Protein Quantification Techniques in Biological Fluids
Summary
Protein quantification in biological fluids is fundamental to clinical diagnostics, drug development and bioprocess monitoring. Common approaches include ultraviolet absorbance, colourimetric assays (biuret, Lowry, Bradford and bicinchoninic acid), fluorometric methods and immunoassays. Mass-spectrometric and microfluidic platforms offer increasing sensitivity and multiplexing capabilities, while point-of-care biosensors address the need for rapid field-deployable measurements. Key challenges arise from complex sample matrices such as blood plasma, urine and cerebrospinal fluid, which may contain interfering substances that affect assay linearity and accuracy. Sample pretreatment—precipitation, desalting or dilution—often mitigates these effects but adds time and labour. Innovations in labelling chemistry, miniaturised formats and digital imaging seek to reduce sample volumes to microlitre or nanolitre scales, improve throughput and lower costs. The global significance of reliable protein quantification spans monitoring nutritional status in resource-limited settings, guiding personalised medicine and ensuring consistent product quality in biomanufacturing.
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Protein Quantification Techniques in Biological Fluids publication trend
The graph below shows the total number of articles in protein quantification techniques in biological fluids across all publications each year (not limited to Nature Index journals).
Technical terms
Bicinchoninic acid (BCA) assay: A colourimetric method in which protein-mediated reduction of Cu2+ to Cu+ is detected by BCA, yielding a purple complex.
Bradford assay: A dye-binding technique based on the increase in absorbance when Coomassie Brilliant Blue G-250 binds to basic and aromatic amino acid residues.
Lowry assay: A two-step method combining copper reduction by peptide bonds and subsequent reaction with the Folin–Ciocalteu reagent to produce a blue colour.
Biuret method: A direct copper-based assay where peptide bonds chelate Cu2+ in alkaline solution, producing a violet-blue complex proportional to protein concentration.
Dumas method: A combustion-based nitrogen analysis that estimates protein content by measuring total nitrogen released from a sample.
Flow injection analysis: An automated technique for injecting samples into a continuous carrier stream for reagent mixing and spectrophotometric detection.
Microvolume assay: A quantification format requiring only microlitre to nanolitre sample volumes, often paired with digital imaging or fluorescence detection.
References
- Comparative study of the most commonly used methods for total protein determination in milk of different species and their ultrafiltration products. Frontiers in Nutrition (2022).
- Sensitive and rapid Bradford and BCA protein assay by a common desktop scanner. BIOMEDICINE (2023).
- Espectrofotometria de proteínas totais em plasma de sangue bovino por análise em fluxo. Scientia Agricola (2002).
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