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Construction of carbon quantum dots-based (CQDs) fluorescent probes for real-time monitoring pH in cells is still unsatisfied. Here, we propose the synthesis of nitrogen, sulfur-doped CQDs (N,S-CQDs) using one-pot hydrothermal treatment, and serve it as fluorescent probes to realize the real-time sensing of intracellular pH. These pH-responsive N,S-CQDs were proved exhibited a diversity of admirable properties, including great photostability, nontoxicity, favorable biocompatibility, and high selectivity. Particularly, due to the doping of nitrogen and sulfur, N,S-CQDs possessed long-wavelength emission and large Stokes Shift (190 nm), which could avoid self-absorption of tissue to realize high contrast and resolution bioimaging. The response of the probes to pH showed a good linear in range of 0.93–7.00 with coefficient of determination of 0.9956. Moreover, with advantages of high signal-to-noise ratio and stability against photobleaching, the as-prepared N,S-CQDs were successfully applied to monitor pH in living cells via bioimaging. All findings suggest that N,S-CQDs have significant potential for practical application for sensing and visualizing pH fluctuation in living systems. [Display omitted] • N,S-CQDs as fluorescent probes were synthesized via one-pot hydrothermal method. • The probes can realize reversible real-time detection of pH in human serum and cells. • Large Stocks shift (190 nm) of N,S-CQDs is beneficial to avoid self-absorption. • High selectivity and wide detection range (a good linear range of pH: 0.93−7.00). • CQDs possess favorable biocompatibility, can be applied for intracellular pH imaging. [ABSTRACT FROM AUTHOR]

In this work, biomass-derived carbon quantum dots (CQDs) with excellent water solubility, strong fluorescence and favorable biocompatibility were synthesized via one-step hydrothermal treatment of purple perilla for the first time. The functional group composition, morphology, and pH stability of the synthesized CQDs were systematically investigated. And based on fluorescence quenching of CQDs, the as-prepared CQDs were innovatively developed as an effective "signal-off" fluorescent probe for selective and sensitive detection of silver ion (Ag+) with two linear ranges of 0–10 and 10–3000 nM, and a detection limit 1.4 nM. The specificity and selectivity of this fluorescent probe were also verified through challenging the detection by using similarmetallic cations or in real water samples. In addition, the as-prepared CQDs exhibit a low cytotoxicity and a good biocompatibility, revealing its potential bioimaging applications in living cells. Image 1 • CQDs were synthesized via one-step hydrothermal treatment of purple perilla. • Selective and sensitive detection of Ag+ were achieved based on as-prepared CQDs. • The obtained CQDs have low cytotoxicity and good biocompatibility. • Fluorescence quenching of CQDs by Ag+ was revealed following a static mechanism. [ABSTRACT FROM AUTHOR]

In this work, sulfur and nitrogen co-doped carbon dots (S,N-CQDs) as highly selective fluorescent probe for silver ion (Ag + ) and cysteine (Cys) detection were designed and synthesized directly from citric acid and thiamine hydrochloride via a one-step hydrothermal protocol in 63.8% quantum yield. This probe enabled selective detection of Ag + with a linear range of 0–10 and 10–250 μM and a limit of detection of 0.40 μM with respect to the variation in fluorescence induced by target concentration and electron-transfer from S,N-CQDs to Ag + . Furthermore, S,N-CQDs/Ag + fluorescence can be effectively recovered by virtue of a specific reaction of Cys with silver ion. This fluorescence “turn-on” protocol was applied to determine Cys with two linear ranges of 0–10 and 10–120 μM as well as a detection limit of 0.35 μM. The corresponding cell experiments were also performed, indicating that the prepared S,N-CQDs possessed low cytotoxicity and good biocompatibility. Ultimately, the practicality and viability of this fluorescent probe were demonstrated through the analysis of silver ion in real river water and human serum samples. [ABSTRACT FROM AUTHOR]

In this work, phosphorus, nitrogen co-doped carbon quantum dots (P,N-CQDs) as highly selective fluorescent probe for cobalt ion (Co 2+ ) detection were designed and synthesized via a one-step hydrothermal protocol by employing pyridoxal 5-phosphate and ethanediamine. This probe enables selective detection of Co 2+ with a linear range of 0–60 μM and a limit of detection of 0.053 μM through variation in fluorescence with respect to target concentration and electron-transfer from P,N-CQDs to Co 2+ . Furthermore, ethylenediaminetetraacetic acid-modified Fe 3 O 4 @SiO 2 (Fe 3 O 4 @SiO 2 -EDTA) was tailor-designed and prepared to successfully realize the recovery of P,N-CQDs/Co 2+ fluorescence for the first time. The reusable P,N-CQDs as fluorescent sensors for Co 2+ also show good linearity and sensitivity. Ultimately, this fluorescent probe was applied in the analysis of real river water samples. [ABSTRACT FROM AUTHOR]

• The CDs@ZIF-8 composites have been fabricated via an in-situ embedding strategy. • The CDs@ZIF-8 demonstrates uniform size and excellent FL efficiency. • A fluorescent sensor for DA detection was favorably developed based on CDs@ZIF-8. • By virtue of synergy of ZIF-8 and CDs properties, sensor exhibits good performance. By embedding high quantum yield blue-emitting carbon dots (CDs) into zeolitic imidazolate framework-8 (ZIF-8), the luminescent metal-organic frameworks (LMOFs) - CDs@ZIF-8 composites were fabricated facilely and served as the fluorescent probe for selective and sensitive detection of dopamine (DA). In which the sustainable pores within ZIF-8 would not only provide a natural habitat for analyte but also can selectively capture and concentrate the DA molecules via the interaction between the analyte DA and the basic site of the frame. Meanwhile, the CDs can be served as the signal probes to transform chemical signals of the interaction between CDs and analytes into fluorescent signals. Thus, the as-synthesized CDs@ZIF-8 composites generate new sensing performance when compared with CDs. As a consequence, a wide concentration dynamic range of 0.1–200 μM with a low detection limit (LOD) 16.64 nM was favorably obtained for the CDs@ZIF-8 composites based detection method for DA. Besides, the practicality and viability of the fluorescent composites were also successfully verified via challenging the CDs@ZIF-8 based sensing method to detect DA in complicated serum and urine. [ABSTRACT FROM AUTHOR]