Electronic devices may be provided with imaging modules that include plasmonic light collectors. Plasmonic light collectors may be configured to exploit an interaction between incoming light and plasmons in the plasmonic light collector to alter the path of the incoming light. Plasmonic light collectors may include one or more spectrally tuned plasmonic image pixels configured to preferentially trap light of a given frequency. Spectrally tuned plasmonic image pixels may include plasmonic structures formed form a patterned metal layer over doped silicon layers. Doped silicon layers may be interposed between plasmonic structures and a reflective layer. Plasmonic image pixels may be used to absorb and detect as much as, or more than, ninety percent of incident light at wavelengths ranging from the infrared to the ultraviolet. Plasmonic image pixels that capture light of different colors may be arranged in patterned arrays to form imager modules or imaging spectrometers for optofluidic microscopes.