Nitrogen-doped MoS2 QDs as fluorescent probes for sequential dual-target detection and their microfluidic logic gate operations

Fluorescence sensors show great potential as molecular logic gates to sensitively detect different analytes in trace level. For achieving multi-target analysis, it is desirable for developing complex molecular logic gates by using multi-target fluorescence sensing system. Herein, novel nitrogen-doped molybdenum disulfide quantum dots (MoS2 QDs) have been synthesized and designed as the fluorescent probes for dual-target detection and microfluidic logic gate operations. Nitrogen-doped MoS2 QDs exhibit fluorescence "on-off-on" characteristics by sequential addition of Fe3+ ions and ascorbic acid (AA). The controllably modulating dispersion or aggregation state of nitrogen-doped MoS2 QDs is successfully obtained by addition of Fe3+ or/and AA. The static quenching mechanism of between nitrogen-doped MoS2 QDs and Fe3+ ions is illustrated in detail. This dual-target fluorescence sensor exhibited good sensitivity and selectivity to Fe3+ and AA, and the limit of detection values were 11 mu M and 960 nM, respectively. Inspired by these results, nitrogen-doped MoS2 QDs-based "IMPLY" logic gate is fabricated for intelligent fluorescent sensing of Fe3+ and AA. More importantly, using blue fluorescence of nitrogen-doped MoS2 QDs, fluorescent "IMPLY" logic gate integrating with microfluidic chip is constructed for visually discriminating Fe3+ or/and AA with the naked eyes, which has the advantages of microliter reagent consumption, automated operation and visible readout. This "visible-invisible-visible" photoluminescence property of nitrogen-doped MoS2 QDs and their microfluidic logic gate operations provide a novel strategy for dual-target sensing.