Unlocking Dynamic Luminescent Mapping of pH with Sustainable Lignin-Derived Carbon Dots with Multimodal Readout Capacity

TL;DR

This study introduces a sustainable, lignin-derived carbon dot sensor capable of highly sensitive, reversible, and multimodal pH mapping through simple, low-cost optical methods suitable for large-area and real-time applications.

Contribution

The paper presents a novel, eco-friendly pH sensor using lignin-based carbon dots with multimodal readout, combining ratiometric and visual colorimetric detection for the first time.

Findings

Achieved high pH sensitivity of 137% and 49.5% per pH unit.

Enabled spatial and temporal pH mapping with simple optical devices.

Demonstrated sustainable synthesis from lignin waste.

Abstract

In this work, we demonstrate the use of CQDs synthesized from lignin - currently one of the most abundant and underutilized by-products of paper and pulp production - for advanced pH monitoring applications. The presented approach integrates green chemistry principles with an operator-friendly, low-cost, and practical solution for spatial and temporal pH measurement. CQDs functionalized with m-aminophenylboronic acid enable highly sensitive and reversible pH readouts through two complementary mechanisms: ratiometric monitoring of emission band intensities, and direct visual observation of colorimetric changes reflected in the CIE1931 chromaticity coordinates. The system achieves maximal sensitivities of 137 percent per pH unit and 49.5 percent per pH unit, respectively, while simultaneously maintaining high measurement resolution and full reproducibility of the readouts, placing it among the most effective CQD-based pH sensors reported to date. Here, we demonstrate the capability of 2D luminescent imaging of pH distributions, allowing for both spatially resolved and time-resolved monitoring. Employing just an excitation source, a digital camera or smartphone, and RGB channel analysis, the setup eliminates the necessity for specialized filters or sophisticated instrumentation. The combination of multimodal readout strategies with the capacity for large-area visualization establishes lignin-derived CQDs as a sustainable and practical platform for pH sensing. By simultaneously addressing the challenges of waste valorization and the demand for innovative sensing technologies, this solution fulfills the requirements of both environmentally responsible material design and next-generation pH sensor development.