XFD660 Maleimide

XFD660 maleimide is a thiol-reactive, far-red fluorescent dye with an excitation/emission of 663/691 nm that is used for flow cytometry and microscopy applications.

Versatile Conjugation: Efficiently labels thiol groups on proteins, antibodies, and oligonucleotides with stable thioether bonds
Bright & Stable: Delivers intense fluorescence with resilience to photobleaching and pH variations from 4 to 10
Hydrophilic: Minimizes aggregation, enhancing signal clarity for advanced imaging and live-cell studies

Schematic illustrating the maleimide–thiol reaction between a maleimide‐functionalized dye and a thiol‐modified biomolecule. This method is widely used for site‐specific conjugation to cysteine residues in proteins or to thiolated oligonucleotides. Maleimide–thiol coupling proceeds efficiently at or near physiological pH and results in a stable thioether bond.

Protocol

SDS

Catalog	Size	Price	Quantity
1892	1 mg	Price

Overview

XFD660, synthesized by AAT Bioquest, is chemically identical to Alexa Fluor® 660 (a ThermoFisher trademark). Designed for optimal excitation at 633 or 647 nm laser lines, XFD660 is well-suited for advanced imaging and flow cytometry applications, offering excellent fluorescence brightness and photostability. This dye is water-soluble and demonstrates pH stability within a range from 4 to 10. The maleimide derivative of XFD660 is commonly utilized for conjugation to thiol groups on proteins, oligonucleotide thiophosphates, or low molecular weight ligands, producing conjugates that exhibit significantly brighter fluorescence and enhanced photostability compared to those formed with other spectrally similar fluorophores.

Calculators

Common stock solution preparation

Table 1. Volume of DMSO needed to reconstitute specific mass of XFD660 Maleimide to given concentration. Note that volume is only for preparing stock solution. Refer to sample experimental protocol for appropriate experimental/physiological buffers.

	0.1 mg	0.5 mg	1 mg	5 mg	10 mg
1 mM	98.416 µL	492.082 µL	984.165 µL	4.921 mL	9.842 mL
5 mM	19.683 µL	98.416 µL	196.833 µL	984.165 µL	1.968 mL
10 mM	9.842 µL	49.208 µL	98.416 µL	492.082 µL	984.165 µL

Molarity calculator

Enter any two values (mass, volume, concentration) to calculate the third.

Mass (Calculate)		Molecular weight		Volume (Calculate)		Concentration (Calculate)		Moles
mg	÷	1016.09 g/mol	=	mL	x	mM	=	mmol

References

View all 37 references: Citation Explorer

A decade of blood-brain barrier permeability assays: Revisiting old traumatic brain injury rat data for new insights and experimental design.

Authors:

Bolden, Chris T and Olson, Scott D and Cox, Charles S

Journal:

Microvascular research (2023): 104453

A novel anti-TNF-α drug ozoralizumab rapidly distributes to inflamed joint tissues in a mouse model of collagen induced arthritis.

Authors:

Oyama, Shohei and Ebina, Kosuke and Etani, Yuki and Hirao, Makoto and Kyuuma, Masanao and Fujii, Yasuyuki and Iwata, Katsuya and Ogawa, Bunichiro and Hasegawa, Tomoya and Kawano, Sasagu and Nakanishi, Yutaka and Okada, Seiji and Nakata, Ken

Journal:

Scientific reports (2022): 18102

CD38-specific nanobodies allow in vivo imaging of multiple myeloma under daratumumab therapy.

Authors:

Pape, Luca Julius and Hambach, Julia and Gebhardt, Anna Josephine and Rissiek, Björn and Stähler, Tobias and Tode, Natalie and Khan, Cerusch and Weisel, Katja and Adam, Gerhard and Koch-Nolte, Friedrich and Bannas, Peter

Journal:

Frontiers in immunology (2022): 1010270

A 15-min non-competitive homogeneous assay for microcystin and nodularin based on time-resolved Förster resonance energy transfer (TR-FRET).

Authors:

Akter, Sultana and Lamminmäki, Urpo

Journal:

Analytical and bioanalytical chemistry (2021): 6159-6170

Alpha-MSH Targeted Liposomal Nanoparticle for Imaging in Inflammatory Bowel Disease (IBD).

Authors:

Peñate-Medina, Tuula and Damoah, Christabel and Benezra, Miriam and Will, Olga and Kairemo, Kalevi and Humbert, Jana and Sebens, Susanne and Peñate-Medina, Oula

Journal:

Current pharmaceutical design (2020): 3840-3846

Physical properties

Molecular weight	1016.09
Solvent	DMSO

Spectral properties

Correction factor (260 nm)	0.00
Correction factor (280 nm)	0.10
Extinction coefficient (cm ^-1 M ^-1)	132000
Excitation (nm)	663
Emission (nm)	691

Storage, safety and handling

H-phrase	H303, H313, H333
Hazard symbol	XN
Intended use	Research Use Only (RUO)
R-phrase	R20, R21, R22
Storage	Freeze (< -15 °C); Minimize light exposure
UNSPSC	12171501

Documents

Protocol
Safety Data Sheet
Certificate of Analysis
Brochure: Labeling Antibodies & Biopolymers

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Page updated on December 7, 2025