In this Letter, we describe an accurate antibody detection method using a fabricated extended-gate type organic field-effect-transistor (OFET), which can be operated at below 3 V. The protein-sensing portion of the designed device is the gate electrode functionalized with streptavidin. Streptavidin possesses high molecular recognition ability for biotin, which specifically allows for the detection of biotinylated proteins. Here, we attempted to detect biotinylated immunoglobulin G (IgG) and observed a shift of threshold voltage of the OFET upon the addition of the antibody in an aqueous solution with a competing bovine serum albumin interferent. The detection limit for the biotinylated IgG was 8 nM, which indicates the potential utility of the designed device in healthcare applications.

Body color change associated with sexual maturation—so-called nuptial coloration—is commonly found in diverse vertebrates and invertebrates, and plays important roles for their reproductive success. In some dragonflies, whereas females and young males are yellowish in color, aged males turn vivid red upon sexual maturation. The male-specific coloration plays pivotal roles in, for example, mating and territoriality, but molecular basis of the sex-related transition in body coloration of the dragonflies has been poorly understood. Here we demonstrate that yellow/red color changes in the dragonflies are regulated by redox states of epidermal ommochrome pigments. Ratios of reduced-form pigments to oxidized-form pigments were significantly higher in red mature males than yellow females and immature males. The ommochrome pigments extracted from the dragonflies changed color according to redox conditions in vitro: from red to yellow in the presence of oxidant and from yellow to red in the presence of reductant. By injecting the reductant solution into live insects, the yellow-to-red color change was experimentally reproduced in vivo in immature males and mature females. Discontinuous yellow/red mosaicism was observed in body coloration of gynandromorphic dragonflies, suggesting a cell-autonomous regulation over the redox states of the ommochrome pigments. Our finding extends the mechanical repertoire of pigment-based body color change in animals, and highlights an impressively simple molecular mechanism that regulates an ecologically important color trait.