Red/Green Tunable-Emission Carbon Nanodots for Smart Visual Precision pH Sensing

Abstract

The development of novel carbon nanodots (CDs) with excellent optical properties and promising applications is an attractive but a challenging area. Herein, we demonstrate that the fluorescence properties of CDs can be optimized by simple modification of the molecular structure of the carbon source. Significantly, the final optimized CDs 1 exhibit a rare extremely acidic (pH 1−3) sensitivity. A distinguishable red/brown/green fluorescence color change is achieved for visual readout by simply tuning the pH to 1, 2, or 3. The distinguishable color change combined with ratiometric fluorescence changes greatly improves the naked-eye visual resolution up to 0.2 pH units, which is higher than that of commercial precision pH test strips. Furthermore, a smartphone was employed in a portable, low-cost, rapid, and precise pH measurement method, which satisfied the requirement of point-of-care testing. Inspired by the reversible color change of red/brown/green tri-fluorescence on tuning the pH to 1, 2, or 3, a simple yet efficient molecular logic circuit has been designed. Given the unique pH-dependent photoluminescence properties, these CDs have been further applied in the anti-counterfeiting and information encryption field, making the "burn after reading" encryption technology a reality.

Ratiometric Multimode Detection of pH and Fe3+ by Dual-Emissive Heteroatom-Doped Carbon Dots for Living Cell Applications

“…The pH-sensitive emission stems from both the ground-state (aggregation–disaggregation) and excited-state processes. Earlier literature reports propose that the pH sensitivity of carbon dots originates from the association and dissociation of protons to/from some acidic and alkaline groups present at the surface of the CDs, which directly induces the FL signal alteration. − It is challenging to develop a CD with inherent ratiometric performance to different pH values with accompanying visual color changes. The FL signal stability is further explored at different temperatures (10–70 °C) and 2 h of UV radiation.…”

Facile Synthesis of Multi-Emission Nitrogen/Boron Co-Doped Carbon Dots from Lignin for Anti-Counterfeiting Printing

“…This triple-level anti-counterfeiting process only needs one kind of stimuli factor (excitation lights with 300, 330 and 490 nm) on a single label. Compared with other complicated stimuli factors (temperature, chemical reagents, and mechanical force) [ 7 , 31 , 43 ], this is a simple, fast, and advanced triple-level optical anti-counterfeiting strategy with high security. The multi-emission biomass-derived CDs exhibit the advantages of low cost, green preparation, and high stability, and are expected to become an ideal material for future optical anti-counterfeiting applications [ 4 , 34 ].…”

A facile fluorescent sensor based on nitrogen-doped carbon dots derived from Listeria monocytogenes for highly selective and visual detection of iodide and pH

“…Based on the previous reports, H + can quench the FL of CDs by changing the surface state of CDs. 30,48 Here, for better understanding of the unique pH-dependent phenomenon of NCDs-LM, the FL decay curves and UV-vis absorption spectra at various pH values were examined. Fig.…”