CuFe2O4 magnetic particles assisted construction of a label-free fluorescent sensor for detection of Escherichia coli

An economical and label-free fluorescent sensor was developed for the selective detection of Escherichia coli ( E. coli ) based on the competitive reduction of Cu 2+ in CuFe 2 O 4 magnetic particles (MPs) by E. coli and o -phenylenediamine (OPD). Cu 2+ in CuFe 2 O 4 MPs can oxidize OPD to generate 2,3-diaminophenazine (OPDox) with fluorescent property. The presence of E. coli can weaken the oxidative ability of CuFe 2 O 4 MPs toward OPD owing to the copper reductase activity of NADH dehydrogenase-2 (NDH-2) in E. coli . NDH-2 can reduce Cu 2+ to Cu + , thereby inhibiting the OPD oxidation and resulting in the decrease of the fluorescence of the system. Under the optimum conditions, the fluorescent sensor exhibited a wide linear response to E. coli in the concentration range of 10 3 – 10 6 cfu mL −1 , and the detection limit was calculated to be 5.8 × 10 2 cfu mL −1 . Furthermore, the feasibility of the sensor was verified by successful detection of E. coli in popsicle and swimming pool water samples. More importantly, the sensor utilized the magnetic property of CuFe 2 O 4 MPs to realize the phase separation, thus averting the interference of other impurities in the sample matrix.