A dual-channel “on–off–on” fluorescent probe for the detection and discrimination of Fe3+and Hg2+in piggery feed and swine wastewaterElectronic supplementary information (ESI) available. See https://doi.org/10.1039/d2ay00629d

Blue-fluorescent blood-CDs were synthesized through a one-pot hydrothermal method using a mixture of chicken blood and trisodium citrate and then explored as a fluorescent probe for detecting Fe3+and Hg2+. The probe showed excellent selectivity and sensitivity towards Fe3+and Hg2+with a dramatic “on–off” fluorescence response. F−recovered the fluorescence quenching by Fe3+, and Al3+recovered the fluorescence quenching by Hg2+, showing an “off–on” fluorescence response. The blood-CDs were used as an “on–off–on” dual-channel fluorescent sensor for the detection and discrimination of Fe3+and Hg2+ions. The probe showed wide linear ranges for determination of Fe3+(0–100 μM) and Hg2+(0–120 μM) with low detection limits of 0.23 μM for Fe3+and 0.17 μM for Hg2+. This probe was practically applied for the determination of Fe3+and Hg2+in piggery feed and wastewater with good recoveries. This work provides a fluorescent probe for the quantification of Fe3+and Hg2+in livestock feed and environmental water samples.