Suspension Arrays Prepared from Nanofiber-Based Microparticles for a Platform of SERS-Based Multiplex Immunoassay

Electrospun nano- and microfibers have received considerable attention for various sensing applications owing to their three-dimensional porous structures with a high surface area that can increase the sensitivity of the sensor. Despite the successful use of electrospun fibers in the biosensing field, most applications have been based on a macroscopic fiber matrix, and the use of micrometer-scale fiber particles has not been reported. Here, we propose a simple method for fabricating shape-coded nanofiber microparticles using a water-soluble and photocrosslinkable polymer, poly-(vinyl alcohol) N-methyl-4-(4 '-formylstyryl) pyridinium methosulfate acetal (PVA-SbQ). Electrospinning of PVA-SbQ and the subsequent photopatterning process generated photocrosslinked fibrous micropatterns that could be easily detached from the substrates and collected as nanofiber microparticles in an aqueous environment. The lateral dimensions and shapes of the microparticles were controlled by photomask design, and thickness of the microparticles was determined by electrospinning time. The resultant nanofiber microparticles were decorated with silver nanoparticles and served as capture substrates for a surface-enhanced Raman spectroscopy (SERS)-based immunoassay, where Au-Ag alloy nanocubes were used as SERS tags. Because suspension arrays consisting of nanofiber microparticles of various shapes can be prepared, highly sensitive SERS-based biosensing of multiple targets can be developed using shape-coded nanofiber microparticles. The performance of the devised immunosensor was demonstrated by the very low detection limit for biomolecules with high selectivity.