Lanthanum nitrogen Co-doped carbon quantum dots as optical and smartphone sensors for serotonin detection

A simple bottom up approach using hydrothermal technique was applied to prepare lanthanum and nitrogen Co-doped carbon quantum dots and were characterized by XRD, EDS, TEM, SEM FT-IR, XPS, fluorescence and UV-VIS spectroscopy to study their crystal structure, elemental and chemical composition, particle size, morphology and optical properties. It was found that morphology was spherical and particle size was 3–4 nm. EDS and XPS helps to prove the successful doping of lanthanum and nitrogen to carbon quantum dots with excitation and emission wavelengths 340 and 445 nm respectively. The intense blue color of fluorescent QDs were quenched with addition of serotonin due to the electrostatic interactions, π-π stacking interaction and may be due to complex formation between La,N-CQDs/Ser and the static quenching mechanism with inner filter effect has been observed. These La,N-CQDs were used as fluorescent probes for sensitive and selective detection of serotonin in a good linear range of 0–38 nM with low limit of detection 7.4 nM.The smartphone based portable detection was also developed for detection of serotonin providing the reliable information for analysis of color change and real sample analysis studies were also carried out. The uniqueness, high sensitivity and accuracy of the optical probe that was constructed are confirmed and this method's LOD is also highly competitive.