Microfluidic System for Rapid Detection of Airborne Pathogenic Fungal Spores

Continuous Sampling of Aerosolized Particles Using Stratified Two-Phase Microfluidics

Health and security concerns have made it essential to develop integrated, continuous collection and sensing platforms that are compact and capable of real-time detection. In this study, we numerically investigate the flow physics associated with the single-step collection and enrichment of aerosolized polystyrene microparticles into a flowing liquid using a stratified air-water flow in a U-shaped microchannel. We validate our simulation results by comparing them to experimental data from the literature. Additionally, we fabricate an identical microfluidic device using PDMS-based soft lithography and test it to corroborate the previously published experimental data. Diversion and entrapment efficiencies are used as evaluation metrics, both of which increase with increasing particle diameter and superficial air inlet velocity. Overall, our ANSYS Fluent two-dimensional (2D) and three-dimensional (3D) multiphase flow simulations exhibit a good agreement with our experimental data and data in the literature (average deviation of ∼11%) in terms of diversion efficiency. Simulations also found the entrapment efficiency to be lower than the diversion efficiency, indicating discrepancies in the literature in terms of captured particles. The effect of the Dean force on the flow physics was also investigated using 3D simulations. We found that the effect of the Dean flow was more dominant relative to the centrifugal force on the smaller particles (e.g., 0.65 μm) compared to the larger particles (e.g., 2.1 μm). Increasing the superficial air inlet velocity also increases the effect of the centrifugal forces relative to the Dean forces. Overall, this experimentally validated multiphase model decouples and investigates the multiple and simultaneous forces on aerosolized particles flowing through a curved microchannel, which is crucial for designing more efficient capture devices. Once integrated with a microfluidic-based biosensor, this stratified flow-based microfluidic biothreat capture platform should deliver continuous sensor-ready enriched biosamples for real-time sensing.

Research advances in microfluidic collection and detection of virus, bacterial, and fungal bioaerosols

Bioaerosols are airborne suspensions of fine solid or liquid particles containing biological substances such as viruses, bacteria, cellular debris, fungal spores, mycelium, and byproducts of microbial metabolism. The global Coronavirus disease 2019 (COVID-19) pandemic and the previous emergence of severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), and influenza have increased the need for reliable and effective monitoring tools for bioaerosols. Bioaerosol collection and detection have aroused considerable attention. Current bioaerosol sampling and detection techniques suffer from long response time, low sensitivity, and high costs, and these drawbacks have forced the development of novel monitoring strategies. Microfluidic technique is considered a breakthrough for high performance analysis of bioaerosols. In recent years, several emerging methods based on microfluidics have been developed and reported for collection and detection of bioaerosols. The unique advantages of microfluidic technique have enabled the integration of bioaerosol collection and detection, which has a higher efficiency over conventional methods. This review focused on the research progress of bioaerosol collection and detection methods based on microfluidic techniques, with special attention on virus aerosols and bacterial aerosols. Different from the existing reviews, this work took a unique perspective of the targets to be collected and detected in bioaerosols, which would provide a direct index of bioaerosol categories readers may be interested in. We also discussed integrated microfluidic monitoring system for bioaerosols. Additionally, the application of bioaerosol detection in biomedicine was presented. Finally, the current challenges in the field of bioaerosol monitoring are presented and an outlook given of future developments.

Core-Shell Droplet-Based Microfluidic Screening System for Filamentous Fungi

Filamentous fungi are competitive hosts for the production of drugs, proteins, and chemicals. However, their utility is limited by screening methods and low throughput. In this work, a universal high-throughput system for optimizing protein production in filamentous fungi was described. Droplet microfluidics was used to encapsulate large mutant strain pools in biocompatible core-shell microdroplets designed to avoid mycelial punctures and thus sustain prolonged culture. The self-assembled split GFP was then used to characterize the secretory capacity of the strains and isolate strains with superior production titers according to the fluorescence signals. The platform was applied to optimize the α-amylase secretion of Aspergillus niger, resulting in the isolation of a strain with 2.02-fold higher secretion capacity. The system allows the analysis of >105 single cells per h and will facilitate ultrahigh-throughput screening experiments of filamentous fungi. This method could help identify improved hosts for the large-scale production of biotechnology-relevant proteins. This is a broadly applicable system that can be equally used in other hosts.

On-site bioaerosol sampling and detection in microfluidic platforms

As the recent coronavirus disease (COVID-19) pandemic and several severe illnesses such as Middle East respiratory syndrome coronavirus (MERS-CoV), Influenza A virus (IAV) flu, and severe acute respiratory syndrome (SARS) have been found to be airborne, the importance of monitoring bioaerosols for the control and prevention of airborne epidemic diseases outbreaks is increasing. However, current aerosol collection and detection technologies may be limited to on-field use for real-time monitoring because of the relatively low concentrations of targeted bioaerosols in air samples. Microfluidic devices have been used as lab-on-a-chip platforms and exhibit outstanding capabilities in airborne particulate collection, sample processing, and target molecule analysis, thereby highlighting their potential for on-site bioaerosol monitoring. This review discusses the measurement of airborne microorganisms from air samples, including sources and transmission of bioaerosols, sampling strategies, and analytical methodologies. Recent advancements in microfluidic platforms have focused on bioaerosol sample preparation strategies, such as sorting, concentrating, and extracting, as well as rapid and field-deployable detection methods for analytes on microfluidic chips. Furthermore, we discuss an integrated platform for on-site bioaerosol analyses. We believe that our review significantly contributes to the literature as it assists in bridging the knowledge gaps in bioaerosol monitoring using microfluidic platforms.

Detection of airborne pathogens with single photon counting and a real-time spectrometer on microfluidics

The common practice for monitoring pathogenic bioaerosols is to collect bioaerosols from air and then detect them, which lacks timeliness and accuracy. In order to improve the detection speed, here we demonstrate an innovative airflow-based optical detection method for directly identifying aerosol pathogens, and built a microfluidic-based counter composite spectrometer detection platform, which simplifies sample preparation and collection detection from two steps to one step. The method is based on principal component analysis and partial least squares discriminant analysis for particle species identification and dynamic transmission spectroscopy analysis, and single-photon measurement is used for particle counting. Compared with traditional microscopic counting and identification methods, the particle counting accuracy is high, the standard deviation is small, and the counting accuracy exceeds 92.2%. The setup of dynamic transmission spectroscopy analysis provides high-precision real-time particle identification with an accuracy rate of 93.75%. As the system is further refined, we also foresee potential applications of this method in agricultural disease control, environmental control, and infectious disease control in aerosol pathogen detection.

Application of Microfluidic Chips in the Detection of Airborne Microorganisms

The spread of microorganisms in the air, especially pathogenic microorganisms, seriously affects people's normal life. Therefore, the analysis and detection of airborne microorganisms is of great importance in environmental detection, disease prevention and biosafety. As an emerging technology with the advantages of integration, miniaturization and high efficiency, microfluidic chips are widely used in the detection of microorganisms in the environment, bringing development vitality to the detection of airborne microorganisms, and they have become a research highlight in the prevention and control of infectious diseases. Microfluidic chips can be used for the detection and analysis of bacteria, viruses and fungi in the air, mainly for the detection of Escherichia coli, Staphylococcus aureus, H1N1 virus, SARS-CoV-2 virus, Aspergillus niger, etc. The high sensitivity has great potential in practical detection. Here, we summarize the advances in the collection and detection of airborne microorganisms by microfluidic chips. The challenges and trends for the detection of airborne microorganisms by microfluidic chips was also discussed. These will support the role of microfluidic chips in the prevention and control of air pollution and major outbreaks.

Challenges and Perspectives for Biosensing of Bioaerosol Containing Pathogenic Microorganisms

As an important route for disease transmission, bioaerosols have received increasing attention. In the past decades, many efforts were made to facilitate the development of bioaerosol monitoring; however, there are still some important challenges in bioaerosol collection and detection. Thus, recent advances in bioaerosol collection (such as sedimentation, filtration, centrifugation, impaction, impingement, and microfluidics) and detection methods (such as culture, molecular biological assay, and immunological assay) were summarized in this review. Besides, the important challenges and perspectives for bioaerosol biosensing were also discussed.

Recent Advances on Bioaerosol Collection and Detection in Microfluidic Chips

Bioaerosols containing pathogenic microorganisms have posed a great threat to human and animal health. Effective monitoring of bioaerosols containing pathogenic viruses and bacteria is of great significance to prevent and control infectious diseases. This Feature summarizes recent advances on bioaerosol collection and detection based on microfluidic chips. Besides, the challenges and trends for bioaerosol collection and detection were also discussed.

Selection and characterization of toxic Aspergillus spore-specific DNA aptamer using spore-SELEX

As airborne spores of toxic Aspergillus species cause mild symptoms to invasive fungal infections, their indoor concentration should be controlled through real-time management. Aptamer-based biosensors could provide economical and simple solutions for point-of-care. In this study, we isolated aptamers binding to the spores of three representative toxic Aspergillus species (A. fumigatus, A. flavus, and A. niger) for the first time, using cell-SELEX (systematic evolution of ligands through exponential enrichment). Among the aptamer candidates, Asp-3 showed a broad and high binding affinity for the Aspergillus spores. Considering the low binding affinity with proteinase-treated spores, we speculated that the Asp-3 binding sites could be possibly associated with cell surface proteins. The high Asp-3 specificity was confirmed by comparing the binding affinity between the Aspergillus target species and other common indoor fungal species. Moreover, we also established quantitative linear relationships between Asp-3 and the spore concentration of each Aspergillus species. Therefore, the selected Asp-3 aptamer, conjugated with detection sensors, could be an effective biorecognition element for the spores of three toxic Aspergillus species.

Dynamic Surface Proteomes of Allergenic Fungal Conidia

Fungal spores and hyphal fragments play an important role as allergens in respiratory diseases. In this study, we performed trypsin shaving and secretome analyses to identify the surface-exposed proteins and secreted/shed proteins of Aspergillus fumigatus conidia, respectively. We investigated the surface proteome under different conditions, including temperature variation and germination. We found that the surface proteome of resting A. fumigatus conidia is not static but instead unexpectedly dynamic, as evidenced by drastically different surface proteomes under different growth conditions. Knockouts of two abundant A. fumigatus surface proteins, ScwA and CweA, were found to function only in fine-tuning the cell wall stress response, implying that the conidial surface is very robust against perturbations. We then compared the surface proteome of A. fumigatus to other allergy-inducing molds, including Alternaria alternata, Penicillium rubens, and Cladosporium herbarum, and performed comparative proteomics on resting and swollen conidia, as well as secreted proteins from germinating conidia. We detected 125 protein ortholog groups, including 80 with putative catalytic activity, in the extracellular region of all four molds, and 42 nonorthologous proteins produced solely by A. fumigatus. Ultimately, this study highlights the dynamic nature of the A. fumigatus conidial surface and provides targets for future diagnostics and immunotherapy.

Klarite as a label-free SERS-based assay: a promising approach for atmospheric bioaerosol detection

We present a SERS-based Klarite interface for the rapid and culture-free detection and quantification of atmospheric bioaerosols in the real-world environment.

Increasing access to microfluidics for studying fungi and other branched biological structures

BACKGROUND

Microfluidic systems are well-suited for studying mixed biological communities for improving industrial processes of fermentation, biofuel production, and pharmaceutical production. The results of which have the potential to resolve the underlying mechanisms of growth and transport in these complex branched living systems. Microfluidics provide controlled environments and improved optical access for real-time and high-resolution imaging studies that allow high-content and quantitative analyses. Studying growing branched structures and the dynamics of cellular interactions with both biotic and abiotic cues provides context for molecule production and genetic manipulations. To make progress in this arena, technical and logistical barriers must be overcome to more effectively deploy microfluidics in biological disciplines. A principle technical barrier is the process of assembling, sterilizing, and hydrating the microfluidic system; the lack of the necessary equipment for the preparatory process is a contributing factor to this barrier. To improve access to microfluidic systems, we present the development, characterization, and implementation of a microfluidics assembly and packaging process that builds on self-priming point-of-care principles to achieve "ready-to-use microfluidics."

RESULTS

We present results from domestic and international collaborations using novel microfluidic architectures prepared with a unique packaging protocol. We implement this approach by focusing primarily on filamentous fungi; we also demonstrate the utility of this approach for collaborations on plants and neurons. In this work we (1) determine the shelf-life of ready-to-use microfluidics, (2) demonstrate biofilm-like colonization on fungi, (3) describe bacterial motility on fungal hyphae (fungal highway), (4) report material-dependent bacterial-fungal colonization, (5) demonstrate germination of vacuum-sealed Arabidopsis seeds in microfluidics stored for up to 2 weeks, and (6) observe bidirectional cytoplasmic streaming in fungi.

CONCLUSIONS

This pre-packaging approach provides a simple, one step process to initiate microfluidics in any setting for fungal studies, bacteria-fungal interactions, and other biological inquiries. This process improves access to microfluidics for controlling biological microenvironments, and further enabling visual and quantitative analysis of fungal cultures.

Sensing Cell Membrane Biophysical Properties for Detection of High Quality Human Oocytes

Oocyte quality plays a crucial role in the early development and implantation of the embryos, and consequently has a profound impact on the accomplishment of assisted reproductive technology (ART). A simple and efficient method for detecting high-quality human oocytes is urgently needed. However, the clinically used morphological method is time-consuming, subjective, and inaccurate. To this end, we propose a practical and effective approach for detecting high-quality oocytes via on-chip measurement of the oocyte membrane permeability. We found that oocytes can be divided into two subpopulations (high-quality versus poor-quality oocytes) according to their membrane permeability differences, and as was further confirmed by subsequent in vitro fertilization (IVF) and development experiments (the blastocyst rates of high-quality and poor-quality oocytes were 60% and 0%, respectively). This approach shows great potentials in improving the success of ART, including both the fertilization and development rates, and thus it may have wide applications in the clinic.