Isolation of monoclonal (M-) antibodies (Abs) from Ab-secreting cells (ASCs) is impeded by difficulties in identifying the minority of ASCs secreting Ab(s) of interest. We present a novel label-free system that traps ASCs into biocompatible microwells and detects the binding of secreted Ab(s), to a surface-immobi-lized antigen (Ag), as induced shifts in the extraordinary optical transmission (EOT) spectra through milled nanohole arrays. In this paper, a biotinylated target Ag (Bio-HA and Bio-2F5) is ex-posed to varying known MAb concentrations (17/9 and 2F5). The mean EOT shift in response to MAb concentration is similar in shape to specific MAb-Ag binding as seen in an ELISA. In another experiment, hybridoma cells secreting 17/9 MAb are trapped in wells inset into poly(dimethyl siloxane) (PDMS) (5–20 cells/trap), to which the nanohole arrays of Bio-HA "Sample" and Bio-2F5 "Ag Control" slides are aligned. Simultaneously, a Bio-HA "Media Control" slide is exposed to MAb-free media. The mean "Sample" shift (3 2 0 1 nm) is distinguished from the mean "Ag Control" shift (1 2 0 4 nm), but indistinguishable from the mean "Media Control" shift (3 6 0 3 nm). We have made significant progress in detecting Ab(s) secreted from trapped ASCs. With further devel-opment, our device could identify ASCs of interest rapidly, stream-lining therapeutic MAb discovery. Index Terms—Cell trap, extraordinary optical transmission (EOT), immunobiosensor, surface plasmon resonance (SPR).