Fig. 1

Schematic diagram of counting E. coli under a dark-field by hatting them golden ring structure with MNP probes. a The MNP probes were obtained by incubating anti-E. coli antibodies and the MNP under gently shaking for 4 h at room temperature, followed by washing three times with PBS. b E. coli samples were first mixed with MNP probes to develop probe-E. coli complexes, followed by magnetic separation for counting with dark-field microscope