Abstract: Reactants containing amino, mercapto or hydroxy groups such as proteins, peptides, ligands, coenzymes or enzymes are immobilized on a support containing amino, mercapto or hydroxy groups by coupling the reactant to the support with a compound having the following formula (I) or (IA): ##STR1## wherein X is a halogen and R.sub.1, R.sub.2 are the same or different and are X, R, COR, COOR, wherein R is C.sub.1 -C.sub.8 alkyl, COOH, CNS, N.sub.3 or CN. The support may be first reacted with the compound to produce a derivatized support which is then reacted the reactant or the reactant may be first reacted with the compound and the resultant product then reacted with the support. An electrochemical biosensor can be prepared by using a conductive support.