The device was fabricated using standard photolithography and soft lithography according to the procedure reported previously (20). Briefly, the device was assembled from a glass chip with patterned asymmetric gold electrode structures and a polydimethylsiloxane (PDMS) slab consisting of the microfluidic channel structures. The PDMS slab consisted of five parallel channels, each 3.5 cm long, 400 μm wide, and 500 μm high. The chip accommodated five channels, and each channel was made up of an array of 40 pairs of asymmetric gold electrodes (fig. S1, A and B). The distance between two adjacent electrode pairs was 150 μm. An electrode pair consisted of a small (100 μm width) and large (400 μm width) electrodes that were spaced by a distance of 50 μm (fig. S1C). The nanoscopic fluid flow was generated by applying an alternating potential difference across each asymmetric electrode pair. The potential difference changed the charge distribution in the electrical double layer that gave rise to a lateral fluid movement in nanometer distance to the electrode surface. This lateral fluid movement increased the diffusion of molecules and SERS nanotags, leading to frequent antigen-antibody collisions while simultaneously shearing off weakly bound nonspecific molecules.

The electrode structures were designed in L-Edit (Tanner Research, USA) and written to a 12.7 cm chrome mask (Shenzhen Qingyi Precision Mask Making, Singapore) using a direct laser writer (Heidelberg μPG 101, Germany). Borofloat wafers (Bonda Technology Pte Ltd., Singapore) were rinsed with isopropanol and acetone and dried for 25 min at 150°C. Subsequently, negative photoresist AZ nLOF 2020 (MicroChemicals GmbH, Germany) was spin-coated on the wafer for 30 s at 3000 rpm before a soft bake for 2 min at 110°C. Next, the coated wafer was exposed at a constant dose of 340 mJ/cm with an EVG 620 mask aligner (EV Group, Austria), followed by a postback of 1 min at 110°C. The exposed wafer was then developed for 45 s in AZ 726 MIF (MicroChemicals GmbH, Germany), dried, and subjected to deposition of 10 nm of Ti and 200 nm of Au with a Temescal FC-2000 electron beam evaporator (Ferrotec, USA). After overnight liftoff in Remover PG (MicroChemicals GmbH, Germany), the excess material was washed off and the electrode pattern was revealed (fig. S1B).

PDMS microfluidic channels were prepared by casting an activated silicon elastomer solution (Sylgard 184, Dow, USA) onto the master mold containing microfluidic channels. After curing for 20 min at 80°C, the PDMS was carefully detached from the master. The sample inlet and outlet reservoirs were then punched at the ends of microfluidic channels. The PDMS microfluidic structures were aligned with the array of asymmetric electrodes on the glass chip and thermally bonded overnight at 65°C.

Note: The content above has been extracted from a research article, so it may not display correctly.

Please log in to submit your questions online.
Your question will be posted on the Bio-101 website. We will send your questions to the authors of this protocol and Bio-protocol community members who are experienced with this method. you will be informed using the email address associated with your Bio-protocol account.

We use cookies on this site to enhance your user experience. By using our website, you are agreeing to allow the storage of cookies on your computer.