Summary
A KU Leuven-led bioRxiv preprint describes a modular click-chemistry method for attaching fluorophores and DNA to CRISPR-Cas9 ribonucleoproteins without tying the engineering process to how the complex is assembled. In vitro experiments reported by the authors found that modifying an already formed complex provided two-fold greater accessibility of attached DNA.
A KU Leuven-led research team has described a modular way to attach fluorescent labels and DNA to CRISPR-Cas9 complexes for genome imaging. The work, posted as a bioRxiv preprint on September 13, 2026, uses a bio-orthogonal click-chemistry reaction so that engineering the CRISPR complex can be separated from its assembly.
The authors report that the method worked when modifications were introduced at different stages of CRISPR ribonucleoprotein (RNP) formation in vitro. Their experiments also found that modifying a native CRISPR RNP after it had already formed caused fewer structural perturbations and produced two-fold greater accessibility of the attached DNA.
Why modify CRISPR for genome imaging?
CRISPR-Cas9 is best known as a genome-editing system, but its sequence-specific binding can also be used to locate selected DNA sequences. In genome imaging, Cas9 is directed to a chosen genomic target by a guide RNA, while an attached fluorophore or other signal-generating component makes the bound complex visible.
The challenge is to add these components without interfering with the folding, assembly or target recognition of the Cas9-guide-RNA complex. Earlier engineering approaches have often relied on cells expressing modified CRISPR components. In that arrangement, the final performance can depend on how the components are delivered and assembled inside the cell, as well as on the design of the expression vector.
The new strategy instead uses SPAAC, or strain-promoted azide-alkyne cycloaddition. This is a click-chemistry reaction in which chemical groups placed on the biological components react selectively to form a covalent connection, without requiring the engineering step to be built into the original RNP assembly process.
A modular route to labels and signal amplification
According to the preprint, the researchers used the approach to modify CRISPR with both fluorophores and DNA during all stages of in-vitro RNP assembly. The key comparison concerned modification before versus after the native complex had formed. Post-assembly engineering was associated with reduced structural disruption and two-fold enhanced accessibility of the clicked DNA, a result relevant to designs that need attached DNA to remain available for further reactions.
The team also used SPAAC to join non-native RNA-DNA hybrids to CRISPR components. The conjugation worked regardless of whether the hybrid was attached through its 5′ or 3′ directionality. On this basis, the researchers developed a covalently attached rolling-circle signal-amplification approach. Rolling-circle amplification uses a circular nucleic-acid template to generate repeated copies of a sequence, potentially creating a stronger local signal at a labelled target.
The modular design could make it easier to change the label or attached nucleic-acid element without redesigning the entire CRISPR assembly system. The authors identify genome imaging and prime-editing applications as areas that could benefit from this flexibility.
Evidence and limits of the current result
This is a preprint describing an in-vitro molecular-engineering study with subsequent validation for genome imaging. The source text reports the construction of modified CRISPR RNPs, the comparison of assembly-stage engineering, and the development of the rolling-circle amplification approach. It does not describe an animal study, clinical testing or a therapeutic application.
The reported two-fold improvement concerns accessibility of attached DNA within the engineered complex, rather than a demonstrated improvement in clinical outcomes or genome-editing efficiency. Whether the method performs similarly in living cells, across different genomic targets or in prime-editing systems will require the application-specific experiments identified by the researchers.