Making a cup of carbon dots for ratiometric and colorimetric fluorescent detection of Cu2+ ions

Fluorescence carbon dots (CDs) are firstly obtained from microbial fermented Pu-erh tea by a simple brewing method without high temperature treatment as reported in literature. The obtained CDs contain abundant surface functional groups and exhibit a good ability to detect Fe and Cu ions. Moreover, a new sensing universal platform that can simultaneously apply fluorescent and colorimetric dual-readout for Cu2+ detection is constructed using the obtained CDs and o-phenylenediamine (OPD). Not only does this sensing platform exhibit much higher selectivity and sensitivity than pure CDs, but it also enhances detection scope for Cu2+. Its detection mechanism is dominated by synergistic combination of fluorescence quenching resulted from the coordination reaction of Cu2+ ions and fluorescence resonance energy transfer from CDs to the oxidation product of OPD.