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RELIABLE LIQUID REAGENT HANDLING AND ROTATIONAL RELEASE FOR CENTRIFUGAL SAMPLE-TO-ANSWER AUTOMATION
Abstract
Most point-of-care applications require onboard storage of liquid reagents such as buffers and stains. The reliable handling and release of these reagents is key to enabling the multiple unit operations on these platforms. We present here a centrifugal buoyancy-driven release mechanism [1], where the balance between a stored aqueous reagent (to protect a lipophilic dissolvable-film (DF)) and an ancillary oil liquid allows for controlled release. At the beginning of the assay protocol, the disc is spun to generate sufficient centrifugal pressure allowing the denser ancillary phase to reliably displace the aqueous phase to thus open the DF, due to stratification of the immiscible phases.
... This paper focuses on a novel type of rotationally actuated valve; during storage of an aqueous reagent, a (water) dissolvable film (DF) presents a diffusion barrier which is initially protected by an oleophilic, ancillary liquid having a certain, specific density (Gaughran et al. 2016;Mishra et al. 2015Mishra et al. , 2017Mishra et al. , 2020Ducrée 2021d;Lu et al. 2020). Upon spinning, a centrifugo-hydrostatic equilibrium is reached, in which the interface between the two immiscible liquids contacts and thus dissolves the DF. ...
Decentralized bioanalytical testing in resource-poor settings ranks among the most common applications of microfluidic systems. The high operational autonomy in such point-of-care/point-of-use scenarios requires long-term onboard storage of liquid reagents, which also need to be safely contained during transport and handling, and then reliably released just prior to their introduction to an assay protocol. Over the recent decades, centrifugal microfluidic technologies have demonstrated the capability of integrated, automated and parallelized sample preparation and detection of bioanalytical protocols. This paper presents a novel technique for onboard storage of liquid reagents which can be issued by a rotational stimulus of the system-innate spindle motor, while still aligning with the conceptual simplicity of such “Lab-on-a-Disc” (LoaD) systems. In this work, this highly configurable reagent storage technology is captured by a digital twin, which permits complex performance analysis and algorithmic design optimization according to objectives as expressed by target metrics.
Decentralized bioanalytical testing in resource-poor settings ranges among the prime applications of microfluidic systems. The high operational autonomy in such point-of-care / point-of-use scenarios requires on-board stored liquid reagents, which need to be safely contained during long-term storage, transport and handling, and reliably released prior to activation. Over the recent decades, centrifugal microfluidic technologies have demonstrated the capability of integrated, automated and parallelized sample preparation and detection of bioanalytical protocols. This paper introduces a novel concept for onboard storage of liquid reagents which can be delivered in a well-defined manner by a rotational stimulus of the system-innate spindle motor, while still aligning with the conceptual simplicity of such “Lab-on-a-Disc” (LoaD) concepts. The reagent storage technology is captured by a digital twin which allows making complex performance analysis and algorithmic design optimization according to given objectives as expressed by target metrics.
The centrifugal "lab-on-a-disc" concept has proven to have great potential for process integration of bioanalytical assays, in particular where ease-of-use, ruggedness, portability, fast turn-around time and cost efficiency are of paramount importance. Yet, as all liquids residing on the disc are exposed to the same centrifugal field, an inherent challenge of these systems remains the automation of multi-step, multi-liquid sample processing and subsequent detection. In order to orchestrate the underlying bioanalytical protocols, an ample palette of rotationally and externally actuated valving schemes has been developed. While excelling with the level of flow control, externally actuated valves require interaction with peripheral instrumentation, thus compromising the conceptual simplicity of the centrifugal platform. In turn, for rotationally controlled schemes, such as common capillary burst valves, typical manufacturing tolerances tend to limit the number of consecutive laboratory unit operations (LUOs) that can be automated on a single disc. In this paper, a major advancement on recently established dissolvable film (DF) valving is presented; for the very first time, a liquid handling sequence can be controlled in response to completion of preceding liquid transfer event, i.e. completely independent of external stimulus or changes in speed of disc rotation. The basic, event-triggered valve configuration is further adapted to leverage conditional, large-scale process integration. First, we demonstrate a fluidic network on a disc encompassing 10 discrete valving steps including logical relationships such as an AND-conditional as well as serial and parallel flow control. Then we present a disc which is capable of implementing common laboratory unit operations such as metering and selective routing of flows. Finally, as a pilot study, these functions are integrated on a single disc to automate a common, multi-step lab protocol for the extraction of total RNA from mammalian cell homogenate.
In this article we introduce a novel technology that utilizes specialized water dissolvable thin films for valving in centrifugal microfluidic systems. In previous work (William Meathrel and Cathy Moritz, IVD Technologies, 2007), dissolvable films (DFs) have been assembled in laminar flow devices to form efficient sacrificial valves where DFs simply open by direct contact with liquid. Here, we build on the original DF valving scheme to leverage sophisticated, merely rotationally actuated vapour barriers and flow control for enabling comprehensive assay integration with low-complexity instrumentation on "lab-on-a-disc" platforms. The advanced sacrificial valving function is achieved by creating an inverted gas-liquid stack upstream of the DF during priming of the system. At low rotational speeds, a pocket of trapped air prevents a surface-tension stabilized liquid plug from wetting the DF membrane. However, high-speed rotation disrupts the metastable gas/liquid interface to wet the DF and thus opens the valve. By judicious choice of the radial position and geometry of the valve, the burst frequency can be tuned over a wide range of rotational speeds nearly 10 times greater than those attained by common capillary burst valves based on hydrophobic constrictions. The broad range of reproducible burst frequencies of the DF valves bears the potential for full integration and automation of comprehensive, multi-step biochemical assay protocols. In this report we demonstrate DF valving, discuss the biocompatibility of using the films, and show a potential sequential valving system including the on-demand release of on-board stored liquid reagents, fast centrifugal sedimentation and vigorous mixing; thus providing a viable basis for use in lab-on-a-disc platforms for point-of-care diagnostics and other life science applications.