Electrophoresis - Introduction & History

What is Electrophoresis?

Electrophoresis is one of the techniques in the laboratory, which is used to separate RNA, protein, or DNA molecules based on their electric charge and size (Electrophoresis meaning - ‘to bear electrons’). Electric current is applied to drive the molecules to be separated via a gel. The pores in the gel act like a sieve, which paves the rapid movement of smaller molecules than the larger molecules.

It separates the molecule fragments into pieces through the gel. In addition, it separates molecules in the liquid state.  In the field of molecular biology and biochemistry, it is one of the prominent methods of analysis of biomolecules. A cell’s DNA is too long to go into the well of the gel, so it is digested by restriction enzymes and loaded into the gel. When DNA or proteins get mutated, they are shorter or longer and they run on electrophoresis differently than the normal run, thus some diagnoses can be confirmed by electrophoresis.

It is an electrokinetic process. The separation of molecules is achieved based on purity, density, and size. Electrophoresis of cations is cataphoresis, while that of anions is anaphoresis.

History of Electrophoresis

Electrokinetic Phenomenon

The base for all electrophoretic processes is the electrokinetic phenomenon. It was discovered in 1807 by Ferdinand from Moscow State University. He observed that on the application of a constant electric field, clay particles dispersed in the water started migrating.

Tiselus era

Arne Tiselius developed the “Tiselius Apparatus” for moving boundary electrophoresis in the 1930s with the support from Rockefeller Foundation. Effective zone electrophoresis was developed in the 1940s and 1950s. 

By the 1960s, sophisticated electrophoresis was manufactured to be catered for molecular biology laboratories. Towards the 20th century, U-shaped glass tubes were created for moving boundaries of charged particles. Tiselius apparatus had shortcomings, as the process was run in fully liquid conditions and separation could not be done fully. So, the apparatus was modified to run on solid matrices called gels, so that discrete bands could be obtained. This leads to the development of ‘Zonal Electrophoresis’. After the introduction of starch gel in 1955 as an electrophoretic substrate by Oliver Smithies, the technique became useful to find smaller differences in related proteins and helpful in the analysis of complex protein mixtures.

Filter paper

Filter paper electrophoresis in which filter paper is a supporting medium is used in the separation of blood serum proteins. This method is inexpensive and used as an efficient routine. Azocarmine B, Amidoblack 10 B, and bromophenol blue are used for staining proteins and lipids on filter paper.

Cellulose acetate

In 1957, a German Chemist, Joachin Kohn developed cellulose acetate electrophoresis, which is a modified form of zone electrophoresis. This method is employed for routine diagnosis in clinical laboratories. Here, membranes are made from cellulose acetate as stripes, which act as electrodes for the electrophoresis process. It is used as a rapid screening process, comparing the patterns with a known standard. It is used for hemoglobin profiling in serum analysis.

Development of acrylamide gel

In 1959, Raymond and Winstraub used acrylamide gels for the first time. This technique is being continuously modified and finds widespread use in protein laboratories. Polyacrylamide is the polymer of acrylamide and due to polymerization and crosslinking. Polyacrylamide gel electrophoresis is abbreviated as PAGE.

Isoelectric focussing

In 1961, Svensson developed an isoelectric focussing (IEF) apparatus with the development of a pH gradient from cathode to anode in carrier ampholytes. It is used for the separation of amino acids. The proteins migrate according to the surface charge.

Disc Gel

Davis and Ornstein in 1964, introduced a method known as Disc Gel Electrophoresis, which gives an extremely high resolution of proteins in the cylindrical column of polyacrylamide gel. A huge number of proteins in a complex mixture could be separated and detected at one time.

SDS

In 1969, during electrophoresis of proteins,  Beber and Osborn reported improved separation of proteins using SDS electrophoresis.

In 1971, Laemmli modified SDS electrophoresis with the introduction of stacking gel as a discontinuous gel. Using this, unknown proteins in bacteriophage T4 were discovered.

Cellulose Acetate Modification

In 1971, Meera modified cellulose acetate gel electrophoresis.

2-D Gel Electrophoresis

In 1975, 2-D gel electrophoresis was run by Klose. Larger gels were used without the larger equipment. Ready made and frozen gels were used and results were obtained with good reproducibility. High-resolution protein patterns were obtained.

Sequencing Gel

In 1977, sequencing gels were used for the first time. The sequence was read from the bottom to the top of the gel in the lanes after detection. It is used to resolve the single-stranded biomolecules.

The rise of agarose gel, pulsed field and capillary electrophoresis

In 1979, agarose gel electrophoresis was developed.

In 1983, pulsed-field electrophoresis was developed. It is used in the separation of larger molecules having a size of 12Mb. Due to the application of pulses for longer times, bigger molecule migration happens.

In 1983, the capillary electrophoresis technique was used. It is performed in a capillary tube, ranging from 10 to 100 micrometers. It is a relatively simple technique. It is used in the detection of short tandem repeat (STR) alleles in forensic laboratories.

Conclusion

At first, the electrophoresis technique was naive. Then, it has undergone many modifications to reach its present level. Meanwhile, there are so many events that have led to the evolution of different types of electrophoresis. Now, each variation of electrophoretic techniques is suited and tailor-made for a single application. Depending on the cost and application, the type of technique can be chosen.