Magnetofluid-Integrated Multicolor Immunochip for Visual Analysis of Neutralizing Antibodies to SARS-CoV-2 Variants

Magnetofluidic-Assisted Portable Automated Microfluidic Devices for Protein Detection

To facilitate on-site detection by nonspecialists, there is a demand for the development of portable "sample-to-answer" devices capable of executing all procedures in an automated or easy-to-operate manner. Here, we developed an automated detection device that integrated a magnetofluidic manipulation system and a signal acquisition system. Both systems were controllable via a smartphone. In the device, the mixing of solutions and magnetic beads in the static chamber was enhanced by steel bead agitation, which improved the reaction efficiency. We demonstrate the performance of the device using myoglobin detection as an example. During the detection process, the plasma was separated from the whole blood sample using a homemade mini-centrifuge, and subsequently, the plasma, magnetic beads, and reagents were added to a magnetofluidic chip with multiple chambers. After the chip was loaded, the device was initiated with a smartphone App via Bluetooth. Then, the magnetic beads were shuttled through different chambers of the chip and multiple steps were completed automatically: first, the targets were separated and enriched using antibody-modified magnetic beads, followed by washing, binding with aptamer-functionalized G-quadruplex, signal amplifying (optional), and chromogenic reaction. Finally, the images of colored solutions were captured and processed by a smartphone to obtain the concentrations of myoglobin. The detection limits depended on the mode of signal conversion, which were 0.1 or 2.7 nM (with or without signal amplifying). With its simple operation, compact design, low cost, and ease of scalability, this automated detection device holds potential applications in human health, food safety, environmental monitoring, etc.

Integration of Immunosyringe Sensors with Bar-Chart Chips for Prick-and-Read Testing of Prostate Specific Antigen

Pressure-based signal transduction is of promise in developing microfluidic immunoassays such as volumetric bar-chart chips (V-chips), but new working principles are required to further simplify the methods in point-of-care testing (POCT). Herein, we developed immunosyringe sensors and integrated them with bar-chart chips for simple prick-and-read testing of prostate specific antigen (PSA) as a model target. Disposable syringes served as the host for the construction of the sandwich-type immuno-recognition system. Platinum nanoparticles (Pt NPs) as the peroxidase-mimicking detection probe catalyzed the decomposition of H2O2 to produce O2 in the syringe cylinders, enabling the pressure-driven automatic injection of liquids from the syringes. The immuno-recognition event in the syringes was thereby converted into the quantitative autoinjection behavior of the syringes, namely, immunosyringe sensors. By simply pricking the sensors to bar-chart chips, we visually and quantitatively read the immunoassay signals as the bar-chart injection distance of liquids from the syringes in channels of the chips. The immunoassay showed a limit of detection (LOD) of 0.41 ng/mL in PSA detection with satisfactory accuracy in testing clinical serum samples. Owing to the integration with the immunosyringe sensors, this method, in comparison with conventional V-chips, works in a simpler prick-and-read manner without complex chip configurations and specialized chip operations (e.g., on-chip loading of microvolume reagents and sealing treatments). Therefore, the immunoassay shows great potential in POCT applications.

Centrifugo-Pneumatic Reciprocating Flowing Coupled with a Spatial Confinement Strategy for an Ultrafast Multiplexed Immunoassay

Immunoassays serve as powerful diagnostic tools for early disease screening, process monitoring, and precision treatment. However, the current methods are limited by high costs, prolonged processing times (>2 h), and operational complexities that hinder their widespread application in point-of-care testing. Here, we propose a novel centrifugo-pneumatic reciprocating flowing coupled with spatial confinement strategy, termed PRCM, for ultrafast multiplexed immunoassay of pathogens on a centrifugal microfluidic platform. Each chip consists of four replicated units; each unit allows simultaneous detection of three targets, thereby facilitating high-throughput parallel analysis of multiple targets. The PRCM platform enables sequential execution of critical steps such as solution mixing, reaction, and drainage by coordinating inherent parameters, including motor rotation speed, rotation direction, and acceleration/deceleration. By integrating centrifugal-mediated pneumatic reciprocating flow with spatial confinement strategies, we significantly reduce the duration of immune binding from 30 to 5 min, enabling completion of the entire testing process within 20 min. As proof of concept, we conducted a simultaneous comparative test on- and off-the-microfluidics using 12 negative and positive clinical samples. The outcomes yielded 100% accuracy in detecting the presence or absence of the SARS-CoV-2 virus, thus highlighting the potential of our PRCM system for multiplexed point-of-care immunoassays.

Tyramine-Invertase Bioconjugate-Amplified Personal Glucose Meter Signaling for Ultrasensitive Immunoassay

Highly sensitive and facile detection of low levels of protein markers is of great significance for the early diagnosis and efficacy monitoring of diseases. Herein, aided by an efficient tyramine-signal amplification (TSA) mechanism, we wish to report a simple but ultrasensitive immunoassay with signal readout on a portable personal glucose meter (PGM). In this study, the bioconjugates of tyramine and invertase (Tyr-inv), which act as the critical bridge to convert and amplify the protein concentration information into glucose, are prepared following a click chemistry reaction. Then, in the presence of a target protein, the sandwich immunoreaction between the immobilized capture antibody, the target protein, and the horseradish peroxidase (HRP)-conjugated detection antibody is specifically performed in a 96-well microplate. Subsequently, the specifically loaded HRP-conjugated detection antibodies will catalyze the amplified deposition of a large number of Tyr-inv molecules onto adjacent proteins through highly efficient TSA. Then, the deposited invertase, whose dosage can faithfully reflect the original concentration of the target protein, can efficiently convert sucrose to glucose. The amount of finally produced glucose is simply quantified by the PGM, realizing the highly sensitive detection of trace protein markers such as the carcinoembryonic antigen and alpha fetoprotein antigen at the fg/mL level. This method is simple, cost-effective, and ultrasensitive without the requirement of sophisticated instruments or specialized laboratory equipment, which may provide a universal and promising technology for highly sensitive immunoassay for in vitro diagnosis of diseases.

Magnetically actuated microfluidic chip combined with a G-quadruplex DNAzyme-based fluorescent/colorimetric sensor for the dual-mode detection of ochratoxin A in wheat

In this work, a portable fluorescent/colorimetric sensor based on G-quadruplex DNAzyme was constructed to achieve rapid and dual-mode detection of ochratoxin A (OTA) in wheat. OTA aptamers coupled with magnetic beads (MBs) can self-assemble with two segments of DNA and hemin to form a G-quadruplex DNAzyme structure that can catalyze the oxidation of Amplex Red (ADHP) with H2O2, making the solution red and producing strong fluorescence in solution. However, in the presence of OTA, the structure of the G-quadruplex DNAzyme was damaged, resulting in reduced catalytic activity. According to the principle of detection, a magnet-controlled chip integrating the reaction, washing, and detection was designed in this study. Shuttling the MB-DNAzyme probes onto a magnetically controlled chip considerably reduced the background signal and improved the detection efficiency and sensitivity. In addition, a portable fluorescence and colorimetric detection platform was built for on-site OTA detection.

Magnetofluid-integrated biosensors based on DNase-dead Cas12a for visual point-of-care testing of HIV-1 by an up and down chip

The CRISPR Cas system, as a novel nucleic acid detection tool, is often hindered by cumbersome experimental procedures, complicated reagent transfer processes, and associated aerosol pollution risks. In this study, an integrated nucleic acid detection platform named "up and down chip" was developed, which combined RT-RAA technology for nucleic acid amplification, DNase-dead Cas12a-modified magnetic beads for specific recognition of target nucleic acid, and HRP-TMB chromogenic reaction for signal output in different chambers of a single microfluidic chip. The magnetic beads were migrated in an up-and-down manner between different chambers through magnetic driving, achieving a "sample-in, result-out" detection mode. By introducing a homemade heating box for temperature control during the reaction and using the naked eye or a smartphone APP for color-based signal reading, no professional or precise instruments were required in this platform. Using this platform, highly sensitive detection of the HIV-1 genome as low as 250 copies (CPs) per mL was achieved within 100 min while maintaining good detection performance against common variants as well as excellent specificity and anti-interference ability. In addition, compared with qRT-PCR, it also exhibited good accuracy for 56 spiked plasma samples, indicating its promising potential for clinical application.

Development of an Effective Neutralizing Antibody Assay for SARS-CoV-2 Diagnosis

Introduction

Neutralizing antibodies (NAbs) are essential for preventing reinfection with SARS-CoV-2 and the recurrence of COVID-19; nonetheless, the formation of NAbs following vaccination and infection remains enigmatic due to the lack of a practical and effective NAb assay in routine laboratory settings. In this study, we developed a convenient lateral flow assay for the rapid and precise measurement of serum NAb levels within 20 minutes.

Methods

Receptor-binding domain-fragment crystallizable (RBD-Fc) and angiotensin-converting enzyme 2-histidine tag (ACE2-His) were expressed by the eukaryotic expression systems of Spodoptera frugiperda clone 9 and human embryonic kidney 293T, respectively. Then, colloidal gold was synthesized and conjugated with ACE2. After optimizing various operating parameters, an NAb lateral flow assay was constructed. Subsequently, its detection limit, specificity, and stability were systematically evaluated, and clinical samples were analyzed to validate its clinical feasibility.

Results

RBD-Fc and ACE2-His were obtained with 94.01% and 90.05% purity, respectively. The synthesized colloidal gold had a uniform distribution with an average diameter of 24.15 ± 2.56 nm. With a detection limit of 2 μg/mL, the proposed assay demonstrated a sensitivity of 97.80% and a specificity of 100% in 684 uninfected clinical samples. By evaluating 356 specimens from infected individuals, we observed that the overall concordance rate between the proposed assay and conventional enzyme-linked immunosorbent assay was 95.22%, and we noticed that 16.57% (59/356) of individuals still did not produce NAbs after infection (both by ELISA and the proposed assay). All the above tests by this assay can obtain results within 20 minutes by the naked eye without any additional instruments or equipment.

Conclusion

The proposed assay can expediently and reliably detect anti-SARS-CoV-2 NAbs after infection, and the results provide valuable data to facilitate effective prevention and control of SARS-CoV-2.

Clinical trial registration

Serum and blood samples were used under approval from the Biomedical Research Ethics Subcommittee of Henan University, and the clinical trial registration number was HUSOM-2022-052. We confirm that this study complies with the Declaration of Helsinki.

Research progress in methods for detecting neutralizing antibodies against SARS-CoV-2

The emergence of SARS-CoV-2 has seriously affected the lives of people worldwide. Clarifying the attenuation rule of SARS-CoV-2 neutralizing antibody (NAb) in vivo is the key to prevent reinfection and recurrence of virus. Currently, the commonly used methods for detecting NAb include virus neutralization tests, pseudovirus neutralization assays, lateral flow immunochromatography and enzyme-linked immunosorbent assays. The detection of NAb not only can be used to evaluate the level of immunity after vaccination or infection but also can provide important theoretical support for virus reinfection, recurrence and vaccine iteration. In this research, the related technologies of SARS-CoV-2 NAb detection were reviewed, aiming to provide better research ideas for SARS-CoV-2 epidemic prevention and control.