Preparation and multipurpose applications of nitrogen-sulfur doped carbon dots fluorescent probe for Ga3+ and riboflavin (VB2) detection

Designing versatile carbon quantum dots (CDs) with excellent sensitivity and unique function as efficient fluorescent probe for detection of specific substance from cheap and readily available substrates is still a crucial challenge. A novel nitrogen-sulfur doped carbon dots (N, S-CDs) with blue-green fluorescent emission derived from lactose and 4-amino-3-hydroxy-1-naphthalenesulfonic acid (AHNS) was facilely synthesized by one-step hydrothermal process. The obtained N, S-CDs with graphene structure exhibited good water solubility, excellent biocompatibility, satisfactory stability and striking optical properties. The surface of N, S-CDs is modified by various functional groups which are helpful to combine with Ga³⁺ in the form of complexes N, S-CDs-Ga³⁺ to considerably enhance the fluorescence emission peak of N, S-CDs, further improving the selectivity and sensitivity of Ga³⁺ detection with the detection limit of 0.133 μM. At the meantime, N, S-CDs can cause yellow fluorescence quenching of riboflavin (VB₂) with the detection limit of 0.121 μM under the concentration range from 1.000-20.000 μM. The possible mechanism is the functional groups at the surface of N, S-CDs combined with the hydroxyl, amino and carbonyl group of VB₂ by protonation and hydrogen bonds. Further investigations for practical applications demonstrated that N, S-CDs has good prospects in Ga³⁺ananlysis and detection of VB₂ in food. Moreover, N, S-CDs can be used to determine whether there is Ga³⁺ in transferrin, which can indirectly inhibit the growth of cancer cells through the influence on transporting iron ion. Therefore, it is profitable for preliminary diagnosis and treatment of cancer cells in the field of biomedicine.