Scientific revision note: This version uses precise terminology, avoids unsupported claims, distinguishes established facts from experimental applications, and adds evidence-based limitations and references.
Scientific scope
A laboratory technique should be selected according to the biological question, sample type, required sensitivity, specificity, throughput, and interpretability. The most common mistake in learning biotechnology methods is memorizing procedure names without understanding what each method detects and what type of evidence it produces.
DNA-focused methods
Restriction Fragment Length Polymorphism (RFLP) detects sequence variation that changes restriction-enzyme cutting patterns. DNA is digested, separated by electrophoresis, and compared by band size. RFLP is historically important and conceptually useful, but many applications have been replaced by PCR-based genotyping and sequencing.
Southern blotting detects a specific DNA sequence after restriction digestion, electrophoresis, transfer to a membrane, and hybridization with a labeled probe. It can provide information about fragment size and target presence, but it is slower and less sensitive than many modern PCR or sequencing methods.
Sanger sequencing determines nucleotide order using chain-terminating dideoxynucleotides. It remains the gold-standard confirmatory method for small regions, plasmid inserts, and selected variants, although it is not suited for large-scale genome-wide analysis.
RNA and gene-expression methods
Northern blotting detects RNA molecules, especially mRNA, and can provide information about transcript size and abundance. Its main limitations are RNA instability, lower throughput, and lower sensitivity compared with RT-qPCR and RNA-seq.
Microarrays measure expression of many known genes simultaneously by hybridizing labeled cDNA to immobilized probes. Microarrays require prior knowledge of probe sequences. RNA-seq has largely replaced microarrays for discovery-based transcriptomics because it can detect novel transcripts, splice isoforms, and broader dynamic ranges.
RNA-seq is not simply “sequencing RNA” directly in most workflows; RNA is converted to cDNA, sequenced, and quantified computationally. Experimental design must control for RNA integrity, library type, sequencing depth, batch effects, and biological replication.
Protein and immunological detection methods
Native PAGE separates proteins while preserving native conformation, so mobility depends on size, shape, charge, and oligomeric state. SDS-PAGE denatures proteins and gives them a broadly similar negative charge-to-mass ratio, making separation mainly size-based.
Western blotting detects a specific protein after electrophoretic separation and membrane transfer using antibodies. It provides approximate molecular weight and target specificity, but quantification requires careful normalization and validation of antibody specificity.
ELISA detects or quantifies antigens or antibodies using enzyme-linked detection. Sandwich ELISA is commonly used for antigen quantification, indirect ELISA for antibody detection, competitive ELISA for small molecules or limited epitopes, and direct ELISA for simpler detection formats.
Immuno-PCR combines antibody recognition with DNA amplification. It can be extremely sensitive, but it requires rigorous controls because PCR amplification can magnify contamination and nonspecific binding.
Cellular and genome-wide methods
Fluorescence in situ hybridization (FISH) uses fluorescent probes to locate DNA or RNA sequences in cells or chromosomes. It is valuable for detecting chromosomal rearrangements, deletions, amplifications, microbial identification, and spatial localization.
Chromatin immunoprecipitation followed by sequencing (ChIP-seq) maps DNA regions bound by proteins or associated with histone modifications. Interpretation requires controls, peak calling, replicate consistency, and awareness that binding does not always imply functional regulation.
Molecular typing compares organisms at the molecular level. Techniques include PCR-based typing, MLST, PFGE, 16S rRNA sequencing, and whole-genome sequencing. Whole-genome sequencing now offers the highest resolution for outbreak investigation when sampling and metadata are adequate.
Separation and identification methods
Chromatography separates molecules based on differential interactions between a mobile phase and a stationary phase. Variants include size-exclusion, ion-exchange, affinity, reverse-phase, gas chromatography, and high-performance liquid chromatography. The best type depends on whether the target is a protein, metabolite, drug, lipid, or small molecule.
Edman degradation identifies the amino-acid sequence of peptides from the N-terminus one residue at a time. It is historically important and still useful for purified short peptides, but mass spectrometry is now the dominant method for large-scale protein identification.
Key scientific takeaway
No technique is universally superior. A scientifically correct workflow starts with the biological question, then selects the method that produces the most appropriate and validated evidence.
Technique selection guide
| Question | Suitable method | Typical output | Major caution |
| Is a DNA sequence present? | PCR, Southern blot, targeted sequencing | Band, probe signal, or sequence | Contamination and probe/primer specificity |
| What is the exact nucleotide sequence? | Sanger sequencing or NGS | Base calls and quality scores | Coverage and validation requirements |
| Is a gene expressed? | RT-qPCR, Northern blot, RNA-seq | Expression level or transcript size | RNA quality and normalization |
| Is a protein present? | Western blot, ELISA, mass spectrometry | Band, concentration, or peptide spectra | Antibody specificity or database matching |
| Where is a sequence inside cells? | FISH | Microscopy signal location | Probe specificity and imaging controls |
| Where does a regulatory protein bind? | ChIP-seq | Genome-wide peaks | Antibody quality and false-positive peaks |
References
- Green, M. R., & Sambrook, J. (2012). Molecular Cloning: A Laboratory Manual. Cold Spring Harbor Laboratory Press.
- Southern, E. M. (1975). Detection of specific sequences among DNA fragments separated by gel electrophoresis. Journal of Molecular Biology, 98, 503-517.
- Burnette, W. N. (1981). Western blotting. Analytical Biochemistry, 112, 195-203.
- Engvall, E., & Perlmann, P. (1971). Enzyme-linked immunosorbent assay. Immunochemistry, 8, 871-874.
- Park, P. J. (2009). ChIP-seq: Advantages and challenges of a maturing technology. Nature Reviews Genetics, 10, 669-680.