Succinylated Jeffamine ED-2003 coated polycarbonate chips for low-cost analytical microarrays

A PAM-Free One-Step Asymmetric RPA and CRISPR/Cas12b Combined Assay (OAR-CRISPR) for Rapid and Ultrasensitive DNA Detection

Current research endeavors have focused on the combination of various isothermal nucleic acid amplification methods with CRISPR/Cas systems, aiming to establish a more sensitive and reliable molecular diagnostic approach. Nevertheless, most assays adopt a two-step procedure, complicating manual operations and heightening the risk of contamination. Efforts to amalgamate both assays into a single-step procedure have faced challenges due to their inherent incompatibility. Furthermore, the presence of the protospacer adjacent motif (PAM) motif (e.g., TTN or TTTN) in the target double-strand DNA (dsDNA) is an essential prerequisite for the activation of the Cas12-based method. This requirement imposes constraints on crRNA selection. To overcome such limitations, we have developed a novel PAM-free one-step asymmetric recombinase polymerase amplification (RPA) coupled with a CRISPR/Cas12b assay (OAR-CRISPR). This method innovatively merges asymmetric RPA, generating single-stranded DNA (ssDNA) amenable to CRISPR RNA binding without the limitations of the PAM site. Importantly, the single-strand cleavage by PAM-free crRNA does not interfere with the RPA amplification process, significantly reducing the overall detection times. The OAR-CRISPR assay demonstrates sensitivity comparable to that of qPCR but achieves results in a quarter of the time required by the latter method. Additionally, our OAR-CRISPR assay allows the naked-eye detection of as few as 60 copies/μL DNA within 8 min. This innovation marks the first integration of an asymmetric RPA into one-step CRISPR-based assays. These advancements not only support the progression of one-step CRISPR/Cas12-based detection but also open new avenues for the development of detection methods capable of targeting a wide range of DNA targets.

Flow-Based CL-SMIA for the Quantification of Protein Biomarkers from Nasal Secretions in Comparison with Sandwich ELISA

Protein biomarkers in nasal secretions can be used as a measure to differentiate between allergies, airway diseases and infections for non-invasive diagnostics. The point-of-care quantification of biomarker levels using flow-based microarray facilitates precise and rapid diagnosis and displays the potential for targeted and effective treatment. For the first time, we developed a flow-based chemiluminescence sandwich microarray immunoassay (CL-SMIA) for the quantification of nasal interferon-beta (IFN-β) on the Microarray Chip Reader-Research (MCR-R). Polycarbonate foils are used as a cost-effective surface for immobilizing capture antibodies. By using a commercially available set of anti-human IFN-β antibodies, the CL-SMIA can be compared directly to an enzyme-linked immunosorbent assay (ELISA) performed in microtiter plates concerning the bioanalytical performance and economic issues. Pre-incubation of the sample with detection antibodies facilitates the lower consumption of detection antibodies, as this allows for a longer interaction time between the antibody and the biomarker. The direct injection of pre-incubated samples into the microarray chips eliminates the adsorption of proteins in the tubing as well as the contamination of the tubing and valves of the MCR-R with clinical samples. The small flow cell allows for a low sample volume of 50 μL. The limit of detection of 4.53 pg mL^-1 was slightly increased compared to a sandwich ELISA performed on microtiter plates which were 1.60 pg mL^-1. The possibility to perform the CL-SMIA in a multiplexed mode makes it a promising assay for the rapid and cost-effective non-invasive detection of biomarkers in nasal secretions.

Automated detection of neutralizing SARS-CoV-2 antibodies in minutes using a competitive chemiluminescence immunoassay

The SARS-CoV-2 pandemic has shown the importance of rapid and comprehensive diagnostic tools. While there are numerous rapid antigen tests available, rapid serological assays for the detection of neutralizing antibodies are and will be needed to determine not only the amount of antibodies formed after infection or vaccination but also their neutralizing potential, preventing the cell entry of SARS-CoV-2. Current active-virus neutralization assays require biosafety level 3 facilities, while virus-free surrogate assays are more versatile in applications, but still take typically several hours until results are available. To overcome these disadvantages, we developed a competitive chemiluminescence immunoassay that enables the detection of neutralizing SARS-CoV-2 antibodies within 7 min. The neutralizing antibodies bind to the viral receptor binding domain (RBD) and inhibit the binding to the human angiotensin-converting enzyme 2 (ACE2) receptor. This competitive binding inhibition test was characterized with a set of 80 samples, which could all be classified correctly. The assay results favorably compare to those obtained with a more time-intensive ELISA-based neutralization test and a commercial surrogate neutralization assay. Our test could further be used to detect individuals with a high total IgG antibody titer, but only a low neutralizing titer, as well as for monitoring neutralizing antibodies after vaccinations. This effective performance in SARS-CoV-2 seromonitoring delineates the potential for the test to be adapted to other diseases in the future.

Flow-Based Chemiluminescence Microarrays as Screening Platform for Affinity Binders to Capture and Elute Bacteria

Affinity describes the non-covalent but selective interaction between an affinity binder (e.g., proteins, antibiotics, or antibodies) and its counterpart (e.g., bacteria). These affinity binders can serve to detect bacteria and respond to the need for selective concentration via affinity chromatography for trace analysis. By changing the pH value or salt and protein contents, affinity bindings can be reversed, and bacteria can be recovered for characterisation. Analytical microarrays use multiple affinity binders immobilised on the surface in a distinct pattern, which immensely reduces screening time for the discovery of superior binding motifs. Here, flow-based microarray systems can inform not only about binding, but also about desorption. In this work, we pioneer a screening assay for affinity binders against both gram-positive and negative bacteria based on an automated flow-based chemiluminescence (CL) microarray. Biotinylation of model organisms E. coli and E. faecalis enabled labelling with horseradish-peroxidase-coupled streptavidin, and detection with CL. Polymyxin B, an antibiotic against gram-negative bacteria, was found to bind both E. coli and E. faecalis. Simultaneous screening for desorption methods unexpectedly revealed methyl alpha-D-mannopyranoside as a promising buffer for desorption from Polymyxin B. This proof-of-principle study shows that our new platform greatly facilitates the screening of new affinity binders against bacteria, with promise for future automation.

Fully Automated Chemiluminescence Microarray Analysis Platform for Rapid and Multiplexed SARS-CoV-2 Serodiagnostics

Lateral-flow immunoassays and laboratory diagnostic tests like enzyme-linked immunosorbent assays (ELISAs) are powerful diagnostic tools to help fight the COVID-19 pandemic using them as antigen or antibody tests. However, the need emerges for alternative bioanalytical systems that combine their favorable features─simple, rapid, and cost-efficient point-of-care (POC) analysis of lateral-flow immunoassays and higher reliability of laboratory tests─while eliminating their disadvantages (limited sensitivity and specificity of lateral-flow assays and prolonged time and work expenditure of laboratory analysis). An additional need met by only a few tests is multiplexing, allowing for the analysis of several immunorecognition patterns at the same time. We herein present a strategy to combine all desirable attributes of the different test types by means of a flow-based chemiluminescence microarray immunoassay. Laminated polycarbonate microarray chips were developed for easy production and subsequent application in the fully automated microarray analysis platform MCR-R, where a novel flow cell design minimizes the sample volume to 40 μL. This system was capable of detecting IgG antibodies to SARS-CoV-2 with 100% sensitivity and specificity using recombinant antigens for the SARS-CoV-2 spike S1 protein, nucleocapsid protein, and receptor binding domain. The analysis was accomplished within under 4 min from serum, plasma, and whole blood, making it also useful in POC settings. Additionally, we showed the possibility of serosurveillance after infection or vaccination to monitor formerly unnoticed breakthrough infections in the population as well as to detect the need for booster vaccination after the natural decline of the antibody titer below detectable levels. This will help in answering pressing questions on the importance of the antibody response to SARS-CoV-2 that so far remain open. Additionally, even the sequential detection of IgM and IgG antibodies was possible, allowing for statements on the time response of an infection. While our serodiagnostic application focuses on SARS-CoV-2, the same approach is easily adjusted to other diseases, making it a powerful tool for future serological testing.

A chemiluminescence-based heterogeneous asymmetric recombinase polymerase amplification assay for the molecular detection of mycotoxin producers

The analysis of mold in indoor air is a prominent topic but it is hardly dealt with. The most affected fields of this issue are residential- and occupational safety since mold can have a number of impacts on human health. To date the most used methods for quantification of microorganism contamination in indoor air are culture- or microscopy-based and are not capable of translating the on-site situation to analytical data reliably. Here we present a chemiluminescence-based method to detect mycotoxin producers through isothermal amplification of mycotoxin biosynthesis genes using glass and polycarbonate carriers. In this proof-of-principle study, zearalenone producers were aimed to be detected by heterogeneous asymmetric recombinase polymerase amplification (haRPA). For this, an appropriate lysis method for fungal spores was developed allowing rapid access to DNA. A system calibration with spores of Fusarium culmorum as zearalenone-producing organism resulted in an LOD of 2.7 × 10⁵ spores per ml. The system was shown to be specific for zearalenone producers. This work presents the first application of a heterogeneous isothermal amplification for rapid detection and quantification of mycotoxin producers. In the future, a multiplex detection can be possible by haRPA.

Hybrid elastomer-plastic microfluidic device as a convenient model for mimicking the blood-brain barrier in vitro

In this study, we fabricated a hybrid elastomer-plastic microdevice using the silicone elastomer poly(dimethylsiloxane) (PDMS) and the plastic polycarbonate (PC), to mimic the human blood-brain barrier (BBB) in vitro. Specifically, the microchannel-imprinted elastomer was first coated with 3-aminopropyltriethoxysilane to produce amine-terminated PDMS. Then, simply by conformal contact at room temperature, the amine-functionalized PDMS was bonded to pristine PC through the formation of urethane linkages. Aside from realizing device bonding, the amine functionalization also assisted in subsequent dopamine coating to form polydopamine and provide a stable surface for culturing human endothelial cells and central nervous system-related cells (e.g., astrocytes) inside the microchannels. Successful mimicking of the BBB-like microenvironment was assessed by 3D co-culturing of human endothelial cells and astrocytes, where the microdevice was verified as an acceptable in vitro BBB model according to the following four criteria: the formation of tight junctions at the cell-cell boundaries of the endothelial cells, evaluated by the expression of the tight junction marker ZO-1; the formation of actin filaments, evaluated using rhodamine phalloidin dye; low permeability, tested using the fluorescent tracer 40-kDa FITC-dextran; and good transendothelial electrical resistance (a measure of the tight junction integrity formed between the endothelial cells). The fabricated PDMS-PC microfluidic device ensured simple yet stable device sealing, and simultaneously enhanced BBB-mimicking cell attachment, thus fulfilling all major criteria for its application as a convenient in vitro BBB model.