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Objective: To understand the role of WFDC2 in metastasis of ovarian cancer. Methods: By knockdown or overexpression of WFDC2, we demonstrated the role of WFDC2 in epithelial-mesenchymal transition (EMT). Results: We demonstrated that stable knockdown of WFDC2 suppressed EMT along with the upregulation of E-cadherin and the downregulation of Vimentin. In addition, WFDC2 knockdown decreases matrix metalloproteinase-2 (MMP-2) expression in in vitro cell model and in in vivo nude mice xenografts. The correlation of WFDC2 and MMP-2 expression in the clinical sample confirmed that WFDC2 was tightly correlated with the development of tumor. More importantly, the EMT phenotype and cell invasion induced by WFDC2 overexpressing can be reversed by the siMMP-2 and P13K/AKT signaling inhibitor. Conclusion: WFDC2 contributed to ovarian cancer metastasis and EMT as a positive regulator by activating AKT signaling pathway and inducing MMP-2 expression.

Background WAP four-disulfide core domain protein 2 (WFDC2) shows a tumor-restricted upregulated pattern of expression in ovarian cancer. Methods In this study, we evaluated the role of WFCD2 in tumor mobility, invasion and metastasis of ovarian cancer in clinical tissue and in ovarian cancer cells, both in vitro and in vivo. Results Our results revealed WFCD2 was overexpressed in ovarian tissues, and the expression level of WFCD2 was associated with metastasis and lymph node metastasis. Higher expression of WFCD2 was also observed in aggressive HO8910-PM cells than in HO8910 cells, and WFCD2 knockdown halted cell migration, invasion, tumorigenicity and metastasis in ovarian cancer cells, both in vitro and in vivo. Knockdown of WFDC2 induced the down-regulation of ICAM-1, CD44, and MMP2. Conclusion In summary, our work demonstrates that WFCD2 promotes metastasis in ovarian cancer. These findings suggest that WFCD2 plays a critical role in promoting metastasis and may constitute a potential therapeutic target of ovarian cancer. Electronic supplementary material The online version of this article (doi:10.1186/s13048-017-0329-0) contains supplementary material, which is available to authorized users.

Janus-activated kinase-1 (JAK1) plays an important role in many signaling pathways, including the JAK–STAT and SOCS pathways. The activation of the JAK1–STAT3 pathway is a key role in tumor inflammation and immunity by promoting inflammation. The detection of its interacting proteins is of great significance in many diseases. Although luminescent oxygen channeling is commonly used in immunoassay technologies, its use in the detection of JAK1 and interacting proteins has not been reported to date. We constructed eukaryotic overexpression plasmids pENTER–JAK1-His and pENTER–STAT3-His and, following single transfection and co-transfection, measured their expression by western blotting. Co-immunoprecipitation and luminescent oxygen channeling were then used to identify the protein interactions. JAK1 and STAT3 proteins were shown to be successfully overexpressed, and co-immunoprecipitation identified their interaction in vitro. We also detected protein interactions between JAK1 and interleukin 4 receptor (IL4R), JAK1 and growth hormone receptor (GHR). In conclusion, we verified that JAK1 and STAT3 interact in vitro using co-immunoprecipitation, and demonstrated for the first time the potential application of luminescent oxygen channeling for detecting JAK1 and its interacting proteins. Also we think this assay could help other researchers find unreported proteins that also have interactions in vitro.

Enzyme-linked immunosorbent assay (ELISAs) specific for Epstein–Barr virus nuclear antigen 1 (EBNA1)-immunoglobulin A (IgA) are most commonly used in the clinical diagnosis of EBV infection. But they have a low sensitivity and the enzyme-labeled antibodies are unstable. In this study, a novel immunoassay based on an indirect time-resolved fluoroimmunoassay (TRFIA) was developed. Microtiter plates were coated with recombinant EBNA1. We used Eu3+-labeled anti-human IgA as probe. The precision, sensitivity, specificity, and stability were evaluated, and comparison with traditional and commercially available ELISAs was also made. The cut-off value for our TRFIA was 2.7. Intra- and inter-assay coefficients of variation for the TRFIA were 1.56–4.99% and 3.92–6.95%, respectively; whereas those for the ELISA were 4.54–8.16% and 7.07–10.52%, respectively. Sensitivity was obviously better than traditional ELISA when diluted positive samples serially. Additionally, stability, specificity test and comparison of sensitivity and specificity between the TRFIA and commercial ELISAs all proved satisfactory. In conclusion, the results demonstrated that EBNA1 IgA TRFIA was a sensitive immunoassay and had potential value in large-scale screening of human serum samples in developing countries. J. Med. Virol. 87:1940–1945, 2015. © 2015 Wiley Periodicals, Inc.

Objectives This study established a novel time-resolved fluorescence immunoassay (TRFIA) that allows the simultaneous determination of rubella virus (RV) IgM and cytomegalovirus (CMV) IgM in human serum. Design and methods Lanthanum elements labeled antibody and streptavidin–biotin system were used in the “capture sandwich” format simultaneously. Results The working range of TRFIA for RV IgM was 2–80 AU/mL and for CMV IgM was 5–400 AU/mL. Intra- and inter-assay coefficient of variation (CV) for RV IgM and CMV IgM were both less than 10% and recoveries were from 90% to 110%. No significant statistical difference in sensitivity or specificity was observed between dual-TRFIA and commercial chemiluminescent immunoassays (CLIA) in serum samples. Conclusion The novel dual-TRFIA for RV IgM and CMV IgM detection might have valuable clinical application, with satisfactory sensitivity, specificity and accuracy.

Quantitative hepatitis B core antigen (anti-HBc) measurements could play an important role in evaluating therapeutic outcomes and optimizing the antiviral therapy of chronic hepatitis B infection. In this study, we have developed a simple and rapid fluorescence point-of-care test based on a lateral flow immunoassay (LFIA) method integrated with Eu (III) chelate microparticles to quantitatively determine anti-HBc concentrations in serum. This assay is based on a direct competitive immunoassay performed on lateral flow test strips with an assay time of 15 min. The Eu (III) chelate microparticle-based LFIA assay could quantitatively detect anti-HBc levels with a limit of detection of 0.31 IU mL−1, and exhibited a wide linear range (0.63–640 IU mL−1). The intra- and inter-assay coefficients of variation for anti-HBc were both less than 10% and a satisfactory dilution test and accuracy were demonstrated. There were no statistically significant differences in sensitivity or specificity in serum samples between the Eu (III) chelate microparticle-based LFIA strips and the Abbott Architect kit. A simple, rapid and effective quantitative detection of anti-HBc was possible using the Eu (III) chelate microparticle-based LFIA strips. The strips will provide diagnostic value for clinical application.

Tumor protein p53 acts as a trans-activator that negatively regulates cell division by controlling a set of genes required for cell cycle regulation, making it a tumor suppressor in different types of tumors. Because the transcriptional activity of p53 plays an important role in the occurrence and development of tumors, reactivation of p53 transcriptional activity has been sought as a novel cancer therapeutic strategy. There is great interest in developing high-throughput assays to identify inhibitors of molecules that bind the transcription-activation domain of p53, especially for wt p53-containing tumors. In the present study, taking MDM2 as an example, a novel amplified luminescent proximity homogeneous assay (AlphaLISA) was modified from a binding competition assay to detect the interactions between the transcription-activation domain of p53 and its ligands. This assay can be adapted as a high-throughput assay for screening new inhibitors. A panel of well-known p53-MDM2 binding inhibitors was used to validate this method, and demonstrated its utility, sensitivity and robustness. In summary, we have developed a novel protein-protein interaction detection immunoassay that can be used in a high-throughput format to screen new drug candidates for reactivation of p53. This assay has been successfully validated through a series of p53-MDM2 binding inhibitors.

Enzyme-linked immunosorbent assays (ELISA) specific for anti-HSV glycoprotein G (gG) are most commonly used in the clinical diagnosis of HSV infection. But most of them are qualitative and with narrow detection ranges. A novel time-resolved fluoroimmunoassay (TRFIA) methodology was developed for the quantitative determination of HSV IgG in human serum. The assay was based on an indirect immunoassay format, and performed in 96-well microtiter plates. HSV-1 and HSV-2 were used as the coating antigens. Eu3+-labeled goat anti-(human IgG) polyclonal antibodies were used as tracers. The fluorescence intensity of each well was measured and serum HSV IgG levels quantified against a calibration curve. The detection range of the novel TRFIA was between 5 and 500 AU/mL. Assay sensitivity was 0.568 AU/mL. The intra- and inter-assay coefficients of variation were 0.59–3.63% and 3.65–6.81%, respectively. Analytical recovery, dilution tests and serum panel tests were performed using TRFIA and the results proved satisfactory. There were no statistically significant differences in sensitivity and specificity between the TRFIA and commercial ELISAs. An effective, sensitive and accurate quantitative HSV type 1 and type 2 IgG TRFIA was successfully developed and provided diagnostic value in clinical use. Copyright © 2014 John Wiley & Sons, Ltd.

A highly sensitive, rapid and novel simultaneous measurement method for cytokeratin 19 fragment (CYFRA 21-1) and carcinoembryonic antigen (CEA) in human serum by magnetic nanoparticle-based dual-label time-resolved fluoroimmunoassay was developed. On the basis of a sandwich-type immunoassay format, analytes in the samples were captured by antibodies coated onto the surface of the magnetic beads and sandwiched by other antibodies labeled with europium and samarium chelates. The lower limit of quantitation of the present method for CYFRA 21-1 was 0.77 ng mL−1 and CEA was 0.85 ng mL−1. The coefficient variations of the method were less than 7%, and the recoveries were in the range of 90–110% for serum samples. The concentrations of CYFRA 21-1 and CEA serum samples determined by the present method were compared with those obtained by the chemiluminescence immunoassay. A good correlation was obtained with the correlation coefficients of 0.961 for CYFRA 21-1 and 0.938 for CEA. This novel method demonstrated high sensitivity, wide effective detection range and excellent reproducibility for the simultaneous determination of CYFRA 21-1 and CEA, which can be useful for the early screening and prognosis evaluation of patients with lung cancer.

Current clinically assays, such as enzyme-linked immunosorbent assay and chemiluminescence immunoassay, for hepatitis B surface antigen (HBsAg) are inferior in terms of either sensitivity and accuracy or rapid and high-throughput analysis. A novel assay based on magnetic beads and time-resolved fluoroimmunoassay was developed for the quantitative determination of HBsAg in human serum. HBsAg was captured using two types of anti-HBsAg monoclonal antibodies (B028, S015) immobilized on to magnetic beads and detected using europium-labeled anti-HBsAg polyclonal detection antibody. Finally, the assay yielded a high sensitivity (0.02 IU/mL) and a wide dynamic range (0.02-700 IU/mL) for HBsAg when performed under optimal conditions. Satisfactory accuracy, recovery and specificity were also demonstrated. The intra- and interassay coefficients of variation were 4.7-8.7% and 3.8-7.5%, respectively. The performance of this assay was further assessed against a well-established commercial chemiluminescence immunoassay kit with 399 clinical serum samples. It was revealed that the test results for the two methods were in good correlation (Y = 1.182X - 0.017, R = 0.989). In the current study, we demonstrated that this novel time-resolved fluoroimmunoassay could be used: as a highly sensitive, automated and high-throughput immunoassay for the diagnosis of acute or chronic hepatitis B virus infection; for the screening of blood or organ donors; and for the surveillance of persons at risk of acquiring or transmitting hepatitis B virus.

Background Cytokeratin 19 fragment antigen (CYFRA 21–1) is used to diagnose and monitor neoplasms. However, the main disadvantages of the currently available CYFRA 21–1 assays include heterogenous technology, being time-consuming, and having low through-put with low insensitivity. This study investigated the use of amplified luminescent proximity homogeneous immunoassay (AlphaLISA) for the quantization of CYFRA 21–1 in human serum. Methods The AlphaLISA kit was developed based on AlphaScreen detection technology with two different anti-CYFRA 21–1 monoclonal antibodies. One was coated on AlphaLISA acceptor beads and the other was biotinylated. Donor beads were coated with streptavidin. The test conditions were optimized and analytical performance was studied. Results The measurement range of AlphaLISA CYFRA 21–1 kit was 0.08–500 ng/ml. Assay detection limit was 0.08 ng/ml. The intra- and interassay coefficients of variation were 3.00–9.00% and 4.00–10.00%, respectively. There was no cross-reaction to alpha-fetoprotein (AFP), carcinoembryonic antigen (CEA), neuron-specific enolase (NSE), cancer antigen 19–9 (CA19–9), cytokeratins 8 (CK8), and cytokeratins 18 (CK18). The correlation coefficient of blood samples involved was 0.974 between CYFRA 21–1-AlphaLISA assay and a commercial electrochemiluminescence immunoassay (ECLIA) CYFRA 21–1 kit (Roche). Conclusions The AlphaLISA CYFRA 21–1 kit developed in this study had favorable performance characteristics for clinical application with acceptable analytical sensitivity, specificity, and accuracy.

Measurement of the free β subunit of human chorionic gonadotropin (free β-hCG) in serum is useful for prenatal screening. Concentrations of free β-hCG vary in different races. Conventional assays used for such measurements have limitations. We applied the AlphaLISA to measure levels of free β-hCG in maternal serum during 8-20 weeks of gestation in women from southern China. Two anti-free β-hCG antibodies were used: one was coated on AlphaLISA acceptor beads and the one was biotinylated. The assay also contained donor beads coated with streptavidin. The AlphaLISA assay detection limit was 0.11 ng/mL, and the analytical range was 0.11-200 ng/mL. The intra- and interassay coefficients of variation were 1.32%-2.50% and 3.44%-5.45%, respectively. The correlation with commercial Eu(3+)-labeled free β-HCG-TRFIA assay was good (y = 1.045x + 1.580, r(2) = 0.978). Median levels of free β-hCG in maternal serum at 8-20 weeks gestation were higher in women from southern China compared with those reported in women from other countries. The AlphaLISA for free β-HCG could become the assay of choice for applications in clinical diagnostics. The established median value of free β-HCG is helpful in clinical diagnosis specific for southern Chinese women.

A novel quantum dot-doped polystyrene nanoparticles-based lateral flow test strips (QPs-LFTS) system was developed to simultaneously detect a cytokeratin-19 fragment (CYFRA 21-1) and carcinoembryonic antigen (CEA) in human serum to aid the diagnosis and prognosis of lung cancer. Quantum dot-doped carboxylate-functionalized polystyrene nanoparticles (QPs) were prepared and introduced as fluorescent reporters in QPs-LFTS. The detection was based on a sandwich immunoassay and performed on lateral flow test strips, with an assay time of 15 min. The strips were read by a fluorescence strip reader to obtain the fluorescence peak heights of the test lines (HT) and the control line (HC). The ratio of HT/HC was used for quantitation. The QPs showed excellent photoproperties and good performance. Under optimal conditions, the QPs-LFTS system exhibited a wide linear range for CYFRA 21-1 (1.3–480 ng/mL) and CEA (2.8–680 ng/mL). The detection limits for CYFRA 21-1 and CEA were 0.16 and 0.35 ng/mL, respectively. The recovery and reproducibility of the method were satisfactory. Furthermore, excellent correlations (n =120, R2 =0.9862, P

In this paper, a novel time-resolved fluorescence immunoassay (TRFIA) is described that allows the simultaneous quantitative detection of hepatitis B virus surface antigen (HBsAg) and hepatitis B e antigen (HBeAg) in human serum to aid the diagnosis and monitoring of hepatitis B virus infection. The proposed method was developed based on a two-step sandwich immunoassay protocol in which monoclonal antibodies against HBsAg and HBeAg were co-coated in 96 microtitration wells, then tracer polyclonal antibodies against HBsAg labeled with samarium and tracer monoclonal antibodies against HBeAg labeled with europium chelates were used for detection. The detection range was 0.1–150 IU/mL for HBsAg and 0.5–160 PEIU/mL for HBeAg, and the detection limits were 0.03 IU/L and 0.09 PEIU/ml, respectively. The intra- and inter-assay coefficients of variation were below 8 % for both virus antigens. The dilution linearity and accuracy of the assay were satisfactory. No statistically significant differences were observed in sensitivity or specificity for the serum samples between the dual-label TRFIA and a commercial single-label TRFIA. These results demonstrate that an effective, reliable and convenient HBsAg/HBeAg dual-label TRFIA was successfully developed that may be clinically applicable for blood screening to monitor the course of hepatitis B virus infection and predict treatment responses.

A novel immunoassay for the determination of tumor markers in human serum was established by combining a time-resolved fluoroimmunoassay (TRFIA) and immunomagnetic separation. Based on a sandwich-type immunoassay format, analytes in samples were captured by magnetic beads coated with one monoclonal antibody and "sandwiched" by another monoclonal antibody labeled with europium chelates. The immunocomplex was separated and washed by exposure to a magnetic field and treatment with enhancement solution; fluorescence was then measured according to the number of europium ions dissociated. Levels of the model analyte, carcinoembryonic antigen (CEA), were determined in a linear range (1-1000 ng mL(-1)) with a limit of detection of 0.5 ng mL(-1) under optimal conditions. The reproducibility, recovery, and specificity of the immunoassay were demonstrated to be acceptable. To evaluate this novel assay for clinical applications, 239 serum samples were evaluated. Compared with the conventional TRFIA and chemiluminescence immunoassay (CLIA), the correlation coefficients of the developed immunoassay were 0.985 and 0.975, respectively. These results showed good correlation and confirmed that our method is feasible and could be used for the clinical determination of CEA (or other tumor antigens) in human serum.

Human ubiquitin-conjugating enzyme E2, also known as UbcH10, is defined as a cyclin-selective ubiquitin carrier protein and is essential for selective degradation of many short-lived proteins in eukaryotic cells. Recently more and more data show that UbcH10 could be a potential cancer biomarker. In this study, we have developed a monoclonal antibody (MAb) against UbcH10 using an expression recombinant protein. Hybridomas F001, F007, and F008 with high affinities belong to IgG1 subclass with κ light and are highly specific for UbcH10. Further experimentation showed that MAbs F001, F007, and F008 are suitable for the development of immunoassay core agents with sufficient sensitivity and specificity in vitro by Western-blot, immunofluorescence, and immunohistochemistry. These MAbs can be used as a tool for further investigation on functions related to the role of UbcH10 in tumorigenesis and development.

Background Valid assays measuring free thyroxine (FT4) must perform without bias despite large variations in the concentrations and affinities of serum thyroxine-binding proteins in the population. We developed a new, rapid one-step labelled-antibody time-resolved fluoroimmunoassay (TRFIA) for FT4. Methods Based on the heterologous combination of anti-T4 monoclonal antibody and triiodothyronine–immunoglobulin G conjugate, a one-step TRFIA for FT4 detection was established and compared with the two-step DELFIA® Free Thyroxine Assay. Matrix interference caused by endogenous binders and exogenous non-esterified fatty acids (NEFA) was also accessed in the proposed assay. Results The developed method generally took only one hour, had a detection limit of 0.6 pmol/L and a large linear range of 2.5–120 pmol/L. The inter- and intra-assay coefficients of variation were 3.5–6.6% and 4.4–9.8%, respectively. Results from 110 specimens showed apparent agreement with that from the DELFIA® FT4 Assay with the square of the correlation coefficient of 0.975. This assay indicated that there was no significant dependence on endogenous binders and displayed potential interference by exogenous NEFA up to 5 mmol/L. Conclusions The proposed one-step heterologous TRFIA FT4 assay possesses simplicity, accuracy, high sensitivity and exhibits great potential for FT4 measurement. The combination of heterologous immunoassay with TRFIA may be advantageous for FT4 immunoassay development.

The aim of this study was to produce monoclonal and polyclonal antibodies against procalcitonin (PCT), a valid post-mortem marker of sepsis marker. Monoclonal antibodies (MAbs) were made from hyperimmune Balb/c mice by injecting 50 microg of purified antigen. These mice were immunized four times and given a final boost, and their spleen cells were collected and fused with SP2/0 myeloma cells under the presence of PEG 1450. Hybridomas were screened by indirect enzyme-linked immunosorbent assay (ELISA) using purified protein. Lastly, five MAbs were obtained and designated successfully and were characterized by ELISA and Western immunoblotting. By Western immunoblotting, MAbs were found reactive with the patient's serum specifically. The results showed that the monoclonal antibodies could be used for various pathophysiological analyses in further investigations of procalcitonin and in preparing diagnostic kits.

The Epstein-Barr virus (EBV) transactivator protein (ZEBRA) is an immediate-early protein that plays an important role in the switch from latency to productive cycle in EBV virus. ZEBRA is an important marker of EBV reactivation. In order to diagnose EBV infection status correctly and timely, a novel immunoassay was developed based on an indirect time-resolved fluoroimmunoassay (TRFIA) for Zta IgA, which used recombinant Zta antigen as solid-phase antigen and Eu(3+)-labeled mouse antihuman IgA as corresponding probe. The precision, sensitivity, specificity test, and stability of the TRFIA kit were evaluated, and comparison with the traditional enzyme-linked immunosorbent assay (ELISA) was also investigated. The cutoff value for the TRFIA was 2.5. Intra- and interassay coefficients of variation for the TRFIA were 2.45-3.30% and 3.38-4.61% respectively. There was no cross-reactivity with the antibodies of cytomegalovirus (CMV) or herpes simplex virus (HSV) types 1 and 2, or other potential interferences. The established assay kit also behaved better in sensitivity and stability than the ELISA one. Additionally, the results in 382 serum samples using two analytical methods showed there was good agreement between the TRFIA and commercial ELISA kit. In the current study, the results demonstrated that the TRFIA that was developed for Zta IgA detection was more sensitive and reliable for the diagnosis of EBV infection and had potential value in automation and high-throughput screening.

In order to early screen and detect suspected biomarkers from pathogens and the human body itself, tracers or reaction strategies that can act as signal enhancers have been proposed forth at purpose. In this paper, we discussed the applicability of magnetic microparticles-assisted time-resolved fluoroimmunoassay (MMPs-TRFIA) for sensitive determination of potential analytes. Hepatitis B e antigen, antibody to hepatitis B surface antigen and free triiodothyronine were used as biomarker models to explore the reliability of the method. By coupling with bioprobes, MMPs were used as immunoassay carriers to capture target molecules. Under optimal condition, assay performance, including accuracy, precision and specificity, was outstanding and demonstrated satisfactory. To further evaluate the performance of the MMPs-TRFIA in patients, a total of 728 serum samples from hospital were analyzed for three biomarkers in parallel with the proposed method and chemiluminescence immunoassay kit commercially available. Fairly good agreements are obtained between the two methods via data analysis. Not only that but the reliability of MMPs-TRFIA has also been illustrated by three different reaction models. It is confirmed that the novel method modified with MMPs has been established and showed great potential applications in both biological detection and clinical diagnosis, including big molecule protein and low molecular weight haptens.

A sensitive, specific, and rapid method for the detection of carbohydrate-protein interactions was demonstrated using quantum dots (QDs) as a fluorescence label coupled with protein. 1,3-Dipolar cycloaddition between azide and alkyne was exploited to attach α-D-glucopyranoside to a C 1 4 hydrocarbon chain that noncovalently binds to the microtiter well surface, and the product formation was detected by both electrospray ionization-mass spectrometry (ESI-MS) and QD- (or fluorescein isothiocyanate (FITC))-conjugated lectin binding. It indicated that the peak intensity of the fluorescence emission was proportional to the initial concanavalin A (Con A) concentration in the range of 2 × 10 - 3 μmol/L to 2 x 10 - 2 n-imol/L with a detection limit at least 100 times lower than that of the FITC-based method.

Viral capsid antigen (VCA) IgA is one of the most commonly tested antibodies for Epstein-Barr virus (EBV) in the clinic and is a proven biomarker to predict the risk of nasopharyngeal carcinoma (NPC) and other diseases. At present, a VCA-IgA antibody is used for clinical diagnosis by enzyme-linked immunosorbent assay (ELISA), which can detect samples only qualitatively or semi-quantitatively, with unsatisfactory sensitivity and specificity. In this study, an indirect time-resolved fluoroimmunoassay (TRFIA) using Eu(3+) labeled mouse anti-human IgA monoclonal antibodies as a tracer was developed. This method produced a linear range of 0-30 AU/mL, with a limit of detection of 0.018 AU/mL. The intra- and inter-assay precisions were 1.62-4.30% and 3.56-7.57%, respectively. TRFIA showed no cross-reactivity against potentially interfering substances and a better sensitivity and specificity compared with commercial ELISA. This study confirmed that an indirect TRFIA meets the requirement for clinical testing and could be an alternative to detect VCA-IgA levels in human serum in the clinic.

Quantum dots are not widely used in clinical diagnosis. However, the homogeneous time-resolved fluorescence assay possesses many advantages over current methods for the detection of carcinoembryonic antigen (CEA), a primary marker for many cancers and diseases. Therefore, a novel luminescent terbium chelates- (LTCs) and quantum dots-based homogeneous time-resolved fluorescence assay was developed to detect CEA. Glutathione-capped quantum dots (QDs) were prepared from oil-soluble QDs with a 565 nm emission peak. Conjugates (QDs-6 F11) were prepared with QDs and anti-CEA monoclonal antibody. LTCs were prepared and conjugates (LTCs-S001) were prepared with another anti-CEA monoclonal antibody. The fluorescence lifetime of QDs was optimized for sequential analysis. The Forster distance (R0) was calculated as 61.9 A based on the overlap of the spectra of QDs-6 F11 and LTCs-S001. Using a double-antibody sandwich approach, the above antibody conjugates were used as energy acceptor and donor, respectively. The signals from QDs were collected in time-resolved mode and analyzed for the detection of CEA. The results show that the QDs were suitable for time-resolved fluoroassays. The spatial distance of the donor-acceptor pair was calculated to be 61.9 A. The signals from QDs were proportional to CEA concentration. The standard curve was LogY = 2.75566 + 0.94457 LogX (R = 0.998) using the fluorescence counts (Y) of QDs and the concentrations of CEA (X). The calculated sensitivity was 0.4 ng/mL. The results indicate that water-soluble QDs are suitable for the homogenous immunoassay. This work has expanded future applications of QDs in homogeneous clinical bioassays. Furthermore, a QDs-based homogeneous multiplex immunoassay will be investigated as a biomarker for infectious diseases in future research.