Optimizing the immobilization of gold nanoparticles on functionalized silicon surfaces: amine- vs thiol-terminated silane

Abstract

Immobilization of gold nanoparticles on planar surfaces is of great interest to many scientific communities; chemists, physicists, biologists, and the various communities working at the interfaces between these disciplines. Controlling the immobilization step, especially nanoparticles dispersion and coverage, is an important issue for all of these communities. We studied the parameters that can influence this interaction, starting with the nature of the terminal chemical function. Thus, we have carefully grafted silanes terminated by either amine or thiol groups starting from aminopropyltriethoxysilane (APTES) or mercaptopropyltriethoxysilane. We also changed the chain length for thiol-terminated layers through covalent grafting of mercaptoundecanoic acid (MUA) on APTESmodified layers, and the protocol of nanoparticles deposition to evaluate whether other factors must be taken into consideration to rationalize this interaction. The formed layers were characterized by X-ray photoelectron spectroscopy and gold nanoparticles deposition was monitored by scanning electron microscopy and surface-enhanced Raman scattering. We observed significant differences in terms of nanoparticles dispersion and density depending on the nature of the chemical layer on silicon. The use of ultrasounds during the deposition process was very efficient to limit aggregates formation. The optimal deposition procedures were obtained through the use of APTES and APTES/MUA functionalization. They were compared in terms of coverage, dispersion, and densities of isolated nanoparticles. The APTES/MUA surfaces clearly showed better results that may arise from both the longer chain and the dilution of thiol end groups.

Revealing the Interplay between Adsorbed Molecular Layers and Gold Nanoparticles by Linear and Nonlinear Optical Properties

“…The Si/SAM samples were previously characterized by X-ray photoelectron spectroscopy and contact angle measurements. 10 The results confirmed the successful grafting of APTES on silicon surfaces. Upon adding MUA to the APTES-modified layers, only 24% of the amine functions reacted leading to a mixed layer SH/NH 2 (24%/76%).…”

Self-organization of gold nanoparticles on silanated surfaces

“…One or two of the ethoxy groups from the APTES molecules bonded with hydroxylated glass (type I and type II) may create cross-linking of APTES molecules, which in turn would lead to lower availability of free amine terminal groups for a potential attachment of AuNPs. Another possible scenario (type III) is that hydrogen bonds may form between some of the amine functional groups and –OH from the hydroxylated glass substrate leading the –NH 2 terminal group towards the substrate [24–25]. If APTES molecules are perfectly adsorbed on the –OH terminated glass substrate, a full coverage of AuNPs on the silanized glass substrate can be achieved.…”

Gold colloid-nanostructured surfaces for enhanced piezoelectric immunosensing of staphylococcal enterotoxin A

“…On silicon substrates, whose surface is covered with a thin native silica layer, this was achieved following a previously optimized procedure [50] by first assembling aminopropyltriethoxysilane (APTES) on silanol groups, then, in a second step, by reaction between the surface amino groups and 11-mercaptoundecanoic acid (MUA) whose terminal carboxylic acid group had been converted on the side into an activated N-hydroxysuccinimide ester by reaction with NHS and EDC (Scheme 1-A). This surface chemistry leads to a SelfAssembled Monolayer (SAM) terminated by a mixture of thiols and amine with SH/NH2 ratio (measured by X-Ray Photoelectron Spectroscopy (XPS) directly from the ratio S/N) = 0.24.…”

“…This surface chemistry leads to a SelfAssembled Monolayer (SAM) terminated by a mixture of thiols and amine with SH/NH2 ratio (measured by X-Ray Photoelectron Spectroscopy (XPS) directly from the ratio S/N) = 0.24. This mixed SAM has been previously shown by us to afford a high density of AuNP as well as a limited number of particle aggregates [50]. We applied a similar surface chemistry to gold sensors that were sequentially treated with cysteamine to generate surface amino groups then by activated MUA (Scheme 1-B).…”

“…Furthermore, thanks to the biocompatibility of AuNPs, biomolecules immobilized on such platforms are less prone to lose their bioactivity. In the present study, gold-and silicon-coated quartz crystal sensors were modified with gold nanoparticles according to optimized procedures [50,51] so as to slightly increase their surface area and provide a three-dimensional topography allowing a better accessibility of the recognition sites. These nanostructured sensors were employed as platforms to design immunosensors for the piezoelectric detection of SEA (Scheme 1).…”