Sodium hydroxide-mediated hydrogel of citrus pectin for preparation of fluorescent carbon dots for bioimaging

• NaOH-mediated hydrogel of citrus pectin can be used to synthesize fluorescent CDs.
• The hydrogel can make the hydrothermal reaction of CDs down to 100 °C.
• The hydrogel can avoid visually carbonized precipitates even up to 180 °C.
• The fluorescent CDs with good biocompatibility make them successful in cell imaging.
• The use of citrus pectin will promote pomace utilization of the genus Citrus L.

The citrus process industry produces annually a huge amount of pomace, which is a rich source of citrus pectin. Here, we report the hydrogel of citrus pectin mediated by sodium hydroxide can be used to prepare fluorescent carbon dots (CDs). The introduction of hydrogel can not only make the temperature of the hydrothermal reaction down to 100 °C, but also avoid visually carbonized precipitates in the synthesis process even up to 180 °C. The as-synthesized CDs are well dispersed in water with an average size of 2.7 nm and show cyan fluorescence with high photostability, good biocompatibility. Furthermore, the CDs can act as a potential fluorescent probe for cell imaging. Citrus pectin as a non-toxic carbonaceous precursor for preparation of fluorescent CDs provides a new approach for the efficient utilization of citrus germplasm in future.

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