Measurement of substrate thermal resistance using DNA denaturation temperature

Heat Transfer and Thermal Management have become important aspects of the developing field of uTAS systems particularly in the application of the the uTAS philosophy to thermally driven analysis techniques such as PCR. Due to the development of flowing PCR thermocyclers in the field of uTAS, the authors have previously developed a melting curve analysis technique that is compatible with these flowing PCR thermocyclers. In this approach a linear temperature gradient is induced along a sample carrying microchannel. Any flow passing through the microchannel is subject to linear heating. Fluorescent monitoring of DNA in the flow results in the generation of DNA melting curve plots. This works presents an experimental technique where DNA melting curve analysis is used to measure the thermal resistance of microchannel substrates. DNA in solution is tested at a number of different ramp rates and the di®erent apparent denaturation temperatures measured are used to infer the thermal resistance of the microchannel substrates. The apparent variation in denaturation temperature is found to be linearly proportional to flow ramp rate. Providing knowledge of the microchannel diameter and a non-varying cross-section in the direction of heat flux the thermal resistance measurement technique is independent of knowledge of substrate dimensions, contact surface quality and substrate composition/material properties. In this approach to microchannel DNA melting curve analysis the difference between the measured and actual denaturation temperatures is proportional to the substrate thermal resistance and the ramp-rate seen by the sample. Therefore quantitative knowledge of the substrate thermal resistance is required when using this technique to measure accurately DNA denaturation temperatur

Concentration of white blood cells from whole blood by dual centrifugo-pneumatic siphoning with density gradient medium

Due to the pervasiveness of HIV infections in developing countries there exists a need for a low-cost, user-friendly point-of-care device which can be used to monitor the concentration of T-lymphocytes in the patient’s blood expressing the CD4+ epitope. As a first step towards developing a microfluidic “lab-on-a-disc” platform with this aim we present the concentration of white blood cells from whole blood using a density medium in conjunction with centrifugo-pneumatic siphon valves [1]. Two such valves are actuated simultaneously, removing the bulk of plasma through the upper valve and the bulk of WBCs through the lower valve while leaving the vast majority of red blood cells in the centrifugal chamber

Lumped-Element Modeling for Rapid Design and Simulation of Digital Centrifugal Microfluidic Systems

Since the 1990s, centrifugal microfluidic platforms have evolved into a mature technology for the automation of bioanalytical assays in decentralized settings. These “Lab-on-a-Disc” (LoaD) systems have already implemented a range of laboratory unit operations (LUOs) such as sample loading, liquid transport, metering, aliquoting, routing, mixing, and washing. By assembling these LUOs in highly functional microfluidic networks, including sample preparation and detection, a sizable portfolio of common test formats such as general chemistry, immunoassays/ protein analysis, nucleic acid testing, and cell counting has been established. The availability of these bioanalytical assay types enables a broad range of applications in fields such as life-science research, biomedical point-of-care testing and veterinary diagnostics, as well as agrifood, environmental, infrastructural, and industrial monitoring

Auto-actuated sequential relelase valves for lab-on-a-disc systems

In microfluidic biomedical systems valving is often of critical importance for process control. In centrifugal microfluidics valves are typically actuated through changing the centrifugal force seen by the working liquid. Here we present for the first time a new valving structure (based on dissolvable films) where the entry of liquid into a chamber on the disc can trigger the release of liquid from a chamber located elsewhere on the disc. These valves can be configured such that multiple valves can be released in a sequential manner independent of external inputs

Social behaviour of Jackass penguins at sea

This paper reports flocking, communal feeding and other aspects of sea-based social behaviour in the jackass penguin (Spheniscus demersus). Penguins tend to occur within about 15 km of the mainland, but range farther afield from the islands used for breeding and/or roosting. Relatively large groups of 50 and more birds occur more than 50 km from the nearest island, but seldom more than 15 km from the mainland. The majority of the sea-going population consists of birds occurring in groups. Mean group size is eight birds. In any one particular group the members all tend to perform the same behaviour at the same time. The tendency to form foraging groups and the highly synchronized diving and cohesion of these groups indicate that this behaviour is socially facilitated, suggesting that it is adaptive in terms of both enhanced prey location and capture. Feeding penguins do not submerge for long and do not dive deeply. Birds in diving groups perform head-dipping movements which might signal readiness to dive and thus promote synchronous activity. The paper points out how little is known about jackass penguins at sea - the environment in which they probably spend the majority of their time. Lack of information on the birds at sea precludes proper interpretation of many land-based events attending the biology of the bird and its conservation

A 3d-printed optical reader for cost-efficient enumeration of cd4 cells for point-of-care diagnostics of hiv in resource-poor settings

Here we present a low cost, 3D printed optical reader which is compatible with a disposable, finger actuated chip which can be used for rapid CD4+ enumeration. This portable and widely autonomous device provides the next step in a workflow which can meet the WHO ASSURED requirements for assessment of HIV status in resource-poor settings. The reader is composed of 3D printed parts where the microfluidic chip can be moved along the optical axis of the objective lens for focusing using a screw adapted from a masonry bolt. Performance of the reader shows good agreement with measurements made using a conventional inverted microscope

Disc-embedded grinding mill towards process integtrated hydro-mechanical cell lysis on centrifugal microfluidic platforms

For the first time we utilize the spindle motor intrinsic to centrifugal microfluidic systems to drive a grinding mill for cell lysis in a stator-rotor concept. This mechanical concept particularly enables the lysis of armored cells and, as a further benefit, avoids the addition of chemicals that potentially inhibit subsequent reactions. As a proof of concept we demonstrate the lysis of the silica-shelled algae Phaeodactylum Tricornutum

CD4 cell isolation from blood using finger-actuated on-chip magnetophoresis for rapid HIV/AIDS diagnostics

With timely diagnosis and correct treatment, people living with HIV/AIDS can consider the disease as a chronic rather than a terminal illness. Still, in regions were HIV is endemic, rapid diagnosis is a challenge due to the complexity of the instrumentation required, the poor infrastructure in these countries, as well as the technical expertise required to carry out the diagnosis. This paper presents a microfluidic chip based approach allowing semi-quantitative CD4+ cell coun¬ting on a cheap, rapid, highly portable and instrumentation-free Point-of-Care HIV diagnostic device. Flow is driven by finger-pressing a flexible reservoir, and the target cells are immobilized through magnetophoresis. The fluidic test completes within ca. 30 seconds of sample application to the chip

Reciprocating, buoyancy-driven radial pumping on centrifugal microfluidic platforms

Centrifugal microfluidic systems bear great potential for applications where ruggedness, portability, ease-of-use, and cost efficiency are critical. However, due to the unidirectional nature of the centrifugal pumping force, the number of sequential process steps which can be integrated on these “Lab-on-a-Disc” (LoaD) devices is limited by their finite radial extension. To significantly widen this bottleneck and thus expand the scope of applications that can be ported on these LoaD platforms, various groups have developed a range of centripetal pumping mechanisms. Here, we present two advancements over our previous efforts in this area by combining buoyancy-based pumping with dissolvable film (DF) valves. First, we present a buoyancy-driven, reciprocating flow of a dense liquid initially located an upper reservoir and a sample in a peripheral reservoir. Secondly, we combine buoyancy-driven centripetal pumping with sample discretization and metering to fully integrate and automate a liquid handling protocol towards implementing a multi-parameter bioassay on a disc

On-site methods within DECATHLON – towards point-of-use molecular analysis and next generation sequencing

There is an increasing need for on-site applications of DNA-based methods, both, for inspection services by public authorities, as well as for companies that wish to monitor their supply chain. The capability to apply DNA-based methods in the field, or at ‘point-of-use’, is critical where centralised laboratories are inadequate to meet the demand of prompt answers for early intervention. The application fields addressed by DECATHLON are food analysis with specific emphasis on pathogen detection for food safety, GMO identification and customs issues. In recent years much progress has been made in the development of different types of on-site devices that can accommodate DNA-based methods. Within the DECATHLON project, two primary approaches for on-site use of DNA-based methods are developed in parallel; sample preparation and nucleic acid identification using a centrifugal microfluidic platform, and development of a novel graphene nano-gap sensor for next generation sequencing