Portable and intelligent ratio fluorometry and colorimetry for dual-mode detection of dopamine based on B, N-codoped carbon dots and machine learning

A dual-mode approach was developed for dopamine (DA) assay based on boron (B) and nitrogen (N) co-doped carbon dots (B, N-CDs). This platform enabled highly sensitive and specific detection of DA in biological samples through collaborative ratio fluorometry and colorimetry. B, N-CDs were synthesized via a one-pot hydrothermal method using 3-aminobenzylboric acid (3-APBA) and proline (Pro) as precursors. B, N-CDs exhibited dark blue fluorescence under ultraviolet (UV) light excitation with a quantum yield (QY) of 0.05. In the presence of DA, the fluorescence of B, N-CDs displayed bright blue with the QY at 0.22. The original fluorescence peak intensity at 420 nm of B, N-CDs decreased, while a new peak at 465 nm increased significantly with the increasing concentration of DA. In this case, a ratio fluorometry for DA detection was constructed using B, N-CDs as fluorescence probes. On the other way, the color of B, N-CDs solution changed from colorless to brown with the addition of DA. A colorimetry for DA sensing was established based on the absorbance enhancement of B, N-CDs. There is excellent linear relationship within the concentration range of 2.5–500 μM for DA sensing with limit of detection (LOD) at 0.22 μM (ratio fluorometry) and 1.04 μM (colorimetry) and the relative standard deviations (RSD%) are 0.2170 and 0.02131, respectively. To enable the real-time visual and portable quantification of DA, two intelligent methods were explored by a program named RGB color analysis in a smartphone and machine learning. This dual-mode sensing strategy combined high sensitivity, wide linear range and ease of operation, offering a novel solution for rapid analysis of DA in complex biological substrates.