Fluorescence Probe Based on an Amino-Functionalized Fluorescent Magnetic Nanocomposite for Detection of Folic Acid in Serum

A new fluorescence probe constructed with a multifunctional nanocomposite, Fe3O4–ZnS:Mn2+/SiO2–NH2, was successfully synthesized and then used to detect folic acid in real serum samples. The nanocomposite was characterized by fluorescence spectroscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray powder diffraction, and physical property measurement system. With the addition of analyte, the Fe3O4–ZnS:Mn2+/SiO2–NH2 composite and folic acid formed a new complex because cross-linking of the amino and carboxyl groups participated in the condensation reaction. Then, the energy of quantum dots was transferred to the complex and led to quenching of the fluorescence. Moreover, the fluorescence intensity decreased significantly as the concentration of folic acid increased, and the fluorescence quenching ratio F0/F was related to the folic acid concentration in the range from 0.1 to 5 μg mL–1. This method was used for detecting folic acid in real serum samples and gave recoveries in the range of 89.0%–96.0%, with relative standard deviations of 1.2%–3.9%. The detection limit was 9.6 ng mL–1 (S/N = 3). These satisfactory and simple results showed the great potential of this fluorescence probe in the field of pharmaceutical analysis.