The present disclosure provides devices, systems and methods for sequencing nucleic acid molecules. Nucleic acid molecules can be sequenced with a high accuracy (e.g., greater than 97% in a single pass) using a chip comprising an array of independently addressable nanopore sensors at a density of at least about 500 sites per 1 mm2. An individual nanopore sensor can include a nanopore in a membrane that is adjacent or in proximity to a sensing electrode.