Construction of DNA microarrays on cyclic olefin copolymer surfaces using confined photocatalytic oxidation

During recent research on the fabrication of DNA microarrays, polymers have been intensively investigated as substrates for immobilizing oligonucleotides, due to their low cost, disposability and excellent processing flexibility. Among these, cyclic olefin copolymers (COCs) are of special interest because of their many favorable properties, including high glass transition temperature, low auto-fluorescence, optical clarity and resistance to organic solvents. In the present study a novel strategy has been developed by introducing epoxy groups on the COC surface, based on a confined photocatalytic oxidation (CPO) method. Firstly, a sulfate anion (–SO₄⁻) was introduced on to the COC film by CPO, accompanied by brief (120 s) UV irradiation. The sulfate anions were then hydrolyzed to form hydroxyl groups (–OH), forming a glass-like surface, which readily reacts with a silane coupling agent. In the present study (3-glycidoxypropyl)trimethoxysilane was used as a model for introducing epoxy groups on to COC film, the result confirmed by X-ray photoelectron spectroscopy (XPS), water contact angle measurement and atomic force microscopy (AFM). DNA probes were subsequently spotted on the COC surface and immobilized by reaction between the epoxy groups and amino groups on strands of DNA. The immobilization efficiency of different concentrations of DNA probes on the COC surface ranged from 45% to 65%, comparable to a traditional epoxy-functionalized glass slide. Hybridization with complementary strands of this microarray was successfully achieved, and the fluorescence intensity after hybridization was readily tuned by adjusting the probe immobilization density, or the target DNA sequence concentration in a hybridization solution. This simple approach has considerable potential in the construction of low-cost polymer biochips.