Covalent linker-free immobilization of conjugatable oligonucleotides on polypropylene surfaces

A novel plasma treatment method was used to activate a polymer surface for oligonucleotide immobilization. Polypropylene was treated with plasma immersion ion implantation (PIII) to create radicals on its surface and in its subsurface. Treated polypropylene was shown to retain single stranded oligonucleotides after stringent washing whereas they were easily removed from the untreated surface. The attachment is proposed to occur through a covalent binding by reaction between radicals created in the treated surface and the side chains of oligonucleotide bases. The density of attachment depends on the type of nucleobase; for example, adenine was found to be superior to thymine. A demonstration of using 20-thymine and 20-adenine spacers in the capture sequences significantly improved the density of attachment and provided an orientation supporting hybridization with complementary DNA molecules compared to unmodified capture sequences. PIII treatment is a practical and effective method for immobilizing single stranded oligonucleotides on polymers, offering potential for use in DNA and RNA based diagnostic devices, biosensors and microarrays.