Portable high-throughput multimodal immunoassay platform for rapid on-site COVID-19 diagnostics.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) as a causal agent of Coronavirus Disease 2019 (COVID-19) has led to the global pandemic. Though the real-time reverse transcription polymerase chain reaction (RT-PCR) acting as a gold-standard method has been widely used for COVID-19 diagnostics, it can hardly support rapid on-site applications or monitor the stage of disease development as well as to identify the infection and immune status of rehabilitation patients. To suit rapid on-site COVID-19 diagnostics under various application scenarios with an all-in-one device and simple detection reagents, we propose a high-throughput multimodal immunoassay platform with fluorescent, colorimetric, and chemiluminescent immunoassays on the same portable device and a multimodal reporter probe using quantum dot (QD) microspheres modified with horseradish peroxidase (HRP) coupled with goat anti-human IgG. The recombinant nucleocapsid protein fixed on a 96-well plate works as the capture probe. In the condition with the target under detection, both reporter and capture probes can be bound by such target. When illuminated by excitation light, fluorescence signals from QD microspheres can be collected for target quantification often at a fast speed. Additionally, when pursuing simple detection without using any sensing devices, HRP-catalyzed TMB colorimetric immunoassay is employed; and when pursuing highly sensitive detection, HRP-catalyzed luminol chemiluminescent immunoassay is established. Verified by the anti-SARS-CoV-2 N humanized antibody, the sensitivities of colorimetric, fluorescent, and chemiluminescent immunoassays are respectively 20, 80, and 640 times more sensitive than that of the lateral flow colloidal gold immunoassay strip. Additionally, such a platform can simultaneously detect multiple samples at the same time thus supporting high-throughput sensing; and all these detecting operations can be implemented on-site within 50 min relying on field-operable processing and field-portable devices. Such a high-throughput multimodal immunoassay platform can provide a new all-in-one solution for rapid on-site diagnostics of COVID-19 for different detecting purposes.

SARS-CoV-2 detection using quantum dot fluorescence immunochromatography combined with isothermal amplification and CRISPR/Cas13a.

The development of reliable, sensitive, and fast devices for the diagnosis of COVID-19 is of great importance in the pandemic of the new coronavirus. Here, we proposed a new principle of analysis based on a combination of reverse transcription and isothermal amplification of a fragment of the gene encoding the S protein of the SARS-CoV-2 and the CRISPR/Cas13a reaction for cleavage of the specific probe. As a result, the destroyed probe cannot be detected on an immunochromatographic strip using quantum fluorescent dots. Besides, the results can be obtained by an available and inexpensive portable device. By detecting SARS-CoV-2 negative (n = 25) and positive (n = 62) clinical samples including throat swabs, sputum and anal swabs, the assay showed good sensitivity and specificity of the method and could be completed within 1 h without complicated operation and expensive equipment. These superiorities showed its potential for fast point-of-care screening of SARS-CoV-2 during the outbreak, especially in remote and underdeveloped areas with limited equipment and resources.

Quantitative and Selective DNA Detection with Portable Personal Glucose Meter Using Loop-Based DNA Competitive Hybridization Strategy.

A portable, quantitative, and selective DNA detection biosensor, based on a loop-based DNA competitive hybridization assay and a personal glucose meter (PGM), is an advanced strategy for one-step target DNA recognition and signal reporter generation. In the presence of target DNA, the invertase-DNA conjugates are released due to the competitive binding of target DNA and collected with the help of a magnet subsequently. The released invertase-DNA could catalyze the hydrolysis of sucrose into glucose with millions of turnovers which is target concentration dependent. In addition, the sensor exhibits excellent anti-interference ability, having almost no effect on the detection performance in serum. The biosensor shown here is easier to operate owning its great potential in point of care testing in environments with limited resources and skilled personnel for rapid and sensitive detection of specific DNA sequence in real biological samples.

Rapid and ultra-sensitive detection of African swine fever virus antibody on site using QDM based-ASFV immunosensor (QAIS).

African swine fever (ASF) is a swine viral disease that could cause highly contagious and extremely high mortality, causing huge economic losses to the pig industry. As there is currently no vaccine and effective treatment methods. Therefore, early monitoring is one of the most important solutions to prevent and control ASF. In this study, the dual QDM recombinant virus protein 30 and 54 (P30 and P54) probes and pre-incubation in vitro were proposed for the first time as QDM based-ASFV immunosensor (QAIS) for the ultra-sensitive quantitative detection of ASFV antibodies in serum. In the range from serum dilution of 1:1000 to 1:64000, it showed a good linear relationship (R2 = 0.9947), and its detection sensitivity was 1:64000 dilution. Compared with commercial enzyme-linked immunosorbent assay (ELISA) and colloidal gold immunochromatographic strip (CGICS), its detection sensitivity was improved by at least one order of magnitude and four orders of magnitude respectively. In addition, the whole ASFV antibody screening test can be completed in 25 min with simple operation. The performance and practicability of the established QAIS sensor have been verified by ASF-ELISA kit, and its coincidence rate was as high as 98.7% in 151 clinical samples. We firmly believe that the proposed QAIS sensor could potentially be applied to point-of-care testing (POCT) for quantitative ASFV antibody in pig farms.

Quantum dot microsphere-based immunochromatography test strip enabled sensitive and quantitative on-site detections for multiple mycotoxins in grains.

In this work, we design a sensitive and quantitative on-site detecting solution for Aflatoxin B1 (AFB1), Ochratoxin A (OTA) and Zearalenone (ZEN) as often found in moldy grains and harmful to human health. Using quantum dot microsphere-based immunochromatography test strip, the proposed method can sensitively detect AFB1, OTA and ZEN in low detection limits of 0.01 ng/mL, 0.2 ng/mL and 0.032 ng/mL, and quantitatively measure their concentrations from 0.01 ng/mL to 1 ng/mL, from 0.2 ng/mL to 200 ng/mL and from 0.032 ng/mL to 32 ng/mL in high accuracy and good selectivity. More importantly, these multiple mycotoxin detections only relying on simple manual operations and portable handheld test strip reader can be finished on site within 45 min. Therefore, the proposed method is a promising solution supporting sensitive and quantitative on-site detections for multiple mycotoxins.

Beneficial impacts of fermented celery (Apium graveolens L.) juice on obesity prevention and gut microbiota modulation in high-fat diet fed mice.

Metabolic syndrome caused obesity has long been recognized as a risk of health. Celery and celery extracts have various medicinal properties, such as anti-diabetes and anti-inflammatory properties and blood glucose and serum lipid reduction. However, the effect of probiotic fermentation on celery juice and the association between fermented celery juice (FCJ) and obesity were unclear. This study aimed to evaluate the beneficial effects of FCJ on high-fat diet (HFD) induced obesity and related metabolic syndromes. C57BL/6 mice were randomly divided into six groups (n = 15 per group) fed either a normal diet (ND) or HFD with or without CJ/FCJ (10 g kg-1 day-1) by oral gavage for 12 weeks. Here we demonstrated that the probiotic fermentation of celery juice (CJ) could enhance the active ingredients in celery, such as total polyphenols, flavonoids, vitamin C and SOD. Compared to the slight improvement induced by CJ ingestion, FCJ intake significantly inhibited body weight gain, prevented dyslipidemia and hyperglycemia, and suppressed visceral fat accumulation. Furthermore, 16S rRNA sequencing analysis revealed that FCJ intake altered the composition of gut microbiota, increasing the ratio of Firmicutes/Bacteroidetes and the relative abundance of beneficial bacteria (Lactobacillus, Ruminococcaceae_UCG-014, Faecalibaculum and Blautia), and decreasing the relative abundance of harmful bacteria (Alloprevotella and Helicobacter). These findings suggest that FCJ can prevent HFD-induced obesity and become a novel gut microbiota modulator to prevent HFD-induced gut dysbiosis and obesity-related metabolic disorders.

Amplification-free smartphone-based attomolar HBV detection.

Classical gold standard HBV detection relies on expensive devices and complicated procedures, thus is always restricted in large-scale hospitals and centers for disease control and prevention. To extend HBV detection to primary clinics especially in underdeveloped areas, we design amplification-free smartphone-based attomolar HBV detecting technique based on single molecule sensing. Verified by synthesized HBV target DNA, this technique reaches a detection limit at attomolar concentration (100 aM); and verified by 110 clinical samples, it also reaches a rather high sensitivity of 104 copy/mL (≈2000 IU/mL) with a high accuracy of 93.64% certificated by gold standard HBV detecting devices. Besides, this technique can quantify HBV viral load in 70 min only using portable and inexpensive devices as well as simple operations. Because of its cost-effective, field-portable and operable design, highly sensitive and selective detecting capability and wireless data connectivity, this technique can be potentially used in mobile HBV diagnoses and share HBV epidemic information especially in resource limited situations.

Sensitive antibody fluorescence immunosorbent assay (SAFIA) for rapid on-site detection on avian influenza virus H9N2 antibody.

Avian influenza virus (AIV) is a serious zoonotic disease causing severe damages to both poultry industry and human health. To rapidly detect AIV on-site with high sensitivity and accuracy, we design sensitive antibody fluorescence immunosorbent assay (SAFIA) on AIV H9N2 antibody. In SAFIA, hemagglutinin (HA1) protein coated sample chamber specifically binds targets but remarkably reduces non-specific absorption; Protein L coated polystyrene microsphere captures target through secondary antibody to significantly amplify the fluorescence signal; and a portable fluorescence counter automatically measures the fluorescence spot density for AIV H9N2 antibody detection. Proved by practical applications, SAFIA could probe AIV H9N2 antibody in high sensitivity and selectivity, and distinguish positive and negative serum samples in high accuracy. Additionally, SAFIA can rapidly detect AIV H9N2 antibody at room temperature only requiring simple operations as well as cost-effective and compact devices. Therefore, SAFIA is a potential new-generation tool in rapid on-site testing for agricultures.

Dynamically probing ATP-dependent RNA helicase A-assisted RNA structure conversion using single molecule fluorescence resonance energy transfer.

RNA helicase A (RHA) as a member of DExH-box subgroup of helicase superfamily II, participates in diverse biological processes involved in RNA metabolism in organisms, and these RNA-mediated biological processes rely on RNA structure conversion. However, how RHA regulate the RNA structure conversion was still unknown. In order to unveil the mechanism of RNA structure conversion mediated by RHA, single molecule fluorescence resonance energy transfer was adopted to in our assay, and substrates RNA were from internal ribosome entry site of foot-and-mouth disease virus genome. We first found that the RNA structure conversion by RHA against thermodynamic equilibrium in vitro, and the process of dsRNA YZ converted to dsRNA XY through a tripartite intermediate state. In addition, the rate of the RNA structure conversion and the distribution of dsRNA YZ and XY were affected by ATP concentrations. Our study provides real-time insight into ATP-dependent RHA-assisted RNA structure conversion at the single molecule level, the mechanism displayed by RHA may help in understand how RHA contributes to many biological functions, and the basic mechanistic features illustrated in our work also underlay more complex protein-assisted RNA structure conversions.

Dynamic Dissection of the Endocytosis of Porcine Epidemic Diarrhea Coronavirus Cooperatively Mediated by Clathrin and Caveolae as Visualized by Single-Virus Tracking.

Coronaviruses (CoVs) have caused severe diseases in humans and animals. Endocytic pathways, such as clathrin-mediated endocytosis (CME) and caveolae-mediated endocytosis (CavME), play an important role for CoVs to penetrate the cell membrane barrier. In this study, a novel CoV entry manner is unraveled in which clathrin and caveolae can cooperatively mediate endocytosis of porcine epidemic diarrhea coronavirus (PEDV). Using multicolor live-cell imaging, the dynamics of the fluorescently labeled clathrin structures, caveolae structures, and PEDV were dissected. During CavME of PEDV, we found that clathrin structures can fuse with caveolae near the cell plasma membrane, and the average time of PEDV penetrating the cell membrane was within ∼3 min, exhibiting a rapid course of PEDV entry. Moreover, based on the dynamic recruitment of clathrin and caveolae structures and viral motility, the direct evidence also shows that about 20% of PEDVs can undergo an abortive entry via CME and CavME. Additionally, the dynamic trafficking of PEDV from clathrin and caveolae structures to early endosomes, and from early endosomes to late endosomes, and viral fusion were directly dissected, and PEDV fusion mainly occurred in late endosomes within ∼6.8 min after the transport of PEDV to late endosomes. Collectively, this work systematically unravels the early steps of PEDV infection, which expands our understanding of the mechanism of CoV infection.IMPORTANCE Emerging and re-emerging coronaviruses cause serious human and animal epidemics worldwide. For many enveloped viruses, including coronavirus, it is evident that breaking the plasma membrane barrier is a pivotal and complex process, which contains multiple dynamic steps. Although great efforts have been made to understand the mechanisms of coronavirus endocytic pathways, the direct real-time imaging of individual porcine epidemic diarrhea coronavirus (PEDV) internalization has not been achieved yet. In this study, we not only dissected the kinetics of PEDV entry via clathrin-mediated endocytosis and caveolae-mediated endocytosis and the kinetics of endosome trafficking and viral fusion but also found a novel productive coronavirus entry manner in which clathrin and caveolae can cooperatively mediate endocytosis of PEDV. Moreover, we uncovered the existence of PEDV abortive endocytosis. In summary, the productive PEDV entry via the cooperation between clathrin and caveolae structures and the abortive endocytosis of PEDV provide new insights into coronavirus penetrating the plasma membrane barrier.

Dynamic Dissection of Dynein and Kinesin-1 Cooperatively Mediated Intercellular Transport of Porcine Epidemic Diarrhea Coronavirus along Microtubule Using Single Virus Tracking.

It is now clear that the intercellular transport on microtubules by dynein and kinesin-1 motors has an important role in the replication and spread of many viruses. Porcine epidemic diarrhea virus (PEDV) is an enveloped, single-stranded RNA virus of the Coronavirus family, which can infect swine of all ages and cause severe economic losses in the swine industry. Elucidating the molecular mechanisms of the intercellular transport of PEDV through microtubule, dynein and kinesin-1 will be crucial for understanding its pathogenesis. Here, we demonstrate that microtubule, dynein, and kinesin-1 are involved in PEDV infection and can influence PEDV fusion and accumulation in the perinuclear region but cannot affect PEDV attachment or internalization. Furthermore, we adopted a single-virus tracking technique to dynamically observe PEDV intracellular transport with five different types: unidirectional movement toward microtubule plus ends; unidirectional movement toward microtubule minus ends; bidirectional movement along the same microtubule; bidirectional movement along different microtubules and motionless state. Among these types, the functions of dynein and kinesin-1 in PEDV intercellular transport were further analyzed by single-virus tracking and found that dynein and kinesin-1 mainly transport PEDV to the minus and plus ends of the microtubules, respectively; meanwhile, they also can transport PEDV to the opposite ends of the microtubules different from their conventional transport directions and also coordinate the bidirectional movement of PEDV along the same or different microtubules through their cooperation. These results provided deep insights and references to understand the pathogenesis of PEDV as well as to develop vaccines and treatments.

Quantitative ciprofloxacin on-site rapid detections using quantum dot microsphere based immunochromatographic test strips.

The ciprofloxacin (CIP) abuse has caused many problems threatening to human health. Here, we design the quantum dot microsphere (QDM) based immunochromatographic quantitative CIP test strip: when the sample under detection contains CIP, the QDM-monoclonal antibody (mAb) probes bound with the CIP and cannot be captured by CIP-bovine serum albumin (BSA) conjugation dispersed on the T lines, reducing the fluorescence intensities. These test strips can provide a low detection limit of 0.05 ng/mL and a wide linear detection range from 0.1 ng/mL to 100 ng/mL in high sensitivity and accuracy as well as good selectivity, reproducibility and stability. Moreover, a smartphone based test strip reader with the size of 85 mm × 48 mm × 44 mm is also fabricated using 3-D printing to automatically and quantitatively detect CIP. The whole process of CIP detection can be finished within 15 min, but only cost ~1 RMB (10 cents).

Quantitative protein detection using single molecule imaging enzyme-linked immunosorbent assay (iELISA).

Protein detection is a key step in molecular biology research and is required for pathogen and protein marker testing for disease diagnostics. Here, single molecule imaging enzyme-linked immunosorbent assay (iELISA) is proposed to quantitatively measure the porcine circovirus type 2 (PCV2) Cap protein. The monoclonal antibody against PCV2 Cap protein indirectly immobilized on a polyethylene glycol (PEG) passivated slide by biotin-streptavidin interaction is used to capture the PCV2 Cap protein, and the PCV2 Cap protein can be detected in single molecule level according to the fluorescein isothiocyanate (FITC)-labeled secondary antibody using total internal reflection fluorescence microscopy. The single molecule iELISA measurements can be finished within 1 h skipping the time-consuming sample preparation procedures; moreover, it also exhibits excellent protein selectivity and anti-interference capability. With the proposed single molecule iELISA, linear relation between the fluorescent signals and logarithm of target protein concentrations is obtained with the detection limit of 7 ng/mL. Considering its high accuracy in target protein detection with simple procedures and fast speed, it is believed single molecule iELISA can be potentially adopted in fast trace protein detection.

Measurements on ATP induced cellular fluctuations using real-time dual view transport of intensity phase microscopy.

Dual view transport of intensity phase microscopy is adopted to quantitatively study the regulation of adenosine triphosphate (ATP) on cellular mechanics. It extracts cell phases in real time from simultaneously captured under- and over-focus images. By computing the root-mean-square phase and correlation time, it is found that the cellular fluctuation amplitude and speed increased with ATP compared to those with ATP depletion. Besides, when adenylyl-imidodiphosphate (AMP-PNP) was introduced, it competed with ATP to bind to the ATP binding site, and the cellular fluctuation amplitude and speed decreased. The results prove that ATP is a factor in the regulation of cellular mechanics. To our best knowledge, it is the first time that the dual view transport of intensity phase microscopy was used for live cell phase imaging and analysis. Our work not only provides direct measurements on cellular fluctuations to study ATP regulation on cellular mechanics, but it also proves that our proposed dual view transport of intensity phase microscopy can be well used, especially in quantitative phase imaging of live cells in biological and medical applications.

On-site quantitative Hg2+ measurements based on selective and sensitive fluorescence biosensor and miniaturized smartphone fluorescence microscope.

Mercury is a bio-accumulative and toxic pollutant causing severe damages to human health and environment. Since Hg2+ is the most stable form of mercury, selective and sensitive Hg2+ detection is required. Though classical approaches can realize accurate Hg2+ detection, the complicated instruments and the time-consuming operations inevitably limit their on-site applications. Here, we design a smart Hg2+ detection approach using the fluorescence biosensor, the smartphone fluorescence microscope and the smartphone application for Hg2+ on-site detection. Based on the thymine-Hg2+-thymine coordination chemistry, a selective and sensitive fluorescence biosensor is designed for capturing Hg2+ in aqueous solution; besides, a miniaturized smartphone fluorescence microscope for fluorescence signal collection and an image processing application for quantitative Hg2+ measurements are constructed. A highly specific detection of Hg2+ with a linear relation between 1 nM and 1 µM with a limit of detection of 1 nM is obtained using the smart Hg2+ detection approach. Considering it can realize selective and sensitive quantitative Hg2+ measurements in high precision with simple operations and cost-effective system, it is believed the proposed smart Hg2+ detection approach owns great potentials in Hg2+ detection for routine uses at home and in the field.

Handheld Inkjet Printing Paper Chip Based Smart Tetracycline Detector.

Tetracycline is widely used as medicine for disease treatments and additives in animal feeding. Unfortunately, the abuse of tetracycline inevitably causes tetracycline residue in animal-origin foods. Though classical methods can detect tetracycline in high sensitivity and precision, they often rely on huge and expensive setups as well as complicated and time-consuming operations, limiting their applications in rapid and on-site detection. Here, we propose a handheld inkjet printing paper chip based smart tetracycline detector: tetracycline can be determined by inkjet printing prepared paper chip based enzyme-linked immunosorbent assay (ELISA) with the advantages of high sensitivity, excellent specificity and low cost; moreover, a smartphone based paper chip reader and application is designed for automatically determining tetracycline with simple operations, high precision and fast speed. The smart tetracycline detector with a compact size of 154 mm × 80 mm × 50 mm and self-supplied internal power can reach a rather low detection limit of ~0.05 ng/mL, as proved by practical measurements. It is believed the proposed handheld inkjet printing paper chip based smart tetracycline detector is a potential tool in antibiotic sensing for routine uses at home and on-site detection in the field.

Substrate Determinants for Unwinding Activity of the DExH/D-Box Protein RNA Helicase A.

RNA helicase A (RHA) as a member of the DExH/D-box subgroup of helicase superfamily II is involved in virtually all aspects of RNA metabolism. It exhibits robust RNA helicase activity in vitro. However, little is known about the molecular and physical determinants for RHA substrate recognition and RHA translocation along the nucleic acids. Here, our nondenaturing polyacrylamide gel electrophoresis (PAGE)-based unwinding assays of chemical and structural modified substrates indicate that RHA translocates efficiently along the 3' overhang of RNA, but not DNA, with a requirement of covalent continuity. Ribose-phosphate backbone lesions on both strands of the nucleic acids, especially on the 3' overhang of the loading strand, affect RHA unwinding significantly. Furthermore, RHA requires RNA on the 3' overhang which directly or indirectly connects with the duplex region to mediate productive unwinding. Collectively, these findings propose a basic mechanism of the substrate determinants for RHA backbone tracking during duplex unwinding.

A pH-dependent Antibacterial Peptide Release Nano-system Blocks Tumor Growth in vivo without Toxicity.

In this study, we designed a nano-system where a novel antibacterial peptide RGD-hylin a1 with reduced hemolysis than the commonly studied melittin was loaded onto mesoporous silica (HMS). We found out that the designed nano-system, RGD-hylin a1-HMS, released RGD-hylin a1 in a pH-dependent manner. It caused apoptosis of cancer cells at low dosage of the antibacterial peptide at pH = 5.5, but was safe to the cells at pH = 7. The hemolytic activity of RGD-hylin a1 itself was reduced by 50~100% by the nano-system depending on the dosage. When this nano-system was administered to tumor-bearing mice at low dosage via intravenous injection, the growth of the solid tumor was blocked by the RGD-hylin a1-HMS nano-system with a 50-60% inhibition rate relative to the PBS-treated control group in terms of tumor volume and weight. Further, the hemolytic activity of RGD-hylin a1 was completely eliminated within the delivery system with no other side effects observed. This study demonstrates that this smart pH-dependent antibacterial peptide release nano-system has superior potential for solid tumor treatments through intravenous administration. This smart-releasing system has great potential in further clinical applications.

A label-free and self-assembled electrochemical biosensor for highly sensitive detection of cyclic diguanylate monophosphate (c-di-GMP) based on RNA riboswitch.

Cyclic diguanylate monophosphate (c-di-GMP) is an important second messenger that regulates a variety of complex physiological processes involved in motility, virulence, biofilm formation and cell cycle progression in several bacteria. Herein we report a simple label-free and self-assembled RNA riboswitch-based biosensor for sensitive and selective detection of c-di-GMP. The detectable concentration range of c-di-GMP is from 50 nM to 1 µM with a detection limit of 50 nM.