In order to detect early tumor markers and gain valuable time for treatment, there is an urgent need to develop a fast, cheap, and ultrasensitive multi-reading sensing platform. Herein, a solid/liquid two-phase dual-output biosensor was explored based on a sensitized sonochemiluminescence (SCL) strategy and a multifunctional carbon nano-onion (CNO) probe. It is clear that ultrasonic radiation caused the formation of hydroxyl radicals (˙OH), triggering the SCL signal of the emitter lucigenin (Luc²⁺). Meanwhile, titanium carbide nanodots and ethanol were used to enhance the SCL signal, and an astonishingly linear enhancement of the SCL intensity was produced with increasing ethanol concentration. More importantly, the CNOs, with their excellent photothermal properties and adsorption capacity, can output both the temperature signal and an enhanced SCL strength from the solid–liquid phase. Through inter-calibration of the signals from the two-phases, this biosensor shows excellent analytical performance for the detection of the ovarian cancer biomarker, human epididymis-specific protein 4, from 10⁻⁵ to 10 ng mL⁻¹ with a low detection limit of 3.3 fg mL⁻¹. This work not only provides a novel two-phase signal-output mode that broadens the scope of multiperformance joint applications of CNOs, but also enriches the quantitative detection of point-of-care testing.