There is provided a biosensor for detecting pathogens in a sample. The detection is based on colorimetry. The biosensor comprises one or more particle supports and a magnetic material attached to a planar support. The biosensor embodies magnetic particles that are functionalized using a chemical substrate specific to the pathogens to be detected. The sensor may allow for a simultaneous detection of a plurality of pathogens in the sample. Also, the sensor may be disposable. Moreover, the sensor may be integrated in a portable detection device.