Preparation of chemical gradients on porous silicon by a dip coating method

Abstract

Gradient surfaces have become invaluable tools for the high-throughput characterisation of biomolecule-and cellmaterial surface interactions as they allow for the screening and optimisation of surface parameters such as surface chemistry, topography and ligand density in a single experiment. Here, we have generated surface chemistry gradients on oxidised porous silicon (pSi) substrates using silane functionalisation. In these studies, pSi films with a pore size of 15-30 nm and a layer thickness of around 1.7 µm were utilised. The manufacture of gradient surface chemistries of silanes was performed using a simple dip coating method, whereby an increasing incubation time of the substrate in a solution of the silane led to increasing surface coverage of the silane. In this work, the hydrophobic n-octadecyldimethyl chlorosilane (ODCS) and pentafluorophenyldimethyl chlorosilane (PFPS) were used since they were expected to produce significant changes in wettability upon attachment. Chemical gradients were characterised using infrared (IR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and sessile drop water contact angle measurements. In addition, the surface chemistry of the gradient was mapped using synchrotron IR microscopy. The ODCS gradient displayed sessile drop water contact angles ranging from 12° to 71°, confirming the successful formation of a gradient. IR microscopy and an XPS line scan confirmed the formation of a chemical gradient on the porous substrate. Furthermore, the chemical gradients produced can be used for the high-throughput in vitro screening of protein and cell-surface interactions, leading to the definition of surface chemistry on nanostructured silicon which will afford improved control of biointerfacial interactions.

A Decade of Porous Silicon as Nano‐Explosive Material

“…Drying of the samples after the porous silicon formation can be achieved by rinsing the samples with ethanol or methanol, followed by the drying agent hexane, and also drying it subsequently under a gentle stream of nitrogen [1,25]. The samples can also be rinsed using another drying agent, pentane, to ensure the structural stability of the pores [26].…”

Methods to Evaluate Spatial Uniformity in Porous Silicon

“…Alternatively, the porous silicon layer can be surface-modified to different extents at different sites, either in patches (Lee et al 1996a, b;Buriak 1998, 2001) or as a gradient (Thompson et al 2010(Thompson et al , 2011. Chemical modification gradients across porous silicon have been achieved electrochemically (Thompson et al 2010), by hydrosilylation in the presence of a concentration gradient of a diazonium salt initiator (Thompson et al 2011) or by slow immersion of a sample into a silane solution (for oxidized porous silicon) (Clements et al 2008).…”

Preparation and Characterization of Pore-Wall Modification Gradients Generated on Porous Silicon Photonic Crystals Using Diazonium Salts

“…In our prior efforts to generate chemical gradients in a porous Si film, we were unable to obtain a transverse gradient modification that was constant through a thicker porous silicon layer (∼10 μm) using electrochemical grafting methods. However, a dip-coating method has been shown to generate a gradient pore modification in oxidized porous silicon films using chlorosilane solutions . We hypothesized that such an approach would provide a chemical gradient that would be useful in producing an optical array-based sensor.…”