| Summary: | In order to safeguard the food safety and security of the consumer, a rapid and sensitive detection method for bacteria pathogen has been demanded. An electrochemical biosensor for bacteria (Escherichia coli K12) was being developed in this research. This report presents the synthesis, surface modification of Fe3O4 nanoparticles (Fe3O4 NPs), conjugation of Fe3O4 nanoparticles with rabbit antibodies, immuno-magnetic separation for Escherichia coli K12 (E. coli) and the bacteria detection through electrochemical measurement. Fe3O4 NPs were chosen as the assisting agent to immobilize Escherichia coli on electrode owing to the super-paramagnetic property and the low toxicity. Fe3O4 NPs were first synthesized by thermal decomposition method. The hydrophobic surfaces of as-synthesized Fe3O4 NPs were then modified with PEG-2000 to become hydrophilic in order to be immuno-functionalize with rabbit antibody. After PEGFe3O4 NPs are conjugated with rabbit antibody (Ab-Fe3O4 NPs), the immunomagnetic separation can be carried out by employing Ab-Fe3O4 NPs to extract the target bacteria from the sample solution and attracted them to a graphite paper electrode by applying external magnetic field. The effectiveness and performances of the biosensor under the assistance of Ab-Fe3O4 NPs at different concentration of E. coli K12 were being investigated by Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) measurements. Approximately 1 h is required to obtain the results. The existence E. coli K12 in the solution was detected by CV. However, the EIS & CV changes due to the different concentration of E. coli K12 are not detected as the physical absorption of the NPs on the rough graphite electrode surface is unable to affect the electron transfer of the electrochemical system. Future research may be focus on modifying the surface roughness and the properties of the electrode to allow chemical adsorption of the NPs on to the electrode surface, so as to enable the detection of bacteria at different concentration. Conjugation time for the bacteria with Ab-Fe3O4 NPs in the probe solution, immuno-magnetic separation time of the NPs and the amount of NPs added to the system can be manipulated to further optimize the efficiency electrochemical biosensor.
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