Biomass quantum dots, which are green, cheap and easy to prepare, are promising fluorescence probes. In this study, we prepared biomass nitrogen-codoped carbon dots (B-NCdots) through pyrolysis, using natural soybean as the starting material and introduced the B-NCdots as green fluorescent probes for the ultrasensitive detection of organophosphorus pesticides (OPs). The B-NCdots obtained emitted blue fluorescence, which was quenched by Cu(II) ions. Combining this with an acetylcholinesterase-based cascading enzymatic reaction that produces thiocholine, which can able to cause a reaction with the Cu(II) ions and restore fluorescence. However, OPs can inhibit both the activity of acetylcholinesterase and the recovery of fluorescence. Therefore, a fluorescence off-on-off method based on the B-NCdots probes was developed to detect isocarbophos (ICP). A wider linear detection range was achieved from 1.0x10(-9) to 1.0x10(-4)M (Limit of Detection=3.0x10(-10)). The method developed was successfully applied to the detection of ICP in broccoli samples. The average recoveries were in the range of 94.0-103.0% with a relative standard deviation of less than 3.4%. More importantly, the B-NCdots-Cu(II) ion fluorescent probes were also used successfully in dual-color imaging of living cells, indicating that the green fluorescent probes have potential applications in agricultural and biomedical fields.