A general formula of the cross linking function is thus -A-L, or -A-L2 where L is the above defined leaving group and A is a moiety that is covalently linked to the ODN-MGB. The A ???arm??? moiety itself should be unreactive (other than through the leaving group L) under the conditions of hybridization of the ODN-MGB with the target sequence, and should maintain the leaving group L in a desired st