A knife is provided including a first side and a second side where the first side may be removably coupled to the second side. In one embodiment the method comprises introducing a magnetic sample having magnetic particles into a detection field; detecting weak magnetic field signals of the magnetic particles; forming an image from the detected signals; and determining the location and quantity amount of the magnetic particles. The prepolymer, when reacted with an excess of water, forms a hydrogel polymer. In addition, mechanical design for the PLA with an isolating filter provides for secure mounting while blocking access to a second wall outlet of a duplex unit.