Due to the sturdy photoluminescence and absorption, CQDs emerged as a suitable candidate for optical sensing probe. The present study deals with the synthesis of blue-fluorescent Carbon Quantum Dot (TAA-CQD) using tannic acid and glycine as novel precursors. The TAA-CQD were synthesised hydrothermally with the high production yield and QY to be 86.12 and 21%, respectively, and an average particle size of 1.9 nm. The TAA-CQD aqueous solution displays excitation-dependent fluorescence emission in the excited range from 420 to 650 nm. The CIE co-ordinates in a highly blue region at (0.14, 0.19) confirmed the synthesised TAA-CQD were blue in fluorescent. Fluorescence of TAA-CQD was stable under all pH range, resisted the high ionic strengths condition and stable over 8 months. Furthermore, the fluorescent TAA-CQD was capable in detecting a tetracycline-classed antibiotic Doxycycline (DXY) along with remarkable selectivity and sensitivity. The measures limit of detection (LOD) was very low 2.42 mM in comparison to other methods. Moreover, the applicability of the proposed work has been fruitfully employed on the pharmaceutical waste. Thus, our designed TAA-CQD based fluorescence sensing system hold great promise for the advanced sensing materials in the detection of DXY and we believe that our approach will be promising and viable in a clinical applications.

Fluorometric sensing probe using carbon quantum dots for selective detection of doxycycline antibiotic
    Abstract
    1 Introduction
    2 Experimental section
        2.1 Materials
        2.2 Synthesis of TAA-CQD
        2.3 Characterisations
        2.4 Determination of quantum yield
        2.5 Calculation of product yield (PY)
        2.6 Assay for the detection of Doxycycline
    3 Results and discussion
        3.1 Morphology of TAA-CQD
        3.2 Detection of elements and surface groups
        3.3 Optical properties
        3.4 Durability and pH effect
    4 Application of TAA-CQD as sensing probe towards doxycycline
        4.1 Selectivity towards doxycycline
        4.2 Sensitivity of TAA-CQD towards doxycycline
        4.3 Interference study
        4.4 Mechanism of quenching
        4.5 Real sample analysis
    5 Conclusion
    Acknowledgements 
    References

• Vivek Kumar(Department of Chemistry, Nano-Materials Laboratory, IIT BHU, Varanasi, Uttar Pradesh 221005, India)
• Syed Hadi Hasan(Department of Chemistry, Nano-Materials Laboratory, IIT BHU, Varanasi, Uttar Pradesh 221005, India)
• Deepak Kumar(Department of Chemistry, Nano-Materials Laboratory, IIT BHU, Varanasi, Uttar Pradesh 221005, India, Department of Chemistry, Chhadami Lal Jain P.G. College, Firozabad, Uttar Pradesh, 283203, India)
• Subhash Chandra(Department of Chemistry, Bappa Shri Narain Vocational Post Graduate College, University of Lucknow, Lucknow, Uttar Pradesh 226001, India)
• Pradeep Kumar Yadav(Department of Chemistry, Institute of Science, Banaras Hindu University, Varanasi, Uttar Pradesh 221005, India)