DNA at aqueous/solid interfaces: chirality-based detection via second harmonic generation activity.

We present electronic spectra of single-strand and duplex DNA oligonucleotides covalently attached to fused quartz/aqueous interfaces and demonstrate that a strong nonlinear optical linear dichroism response is obtained when adenine and thymine bases undergo Watson-Crick base pairing to form a double helix. Complementary chi(3) charge screening studies indicate that the signal originates from 5 x 10(11) strands per square centimeter, or 6 attomoles of surface-bound oligonucleotides. The label-free, molecular-specific nature afforded by nonlinear optical studies of DNA at aqueous/solid interfaces allows for the real-time tracking of interfacial DNA hybridization for the first time.

DNA single strands tethered to fused quartz/water interfaces studied by second harmonic generation.

Second harmonic generation (SHG) is used to study oligonucleotides at aqueous/solid interfaces for the first time. Detailed thermodynamic state information for interfacial DNA single strands, namely, the interfacial charge density, the interfacial potential, and the change in the interfacial energy density, is obtained. The phosphate groups on the DNA backbone serve as intrinsic labels that do not require DNA modification other than surface attachment.