ nanorods/mL), and 750 nm (5.77×10¹⁰ nanorods/mL) were purchased from Nanopartz, Inc. (Loveland, CO). According to the manufacturer, their average dimensions were 25×51 nm and 25×71 nm. Ethanol, sodium borohydride, mercury (II) chloride, sodium

Imaging immobilized NRs

Substrates with immobilized Au NRs were prepared according to Okamoto and Yamaguchi [10]. Images of the surface were acquired using scanning electron microscopy. Similar to the example shown in Fig. 1, a low incidence of NRs aggregation was observed on the surface of most solid substrates. The number of nanoparticles on the cover-slide increased with immersion time, but long periods of immersion (>2 h) resulted in particle aggregation. A bright field illumination image of the resulting surface

Conclusion

This article details the analytical capabilities of Au NR immobilized on a glass substrate for sensing mercury in water samples. In comparison to solution measurements, the immobilization of Au NR on a solid substrate improves both the sensitivity and the LOD. No interference was observed from several inorganic ions commonly present in tap water samples. This selectivity results from the amalgamation of mercury to Au. The possibility to using glass substrates with immobilized Au NRs is a

Acknowledgments

We appreciate the assistance of Kirk Scammon in SEM training and support for SEM image acquisition at the Materials Characterization Facility at the University of Central Florida. This work was funded by U.S. Department of Energy (DE-SC0004813).

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Portable mercury sensor for tap water using surface plasmon resonance of immobilized gold nanorods

Abstract

Highlights

Introduction

Section snippets

Chemicals and reagents

Imaging immobilized NRs

Conclusion

Acknowledgments

Eng. Aspects

Anal. Chim. Acta

Anal. Chim. Acta

ACS Nano

Anal. Chem.

J. Am. Chem. Soc.

Chem. Commun.

Nano Lett.

J. Am. Chem. Soc.

PNAS

Chem. Rev.