Nanoplasmonic discrimination of organic solvents using a bimetallic optical tongue

Optical sensor arrays serve as excellent tools for the recognition and discrimination of a variety of liquid and gas mixtures. They achieve this via pattern-based recognition from signals across multiple sensing regions, where each region is modified to produce a different interaction, such as partial-selectivity, with desired analytes. As their use progresses towards rapid, highly personalized diagnosis and component identification devices, reduction in complexity and data-acquisition time is key. One way to achieve this is through reducing the number of elements in the array without compromising the differential capabilities of the device. Here, we present a device with elements consisting of plasmonic sensors of two superimposed plasmonic nanoarrays; one fabricated using gold and the other aluminum. Each material produces a distinct plasmonic response while also allowing us to selectively functionalize each pattern with a different ‘sensing chemistry.’ This allows for the development of different partially-selective elements, via modification with functional thiols and silanes, respectively. Since optical sensing arrays of this type require multiple sensing regions, each producing a different optical response, our bimetallic method results in twice as much data from one measurement, providing the same amount of data necessary to allow for successful differentiation with fewer elements in the sensing array. We demonstrate that by altering the surface chemistry of the nanostructures we can tune their partial selectivity to organic solvents. We believe this technology could be useful in areas that rely on assays for simultaneous determination of multiple analytes, such as the medical, food and drug, and security industries.