Rapid Fluorescent Lateral-Flow Immunoassay for Hepatitis B Virus Genotyping

Fully Inter-restricted Assembly of Aggregation-Induced Emission Luminogens and Polymers Enables Ultra-bright Nanoparticles for Sensitive Point-of-Care Diagnosis

Fluorescent lateral flow immunoassay (LFIA) is recognized as a leading quantitative point-of-care (POC) platform for precise clinical diagnostics. However, conventional fluorescent nanoprobes are hampered by low quantum yield (QY), which constrain the sensitivity of fluorescent LFIA. Herein, we employed a butterfly aggregation-induced emission luminogen (AIEgen) and developed the fully inter-restricted assembly with a polyphenyl polymer poly(maleicanhydride-styrene) (PMPS) to create highly fluorescent homogeneous nanoparticles (ho-AIENPs) with QY over 91%. Compared to conventional fluorescent nanoparticles with a core-shell heterostructure (he-AIENPs), ho-AIENPs demonstrate a homogeneous structure with AIEgens uniformly dispersed in the PMPS matrix nanoparticles. The robust and broad intermolecular interaction (e.g., π-π interactions) between PMPS and AIEgens effectively restricts the molecular motion of AIEgens, producing a 30% increase in the QY of ho-AIENPs than he-AIENPs. Ho-AIENPs exhibit a 5-fold and 80-fold improved sensitivity compared to traditional he-AIENP-based fluorescent LFIAs and AuNP-based colorimetric LFIAs. Owing to the excellent optical properties of ho-AIENPs, we developed ho-AIENP-based multiplex LFIAs, which can simultaneously detect lung cancer biomarkers with exceptionally high sensitivity. In contrast to the conventional core-shell assembly and physical encapsulation strategies, the fully inter-restricted assembly strategy is promising, versatile, and efficient in enhancing the polymer matrix-derived fluorescent particles and sensitizing the immunoassays.

ELISA genotyping of hepatitis B virus in China with antibodies specific for genotypes B and C

Hepatitis B virus (HBV) causes hepatitis B (HB) and distinct HBV genotypes can lead to different prognoses. However, HBV genotyping is rarely done in clinics, because the traditional method by PCR-based DNA sequencing is impractical for clinical diagnosis with tedious process and low success rate. Herein, we have established an ELISA-based genotyping method to quickly determine the HBV genotypes of HB patients in China. First, two commercial antibodies, 16D12 and 6H3 specific for HBV genotypes B and C respectively, are chosen as capture antibodies, since these two genotypes dominate in China. Then two home-made genotype-specific antibodies, B19 and C04, are used as the detection antibodies for genotypes B and C in sandwiched ELISA. The ELISA kit shows high sensitivity (> 95%) and specificity (> 95%) in detecting genotypes B and C of Chinese HB patients. Moreover, the ELISA kit has demonstrated higher success rate (98.7%) than PCR-based DNA sequencing (93.5%) and a commercial PCR-based genotyping kit (92.2%) for sera with HBV DNA ≥ 1000 IU/mL and HBsAg ≥ 250 IU/mL. Such an advantage is more obvious for the sera with HBV DNA < 1000 IU/mL. The kappa analysis between the ELISA and PCR-based DNA sequencing results exhibits a kappa of 0.836, indicating a good correlation.

Both middle and large envelope proteins can mediate neutralization of hepatitis B virus infectivity by anti-preS2 antibodies: escape by naturally occurring preS2 deletions

Hepatitis B virus (HBV) expresses co-terminal large (L), middle (M), and small (S) envelope proteins containing preS1/preS2/S, preS2/S, and S domain alone, respectively. S and preS1 domains mediate sequential virion attachment to heparan sulfate proteoglycans and sodium taurocholate cotransporting polypeptide (NTCP), respectively, which can be blocked by anti-S and anti-preS1 antibodies. How anti-preS2 antibodies neutralize HBV infectivity remains enigmatic. The late stage of chronic HBV infection often selects for mutated preS2 translation initiation codon to prevent M protein expression, or in-frame preS2 deletions to shorten both L and M proteins. When introduced to infectious clone of genotype C or D, both M-minus mutations and most 5' preS2 deletions sustained virion production. Such mutant progeny viral particles were infectious in NTCP-reconstituted HepG2 cells. Neutralization experiments were performed on the genotype D clone. Although remaining susceptible to anti-preS1 and anti-S neutralizing antibodies, M-minus mutants were only partially neutralized by two anti-preS2 antibodies tested while preS2 deletion mutants were resistant. By infection experiments using viral particles with lost versus increased M protein expression, or a neutralization escaping preS2 deletion only present on L or M protein, we found that both full-length L and M proteins contributed to virus neutralization by the two anti-preS2 antibodies. Thus, immune escape could be a driving force for the selection of M-minus mutations, and especially preS2 deletions. The fact that both L and M proteins could mediate neutralization by anti-preS2 antibodies may shed light on the underlying molecular mechanism.IMPORTANCEThe large (L), middle (M), and small (S) envelope proteins of hepatitis B virus (HBV) contain preS1/preS2/S, preS2/S, and S domain alone, respectively. The discovery of heparan sulfate proteoglycans and sodium taurocholate cotransporting polypeptide (NTCP) as the low- and high-affinity HBV receptors could explain neutralizing potential of anti-S and anti-preS1 antibodies, respectively, but how anti-preS2 neutralizing antibodies work remains enigmatic. In this study, we found two M-minus mutants in the context of genotype D partially escaped two anti-preS2 neutralizing antibodies in NTCP-reconstituted HepG2 cells, while several naturally occurring preS2 deletion mutants escaped both antibodies. By point mutations to eliminate or enhance M protein expression, and by introducing preS2 deletion selectively to L or M protein, we found binding of anti-preS2 antibodies to both L and M proteins contributed to neutralization of wild-type HBV infectivity. Our finding may shed light on the possible mechanism(s) whereby anti-preS2 antibodies neutralize HBV infectivity.

Realm of hepatitis E: Challenges and opportunities

Hepatitis E virus (HEV), responsible for widespread viral hepatitis, infects approximately 2.3 billion individuals globally, with a significant mortality burden in Asia. The virus, primarily transmitted through contaminated water and undercooked meat, is often underdiagnosed, particularly in immunocompromised patients. Current HEV treatments, while effective, are limited by adverse effects, necessitating research into safer alternatives. Moreover, HEV's extrahepatic manifestations, impacting the nervous and renal systems, remain poorly understood. This study underscores the imperative for enhanced HEV research, improved diagnostic methods, and more effective treatments, coupled with increased public health awareness and preventive strategies.

Point-of-Care Testing for Hepatitis Viruses: A Growing Need

Viral hepatitis, caused by hepatitis A virus (HAV), hepatitis B virus (HBV), hepatitis C virus (HCV), hepatitis D virus (HDV), or hepatitis E virus (HEV), is a major global public health problem. These viruses cause millions of infections each year, and chronic infections with HBV, HCV, or HDV can lead to severe liver complications; however, they are underdiagnosed. Achieving the World Health Organization's viral hepatitis elimination goals by 2030 will require access to simpler, faster, and less expensive diagnostics. The development and implementation of point-of-care (POC) testing methods that can be performed outside of a laboratory for the diagnosis of viral hepatitis infections is a promising approach to facilitate and expedite WHO's elimination targets. While a few markers of viral hepatitis are already available in POC formats, tests for additional markers or using novel technologies need to be developed and validated for clinical use. Potential methods and uses for the POC testing of antibodies, antigens, and nucleic acids that relate to the diagnosis, monitoring, or surveillance of viral hepatitis infections are discussed here. Unmet needs and areas where additional research is needed are also described.

Novel Assays to Solve the Clinical and Scientific Challenges of Chronic Hepatitis B

Chronic infection with Hepatitis B is a common, incurable, and deadly infection. Despite inexpensive laboratory tests for diagnosis and management that have been established for decades, the worldwide rate of diagnosis is only ∼10%, and ∼5% of people are under treatment. Novel assays have been developed to improve linkage to care by providing more flexible approaches to determine a patient's health status. Other assays have been established to better investigate intrahepatic host-virus interactions to support clinical trials for cure research. This review outlines the clinical and scientific challenges still to be solved and the upcoming methods used to address them.

New technologies and reagents in lateral flow assay (LFA) designs for enhancing accuracy and sensitivity

Lateral flow assays (LFAs) are a popular method for quick and affordable diagnostic testing because they are easy to use, portable, and user-friendly. However, LFA design has always faced challenges regarding sensitivity, accuracy, and complexity of the operation. By integrating new technologies and reagents, the sensitivity and accuracy of LFAs can be improved while minimizing the complexity and potential for false positives. Surface enhanced Raman spectroscopy (SERS), photoacoustic techniques, fluorescence resonance energy transfer (FRET), and the integration of smartphones and thermal readers can improve LFA accuracy and sensitivity. To ensure reliable and accurate results, careful assay design and validation, appropriate controls, and optimization of assay conditions are necessary. Continued innovation in LFA technology is crucial to improving the reliability and accuracy of rapid diagnostic testing and expanding its applications to various areas, such as food testing, water quality monitoring, and environmental testing.

Recent Advances in Quantum Dot-Based Lateral Flow Immunoassays for the Rapid, Point-of-Care Diagnosis of COVID-19

The COVID-19 pandemic has spurred demand for efficient and rapid diagnostic tools that can be deployed at point of care to quickly identify infected individuals. Existing detection methods are time consuming and they lack sensitivity. Point-of-care testing (POCT) has emerged as a promising alternative due to its user-friendliness, rapidity, and high specificity and sensitivity. Such tests can be conveniently conducted at the patient's bedside. Immunodiagnostic methods that offer the rapid identification of positive cases are urgently required. Quantum dots (QDs), known for their multimodal properties, have shown potential in terms of combating or inhibiting the COVID-19 virus. When coupled with specific antibodies, QDs enable the highly sensitive detection of viral antigens in patient samples. Conventional lateral flow immunoassays (LFAs) have been widely used for diagnostic testing due to their simplicity, low cost, and portability. However, they often lack the sensitivity required to accurately detect low viral loads. Quantum dot (QD)-based lateral flow immunoassays have emerged as a promising alternative, offering significant advancements in sensitivity and specificity. Moreover, the lateral flow immunoassay (LFIA) method, which fulfils POCT standards, has gained popularity in diagnosing COVID-19. This review focuses on recent advancements in QD-based LFIA for rapid POCT COVID-19 diagnosis. Strategies to enhance sensitivity using QDs are explored, and the underlying principles of LFIA are elucidated. The benefits of using the QD-based LFIA as a POCT method are highlighted, and its published performance in COVID-19 diagnostics is examined. Overall, the integration of quantum dots with LFIA holds immense promise in terms of revolutionizing COVID-19 detection, treatment, and prevention, offering a convenient and effective approach to combat the pandemic.

Lateral Flow Assay for Hepatitis B Detection: A Review of Current and New Assays

From acute to chronic hepatitis, cirrhosis, and hepatocellular cancer, hepatitis B infection causes a broad spectrum of liver diseases. Molecular and serological tests have been used to diagnose hepatitis B-related illnesses. Due to technology limitations, it is challenging to identify hepatitis B infection cases at an early stage, particularly in a low- and middle-income country with constrained resources. Generally, the gold-standard methods to detect hepatitis B virus (HBV) infection requires dedicated personnel, bulky, expensive equipment and reagents, and long processing times which delay the diagnosis of HBV. Thus, lateral flow assay (LFA), which is inexpensive, straightforward, portable, and operates reliably, has dominated point-of-care diagnostics. LFA consists of four parts: a sample pad where samples are dropped; a conjugate pad where labeled tags and biomarker components are combined; a nitrocellulose membrane with test and control lines for target DNA-probe DNA hybridization or antigen-antibody interaction; and a wicking pad where waste is stored. By modifying the pre-treatment during the sample preparation process or enhancing the signal of the biomarker probes on the membrane pad, the accuracy of the LFA for qualitative and quantitative analysis can be improved. In this review, we assembled the most recent developments in LFA technologies for the progress of hepatitis B infection detection. Prospects for ongoing development in this area are also covered.

Lateral Flow Immunoassay for Proteins

Protein biomarkers are useful for disease diagnosis. Identification thereof using in vitro diagnostics such as lateral flow immunoassays (LFIAs) has attracted considerable attention due to their low cost and ease of use especially in the point of care setting. Current challenges, however, do remain with respect to material selection for each component in the device and the synergistic integration of these components to display detectable signals. This review explores the principle of LFIA for protein biomarkers, device components including biomaterials and labeling methods. Medical applications and commercial status are examined as well. This review highlights critical methodologies in the development of new LFIAs and their role in advancing healthcare worldwide.

Methods and Advances in the Design, Testing and Development of In Vitro Diagnostic Instruments

With the continuous improvement of medical testing and instrumentation engineering technologies, the design, testing and development methods of in vitro diagnostic instruments are developing rapidly. In vitro diagnostic instruments are also gradually developing into a class of typical high-end medical equipment. The design of in vitro diagnostic instruments involves a variety of medical diagnostic methods and biochemical, physical and other related technologies, and its development process involves complex system engineering. This paper systematically organizes and summarizes the design, testing and development methods of in vitro diagnostic instruments and their development in recent years, focusing on summarizing the related technologies and core aspects of the R&D process, and analyzes the development trend of the in vitro diagnostic instrument market.

Colorimetric-photothermal-magnetic three-in-one lateral flow immunoassay for two formats of biogenic amines sensitive and reliable quantification

Rapid, simple, sensitive and reliable approaches for biogenic amines quantification in various food samples are essential to food safety. Lateral flow immunoassay (LFIA) has been wildly utilized in point-of-care testing (POCT) owing to its advantage of flexibility and feasibility. Here, we reported a Fe₃O₄@Au nanoparticles (NPs) (Fe₃O₄@AuNPs) based multimodal readout LFIA for rapid putrescine (Put) and histamine (His) quantification with a LOD down to 10 and 10 ng/mL in naked eye mode, 2.31 and 4.39 ng/mL in photothermal mode, 0.17 and 0.31 ng/mL in magnetic mode, respectively. Such multi-mode assay has been successfully used to detect Biogenic amines (BAs) in raw aquatic foods, including fish, prawns, beef, and pork, with overall recoveries ranging from 93.68 to 109.34%. Meanwhile, it is easily expanded to detect other typical BAs with high sensitivity by simply replacing antibodies. In view of the multi-signal reading, two quantitative formats, and high sensitivity, it may greatly widen the application of lateral flow detection in food safety.

High brightness red emitting polymer beads for immunoassays: Comparison between trifluoroacetylacetonates of Europium

Efficiently luminescing spherical polymer particles (beads) in the nanoscale regime of up to approximately 250 nm have become very valuable tools in bioanalytical assays. Eu³⁺- complexes imbedded in polymethacrylate and polystyrene in particular proved to be extraordinarily useful in sensitive immunochemical and multi-analyte assays, and histo- and cytochemistry. Their obvious advantages derive from both, the possibility to realize very high ratios of emitter complexes to target molecules, and the intrinsically long decay times of the Eu³⁺-complexes, which allows an almost complete discrimination against bothersome autofluorescence via time-gated measuring techniques; the narrow line emission in conjunction with large apparent Stokes shifts are additional benefits with regard to spectral separation of excitation and emission with optical filters. Last but not least, a reasonable strategy to couple the beads to the analytes is mandatory. We have thus screened a variety of complexes and ancillary ligands; the four most promising candidates evaluated and compared to each other were β-diketonates (trifluoroacetylacetonates, R-CO-CH-CO-CF₃, R = - thienyl, -phenyl, -naphthyl and -phenanthryl); highest solubilities in polystyrene were obtained with trioctylphosphine co-ligands. All beads had overall quantum yields in excess of 80% as dried powders and lifetimes well beyond 600 µs. Core-shell particles were devised for the conjugation to model proteins (Avidine, Neutravidine). Their applicability was tested in biotinylated titer plates using time gated measurements and a Lateral Flow Assay as practical examples.

An integrated fluorescent lateral flow assay for multiplex point-of-care detection of four respiratory viruses

This work established a highly sensitive and specific quantum dot nanobeads-based lateral flow assay for multiplex detection of four respiratory virus markers at point of care. The respiratory virus antigens were detected by fluorescent lateral flow strips within 20 min. The limits of detection for SARS-CoV-2 antigen, IAV antigen, IBV antigen, and ADV antigen were 0.01 ng/mL, 0.05 ng/mL, 0.31 ng/mL, and 0.40 ng/mL, respectively, which were superior to that of conventional AuNPs-based colorimetric lateral flow assay. The coefficients of variation of the test strip were 6.09%, 2.24%, 7.92%, and 12.43% for these four antigens, which indicated that the proposed method had good repeatability. The specificity of the detection system was verified by different combinations of these four respiratory viruses and several other respiratory pathogens. These results indicated that this method could simultaneously detect SARS-CoV-2, IAV, IBV and ADV in a short assay time, showing the remarkable potential for the rapid and multiplex detection of respiratory viruses in resource-limited settings.

Lateral flow assays for viruses diagnosis: Up-to-date technology and future prospects

Bacteria, viruses, and parasites are harmful microorganisms that cause infectious diseases. Early detection of diseases is critical to prevent disease transmission and provide epidemic preparedness, as these can cause widespread deaths and public health crises, particularly in resource-limited countries. Lateral flow assay (LFA) systems are simple-to-use, disposable, inexpensive diagnostic devices to test biomarkers in blood and urine samples. Thus, LFA has recently received significant attention, especially during the pandemic. Here, first of all, the design principles and working mechanisms of existing LFA methods are examined. Then, current LFA implementation strategies are presented for communicable disease diagnoses, including COVID-19, zika and dengue, HIV, hepatitis, influenza, malaria, and other pathogens. Furthermore, this review focuses on an overview of current problems and accessible solutions in detecting infectious agents and diseases by LFA, focusing on increasing sensitivity with various detection methods. In addition, future trends in LFA-based diagnostics are envisioned.

Quantum Dot-Based Lateral Flow Immunoassay as Point-of-Care Testing for Infectious Diseases: A Narrative Review of Its Principle and Performance

Infectious diseases are the world’s greatest killers, accounting for millions of deaths worldwide annually, especially in low-income countries. As the risk of emerging infectious diseases is increasing, it is critical to rapidly diagnose infections in the early stages and prevent further transmission. However, current detection strategies are time-consuming and have exhibited low sensitivity. Numerous studies revealed the advantages of point-of-care testing, such as those which are rapid, user-friendly and have high sensitivity and specificity, and can be performed at a patient’s bedside. The Lateral Flow Immunoassay (LFIA) is the most popular diagnostic assay that fulfills the POCT standards. However, conventional AuNPs-LFIAs are moderately sensitive, meaning that rapid detection remains a challenge. Here, we review quantum dot (QDs)-based LFIA for highly sensitive rapid diagnosis of infectious diseases. We briefly describe the principles of LFIA, strategies for applying QDs to enhance sensitivity, and the published performance of the QD-LFIA tested against several infectious diseases.

A gold nanoparticle-based lateral flow immunoassay for atrazine point-of-care detection using a handhold scanning device as reader

A method is described to achieve accurate quantitative detection of atrazine (ATZ) in maize by using lateral flow strips based on gold nanoparticles (GNPs) and a handheld scanning reader. GNPs of 15 nm in diameter were applied as label, and a lateral flow immune assay strip was prepared. The linear range was 5.01-95.86 ng mL^-1 with a detection limit of 4.92 ng mL^-1 in phosphate buffer, 4 times better than the readout by the naked eye. ATZ-spiked corn samples were also analysed. The accuracy of results of spiked samples was confirmed by ELISA and liquid chromatography-tandem mass spectrometry (HPLC), which proved the reliability of the proposed method. A handhold device with an optical scanning system was designed for on-site quantitative detection. Combined with the pretreatment, the assay could be completed in less than 20 min.

5' preS1 mutations to prevent large envelope protein expression from hepatitis B virus genotype A or genotype D markedly increase polymerase-envelope fusion protein

Hepatitis B virus (HBV) large (L) envelope protein is translated from 2.4-kb RNA. It contains preS1, preS2, and S domains and is detected in Western blot as p39 and gp42. The 3.5-kb pregenomic RNA produces core and polymerase (P) proteins. We generated L-minus mutants of a genotype A clone and a genotype D clone from 1.1mer or 1.3mer construct, with the former overproducing pregenomic RNA. Surprisingly, mutating preS1 ATG codon(s) or introducing a nonsense mutation soon afterwards switched secreted p39/gp42 into p41/p44 doublet, with its amount further increased by a nonsense mutation in the core gene. A more downstream preS1 nonsense mutation prevented p41/p44 production. Tunicamycin treatment confirmed p44 as glycosylated form of p41. In this regard splicing of 3.5-kb RNA to generate nt2447-nt2902 junction for genotype D enables translation of p43, with N-terminal 47 residues of P protein fused to C-terminal 371 residues of L protein. Indeed p41/p44 were detectable by an antibody against N-terminus of P protein, and eliminated by a nonsense mutation at 5' P gene or a point mutation to prevent that splicing. Therefore, lost L (and core) protein expression from 1.1mer or 1.3mer construct markedly increased p41/p44 (p43), the P-L fusion protein. Co-transfection with an expression construct for L/M proteins reversed high extracellular p41/p44 associated with L-minus mutants, suggesting that L protein retains p43 in wild-type HBV to promote its intracellular degradation. Considering that p43 lacks N-terminal preS1 sequence critical for receptor binding, its physiological significance during natural infection and therapeutic potential warrant further investigation. IMPORTANCE The large (L) envelope protein of hepatitis B virus (HBV) is translated from 2.4-kb RNA and detected in Western blot as p39 and gp42. Polymerase (P) protein is expressed at a low level from 3.5-kb RNA. The major spliced form of 3.5-kb RNA will produce a fusion protein between the first 47 residues of P protein and a short irrelevant sequence, although also at a low level. Another spliced form has the same P protein sequence fused to L protein missing its first 18 residues. We found that some point mutations to eliminate L and core protein expression from overlength HBV DNA constructs converted p39/gp42 into p41/gp44, which turned out to be that P-L fusion protein. Thus, the P-L fusion protein can be expressed at extremely high level when L protein expression is prevented. The underlying mechanism and functional significance of this variant form of L protein warrant further investigation.

Tailor-Made Immunochromatographic Test for the Detection of Multiple 17α-Methylated Anabolics in Dietary Supplements

In recent years, the undeclared presence of various anabolic androgenic steroids (AAS) in commercial supplements has been confirmed. This fact can be a potential threat to all athletes using these supplements, and therefore, there is of increased interest in the implementation of rapid methods for the detection of AAS. The presented study describes the development of an immunostrip test for the detection of multiple 17α-methylated AAS based on direct and indirect competitive principle using gold nanoparticles as a label. As a capture reagent on test lines conjugated stanazolol to rabbit serum albumin (RSA/ST-3) was used, the intensity of color formed in the test line of the AAS-positive sample was visually distinguishable from that of negative sample within 10 min. The optimized closed direct and indirect format of the test provided a similar visual detection limit (0.7 and 0.9 ng/mL, respectively). The most commonly orally abused AAS (17α-methyltestosterone, methandienone, methyldihydrotestosterone, oxandrolone and oxymetholone) showed a strong cross-reaction. Developed immunostrips were successfully applied to analysis of artificially contaminated dietary supplements with 17α-methylated AASs. The developed immunostrips offer potential as a useful user-friendly method for capturing suspicious dietary supplement samples with different contents of AAS at levels far below the usually used concentrations of AAS.

Lateral flow immunoassay for furazolidone point-of-care testing: Cater to the call of saving time, labor, and cost by coomassie brilliant blue labeling

Furazolidone (FZD) and its metabolite called 3-amino-2-oxazolidinone (AOZ) would induce carcinogenic and mutagenic effects to human. In this work, to develop a novel, stable, and simple point of care testing (POCT) with a potential to social applied for FZD detection, we utilized the aspect of protein staining of coomassie brilliant blue (CBB) to exploit a new CBB-LFIA strategy free of NPs. Only one mixing step is needed during the probe manufacturing process, which requires just 2 h and is a great time saving strategy compared with other methods (requiring 4-33 h for probe preparation). Besides, the cost of CBB-LFIA is 300 times lesser than other LFIA with respect to obtaining the label. The developed CBB-LFIA was successfully applied to detect AOZ with a detection limit of 2 ng mL^-1, without any influence from other potential interfering compounds. The proposed CBB-LFIA exhibited prominent practical application, and possesses considerable utilization potential in the related field.

Gas-propelled biosensors for quantitative analysis

Gas-propelled biosensors display a simple gas-based signal amplification with quantitative detection features based on the target recognition event in combination with gas propulsion. Due to the liquid-gas conversion, the gas not only pushes the ink bar forward in the microchannel, but also serves as the power to propel the micromotors in the liquid. Thus, this continuous motion leads to a shift in distances which is associated with the target amount. Therefore, gas-propelled biosensors provide a visual quantification based on distance or speed signals without the need for expensive instruments. In this review, we focus on current developments in gas-propelled biosensors for quantitative analysis. First, we list the types of gas utilized as actuators in biosensors. Second, we review the representative gas-propelled biosensors, including the propulsion mechanisms and fabrication methods. Moreover, gas-propelled quantification based on distance and speed is summarized. Finally, we cover applications and provide a future perspective of gas-propelled biosensors.

Upconverting nanoparticle reporter-based highly sensitive rapid lateral flow immunoassay for hepatitis B virus surface antigen

Detection of hepatitis B Virus surface antigen (HBsAg) is an established method for diagnosing both acute and chronic hepatitis B virus (HBV) infection. In addition to enzyme immunoassays (EIAs), rapid diagnostic tests (RDTs) are available for the detection of HBsAg in resource-poor settings. However, the available RDTs have inadequate sensitivity and therefore are not suitable for diagnosis of patients with low levels of HBsAg and for blood screening. To provide a high-sensitivity RDT, we developed a lateral flow immunoassay (LFIA) for HBsAg utilizing upconverting nanoparticle (UCNP) reporter. The UCNP-LFIA can use whole blood, serum, or plasma and the results can be read in 30 min using a reader device. When compared with a commercial conventional visually read LFIA, the developed UCNP-LFIA had a Limit of Detection (LoD) of 0.1 IU HBsAg/ml in spiked serum, whereas the LoD of the conventional LFIA was 3.2 IU HBsAg/ml. The developed UCNP-LFIA fulfills the WHO criterion for blood screening (LoD ≤ 0.13 IU HBsAg/ml) in terms of LoD. The UCNP-LFIA and conventional LFIA were evaluated with well-characterized sample panels. The UCNP-LFIA detected 20/24 HBsAg-positive samples within the HBsAg Performance Panel and 8/10 samples within the Mixed Titer Performance Panel, whereas the conventional LFIA detected 8/24 and 4/10 samples in these panels, respectively. The performance of the assays was further evaluated with HBsAg-positive (n = 108) and HBsAg-negative (n = 315) patient samples. In comparison with a central laboratory test, UCNP-LFIA showed 95.4% (95% CI: 89.5-98.5%) sensitivity whereas sensitivity of the conventional LFIA was 87.7% (95%CI: 79.9-93.3%).

A quantum dot-based lateral flow immunoassay for the rapid, quantitative, and sensitive detection of specific IgE for mite allergens in sera from patients with allergic rhinitis

The prevalence of allergic rhinitis (AR) is increasing worldwide. However, the current systems used to measure levels of immunoglobulin E (IgE) in sera are associated with several disadvantages that limit their further application. Consequently, there is a need to develop novel highly sensitive strategies that can rapidly detect IgE in a quantitative manner. The development of such systems will significantly enhance our ability to diagnose, treat, and even prevent AR. Herein, we describe our experience of using quantum dot-based lateral flow immunoassay (QD-LFIA), combined with a portable fluorescence immunoassay chip detector (PFICD), to detect serum-specific IgE against Dermatophagoides pteronyssinus (Der-p) and Dermatophagoides farinae (Der-f), two common mite allergens in China. Our data showed that our system could detect serum-specific levels of IgE against Der-p and Der-f as low as 0.093 IU/mL and 0.087 IU/mL, respectively. We also established a standard curve to determine serum-specific IgE concentrations that correlated well with the clinical BioIC microfluidics system. The sensitivity of our assay was 96.7% for Der-p and 95.5% for Der-f, while the specificity was 87.2% for Der-p and 85.3% for Der-f. Collectively, our results demonstrate that QD-LFIA is a reliable system that could be applied to detect serum-specific IgE in accordance with clinical demands. This QD-LFIA strategy can be applied at home, in hospitals, and in pharmacies, with reduced costs and time requirements when compared with existing techniques. In the future, this system could be developed to detect other types of allergens and in different types of samples (for example, whole blood).

Graphical abstract

Dual-color magnetic-quantum dot nanobeads as versatile fluorescent probes in test strip for simultaneous point-of-care detection of free and complexed prostate-specific antigen

Simultaneous detection of free and complexed prostate-specific antigen (f-PSA and c-PSA) is critical to the prostate cancer (PCa) diagnostic accuracy for clinical samples with PSA values in the diagnostic gray zone between 4 and 10 ng mL^-1. Herein, red and green magnetic-quantum dot nanobeads (MQBs) with superior magnetic property and high luminescence were fabricated via polyethyleneimine-mediated electrostatic adsorption of numerous quantum dots onto superparamagnetic Fe₃O₄ magnetic cores, and were conjugated with f-PSA antibody and c-PSA antibody, respectively, as versatile fluorescent probes in test strip for immune recognition, magnetic enrichment, and simultaneous detection of f-PSA and c-PSA analytes in complex biological matrix with t-PSA antibody on the test line. A low-cost and portable smartphone readout device with an application was also developed for the imaging of dual-color test strips and data processing. This assay can simultaneously detect f-PSA and c-PSA with the limits of detection of 0.009 ng mL^-1 and 0.087 ng mL^-1, respectively. Clinical serum samples of PCa and benign prostatic hyperplasia patients were evaluated to confirm the clinical feasibility. The results suggest that the proposed dual-color MQBs-based fluorescent lateral flow immunoassay is a promising point-of-care diagnostics technique for the accurate diagnosis of PCa even in resource-limited settings.

Lateral and Vertical Flow Assays for Point-of-Care Diagnostics

Lateral flow assays (LFAs) have been the pillar of rapid point-of-care (POC) diagnostics due to their simplicity, rapid process, and low cost. Recent advances in sensitivity, selectivity, and chemical stability enhancement have ensured the foothold of LFAs in commercial POC diagnostics. This paper reviews recent developments in labeling strategies and detection methods of LFAs. Moreover, vertical flow assays (VFAs) have emerged as an alternate paper-based assay due to faster detection time and unique multiplexing capabilities. Smartphones as LFA readers have been transformed into a universal integrated platform for imaging, data processing, and storage, providing quantitative results in low-resource settings. Commercial LFAs and VFAs products are evaluated with regards to their performance, market trends, and regulatory issues. The future outlook of the flow-based assays for POC diagnostics is also discussed.

Smartphone-based fluorescent lateral flow immunoassay platform for highly sensitive point-of-care detection of Zika virus nonstructural protein 1

Simple, inexpensive, and rapid diagnostic tests in low-resource settings with limited laboratory equipment and technical expertise are instrumental in reducing morbidity and mortality from epidemic infectious diseases. We developed a smartphone-based fluorescent lateral flow immunoassay (LFIA) platform for the highly sensitive point-of-care detection of Zika virus nonstructural protein 1 (ZIKV NS1). An attachment was designed and 3D-printed to integrate the smartphone with external optical and electrical components, enabling the miniaturization of the instrument and reduction in cost and complexity. Quantum dot microspheres were utilized as probes in fluorescent LFIA because of their extremely bright fluorescence signal. This approach can achieve quantitative point-of-care detection of ZIKV NS1 within 20 min. Limits of detection (LODs) in buffer and serum were 0.045 and 0.15 ng mL^-1, respectively. Despite the high structural similarity, a high-level Dengue virus NS1 as interferent showed limited cross-reactivity. Furthermore, this assay was successfully applied to detecte ZIKV NS1 and virions spiked in complex biological samples, indicating its practical application capability. Given its low cost, compact size, and excellent analytical performance, the proposed smartphone-based fluorescent LFIA platform holds considerable potential in rapid and accurate point-of-care detection of ZIKV NS1 and provides new insight into the design and application of molecular diagnostic methods in low-resource settings.

Voltammetric determination of attomolar levels of a sequence derived from the genom of hepatitis B virus by using molecular beacon mediated circular strand displacement and rolling circle amplification

The authors describe an electrochemical method for the determination of the single-stranded DNA (ssDNA) oligonucleotide with a sequence derived from the genom of hepatitis B virus (HBV). It is making use of circular strand displacement (CSD) and rolling circle amplification (RCA) strategies mediated by a molecular beacon (MB). This ssDNA hybridizes with the loop portion of the MB immobilized on the surface of a gold electrode, while primer DNA also hybridizes with the rest of partial DNA sequences of MB. This triggers the MB-mediated CSD. The RCA is then initiated to produce a long DNA strand with multiple tandem-repeat sequences, and this results in a significant increase of the differential pulse voltammetric response of the electrochemical probe Methylene Blue at a rather low working potential of -0.24 V (vs. Ag/AgCl). Under optimal experimental conditions, the assay displays an ultrahigh sensitivity (with a 2.6 aM detection limit) and excellent selectivity. Response is linear in the 10 to 700 aM DNA concentration range. Graphical abstract Schematic of a voltammetric method for the determination of attomolar levels of target DNA. It is based on molecular beacon mediated circular strand displacement and rolling circle amplification strategies. Under optimal experimental conditions, the assay displays an ultrahigh sensitivity with a 2.6 aM detection limit and excellent selectivity.

Infectious pathogens meet point-of-care diagnostics

The field of point-of-care (POC) diagnostics provides the rapid diagnosis of infectious diseases which is essential and critical for improving the general public health in resource-limited settings. POC platforms offer many advantages for detection of various pathogens including portability, automation, speed, cost, and efficiency. In this review, we provide an overview of the recent trends for POC diagnostics of infectious diseases with focus on portable platforms. We review here the present status of POC platforms, emphasizing in period of the past three years, then extrapolate their advance into the future applications for diagnosis of infectious pathogens.

Role of quantitative hepatitis B core antibody levels in predicting significant liver inflammation in chronic hepatitis B patients with normal or near-normal alanine aminotransferase levels

AIM

Chronic hepatitis B (CHB) patients with normal alanine aminotransferase (ALT) levels are not free from significant hepatic lesions. Recently, there has been an improved understanding of the clinical significance of quantitative hepatitis B core antibody levels (qAnti-HBc) during CHB management. In this cross-sectional study, we evaluated the utility of qAnti-HBc in identifying significant liver inflammation in CHB patients.

METHODS

A total of 469 patients (training set, n = 363; validation set, n = 106) who underwent liver biopsy (LB) were included. The qAnti-HBc levels were quantified and the relationship between histology and serum markers was systematically analyzed.

RESULTS

In the training set, qAnti-HBc levels were found to have significant diagnostic value for moderate to severe liver inflammation (≥G2) in all patients (area under the receiver operating characteristic curve [AUROC] = 0.768; 95% confidence interval [CI], 0.721-0.810; P < 0.001) and in patients with normal or near-normal ALT levels (AUROC = 0.767; 95% CI, 0.697-0.828; P < 0.001). Our novel index (AC index) for the identification of ≥G2 inflammation, which combined the qAnti-HBc and ALT levels, significantly improved diagnostic performance (AUROC = 0.813; 95% CI, 0.768-0.852) compared to the use of ALT alone (AUROC = 0.779; 95% CI, 0.732-0.821) in all patients. In the validation set, the AC index showed an improved AUROC of 0.890 (95% CI, 0.814-0.942) and 0.867 (95% CI, 0.749-0.943) in all patients and patients with normal ALT levels, respectively.

CONCLUSIONS

The qAnti-HBc level predicts significant liver inflammation well, even in patients with normal or near-normal ALT levels. Compared with the conventional ALT level, the AC index is a more reliable non-invasive biomarker for significant liver inflammation in CHB patients.

Inkjet-printed barcodes for a rapid and multiplexed paper-based assay compatible with mobile devices

This study reports a simple, rapid, low-cost, robust, and multiplexed barcoded paper-based assay (BPA) compatible with mobile devices. An inkjet printer and an XYZ dispensing platform were used to realize mass-manufacturing of barcoded paper-based analytical devices (BPADs) with high precision and efficiency. We designed a new group of barcodes and developed an application (APP) for the reading of the new code. The new barcodes possess a 16 times higher coding capacity than the standard Codabar code in our experiment on drug residue detection. The BPA system allows applications in the assays of blood-transmitted infections, drug residues in milk and multiplex nucleic acids. The whole detection process and the readout of the results can be completed within 10 minutes. The limit of detection for enrofloxacin (ENR) (8 ng mL^-1) satisfies the requirements of drug residue monitoring. Its high rapidity, simplicity, efficiency and selectivity make the BPA system extremely suitable to be applied in rapid and on-site detection.

Classification of human and zoonotic group hepatitis E virus (HEV) using antigen detection

Hepatitis E virus (HEV) is one of the major pathogens that cause acute viral hepatitis. The human (genotypes 1 and 2) and zoonotic (genotypes 3 and 4) groups of HEV present different epidemiology and clinical features. In this study, we developed a classification method for rapidly classifying HEV into human or zoonotic groups that combines a general antigen test with a zoonotic group-specific antigen test. Evaluation of serial samples from HEV-infected rhesus monkeys indicated that HEV antigen-positive samples can be classified using the antigen-based classification method. The antigen-based classification method was evaluated further on 55 genotyped samples from acute hepatitis E patients, including 9 human and 46 zoonotic groups. The novel method was completely consistent with the sequencing results: 9/9 for the human groups (100%, 95% confidence interval [CI] 66.4-100%) and 46/46 for the zoonotic groups (100%, 95% CI 92.3-100%). This method was also successfully used for the clustering of some samples that could not be clustered by sequencing. Compared with the sequencing-based method, this method is less time-consuming, less expensive, and less technically complex and is therefore ideal for large numbers of samples. In conclusion, this study provides a convenient and sensitive method for classifying different groups of HEV, and it has potentially important public health applications, especially in underdeveloped areas that cannot afford the high cost of nucleic acid testing.

Lateral flow assays

Lateral flow assays (LFAs) are the technology behind low-cost, simple, rapid and portable detection devices popular in biomedicine, agriculture, food and environmental sciences. This review presents an overview of the principle of the method and the critical components of the assay, focusing on lateral flow immunoassays. This type of assay has recently attracted considerable interest because of its potential to provide instantaneous diagnosis directly to patients. The range and interpretation of results and parameters used for evaluation of the assay will also be discussed. The main advantages and disadvantages of LFAs will be summarized and relevant future improvements to testing devices and strategies will be proposed. Finally, the major recent advances and future diagnostic applications in the LFA field will be explored.

Antibody-mediated immunotherapy against chronic hepatitis B virus infection

The currently available drugs to treat hepatitis B virus (HBV) infection include interferons and nucleos(t)ide analogs, which can only induce disease remission and are inefficient for the functional cure of patients with chronic HBV infection (CHB). Since high titers of circulating hepatitis B surface antigen (HBsAg) may be essential to exhaust the host anti-HBV immune response and they cannot be significantly reduced by current drugs, new antiviral strategies aiming to suppress serum hepatitis B surface antigen (HBsAg) could help restore virus-specific immune responses and promote the eradication of the virus. As an alternative strategy, immunotherapy with HBsAg-specific antibodies has shown some direct HBsAg suppression effects in several preclinical and clinical trial studies. However, most described previously HBsAg-specific antibodies only had very short-term HBsAg suppression effects in CHB patients and animal models mimicking persistent HBV infection. More-potent antibodies with long-lasting HBsAg clearance effects are required for the development of the clinical application of antibody-mediated immunotherapy for CHB treatment. Our recent study described a novel mAb E6F6 that targets a unique epitope on HBsAg. It could durably suppress the levels of HBsAg and HBV DNA via Fcγ receptor-dependent phagocytosis in vivo. In this commentary, we summarize the current research progress, including the therapeutic roles and mechanisms of antibody-mediated HBV clearance as well as the epitope-determined therapeutic potency of the antibody. These insights may provide some clues and guidance to facilitate the development of therapeutic antibodies against persistent viral infection.

A novel toolbox for the in vitro assay of hepatitis D virus infection

Hepatitis D virus (HDV) is a defective RNA virus that requires the presence of hepatitis B virus (HBV) for its life cycle. The in vitro HDV infection system is widely used as a surrogate model to study cellular infection with both viruses owing to its practical feasibility. However, previous methods for running this system were less efficient for high-throughput screening and large-scale studies. Here, we developed a novel method for the production of infectious HDV by adenoviral vector (AdV)-mediated transduction. We demonstrated that the AdV-based method yields 10-fold higher viral titers than the transient-transfection approach. The HDV-containing supernatant derived from AdV-infected Huh7 cells can be used as the inoculum in infectivity assays without requiring further concentration prior to use. Furthermore, we devloped a chemiluminescent immunoassay (HDV-CLEIA) to quantitatively determine intracellular HDAg with a dynamic range of 5–11,000 pg/mL. HDV-CLEIA can be used as an alternative approach to assess HDV infection. The advantages of our updated methodology were demonstrated through in vitro HDV infection of HepaRG cells and by evaluating the neutralization activity using antibodies that target various regions of the HBV/HDV envelope proteins. Together, the methods presented here comprise a novel toolbox of in vitro assays for studying HDV infection.

Development of Lateral Flow Assay Based on Size-Controlled Gold Nanoparticles for Detection of Hepatitis B Surface Antigen

In this study, we developed lateral flow assay (LFA) biosensors for the detection of hepatitis B surface antigens using well-controlled gold nanoparticles (AuNPs). To enhance colorimetric signals, a seeded growth method was used for the preparation of size-controlled AuNPs with a narrow size distribution. Different sizes of AuNPs in the range of 342–137.8 nm were conjugated with antibodies and then optimized for the efficient detection of LFA biosensors. The conjugation stability was investigated by UV-vis spectroscopy of AuNP dispersion at various pH values and concentrations of antibody. Based on optimized conjugation conditions, the use of 42.7 ± 0.8 nm AuNPs exhibited superior performance for the detection of LFAs relative to other sizes of AuNPs.

A Smartphone-Based Genotyping Method for Hepatitis B Virus at Point-of-Care Settings

We reported a rapid, convenient, and easy-to-use genotyping method for hepatitis B virus (HBV) based on the smartphone at point-of-care (POC) settings. To perform HBV genotyping especially for genotypes A, B, C, and D, a smartphone is used to image and analyze a one-step immunoassay lateral flow strip functionalized with genotype-specific monoclonal antibodies (mAbs) on multiple capture lines. A light-emitting diode (LED) positioned on the top of the lateral flow strip is used to shine the multiple capture lines for excitation. Fluorescence detection is obtained with a smartphone whose camera is used to take the fluorescent images. An intelligent algorithm is developed to first identify each capture line from the fluorescent image and then determine the HBV genotype based on a genotyping model. Based on the pattern of the detection signal from different samples, a custom HBV genotyping model is developed. Custom application software running on a smartphone is developed with Java to collect and analyze the fluorescent image, display the genotyping result, and transmit it if necessary. Compared with the existing methods with nucleic acid analysis, more convenient, instant, and efficient HBV genotyping with significantly lower cost and a simpler procedure can be obtained with the developed smartphone POC HBV genotyping method.

Screening and diagnosis of HBV in low-income and middle-income countries

HBV testing and diagnosis of HBV-related liver disease in low-income and middle-income countries differs substantially from that in developed countries in terms of access to resources and expensive technologies requiring highly specialized staff. For identification and classification of HBV infection, genomic amplification methods to detect and quantify HBV DNA are often nonexistent or available only in central laboratories of major cities. When samples from peripheral locations do arrive, delays in receiving results generate loss to follow-up. Testing is often limited to measurement of hepatitis B surface antigen (HBsAg), alanine aminotransferase levels, aspartate aminotransferase to platelet ratio index and hepatitis B e antigen (HBeAg) to determine indications for antiviral therapy (AVT). Utilization of AVT is limited by cost and availability, particularly when patients are not covered by health insurance. The natural history of HBV infection is influenced by genotypes B and C in East Asia, where decades of immune tolerance have led to mostly vertical transmission; in sub-Saharan Africa, where genotypes A1 and E predominate, infection is transmitted horizontally between young children, followed by a nonreplicative phase. In both regions, cirrhosis and hepatocellular carcinoma are common and would be considerably ameliorated by AVT. Implementation of the HBV vaccine since the 1990s in Asia and 2000s in Africa has decreased the incidence of HBV, but vaccine failure and insufficiently effective prevention remain concerning issues.

Surface-enhanced Raman scattering based lateral flow immunochromatographic assay for sensitive influenza detection

A novel sensitive SERS-lateral flow immunochromatographic integration system using Raman active molecule-coated gold nanostar as reporters for influenza virus detection is reported. Qualitative and quantitative SERS signal detection can be achieved.

Lanthanide chelate-encapsulated polystyrene nanoparticles for rapid and quantitative immunochromatographic assay of procalcitonin

Procalcitonin (PCT) is a potentially specific early marker of bloodstream infection and sepsis.