Co-printing of micro/nanostructures integrated with preconcentration to enhance protein detection

This paper reports a fabrication method that can make microstructures such as microfluidic channels and nanostructures to generate surface plasmon resonance (SPR) signals in one-step using hot embossing. We first made a micro/nanostructural mold on a silicon substrate through sequential e-beam lithography, reactive ion etching (RIE), photolithography, and inductively coupled plasma RIE. The fabricated mold and cyclo-olefin polymer (COP) film were pressed between two flat, heated metal bases under optimal conditions, and the micro/nanostructures were complementarily transferred to the COP film. After depositing a thin aluminum film onto the nanostructure, the device was completed by patterning Nafion that crossed two channels and a nearby nanostructure, and by bonding the COP film to a flat polydimethylsiloxane (PDMS) substrate with holes punched for the inlets and outlets. SPR signals of the nanostructures of the microfluidic channel were calibrated using glycerol solutions of different percentages, and a wavelength sensitivity of 393 nm/refractive index unit was found for the Al-based nanoslit SPR sensing chip. To detect macromolecules, we first modified bovine serum albumin (BSA) onto the surface of the SPR chip and then allowed different concentrations of anti-BSA samples to flow into the device. A calibration curve for detecting anti-BSA was constructed, and anti-BSA detection levels with and without preconcentration were compared.