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In molecular biology laboratories, electrophoresis is the core technique for separating and identifying nucleic acids and proteins. Acting as the "blood" of the electrophoresis system, electrophoresis running buffer not only conducts electric current but also serves as a critical factor to maintain sample stability and experimental reproducibility.

Whether for DNA fingerprinting, gene cloning verification, or proteomic research, proper selection of electrophoresis buffer directly determines experimental success or failure. This article thoroughly introduces this indispensable laboratory reagent, elaborating on its underlying scientific principles and practical applications.

01 Understanding Electrophoresis Running Buffer

Electrophoresis running buffer refers to the buffer solution used for molecular electrophoresis. It is an essential component of nucleic acid and protein gel electrophoresis systems, functioning as the conductive medium within the electric field and an indispensable medium to stabilize constant pH throughout the system.

During electrophoresis, buffer composition and ionic strength directly govern the electrophoretic mobility of target analytes.

Performing electrophoresis in pure water without buffer will cause severe issues: dramatic pH fluctuation, inefficient heat dissipation, and potential sample degradation or precipitation.

Precisely formulated high-quality electrophoresis buffers effectively resolve these problems and establish a stable, reliable environment for electrophoresis assays.

02 Core Functions of Electrophoresis Running Buffer

Maintain Stable pH Conditions

Electrolytic reactions continuously occur at both electrodes during electrophoresis: oxidation takes place at the anode (4OH⁻-4e⁻→2H₂O+O₂), while reduction occurs at the cathode (4H⁺+4e⁻→2H₂).

Prolonged electrophoresis will gradually acidify the anode solution and alkalize the cathode solution. A robust buffer system possesses powerful buffering capacity to keep pH nearly constant at both poles.

Provide Appropriate Electrical Conductivity

Electrophoresis buffer endows the solution with suitable conductivity to facilitate the migration of DNA molecules. Conventional electrophoresis buffers typically contain Na⁺ at a concentration of 0.01–0.04 mol/L.

Insufficient Na⁺ concentration slows down electrophoretic velocity, whereas excessively high ionic strength generates excessive current, leading to gel overheating or even melting.

Preserve Sample Integrity

EDTA contained in running buffers chelates divalent cations such as Mg²⁺, preventing DNase activation and nucleic acid precipitation induced by Mg²⁺ during electrophoresis, usually applied at a concentration of 1–2 mmol/L.

This protective mechanism prevents sample degradation and unwanted chemical reactions throughout electrophoresis, which is essential for acquiring sharp, credible experimental results.

03 Common Types & Characteristics of Electrophoresis Running Buffers

TAE Buffer

TAE is the most widely adopted buffer system. Supercoiled DNA exhibits molecular weight readings closer to its actual value in TAE (molecular weight values measured in TBE are higher than the true mass).

In addition, linear double-stranded DNA migrates approximately 10% faster in TAE than in the other two buffers, delivering superior separation performance for DNA fragments larger than 13 kb.

TAE is also preferred for electrophoresis prior to DNA fragment recovery. Its main drawback lies in limited buffering capacity, making it unsuitable for extended overnight electrophoresis unless equipped with a circulation device to exchange buffer between the two electrode chambers.

TBE Buffer

TBE features strong buffering capacity, ideal for long-duration electrophoresis. It achieves optimal separation resolution for DNA fragments smaller than 1 kb.

Nevertheless, TBE induces significant electroendosmosis in agarose gels. Non-covalent tetrahydroxyborate complexes form via interaction between borate and agarose matrix, reducing DNA recovery efficiency. Hence, TBE is not recommended for electrophoresis intended for subsequent DNA extraction.

TPE Buffer

TPE also possesses robust buffering capability. However, phosphate salts readily precipitate during ethanol precipitation, so TPE is likewise inappropriate for electrophoresis followed by DNA recovery.

Specialized Buffers for Specific Assays

Apart from the three standard nucleic acid electrophoresis buffers above, multiple customized buffers are available for specialized applications:

MOPS buffer is designated for RNA electrophoresis, while Tris-glycine-SDS buffer is the standard system for SDS-PAGE protein electrophoresis, formulated with 25 mmol/L Tris base, 192 mmol/L glycine, 0.1% SDS at pH 8.3.

pH 8.6 buffer is commonly used in cellulose acetate membrane electrophoresis for serum protein separation and other specimen analyses.

04 Practical Experimental Applications of Electrophoresis Running Buffers

Nucleic Acid Analysis

Appropriate buffer selection is critical for high-resolution nucleic acid separation. TAE buffer is optimized for large DNA fragment separation (>13 kb) and DNA recovery experiments.

TBE buffer is more suitable for small DNA fragment separation (<1 kb) and long-time electrophoresis runs.

For example, selecting the correct buffer according to amplicon size during PCR product identification yields crisp bands and accurate molecular weight estimation.

Protein Research

Distinct buffer systems fulfill diverse separation requirements in protein electrophoresis. Tris-glycine-SDS buffer serves as the gold standard for SDS-PAGE, applied for protein molecular weight determination and purity testing.

pH 8.6 buffer enables complete fractionation of serum protein components in cellulose acetate membrane electrophoresis.

For two-dimensional electrophoresis, samples are dissolved in complex rehydration loading buffer containing urea, thiourea, CHAPS and ampholytes, enabling dual separation based on isoelectric point and molecular weight.

Immunological Assays

For immunoelectrophoresis such as counterimmunoelectrophoresis, TAE buffer can replace conventional barbital-sodium barbital buffer, delivering sharper precipitin lines, improved reagent safety and reduced experimental costs.

Similarly, borate buffer is a safe alternative to toxic barbital buffer for serum protein cellulose acetate electrophoresis. Borate buffer at an ionic strength of 0.08 resolves 5 distinct clear protein bands, maintaining stable performance after 10 consecutive electrophoresis runs.

05 Buffer Selection, Preparation & Usage Guidelines

How to Select the Optimal Buffer

Multiple factors must be considered when choosing electrophoresis running buffer:

• Sample type: Nucleic acid or protein? TAE/TBE for DNA, MOPS for RNA, Tris-glycine system for protein assays
• Target fragment size: TAE preferred for large DNA fragments (>13 kb), TBE optimal for small fragments (<1 kb)
• Electrophoresis duration: TAE for short runs, TBE recommended for long-time electrophoresis
• Downstream processing: Avoid TBE and TPE if DNA fragment recovery is required post-electrophoresis

Preparation & Storage Key Points

Preparation of 50× TAE Stock Buffer: Weigh 242 g Tris and 37.2 g Na₂EDTA·2H₂O into a 1 L beaker; add approximately 600 mL deionized water and stir thoroughly; introduce 57.1 mL glacial acetic acid until fully dissolved; dilute 50-fold with pure water to obtain 1× working TAE buffer before use.

Preparation of 10× TBE Stock Buffer: Weigh 108 g Tris, 7.44 g Na₂EDTA·2H₂O and 55 g boric acid into a 1 L beaker; add around 700 mL deionized water and stir to dissolve; adjust pH to 8.3 with NaOH solution, bring the final volume to 1 L with deionized water, and store at room temperature.

Concentrated stock electrophoresis buffers can be stored at room temperature for several months, yet freshly diluted working solution is recommended to guarantee optimal performance. Discard and re-prepare new buffer if precipitation or microbial contamination is observed.

From routine agarose DNA electrophoresis to sophisticated proteomic analysis, from traditional cellulose acetate membrane electrophoresis to high-throughput capillary electrophoresis, proper selection and formulation of running buffer remain decisive for reliable experimental outcomes.

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