Fluorophores & Labeling in FICT: The Chemistry Behind the Signal¶
The sensitivity of FICT ultimately comes down to the fluorophore — the molecule that emits light when excited. This page explains the fluorophore chemistry and why it determines assay performance.
What a Fluorophore Does¶
A fluorophore absorbs light at one wavelength (excitation) and re-emits it at a longer wavelength (emission). In FICT:
Excitation light (e.g., 365 nm) → fluorophore absorbs → emits (e.g., 615 nm) → photodetector measures
The Fluorophore Choice Matters¶
| Property | Impact on assay |
|---|---|
| Brightness (quantum yield) | Higher → better sensitivity |
| Stokes shift (excitation−emission gap) | Larger → less background interference |
| Photostability | Higher → more reproducible signal |
| Matrix resistance | Better → less interference from sample |
Time-Resolved Fluorescence: The Key Advantage¶
Many FICT systems use lanthanide chelates (e.g., europium) with time-resolved fluorescence:
- Lanthanides emit over a long lifetime (microseconds vs nanoseconds).
- The detector waits out the short-lived background fluorescence, then measures the lanthanide signal.
- Result: near-zero background, dramatically improving the signal-to-noise ratio — the basis of pg/ml sensitivity.
Why This Beats Colloidal Gold¶
| Factor | Colloidal gold | Lanthanide fluorescence |
|---|---|---|
| Signal | Color (absorbance) | Long-lived emission |
| Background | Sample haze | Time-resolved elimination |
| Detection limit | ~1 ng/ml | pg/ml |
FAQ¶
What is the Stokes shift, and why does it matter? It is the gap between excitation and emission wavelengths. A larger gap lets the detector separate the signal from scattered excitation light, reducing background.
Why use time-resolved fluorescence? It eliminates short-lived background fluorescence (from sample components) by measuring only the long-lived lanthanide signal — the core reason FICT reaches pg/ml sensitivity.
For the full detection principle, see the FICT technical white paper.
Authored by: Migibio Clinical & Scientific Affairs, Guangzhou Magic Biotech Co., Ltd.
Reviewed by: Migibio R&D Quality Committee
Last updated: 2026-08-13
Disclosure: Migibio (Guangzhou Magic Biotech Co., Ltd.) is the manufacturer of the FIA680/FIA880 analyzers and FICT reagents referenced in this content. See our Editorial & Review Policy.