S1805 photoresist

Nanostructures were patterned onto p- and n-type (100) silicon wafers with resistivity 1–10 Ω cm (Pi-Kem, UK) spin-coated with polymethyl methacrylate 950-A2 (Microchem, USA), and patterned using a RAITH 150 TWO electron beam lithography system (Raith GmbH, Germany). Following exposure, patterns were developed in a 1:3 mixture of methyl isobutyl ketone in isopropyl alcohol and treated in oxygen plasma in a Diener plasma generator (Diener electronic GmbH & Co. KG, Germany) to remove excess photoresist scum and produce final circular features with an approximate diameter of 200 nm. Microstructures were patterned onto silicon wafers spin-coated with S1805 photoresist (Microchem, USA) using phase shift lithography. A borosilicate mask etched with lines 1.5 in. in length and 1.5 μm thick with 1.5 μm spacing was used to perform double exposures at 5 mJ cm⁻² with the mask turned 90° in between exposures on a Quintel Q4000-6 Mask Aligner (Neutronix Quintel, USA). Patterns were developed in MICROPOSIT MF-26A (Dow Electronic Materials, USA) to produce final rectangular patterns measuring approximately 1 × 1.3 μm.

The following chemicals were ordered from Sigma (St. Louis, MO): CHES, hydroxypropyl cellulose (HPC; 10⁶ Da), poly(ethylene glycol) diacrylate (PEGDA; 575 Da), inhibitor remover beads, DMSO, and benzoin methyl ether (BME). FITC was purchased from Life Technologies (Carlsbad, CA). PTB biomarkers were obtained from the following sources: Fer from EMD Millipore (Billerica, MA), LF from Sigma (St. Louis, MO), P1 and P2 from Biomatik (Wilmington, DE), CRF and FITC-labeled P1 from GenScript (Piscataway, NJ), and TNF from ProSpec (East Brunswick, NJ). All solutions were made with deionized water (18.3 MΩ cm) from a Barnstead EASYpure UV/UF system (Dubuque, IA). Methanol was purchased from Macron (Center Valley, PA), sodium hydroxide from Mallinckrodt Baker (Paris, KY), and sodium bicarbonate from Merck (Darmstadt, Germany). HEPES, cyclohexane, and Amicon ultra 0.5 mL centrifugal (3, 10, 30, and 50 kDa cutoff) filters were purchased from EMD Millipore. Zeonor 1060R cyclic olefin copolymer (COC) was purchased in 1 and 2 mm thick sheets (Zeon Chemicals; Louisville, KY) cut to 2.2 x 5 cm pieces with an industrial bandsaw. Silicon wafers were from Fairchild (Phoenix, AZ) and S1805 photoresist came from MicroChem (Westborough, MA).