Introduction
Chemiluminescence Immunoassay (CLIA) is one of the most sensitive, widest linear range, and most automated technology platforms in the immunoassay field. It combines the high specificity of immunological reactions with the high sensitivity of chemiluminescence reactions and is widely used in tumor marker testing, thyroid function, hormones, cardiac markers, infectious diseases, and other applications. Compared with ELISA, CLIA achieves detection sensitivity at the fM or even sub-fM level, a linear range spanning 3-6 orders of magnitude, and a detection time reduced to 15-30 minutes, making it the platform of choice for large central laboratories and emergency testing. The performance of high-quality CLIA reagents heavily depends on the proper selection and combination of magnetic beads, antibody labels, chemiluminescent substrates, calibrators, stabilizers, and other raw materials. this article systematically introduces the technical principles, main application areas, key raw material selection points, formulation examples, and frequently asked questions for CLIA, providing a complete raw material technical reference for CLIA reagent development.
I. Overview of CLIA Technology
1.1 Basic Principles of Chemiluminescence
Chemiluminescence refers to the phenomenon where energy generated during a chemical reaction is released in the form of light. In CLIA, chemiluminescence reactions are typically achieved in the following ways:
Principle:Excited state reactant → Ground state + Photon (light emission)
CLIA is mainly divided into three types based on the label and luminescence principle:
| Type | Label | Luminescence Principle | Luminescence Characteristics | Representative Manufacturers |
|---|---|---|---|---|
| Enzymatic Chemiluminescence | HRP or AP | Enzyme catalyzes luminescent substrate to produce light signal | Glow type (lasts minutes to tens of minutes) | Abbott, Siemens |
| Direct Chemiluminescence | Acridinium ester (AE) | H₂O₂/NaOH triggers flash luminescence | Flash type (instantaneous, 1-3 seconds) | Beckman Coulter |
| Electrochemiluminescence | Ruthenium complex [Ru(bpy)₃]²⁺ | Redox reaction on electrode surface produces light | Glow type, highly controllable | Roche |
Most commonly used types: Enzymatic chemiluminescence (HRP-Luminol system, AP-AMPPD system) and direct chemiluminescence (Acridinium ester system).
1.2 CLIA Methodology Principles
CLIA commonly uses the sandwich method (for large molecules) or competitive method (for small molecules), with magnetic beads as the solid-phase carrier to achieve rapid separation and automation.
Sandwich Method Principle (HRP-Luminol system as example):
1. Capture antibody coated on magnetic beads
2. Add sample; target antigen binds to antibody on magnetic beads
3. Add HRP-labeled detection antibody; forms "magnetic bead-antibody-antigen-antibody-HRP" complex
4. Wash to remove unbound substances
5. Add luminescent substrate (Luminol + enhancer + H₂O₂); HRP catalyzes light signal production
6. Chemiluminescence detector measures light intensity, proportional to antigen concentration
HRP Enzymatic Chemiluminescence Principle:
HRP + Luminol + H₂O₂ → Excited state product → Light emission (425 nm)
AP Enzymatic Chemiluminescence Principle:
AP + AMPPD → Dephosphorylation → Excited state product → Light emission (470 nm)
Acridinium Ester Direct Chemiluminescence Principle:
Acridinium ester-labeled antibody + H₂O₂ + NaOH → Excited state product → Light emission (430 nm, flash)
II. Main Application Areas of CLIA
| Application Area | Specific Test Items | Methodology | Clinical Significance |
|---|---|---|---|
| Tumor Markers | AFP, CEA, CA19-9, CA125, CA15-3, PSA, HE4, SCCA | Sandwich | Cancer screening, treatment monitoring |
| Thyroid Function | TSH, T3, T4, FT3, FT4, TGAb, TPOAb | Sandwich/Competitive | Hyperthyroidism/hypothyroidism diagnosis |
| Sex Hormones | E2, P, T, FSH, LH, PRL, HCG, AMH | Competitive/Sandwich | Reproductive health, assisted reproduction |
| Cardiac Markers | hs-cTnI, hs-cTnT, NT-proBNP, BNP, CK-MB, Myo | Sandwich | Myocardial infarction, heart failure diagnosis |
| Infectious Diseases | HIV Ag/Ab, HBsAg, HBcAb, HBeAg, HCV antibody, Syphilis antibody | Sandwich/Indirect | Blood screening, diagnosis |
| Bone Metabolism | PTH, 25-OH-VD, CTX-1, PINP | Competitive/Sandwich | Osteoporosis assessment |
| Inflammation Markers | PCT, IL-6, hs-CRP | Sandwich | Infection, sepsis diagnosis |
| Diabetes | Insulin, C-peptide, GAD antibody | Sandwich | Diabetes classification |
III. Key Raw Materials and Solutions for CLIA
3.1 Magnetic Beads — The "Carrier" and "Separator" of the Reaction
Magnetic beads are the core solid-phase carrier of CLIA. Their quality directly affects reagent sensitivity, reproducibility, and stability. Magnetic beads covalently couple capture antibodies and enable rapid separation and washing under an external magnetic field.
| Raw Material Name | Function | Recommended Specification | Selection Points |
|---|---|---|---|
| Carboxyl Magnetic Beads | Covalent antibody coupling (EDC/NHS activation) | Particle size 1-3 μm, solid content 1-2.5% | Good dispersibility, fast magnetic response, low non-specific adsorption |
| Tosyl Magnetic Beads | Covalent antibody coupling (direct coupling) | Particle size 1-3 μm, solid content 1-2.5% | High coupling efficiency, no additional activation needed |
| Streptavidin Magnetic Beads | Capture biotinylated antibodies | Loading capacity ≥500 pmol/mg, size 1-3 μm | Signal amplification, batch consistency |
| Amino Magnetic Beads | Covalent antibody coupling | Particle size 1-3 μm | Less commonly used |
Key Indicators for Magnetic Bead Selection:
| Indicator | Recommended Range | Impact |
|---|---|---|
| Particle Size | 1-3 μm | Smaller size = larger surface area = higher loading; but slower magnetic response |
| Magnetic Response Time | ≤30 seconds | Affects washing efficiency and detection speed |
| Non-Specific Adsorption | Low (≤5%) | Affects signal-to-noise ratio and background |
| Carboxyl Content | 0.1-0.5 meq/g | Affects antibody coupling loading |
| Dispersion Stability | No aggregation | Affects batch consistency |
3.2 Antibody Labeling — The "Source" of Signal
There are three main types of antibody labeling in CLIA: HRP labeling (enzymatic chemiluminescence), AP labeling (enzymatic chemiluminescence), and acridinium ester direct labeling (direct chemiluminescence).
(1) HRP Labeling
| Parameter | Recommended Specification | Explanation |
|---|---|---|
| HRP Specification | RZ≥3.0, ≥250 U/mg | High purity, high specific activity |
| Labeling Method | Sodium periodate method | High labeling efficiency |
| Labeling Molar Ratio | HRP:antibody = 2-4:1 | Too high ratio may affect antibody activity |
| Storage Buffer | 50% glycerol + BSA + ProClin 300 | Store at 2-8°C |
(2) AP Labeling
| Parameter | Recommended Specification | Explanation |
|---|---|---|
| AP Specification | ≥1000 U/mg | High specific activity |
| Labeling Method | Glutaraldehyde method or commercial kit | Simple operation |
| Storage Buffer | Tris buffer + Mg²⁺ + Zn²⁺ + stabilizers | AP requires divalent ion protection |
(3) Acridinium Ester (AE) Direct Labeling
| Parameter | Recommended Specification | Explanation |
|---|---|---|
| Acridinium Ester Specification | ≥95%, NHS-activated | Direct antibody labeling |
| Labeling Method | NHS-AE couples with antibody amino groups | One-step reaction |
| Labeling Molar Ratio | AE:antibody = 5-10:1 | Ratio affects luminescence intensity |
| Storage Condition | -20°C, protect from light | AE is light-sensitive |
Acridinium Ester Labeling Principle:
NHS-Acridinium ester + Antibody (-NH₂) → Amide bond linkage → AE-labeled antibody
Trigger luminescence: H₂O₂ + NaOH → Flash luminescence (430 nm)
3.3 Chemiluminescent Substrates — The "Fuel" for Luminescence
(1) HRP-Luminol System
| Raw Material Name | CAS No. | Function | Recommended Specification |
|---|---|---|---|
| Luminol | 521-31-3 | Luminescent substrate | ≥98% |
| H₂O₂ (Hydrogen Peroxide) | 7722-84-1 | Oxidizing agent | ≥30% |
| Enhancers (4-Iodophenol, p-Phenylphenol) | 540-38-5 / 92-69-3 | Enhance luminescence signal, prolong glow time | ≥98% |
| Buffer (Tris-EDTA, Borate buffer) | — | Maintains reaction pH 8.0-8.5 | ≥99% |
Luminol System Optimization Parameters:
| Parameter | Recommended Range | Impact |
|---|---|---|
| Luminol Concentration | 0.5-1.5 mM | Too low concentration gives weak signal |
| H₂O₂ Concentration | 1-5 mM | Affects luminescence intensity and duration |
| Enhancer Concentration | 0.5-1 mM | Can enhance signal 3-10 times |
| pH | 8.0-8.5 | Affects enzyme activity and luminescence efficiency |
(2) AP-AMPPD System
| Raw Material Name | CAS No. | Function | Recommended Specification |
|---|---|---|---|
| AMPPD | 122341-56-4 | Luminescent substrate (glow type) | ≥98% |
| Buffer (Tris-HCl + Mg²⁺) | — | Maintains pH 9.5-10.0 | — |
AP-AMPPD System Characteristics:
-
Glow-type luminescence, long duration (tens of minutes)
-
Lower background, higher signal-to-noise ratio
-
Suitable for applications requiring long readout times
(3) Acridinium Ester Trigger Solution
| Raw Material Name | Function | Recommended Concentration |
|---|---|---|
| H₂O₂ | Oxidizing agent | 0.1-0.5% |
| NaOH | Alkaline environment | 0.1-0.5 M |
| HNO₃ (Pre-trigger solution) | Acidic cleaning | 0.1-0.2 M |
Acridinium Ester Luminescence Characteristics:
-
Flash-type luminescence, completed within 1-3 seconds
-
No enzyme involvement, fast reaction speed
-
Suitable for high-throughput testing
3.4 Calibrators and Controls — The "Ruler" for Accurate Quantification
| Raw Material Name | Function | Recommended Specification | Selection Points |
|---|---|---|---|
| Calibrators | Establish dose-response curve | Traceable to international standards (WHO, IFCC) | At least 5-6 concentration points |
| Controls | Monitor detection performance | Low, medium, high three concentrations | Matrix-matched |
| Blank Matrix | Diluent for calibrators/controls | Target-removed serum/buffer | Consistent with sample matrix |
Calibrator Preparation Points:
-
Matrix matching: Calibrators should have the same matrix as actual samples (e.g., human serum)
-
Traceability: Should be traceable to international standard materials
-
Stability: Liquid calibrators store at 2-8°C; lyophilized calibrators store at room temperature
3.5 Buffers and Wash Solutions
| Raw Material Name | Function | Recommended Formulation | Key Parameters |
|---|---|---|---|
| Magnetic Bead Storage Buffer | Maintains magnetic bead dispersion stability | PBS + 0.1-0.5% BSA + 0.05% Tween-20 + preservative | Avoid aggregation |
| Wash Solution | Washes away unbound substances | PBS + 0.05-0.1% Tween-20 + preservative | Wash cycles 3-5 times |
| Sample Diluent | Dilutes samples, reduces matrix effects | PBS + 1% BSA + 0.05% Tween-20 + preservative | Can add blocking agents |
| Antibody Diluent | Dilutes labeled antibodies | PBS + 1% BSA + 0.05% Tween-20 + stabilizers | Can add glycerol |
3.6 Stabilizers and Preservatives
| Raw Material Name | CAS No. | Recommended Concentration | Main Application | Precautions |
|---|---|---|---|---|
| BSA | 9048-46-8 | 0.1-1% | Protein stabilization, reduces adsorption | Fatty acid-free |
| Trehalose | 6138-23-4 | 2-5% | Lyoprotection, thermal stability | Extends shelf life |
| EDTA·2Na | 6381-92-6 | 1-2 mM | Chelates heavy metal ions | Protects enzyme activity |
| ProClin 300 | — | 0.02-0.05% | Preservative | Compatible with HRP/AP |
| Sodium azide | 26628-22-8 | — | ⚠️ Prohibited for CLIA reagents | Inhibits HRP/AP activity |
Core Warnings:
-
⚠️ HRP or AP-containing CLIA reagents must NOT use sodium azide
-
⚠️ ProClin 300 (0.02-0.05%) is recommended as the alternative preservative
IV.CLIA Procedure Example (Sandwich Method)
| Step | Operation | Conditions | Key Parameters |
|---|---|---|---|
| 1. Add sample | Sample + magnetic bead-capture antibody | 37°C, 10-20 minutes | Antigen binds to magnetic beads |
| 2. Add detection antibody | Add labeled detection antibody | 37°C, 10-20 minutes | Forms double antibody sandwich |
| 3. Wash | Magnetic separation, wash 3-5 times | Add wash solution each time, magnetic pull | Remove unbound substances |
| 4. Add substrate | Add luminescent substrate solution | Read immediately or incubate before reading | Glow type requires timing |
| 5. Detect | Chemiluminescence detector measures light intensity | 1-5 seconds/well | Record RLU values |
Total detection time: 15-30 minutes
V.Frequently Asked Questions (FAQ)
Q1: How can I improve low sensitivity in CLIA?
A: Low sensitivity is usually related to antibodies, magnetic beads, or luminescent substrates.
| Cause | Solution |
|---|---|
| Insufficient antibody affinity | Select high-affinity antibodies with affinity ≥10⁹ L/mol |
| Low magnetic bead loading capacity | Increase magnetic bead用量 or select high-loading beads |
| Low antibody labeling efficiency | Optimize labeling molar ratio (AE:antibody = 5-10:1; HRP:antibody = 2-4:1) |
| Low luminescent substrate sensitivity | Switch to a different luminescent substrate system (e.g., HRP-Luminol to AP-AMPPD) |
| Incorrect coating orientation | Use oriented coating (e.g., Protein A/G or streptavidin-biotin system) |
Q2: Why is the background signal too high in CLIA?
A: High background is usually related to magnetic beads, antibodies, or washing.
| Cause | Solution |
|---|---|
| High non-specific adsorption of magnetic beads | Replace with low-adsorption magnetic beads; increase blocking agent concentration |
| Non-specific binding of labeled antibody | Optimize labeled antibody concentration; add blocking agents |
| Insufficient washing | Increase wash cycles (5-7 times) or increase Tween-20 concentration |
| Spontaneous luminescence of substrate | Check substrate storage conditions; avoid contamination |
| Magnetic bead aggregation | Sonicate to disperse; optimize storage buffer |
Q3: How to solve magnetic bead aggregation?
A: Magnetic bead aggregation leads to batch failure and abnormal results.
| Cause | Solution |
|---|---|
| Inappropriate storage buffer | Use PBS buffer containing BSA (0.1-0.5%) and Tween-20 (0.05%) |
| Excessive drying | Keep magnetic beads moist; avoid drying |
| Freeze-thaw cycles | Avoid repeated freeze-thaw; aliquot for storage |
| Incorrect pH | Maintain pH 7.0-7.4 |
| Sonication | Sonicate before use (water bath sonication, 30-60 seconds) |
Q4: How to control large inter-batch variability in CLIA reagents?
A: Large inter-batch variability is usually related to inconsistent raw material batches or process control.
| Cause | Solution |
|---|---|
| Inconsistent antibody batches | Purchase large packaging of antibodies; retain samples for testing |
| Magnetic bead batch variability | Use the same batch of magnetic beads (stock large packaging) |
| Labeling process variation | Standardize labeling process; add quality control points |
| Calibrator batch variability | Calibrators should be traceable to the same reference material |
| Control monitoring | Use multi-concentration controls to monitor each reagent batch |
Q5: Can I use sodium azide as a preservative for CLIA reagents?
A: No. Sodium azide is prohibited for CLIA reagents.
-
Sodium azide (CAS: 26628-22-8) strongly inhibits HRP and AP activity
-
HRP and AP are key enzymes in CLIA (enzymatic chemiluminescence)
Recommended alternative: ProClin 300 (0.02-0.05%) — broad-spectrum antimicrobial, compatible with HRP/AP.
Q6: What should I do if acridinium ester-labeled antibody has reduced activity?
A: Reduced labeling activity is usually related to labeling conditions or antibody properties.
| Cause | Solution |
|---|---|
| AE:antibody molar ratio too high | Reduce labeling molar ratio (from 10:1 to 5:1) |
| Labeling reaction time too long | Shorten labeling time (30 minutes is sufficient) |
| Antibody does not tolerate labeling conditions | Change antibody clone or use site-specific labeling |
| Purification process damages antibody | Use gentle purification methods |
| Improper storage conditions | Store at -20°C, protect from light, avoid repeated freeze-thaw |
VI.Summary
CLIA, as the most sensitive and widest linear range technology platform in immunoassay, has reagent performance that heavily depends on the proper selection and combination of magnetic beads, antibody labels, chemiluminescent substrates, calibrators, stabilizers, and other raw materials. Enzymatic chemiluminescence (HRP-Luminol, AP-AMPPD) and direct chemiluminescence (Acridinium ester) each have their advantages; the choice depends on the testing requirements and equipment platform.
艳 李
