Quartz 4

Total Amine Screen

3 min read

Total Amine Screen

Principle

Gold nanoparticles (AuNPs) aggregate in the presence of biogenic amines (histamine, putrescine, cadaverine, tyramine, etc.), shifting their surface plasmon resonance peak from ~522nm (red) to ~650nm (blue). The red→blue color shift is visible to the naked eye above ~7ppm and quantifiable by measuring the absorbance ratio A650/A522.

Important: This assay is NOT specific to histamine. It detects all biogenic amines. Use as a triage screen:

  • Negative/low → sample is probably low in all biogenic amines, no further testing needed
  • Elevated → run Histamine Strip for histamine-specific quantification

This is the intended workflow. The AuNP screen costs fractions of a cent per test; the enzyme strip costs ~$8. Gate the expensive test with the cheap one.

Reagents

Gold Nanoparticle Solution

AuNPs synthesized by citrate reduction method (25nm target size):

Synthesis (one-time batch, stores refrigerated 30 days):

  1. Bring 100ml distilled water to boil in clean glassware
  2. Add 1ml of 1% chloroauric acid (HAuCl₄) solution
  3. Immediately add 2ml of 1% sodium citrate solution while stirring
  4. Continue boiling and stirring ~10 minutes — solution turns wine red
  5. Cool, store in amber bottle at 4°C
  6. Verify: should be clear wine red, SPR peak ~522nm

Sourcing chloroauric acid: Available from lab suppliers (Sigma, Strem) ~$20-40 for small quantities. Handle with care — gold(III) compounds are irritants.

Calibration Standard (histamine dihydrochloride)

  • Available from lab suppliers
  • Prepare known concentration solutions for semi-quantitative calibration

Procedure

  1. Take Tube C from Unified Sample Prep (acidic extract, pH ~3-4)
  2. Neutralize to pH 6-7 with small amount of NaOH
  3. Add 0.5ml neutralized extract to 0.5ml AuNP solution
  4. Mix, wait 1 minute
  5. Observe color:
    • Red/unchanged = low/no amines
    • Purple = moderate amines
    • Blue = high amines
  6. Read absorbance ratio A650/A522 for semi-quantification

Sensitivity

  • Naked eye detection: ~7ppm histamine equivalent
  • Instrument detection (ratio method): ~0.72µM (~0.08ppm) with 25nm AuNPs
  • Regulatory concern threshold for fish: 35-50ppm
  • Fresh vegetables: typically low, fermented/aged/cured foods: potentially high

Triage Decision

Screen ResultAction
No color changeLog as low amine, no strip needed
Slight purpleBorderline — consider strip if food is high-risk category
Clear blueRun histamine strip

Notes

  • AuNP solution stability: 30 days at 4°C. SPR peak should remain at 522nm — check before use
  • Non-specific: putrescine and cadaverine trigger same response as histamine. This is a feature for triage (total amine burden) but not for specificity
  • Meat samples: defatting the extract may improve sensitivity — hot water extraction already helps
  • Dry/cured meats can have very high amine levels (studies show up to 1691 mg/kg total BAs in some beef jerky samples)

References

Graph View