Home › Microscopy & Imaging › Immunohistochemistry Protocol for Paraffin embedded Tissue Sections

Steps

1 Sample Preparation and Deparaffinization/Rehydration 01:39
2 Antigen Unmasking 02:45
3 Chromogenic Staining 03:48

Microscopy & Imaging Cell Signaling Technology

Immunohistochemistry Protocol for Paraffin embedded Tissue Sections

Protocol

IHC on paraffin-embedded tissue sections: deparaffinization, antigen retrieval, peroxidase blocking, primary and secondary antibody incubation, DAB detection, and counterstaining.

Difficulty

intermediate

Total time

6-8 hours (or overnight)

Biosafety

BSL-1

Steps

1

Sample Preparation and Deparaffinization/Rehydration

Bake slides at 60 C for 1 hour to melt paraffin. Pass slides through xylene (3 x 5 min) to remove paraffin, then graded ethanol (100%, 95%, 70%) and water to rehydrate the tissue for downstream staining.

▶ 01:39

2

Antigen Unmasking

Restore epitopes masked by formalin fixation: heat slides in citrate buffer (pH 6) or EDTA buffer (pH 9) at near-boiling for 10-20 min using a steamer or pressure cooker; cool slowly to room temperature.

▶ 02:45

3

Chromogenic Staining

Block endogenous peroxidase (3% H2O2, 10 min) and non-specific binding (normal serum). Apply primary antibody overnight at 4 C; wash with TBST; apply HRP-conjugated secondary antibody (30 min); develop with DAB substrate until brown signal appears. Counterstain nuclei with hematoxylin, dehydrate, and mount.

▶ 03:48

🚨 Failure Case Library (24) + Submit your own case

False negative — no staining at all

Even the positive control shows no staining; expected positive regions are completely blank; the experiment failed.

💡 4 · ✓ 4

False-Positive Signal from Endogenous Enzyme Activity

High background signal observed when using enzyme-conjugated antibodies (HRP or AP), caused by endogenous alkaline phosphatase or peroxidase activity in tissue generating false-positive results.

💡 4 · ✓ 4

Tissue detachment / sections fall off the slide

Tissue falls off during staining; sections become broken or missing; results cannot be interpreted.

💡 4 · ✓ 4

Abnormal nuclear staining (wrong subcellular localization)

Cell nuclei show strong staining when they shouldn't, or expected positive nuclei show no staining; nuclear/cytoplasmic localization is wrong.

💡 4 · ✓ 4

High Background from Excessive Antibody Concentrations

Elevated background staining throughout tissue sections due to excessively high concentrations of primary or secondary antibodies leading to non-specific binding.

💡 4 · ✓ 5

Complete absence of IHC signal due to reagent degradation

No staining is observed in immunohistochemistry despite proper protocol execution. Previously validated antibodies or detection kits fail to produce any signal.

💡 4 · ✓ 6

Incorrect Antibody Diluent Selection

Suboptimal signal intensity or background issues despite correct antibody concentration. Different antibodies show dramatically different performance in TBST/5% NGS versus SignalStain Antibody Diluent.

💡 3 · ✓ 3

Strong positive background / non-specific staining

Whole slide appears brown/diffuse stained; negative control also shows signal; impossible to distinguish true positive signal.

💡 5 · ✓ 5

Weak staining / signal too faint

Positive regions show very pale staining; barely distinguishable from negative control; signal appears dotted or discontinuous.

💡 5 · ✓ 5

Autofluorescence from Formaldehyde-Based Fixatives

High fluorescent background signal when using formaldehyde-based fixatives (formalin/PFA) with fluorescent detection, particularly at green wavelengths where these fixatives naturally fluoresce.

💡 4 · ✓ 4

Target protein absent or below detection threshold in tissue

No staining observed in experimental tissue samples. The target protein may not be expressed in the tissue type or developmental stage being examined, or present at undetectable levels.

💡 4 · ✓ 6

Weak or Suboptimal IHC Staining Intensity

Staining signal is present but significantly weaker than expected, with poor contrast between positive cells and background, making interpretation difficult.

💡 5 · ✓ 5

Inadequate Detection System Sensitivity

Weak signal or no staining despite proper primary antibody performance. Standard HRP-conjugated secondary antibodies fail to provide sufficient signal amplification.

💡 4 · ✓ 4

Suboptimal Antigen Retrieval Method Selection

Weak or absent staining despite proper antibody concentration and incubation. Clear performance differences observed when comparing different antigen retrieval heating methods.

💡 4 · ✓ 4

FFPE tissue shows no staining from incomplete deparaffinization

Paraffin-embedded tissue sections show no immunostaining. Residual paraffin creates a physical barrier preventing antibody access to tissue antigens.

💡 3 · ✓ 4

Weak or absent signal from inadequate antibody concentration or incubation

No detectable staining despite proper protocol execution. Insufficient antibody-antigen binding due to suboptimal concentration or incubation conditions.

💡 4 · ✓ 5

Primary-secondary antibody incompatibility preventing detection

No signal detected despite proper primary antibody binding. Secondary antibody fails to recognize or bind to the primary antibody, breaking the detection chain.

💡 4 · ✓ 5

Spotty or Uneven Background Staining Pattern

Staining pattern shows irregular, patchy, or spotty background with uneven distribution across tissue sections, indicating technical artifacts rather than biological variation.

💡 3 · ✓ 3

Incorrect Antibody Diluent Selection

Staining quality is significantly reduced or inconsistent when using generic diluent instead of product-specific recommended diluent, as different antibodies perform optimally in different buffer compositions.

💡 3 · ✓ 4

Insufficient Detection System Sensitivity

Signal is weak or undetectable despite correct antibody and protocol, particularly for low-abundance targets, indicating that the detection system lacks sufficient signal amplification.

💡 3 · ✓ 4

Endogenous Biotin Interference

High background staining specifically in kidney, liver, or other biotin-rich tissues when using biotin-based detection. Background not resolved by standard blocking procedures.

💡 3 · ✓ 3

Edge effect / uneven staining across the slide

Slide edges show darker staining than center, or one half stains more than the other; reproducibility between fields is poor.

💡 4 · ✓ 4

Loss of membrane protein staining after permeabilization

No staining is detected when targeting membrane proteins in IHC. Signal is absent despite antibody validation, suggesting structural damage to membrane epitopes.

💡 3 · ✓ 4

Suboptimal Primary Antibody Incubation

Inconsistent or weak staining results despite following protocol. Staining intensity varies between experiments using same antibody lot and tissue type.

💡 3 · ✓ 3

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