Spatial Characteristics of Contact Pin-Printed Silanes and Bioconjugates on Oxidized Porous Silicon

Porous silicon (pSi) exhibits strong, visible photoluminescence (PL) at room temperature. To stabilize the pSi PL and simultaneously impart chemical functionality we oxidize pSi (ox-pSi) and then contact pin-print organically modified silanes onto the ox-pSi surface. This strategy allows rapid microarray production for numerous applications; however, spot size and chemical homogeneity across the spot are crucial factors controlling microarray spot density and utility. In this article we used a 200 μm diameter solid tungsten pin to contact pin-print 3-aminopropyltriethoxysilane (APTES-) and butyraldehydetriethoxysilane (BATES-) derived spots onto ox-pSi and then used PL and Fourier transform infrared spectroscopy (FT-IR) imaging to characterize the spot size, shape, and spatial homogeneity. The APTES-derived spots formed >30× faster and spread ∼15% further in comparison to BATES-derived spots; however, the majority of feature spreading is attributed to an oxidized, silane-free halo, which surrounds the silanized core. In contrast, BATES-derived spots were composed of a single region that was silanized throughout. Bioconjugation studies with bovine serum albumin revealed that bioconjugate spot sizes on APTES-derived features were 40% smaller in comparison to BATES-derived features. For applications requiring higher-density microarrays on an ox-pSi platform, APTES is the more suitable organosilane.