Homologous nanocellulose modification: A "like cures like" strategy against coffee-ring and infiltration effects in...

While paper-based colorimetric assays have seen significant progress in recent years, persistent challenges including the coffee-ring effect and infiltration effect continue to affect the color uniformity of detection results, leading to decreased sensitivity and accuracy of the detection. Recent advancements in suppressing these two effects mainly depend on chemical modification of cellulose fibers or application of specific functional coatings. However, the former's complex procedures impede large-scale implementation, while the latter's non-cellulosic additives risk unpredictable interactions with analytes or interference in colorimetric reactions.

Herein, we propose a "like cures like" strategy by modifying cellulose-based paper substrates with nanocellulose materials, that is, cellulose nanofibers (CNFs) and cellulose nanocrystals (CNCs). This approach aims to suppress the capillary flow of the liquid sample and prevent penetration of chromogenic products within the paper substrate. Systematic characterization of the modified paper substrates focused on key aspects including fluid transport capacity and chromogenic performance of the resulting sensors. The optimized modified substrates were tested for detecting Ni²⁺ using dimethylglyoxime and Fe²⁺ using bathophenanthroline. The distribution of their colorimetric products in the paper substrates demonstrated effective suppression of both the coffee-ring and infiltration effects. Compared to untreated counterparts, the CNCs-treated paper sensors exhibited enhanced detection accuracy and sensitivity. The linear correlation coefficients were 0.99 for Ni²⁺ and Fe²⁺ detection, with limits of detection of 0.4520 ppm for Ni²⁺ and 0.1564 ppm for Fe²⁺, respectively.

This study presents a novel strategy for constructing paper-based colorimetric sensors by in situ formation of micro-nano composite structures via nanocellulose modification. By leveraging the shared cellulose origin between the substrate and the modifier, this approach eliminates the need for foreign additives and enhances the colorimetric performance through improved uniformity and signal intensity. Consequently, this method enhances the accuracy and sensitivity of paper-based colorimetric detection while avoiding potential interferences from non-cellulosic additives.