l-valine functionalized nitrogen doped non-graphitic carbon dots as a photoluminescent probe for detection of tetracycline

Here we present l-valine functionalized non-graphitic carbon dots (denoted as N-CDvaline) as a photoluminescent (PL) probe for highly sensitive and selective detection of tetracycline antibiotic. The probe, synthesized by heating of ethylene glycol with l-valine at 170 °C for 10 min, exhibited bright bluish photoluminescence at λemission = 445 nm by exciting at λexcitation = 370 nm with 11.4% photoluminescence quantum yield. The higher resolution transmission electron micrograph, selected area electron diffraction, Fourier transformed infrared spectroscopy and X-ray photoelectron spectroscopy of N-CDvaline suggested highly ordered arrangement of linear transverse chains of oligomers of ethylene glycol and l-valine, attributable to self-assembly. Under optimized conditions, the probe exhibited linear PL quenching by tetracycline in the concentration range between 0.25 and 5.00 μM and satisfied the Stern-Volmer equation, with a detection limit of 0.054 μM. This method is highly selective towards tetracycline detection against host of interfering agents e.g., some common cations, anions and other classes of antibiotics. The PL quenching mechanism is attributed to ground state complex formation between the probe and tetracycline, corroborated by time resolved fluorescence spectroscopy studies and due to inner filter effect (IFE) owing to strong spectral overlap between UV–vis absorption spectrum of tetracycline with excitation and emission spectra of N-CDvaline. The scope for using this method for detection of tetracycline in real samples e.g., river water and milk is successfully demonstrated by spike analysis.