MXene quantum dots (MQDs), originating from 2D transition metal carbides or nitride MXenes, show appealing physical and chemical properties including abundant metal-deficient sites, excellent charge or electrons transport ability, and good biocompatibility, which greatly contribute to the wide range of applications in energy storage, catalysis, sensors, thermoelectricity, and bio-imaging, etc.1–4 In recent years, in combination of the appropriate band gap, easy surface modification, and the quantum size effect, the fluorescent properties of MQDs are gradually emerging as a great application prospect in the optical-sensing field such as the detection of metal ions, hypochlorite, glutathione, hypochlorite and so on.5–7 As reported, the performance of MQDs-based sensors substantially depends on the optical and interfacial properties of materials.8, 9 Meanwhile, considerable research efforts have been devoted into the synthesis of MQDs and understanding the critical roles of the surface capping organic ligands and the solvents used in the synthesis process. For example, Zhou et al. synthesized nitrogen-doped Ti3C2 QDs, which combined with 2,3-diaminephenazine and presented a sensitively ratiometric sensor for H2O2 and xanthine. The limit of detection was determined to be 0.57 and 0.34 µM, respectively.10 By integrating the electron transfer and inner filter effect, Liu et al. reported fluorescent MQDs synthesized in dimethyl sulfoxide (DMSO) for the detection of Fe3+ with high sensitivity and selectivity.11 Despite of these, the current literatures about fluorescent MQDs-based sensors are still limited, while in particular the exploration of the relationship between optical and interfacial properties of MQDs is still in infancy.
Iron, as an indispensable metal, has been widely used in all kinds of areas. On one hand, large quantities of waste water containing ferric ions are constantly released to the natural environment, which is detrimental to the microorganism and the food chain.12–14 On the other hand, the level of iron ions in blood is critical to the health of human body, and the corresponding disorder can cause the serious physiological responses, including cardiopalmus, anemia, and the dysfunction of organs.15,16 Therefore, the accurate determination of iron content is of great importance to the sustainable development of mankind and society. To date, all kinds of analytical techniques have been utilized to the detection of Fe3+, including atomic absorption spectrometry, inductively coupled plasma mass spectrometry, colorimetry, and electrochemistry, etc.17–19 Among these methods, fluorometric analysis offers some unique advantages such as high sensitivity, rapid response, and good selectivity. Various fluorescent nanomaterials have also been developed for the analysis of Fe3+, e.g., quantum dots, small molecule probes, metal-organic frameworks, and metal nanoclusters etc.20–24 However, it is worthy to be mentioned that the existing sensitivity and selectivity remain significant challenges for in-situ and portable detection. The research and development of direct, fast, and highly sensitive probes for Fe3+ is still desirable and important.
Therefore, in this work, a kind of fluorescent MQDs were synthesized via an intermittent ultrasound process with N,N-dimethyl formamide as solvent. The prepared MQDs were characterized by UV-Vis absorption, fluorescence spectra, X-ray photoelectron energy spectra, and Fourier transform infrared spectroscopy. Based on the electrostatic induced aggregation quenching mechanism, the fluorescent MQDs probes exhibited excellent sensing performance for the detection of Fe3+. The sensitivity was determined to be 0.6377 mM− 1 with the detection limit of 1.4 µM, superior to those reported in literatures. We believe that the present MQDs-based probes will be a promising candidate for the sensing device of Fe3+.