Paper and pseudo-paper based flexible membrane devices

With unique advantages of thin, porous, flexible, flammable and affordable, paper has been widely used in our daily life. Early in the 19th century, paper was first applied in biochemical analysis. Since then, paper had been used as a unique analytical platform. Paper-based analysis devices are easy to use, cheap, portable and disposable, thus they are widely considered as platform for POCT (point-of-care testing) and on-site detection. Liquid can automatically transport in paper cellulose networks without external pumps or energy, thus do not require extra instruments. The large specific surface area of fiber networks are ideal places for storing testing bio-chemical substances. Paper is also flexible and easy to fold together to form multilayer substrates of 3D chips, make it suitable for 3D cell culture and building multifunctional microfluidic chips. Meanwhile, paper-based analysis devices also have restrictions as chaos porous structure of the fibers interferes the optical signals and nonspecific adsorbs the testing samples, leading a low sensitivity of detection based on colorimetric. Due to the roughness of the fibers, it is still difficult to process the paper with high precision. In order to solve this, new types of paper (pseudo-paper) have emerged. In addition to biochemical analysis, paper also shows great prospect in the field of microelectronics. Currently, paper-based materials have been widely used in fields of flexible electronic devices, for example electronic circuits and energy storage devices. Paper exhibits piezoelectric behavior and is porous, degradable, make it promising materials in fabricating flexible electronics, display, soft robots and energy storage devices. Recently, enormous paper-based and pseudo-paper devices have been reported by researchers in various fields. These devices focus on the construction of new cost-effective microfluidics and electronics. The combination of paper-based microfluidic devices and electronic devices promotes the development of artificial skin, soft robots and flexible electronics. Considerable breakthroughs of new highly integrated paper-based chips have been achieved. In order to summarize the modern developing of paper and pseudo-paper devices and inspire scientists in various research fields, we present here an overall review that focuses on the historical developments to recent advances and future prospects of paper-based and pseudo-paper devices. These aspects include the preparation methods, the manipulation of microfluidics and electrons and multiple applications based on such manipulation. We hope that this review will promote the development of paper devices in various research fields such as analytical chemistry, materials science and electronic science.