# H⁺ Exchange‐Driven ppb‐Level and High‐Selective Formaldehyde Detection at Room Temperature for Environmental and Clinical Applications

## TL;DR

A new room-temperature sensor detects formaldehyde at very low levels with high accuracy, useful for air quality and cancer screening.

## Contribution

The H⁺ exchange method significantly improves formaldehyde detection by enhancing selectivity and lowering the detection limit.

## Key findings

- H⁺-exchanged sodium titanate achieves a detection limit of 2 ppb formaldehyde.
- The sensor shows high selectivity against common VOCs like methanol.
- A handheld prototype with machine learning achieved accurate breast cancer screening via breath analysis.

## Abstract

Formaldehyde is both a pervasive air pollutant and a critical breath biomarker for tumor‐related diseases, yet its reliable detection remains difficult due to ultralow concentrations and interference from ubiquitous volatile organic compounds (VOCs). Here, an H⁺‐exchange strategy is reported that markedly enhances the sensing performance of sodium titanate (Na2Ti3O7, NTO) by introducing abundant surface hydroxyl groups and tuning conduction pathways. In H⁺‐exchanged NTO (H‐NTO), hydroxyl groups act as selective adsorption sites for formaldehyde, while formaldehyde adsorption simultaneously suppresses surface‐proton and internal‐electron conduction by increasing the activation energy for proton hopping and generating electron‐trapping states. This dual modulation effectively eliminates cross‐sensitivity to other VOCs (e.g., methanol), enabling H‐NTO to achieve an ultralow detection limit of 2 ppb, a wide dynamic range up to 100 ppm, and stable operation over two months—contrasting with the negligible response of pristine NTO. To demonstrate practical utility, we developed a handheld H‐NTO prototype for wireless indoor air‐quality monitoring and non‐invasive breath‐based breast cancer screening. Coupled with machine learning, the system achieved high diagnostic accuracy, establishing H⁺‐exchange as a powerful route toward next‐generation intelligent formaldehyde sensors.

This article presents an innovative room‐temperature formaldehyde sensor based on H⁺ exchange method, achieving ppb‐level detection limit and exceptional selectivity. The study highlights its practical potential for real‐time environmental monitoring and clinical diagnostic applications.