Highly sensitive polysilicon wire sensor for DNA detection using silica nanoparticles/γ-APTES nanocomposite for surface modification

Poly-silicon wire (PSW) coated with a nanocomposite composed of a mixture of 3-aminopropyltriethoxysilane (γ-APTES) and polydimethylsiloxane (PDMS)-treated hydrophobic fumed silica nanoparticles (NPs) plus UV light illumination (γ-APTES + NPs + UV) is proposed for label-free DNA detection. We found that the linear detection range extended from 1 fM to 10 μM, with a lowest detection limit of 0.3 fM, could be achieved using the PSW sensor for the analysis of 10-base-long synthetic DNA including the single-strained (ss)-homopolymers poly-adenine [poly(A)], poly-thymine [poly-(T)], poly-cytosine [poly(C)], and poly-guanines [poly(G)]. The proposed PSW sensor can detect a single base change within a trace amount of a 5-base-long DNA molecule solution with an ultra-low concentration of 10 fM, which is loaded and transferred by the focus-ion-beam (FIB) milled AFM tip. The adsorption of DNA molecules onto the γ-APTES + NPs + UV surface is extremely efficient and follows the Langmuir adsorption isotherm. Fourier transform infrared (FTIR) spectroscopy analysis showed the improvement was attributable to the ethoxy groups in the γ-APTES that reacted chemically with the silica NPs surfaces, forming a large clustered surface which increased the interaction between the DNA molecules and the NH2 ligand of γ-APTES.