A new all-metal photodetector with an ultranarrow absorption band could lead to biosensors with greater sensitivity than ever. The device achieved a bandwidth of 12 nm by exploiting plasmonic surface lattice resonances of nanowire and nanoring arrays on optically thick, reflective metallic films. “It's been a challenge to sense very small particles or very low concentrations of a substance,” said Northwestern University professor Dr. Koray Aydin, one of the developers. “The beauty of our design is that we found a way to engineer the material by using a different substrate.” Typical absorber designs use two metal sheets with a nonmetallic insulating material in between. Aydin's team found that removing the insulating layer and leaving only metallic nanostructures caused the structure to absorb a much narrower band of light. In the new device, light absorption reaches 90 percent at visible frequencies. The resonance absorption wavelength, amplitude of the absorption peak and the bandwidth can be tuned by altering the periodicity and thickness of arrays. In addition to biosensors, Aydin said the design could also be used for applications in photothermal therapy, thermophotovoltaics, heat-assisted magnetic recording, thermal emission and solar steam generation. The research was published in ACS Nano (doi: 10.1021/nn502617t). For more information, visit www.northwestern.edu.