Fluorescent and colorimetric dual-mode recognition of Al³⁺ in tablets based on chrome azurol S and pH-switchable boron, nitrogen co-doped carbon dots

The synthesis and characterization of pH-sensitive boron and nitrogen co-doped CDs (B, N-CDs) is reported. The fluorescence of B, N-CDs exhibited pH-responsive behavior within the range pH 3.0-6.0, attributed to their controlled aggregation and disaggregation. Interestingly, the fluorescence of B, N-CDs was quenched by the inner filter effect from chrome azurol S (CAS). With the subsequent addition of Al³⁺, the fluorescence of B, N-CDs was restored due to the formation of blue Al³⁺-CAS and B, N-CDs-Al³⁺ complexes. Consequently, a fluorescent and colorimetric dual-mode sensor for Al³⁺ detection was developed. The proposed sensor enabled Al³⁺ detection in the ranges and limits of detection of 3.75-22.5 μM and 2.67 μM for the fluorescent mode and 5-20 μM and 4.8 μM for the colorimetric mode, respectively. Furthermore, the efficacy of the sensor was validated through successful detection of Al³⁺ in tablet samples. The obtained B, N-CDs promised the application in acid condition and the proposed sensor is expected to be applied to in situ on-line detection of Al³⁺.