Non-contact photothermal control of enzyme reactions on a microchip by using a compact diode laser

Photothermal temperature control of an enzyme-catalyzed reaction in a micro chip using a diode laser was demonstrated. A laser beam with energy of 10 m W was used to irradiate an absorbing target placed on top of the microchip cover plate. Theoretical calculations have shown that temperature in the mi crochannel can be locally increased by 5-7 degrees C during short time inte rvals, due to heat released by the target. The rate of the enzyme reaction, which was initially inhibited due to cooling of the chip to low temperatur e, was increased when the target was irradiated. The products were detected by a thermal lens microscope. The product concentration was shown to depen d on irradiation time, laser intensity and substrate concentration. Reactio n characteristics (rate constant of the reaction) were then derived from th ese dependencies. The reaction volume and absolute quantity of the reaction product were estimated as 10 nl and 100 fmol, respectively. It was also de monstrated that a direct solvent heating method using infrared radiation co uld control the reaction in the microchannel. (C) 2000 Elsevier Science B.V . All rights reserved.