Carbon dots with polarity-tunable characteristics for the selective detection of sodium copper chlorophyllin and copper ions

Compared to water-soluble carbon dots (CDs) the properties and applications of hydrophobic CDs are rarely addressed. In this study, a one-pot, simple chemical oxidation approach has been applied to synthesize hydrophobic carbon dots (TO-CDs) at room temperature from triolein (TO) in concentrated sulfuric acid solution. Sodium copper chlorophyllin (SCC) quenches the fluorescence of TO-CDs by a photoinduced electron transfer process. Upon excitation at 400 nm, the fluorescence intensity of TO-CDs probe at 500 nm shows a linear response against the SCC concentration ranging from 1.0 to 10 μM, with a limit of detection (LOD) of 0.61 μM. Quantitation of SCC in flavored drinks shows percentage recovery (%R) vaues of 98–103% and relative standard deviation (RSD) values less than 6.5%. The hydrophobic TO-CDs can be converted into hydrophilic TO-CDs through hydrolysis in NaOH solution. The presence of sulfonyl groups on the hydrophilic TO-CDs enhances the coordination ability of the CDs toward Cu²⁺ ions, leading to fluorescence quenching which allows for the detection of Cu²⁺ ions with LOD of 0.21 μM and a linear range of 0.5–10 μM. The hydrophilic TO-CD probe possesses high selectivity toward Cu²⁺ ions (tolerance at least ten-fold comparative to other metal ions). The assay has been validated with the analysis of spiked soil samples, with %R values of Cu concentration of 97.8–99.0% and RSDs below 2.0%. The surface tunable CD probes demonstrate their potential for the rapid screening of Cu²⁺ ions in environmental samples and SCC in foods.