Fast prototyping microfluidics: Integrating droplet digital lamp for absolute quantification of cancer biomarkers

UID/CTM/50025/2019 UID/Multi/04378/2019 Inn-INDIGO/0002/2015 PTDC/BTM-SAL/31201/2017 SFRH/BPD/124311/2016Microfluidic (MF) advancements have been leveraged toward the development of state-of-the-art platforms for molecular diagnostics, where isothermal amplification schemes allow for further simplification of DNA detection and quantification protocols. The MF integration with loop-mediated isothermal amplification (LAMP) is today the focus of a new generation of chip-based devices for molecular detection, aiming at fast and automated nucleic acid analysis. Here, we combined MF with droplet digital LAMP (ddLAMP) on an all-in-one device that allows for droplet generation, target amplification, and absolute quantification. This multilayer 3D chip was developed in less than 30 minutes by using a low-cost and extremely adaptable production process that exploits direct laser writing technology in “Shrinky-dinks” polystyrene sheets. ddLAMP and target quantification were performed directly on-chip, showing a high correlation between target concentration and positive droplet score. We validated this integrated chip via the amplification of targets ranging from five to 500,000 copies/reaction. Furthermore, on-chip amplification was performed in a 10 µL volume, attaining a limit of detection of five copies/µL under 60 min. This technology was applied to quantify a cancer biomarker, c-MYC, but it can be further extended to any other disease biomarker.publishersversionpublishe

Impact of variance components on reliability of absolute quantification using digital PCR

Background: Digital polymerase chain reaction (dPCR) is an increasingly popular technology for detecting and quantifying target nucleic acids. Its advertised strength is high precision absolute quantification without needing reference curves. The standard data analytic approach follows a seemingly straightforward theoretical framework but ignores sources of variation in the data generating process. These stem from both technical and biological factors, where we distinguish features that are 1) hard-wired in the equipment, 2) user-dependent and 3) provided by manufacturers but may be adapted by the user. The impact of the corresponding variance components on the accuracy and precision of target concentration estimators presented in the literature is studied through simulation. Results: We reveal how system-specific technical factors influence accuracy as well as precision of concentration estimates. We find that a well-chosen sample dilution level and modifiable settings such as the fluorescence cut-off for target copy detection have a substantial impact on reliability and can be adapted to the sample analysed in ways that matter. User-dependent technical variation, including pipette inaccuracy and specific sources of sample heterogeneity, leads to a steep increase in uncertainty of estimated concentrations. Users can discover this through replicate experiments and derived variance estimation. Finally, the detection performance can be improved by optimizing the fluorescence intensity cut point as suboptimal thresholds reduce the accuracy of concentration estimates considerably. Conclusions: Like any other technology, dPCR is subject to variation induced by natural perturbations, systematic settings as well as user-dependent protocols. Corresponding uncertainty may be controlled with an adapted experimental design. Our findings point to modifiable key sources of uncertainty that form an important starting point for the development of guidelines on dPCR design and data analysis with correct precision bounds. Besides clever choices of sample dilution levels, experiment-specific tuning of machine settings can greatly improve results. Well-chosen data-driven fluorescence intensity thresholds in particular result in major improvements in target presence detection. We call on manufacturers to provide sufficiently detailed output data that allows users to maximize the potential of the method in their setting and obtain high precision and accuracy for their experiments

A novel approach for chip-based digital LAMP towards the quantification of prostate cancer biomarkers

Nucleic acids amplification-based methods can profit from the features offered by Lab-on-a-chip technologies, in particular those that aimed for molecular diagnosis purposes. Currently, isothermal amplification approaches, more precisely LAMP, have become promising alternatives to the current gold standard technology (PCR). Regardless the amplification mechanism, accurate target quantification is still challenging. To this end, the development of digital amplification methods has helped to circumvent this limitation. This thesis focused on the development of a chip-based digital LAMP system towards the quantification of prostate cancer biomarkers. For this, LAMP was integrated with droplet-based digital amplification concept. LAMP positive amplification was achieved after 60 minutes, leading to a 2-fold increase in fluorescence when compared to the negative amplification controls, in a vortex-based droplet generation approach. However, aspects inherent to this method prevented a quantitative assessment of LAMP amplification. In order to overcome these limitations, a novel microfluidics chip-based device was developed and implemented towards dLAMP quantification of c-Myc gene. The T-junction type droplet generator chip achieved droplets of 1.5 nL with a coefficient of variation bellow 3%, in line with the standard for this technique. This system showed a sharp response to template concentration, observable by the raise in the fraction of positive droplets. Additionally, the target quantification proven to be precise (R2 =0.99) for 4 orders of magnitude of copies/µL (5 copies/µL - 5x105 copies/µL) after Poisson’s modulation. Aiming for the implementation of this chip-based dLAMP system into the detections of prostate cancer-associated biomarkers, amplification reactions of SChLAP1 and PCA3 genes were developed and further optimized for real-time fluorescence monitoring. As a result, it was possible to develop a quantitative method for cDNA amplification, that presented higher amplification efficiencies and a reduction on the overall reaction time, when compared to the gold standard RT-PCR. Furthermore, the proposed strategy is compatible with the integration into the chip-based microfluidics device, hence easily extended to the monitorization of gene expression levels

Droplet Microfluidics

Droplet microfluidics has dramatically developed in the past decade and has been established as a microfluidic technology that can translate into commercial products. Its rapid development and adoption have relied not only on an efficient stabilizing system (oil and surfactant), but also on a library of modules that can manipulate droplets at a high-throughput. Droplet microfluidics is a vibrant field that keeps evolving, with advances that span technology development and applications. Recent examples include innovative methods to generate droplets, to perform single-cell encapsulation, magnetic extraction, or sorting at an even higher throughput. The trend consists of improving parameters such as robustness, throughput, or ease of use. These developments rely on a firm understanding of the physics and chemistry involved in hydrodynamic flow at a small scale. Finally, droplet microfluidics has played a pivotal role in biological applications, such as single-cell genomics or high-throughput microbial screening, and chemical applications. This Special Issue will showcase all aspects of the exciting field of droplet microfluidics, including, but not limited to, technology development, applications, and open-source systems

Development of microsystems for point-of-use microorganism detection

2018 Summer.Includes bibliographical references.To view the abstract, please see the full text of the document

Advances in Microfluidics Technology for Diagnostics and Detection

Microfluidics and lab-on-a-chip have, in recent years, come to the forefront in diagnostics and detection. At point-of-care, in the emergency room, and at the hospital bed or GP clinic, lab-on-a-chip offers the potential to rapidly detect time-critical and life-threatening diseases such as sepsis and bacterial meningitis. Furthermore, portable and user-friendly diagnostic platforms can enable disease diagnostics and detection in resource-poor settings where centralised laboratory facilities may not be available. At point-of-use, microfluidics and lab-on-chip can be applied in the field to rapidly identify plant pathogens, thus reducing the need for damaging broad spectrum pesticides while also reducing food losses. Microfluidics can also be applied to the continuous monitoring of water quality and can support policy-makers and protection agencies in protecting the environment. Perhaps most excitingly, microfluidics also offers the potential to enable entirely new diagnostic tests that cannot be implemented using conventional laboratory tools. Examples of microfluidics at the frontier of new medical diagnostic tests include early detection of cancers through circulating tumour cells (CTCs) and highly sensitive genetic tests using droplet-based digital PCR.This Special Issue on “Advances in Microfluidics Technology for Diagnostics and Detection” aims to gather outstanding research and to carry out comprehensive coverage of all aspects related to microfluidics in diagnostics and detection

Challenges in microfluidic and point-of-care phenotypic antimicrobial resistance tests

To combat the threat to public health of antimicrobial resistance, there is a need for faster, more portable diagnostic tools to aid in antibiotic selection. Current methods for determining antimicrobial resistance of pathogens in clinical samples take days to result and require high levels of user input. Microfluidics offers many potential benefits, reducing time to result, user input, and allowing point of care testing. This review focuses on the challenges of developing functional or phenotypic microfluidic antimicrobial susceptibility tests; such methods complement other vital tools such as nucleic acid detection. Some of the most important challenges identified here are not unique to microfluidics but apply to most antimicrobial susceptibility testing innovations and relate to the nature of the sample being tested. For many high priority samples, mixtures of bacteria, highly variable target cell density, and the sample matrix can all affect measurements, and miniaturization can create sensitivity problems if target bacteria are dilute. Recent advances including smartphone capability, new sensors, microscopy, and a resurgence in paper microfluidics offer important opportunities for microfluidic engineering to simplify functional and phenotypic antimicrobial susceptibility testing. But the complexity of most clinical samples remains one of the biggest barriers to rapid uptake of microfluidics for antimicrobial resistance testing