Transfer membranes are core porous support materials widely applied in molecular blotting technologies, including Western blotting, Southern blotting and Northern blotting. Serving as a stable solid‑phase carrier, they enable the immobilization, preservation and subsequent detection of biomolecules such as proteins, DNA and RNA after electrophoretic separation. Unlike fragile polyacrylamide or agarose gels that are prone to damage and difficult to store, transfer membranes feature excellent mechanical stability, specific molecular binding capacity and low non‑specific background interference, laying a foundation for efficient biomolecular qualitative and quantitative analysis.
Figure 1: Transfer membrane
The most commonly used transfer membrane materials in biochemical experiments are nitrocellulose (NC) and polyvinylidene difluoride (PVDF). NC membranes exhibit moderate protein binding affinity and fast molecular adsorption, making them easy to use for routine immunoblot detection. PVDF membranes, with stronger hydrophobicity and higher protein binding capacity, require methanol activation before use. Due to their superior toughness and molecule retention ability, they excel in complex applications such as repeated stripping and reprobing, as well as protein sequencing. However, NC membranes are not suitable for stripping and reprobing due to their relatively fragile structure and weaker protein retention during repeated washes. Both membranes are available in precise pore sizes (0.2 μm and 0.45 μm), which can be selected based on the molecular weight of the target biomolecules to ensure optimal transfer efficiency.
The working principle of transfer membranes relies on electrostatic adsorption and hydrophobic interaction. Under the electric field of electrotransfer equipment, charged biomolecules separate from the gel and migrate directionally, then stably bind to the membrane surface. This process converts the invisible molecular separation pattern in the gel into a detectable and storable membrane imprint, facilitating subsequent antibody hybridization, color development and signal analysis.
A sandwich transfer membrane is not an independent membrane material, but a standardized assembled transfer structure formed by stacking filter paper, gel, transfer membrane and auxiliary sponges in a specific order, which is the mainstream assembly mode for electrotransfer experiments. Its core design simulates a "sandwich" layered structure, solving the problems of uneven electric field, bubble interference and incomplete molecular transfer in traditional single‑sided transfer, and greatly improving the stability and repeatability of experiments.
Sandwich transfer membrane：
Figure 2: Sandwich Transfer membrane
The standard assembly sequence of the sandwich transfer structure is fixed and directional. From the negative electrode to the positive electrode of the transfer cassette, the layers are thick sponge pad, filter paper, electrophoresis gel, transfer membrane, filter paper and thick sponge pad in turn. The directional assembly is critical: biomolecules migrate from the negative electrode to the positive electrode, so the membrane must be closely attached to the gel's positive side to capture migrating molecules accurately. The filter paper layers on both sides absorb excess transfer buffer, eliminate bubbles between layers, and ensure uniform current distribution across the gel and membrane surface.
Figure 3: Assembly structure of sandwich transfer membrane system
The biggest advantage of the sandwich transfer mode is its tight fitting structure. The sponge pads provide uniform pressure to eliminate gaps between layers, avoiding bubble‑induced transfer dead zones and incomplete molecular transfer. This structure is compatible with both wet tank transfer and semi‑dry transfer systems, applicable to almost all protein and nucleic acid transfer scenarios. Wet transfer is preferred for high‑molecular‑weight proteins, while semi‑dry transfer offers faster processing for routine applications. Compared with simple diffusion transfer, the sandwich configuration features faster transfer rates, higher molecular retention and more uniform transfer results.
In practical experiments, the sandwich transfer membrane system requires strict adherence to operating procedures. All layers must be fully infiltrated with transfer buffer, and no wrinkles or bubbles are allowed during assembly. After assembly, the compactly stacked sandwich structure ensures stable and efficient transfer. This standardized structure has become the gold standard for modern blotting experiments, widely used in biomedical research, disease marker detection and molecular biology verification.
In conclusion, transfer membranes are the core functional carrier for biomolecular transfer, while the sandwich transfer structure is the optimal assembly and application mode of transfer membranes. The combination of the two enables efficient, stable and repeatable biomolecular transfer, providing indispensable technical support for modern molecular biology and biochemical detection.