Carbon dots have attracted considerable attention in the field of biosensors and bioimaging because of their excellent optical performance and low toxicity. However, the cellular uptake of the reported carbon dots generally has a low efficiency, which limits their practical applications. In this study, we reported a novel red fluorescent sulfur and nitrogen co-doped carbon dots with small molecular phenylboronic acid tags (i.e. S, N-CDs-PBA). The S, N-CDs-PBA can be taken up rapidly by PC12 cells in twenty minutes and showed high sensitivity for the detection of Fe3+ ions. The maximum emission wavelength is at 593 nm under the excitation of 550 nm. The absolute fluorescence quantum yield is 23% in water. The fluorescence can be effectively and selectively quenched by Fe3+ ions and the linear response range of Fe3+ ions was obtained from 0.3 mu M to 5.0 mu M with a detection limit as low as 0.1 mu M. It could be concluded that the rapid uptake of S, N-CDs-PBA into cells and high photoluminescence quantum yield of red emission are beneficial for quick detection of Fe3+ ions. (C) 2018 Elsevier Inc. All rights reserved.