Electronic Supplementary Material

Bottom-up assembly of silicon nanowire conductometric sensors for the detection of apolipoprotein A1, a biomarker for bladder cancer

Yen-Heng Lin1,2,3,*, Wei-Siao Lin1, Jing-Chao Wong2, Wei-Chieh Hsu1, Yong-Sheng Peng1, Chien-Lun Chen4,5

1Department of Electronic Engineering, Chang Gung University, Taoyuan 333, Taiwan

2Graduate Institute of Medical Mechatronics, Chang Gung University, Taoyuan 333, Taiwan

3Department of Otolaryngology-Head & Neck Surgery, Chang Gung Memorial Hospital, Taoyuan 333, Taiwan

4Department of Urology, Chang Gung Memorial Hospital, Taoyuan 333, Taiwan

5Collage of Medicine, Chang Gung University, Taoyuan 333, Taiwan

*Corresponding author, E-mail address:

Schematic of the electrodes

Fig. S1 Nine pairs of electrodes were arranged on the substrate. Each pair of electrodes has a 15-µm gap in the middle of the layout (electrode front end), as shown in the inset. The width and length of the front end electrodes were 20 µm and 200 µm, respectively. The distance between each electrode at the front end was 80 µm. The wires connected to the back ends of the electrodes were 200 µm in width and 8.5 mm in length.

Details of the photolithography process for the second lift-off

After the nanowires were connected to the gap of the electrode and the suspended solution IPA was evaporated, the substrate was cleaned using oxygen plasma (30 W, PDC-001, Harrick Plasma, USA) for 5 min. A lift-off promotion photoresist LOR was (LOR, MicroChem Corp., USA) spin-coated on the substrate with a spin velocity of 1000 rpm for 10 s and 6000 rpm for 30 s. Then, the LOR layer was baked on a hot plate at 150 °C for 2.5 min. After cooling the substrate, an imaging photoresist (S1818, Dow Electronic Materials, USA) was then spin-coated on the LOR layer with a spin velocity of 1000 rpm for 10 s and 4000 rpm for 30 s. The imaging photoresist was then baked on a hot plate at 120 °C for 1 min. After cooling the substrate, it was exposed with a total energy of 150 mJ/cm2. Then, the S1818 and LOR were developed in a developer (AZ 300MIF, Merck, USA) for 7-9 s, and the substrate was ready for the metal deposition process. The process parameters are summarized in Table S1.

Table S1 Experimental details of the photolithography process

Photoresist / Spin velocity / Soft bake / Exposure / Development/lift-off time
LOR / 1000 rpm, 10 s
6000 rpm, 30 s / 150 °C
2.5 min / No need / 1 min (for lift-off)
S1818 / 1000 rpm, 10 s
4000 rpm, 30 s / 120 °C
1 min / 4.5 s
(150 mJ/cm2) / 7-9 s (for development including LOR layer)

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