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Nucleic Acid Modifications and Labeling
Modifying and labeling nucleic acids is an essential aspect of genomics and molecular biology, unlocking applications such as qPCR, FISH, molecular beacons and next generation sequencing (NGS). Because of the importance of its downstream applications, AAT Bioquest has developed a multitude of reagents and kits that enable both direct and indirect modification and labeling of nucleic acids, through chemical, and biological, means. A summary of the methods is provided below:
Method Name | Can Label Unmodified Nucleic Acid | Targets | Labels Available |
|---|---|---|---|
Helixyte™ iFluor® Labeling Dyes | Yes, labeling dyes directly and covalently bind N7 of unmodified guanine residues | DNA, RNA | iFluor® dyes |
ReadiLink™ Labeling Kits | Yes, labeled nucleotides are enzymatically incorporated (by Pol I or TdT) | dsDNA, ssDNA, oligonucleotides | DIG, biotin, iFluor® dyes |
Psoralens | Yes, UV 365 nm irradiation photoactivates reagents, forming covalent bonds | dsDNA | Biotin, reactive moieties (e.g., azides, alkynes, etc.) |
Labeled NTPs and dNTPs | Yes, labeled nucleotides are enzymatically incorporated (by Pol I or TdT) | DNA, RNA | Varied, see Nucleotides, NTPs and dNTPs |
Standard Labeling Dyes | No, labeling dyes react with pre-functionalized nucleotides (e.g., amine, azide, etc.) | DNA, RNA | iFluor®, Tide Fluor™, Tide Quencher™, AATOM™ |
Phosphoramidites and CPGs | No, labels are incorporated at 5'- or 3'- end during oligonucleotide synthesis | Oligonucleotides | Varied, see Oligonucleotide Building Blocks |
Direct Labeling Methods
Direct labeling methods chemically attach fluorophores or functional groups directly to unmodified nucleic acids without enzymatic reactions. These approaches are ideal for labeling intact DNA or RNA samples where enzymatic activity might be limited or undesirable.
Helixyte™ iFluor® Labeling Dyes
Helixyte™ iFluor® nucleic acid labeling dyes provide a simple, non-enzymatic method for fluorescently labeling unmodified DNA or RNA. These reactive dyes covalently attach to nucleic acids through a platinum-based coordination chemistry that does not require prior modification of the nucleic acid substrate. The resulting labeled probes exhibit excellent brightness and photostability, making them ideal for FISH, microarray, and other hybridization-based applications.
Key Features
- Non-enzymatic labeling — Direct chemical attachment without need for polymerases or other enzymes
- Works with intact nucleic acids — Labels purified DNA or RNA without prior modification
- High labeling efficiency — Optimized for 100-300 µg DNA/RNA per reaction
- Superior brightness — iFluor® dyes outperform traditional fluorophores like FITC and Cy dyes
- Full spectral coverage — From UV (350 nm) to near-infrared (750 nm)
Psoralens
Psoralens are photoactivatable intercalating agents that form covalent crosslinks with pyrimidine bases (primarily thymine) in double-stranded DNA upon UV irradiation (~350 nm). This unique photochemistry makes psoralens valuable tools for studying nucleic acid structure and protein-DNA interaction.
Key Features
- Photoactivatable crosslinking — Forms covalent bonds only upon UV exposure (~350 nm)
- Sequence-selective — Preferentially targets AT-rich regions in double-stranded nucleic acids
- Multiple reactive formats — Available with NHS ester, maleimide, azide, and alkyne groups for diverse downstream conjugation strategies
- Biotin conjugates — Pre-made biotinylated psoralens for streptavidin-based detection
Enzymatic Labeling Methods
Enzymatic labeling methods use DNA polymerases or terminal deoxynucleotidyl transferase (TdT) to incorporate labeled nucleotides into newly synthesized DNA strands. These approaches generate highly labeled probes with excellent signal intensity and are the preferred method for preparing FISH probes and microarray targets.
ReadiLink™ Labeling Kits
ReadiLink™ labeling kits provide complete, optimized solutions for enzymatic labeling of DNA. Nick translation kits use DNase I and DNA Polymerase I to uniformly label double-stranded DNA templates, while oligo/ssDNA labeling kits use terminal transferase to add labeled nucleotides to the 3' ends of single-stranded oligonucleotides.
Key Features
- Complete kit format — All reagents optimized and validated for consistent results
- Multiple label options — Fluorescent dyes (iFluor®, Cy3, Cy5) and haptens (biotin, digoxigenin)
- Two labeling methods — Nick translation for dsDNA; terminal transferase for oligos/ssDNA
- High labeling efficiency — Generates probes with excellent signal-to-noise ratios
- FISH-ready — Labeled probes work directly in hybridization applications
Labeled NTPs and dNTPs
Fluorescently labeled and hapten-conjugated nucleotides (dUTP, UTP, dCTP, etc.) serve as substrates for enzymatic incorporation during PCR, in vitro transcription, nick translation, and random priming reactions. These building blocks provide flexibility for researchers who prefer to optimize their own labeling protocols.
For a complete selection of labeled nucleotides including iFluor®-dUTP, Biotin-dUTP, DIG-dUTP, aminoallyl-dUTP, and other modified nucleotides, see our Nucleotides, NTPs and dNTPs catalog.
Labeling Reactive Moieties (Amine, Thiol, Azide, Alkyne, DBCO)
Pre-modified oligonucleotides containing reactive functional groups (amino, azido, alkynyl, thiol) can be conjugated post-synthetically with appropriately reactive fluorescent dyes. This approach offers maximum flexibility in dye selection and allows labeling after oligonucleotide purification.
Oligo Modification | Use Dye With | Chemistry | Conditions |
|---|---|---|---|
Amino (NH₂) | NHS ester (SE) | Amide bond | pH 8-9, aqueous buffer |
Thiol (SH) | Maleimide | Thioether bond | pH 6.5-7.5, reduce disulfides first |
Azido (N₃) | Alkyne | CuAAC click (triazole) | Cu(I) catalyst required |
Alkynyl (≡CH) | Azide | CuAAC click (triazole) | Cu(I) catalyst + ligand |
DBCO | Azide | SPAAC click (triazole) | No catalyst, copper-free |
For complete selections of reactive dyes for post-synthetic nucleic acid labeling, see our Bioconjugation and Tags catalog.
iFluor® Dyes
iFluor® dyes are AAT Bioquest's premium fluorophores offering superior brightness and photostability compared to traditional dyes. Available with NHS ester, maleimide, azide, and alkyne reactive groups for conjugation to amino-, thiol-, alkynyl-, or azido-modified oligonucleotides.
For the complete iFluor® dye portfolio with all reactive formats, see our iFluor® Labeling Dyes catalog.
Tide Fluor™ and Tide Quencher™ Dyes
Tide Fluor™ fluorophores and Tide Quencher™ dark quenchers are optimized for FRET-based applications including molecular beacons, TaqMan probes, and other dual-labeled oligonucleotide probes. Each Tide Fluor™ dye is spectrally matched with a corresponding Tide Quencher™ for maximum FRET efficiency.
For the complete Tide Fluor™ and Tide Quencher™ portfolio, see our FRET Building Blocks catalog.
AATOM™ Dyes
AATOM™ dyes provide excellent brightness and photostability for demanding applications including single-molecule detection and super-resolution microscopy. They are available with multiple reactive groups for oligonucleotide labeling.
For the complete AATOM™ dye portfolio, see our AATOM™ Labeling Dyes catalog.
Labeling During Oligonucleotide Synthesis
Phosphoramidites and controlled pore glass (CPG) supports enable direct incorporation of fluorescent labels, quenchers, and other modifications during automated oligonucleotide synthesis. This approach produces internally labeled or terminally modified oligonucleotides in a single synthesis without post-synthetic conjugation steps.
Phosphoramidites and CPGs
Phosphoramidites are the standard building blocks for automated oligonucleotide synthesis. Fluorescent dye phosphoramidites enable internal labeling at any position in the oligonucleotide sequence, while CPG supports provide 3'-terminal modifications. Our portfolio includes phosphoramidites for popular fluorophores (FAM, TAMRA, Cy3, Cy5) as well as quenchers (BHQ, DABCYL) and functional groups (amino, biotin, azido).
For the complete selection of phosphoramidites and CPG supports for oligonucleotide synthesis, see our Oligonucleotide Building Blocks catalog.
This document (01.0310.251203r1) was last updated on Sat Feb 28 2026. All trademarks and registered trademarks mentioned herein are the property of their respective owners.
Nucleic Acid Modifications and Labeling