Microfluidic chip with porous anodic alumina integrated with PDMS/glass substrate for immuno-diagnosis

An efficient system for diagnosis of disease marker molecules in microfluidic devices was developed by employing anodic aluminum oxide (AAO) which has highly ordered, uniform, and straight nanopore arrays by a two-step anodization process. AAO on glass substrate was integrated within poly(dimethylsiloxane) (PDMS) microchannel structure. Vacuum-deposited aluminum thin film was anodized by variation of electrolyte composition, applied voltage and anodizing time, for specific pore sizes and depth. The pore was tunable to achieve a size corresponding to target proteins. For enhancement of antibody immobilization and adhesiveness with a PDMS micro-pattern, surface activation of AAO was performed by TMOS–sol spin-coating and calcinations to form a SiO2 layer. The demonstration of diagnosis of bio-marker protein was performed by employing conventional sandwich-type immuno-assay for hepatitis B virus (HBV). The anti-hepatitis B surface antigen (anti-HBsAg) was immobilized by bridges using γ-aminopropyltriethoxysilane and glutaraldehyde. The hepatitis B surface antigen (HBsAg) was coupled with anti-HBsAg and sheep anti-HBs/horseradish peroxidase conjugate. The result was analyzed by colorimetric assay for comparison with the result using conventional immuno-assay and it showed higher efficiency using microfluidic channels. The AAO inside the PDMS microfluidic channel allows specific immobilization of proteins by controlling the size for access. This study can be extended for a high-throughput system for bio-marker proteins.