Two simple approaches to fabricate Au microlines on the outer surfaces of micropipettes

Various lithographic approaches have been developed to generate patterns on flat and non-flat surfaces. However, it still remains a challenge to produce patterns on irregular surfaces, such as on the curved tip of a glass micropipette. To overcome this challenge, we have developed two new approaches in this work, and explored the possibility of applying them to generate Au microlines on the outer surfaces of glass micropipettes. A glass micropipette includes a straight tube and a curved tip. In either approach, the outer surface of the glass micropipette was first thermally coated with a thin Au film. A photoresist (PR)-coated membrane was then pushed against this glass micropipette when the PR was still wet. During the contact, part of the PR was transferred from the membrane to the micropipette. After the membrane was removed, a continuous PR line was left on the outer surface of the glass micropipette. This line extended from the straight tube to the end of the curved tip. Another PR line was further generated on the other side of this micropipette using the same process. Finally, after the Au film was etched using the two PR lines as the masking patterns, followed by the removal of the PR using acetone, two Au lines were generated on the outer surface of the glass micropipette. The two approaches mainly differed in the ways of pressing the PR-coated membrane against the curved tip of the micropipette. In the first approach, a clip was applied for this purpose, while in the second approach a nitrogen flux was employed to make the membrane have intimate contact with the curved tip. To date, we have successfully fabricated Au lines on glass micropipettes of tip sizes down to 35 and 5 μm, respectively, using the two approaches.