Pain measurement is commonly required in biomedical and other emergency situations, yet there has been no pain biosensor reported in literature. Conventional approaches for pain measurement relies on Wong-Baker face diagrams, which are grossly inadequate for situations involving children or unconscious people. We report a label-free immunosensor for monitoring the pain biomarker cylooxygenase-2 (COX-2) in blood. The sensor is based on the concept of metalenhanced detection (MED). MED relies on the idea that the immobilization of underpotential deposition (upd) metallic films deposited either as a monolayer or electrostatically held onto a solid gold substrate could significantly amplify bimolecular recognition such as involving antigen-antibody (Ab-Ag) interactions. The surface bound Ab-Ag complex insulates the electrode; causing a decrease in concentration-dependent redox signals. A linear detection range of (3.64-3640.00)×10 −4 ng/mL was recorded with a detection limit of 0.25×10 −4 ng/mL, which was 4 orders of magnitude lower than that reported for ELISA for the same biomarker. The immunosensor exhibited selectivity of less than 6 % for potential interferents.