Fluorescein Labeling

Updated: 2026-07-25

Overview

Fluorescein isothiocyanate (FITC) is a derivative of fluorescein, modified with an isothiocyanate group (-N=C=S) that reacts with primary amines in proteins and other biomolecules. This reaction forms stable thiourea bonds, enabling covalent labeling for tracking and detection. FITC’s bright green fluorescence makes it a staple in life sciences, particularly for imaging and diagnostic applications. First synthesized in the mid-20th century, FITC remains popular due to its compatibility with common fluorescence instruments. Its excitation and emission peaks align well with standard filter sets, ensuring broad utility across laboratories.

Physical and Chemical Properties

FITC is an orange-brown powder with moderate solubility in polar organic solvents like dimethyl sulfoxide (DMSO) and dimethylformamide (DMF). It exhibits maximal excitation at 495 nm and emits at 519 nm, producing a characteristic green signal. The isothiocyanate group is highly reactive but degrades in aqueous solutions, requiring anhydrous storage. Under alkaline conditions (pH ≥8), FITC efficiently conjugates to lysine residues or N-termini of proteins. However, its fluorescence intensity is pH-dependent, diminishing in acidic environments. Photostability is moderate; prolonged exposure to light accelerates bleaching.

Main Applications

FITC is extensively used to label antibodies for immunofluorescence assays, enabling visualization of cellular targets under microscopes. In flow cytometry, FITC-labeled probes help quantify cell populations based on marker expression. It also serves in ELISA and Western blotting for detection. Beyond research, FITC aids in clinical diagnostics, such as identifying pathogens or monitoring immune responses. Its low cost and ease of use make it a preferred choice for high-throughput screening and educational demonstrations.

Safety and Storage

FITC is a skin and eye irritant, requiring gloves, goggles, and lab coats during handling. Inhalation of powder should be avoided; work in a fume hood for weighing. Spills must be neutralized with a damp cloth and disposed of as hazardous waste. To preserve reactivity, store FITC in airtight containers at -20°C, shielded from light and humidity. Lyophilized forms are more stable than solutions, which degrade within weeks even at 4°C. Always check expiration dates before use.

B2B Procurement Guide

When sourcing FITC, prioritize suppliers providing certificates of analysis (CoA) with HPLC purity data (>90% recommended). Batch-to-batch variability in fluorescence efficiency is common; request performance test results if available. Bulk purchases (e.g., 10-100 g) often reduce costs by 20-30%. Consider logistics: temperature-controlled shipping is essential to prevent degradation. For specialized applications (e.g., single-molecule imaging), opt for ultra-pure grades with lower impurities. Compare lead times, as custom conjugations may require additional weeks.