Provided is a method for modifying a ssRNA at the 3′ end, the method including contacting the strand with a ssRNA 2′-O-methyltransferase in the presence of a co-factor, under conditions which allow for the transfer by the ssRNA 2′-O-methyltransferase of a part of the co-factor onto the 3′ end of the ssRNA to form a modified ssRNA, wherein the ssRNA bears 2′-OH group at 3′ terminal nucleotide and wherein the part of the co-factor transferred includes a reporter group or a functional group.