Detection Of Immunoglobulin G Research Articles

Paper-Based Microfluidic Devices: Low-Cost Platforms for Rapid Biochemical Detection.

We developed low-cost, portable paper-based diagnostic devices for detection of human immunoglobulin M (IgM) and immunoglobulin G (IgG) in serum without any sample preparation. These devices can be used to help identify presence of diseases, used to provide rapid results (<5 minutes), readily used by untrained personnel, employed in austere environments, configured to obtain multiplexed assays, and easily disposed of. We successfully accomplished colorimetric detection of human IgG and human IgM using a sandwich-style assay within the microfluidic paper device via vertical flow immunoassay configuration. The reaction zone in the wax printed paper layer is a small circular pattern. Gold nanoparticles conjugated with anti-human IgG and IgM antibodies have been used for colorimetric detection of IgG or IgM by naked eye. Colorimetric signal can be precisely quantified through implementation of image analysis software which can be developed as an app for a smartphone. The size of the device is 2 cm × 2 cm × 1 mm. Colorimetric detection of human IgG was accomplished at 100 fg/mL concentration using a gold nanoparticle-conjugated anti-human IgG antibody. The developed platform has a dynamic range of IgM and IgG concentrations between 0.1 pg/mL and 100 μg/mL. These devices provided a color readout in <5 minutes using 20 µL of serum. We also demonstrated that the devices show a significant degree of ruggedness and temperature stability as they were able to provide satisfactory results (detection of 0.1 pg/mL IgG) after 14 days of long stability and shelf-life experiment at an elevated temperature of at least 50 ˚C-the shelf life can be as long as 180 days under ambient conditions for detection of 100 µg/mL IgG. Because of the inherent simplicity of the device operation and their ease of use, there is no variation between samples and users of the device. This low-cost approach enables multiplexing with >1 measurement performed in parallel at the same time. We anticipate that because of the sensitivity, specificity, ease of use, and overall reliability, this approach will become a standard for diagnosis of diseases and health conditions.

Detection of Immunoglobulin G (IgG) and Immunoglobulin M (IgM) Antibodies Using Circular Photonic Crystal Fiber Sensor

In this paper, a circular Photonic Crystal fiber (C-PCF) is designed to detect two types of antibodies such as Immunoglobulin G (IgG) and Immunoglobulin M (IgM). Light guiding property of different refractive index (RI) of IgG and IgM are analyzed. For various RI value confinement losses, relative sensitivity and effective mode area are analyzed. The projected C-PCF sensor produces low confinement loss and high sensitivity for the detection of IgM and IgG. Realistic execution of the proposed PCF sensor is viable by accessible technology and it is applicable to sense corona virus disease.

Use of oral fluids to detect anti Lawsonia intracellularis antibodies in experimentally infected pigs

ABSTRACT: Several pathogens and antibodies derived from serum or produced in tissues associated with the oral cavity are present in the oral fluid (OF). Considering the applicability of this alternative sample, recent studies in veterinary medicine have tested OF as a replacement for serum in diagnostic assays. The aim of this study was to standardize the immunoperoxidase monolayer assay (IPMA) to detect anti-Lawsonia intracellularis immunoglobulin A (IgA) and immunoglobulin G (IgG) in OF samples from experimentally infected pigs. Sixty-two pigs were divided into two groups: control (T1, n=30) and inoculated with L. intracellularis (T2, n=32). Blood, OF and fecal samples were collected at 0, 7, 14, 21, 28 and 42 days post-inoculation (dpi). Some adaptations of the standard technique for serum were made to IPMA for the detection of IgA and IgG in OF. The IPMA showed high specificity and sensitivity for serum samples and high specificity and moderate sensitivity for the detection of IgA and IgG in OF. There was high agreement between the results of serum IgG and OF IgA and IgG. Based on our results, oral fluid samples may be used for the evaluation and determination of anti-L. intracellularis antibodies in pigs, but not for individual diagnosis of swine proliferative enteropathy.

Seroprevalence of SARS-CoV-2 IgG Antibodies in Corsica (France), April and June 2020.

Our aim was to assess the seroprevalence of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection after the lockdown in a sample of the Corsican population. Between 16 April and 15 June 2020, 2312 residual sera were collected from patients with a blood analysis conducted in one of the participating laboratories. Residual sera obtained from persons of all ages were tested for the presence of anti-SARS-CoV-2 Immunoglobulin G (IgG) using the EUROIMMUN enzyme immunoassay kit for semiquantitative detection of IgG antibodies against the S1 domain of viral spike protein (ELISA-S). Borderline and positive samples in ELISA-S were also tested with an in-house virus neutralization test (VNT). Prevalence values were adjusted for sex and age. A total of 1973 residual sera samples were included in the study. The overall seroprevalence based on ELISA-S was 5.27% (95% confidence interval (CI), 4.33–6.35) and 5.46% (4.51–6.57) after adjustment. Sex was not associated with IgG detection. However, significant differences were observed between age groups (p-value = 1 E-5). The highest values were observed among 10–19, 30–39, and 40–49 year-old age groups, ranging around 8–10%. The prevalence of neutralizing antibody titers ≥40 was 3% (2.28–3.84). In conclusion, the present study showed a low seroprevalence for COVID-19 in Corsica, a finding that is in accordance with values reported for other French regions in which the impact of the pandemic was low.

Design and Fabrication of Silicon Nanowire-Based Biosensors with Integration of Critical Factors: Toward Ultrasensitive Specific Detection of Biomolecules.

As critical factors affecting the sensing performance of silicon nanowire (SiNW) biosensors, the structure, functional interface, and detection target were analyzed and designed to improve sensing performance. For an improved understanding of the dependence of sensor structure on sensitivity, a simple theoretical analysis was proposed to predict the sensitivity of biosensors with different SiNW types, widths, and doping concentrations. Based on the theoretical analysis, a biosensor integrating optimized critical factors was designed and fabricated. Optimizations focusing on the following aspects are considered: (1) employing n-type SiNW and controlling the impurity doping concentration of SiNW at approximately 2 × 1016-6 × 1016 atoms/cm3 to obtain a suitable charge density, (2) minimizing the SiNW width to 16.0 nm to increase the surface area-to-volume ratio, (3) using a native oxide layer on SiNW as a gate insulator to transport the captured charge molecules closer to the SiNW surface, (4) modifying the SiNW surface by 2-aminoethylphosphonic acid coupling to form a high-density self-assembled monolayer for enhancing the stability bound molecules, and (5) functionalizing the SiNW with ovalbumin molecules for specifically capturing the target immunoglobulin G (IgG) molecules. The sensing performance was evaluated by detecting IgG with concentrations ranging from 6 aM to 600 nM and control experiments. The SiNW biosensor revealed ultrahigh sensitivity and specific detection of target IgG with a measured limit of detection of 6 aM. The integration of the critical SiNW biosensor factors provides a significant possibility of a rapid and ultrasensitive diagnosis of diseases at their early stages.

Seroconversion in patients with cancer and oncology health care workers infected by SARS-CoV-2

BackgroundPatients with cancer have high risk for severe complications and poor outcome to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-related disease [coronavirus disease 2019 (COVID-19)]. Almost all subjects with COVID-19 develop anti-SARS-CoV-2 immunoglobulin G (IgG) within 3 weeks after infection. No data are available on the seroconversion rates of cancer patients and COVID-19.Patients and methodsWe conducted a multicenter, observational, prospective study that enrolled (i) patients and oncology health professionals with SARS-CoV-2 infection confirmed by real-time RT-PCR assays on nasal/pharyngeal swab specimens; (ii) patients and oncology health professionals with clinical or radiological suspicious of infection by SARS-CoV-2; and (iii) patients with cancer who are considered at high risk for infection and eligible for active therapy and/or major surgery. All enrolled subjects were tested with the 2019-nCoV IgG/IgM Rapid Test Cassette, which is a qualitative membrane-based immunoassay for the detection of IgG and IgM antibodies to SARS-CoV-2. The aim of the study was to evaluate anti-SARS-CoV-2 seroconversion rate in patients with cancer and oncology health care professionals with confirmed or clinically suspected COVID-19.ResultsFrom 30 March 2020 to 11 May 2020, 166 subjects were enrolled in the study. Among them, cancer patients and health workers were 61 (36.7%) and 105 (63.3%), respectively. Overall, 86 subjects (51.8%) had confirmed SARS-CoV-2 diagnosis by RT-PCR testing on nasopharyngeal swab specimen, and 60 (36.2%) had a clinical suspicious of COVID-19. Median time from symptom onset (for cases not confirmed by RT-PCR) or RT-PCR confirmation to serum antibody test was 17 days (interquartile range 26). In the population with confirmed RT-PCR, 83.8% of cases were IgG positive. No difference in IgG positivity was observed between cancer patients and health workers (87.9% versus 80.5%; P = 0.39).ConclusionsOur data indicate that SARS-CoV-2-specific IgG antibody detection do not differ between cancer patients and healthy subjects.

Dynamic changes of IgM and IgG in confirmed COVID-19 cases: detection results analysis

Objective To analyze dynamic changes of immunoglobulin M (IgM) and immunoglobulin G (IgG) in 49 confirmed cases of coronavirus disease 2019 (COVID-19) during various periods of the disease and to explore regulations and characteristics of antibodies production against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) for providing evidences for effective prevention and control of COVID-19 epidemic. Methods Totally 114 blood samples were collected from 49 viral nucleic acid detection-confirmed COVID-19 patients (one sample for 17 cases and 2 – 7 samples for 32 cases) and blood samples from another 49 viral nucleic acid negative cases were also collected as controls in Changde city, Hunan province between January 24 and February 22, 2020. Fluorescent immunochromatography was used to detect serum SARS-CoV-2 IgM and IgG and dynamic changes in IgM and IgG were statistically analyzed. Results Of the 114 serum specimens from 49 viral nucleic acid positive cases, 96 (84.21%) were IgM positive and 108 (94.74%) were IgG positive, with a significant difference between the two positive rates (P Conclusion The detection of IgM and IgG is an effective supplement to the nucleic acid tesing for COVID-19. The dynamic monitoring of SARS-CoV-2 IgM and IgG antibody are of significance for COVID-19-related epidemiological survey, therapeutic effect evaluation, and vaccine development.

SARS-CoV-2 seroprevalence and neutralizing activity in donor and patient blood

Given the limited availability of serological testing to date, the seroprevalence of SARS-CoV-2-specific antibodies in different populations has remained unclear. Here, we report very low SARS-CoV-2 seroprevalence in two San Francisco Bay Area populations. Seroreactivity was 0.26% in 387 hospitalized patients admitted for non-respiratory indications and 0.1% in 1,000 blood donors in early April 2020. We additionally describe the longitudinal dynamics of immunoglobulin-G (IgG), immunoglobulin-M (IgM), and in vitro neutralizing antibody titers in COVID-19 patients. The median time to seroconversion ranged from 10.3–11.0 days for these 3 assays. Neutralizing antibodies rose in tandem with immunoglobulin titers following symptom onset, and positive percent agreement between detection of IgG and neutralizing titers was >93%. These findings emphasize the importance of using highly accurate tests for surveillance studies in low-prevalence populations, and provide evidence that seroreactivity using SARS-CoV-2 anti-nucleocapsid protein IgG and anti-spike IgM assays are generally predictive of in vitro neutralizing capacity.

An advanced molecularly imprinted electrochemical sensor for the highly sensitive and selective detection and determination of Human IgG

An advanced molecularly imprinted electrochemical sensor with high sensitivity and selectivity for the detection of Human immunoglobulin G (IgG) was successfully constructed. With acrylamide imprinting systems, surface imprinting on the nanoparticles CuFe2O4 targeted at IgG was employed to prepare molecularly imprinted polymer, which served as recognition element for the electrochemical sensor. Furthermore, the sensor harnessed a molybdenum disulfide (MoS2)@nitrogen doped graphene quantum dots (N-GQDs) with ionic liquid (IL) nanocomposite for signal amplification. Under optimized experimental conditions, the sensor shortened the response time to less than 8 min, and the response was linear at the IgG concentration of 0.1–50 ng·mL−1 with a low detection limit of 0.02 ng·mL−1 (S/N = 3). Our findings suggested that, the sensor exhibited high detectability and long-time stability. The satisfactory results of human serum sample analysis showed that the developed IgG sensor had promising potential clinical applications in detecting IgG content.

Enzyme-amplified SERS immunoassay with Ag-Au bimetallic SERS hot spots

Surface-enhanced Raman scattering (SERS) enables rapid detection of single molecules with high specificity. However, quantitative and sensitive SERS analysis has been a challenge due to the lack of reliable SERS-active materials. In this study, we developed a quantitative SERS-based immunoassay using enzyme-guided Ag growth on Raman labeling compound (RLC)-immobilized gold nanoparticle (Au NP)-assembled silica NPs (SiO2@Au-RLC@Ag). The enzyme amplified Ag+ reduction as well as Ag growth on the RLC-immobilized Au NP-assembled silica NPs (SiO2@Au-RLC), which resulted in a significant increase in SERS signal. In the presence of target antigens such as immunoglobulinG (IgG) or prostate-specific antigen (PSA), Ab1-Antigen-Ab2 immune complex with alkaline phosphatase triggered an enzyme- catalyzed reaction to convert 2-phospho-L-ascorbic acid (2-phospho-L-AA) to ascorbic acid (AA). As produced AA reduced Ag+ to Ag, forming an Ag hot spot on the surface of SiO2@Au-RLC, which enhanced the SERS signal of SiO2@Au-RLC@Ag in a solution with a target antigen concentration. The plasmonic immunoassay for IgG detection showed a high linearity of SERS intensity in the range of 0.6 to 9.0 ng/mL with a detection limit (LOD) of 0.09 ng/mL, while an LOD of 0.006 ng/mL was obtained for PSA. The results indicate that the sensitivity of our novel SERS-based immunoassay is higher than that of conventional enzyme-based colorimetric immunoassays.

Real-Time and Label-Free Monitoring of Biomolecular Interactions within Complex Biological Media Using a Silica Colloidal Crystal Film.

A method capable of real-time and label-free monitoring of biomolecular interactions within whole blood, without any sample separation and label process, is described. This was accomplished using silica colloidal crystal (SCC) films, three-dimensionally ordered silica particle arrays whose interference effect is a function of their optical thickness, as interference-sensitive substrates. Interactions between immunoglobulin G (IgG) and protein A from Staphylococcus aureus (SPA) conjugates with changes in the optical thickness of SCC films were monitored spectroscopically. Successful detection of IgG was achieved in the buffer and whole blood. This system constitutes a simple label-free analysis showing great potential in monitoring interactions between biomolecules in complex biological media.

An Optical Fiber Immunosensor With a Low Detection Limit Based on Plasmon Coupling Enhancement

An optical fiber immunosensor with a low detection limit based on plasmon coupling enhancement is proposed for detecting human immunoglobulin G (IgG). Graphene oxide (GO)-gold nanorod composites are synthesized and modified onto a photonic crystal fiber (PCF) surface coated with a Au film. GO, as a biosensitive layer, is used to decorate the gold nanorods and concentrate target molecules. The experimental result indicates that the refractive index sensitivity is drastically enhanced to 22248 nm/RIU because of plasmon coupling. Correspondingly, the human IgG detection limit decreases to 6 ng/mL. Moreover, the PCF is insensitive to temperature fluctuation, which can further reduce the measurement error.

Diagnostic performance of immunochromatography assay for rapid detection of IgM and IgG in coronavirus disease 2019

Serologic assays have been developed to detect infection with coronavirus disease 2019 (COVID‐19). This study was conducted to evaluate the diagnostic performance of an immunochromatography‐based assay of human serum for COVID‐19. The present study enrolled 149 subjects who had been tested by real‐time reverse transcription‐polymerase chain reaction (RT‐PCR) for COVID‐19 and were classified into two groups: 70 who were positive for COVID‐19 and 79 who were negative for COVID‐19 based on RT‐PCR. An immunochromatography‐based COVID‐19 immunoglobulin G (IgG)/immunoglobulin M (IgM) rapid test on the sera of the study population was applied to measure the sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and receiver operating characteristic (ROC) curve compared to RT‐PCR, with a 95% confidence interval (CI). IgM or IgG antibodies were detected in 65 subjects (92.9%) classified as positive for COVID‐19 and in three subjects (3.8%) classified as negative for COVID‐19. The sensitivity and specificity percentages for IgM or IgG antibodies were 92.9% (95% CI: 84.1‐97.6) and 96.2% (95% CI: 89.3‐99.2), respectively, with 95.6% PPV and 93.8% NPV. The PPV rapidly improved with increasing disease prevalence from 19.8% to 96.1% in the presence of either IgM or IgG, while the NPV remained high with a change from 99.9% to 93.1%. The area under the ROC curve was 0.945 (95% CI: 0.903‐0.988) for subjects with either IgM or IgG positivity. In conclusion, the immunochromatography‐based COVID‐19 IgG/IgM rapid test is a useful and practical diagnostic assay for detection of COVID‐19, especially in the presence of IgM or IgG antibodies.

Detection of Circulating Antibodies to p16 Protein-Derived Peptides in Hepatocellular Carcinoma.

This study aimed at confirming the alteration of circulating anti-p16 immunoglobulin G (IgG) levels in hepatocellular carcinoma (HCC). An in-house-developed enzyme-linked immunosorbent assay was used for determining plasma IgG antibodies against p16-derived antigens in 122 HCC patients and 134 healthy controls. Plasma anti-p16 IgG levels were significantly higher in HCC patients than in the controls (Z = 3.51, P = 0.0004), with no difference between males and females. A trend of increasing plasma anti-p16 IgG levels was associated with increasing HCC stage, with group 3 patients having the highest anti-p16 IgG levels (Z = 3.38, P = 0.0008). Group 3 exhibited the best sensitivity (19.6%) and specificity (95%) for plasma anti-p16 IgG detection, with an area under the receiver operating characteristic curve of 0.659 (95% confidence interval, 0.564-0.754). Circulating IgG antibody to p16 protein might be a useful biomarker for HCC prognosis assessment rather than for early malignancy diagnosis.

Preparation of a Sandwich-like Complex "MIPs-Target Molecule-Magnetic SERS Probe" and SERS Determination of Immunoglobulin G.

Based on the reversible covalent binding between borates and glycoproteins, we proposed a scheme that can specifically recognize and detect immunoglobulin G (IgG). The application of magnetic materials to enrich SERS probes can provide an enhanced signal and repeatability. The results showed that the prepared sandwich-like complex displayed high sensitivity and excellent selectivity for IgG. The Raman peak intensity showed a good linear relationship in the concentration range of 1 mg/mL - 1 ng/mL. The linear equation was y = 657.93x + 2963.9, R2 = 0.996. Parallel testing of this sandwich-like complex proved to have excellent repeatability. This method provided a new possibility for clinical non-immunity and the quantitative detection of IgG.

A dual channel self-compensation optical fiber biosensor based on coupling of surface plasmon polariton

We propose a dual-channel fiber-optic biosensor based on electronic field coupling between surface plasmon resonance (SPR) and localized surface plasmon resonance (LSPR). One sensing channel is coated with a bilayer of graphene oxide/Au, whose surface is modified with goat anti-human immunoglobulin G (IgG) to detect human IgG labeled with Au nanoparticles (Au NPs). The graphene oxide film in the region of the coupled electric fields increases the loading of biomolecules on the sensor surface and the immunological response. This sandwich structure can make full use of the coupled electric field excited by Au film and Au NPs, compared to the traditional LSPR sensor. The other sensing channel is coated only with Ag film as a reference channel to eliminate measurement error caused by non-specific binding and temperature cross-sensitivity. We numerically investigate the electric field coupling strength of SPR/LSPR and conducted corresponding experiments. The sensor had a high refractive index sensitivity with 13,592 nm/RIU and limit of detection of human IgG can be reduced to 15 ng/mL, which is 15.3 times lower than that of conventional SPR sensors. The proposed biosensor has sensing superiorities of high sensitivity, accuracy and temperature insensitive.

Genetically engineered bio-nanoparticles with co-expressed enzyme reporter and recognition element for IgG immunoassay

A bioluminescence-based immunoassay, relying on genetically engineered multifunctional outer membrane vesicles (OMVs, ∼50 nm) with co-expressed enzyme reporter and IgG-binding domain, has been developed for detection of immunoglobulin G (IgG), an important biomacromolecule in humoral immunity. OMVs with co-expressed IgG-binding domain (Z domain) and ATP-independent NanoLuc luciferase (∼150-fold more active than either the firefly (Photinus pyralis) or Renilla reniformis luciferase) were produced through simple fermentation of genetically engineered nano-vesicle-forming E. coli. The size and concentration of the as-produced multifunctional OMVs were determined by Dynamic Light Scattering (DLS) and Nanoparticle Tracking Analysis, respectively. To reduce the non-specific binding of OMVs during immunoassay, blocking agent test was systematically carried out before IgG detection. Sensitive detection of IgG was further demonstrated with the limit of detection of 5 ng/mL IgG, comparable to that of commercial IgG ELISA kit. The advantages of genetically engineered bio-nanoparticles (bio-NPs) containing both reporter and recognition element are cost-effective and scalable through simple cell cultures with high reproducibility and pre-determined biological functions, in comparison with the conventional costly enzyme-antibody conjugation used in immunoassay. This study opens a new pathway on the low-cost immunoassay by rational design of genetically engineered bio-NPs with integrated reporter/recognition function.

Seroprevalence Study of Anti-HEV IgG among Different Adult Populations in Corsica, France, 2019.

Hepatitis E virus (HEV) is a major cause of acute hepatitis worldwide. In France, hyperendemic areas including Corsica have an anti-HEV Immunoglobulin G (IgG) prevalence higher than 50%. The aim of this study was to determine the seroprevalence of anti-HEV IgG in three adult populations in Corsica and the risk factors associated with antibody detection. Between 2017 and 2019, a total of 930 individuals, including 467 blood donors, 393 students or university staff members and 70 patients from general practice, were tested for the presence of anti-HEV IgG using the Wantai HEV IgG enzyme immunoassay kit and filled a questionnaire. The association between seropositivity and potential risk factors was tested with univariate and multivariate analyses. Out of the 930 samples, 52.3% (486/930) were seropositive—54.4% (254/467) among blood donors, 47.6% (187/393) among university students and 64.3% (45/70) among patients of general practice. Three main risk factors were identified: (i) skinning and butchering (Adjusted Odds Ratio aOR = 2.76, 95% confidence interval [95% CI] [1.51–5.37]; p-value < 10−3), (ii) consumption of a local pork live raw sausage (fittonu) (aOR = 1.95 95% CI [1.45–2.64]; p-value = 10−5), and (iii) increasing age (p-value = 0.003). Seropositivity rates between the different populations were homogeneous after age stratification. This cross-sectional study indicates a high anti-HEV IgG seroprevalence in the Corsican adult population, not significantly different between women and men and increasing with age. This serosurvey also showed homogeneity regarding the exposure to HEV among three different types of populations. Finally, we confirmed the endemicity of Corsica with respect to HEV and identified a strong association between consumption of figatellu/fittonu and the practice of skinning and butchering with the detection of anti-HEV IgG.

Highly Sensitive SPR Biosensor Based on Graphene Oxide and Staphylococcal Protein A Co-Modified TFBG for Human IgG Detection

A highly sensitive optical fiber surface plasmon resonance (SPR) biosensor based on graphene oxide (GO) and staphylococcal protein A (SPA) co-modified tilted fiber Bragg grating (TFBG) is proposed and demonstrated for the detection of human immunoglobulin G (IgG) for the first time. The gold film on the surface of the sensor was first fixed with GO and then modified with an SPA to improve the sensitivity of the sensor. Large specific surface area and abundant functional groups of GO can adsorb more antibodies. The combination of SPA and the antibody molecule Fc region makes the Fab area with antigen-binding sites extend outward, resulting in highly oriented antibody immobilization on the sensor surface and high antigen–antibody binding efficiency. The experimental results show that the sensitivity as well as the limit of detection of GO-SPA-modified TFBG-SPR biosensor is around 0.096 dB/( $\mu \text{g}$ /mL) and $0.5~\mu \text{g}$ /mL, showing better responses to human IgG solutions with a concentration range of 30– $100~\mu \text{g}$ /mL compared with the TFBG-SPR biosensors modified singly with GO or SPA. The biosensor exhibits the advantages of small size, ease of fabrication, high sensitivity, label-free, and rapid response, and provides a new solution for detecting low concentration of biological solution, presenting great application potential in the biochemistry field.

Human Serum Anti-aquaporin-4 Immunoglobulin G Detection by Cell-based Assay.

Anti-aquaporin-4 (AQP4) immunoglobulin G (IgG) is the core diagnostic biomarker for neuromyelitis optica spectrum disorders (NMOSD). The cell-based assay (CBA) is a widely used method to detect anti-AQP4 IgG in human serum with high sensitivity and specificity. Briefly, serum anti-AQP4 IgG is captured by AQP4-transfected cell that is fixed on the biochip then detected by a fluorescein-labelled secondary antibody. Fluorescence microscopy is utilized to visualize the fluorescence, and the intensity of fluorescence is evaluated by at least two experienced clinicians. A final diagnosis of NMOSD can be made based on the combination of anti-AQP4 IgG detection results, clinical manifestations, and neuroradiological findings. According to previous studies, CBA is more sensitive and specific than other anti-AQP4 IgG detection methods, and it can be applied to both clinical diagnosis and studies of NMOSD. The method has limitations; for example, an international scale to evaluate serum anti-AQP4 IgG titers is still lacking. Here, a detailed protocol for human serum anti-AQP4 IgG detection using CBA is described.