Outer-surface charge modulation of photothermal diffusion voltage enables ultrasensitive sensing in nanofluidic membranes

Abstract

Precise ionic transport regulation is central to nanofluidic sensing, yet quantitative readout at ultratrace analyte levels remains challenging because conventional externally biased measurements primarily transduce target binding through resistance changes. When trace analytes induce negligible steric variation, the system resistance is essentially unchanged, yielding insufficient ionic current contrast. Here we develop an outer-surface charge-modulated, photothermal diffusion voltage-driven strategy in a MXene nanofluidic membrane. Under 808 nm illumination, the strong photothermal conversion of Ti₃C₂T_x establishes a stable transmembrane temperature gradient across K⁺-permselective lamellar nanochannels, generating a tunable photothermal diffusion voltage (V_diff). Trace-level binding events markedly modulate the outer-surface charge density, thereby altering the K⁺ transference number and amplifying minute charge variations into pronounced changes in V_diff and the zero-bias ionic current, even when steric hindrance and resistance remain nearly constant. Using microcystin-LR (MC-LR) as a model toxin, this strategy enables ultratrace detection down to 1 × 10⁻⁷ μg/L, delivering a 10⁵-fold sensitivity enhancement over conventional external voltage-driven readout while maintaining high selectivity against structural analogues and reliable quantification in real water matrices. This work establishes a light-addressable route to actively regulate nanofluidic voltages via outer-surface charge, opening opportunities for photoresponsive nanofluidic sensors and iontronic circuitry.