Colorimetric and fluorescent dual-mode pH sensor with PMIA as substrate and CQDs as probe for high accuracy detection of full range pH

The pH test is particularly important in many fields, such as chemical production and medical diagnosis. However, the most commonly used pH test strips for pH detection have disadvantages such as low strength, poor stability, only qualitative measurement and only a single-color response. Therefore, a dual-mode pH sensor prepared by a phase conversion method with Poly(m-phenylene isophthalamide) (PMIA) as the substrate and carbon quantum dots (CQDs) as probes was developed. This sensor is capable of producing dual changes in fluorescence color and fluorescence intensity over the full range of pH. The -COOH and -NH2 groups in CQDs can interact with the amide group in PMIA to make the sensor highly stable. Three correlations were established based on the fluorescence color and fluorescence intensity at different pH, which compensated the shortage of traditional pH test paper that could not be quantitatively detected. More importantly, the sensor can be used for pH detection in a wide range of water samples, and both colorimetric and fluorescence detection modes exhibit extremely high fit coefficients (R2 > 0.99) and short response times (∼5 s). Therefore, the dual-mode pH sensor provides an important solution for the development of pH detection devices with high stability and accuracy.