Controlled Electrokinetic Particle Manipulation using Paper-and-Pencil Microfluidics

Dielectrophoresis is a very promising technique for particle manipulation on a chip. In this study, we demonstrate a controlled mannuvering of polystryrene particles on a simple paper-and-pencil based device by exploiting the underlying electrokinetics with primary contribution from dielectrophoretic (DEP) forces. On contrary to other reported DEP devices, the present configuration does not demand a shophitcated laboratory module for creating a non-uniform electric field, which is essential requirement in DEP settings. We demonstrate positive dielectrophoresis (pDEP) to trap 1 um size polystyrene particle for low-conductivity suspending medium, at an applied field strength of 100 V/cm. In addition, the switching of the trapping direction (positive to negative dielectrophoresis) can be simply achieved by manipulating the conductivity of the media. We further bring out an optimum range of pH for effective particle trapping. These results have significant implications towards designing cell-on-a-chip based point of care diagnostic devices for resource limited settings.Comment: 21 page

Electrokinetic Energy Harvesting using Paper and Pencil

We exploit the combinatorial advantage of electrokinetics and tortutosity of cellulose-based paper network on a laboratory grade filter paper for the development of a simple, inexpensive, yet extremely robust (shows constant performance till 12 days) paper-and-pencil-based device for energy harvesting application. We successfully achieve to harvest maximum output power of 640 pW in single channel, while the same is significantly improved (by about 100 times) with the use of multichannel microfluidic array (maximum up to 20 channels). We envisage that such ultra-low cost devices may turn out to be extremely useful in energizing analytical microdevices in resource limited settings, for instance for extreme point of care diagnostics applications.Comment: 12 page

Microfluidics on porous substrates mediated by capillarity-driven transport

Microfluidic systems on porous substrates, including paper-based analytical platforms, have attracted significant attention recently, primarily attributed to their diversified applications, ranging from bioanalytical devices for healthcare technologies to green energy generation and flexible electronics. In this short Review, we attempt to provide a concise overview about the fundamental premises of functionalities of these devices, starting from the understanding of flow in single one-dimensional conduit. This can be extended to more-complex systems, where an intrinsic capillary action offers the necessary provisions for continuous maintenance of heterogeneous flow over multiple spatiotemporal scales, which essentially facilitates the needs of specific applications. We discuss a few specific applications as demonstrative examples that are solely triggered by the intrinsic capillary action of the porous media. These specific examples delineate the fact that flexible architecture of the devices, in combination with the inherent capillary-driven phenomena, makes it suitable to meet the desired user-specific demands at affordable costs, rendering them immensely suitable for the low-resource-settings environment

Optoelectronic Trajectory Reconfiguration and Directed Self‐Assembly of Self‐Propelling Electrically Powered Active Particles

Abstract Self‐propelling active particles are an exciting and interdisciplinary emerging area of research with projected biomedical and environmental applications. Due to their autonomous motion, control over these active particles that are free to travel along individual trajectories, is challenging. This work uses optically patterned electrodes on a photoconductive substrate using a digital micromirror device (DMD) to dynamically control the region of movement of self‐propelling particles (i.e., metallo‐dielectric Janus particles (JPs)). This extends previous studies where only a passive micromotor is optoelectronically manipulated with a translocating optical pattern that illuminates the particle. In contrast, the current system uses the optically patterned electrode merely to define the region within which the JPs moved autonomously. Interestingly, the JPs avoid crossing the optical region's edge, which enables constraint of the area of motion and to dynamically shape the JP trajectory. Using the DMD system to simultaneously manipulate several JPs enables to self‐assemble the JPs into stable active structures (JPs ring) with precise control over the number of participating JPs and passive particles. Since the optoelectronic system is amenable to closed‐loop operation using real‐time image analysis, it enables exploitation of these active particles as active microrobots that can be operated in a programmable and parallelized manner