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This paper describes the use of a printed circuit technology to generate hydrophilic channels in a filter paper. Patterns of channels were designed using Protel soft, and printed on a blank paper. Then, the patterns were transferred to a sheet copper using a thermal transfer printer. The sheet copper with patterns was dipped into ferric chloride solution to etch the whole patterns of the sheet copper. At last, the etched sheet copper was coated with a film of paraffin and then a filter paper. An electric iron was used to heat the other side of the sheet copper. The melting paraffin penetrated full thickness of the filter paper and formed a hydrophobic “wall”. Colorimetric assays for the presence of protein and glucose were demonstrated using the paper-based device. The work is helpful to researchers to fabricate paper-based microfluidic devices for monitoring health and detecting disease

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A new method for splitting a droplet with oil encapsulation is presented. An interdigital transducer and a reflector are fabricated on a 128° yx-LiNbO3 piezoelectric substrate using microelectric technology. An electric signal with the power of 12.3 dBm is applied to the interdigital transducer to generate surface acoustic wave, which is radiated into a droplet with oil encapsulation, leading to surface acoustic wave streaming force. When the electric signal is suddenly moved off, the breakup of the droplet occurs due to inertial force. Color dye solution droplets encapsulated by oil droplets are demonstrated. The effects of electric power, the volume ratio of color dye solution to oil, and the volume of mother droplet on the breakup of droplets are studied. As applications, the presented method is successfully applied to mixture operation and color development reaction of two droplets. The method provides a new sample preparation technique, which is helpful for microfluidic biochemical analysis in a piezoelectric microfluidic system.

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