Short answer
All three are candidates for 488 nm excitation and green detection. Alexa Fluor 488 has manufacturer data on photostability and pH behavior. Qihe's current SF488 flow example reports the proportion of events in a CD4-positive gate, which cannot establish a brightness ranking. Choose using instrument requirements, conjugation methods, and relevant experimental evidence.
Spectral position: similar channels still require validation
These dyes have similar spectral positions and are commonly considered for green detection with 488 nm excitation. Their spectra should not be described as identical or fully interchangeable. Qihe's SF manual lists SF488 excitation/emission peaks at 494/517 nm. Check values for the actual dye form and measurement conditions, and use the fluorophore chart to assess instrument compatibility.
After changing a dye or conjugate, re-titrate the staining concentration and check background, signal separation, and compensation or unmixing performance in multicolor assays.
Difference 1: brightness and photostability
FITC performance depends on illumination and experimental conditions. A photostability comparison needs the illumination intensity, exposure time, and sample preparation; a universal claim that it visibly fades within tens of seconds is inappropriate.
Thermo Fisher provides examples comparing Alexa Fluor 488 with FITC/fluorescein for brightness and photobleaching. Alexa Fluor 488 here means the manufacturer's branded product; Qihe AF488 means Qihe's own AF-series product. Their performance data must be attributed separately.
In Qihe's published Mouse CD4 (GK1.5) flow example at 0.4 µg/test, the proportion of events in the CD4+ gate was 23.08% for SF488 and 20.59% for the Qihe AF488 control. The difference is 2.49 percentage points, or approximately 12.1% relative change in that proportion. Gate-positive event proportion is not fluorescence brightness and does not demonstrate photostability. This observation applies to the reported conditions, is not a comparison with branded Alexa Fluor 488, and does not establish an advantage for every low-expression target. See the original plots and conditions on the homepage.
Difference 2: pH sensitivity
For experiments spanning different pH conditions, review the selected product's response data and distinguish measurements of dye solutions, conjugates, and actual samples.
The manufacturer describes Alexa Fluor 488 NHS Ester dye as pH-insensitive from pH 4 to 10. This claim cannot be transferred to Qihe AF488 or SF488. The SF manual checked for this article does not provide a corresponding pH response curve, so this article makes no equivalent pH-range claim or recommendation for quantitative measurements in acidic organelles.
Difference 3: reactive chemistry and cost
- FITC: its isothiocyanate group differs from an NHS ester. Follow the instructions for the exact reagent.
- Alexa Fluor 488 NHS Ester / Qihe AF488 NHS: select amine-labeling conditions from each product's own instructions. Do not transfer branded-product performance data to Qihe AF488 NHS.
- SF488: the SF manual reviewed here describes antibody modification, SMCC activation, and subsequent conjugation. Do not directly substitute an AF488 NHS ester protocol. Follow the finalized manual for the purchased product.
Compare total experimental cost, including reagent consumption, purification, quality checks, and repeats. This article has not compared equivalent pack sizes and labeling tasks, so it gives no fixed price ranking. The protein labeling calculator and protocol resources provide general support; use the relevant product manual for the actual procedure.
How to choose: a decision table
| Scenario | Recommendation |
|---|---|
| Flow cytometry, especially low-expression targets | Re-titrate candidate conjugates and compare signal separation and background; do not infer brightness from gate percentages |
| Long-exposure imaging | Look for photobleaching data for the actual conjugate under comparable illumination |
| Quantitation across acidic conditions | Check product-specific pH response and sample suitability; do not borrow another brand's or series' pH range |
| Budget-sensitive pilot work | Compare the full cost of the required labeling task and run a small validation |
| Green channel in a multicolor panel | Check spectral overlap, instrument setup, and compensation or unmixing; avoid assigning highly similar dyes to independent markers |
Frequently asked questions
Can FITC and AF488 be used together in one multicolor panel? In a conventional flow cytometer's same green detection channel, FITC and AF488 should not label two independent markers because their spectra overlap strongly. For other configurations, including spectral flow, assess instrument-specific single-stain controls and unmixing validation.
Can SF488 drop into an existing FITC protocol? First assess green-channel compatibility. Do not copy the labeling procedure unchanged: follow the purchased SF488 product's instructions for conjugation, purification, and staining, then validate antibody function, background, and detection performance.
Why did my FITC staining weaken after two days? Possible factors include illumination, buffer changes, storage conditions, and sample state. Compare fresh and light-protected samples under identical instrument settings, then troubleshoot using the product instructions. Two days of storage alone cannot identify the cause or guarantee that changing dyes or adding an antifade reagent will solve it.
Related resources: Fluorophore chart — dyes by laser line · SF series dyes · AF series dyes · NHS ester protein labeling protocol · Protein labeling calculator
For dye selection or a labeling assessment, share your antibody or protein information, available sample amount, instrument configuration, and intended application with Qihe's technical team to discuss suitable reagents and labeling services.