DNA hybridization-enhanced porous silicon corrosion: mechanistic investigators and prospect for optical interferometric biosensing

摘要

Hybridization of DNA oligonucleotides in neutral aqueous solutions with complementary sequences immobilized on highly doped p-type porous silicon matrix is shown to result in an unexpectedly large shift in the Fabry-Perot interference pattern to lower wavelengths implying a decrease in effective optical thickness of the porous matrix. We have determined that the observed optical effects are due to enhanced corrosion (oxidation-hydrolysis) of the porous silicon layer triggered by the formation of complementary DNA duplexes. Scanning force microscopy and reflectance spectroscopy were employed at various stages of the signal evolution process to monitor and establish the material changes induced by the DNA binding events. We postulate that the slow background corrosion process initiated at the exposed Si-H-x, groups is dramatically enhanced as a result of the change in carrier charge density of the porous silicon layer in response to the local increase in the electrostatic field generated by the nucleic acid hybridization. The proposed mechanism is consistent with the experimental observations that the characteristics of the porous silicon matrix and the charge density of the hybridized DNA complexes can both influence the corrosion process. Functionalized porous silicon matrices prepared from highly doped silicon wafers (resistivity 1 mOmega(.)cm) produce large corrosion rates and improved signal to noise ratios. Moreover, the enhanced decrease in the effective optical thickness could be prevented by either shielding the negative charges of the DNA duplex in the presence of Mg2+ ions, or by using backbone charge neutral peptide nucleic acids (PNA) in the DNA hybridization experiments. The observed phenomenon is thus an example of an active sensor matrix in which the molecular recognition signal is transduced and amplified by a profound change in the chemical reactivity and physical property of the solid support itself. With the signal amplification mechanism described, binding of unlabeled complementary DNA oligonucleotides of approximately 0.1 amol/mm(2) has been detected suggesting the potential utility of this new approach in DNA sensing. (C) 2004 Elsevier Ltd. All rights reserved.