Multienzyme catalysis in microfluidic biochips

The attachment of enzymes to glass microfluidic channels has been achieved using a highly reactive poly(maleic anhydride-alt-alpha-olefin) (PMA)-based coating that is supplied to the microchannel in a toluene solution. The PMA reacts with 3-aminopropyltriethoxysilane groups linked to the glass surface to form a matrix that enables additional maleic anhydride groups to react with free amino groups on enzymes to give a mixed covalent-noncovalent immobilization support. Using a simple T-channel microfluiclic design, with reaction channel dimensions of 200 mum wide (at the center), 15 mum deep, and 30 mm long giving a reaction volume of 90 nL, soybean peroxidase (SBP) was attached at an amount up to 0.6 mug/channel. SBP-catalyzed oxidation of p-cresol was performed in aqueous buffer (with 20% [v/v], dimethylformamide) containing H2O2, with microfluidic transport enabled by electroosmotic flow (EOF). Michaelis-Menten kinetics were obtained with K-m and V-max values of 0.98 mM and 0.21 pmol H2O2 converted/mg SBP per minute, respectively. These values are nearly identical to nonimmobilized SBP kinetics in aqueous-DMF solutions in 20-muL volumes in 384-well plates and 5-mL reaction volumes in 20-mL scintillation vials. These results indicate that SBP displays intrinsically native activity even in the immobilized form at the microscale, and further attests to the mild immobilization conditions afforded by PMA. Bienzymic and trienzymic reactions were also performed in the microfluiclic biochip. Specifically, a combined Candida antarctica lipase B-SBP bienzymic system was used to convert tolyl acetate into poly(p-cresol), and an invertase-glucose oxidase SBP trienzymic system was used to take sucrose and generate H2O2 for SBP-catalyzed synthesis of poly(p-cresol). (C) 2003 Wiley Periodicals, Inc.