The invention relates to a method for detecting specific target-cells in a simple and time saving way, using paramagnetic particles, antibodies recognizing the Fc portions of target-cell associating antibodies and target-cell associating antibodies directed to specific antigen determinants in the target-cell membranes. In particular, phage particles and phagemid vectors are described for expression and display of heterodimeric proteins such as antibody Fv heterodimers in combinatorial libraries, and uses thereof. In an alternative embodiment, the present invention is directed to forming a metal oxide or silicate on a semiconductor wafer. The signal holder arm extends from the mailbox body such that the position of the signal ball can be easily observed from the rear of the mailbox.