Effects of free biotin on detection
Free biotin occupies streptavidin-binding sites and can reduce detection of biotinylated targets.
Applies to: For prepared streptavidin probes; check competition from free biotin.
Fluorescent dye index
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Principles and applications
Labeling and detection
Reactive dyes are used to prepare labels; fluorescent conjugates, nucleic-acid probes and assay kits address specific detection workflows. Establish whether the task requires conjugation or direct detection.
Coupling and supporting reagents
Linkers, labeling kits, transfection reagents and labeling services address different sample-handling tasks and experimental objectives.
Selection criteria
Define the objective
Distinguish protein or nucleic-acid labeling, cell staining, affinity detection and sample delivery, then choose the corresponding category.
Match sample and channel
Confirm the sample, reactive sites and readout. For fluorescence, compare the actual excitation and emission parameters.
Confirm packs and documentation
Open the product page to check catalog number, pack, formulation and use requirements, and request a manual, CoA or SDS as needed.
Sample and experimental preparation
Retain controls
Retain unstained or unlabeled samples and suitable single-stain references for multicolor experiments.
Record the catalog number
Use parameters for the exact catalog number in preparation, reagent-input and detection calculations. Match lot test results to the vial label.
Technical articles
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Analysis of endogenous biotin and nonspecific background
Use unstained, streptavidin-only and non-biotinylated-probe controls to distinguish autofluorescence, endogenous biotin and adsorption.
Applies to: For biotin-affinity detection; distinguish endogenous biotin from nonspecific adsorption.
Streptavidin fluorescence detection and multivalent binding
Multivalent streptavidin can crosslink biotinylated targets, affecting live-cell motion and clustering measurements.
Applies to: For assessing probe-induced crosslinking; the cited engineered monovalent protein does not establish that current products are monovalent.
Activation and conjugation of free-acid dyes
Distinguish free acids from NHS esters, plan carboxyl activation, amine coupling and product analysis, and retain positional-isomer identity for FAM and ROX.
Applies to: For free-acid FAM/ROX starting materials; a free acid is not a preactivated NHS ester.
Sample and buffer checks before SPAAC
Target-bound azides enable coupling; free azide reagents and sodium azide can compete for DBCO.
Applies to: For the SPAAC step between DBCO and a target azide; ordinary amines and thiols are not reaction partners.
Detection and performance assessment of FITC, AF488 and SF488
Compare detection windows, labeling chemistry, signal intensity, photobleaching and pH response separately.
Applies to: Includes a defined Qihe SF488/AF488 flow example; it does not rank brightness or photostability against original Alexa Fluor 488.
Stepwise SMCC conjugation of NH2 dyes
Couple the dye amine, isolate the intermediate and react it with target thiols; check free SMCC, competing reductants and small-molecule separation.
Applies to: For NH2 dyes converted to maleimides via SMCC before thiol coupling; validate separation of the small-molecule intermediate.
Buffer checks before NHS labeling
Tris and glycine consume NHS dye. BSA and gelatin require separation from the target protein; routine buffer exchange is insufficient.
Applies to: For protein preparation before NHS-ester labeling; check competing amines and carrier proteins.
Antibody DOL calculation and quality assessment
Calculate DOL with absorbance correction, distinguish input ratio from attached dye, and assess recovery and binding.
Applies to: For purified protein conjugates; use this dye’s absorbance parameters and distinguish input ratio from DOL.
WGA signal and membrane outlines
WGA labels accessible glycans. Check outline continuity for segmentation; intensity is not a direct measure of membrane amount.
Applies to: For WGA conjugates; glycan accessibility and membrane outlines do not establish protein-specific targeting.
Fixation and permeabilization conditions for WGA staining
Fixation and permeabilization can change glycan accessibility. Compare outlines, intracellular signal and background separately.
Applies to: For comparing fixation and permeabilization with WGA probes, not for free-dye conjugation.
Thiol status and reduction pretreatment
Cysteines may be disulfide-bound or protected. Confirm free thiols before deciding on reduction.
Applies to: For maleimide reactive dyes; first establish accessible thiols on the sample.
Reductant handling before maleimide labeling
DTT and β-mercaptoethanol compete for maleimide; residual TCEP can also interfere.
Applies to: For maleimide routes; assess reductant carryover and removal.
CuAAC and SPAAC route selection
Use CuAAC for terminal alkynes and SPAAC for strained alkynes. Identify the handle before assessing copper compatibility.
Applies to: For azide reactive dyes; distinguish terminal from strained alkynes before choosing CuAAC or SPAAC.
CTB signal and lipid raft interpretation
CTB fluorescence reports GM1-associated distribution; puncta alone do not establish native lipid-raft structure.
Applies to: For CTB–GM1 localization, including perturbation of membrane organization by multivalent binding.
Time-course analysis of CTB binding and uptake
Distinguish peripheral and intracellular CTB signals over time; one endpoint cannot establish a trafficking route.
Applies to: For CTB surface binding and trafficking; total intensity alone does not quantify uptake.
References
Anomalous fluorescence enhancement of Cy3 and cy3.5 versus anomalous fluorescence loss of Cy5 and Cy7 upon covalent linking to IgG and noncovalent binding to avidin
Gruber HJ, Hahn CD, Kada G, et al. · Bioconjugate Chemistry · 11(5):696–704 · 2000
Compares fluorescence changes when Cy3, Cy3.5, Cy5 and Cy7 associate with IgG or avidin, informing joint assessment of labeling density and the purified conjugate’s signal.
DOI: 10.1021/bc000015m
EDC/NHS carboxyl-to-amine coupling
Thermo Fisher Scientific · Carbodiimide crosslinker chemistry
Explains carboxyl activation, intermediate hydrolysis and self-crosslinking risks in multi-handle samples, informing free-acid dye activation and product analysis.
Stepwise amine-to-thiol coupling with SMCC
Thermo Fisher Scientific · SMCC and Sulfo-SMCC · MAN0011295 Rev. C.0
Distinguishes the partners and reaction order of the NHS and maleimide ends and removal of free linker, supporting bridging routes for NH2 dyes.
ATTO-TEC primary-amine protein labeling procedures
ATTO-TEC / Leica Microsystems · ATTO Antibody Labeling Kit · 2025-03-19
Manufacturer IgG/NHS-ester example for preparation, purification and absorbance measurements. Its catalog numbers, spectral peaks, extinction coefficients and kit doses do not replace documentation for Qihe catalog numbers.
BODIPY dyes and their derivatives: syntheses and spectroscopic properties
Loudet A, Burgess K. · Chemical Reviews · 107(11):4891–4932 · 2007
Reviews BODIPY synthesis, derivatization and spectroscopic properties as background for distinguishing members of the dye family.
DOI: 10.1021/cr078381n
Amine-Reactive BODIPY Dye: Spectral Properties and Application for Protein Labeling
Ksenofontova KV, Kerner AA, Ksenofontov AA, et al. · Molecules · 27(22):7911 · 2022
Studies solvent and protein-conjugation effects on NHS-Ph-BODIPY spectra, informing evaluation of a conjugate in its final sample environment.
Quenched BODIPY dye-labeled casein substrates for the assay of protease activity by direct fluorescence measurement
Jones LJ, Upson RH, Haugland RP, et al. · Analytical Biochemistry · 251(2):144–152 · 1997
Studies quenching and proteolytic dequenching of densely labeled BODIPY casein. This substrate system does not establish ordinary reactive BODIPY dyes as direct protease or lipid-oxidation probes.
Cyanine dye labeling reagents: sulfoindocyanine succinimidyl esters
Mujumdar RB, Ernst LA, Mujumdar SR, Lewis CJ, Waggoner AS. · Bioconjugate Chemistry · 4(2):105–111 · 1993
Studies sulfoindocyanine active-ester structures, spectra and labeling of amine-bearing biomolecules, providing background for cyanine NHS-labeling workflows.
DOI: 10.1021/bc00020a001
Rare earth cryptates and homogeneous fluoroimmunoassays with human sera
Mathis G. · Clinical Chemistry · 39(9):1953–1959 · 1993
Describes europium-cryptate donors, energy transfer to an acceptor and time-resolved signal correction, informing donor, acceptor and background controls.
Thermo Fisher · Biotin binding and interference
Thermo Fisher Scientific
Sample preparation, free biotin and background control in biotin-affinity detection.
Thermo Fisher · Fluorescent streptavidin methods
Thermo Fisher Scientific
Sample preparation, free biotin and background control in biotin-affinity detection.
A monovalent streptavidin with a single femtomolar biotin binding site
Howarth M, Chinnapen DJF, Gerrow K, et al. · Nature Methods · 3:267–273 · 2006
Uses an engineered monovalent protein to investigate crosslinking by multivalent binding. It informs assessment of probe valency in membrane-protein motion and clustering studies.
DOI: 10.1038/nmeth861
Membrane-integrity dyes and viability methods
Thermo Fisher Scientific · Molecular Probes Handbook · Section 15.2
Explains nucleic-acid dyes in membrane-integrity assays and considerations for combined controls.
Guidelines for the use of flow cytometry and cell sorting in immunological studies (third edition)
Cossarizza A, Chang HD, Radbruch A, et al. · European Journal of Immunology · 51(12):2708–3145 · 2021
Provides methodological guidance on detection settings, controls and experimental records for downstream conjugate evaluation.
Nucleic-acid stain binding and membrane permeability
Thermo Fisher Scientific · Molecular Probes Handbook · Section 8.1
Distinguishes DNA preference, membrane permeability and suitable readouts among nucleic-acid stains.
SYBR nucleic-acid gel staining methods
Thermo Fisher Scientific · SYBR Nucleic Acid Gel Stains · TD004
Selection of nucleic-acid type, gel staining and imaging conditions; reagent amounts depend on the actual formulation.
Fluorescent phosphoramidites in oligonucleotide synthesis
Thermo Fisher Scientific · Specialty Phosphoramidites
Explains dye-phosphoramidite incorporation during synthesis. Confirm coupling, cleavage and deprotection for the actual dye structure; this source does not establish a common process for TAMRA and fluorescein reagents.
Thermo Fisher · Amine-reactive chemistry
thermofisher.com
Distinguishes amine-reactive forms such as NHS and isothiocyanate and competing buffers; separately establish whether a nucleic-acid sample has accessible amines.
Aza-dibenzocyclooctynes for fast and efficient enzyme PEGylation via copper-free (3+2) cycloaddition
Debets MF, van Berkel SS, Schoffelen S, et al. · Chemical Communications · 46(1):97–99 · 2010
Reports copper-free reaction of a strained alkyne with azides and its application to enzyme PEGylation.
DOI: 10.1039/b917797c
A Strain-Promoted [3 + 2] Azide–Alkyne Cycloaddition for Covalent Modification of Biomolecules in Living Systems
Agard NJ, Prescher JA, Bertozzi CR. · Journal of the American Chemical Society · 126(46):15046–15047 · 2004
Introduces ring-strain-driven azide–alkyne coupling without copper, a foundational study in SPAAC bioconjugation.
DOI: 10.1021/ja044996f
Reaction of Tris(2-carboxyethyl)phosphine (TCEP) with maleimide and alpha-haloacyl groups: anomalous elution of TCEP by gel filtration
Shafer DE, Inman JK, Lees A. · Analytical Biochemistry · 282(1):161–164 · 2000
Examines TCEP interactions with reactive groups, informing evaluation of reductant carryover and buffer exchange.
Labeling a protein with fluorophores using NHS ester derivitization
Nanda JS, Lorsch JR. · Methods in Enzymology · 536:87–94 · 2014
Uses FAM ester labeling of a protein to explain primary-amine chemistry and labeling-efficiency assessment. It informs NHS workflow design; input and reaction conditions depend on the actual dye and sample.
Fluorescent-labeled antibodies: Balancing functionality and degree of labeling
Vira S, Mekhedov E, Humphrey G, Blank PS. · Analytical Biochemistry · 402(2):146–150 · 2010
Uses FITC-labeled anti-HA antibody to assess changes in labeling density and antigen binding. It informs input-series design and post-purification functional testing; DOL alone is insufficient for selecting a conjugate.
Labeling membrane glycoproteins or glycolipids with fluorescent wheat germ agglutinin
Chazotte B. · Cold Spring Harbor Protocols · 2011(5):pdb.prot5623 · 2011
Describes glycan-dependent membrane labeling with WGA, informing sample preparation and imaging design.
DOI: 10.1101/pdb.prot5623
Tunable degradation of maleimide-thiol adducts in reducing environments
Baldwin AD, Kiick KL. · Bioconjugate Chemistry · 22(10):1946–1953 · 2011
Studies exchange reactions of model adducts in thiol-containing environments to inform conjugate stability assessment.
DOI: 10.1021/bc200148v
Copper-Catalyzed Azide–Alkyne Click Chemistry for Bioconjugation
Presolski SI, Hong VP, Finn MG. · Current Protocols in Chemical Biology · 3(4):153–162 · 2011
Describes CuAAC catalyst systems and reaction assessment for terminal-alkyne substrates.
Structured clustering of the glycosphingolipid GM1 is required for membrane curvature induced by cholera toxin
Kabbani AM, Raghunathan K, Lencer WI, Kenworthy AK, Kelly CV. · PNAS · 117(26):14978–14986 · 2020
Examines how multivalent CTB binding affects GM1 organization and membrane shape, highlighting probe-induced perturbation.
TR-FRET donors, acceptors and time-resolved detection
Revvity · HTRF Principle
Explains Eu donors, compatible acceptors, proximity-dependent transfer and delayed detection. A Eu dye alone is not a complete TR-FRET assay; HTRF kit settings are not interchangeable product specifications.
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Product use, preparation, operating conditions and storage.
Spectra and measurement conditions
Spectra, measurement conditions and detection settings for the exact catalog number.
Certificate of analysis (CoA)
Lot-specific test results. Include the lot number from the vial.
Safety data sheet (SDS)
Handling, storage and emergency response information.
Frequently asked questions
Should the dye or reactive form be selected first?
Establish accessible sample sites and the instrument configuration, then match both dye and reactive form. Select preconjugated probes and assay kits by their intended use.
How is documentation requested?
Use the Documents & quality tab of the product page. Include the catalog number and vial lot number for a CoA.