Combining vapour sensors into arrays is an accepted compromise to mitigate poor selectivity of conventional sensors. Here we show individual nanofabricated sensors that not only selectively detect separate vapours in pristine conditions but also quantify these vapours in mixtures, and when blended with a variable moisture background. Our sensor design is inspired by the iridescent nanostructure and gradient surface chemistry of Morpho butterflies and involves physical and chemical design criteria. The physical design involves optical interference and diffraction on the fabricated periodic nanostructures and uses optical loss in the nanostructure to enhance the spectral diversity of reflectance. The chemical design uses spatially controlled nanostructure functionalization. Thus, while quantitation of analytes in the presence of variable backgrounds is challenging for most sensor arrays, we achieve this goal using individual multivariable sensors. These colorimetric sensors can be tuned for numerous vapour sensing scenarios in confined areas or as individual nodes for distributed monitoring.

Significance Morpho butterflies are a brilliant spectacle of nature’s capability for photonic engineering. Their conspicuous appearance arises from the interference and diffraction of light within tree-like nanostructures on their scales. Scientific lessons learned from these butterflies have already inspired designs of new displays, fabrics, and cosmetics. This study reports a vertical surface polarity gradient in these tree-like structures. This biological pattern design may be applied to numerous technological applications ranging from security tags to self-cleaning surfaces, gas separators, protective clothing, and sensors. Here it has allowed us to unveil a general mechanism of selective vapor response in photonic Morpho nanostructures and to demonstrate attractive opportunities for chemically graded sensing units for high-performance sensing.

Chemical vapor deposition (CVD) has been used historically for the fabrication of thin films composed of inorganic materials. But the advent of specialized techniques such as plasma-enhanced chemical vapor deposition (PECVD) has extended this deposition technique to various monomers. More specifically, the deposition of polymers of responsive materials, biocompatible polymers, and biomaterials has made PECVD attractive for the integration of biotic and abiotic systems. This review focuses on the mechanisms of thin-film growth using low-pressure PECVD and current applications of classic PECVD thin films of organic and inorganic materials in biological environments. The last part of the review explores the novel application of low-pressure PECVD in the deposition of biological materials.

Nanofi bers consisting of the bulk heterojunction organic photovoltaic (BHJ-OPV) electron donor-electron acceptor pair poly(3-hexylthiophene):phenyl-C 61 -butyric acid methyl ester (P3HT:PCBM) are produced through a coaxial electrospinning process. While P3HT:PCBM blends are not directly electrospinnable, P3HT:PCBM-containing fi bers are produced in a coaxial fashion by utilizing polycaprolactone (PCL) as an electrospinnable sheath material. Pure P3HT:PCBM fi bers are easily obtained after electrospinning by selectively removing the PCL sheath with cyclopentanone (average diameter 120 ± 30 nm). These fi bers are then incorporated into the active layer of a BHJ-OPV device, which results in improved short-circuit current densities, fi ll factors, and power-conversion effi ciencies (PCE) as compared to thin-fi lm devices of identical chemical composition. The best-performing fi ber-based devices exhibit a PCE of 4.0%, while the best thin-fi lm devices have a PCE of 3.2%. This increase in device performance is attributed to the increased in-plane alignment of P3HT polymer chains on the nanoscale, caused by the electrospun fi bers, which leads to increased optical absorption and subsequent exciton generation. This methodology for improving device performance of BHJ-OPVs could also be implemented for other electron donor-electron acceptor systems, as nanofi ber formation is largely independent of the PV material.