Metal-organic frameworks encapsulating gold nanoclusters and carbon dots for ratiometric fluorescent detection of formaldehyde in real food samples, construction materials and indoor environments

Abstract

A novel fluorescence sensing nanoplatform (CDs/AuNCs@ZIF-8) encapsulating carbon dots (CDs) and gold nanoclusters (AuNCs) within a zeolitic imidazolate framework-8 (ZIF-8) was developed for ratiometric detection of formaldehyde (FA) in the medium of hydroxylamine hydrochloride (NH₂OH·HCl). The nanoplatform exhibited pink fluorescence due to the aggregation-induced emission (AIE) effect of AuNCs and the internal filtration effect (IFE) between AuNCs and CDs. Upon reaction between NH₂OH·HCl and FA, a Schiff base formed via aldehyde-diamine condensation, releasing hydrochloric acid. The acid triggered the degradation of ZIF-8, releasing CDs and AuNCs, and thereby shifting the fluorescence to blue as the CDs disperse. The nanoplatform demonstrated high sensitivity (LOD of 0.26-2.19 μM), exceptional selectivity, and rapid response time (<1 min) toward FA. Additionally, test strips and hydrogel films integrated with smartphones were prepared for on-site and visual detection of FA. The portable and smartphone-assisted test strips effectively detected indoor FA gas, while wearable and intelligent hydrogel films provided reliable surface measurements of FA on fruits and vegetables. Real sample analyses achieved satisfactory FA recoveries (99.06-115.30%) with relative standard deviations (RSD) from 1.86% to 3.81%. The innovative sensing nanoplatform served as a promising approach for FA detection in food, construction materials, and indoor air quality, offering both analytical accuracy and convenient visualization.

Keywords: Carbon dots; Color recognition app; Formaldehyde; Gold nanoclusters; Hydroxylamine hydrochloride; Sensing; Fluorescence; Smartphone-assisted detection; Test strips; Zeolitic imidazolate framework-8.