a method is provided for direct coating of transiently stable , colloidal particulate magnetic substrates with various synthetic or naturally - occurring polymers , particularly biologically - active peptides and proteins . the resulting coated resuspendable , colloidal magnetic particles are particularly adapted for use in bioanalytical procedures involving affinity separation , or the like . there is also provided a method for selectively binding chemically - treated colloidal magnetic particles to polyelectrolytes , e . g ., to facilitate extraction of nucleic acids from cell lysates .