Single-Molecule Discrimination of Labeled DNAs and Polypeptides Using Photoluminescent-Free TiO2 Nanopores

Multicolor fluorescence substantially expands the sensing capabilities of nanopores by complementing or substituting the resistive pulsing signals. However, to date single-fluorophore detection in multiple color channels has proven to be challenging primarily due to high photoluminescence (PL) emanating from the silicon nitride (SiNx) membrane. We hypothesize that the high bandgap of titanium oxide (TiO2) would eliminate the PL background when used as a substrate for a nanopore, and hence enable individual fluorophore sensing during the fast passage of biomolecules through the pore. Herein, we introduce a method for fabricating locally supported, free-standing, TiO2 membranes, in which solid-state nanopores can be readily drilled. These devices produce essentially no PL in the blue-to-red visible spectral range, even when excited by multiple lasers simultaneously. At the same time, the TiO2 nanopores exhibit low electrical noise comparable with standard SiNx devices. Importantly, the optical signal-to-bac...