In the present experimental work, it is shown for the first time that liquid filled multi-walled carbon nanotubes (MWCNTs) exhibit remarkably enhanced characteristics for sensor applications, the detection threshold being lowered by as much as an order of magnitude, while detection sensitivity is doubled for a number of molecules including ascorbic acid, dopamine, and uric acid. The sensitivity obtained for DA is 84 μA mM−1 (linear range 3 to 30 μM) detection limit is 1.6 μM. NMR relaxometry at a moderately low field confirms that the improved sensor characteristics are correlated with the filling of MWCNTs with solvents such as acetonitrile, dimethyl sulfoxide, etc., such confinement resulting in increased solvent relaxation rates. The filling of MWCNTs appears to relate to solvent-CNT interactions that are in line with the principle of hard and soft acids and bases, and also correlates with solvent dipole moments. © 2019 The Electrochemical Society.