Ratiometric fluorescent detection of copper ions using coumarin-functionalized carbon dots based on FRET

A novel FRET ratiometric fluorescent probe (CMH-GA-CDs) was designed for the detection of Cu2+ in aqueous solution. The CMH-GA-CDs were prepared through grafting 7-diethylaminocoumarin-3-carbohydrazide (HCM) on the surface of glyoxylic acid-modified carbon dots (GA-CDs) by amidation reaction. In the absence of Cu2+, a FRET pair from the CDs to CMH units was established, in which the CMH-GA-CDs exhibited dual emission bands centered at 400 nm (CDs) and 458 nm(CMH), respectively, under optimal excitation wavelength of CDs (λex = 340 nm). Upon addition of 30 μM Cu2+ to CMH-GA-CDs solution, Cu2+ coordinated with the heteroatoms N and O, which caused the inhibition of FRET process and the change of fluorescence intensity ratio I458/I400 from 1.95 to 0.91. The ratio of I458/I400 exhibited a good linear relationship with the concentration of Cu2+ in the range of 0–10 μM and the limit of detection was as low as 0.21 μM. Furthermore, The CMH-GA-CDs were used for the detection of Cu2+ in tap water and lake water with satisfactory recovery ratio between 91% and 104%, demonstrating the promising applicability for detecting Cu2+ in water samples.