Cu underpotential deposition on Au controlled by in situ Spectroscopic Ellipsometry

Prato, Mirko; Gussoni, A.; Panizza, Marco; Cavalleri, Ornella; Mattera, L.; Canepa, M.

doi:10.1002/pssc.200777882

Cited by 15 publications

(10 citation statements)

References 22 publications

(33 reference statements)

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“…In facts, the formation of films uniformly spread on gold-like substrates, even if very thin, usually induces a well-defined relative maximum of δΔ i +1 ,i at about 500 nm [ 46 , 52 ]. This is actually missing in the data, possibly indicating the formation of a low-coverage sub-monolayer [ 58 ], a situation that is compatible with non-specific His 6 –NTA interactions, in accordance with literature [ 10 ].…”

Section: Resultssupporting

confidence: 81%

Investigating organic multilayers by spectroscopic ellipsometry: specific and non-specific interactions of polyhistidine with NTA self-assembled monolayers

Solano¹,

Parisse²,

Cavalleri³

et al. 2016

Beilstein J. Nanotechnol.

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Summary Background: A versatile strategy for protein–surface coupling in biochips exploits the affinity for polyhistidine of the nitrilotriacetic acid (NTA) group loaded with Ni(II). Methods based on optical reflectivity measurements such as spectroscopic ellipsometry (SE) allow for label-free, non-invasive monitoring of molecule adsorption/desorption at surfaces. Results: This paper describes a SE study about the interaction of hexahistidine (His6) on gold substrates functionalized with a thiolate self-assembled monolayer bearing the NTA end group. By systematically applying the difference spectra method, which emphasizes the small changes of the ellipsometry spectral response upon the nanoscale thickening/thinning of the molecular film, we characterized different steps of the process such as the NTA-functionalization of Au, the adsorption of the His6 layer and its eventual displacement after reaction with competitive ligands. The films were investigated in liquid, and ex situ in ambient air. The SE investigation has been complemented by AFM measurements based on nanolithography methods (nanografting mode). Conclusion: Our approach to the SE data, exploiting the full spectroscopic potential of the method and basic optical models, was able to provide a picture of the variation of the film thickness along the process. The combination of δΔi +1 ,i(λ), δΨi +1 ,i(λ) (layer-addition mode) and δΔ† i ', i +1(λ), δΨ† i ', i +1(λ) (layer-removal mode) difference spectra allowed us to clearly disentangle the adsorption of His6 on the Ni-free NTA layer, due to non specific interactions, from the formation of a neatly thicker His6 film induced by the Ni(II)-loading of the NTA SAM.

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Section: Resultssupporting

confidence: 81%

Investigating organic multilayers by spectroscopic ellipsometry: specific and non-specific interactions of polyhistidine with NTA self-assembled monolayers

Solano¹,

Parisse²,

Cavalleri³

et al. 2016

Beilstein J. Nanotechnol.

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“…In-liquid measurements were performed in a home-made Teflon cell described in ref. 51 (angle of incidence 651) and data are reported in the range of high transparency of the medium. The spot size on the sample was of the order of a few mm 2 .…”

Section: Methodsmentioning

confidence: 99%

Spectroscopic ellipsometry meets AFM nanolithography: about hydration of bio-inert oligo(ethylene glycol)-terminated self assembled monolayers on gold

Solano

Parisse

Gramazio

et al. 2015

Phys. Chem. Chem. Phys.

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For the first time, to our knowledge, spectroscopic ellipsometry (SE) has been combined with state-of-the-art AFM differential height measurements conducted after shaving nano-lithography of ultrathin, soft-matter films for thickness determination. We investigated self-assembled monolayers of SH-(CH2)11-EGn-OH molecules on gold, where EG is ethylene glycol units and n = 3 and 6, a prototypical non-fouling system. We performed SE measurements (245-1200 nm) focusing on the changes induced by the formation of the film (difference spectra). SE measurements, analysed by simple models, confirm the formation of the S-Au interface, transparency of the SAMs and provide a sharp picture of the ability of the EG functionality to protect the surface from unspecific adsorption of proteins. A quantitative assessment of the film thickness by SE was carried out ex situ, thanks to the optical contrast between the film and the ambient, and by AFM in liquid. The cross-check between SE and AFM height measurements combined with the comparison between in-liquid and ex situ SE measurements allowed obtaining non-perturbative information about the vertical density profile of the SAM. The in-liquid SE measurements indicate a refractive index matching between the aqueous medium and the outer part of the SAM, consistent with a disordered configuration of OEG and/or the penetration of water amid the OEG strands. A critical discussion provides a detailed insight into the subtle issues and pitfalls related to the thickness determination of soft-matter films to the monolayer limit.

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“…Woollam Co. Inc.), and in situ characterizations were carried out at RT in a home-made Teflon cell [35] in the 245-1,000-nm spectral range, where they are not perturbed by solvent effects. Data analysis was performed using the WVASE software.…”

Section: Methodsmentioning

confidence: 99%

Yeast Cytochrome c Monolayer on Flat and Nanostructured Gold Films Studied by UV–Vis Spectroscopic Ellipsometry

et al. 2011

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Spectroscopic ellipsometry (SE) has been used to investigate the adsorption of yeast cytochrome c (YCC) on gold films. YCC is a prototypical molecular system to evaluate the sensitivity and reliability of optical methods in probing conformational changes upon adsorption at surfaces. Measurements have been performed in situ in aqueous solutions at room temperature. We have applied to monolayer-thick YCC films the same scheme of analysis of SE spectra used in our recent works on thiolate self-assembled monolayers on gold, exploiting the so-called δ and δ difference spectra. A comparison between δ and δ spectra obtained from YCC adsorption on flat and cluster-assembled nanostructured gold films, obtained by supersonic cluster beam deposition is proposed. For both kinds of substrate δ and δ , difference spectra show well-defined features related to molecular optical absorptions typical of the so-called heme group, in particular the Soret band at about 410 nm. These features appear in the same position found for molecules in solution, suggesting that YCC native conformation is maintained upon adsorption also in the case of a substrate with typical roughness at the nanoscale.

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Cu underpotential deposition on Au controlled by in situ Spectroscopic Ellipsometry

Cited by 15 publications

References 22 publications

Investigating organic multilayers by spectroscopic ellipsometry: specific and non-specific interactions of polyhistidine with NTA self-assembled monolayers

Investigating organic multilayers by spectroscopic ellipsometry: specific and non-specific interactions of polyhistidine with NTA self-assembled monolayers

Spectroscopic ellipsometry meets AFM nanolithography: about hydration of bio-inert oligo(ethylene glycol)-terminated self assembled monolayers on gold

Yeast Cytochrome c Monolayer on Flat and Nanostructured Gold Films Studied by UV–Vis Spectroscopic Ellipsometry

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