For tissue and cell samples in ELISA experiments, homogenization pretreatment is required in advance. The brief operating procedures are described below:

1. Sample Homogenization Procedures

1.1 Tissue Homogenization

Take an appropriate amount of tissue blocks, rinse them in pre-cooled PBS (0.01 M, pH 7.0-7.2) to remove blood (lysed red blood cells in homogenate will interfere with test results). Weigh and mince the tissue, then transfer it into a glass homogenizer with corresponding volume of PBS (mass-to-volume ratio of 1:9 is generally recommended; the volume can be adjusted appropriately according to experimental requirements with proper records. Protease inhibitors are suggested to be supplemented in PBS). Perform thorough grinding on ice.

To achieve complete cell lysis, sonication or repeated freeze-thaw cycles can be applied to the homogenate. Keep samples cooled in ice-water bath during sonication; for freeze-thaw treatment, repeat the cycle twice. Centrifuge the final homogenate at 5000 × g for 5-10 min, and collect the supernatant for subsequent detection.

1.2 Cell Lysate Preparation

Harvest cell pellets and add a certain volume of PBS (200-300 μL is recommended; the exact volume varies depending on target analytes). If available, add mild detergent Triton X-100 (0.5 %) to facilitate lysis. Lyse cells via sonication or repeated freeze-thaw cycles.

• Sonication: approximately 5 min, followed by centrifugation at 12000 × g for 5 min.
• Freezethaw: repeat 3-4 cycles using liquid nitrogen or −80 °C freezer, then centrifuge at 12000 × g for 5 min.

Collect the supernatant for detection.

For detailed lysis protocols, please refer to: https://www.elkbiotech.cn/view/1808.html

2. Mandatory BCA Protein Quantification Prior to ELISA Loading for Tissue & Lysate Samples

1. Cell numbers cannot be perfectly consistent across samples. Variations also exist in tissue block size, sampling location and lysis efficiency (some samples are fully lysed while others contain abundant debris). Therefore, BCA protein quantification should be performed after lysis for homogenized samples.
2. ELISA on lysate samples measures the relative abundance of target protein. BCA quantification corrects loading discrepancies and eliminates deviations caused by inconsistent cell quantities and variable lysis efficiency among different samples.
3. BCA enables data normalization: ELISA signals can be converted into target protein signal / μg total protein, yielding target analyte content per μg/mg total protein. This calculation delivers higher accuracy compared with volume-based normalization.

3. BCA Protein Quantification for Experimental Quality Control

1. Evaluate lysis performance: Extremely low BCA readings indicate lysis failure or sample loss.
2. Identify abnormal samples: Samples with total-protein concentrations deviating significantly from the overall population suggest sampling errors or protein degradation, which can be flagged and excluded.
3. Determine optimal dilution factor for ELISA: Estimate sample dilution fold based on BCA-measured protein concentration, so as to avoid matrix effect and hook effect caused by high total-protein content.

Practical experience:

• For samples with protein concentration ＜ 2 mg/mL: 10- to 20-fold dilution is recommended for ELISA.
• For samples with protein concentration ≥ 2 mg/mL: 20- to 100-fold dilution is recommended.

Higher total-protein concentration requires greater dilution. Exact dilution folds should be confirmed by preliminary experiments.

Summary

After homogenization or lysis, tissue and cell samples should undergo BCA protein quantification before ELISA loading. On one hand, BCA corrects sample loading variations and normalizes target-protein signals by totalprotein concentration. Results are converted to target analyte levels per unit total protein to improve accuracy and comparability across different samples. On the other hand, BCA serves as experimental quality control, helping assess lysis efficiency, screen out aberrant samples and define proper ELISA dilution factors, thus mitigating matrix effect and hook effect induced by high total-protein content. Proper BCA quantification is an essential prerequisite for obtaining reliable and reproducible ELISA data.