In this report, we present a straightforward method for bridging a nanoplasmonic sensor with a conventional plate reader. By attaching lithographically prepared plasmonic nanostructures to a commercially available microwell strip, which has a perforated bottom, we could measure highly sensitive optical signals of plasmonic nanostructures using a conventional plate reader. The absorbance measurements and electromagnetic simulations show that a proper alignment between light polarization and the plasmonic nanostructure improves the sensing performance, which can be achieved with a linear polarizing film. Furthermore, the multiplexed detection capability of the proposed nanoplasmonic sensor chip was successfully demonstrated by monitoring four different enzyme–substrate reactions. These results illustrate the potential of the proposed nanoplasmonic sensor chip, which can combine advanced nanoplasmonic sensors with the well-developed microwell plate reader.