•News & Views• November 2020 Vol.63 No.11: 2464–2466 https://doi.org/10.1007/s11431-020-1690-y Meta photonic crystal paper devices GUO MaoZe 1 , WANG YuQiu 2 , HE BingFang 1,2* & GAO BingBing 1* 1 School of Pharmaceutical Sciences, Nanjing Tech University, Nanjing 211816, China; 2 College of Biotechnology and Pharmaceutical Engineering, Nanjing Tech University, Nanjing 211816, China Received May 7, 2020; accepted July 10, 2020; published online October 12, 2020 Citation: Guo M Z, Wang Y Q, He B F, et al. Meta photonic crystal paper devices. Sci China Tech Sci, 2020, 63: 2464–2466, https://doi.org/10.1007/s11431- 020-1690-y With its unique properties of thin, porous, flexible and af- fordable, paper has been widely used as a multifunctional material in daily life since its invention [1]. Commonly, paper is the most popular carrier for information transmis- sion such as writing and printing. However, since the ap- plications of paper has been broadened continuously, it has also shown great prospect in the field of biochemical ana- lysis. Paper-based analytical devices are easy to use, low cost, portable and disposable, thus playing an important role in the field of rapid detection [2]. With the development of paper-based materials, the iden- tification of paper is no longer strict: membranes with flex- ible or porous structures could also be defined as “paper” [3]. Among various paper-based devices, photonic crystal (PC) paper has gained more attention. Photonic crystals (PCs) are regular optical structures due to the periodically arranged media of various refractive indices, occurring in nature in the form of structural coloration such as wings of some butter- flies and skin of chameleons [4]. PC paper is a kind of flexible membrane devices which combined with PC struc- tures. PC structure has photonic bandgap characteristics, which could allow light of a specific wavelength go through the structure while reflect the light of other wavelength. Therefore, compared with traditional cellulose paper, PC paper possesses unique optical properties. Currently, con- siderable PC paper devices are widely used in the field of biochemical analysis [5–9]. However, these devices suffer the monotonous function and poor adherence. It is highly desired to design a multifunctional and super adhesive PC paper device. Recently, inspired by tree frog’s toe pads and gecko feet microstructures, Gu’s group [10] designed a PC paper device with micropillar array structure by simply self-assembled elastic P(MMA-BA) copolymer nanoparticles on a micro- patterned polydimethylsiloxane (PDMS) substrates for multifunctional applications (Figure 1(a)). Thanks to the micropillar array structure, the device achieved features as super adherence and spontaneous liquid transfer. The ordered microbionic arrays exhibit the great ability of interacting extensively with almost any surface, thereby enabling the device to adhere to skin surfaces stably. For mechanism, the device also showed significant mechanical property. In na- noindentation experiments and stretch-and-recover tests, the device could be completely restored under dry or wet con- dition after removing the strain, indicating that the device possessed excellent reversible mechanical property. In ad- dition, Elastic polymer nanoparticles were self-assembled during the drying process and the transparent device can show vivid structure color after liquid was introduced, thus enhanced fluorescence (Figure 1(b)). This novel design successfully addresses the poor adherence of conventional PC paper, achieving multifunctional applications on PC pa- per. It is found that when liquid was introduced on the PC paper, the highly ordered micropillar structures can manip- ulate the fluids, thereby microfluidics applications such as biochemical analysis could be achieved. To demonstrate the applicability of the PC paper in biological analysis, two © Science China Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 tech.scichina.com link.springer.com SCIENCE CHINA Technological Sciences *Corresponding authors (email: bingfanghe@njtech.edu.cn; gaobb@njtech.edu.cn)