# Stacked-overlapped graphdiyne nano-iontronics enabling enhanced monovalent/divalent cation selectivity for single-cell pH detection

## TL;DR

A new nano-iontronic device using graphdiyne enables precise, real-time pH measurements at the single-cell level with high cation selectivity.

## Contribution

First single-cell pH sensing with high monovalent/divalent cation selectivity using stacked graphdiyne's sub-nanometer pores and tunable chemistry.

## Key findings

- so-GDY-based pH sensor shows linear ionic current decrease with pH reduction due to protonation of surface functional groups.
- Device exhibits 5x faster transport of monovalent cations compared to divalent cations, with resistance to interference.
- Sensor maintains stability, repeatability, and biocompatibility for single-cell and single-organelle pH detection.

## Abstract

Developing nano-iontronic devices that minimize ionic interference is essential for precise measurements in complex physiological systems. Graphdiyne (GDY), a novel carbon allotrope featuring sub-nanometer pores, enables effective regulation of ionic transport and is therefore a promising material for high-performance iontronic applications. Here, we report a pH-responsive nano-iontronic device fabricated by stacking and overlapping graphdiyne (so-GDY) layers onto the tip of the nanopipette. This so-GDY-based pH nano-iontronic sensor exhibits a linear decrease in ionic current under negative potential as the pH decreases from 8.00 to 5.50. This response is attributed to protonation of the oxygen-containing functional groups on the so-GDY surface and edges, which diminishes the negative surface charge and thereby reduces ionic conductivity. A key advantage of this nano-iontronic device is its excellent selectivity, demonstrating robust resistance to interference from divalent cations (Mg2+, Ca2+) and small molecules within the pH range of 8.00–5.50, while maintaining stable detection currents. The so-GDY-based pH nano-iontronic device transports monovalent cations up to 5 times more rapidly than divalent cations, alongside excellent repeatability, reversibility, and stability. This combination of features yields a biocompatible, high-resolution tool for minimally invasive, real-time pH measurements at the single-cell and even at a single-organelle level, opening new avenues for investigating cellular dynamics and disease pathogenesis with enhanced clarity.

We have for the first time reported a single-cell pH iontronic sensing with high monovalent/divalent cation selectivity by using the sub-nanometer pores and tunable surface chemistry of stacked graphdiyne.