Hierarchical Graphene-Dye Bilayers for Multimodal Optoelectronic Sensing and Decoupling of Complex Stimuli

Signals obtained by chemical or calorimetric sensors are highly coupled and complex, making it very challenging to precisely detect and discriminate between simultaneous stimuli. The development of sensors that provide multiple sensory outputs is a good way to tackle such a long-lasting challenge. Herein, a new design of multimodal sensors capable of generating both colorimetric and electrical sensory outputs is introduced. This is achieved by coupling two functional nanolayers, graphene (electrically active) and dyes (colorimetric) in which each layer can work either autonomously or in conjugation with the other sensing layer. It is shown that the interfacial interaction of graphene with the wide variety of dyes creates unique interfacial sensing sites for the detection of chemicals. This endows each sensor or sensor array, in the format of (opto)electronic nose, with a "fingerprint" of varying bonding possibilities, enlarging the spectrum of gas-sensor interactions. Furthermore, it is shown that the hierarchical nanobilayer structure allows the separation and discrimination of volatile organic compounds (VOCs) based on their diffusion kinetics. Taken together, the bilayer design qualifies as a superior sensor compared to unimodal devices by offering improved detection limits, wider dynamic ranges, and higher sensitivity and selectivity in the binary discrimination of a wide range of stimuli (temperature, relative humidity, and VOCs).