A colorimetric strategy for quantifying amino acids using E. coli auxotrophs displaying gold-binding proteins

Area of Science:

• Biotechnology
• Analytical Chemistry
• Microbiology

Background:

• Accurate amino acid quantification is crucial for diagnosing metabolic disorders.
• Existing methods can be complex, time-consuming, or require specialized equipment.

Purpose of the Study:

• To develop a novel, cell-based colorimetric assay for sensitive and specific amino acid quantification.
• To demonstrate the assay's utility in detecting amino acid imbalances associated with inherited metabolic diseases.

Main Methods:

• Engineered *Escherichia coli* auxotrophs displaying gold-binding proteins (GBPs) on their surface were utilized.
• The assay relies on GBP-mediated aggregation of gold nanoparticles (AuNPs), causing a visible color shift.
• Quantitative analysis was performed using absorbance measurements.

Main Results:

• The assay successfully detected ten essential amino acids with high specificity and linearity (R² > 0.96).
• Low detection limits (0.43–1.04 μM) and excellent analytical precision (CV < 4%) were achieved.
• The assay accurately identified elevated amino acid levels in models of phenylketonuria, homocystinuria, and maple syrup urine disease, with high recovery rates (98–102%).

Conclusions:

• This cell-based colorimetric assay offers a sensitive, specific, and quantitative method for amino acid analysis.
• The assay provides a simple, instrument-free readout, making it suitable for various diagnostic and research applications.
• This technology represents a promising platform for accessible amino acid quantification.