Bio-functionalized magnetic nanoparticles for the immunoassay of fetal fibronectin: a feasibility study for the prediction of preterm birth
Bio-functionalized magnetic nanoparticles for the immunoassay of fetal fibronectin: a feasibility study for the prediction of preterm birth
Research Highlights
- Ultra-High Sensitivity: IMR assay achieves a low detection limit of 0.0001 ng/mL, compared to 0.789 ng/mL for ELISA
- Superior Accuracy: Sensitivity of 0.833 and specificity of 0.944 for IMR assay vs. 0.583 and 0.611 for ELISA
- Clinical Threshold: Optimal cut-off value of 5.93 ng/mL for preterm birth prediction using IMR assay
- Dynamic Range: IMR assay covers 0.0001–1000 ng/mL, significantly broader than ELISA (0.789–1000 ng/mL)
Abstract
Preterm birth is an important cause of perinatal morbidity and mortality. Various biomarkers in cervicovaginal secretions related to preterm birth have been investigated, of which foetal fibronectin (fFN) shows the greatest potential because of its high negative predictive value. The immunomagnetic reduction (IMR) assay has emerged as a novel quantitative method to detect biomarkers. In this prospective case-control study, we analysed 33 samples of cervicovaginal secretions from pregnant women between 22 and 34 weeks of gestation at high risk of preterm birth.
Key Findings
Study Design
This prospective case-control study was conducted at Mackay Memorial Hospital, Taipei, Taiwan from July 2014 to March 2015. The study enrolled pregnant women with gestational age between 22 and 34 weeks presenting with symptoms of preterm uterine contractions.
- Total Samples: 33 cervicovaginal secretions
- Negative Group (Term Delivery): 17 samples (gestational age 37-41 weeks)
- Positive Group (Preterm Delivery): 16 samples (gestational age 24-36 weeks)
Comparison of IMR Assay and ELISA
| Method | Low Detection Limit (ng/mL) | Dynamic Range (ng/mL) | Threshold (ng/mL) | Sensitivity | Specificity |
|---|---|---|---|---|---|
| IMR Assay | 0.0001 | 0.0001–1000 | 5.93 | 0.833 | 0.944 |
| ELISA | 0.789 | 0.789–1000 | 54.49 | 0.583 | 0.611 |
Magnetic Nanoparticle Characterization
The anti-fFN functionalized magnetic nanoparticles were characterized using multiple techniques:
- Core Material: Fe₃O₄ (magnetite) with superparamagnetic properties
- Coating: Dextran polymer with anti-fFN antibodies
- Mean Diameter: 50.50 nm (±12.84 nm) measured by dynamic laser scattering (DLS)
- Size Distribution: 68.2% of particles measured 37.66-63.34 nm
- Magnetic Concentration: 8 mg-Fe/mL
IMR Assay Mechanism
The immunomagnetic reduction (IMR) assay operates on the principle of detecting changes in magnetic susceptibility when antibody-functionalized magnetic nanoparticles bind to target fFN molecules:
- Free magnetic nanoparticles rotate freely under alternating current (AC) magnetic fields
- Upon binding with fFN, immune complexes become larger and rotate more slowly
- This leads to attenuation of the AC magnetic susceptibility (χac)
- The IMR signal is calculated as the percentage reduction: IMR(%) = (χac,o - χac,φ)/χac,o × 100%
- Equilibrium is reached after approximately 4 hours of incubation
Clinical Significance
The superior performance of the IMR assay offers several clinical advantages:
- Early Detection: Much lower threshold (5.93 ng/mL) enables earlier identification of at-risk patients
- Improved Decision Making: Higher sensitivity and specificity support more accurate clinical decisions
- Rapid Results: Label-free, quantitative method provides timely diagnostic information
- Clinical Applications: Enables timely administration of tocolytic agents, corticosteroids, and appropriate referral to tertiary care centers
Advantages of IMR Over ELISA
The study identified three key advantages of the IMR assay:
- Homogeneous Assay: Well-suspended nanoparticles can bind to fFN molecules throughout the entire sample volume, not just at the bottom of a test well. The total surface area of nanoparticles (≈1000 cm²/mL) is 180 times larger than a 96-well ELISA plate well (0.45 cm²)
- Suppression of Non-specific Binding: High-frequency oscillation (≈20 kHz) of magnetic nanoparticles generates centrifugal force that breaks weak non-specific bonds while preserving strong antibody-target interactions
- Color Interference Elimination: Magnetic signals are transparent to sample colors (hemoglobin, bilirubin, lipids), unlike optical signals used in ELISA
Conclusions
This feasibility study demonstrates that measuring fFN concentration using the IMR assay is a superior alternative method to accurately predict the risk of preterm birth. The ultra-high sensitivity, excellent specificity, and rapid quantitative results make the IMR assay a promising tool for clinical application in obstetric practice. The ability to detect extremely low concentrations of fFN may enable earlier intervention and improved outcomes for pregnancies at risk of preterm birth.
Citation
Chian-Huey Wong, Chie-Pein Chen, Chia-Chen Chang, Chen-Yu Chen, "Bio-functionalized magnetic nanoparticles for the immunoassay of fetal fibronectin: a feasibility study for the prediction of preterm birth", Scientific Reports 7: 42461 (2017).
Article Link
Acknowledgements
This work was supported by Mackay Memorial Hospital (MMH-103-68, and 104DMH0100099), and Ministry of Science and Technology of Taiwan (MOST 104-2314-B-195-015, and MOST 105-2314-B-195-010).
