Low-voltage, low-cost, high-performance monolayer field-effect transistors are demonstrated, which comprise a densely packed, long-range ordered monolayer spin-coated from core-cladding liquid-crystalline pentathiophenes and a solution-processed high-k HfO2-based nanoscale gate dielectric. These monolayer field-effect transistors are light-sensitive and are able to function as reporters to convert analyte binding events into electrical signals with ultrahigh sensitivity (approximate to 10 ppb).