Optimizing FRET on Aluminum Surfaces via Controlled Attachment of Fluorescent Dyes

Alexandra Petreto,Marcelina Cardoso Dos Santos,Gabriel Ribeiro Dos Santos,Olivier Lefebvre,Francesco De Angelis,Mehdi Ammar,Niko Hildebrandt,Denis Garoli,Paolo Ponzellini

doi:10.1021/acsomega.8b02774

Abstract

Forster resonance energy transfer (FRET) between fluorescent dyes is a frequently applied technique for analyzing concentrations and conformations of biomolecules. Optimizing FRET by controlled dye-surface functionalization is an important requirement to develop sensors based on surface–biomolecule interactions. Here, we investigate the silanization of silica with aminosilanes ((3-aminopropyl)triethoxysilane, APTES) and their subsequent functionalization with commercial organic fluorophores (ATTO-550 and ATTO-647N) for controlling the fluorescence intensity and FRET interaction between the dyes. Owing to the growing application of aluminum in plasmonics and the possibility to enhance FRET with aluminum nanostructures, we used plasma-enhanced atomic layer deposition (PEALD) to cover aluminum layers with thin silica coatings (∼4 nm) as a prototypical system to apply and characterize our controlled APTES–dye functionalization procedure. Detailed spectroscopic and fluorescence imaging analyses were used to op...

Highlights

Silanization is a well-known and stable surface functionalization method that has been applied for the attachment of various biomolecules on silicon, silica, glass, or poly(dimethylsiloxane) for bioanalytical devices, biosensors, diagnostics, and microfluidics.[1−4] Many of these biosensing applications based on silanized substrates used optical detection, including plasmonics,[5] fluorescence,[6,7] and Förster resonance energy transfer (FRET).[8]
We have used Al-coated silicon wafers as a prototypical system to demonstrate that the deposition of thin silica layers (∼4 nm) and a subsequent silanization with APTES can be used to attach fluorescent dyes in a controlled, homogeneous, and reproducible manner
Successful attachment of silanes was confirmed by contact angle and Fourier-transform infrared (FTIR) measurements, and dye functionalization was followed by fluorescence imaging

Summary

Introduction

Silanization is a well-known and stable surface functionalization method that has been applied for the attachment of various biomolecules on silicon, silica, glass, or poly(dimethylsiloxane) for bioanalytical devices, biosensors, diagnostics, and microfluidics.[1−4] Many of these biosensing applications based on silanized substrates used optical detection, including plasmonics,[5] fluorescence,[6,7] and Förster resonance energy transfer (FRET).[8]. Plasmon-based sensing via enhanced fluorescence on the surfaces of metal nanoparticles or nanostructured metal surfaces has become an important method for the detection of biological or biochemical molecules and interactions.[16−28] gold and silver are arguably the most applied plasmonic materials, which can be functionalized by sulfhydrylreactive chemistry without additional surface modification,[29] the advantages of aluminum concerning costs, natural abundance, and manufacturing have resulted in many. ACS Omega applications of aluminum plasmonics.[30−35] Recently, Wenger et al demonstrated significant enhancement of FRET when a DNA conjugated with a dye−dye (ATTO-550 and ATTO647N) FRET pair moved into close proximity of aluminum nanoapertures or nanoantennas.[36,37] The combination of these plasmonic-FRET results, the successful coating of gold nanostructures by thin silica layers using plasma-enhanced atomic layer deposition (PEALD),[38] and the general higher flexibility of PEALD39 motivated us to develop a surface functionalization strategy for aluminum. Direct and controlled dye functionalization of aluminum via thin silanized silica coatings should be able to take into account the fine line between decreasing (very short fluorophore−surface distances) and increasing (few nanometers of fluorophore−surface distances) fluorescence intensities.[26,40−43] it has the potential to become useful for investigating label-free biomolecules in future plasmonic studies using nanostructured metal surfaces

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Conclusion