Elsevier

Electrochimica Acta

Volume 48, Issue 28, 15 December 2003, Pages 4291-4299
Electrochimica Acta

Optical and electrochemical evaluation of colloidal Au nanoparticle-ITO hybrid optically transparent electrodes and their application to attenuated total reflectance spectroelectrochemistry

https://doi.org/10.1016/j.electacta.2003.08.004Get rights and content

Abstract

Colloidal Au nanoparticle monolayers covalently deposited on conductive layers of indium tin oxide (ITO) were fabricated and evaluated as optically transparent electrodes (OTEs) for spectroelectrochemical applications. Specifically, the electrodes were characterized using UV-Vis spectroscopy and cyclic voltammetry; comparisons are made with other types of hybrid ITO optically transparent electrodes. The optical modulation of surface-bound colloidal Au in response to potential cycling over a wide potential window (0.6 to −1.0 V) was acquired in an attenuated total reflectance (ATR) spectroelectrochemical cell. Finally, uptake of a model analyte, tris-(2,2′-bipyridyl)ruthenium(II) chloride, into a Nafion charge selective film spin coated onto the colloidal Au-ITO hybrid electrode was examined using ATR absorbance spectroelectrochemistry. Dependence of uptake on film thickness is addressed, and non-optimized detection limits of 10 nM are reported.

Introduction

In recent years, interest in chemical sensors has soared because of the technological advances that have been made, especially in materials science and device miniaturization, to increase the efficiency and range of application of these devices [1]. One problem that continues to limit many sensor designs, however, is lack of sufficient selectivity. The highest degree of selectivity is often offered by biosensors, which rely on highly specific biological interactions to distinguish between analyte and interferences [1]. Unfortunately, these designs lack ruggedness and are often inappropriate for sensing of non-biological analytes, or those of environmental interest.

In an effort to improve chemical selectivity, we have been for some time developing spectroelectrochemical sensors possessing three modes of selectivity [2]. We combine the dual selectivity offered by the traditional spectroelectrochemical cell [3] (applied potential and optical absorbance) with a chemically selective film coating the electrode surface that blocks access of certain species based on, for example differences in charge. Optical interrogation is restricted to the contents of the film by employing attenuated total reflectance (ATR) spectroscopy, in which light is introduced into a multiple internal reflectance medium at an angle greater than the critical angle, as defined by Snell’s Law. In this situation, an evanescent wave penetrates the film to a thickness of ca. one wavelength at each reflection point, so film thickness is often matched to the wavelength of light employed. Therefore, using this trimodal scheme, an analyte can only be detected if it satisfies three criteria: (1) it gains entry into the selective film, (2) it undergoes electrochemical oxidation or reduction at the applied potential, and (3) it exhibits a change in spectral property (i.e. absorbance or fluorescence) at a given wavelength upon oxidation or reduction at the electrode surface.

We have demonstrated the concept of the ATR spectroelectrochemical sensor using a variety of analytes [2], [4], probed its ability to function in the presence of direct interferences [5], and have even applied it to detection of ferrocyanide in radioactive tank waste at the Hanford nuclear waste storage site near Richland, WA [6], [7]. More recently, we have extended the general principle of the sensor to fluorescence measurements, obtaining detection limits on the order of 10−12 M for Ru(bipy)32+ [8].

In the interest of improving the performance of the ATR spectroelectrochemical sensor, we are constantly exploring new chemically selective films, cell geometries, and electrode materials. One of our recent interests in this vein has been the development and characterization of novel noble metal– and carbon–indium tin oxide (ITO) optically transparent electrodes (OTEs) [9]. Most of the work we have reported to this point was obtained using conductive indium tin oxide films on glass substrates; metal or carbon hybrid ITO electrodes were investigated as a means of improving electrochemical responses for a wider range of redox species. Of all of the hybrid electrodes investigated, Au-ITO hybrids provided the best compromise between facile electron transfer kinetics for a wide variety of inorganic and organic redox species and optical transparency [9]. However, we note that complex sputtering facilities are required to manufacture these hybrids, and they have not been investigated in an ATR spectroelectrochemical application.

With the aforementioned considerations in mind, we have decided to investigate colloidal Au nanoparticle-modified ITO hybrid OTEs as candidates for spectroelectrochemical ATR measurements. Conductive films of colloidal Au nanoparticles formed on conductive [10] and non-conductive [11] substrates have been frequently reported in the literature and have found electrochemical applications based on their ease of preparation and excellence as voltammetrically addressable surfaces [12], [13], [14], [15], [16], [17], [18]. However, there have been few reports of their use as optically transparent electrodes [19], [20], [21] and none as electrodes for ATR spectroelectrochemical measurements.

In this paper, we examine the voltammetric responses of colloidal Au-ITO hybrid OTEs to a series of redox probes including potassium ferricyanide [K3Fe(CN)6], tris-(2,2′-bipyridyl)ruthenium(II) chloride [Ru(bipy)3Cl2], and para-aminophenol (PAP). Since these species were also evaluated in our previous study of hybrid OTEs, comparisons are made with the sputtered Au-ITO hybrids as well as with bare ITO and commercially available Au disk electrodes. Also examined are accessible potential window and electrolyte dependence, as well as optical transmittance; comparisons with other hybrids and bare ITO are again made whenever possible.

Of particular interest here, however, is a careful evaluation of the optical modulation of the Au nanoparticle layer in response to potential cycling over a wide potential window. While this phenomenon has been previously reported [21], we examine it closely within the context of the ATR spectroelectrochemical sensing experiment. Finally, we demonstrate the utility of these hybrid OTEs toward application as sensor platforms in our latest generation selective film-based ATR spectroelectrochemical sensing apparatus.

Section snippets

Reagents

Potassium ferricyanide (Aldrich), tris-(2,2′-bipyridyl)ruthenium(II) chloride (Aldrich), and para-aminophenol (Sigma–Aldrich) were used as redox and/or spectroelectrochemical probes. Supporting electrolyte solutions consisted of either (1) 0.1 M KNO3 (Aldrich), or (2) 0.1 M phosphate buffered saline (PBS) prepared using sodium phosphate (dibasic and monobasic, Sigma) and NaCl (Aldrich). All solutions were diluted using 18  cm distilled water sourced from a Barnstead Nanopure water purification

Results and discussion

The work described in this paper resulted from our interest in developing new electrodes for general spectroelectrochemical analysis as well as the more specific needs associated with ATR spectroelectrochemistry. To this end, we have been developing and testing so-called hybrid electrodes that consist of noble metal or carbon films sputtered or evaporated onto conductive ITO substrates. Most noteworthy is the fact that these electrodes can provide vastly improved electrochemical responses for

Conclusions

Colloidal Au-ITO hybrid OTEs have been demonstrated to be excellent candidates for routine spectroelectrochemical analysis, as well as effective sensor platforms for ATR based spectroelectrochemical sensors employing thin chemical-selective films. When compared with previously reported sputtered Au-ITO hybrid OTEs, the colloidal Au hybrids have proved equal or superior in terms of optical transparency, electrochemical response to a wide range of redox species, and robustness to both repeated

Acknowledgements

We wish to thank the US Department of Energy (DE-FG07-99ER62311-70010) for financial support, as well as the Hayes Fund which aided in the purchase of the ellipsometer and electrochemical workstation.

References (24)

  • M. Lu et al.

    J. Coll. Int. Sci.

    (2002)
  • B.R. Eggins, Chemical Sensors and Biosensors, Wiley, New York,...
  • W.R. Heineman et al.

    Aust. J. Chem.

    (2003)
  • R.J. Gale (Ed.) Spectroelectrochemisty: Theory and Practice, Plennum Press, New York,...
  • Y. Shi et al.

    Anal. Chem.

    (1997)
  • Y. Shi et al.

    Anal. Chem.

    (1997)
  • M. Maizels et al.

    Electroanalysis

    (2002)
  • M.L. Stegemiller et al.

    Environ. Sci. Technol.

    (2003)
  • N. Kaval, C.J. Seliskar, W.R. Heineman, Anal. Chem., in...
  • I. Zudans, J.R. Paddock, H. Kuramitz, A.T. Maghasi, C.M. Wansapura, S.D. Conklin, N. Kaval, T. Shtoyko, D.J. Monk, S.A....
  • K.R. Brown et al.

    J. Am. Chem. Soc.

    (1996)
  • M.D. Musick et al.

    Chem. Mater.

    (1997)
  • Cited by (22)

    • Electrochemical sensor based on direct electron transfer of HIV-1 Virus at Au nanoparticle modified ITO electrode

      2013, Biosensors and Bioelectronics
      Citation Excerpt :

      However, Au nanoparticle modified ITO electrode shows a remarkable oxidation peak at 0.137 V and a reduction peak at 0.100 V. This sharp oxidation peak is due to oxide formation and the occurrence of Au stripping in the presence of phosphate ion, which forms a complex ion with Au3+ (Richardson et al., 2003). In addition, a large background current was observed for an Au nanoparticle modified ITO electrode in comparison with bare ITO electrode which is due to the large electroactive surface area (Arrigan, 2004).

    • Fluorescence quenching/enhancement surface assays: Signal manipulation using silver-coated gold nanoparticles

      2008, Chemical Physics Letters
      Citation Excerpt :

      It was verified that colloidal gold nanoparticles were monodisperse (ca. 12–13 nm) using UV–visible spectra [17]. The gold nanoparticles were covalently attached to ITO slides as previously described [18]. Briefly, the ITO slides were scrupulously washed with soap (Alconox) and rinsed with distilled water, then slides were soaked overnight in 0.1 M NaOH to activate the surface, rinsed copiously with distilled water, and soaked overnight at 80–90 °C in a solution of 5% (v/v) aminopropyltriethoxysilane in 0.1 M acetic acid (pH 5.5).

    • Gold nanoparticle arrays directly grown on nanostructured indium tin oxide electrodes: Characterization and electroanalytical application

      2005, Analytica Chimica Acta
      Citation Excerpt :

      Moreover, ITO has a wide potential window and possesses stable electrochemical and physical properties, which allows it to be an excellent electrode substrate for constructing metal and semiconductor nanoparticle arrays. The electrochemical characteristics and applications of various gold nanoparticle-modified ITO electrodes have been extensively studied [4–16]. Because gold tends to bond with some organic molecules, the attachment of gold nanoparticles on ITO usually uses peculiar binder molecules such as (aminopropyl)siloxane, (mercaptopropyl)siloxane and other analogues utilizing the bonding ability of the silanol group to the ITO glass surface and the affinity of the –SH or –NH2 group toward the gold particles [17].

    View all citing articles on Scopus
    View full text