Ultrafast humidity sensor based on liquid phase exfoliated graphene.

Humidity sensing is important to a variety of technologies and industries, ranging from environmental and industrial monitoring to medical applications. Although humidity sensors abound, few available solutions are thin, transparent, compatible with large-area sensor production and flexible, and almost none are fast enough to perform human respiration monitoring through breath detection or real-time finger proximity monitoring via skin humidity sensing. This work describes chemiresistive graphene-based humidity sensors produced in few steps with facile liquid phase exfoliation followed by Langmuir-Blodgett assembly that enables active areas of practically any size. The graphene sensors provide a unique mix of performance parameters, exhibiting resistance changes up to 10% with varying humidity, linear performance over relative humidity (RH) levels between 8% and 95%, weak response to other constituents of air, flexibility, transparency of nearly 80%, and response times of 30 ms. The fast response to humidity is shown to be useful for respiration monitoring and real-time finger proximity detection, with potential applications in flexible touchless interactive panels.

Photosynthetic Reaction-Center/Graphene Biohybrid for Optoelectronics.

Photosynthetic reaction center proteins (RC) purified from purple bacterial strains were deposited on graphene layer prepared by liquid phase exfoliation and light-induced resistance change was measured. By measuring the temperature dependence of the resistance change of the bare and RC covered graphene and comparing with the one inactivated by protein unfolding, two effects were possible to separate. One of them is the resistance change due to temperature effect. The other one clearly indicates a possible electric/electronic interaction between the charge flow in the graphene and the light-induced charge pair within the protein, which is, essentially, different in the open (dark, PBPheo) and closed (light, P+BPheo-) states. These results provide useful information for designing hybrid bio-photonic devices which are able to absorb and convert light energy.