Special Issue "Recent Developments in Microfluidics"

A special issue of Biosensors (ISSN 2079-6374). This special issue belongs to the section "Biosensor and Bioelectronic Devices".

Deadline for manuscript submissions: 31 October 2021.

Special Issue Editor

Dr. Yunus Alapan
E-Mail Website
Guest Editor
Physical Intelligence Department, Max Planck Institute for Intelligent Systems, 70569 Stuttgart, Germany
Interests: microrobotic sensors; single-cell sensing; Bio-MEMS; microfluidics; lab-on-a-chip; organ-on-a-chip; point-of-care biosensors; disease diagnostics; global health

Special Issue Information

Dear Colleagues,

The advent of microfluidics has revolutionized many fields within life sciences by enabling the rapid isolation and detection of molecules and proteins, extracellular vesicles, bacteria, and cells in complex biological fluids with major applications in medical diagnostics, patient monitoring, drug screening, and food safety. Microfluidic technologies are rapidly evolving with new fabrication techniques, channel architecture, and materials (flexible elastomers, paper, 2D materials), along with developments in sensing modalities (optical, electrical, and magnetic) and integrated molecular biology techniques (CRISPR-based approaches). These developments enable faster and higher detection sensitivity in complex environments and challenging applications ranging from unamplified nucleic acid and extracellular vesicle detection to real-time monitoring of physiological signals from wearables. On the other hand, cost-effective, disposable, and simple-use microfluidic technologies are at the frontlines of point-of-care diagnostics and screening of infectious diseases and genetic disorders, especially in low-resource settings; the importance and urgency of which has become evident once more during the recent COVID-19 pandemic.

In this Special Issue, we are pleased to invite contributions on “Recent Developments in Microfluidics” dedicated to covering the most recent innovations in next-generation microfluidic technologies. Research articles and comprehensive review articles reporting on the latest developments in new fabrication techniques and materials, novel sensing approaches, and applications in molecular and cellular diagnostics and wearable physiological monitoring technologies are of great interest.

Dr. Yunus Alapan
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Biosensors is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • microfluidic biosensors
  • lab-on-a-chip
  • paper-based microfluidics
  • wearable microfluidics
  • Microfluidic assays
  • molecular diagnostics
  • cellular diagnostics
  • point-of-care diagnostics
  • physiological monitoring
  • global health

Published Papers (5 papers)

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Research

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Communication
3D-PAD: Paper-Based Analytical Devices with Integrated Three-Dimensional Features
Biosensors 2021, 11(3), 84; https://0-doi-org.brum.beds.ac.uk/10.3390/bios11030084 - 17 Mar 2021
Cited by 2 | Viewed by 880
Abstract
This paper describes the use of fused deposition modeling (FDM) printing to fabricate paper-based analytical devices (PAD) with three-dimensional (3D) features, which is termed as 3D-PAD. Material depositions followed by heat reflow is a standard approach for the fabrication of PAD. Such devices [...] Read more.
This paper describes the use of fused deposition modeling (FDM) printing to fabricate paper-based analytical devices (PAD) with three-dimensional (3D) features, which is termed as 3D-PAD. Material depositions followed by heat reflow is a standard approach for the fabrication of PAD. Such devices are primarily two-dimensional (2D) and can hold only a limited amount of liquid samples in the device. This constraint can pose problems when the sample consists of organic solvents that have low interfacial energies with the hydrophobic barriers. To overcome this limitation, we developed a method to fabricate PAD integrated with 3D features (vertical walls as an example) by FDM 3D printing. 3D-PADs were fabricated using two types of thermoplastics. One thermoplastic had a low melting point that formed hydrophobic barriers upon penetration, and another thermoplastic had a high melting point that maintained 3D features on the filter paper without reflowing. We used polycaprolactone (PCL) for the former, and polylactic acid (PLA) for the latter. Both PCL and PLA were printed with FDM without gaps at the interface, and the resulting paper-based devices possessed hydrophobic barriers consisting of PCL seamlessly integrated with vertical features consisting of PLA. We validated the capability of 3D-PAD to hold 30 μL of solvents (ethanol, isopropyl alcohol, and acetone), all of which would not be retained on conventional PADs fabricated with solid wax printers. To highlight the importance of containing an increased amount of liquid samples, a colorimetric assay for the formation of dimethylglyoxime (DMG)-Ni (II) was demonstrated using two volumes (10 μL and 30 μL) of solvent-based dimethylglyoxime (DMG). FDM printing of 3D-PAD enabled the facile construction of 3D structures integrated with PAD, which would find applications in paper-based chemical and biological assays requiring organic solvents. Full article
(This article belongs to the Special Issue Recent Developments in Microfluidics)
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Article
Determination of the Empirical Electrokinetic Equilibrium Condition of Microorganisms in Microfluidic Devices
Biosensors 2020, 10(10), 148; https://0-doi-org.brum.beds.ac.uk/10.3390/bios10100148 - 19 Oct 2020
Cited by 7 | Viewed by 966
Abstract
The increased concern regarding emerging pathogens and antibiotic resistance has drawn interest in the development of rapid and robust microfluidic techniques to analyze microorganisms. The novel parameter known as the electrokinetic equilibrium condition (EEEC) was presented in recent [...] Read more.
The increased concern regarding emerging pathogens and antibiotic resistance has drawn interest in the development of rapid and robust microfluidic techniques to analyze microorganisms. The novel parameter known as the electrokinetic equilibrium condition (EEEC) was presented in recent studies, providing an approach to analyze microparticles in microchannels employing unique electrokinetic (EK) signatures. While the EEEC shows great promise, current estimation approaches can be time-consuming or heavily user-dependent for accurate values. The present contribution aims to analyze existing approaches for estimating this parameter and modify the process into an accurate yet simple technique for estimating the EK behavior of microorganisms in insulator-based microfluidic devices. The technique presented here yields the parameter called the empirical electrokinetic equilibrium condition (eEEEC) which works well as a value for initial approximations of trapping conditions in insulator-based EK (iEK) microfluidic systems. A total of six types of microorganisms were analyzed in this study (three bacteria and three bacteriophages). The proposed approach estimated eEEEC values employing images of trapped microorganisms, yielding high reproducibility (SD 5.0–8.8%). Furthermore, stable trapping voltages (sTVs) were estimated from eEEEC values for distinct channel designs to test that this parameter is system-independent and good agreement was obtained when comparing estimated sTVs vs. experimental values (SD 0.3–19.6%). The encouraging results from this work were used to generate an EK library of data, available on our laboratory website. The data in this library can be used to design tailored iEK microfluidic devices for the analysis of microorganisms. Full article
(This article belongs to the Special Issue Recent Developments in Microfluidics)
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Article
Combining Electrostatic, Hindrance and Diffusive Effects for Predicting Particle Transport and Separation Efficiency in Deterministic Lateral Displacement Microfluidic Devices
Biosensors 2020, 10(9), 126; https://0-doi-org.brum.beds.ac.uk/10.3390/bios10090126 - 16 Sep 2020
Cited by 2 | Viewed by 1049
Abstract
Microfluidic separators based on Deterministic Lateral Displacement (DLD) constitute a promising technique for the label-free detection and separation of mesoscopic objects of biological interest, ranging from cells to exosomes. Owing to the simultaneous presence of different forces contributing to particle motion, a feasible [...] Read more.
Microfluidic separators based on Deterministic Lateral Displacement (DLD) constitute a promising technique for the label-free detection and separation of mesoscopic objects of biological interest, ranging from cells to exosomes. Owing to the simultaneous presence of different forces contributing to particle motion, a feasible theoretical approach for interpreting and anticipating the performance of DLD devices is yet to be developed. By combining the results of a recent study on electrostatic effects in DLD devices with an advection–diffusion model previously developed by our group, we here propose a fully predictive approach (i.e., ideally devoid of adjustable parameters) that includes the main physically relevant effects governing particle transport on the one hand, and that is amenable to numerical treatment at affordable computational expenses on the other. The approach proposed, based on ensemble statistics of stochastic particle trajectories, is validated by comparing/contrasting model predictions to available experimental data encompassing different particle dimensions. The comparison suggests that at low/moderate values of the flowrate the approach can yield an accurate prediction of the separation performance, thus making it a promising tool for designing device geometries and operating conditions in nanoscale applications of the DLD technique. Full article
(This article belongs to the Special Issue Recent Developments in Microfluidics)
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Review

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Review
PDMS Bonding Technologies for Microfluidic Applications: A Review
Biosensors 2021, 11(8), 292; https://0-doi-org.brum.beds.ac.uk/10.3390/bios11080292 - 23 Aug 2021
Viewed by 841
Abstract
This review summarizes and compares the available surface treatment and bonding techniques (e.g., corona triggered surface activation, oxygen plasma surface activation, chemical gluing, and mixed techniques) and quality/bond-strength testing methods (e.g., pulling test, shear test, peel test, leakage test) for bonding PDMS (polydimethylsiloxane) [...] Read more.
This review summarizes and compares the available surface treatment and bonding techniques (e.g., corona triggered surface activation, oxygen plasma surface activation, chemical gluing, and mixed techniques) and quality/bond-strength testing methods (e.g., pulling test, shear test, peel test, leakage test) for bonding PDMS (polydimethylsiloxane) with other materials, such as PDMS, glass, silicon, PET (polyethylene terephthalate), PI (polyimide), PMMA (poly(methyl methacrylate)), PVC (polyvinyl chloride), PC (polycarbonate), COC (cyclic olefin copolymer), PS (polystyrene) and PEN (polyethylene naphthalate). The optimized process parameters for the best achievable bond strengths are collected for each substrate, and the advantages and disadvantages of each method are discussed in detail. Full article
(This article belongs to the Special Issue Recent Developments in Microfluidics)
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Review
Surface Modification Techniques for Endothelial Cell Seeding in PDMS Microfluidic Devices
Biosensors 2020, 10(11), 182; https://0-doi-org.brum.beds.ac.uk/10.3390/bios10110182 - 19 Nov 2020
Cited by 10 | Viewed by 1970
Abstract
Microfluidic lab-on-a-chip cell culture techniques have been gaining popularity by offering the possibility of reducing the amount of samples and reagents and greater control over cellular microenvironment. Polydimethylsiloxane (PDMS) is the commonly used polymer for microfluidic cell culture devices because of the cheap [...] Read more.
Microfluidic lab-on-a-chip cell culture techniques have been gaining popularity by offering the possibility of reducing the amount of samples and reagents and greater control over cellular microenvironment. Polydimethylsiloxane (PDMS) is the commonly used polymer for microfluidic cell culture devices because of the cheap and easy fabrication techniques, non-toxicity, biocompatibility, high gas permeability, and optical transparency. However, the intrinsic hydrophobic nature of PDMS makes cell seeding challenging when applied on PDMS surface. The hydrophobicity of the PDMS surface also allows the non-specific absorption/adsorption of small molecules and biomolecules that might affect the cellular behaviour and functions. Hydrophilic modification of PDMS surface is indispensable for successful cell seeding. This review collates different techniques with their advantages and disadvantages that have been used to improve PDMS hydrophilicity to facilitate endothelial cells seeding in PDMS devices. Full article
(This article belongs to the Special Issue Recent Developments in Microfluidics)
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