Az1505 photoresist

Pyrex glass wafers are coated with 10 nm chromium and 50 nm gold. This metal layer is patterned as metal tracks to form independent conductive domains on the wafer. Subsequently, AZ1505 photoresist (MicroChemicals GmbH) is spin-coated and patterned with circular openings towards the underlying metal tracks. The metal tracks are meander-shaped to accommodate an array of sensors in a small area, increasing the density of sensing nodes. The metal tracks end in pads that are connected to an external circuit which provides the negative bias voltage to collect positively charged nanoparticles produced by spark ablation. The total substrate size is 23 × 23 mm; however, the sensing area is 1600 × 600 µm² located at the center of the chip. The chip is designed in such a way that it can be incorporated into an integrated circuit to form a plug-and-play device at a later stage.

LB, phosphate buffered saline (PBS), sodium chloride, Tween 40, Tween 60, and Tween 80 were purchased from Sigma Aldrich (Oakville, ON, USA). Fluorinert FC-40 was purchased from 3M (St. Paul, MN, USA) and chemicals for photolithography were supplied by Rohm and Haas (Marlborough, MN, USA). Fluoroalkylsilane Dynasylan F 8263 was supplied by Evonik (Essen, Germany). AZ1505 photoresist and Teflon-AFR were procured from Microchemicals GmbH (Ulm, Germany) and DuPont (Wilmington, DE, USA), respectively. Parylene-C dimer and Silane A174 were purchased from Plasma Parylene Coating Services (Rosenheim, Germany) and superparamagnetic Dynabeads M-280 Tosylactivated were purchased from Thermo Fisher Scientific (Waltham, MA, USA). Ampicillin and isopropyl β-D-1-thiogalactopyranoside (IPTG) were procured from Applichem, Darmstadt, Germany, and L-Arabinose from Acros Organics. Mouse monoclonal anti-Salmonella typhimurium LPS antibody (ab8274) was obtained from Abcam (Cambridge, UK).