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California Red™ & SunRed™ Superior Replacements for Texas Red® and Texas Red®-X

Spectral comparison of California Red™ and Texas Red®conjugated to Gly-Gly-Sor-Ser-Arg-Trp (Red: Texas Red®; Blue: California Red™).
Although sulforhodamine 101 acid chloride (also called Texas Red®) is the most popular labeling reagent of sulfonyl chlorides, it is quite unstable in water, especially at the higher pH required for reactions with aliphatic amines. Texas Red® reacts with both aliphatic amines and aromatic amines indiscriminately. In addition, the labeling efficiency of Texas Red® is extremely low compared to dye succinimidyl esters. California Red™ SE is a succinimidyl ester. It is an excellent replacement for Texas Red®. California Red™ reacts with amine compounds, such as amino acids, peptides and proteins, to give bright red fluorescent conjugates that are extremely stable. Compared to Texas Red®, California Red™ has much higher labeling efficiency, and more importantly, the resulted conjugates are more fluorescent than the corresponding Texas Red® conjugates for long peptides and oligonucleotides. The conjugates of California Red™ have the identical excitation and emission wavelengths to those of Texas Red®. Our in-house studies indicated that California Red™ is more stable than Texas Red® under the same labeling conditions.

SunRed™ has even better water solubility than Texas Red®, Texas Red®-X and California Red™. It is extremely useful for labeling hydrophobic peptides and oligonucleotides that are often poorly labeled by Texas Red® or Texas Red®-X. The conjugates of hydrophobic peptides and oligonucleotides with Texas Red® are difficult to use for measuring biological activities due to their poor water solubility.

Features and Benefits of California Red™ and SunRed™:

  • Spectral properties almost identical to those of Texas Red®
  • Fluorescence less-quenched on proteins than Texas Red®
  • More stable than Texas Red®
  • Higher conjugation yield


Table 1. Comparison of California Red™ and SunRed™ with Texas Red®

Dye Properties
California Red™
Texas Red®
Maximum Absorption Wavelength (nm) 595595594*
Maximum Fluorescence Wavelength (nm) 615615613*
Extinction Coefficient (cm-1M-1) 100,000100,000100,000
Purity Single Isomer Single Isomer Mixture of 3 Isomers
Reactive Group NHS Ester NHS Ester Sulfonyl Chloride
Water Solubility (pH 7.0) <1 mg/mL >10 mg/mL <1 mg/mL
Conjugation Yield (after HPLC Purification)** 76% 71% 26%
  1. *Glycine conjugate; ** Based on the reaction with Gly-Gly-Ser-Ser-Arg-Trp.


Table 2. Superior Replacement Dyes for Texas Red®

Cat No.
Product Name
Ex (nm)
Em (nm)
EC (cm-1M-1)
Unit Size
473California Red™ SE583603100,000 0.4560.3605 mg
480Sulforhodamine 101 sulfonyl chloride [Texas Red®] *CAS 82354-19-6* 588601100,000 0.4560.36010 mg
472SunRed™ SE 58360398,0000.2400.3665 mg
485Texas Red® alkyne *Single Isomer*58860195,0000.4560.3605 mg
484Texas Red® azide *Single Isomer*58860195,0000.4560.3605 mg
481Texas Red® hydrazide *Single Isomer*58260295,0000.4560.3605 mg
483Texas Red® maleimide *Single Isomer*58860195,0000.4560.3605 mg