We report that a droplet dispensed from a micropipette almost always has a considerable electrical charge of a magnitude dependent on the constituents of the droplet, on atmospheric humidity and on the coating material of pipette tip. We show that this natural electrification of a droplet originates from the charge separation between a droplet and pipette tip surface by contact with water due to the ionization of surface chemical groups. Charge on a droplet can make it difficult to detach the droplet from the pipette tip, can decrease its surface tension, can affect the chemical characteristics of solutions due to interactions with charged molecules, and can influence the combination and localization of charged bio-molecules; in all cases, the charge may affect results of experiments in which any of these factors is important. Thus, these findings reveal experimental parameters that should be controlled in experiments that use micropipettes.

expand the range of accessible 3D geometries. [5-8] Due to their shape-adaptive nature, origami and kirigami, originally applied only to paper, can serve as routes to large-scale structural systems that require packaging and deployment, such as foldable solar panels, [9,10] retractable roofs, [11] deployable sunshields, [12] and many others. [13] More recent work demonstrates that these and related methods for assembling planar materials into complex 3D structures can exploit sophisticated 2D fabrication technologies and thin film materials from the electronics/optoelectronics industries, to yield functional systems in 3D designs that were previously unachievable. [14-18] In this way, the techniques of origami/kirigami can enable many classes of nontraditional devices not only at the macroscale but also at the micro/ nanoscale, with the potential to open up opportunities for unusual engineering designs in microsystems technologies. [19-22] Much research in origami/kirigami assembly aims to extend the range of length scales and the scope of functional materials that can be realized in 3D systems, and to transfer those ideas and Origami and kirigami, the ancient techniques for making paper works of art, also provide inspiration for routes to structural platforms in engineering applications, including foldable solar panels, retractable roofs, deployable sunshields, and many others. Recent work demonstrates the utility of the methods of origami/kirigami and conceptually related schemes in cutting, folding, and buckling in the construction of devices for emerging classes of technologies, with examples in mechanical/optical metamaterials, stretchable/ conformable electronics, micro/nanoscale biosensors, and large-amplitude actuators. Specific notable progress is in the deployment of functional materials such as single-crystal silicon, shape memory polymers, energy-storage materials, and graphene into elaborate 3D micro and nanoscale architectures. This review highlights some of the most important developments in this field, with a focus on routes to assembly that apply across a range of length scales and with advanced materials of relevance to practical applications. Hall of Fame Article The ORCID identification number(s) for the author(s) of this article can be found under

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