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

Transient drift of Escherichia coli under diffusing Step nutrient profile

Bacteria such as Escherichia coli (E. coli) exhibit biased motion if kept in a spatially non-uniform chemical environment. Here, we bring out unique time-dependent characteristics of bacterial chemotaxis, in response to a diffusing spatial step ligand profile. The experimentally obtained temporal characteristics of the drift velocity are compared with the theoretical and Monte-Carlo simulation based estimates, and excellent agreements can be obtained. These results bring in new insights on the time-responsive facets of bacterial drift, bearing far reaching implications in understanding their migratory dynamics in the quest of finding foods by swimming toward the highest concentration of food molecules, or for fleeing from poisons, as well as towards the better understanding of therapeutic response characteristics for certain infectious diseases

Diffusive dynamics on paper matrix

Writing with ink on a paper and the rapid diagnostics of diseases using paper cartridge, despite their remarkable diversities from application perspective, both involve the motion of a liquid from a source on a porous hydrophilic substrate. Here we bring out a generalization in the pertinent dynamics by appealing to the concerned ensemble-averaged transport with reference to the underlying molecular picture. Our results reveal that notwithstanding the associated complexities and diversities, the resultant liquid transport characteristics on a paper matrix, in a wide variety of applications, resemble universal diffusive dynamics. Agreement with experimental results from diversified applications is generic and validates our unified theory

Microfluidics-based low-cost medical diagnostic devices: some recent developments

Here we present a short review of recently developed low-cost microfluidic devices aimed towards medical diagnostic applications. This review specifically focuses on three inexpensive devices, namely lab-on-a-compact-disc, paper-based, and thread-based devices. Here, we present a concise summary of all the recently developed protocols for simple bioassays to complex diagnostics. We also provide a new outlook on how the present practice of pathological diagnostics can be improved with the usage of such recent developments

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

Predicting Escherichia coli's chemotactic drift under exponential gradient

Bacterial species are known to show chemotaxis, i.e., the directed motions in the presence of certain chemicals, whereas the motion is random in the absence of those chemicals. The bacteria modulate their run time to induce chemotactic drift towards the attractant chemicals and away from the repellent chemicals. However, the existing theoretical knowledge does not exhibit a proper match with experimental validation, and hence there is a need for developing alternate models and validating experimentally. In this paper a more robust theoretical model is proposed to investigate chemotactic drift of peritrichous Escherichia coli under an exponential nutrient gradient. An exponential gradient is used to understand the steady state behavior of drift because of the logarithmic functionality of the chemosensory receptors. Our theoretical estimations are validated through the experimentation and simulation results. Thus, the developed model successfully delineates the run time, run trajectory, and drift velocity as measured from the experiments

Evolution of paper microfluidics as an alternate diagnostic platform

Since the inception of paper microfluidics, there has been a significant leap in developing microfluidic assays for wide range of applications, particularly in healthcare. Considering the average economic status of the population and epidemic outbreaks of diseases within territory of developing nations, it is indeed an essential demand to have an alternate diagnostic plat-form which is ideally expected to serve the purpose at faster and affordable means. In this context, introduction of the paper devices started with qualitative assays and thereafter it has subsequently evolved for semi-quantitative and quantitative platforms. Conventional diagnostic procedures involve time consuming multi step processes that are rather elaborate and expensive, necessitating the involvement of highly trained personnel for analysis. Paper based diagnostic procedures; on the other hand, normally deploy tiny amounts of physiological fluids and consumables, to achieve the same end objective at much reduced expenses and time. Towards this, colorimetric assays have shown significant promises, but are limited by the sensitivity of the diagnostic method. In an effort to improve the sensitivity of the detection, other approaches like fluorescent, electrochemical, luminescence have been progressively explored. In this Chapter, the discussion is systematically organized from fabrication of paper-based devices to their different applications in the diagnostic arena. Starting from the fabrication fundamentals and working principles, we delve deep on different colorimetric detection of bio-molecules, bacteria etc. We also focus on the critical aspect of plasma separation from the whole blood, which is a key for most colorimetric detections. Finally, we summarize the key findings about the advancements of these devices for practical use in resource-limited settings and bring out some new and unaddressed questions as well as challenges in the field

Capillarity-driven blood plasma separation on paper-based devices

We demonstrate capillarity-driven plasma separation from whole blood on simple paper-based H-channels. This methodology, unlike other reported techniques, does not necessitate elaborate and complex instrumentation, and the usage of expensive consumables. We believe that this technique will be ideally suited to be implemented in rapid and portable blood diagnostic devices designed to be operative at locations with limited resources