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Chemistry & Reactive Handles for Bioconjugation

End-to-end bioconjugation for proteins, antibodies, oligonucleotides & nanomaterials

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Overview

Bio-Synthesis bioconjugation services span feasibility to scale-up for antibody conjugation, protein–oligo hybrids, and nanoparticle functionalization. We deploy NHS/PFP esters for amines; maleimide, iodoacetyl, and SPDP for thiols; PEG spacers to tune solubility and reach; and click chemistry—SPAAC (DBCO/BCN) and iEDDA (TCO–tetrazine)—for orthogonal, site-specific assembly. Carbonyl strategies (oxime/hydrazone) and zero-length EDC coupling expand route flexibility. Every build is polished and QC-backed with UV–Vis/DAR, LC-MS, and SEC-HPLC, ensuring consistency for diagnostics, imaging, and ADC-like prototypes.

Explore our related payload, label, and tag conjugation or site-specific conjugation platforms.

ISO 9001:2015 / ISO 13485:2016 45+ Years of Expertise U.S. Facilities – Texas Bench to Kilo Scale Production Confidential & IP-Protected
Functional Groups

Amine-reactive (NHS/PFP/TFP), thiol-reactive (maleimide, iodoacetyl, vinyl sulfone, SPDP), carboxylate activation (EDC/sulfo-NHS), and carbonyl capture (aminooxy/hydrazide).

Click Modalities

CuAAC (azide–alkyne), SPAAC (DBCO/BCN), and ultrafast iEDDA (tetrazine–TCO/BCN); plus oxime and SuFEx where appropriate.

Site-Specific

Cys targeting & re-bridging, N-terminus strategies, glycan-directed aldehydes, enzymatic tags (Sortase, TGase, FGE) and orthogonal handles.

Linker & Spacer Library

R-NH₂
NHS-Ester → Amide
Labeled R
Product Highlights
  • NHS-PEG-X series for solubility & reduced aggregation.
  • Di-NHS homobifunctionals for protein↔protein crosslinks.
  • NHS-Azide / NHS-DBCO / NHS-TCO to install click handles.
  • PFP/TFP esters for better hydrolytic stability.

Preferred: general dye/biotin labeling, surface coupling, installing azide/ DBCO/TCO.

Preferred Applications
  • High-density labeling on Lys-rich proteins (controlled stoichiometry).
  • Heterobifunctional builds (NHS→maleimide bridges).
  • Surface immobilization onto amine-functional substrates.
Technical Notes
  • Avoid Tris/glycine during coupling; use PBS/HEPES; ≤20% DMF if needed.
  • Work near pH 7.5–8.5; minimize hydrolysis with chilled buffers and staged additions.
  • Quench with glycine/Tris after reaction; polish by SEC/desalting.
Sample Submission
Protein amount:
Buffer:
Data:
≥ 50–200 µg for scouting; higher for production.
PBS/HEPES without primary amines; ≤5% glycerol, no azide.
Sequence, concentration (UV/A280), extinction coefficient if known.

R-SH
Maleimide → Thioether
R-S-(Linker)
Product Highlights
  • Maleimide-PEG-X (±sulfo) for stable Cys labeling.
  • Iodoacetyl-PEG-X for tougher matrices.
  • SPDP/HPDP for reversible disulfide linkages (343 nm release handle).
  • Bis-maleimide for intra/inter-molecular bridges.

Preferred: antibody Cys labeling, disulfide re-bridging, enzyme conjugation.

Preferred Applications
  • ADC-like prototypes (Cys-selective; cleavable/non-cleavable spacers).
  • Re-bridging with dibromomaleimides/bis-sulfones/pyridazinediones.
  • Site isolation on engineered single-Cys constructs.
Technical Notes
  • Prefer TCEP ≤1 mM just-in-time; remove excess before maleimide steps.
  • Maintain pH 6.5–7.2 to limit maleimide hydrolysis; keep neutral & cool after.
  • Track SPDP via 2-thiopyridone at 343 nm.
Sample Submission
Free thiols:
Buffer:
Add-ons:
State expected Cys count; note disulfides.
Degassed PBS; avoid reductant carry-over.
Request PEG length; cleavable vs non-cleavable.

R-N₃
DBCO/BCN → Triazole
Conjugate
Product Highlights
  • DBCO-PEG-X / BCN-PEG-X for SPAAC.
  • Tetrazine-PEG-X & TCO-PEG-X for ultrafast iEDDA.
  • Alkyne/Azide-NHS to install handles on proteins.
Preferred Applications
  • Two-step orthogonal builds (NHS-azide install → SPAAC with DBCO-payload).
  • Live-cell labeling with tetrazine↔TCO pairs.
  • Oligo–protein assembly via click handle exchange.
Technical Notes
  • CuAAC available with biocompatible ligands and copper removal.
  • Use SPAAC/iEDDA for copper-sensitive systems.
Sample Submission
Handle preference:
Payload:
Compatibility:
Azide vs DBCO vs TCO/Tetrazine.
Dye/biotin/payload identity & target DAR.
State copper sensitivity if CuAAC is considered.

Conjugate
Stimulus → Cleavage
Released payload
Product Highlights
  • Disulfide linkers (reducible in cytosol).
  • Hydrazone/oxime (acid-labile/stabilizable).
  • Dipeptide + self-immolative spacers.
  • Photocleavable (o-nitrobenzyl/coumarin).
Preferred Applications
  • Release-on-demand payload studies.
  • Controlled elution from surfaces/affinity supports.
Technical Notes
  • Select the trigger by matrix: reductive (GSH), acidic, photolytic, or enzyme-rich environments.
  • We can compare non-cleavable vs cleavable linkers under matched conditions.
Sample Submission
Release profile:
Matrix:
Target trigger & desired half-life window.
Intended environment (buffer, serum-like, lysate, live-cell).

Protein
PEG / Rigid spacer
Payload
Product Highlights
  • PEG2–PEG48 ladders to tune hydrophilicity & reach.
  • Rigid/aromatic spacers for defined distance constraints.
  • Charge-tuned/zwitterionic spacers to mitigate aggregation.
Preferred Applications
  • Reduce dye self-quenching & increase accessibility.
  • Mitigate hydrophobic payload effects and stickiness.
Technical Notes
  • Spacer choice impacts activity, solubility, off-target binding, and assay performance.
Sample Submission
Constraints:
Distance/steric goals; preferred PEG length range.

Applications of Crosslinkers — What to Use & When

Protein↔Protein ADC-like Live-cell Surfaces Oligo↔Protein Nanoparticles
Protein ↔ Protein crosslinking (mapping & stabilization)

Recommend: Homobifunctional sulfo-NHS crosslinkers for Lys↔Lys (water-soluble), or heterobifunctional NHS–maleimide for Lys→Cys targeting; EDC for zero-length Asp/Glu↔Lys proximity links.

  • Buffers: HEPES/PBS (no amines) for NHS; pH 7.5–8.2.
  • Readouts: MS crosslink maps, SEC shifts, SDS-PAGE.
ADC-like prototypes (payload attachment & release)

Recommend: Maleimide-PEG for Cys labeling; choose disulfide or dipeptide/self-immolative linkers for controlled release; consider oxime/hydrazone for acid-labile designs.

  • DAR targeting with engineered Cys or rebridging reagents.
Live-cell & sensitive targets

Recommend: SPAAC (DBCO/BCN↔azide) or iEDDA (tetrazine↔TCO) — fast, copper-free; avoid CuAAC when copper-sensitive.

  • Pair NHS-azide install on protein with DBCO-payload.
Surface immobilization & biosensors

Recommend: EDC/sulfo-NHS to couple to carboxylated surfaces; or amine-functional surfaces with NHS-activated payloads; use PEG spacers to reduce steric hindrance.

Oligonucleotide ↔ Protein hybrids

Recommend: Install azide on the protein (NHS-azide) and click with DBCO-oligo (SPAAC), or use maleimide for thiol-modified oligos.

Nanoparticle functionalization

Recommend: Thiol-to-gold coatings plus NHS handles for protein attachment; consider PEG spacers to minimize aggregation and nonspecific binding.

Technical Summary

Workflow
  • Intake: sample/buffer review & handle selection
  • Scout: small-scale stoichiometry & pH/time screen
  • Build: conjugation with chosen linker & spacer
  • Polish: desalting/SEC; remove free linker/dye
  • QC: UV–Vis/DAR, LC-MS, SEC-HPLC; optional CE-SDS
Buffer Considerations
  • NHS/PFP: avoid primary amines; HEPES/PBS ideal
  • Maleimide: avoid excess thiols during coupling
  • CuAAC: ligand & copper removal as needed; prefer SPAAC/iEDDA for sensitive systems
QC Options
  • DAR / degree-of-labeling (UV–Vis/MS)
  • SEC-HPLC & CE-SDS for aggregation/integrity
  • Residual copper (if CuAAC), free dye/linker checks

FAQ

SPAAC vs iEDDA — what's the difference?
SPAAC reacts azides with strained cyclooctynes (DBCO/BCN) without copper; iEDDA couples tetrazines with TCO/BCN at even faster rates, helpful for live-cell or rapid labeling.
Maleimide vs SPDP for thiol coupling?
Maleimide gives a stable thioether; SPDP forms a reducible disulfide useful for cleavable linkages or reversible capture (monitor 343 nm release).
Which buffers work for NHS/PFP labeling?
Use PBS/HEPES around pH 7.5–8.5 and avoid primary amines (Tris/glycine) during coupling.
How do you report degree-of-labeling (DAR)?
We report average DAR/DoL from UV–Vis and LC-MS when applicable; SEC-HPLC monitors aggregation and CE-SDS monitors integrity.
When should I choose SPAAC vs. iEDDA?
Use SPAAC (azide↔DBCO/BCN) for copper-free labeling with broad compatibility. Choose iEDDA (tetrazine↔TCO) when you need the fastest kinetics and ultra-short incubation times.
Is SPAAC fast enough for live-cell labeling?
Yes, especially with high-strain cyclooctynes (e.g., DBCO). Buffers, pH, and temperature can shift SPAAC rates; optimize for your matrix and dwell time.
Maleimide vs. iodoacetyl — which is better?
Maleimide: fast, Cys-selective thioethers. Iodoacetyl: tougher matrices but less selective; choose by pH, nucleophiles, and stability needs.
EDC “zero-length” — what does it connect?
Carboxylates to primary amines (amide) with no spacer; buffer choice & timing matter due to short-lived intermediates.
PEG spacers — what do they change?
Reduce aggregation/non-specific binding, improve solubility, and increase accessibility; PEG2–PEG48 tunes reach & hydrophilicity.
Can I mix orthogonal handles?
Yes. Common: install an azide via NHS chemistry, then SPAAC with a DBCO payload. For ultra-fast 2-step builds, use tetrazine↔TCO iEDDA pairs.
Best buffers for NHS, maleimide, SPAAC, iEDDA?
NHS/PFP: HEPES or PBS, pH ~7.5–8.5 (no primary amines). Maleimide: pH ~6.5–7.2, remove excess thiols. SPAAC/iEDDA: generally tolerant; still optimize.
Do you support site-specific antibody conjugation?
Yes—Cys re-bridging, glycan-to-aldehyde routes, N-terminus targeting, and enzymatic tags (Sortase, TGase, FGE).
What to include in sample submission?
Sample/buffer, sequence, concentration/A280, desired handle (azide/DBCO/TCO/tetrazine/maleimide), target DoL/DAR, PEG length, copper sensitivity.
Cleavable vs non-cleavable linkers?
Cleavables (disulfide, acid-labile hydrazones, dipeptide/self-immolative, photo-labile) enable triggered release; non-cleavables maximize durability.
Is CuAAC available if copper is acceptable?
Yes—run with biocompatible ligands and copper removal. For copper-sensitive systems, prefer SPAAC/iEDDA.
How should I pack and ship samples for conjugation?
Ship cold (4 °C) for short transits or on dry ice for frozen material; avoid repeated freeze–thaw. Use PBS/HEPES (no Tris/glycine during NHS steps), note any reductants/chelators/preservatives, and include concentration (A280), buffer composition, and desired handle/DAR. Pack leak-proof tubes with secondary containment.
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Contact

Talk to Our Bioconjugation Team

Share your target, linker chemistry, payload, and QC needs. We’ll scope the route (NHS/PFP, maleimide/SPDP, PEG spacers, SPAAC/iEDDA, oxime/hydrazone, EDC) and return a quote with recommended controls and analytics (UV–Vis/DAR, LC-MS, SEC-HPLC).

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Recommended Reading

  • Lang, K. & Chin, J. W. (2014). Bioorthogonal reactions for labeling proteins. Nat. Chem. Rev. — Overview of SPAAC and iEDDA mechanisms and kinetics.
  • Devaraj, N. K. (2018). The future of bioorthogonal chemistry. ACS Cent. Sci. — Comparative review of CuAAC, SPAAC, and iEDDA for biological systems.
  • Jewett, J. C. & Bertozzi, C. R. (2010). Copper-free click chemistry in living systems. Chem. Soc. Rev. — Foundational paper on SPAAC and DBCO chemistry.
  • Wu, H. et al. (2016). Reaction kinetics of the tetrazine–TCO ligation. Angew. Chem. Int. Ed. — Benchmark study on iEDDA rate constants and stability.
  • Hermanson, G. T. (2013). Bioconjugate Techniques, 3rd Edition. Academic Press. — Comprehensive handbook on NHS, maleimide, SPDP, and EDC chemistries.
  • Brossmer, R. & Ernst, B. (2008). PEG linkers and spacer engineering for bioconjugation. Adv. Drug Deliv. Rev. — PEG length, solubility, and pharmacokinetics.
  • Chudasama, V. et al. (2016). Next-generation maleimides for stable cysteine bioconjugation. Chem. Sci. — Ring-opening stabilization of maleimide–thiol conjugates.
  • Wagner, A. & Cabral, H. (2019). Cleavable linkers in antibody–drug conjugates. J. Controlled Release. — Disulfide, hydrazone, enzyme-sensitive linkers.
  • Grabarek, Z. & Gergely, J. (1990). Zero-length crosslinking with EDC. Anal. Biochem. — Classic EDC carboxyl–amine coupling.
  • Tornøe, C. W. & Meldal, M. (2002). Copper-catalyzed azide–alkyne cycloaddition. J. Org. Chem. — Original CuAAC paper.

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