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⁺.