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Microfluidic & nanofluidic technologies for chemistry, physics, biology, and bioengineering
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Paper
Lab Chip, 2009, 9, 1789 - 1796, DOI: 10.1039/b900748m
Directing polyallylamine adsorption on microlens array patterned silicon for microarray fabrication
Gaurav Saini, Richard Gates, Matthew C. Asplund, Steve Blair, Sachin Attavar and Matthew R. Linford
The selective adsorption of reagents is often essential for bioarray and lab-on-a-chip type devices. As the starting point for a bioarray, alkyl monolayer terminated silicon shards were photopatterned in a few nanoseconds with thousands of wells (spots) using an optical element, a microlens array. Polyallylamine (PAAm), a primary amine containing polymer, adsorbed with little selectivity to the spots, i.e., silicon oxide, over the hydrophobic background. However, at appropriate concentrations, addition of a cationic surfactant to the PAAm deposition solution, cetyltrimethylammonium chloride, prevented the nonspecific adsorption of PAAm onto the hydrophobic monolayer, while directing it effectively to the active spots on the device. A nonionic surfactant was less effective in preventing the nonspecific adsorption of PAAm onto the hydrophobic monolayer. The localized reactions/interactions of adsorbed PAAm with four species that are useful for bioconjugate chemistry: glutaric anhydride, phenylenediisothiocyanate, biotin NHS ester, and an oligonucleotide (DNA) were shown in the spots of an array. The reactivity of PAAm was further demonstrated with an isocyanate. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) played an important role in confirming selective surface reactivity and adsorption. X-ray photoelectron spectroscopy (XPS), spectroscopic ellipsometry, and wetting confirmed PAAm reactivity on planar substrates.
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