Optimized DNA hybridization detection on nanocolloidal particles by dielectrophoresis.

Oligonucleotides of varying surface coverage are functionalized onto the surface of 100 nm silica particles and the corresponding hybridization reaction with target ssDNA is studied using dielectrophoresis (DEP). The measured DEP cross-over frequency (cof) is found to be sensitive to the oligonucleotide surface conformation. Zeta potential and particle size measurements suggest that at low oligo surface concentrations, non-specific binding of oligo to the particle surface prevents efficient hybridization. At high surface coverage, steric hindrance due to the fully stretched, tightly packed oligo conformation prevents diffusion of DNA molecules to the particle surface. The optimum surface coverage exists at intermediate coverage where the particle is found to be the least electrically conductive, and hence exhibits the lowest measured cof. A simple DEP cof measurement hence allows one to determine the optimal oligo surface coverage for increased hybridization efficiency and detection sensitivity.