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A transmission-based surface plasmon resonance (SPR) sensor for label-free detection of protein-carbohydrate and protein-protein binding proximate to a perforated gold surface is demonstrated. An SPR instrument makes real-time measurements of the resonant wavelength and/or the resonant angle of incidence of transmitted light; both are influenced by the presence of proteins at the gold surface-liquid interface. Ethylene glycol solutions with known refractive indexes were used to calibrate the instrument. A paired polarization-sensitive detector achieved an overall detection resolution of ~ 6.6 times 10-5 refractive index units (RIU). Proof of principle experiments was performed with concanavalin A (Con A) binding to gold-adsorbed ovomucoid and anti-bovine serum albumin (BSA) binding to gold-adsorbed BSA.