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

## TL;DR

A new nanofluidic sensing method uses light to detect tiny amounts of toxins with much higher sensitivity than traditional techniques.

## Contribution

A photothermal diffusion voltage strategy in MXene nanofluidic membranes enables ultrasensitive detection via outer-surface charge modulation.

## Key findings

- The method achieves 10⁵-fold sensitivity enhancement for microcystin-LR detection.
- It retains high selectivity against structural analogs and works in real water samples.
- Outer-surface charge modulation amplifies charge variations into detectable voltage changes.

## 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 an MXene nanofluidic membrane. Under 808 nm illumination, the strong photothermal conversion of Ti3C2Tx establishes a stable transmembrane temperature gradient across K+-permselective lamellar nanochannels, generating a tunable photothermal diffusion voltage (Vdiff). 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 Vdiff 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−1, delivering a 105-fold sensitivity enhancement over conventional external voltage-driven readout while retaining 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.

A photothermal diffusion voltage-driven strategy in MXene nanofluidic membranes amplifies outer-surface charge modulation, achieving ultrasensitive sensing with a 105-fold enhancement over conventional methods.