Improving the Limit of Detection of an infectious disease rapid antigen test: Latex beads vs K-One coated gold nanoparticles

Products & Applications

Kimialys develops custom bioconjugates for Lateral Flow Assay (LFA), leveraging their patented surface chemistry, K-One. K-One optimises the immobilisation of the ligand (such as antibody, antigen or protein) on the nanoparticle surface, while fully protecting the remaining surface against non-specific interactions.

With this double benefit, Kimialys’ K-One allows LFA developers to reach their target Limit of Detection (LoD), while maintaining the reliability of their assays, but without requiring any further adjustments to the assay manufacturing parameters.

This application note provides a case study of Kimialys’ technology integrated into a rapid diagnostic test targeting an infectious disease protein marker.

Proof of Concept

Here we compare the performance of a rapid antigen test in dipstick format (no sample pads or conjugate pads) as a function of the bioconjugates used: latex beads verses Kimialys’ gold nanoparticles, with all other components remaining the same (strip, absorption pad, migration buffer, target antigen, capture antibody).

The latex bioconjugates were optimized by a third party through passive adsorption of the capture antibody, while Kimialys’ gold bioconjugates relied on K-One covalent chemistry.

The size of the latex beads was not known, while Kimialys’ gold nanoparticles had a diameter of 40nm ± 3nm.

All the experiments were carried out in a migration buffer.

Latex Bioconjugates

Detection Carried Out With Latex Conjugates
Figure 1: Detection carried out with latex bioconjugates
  • Visual detection around 78 pg/mL
  • No false positive observed (no non-specific interaction)
  • Background noise after 20 minutes visible as pink staining on membrane

Kimialys’ Bioconjugates

Detection Carried Out With Kimialys Bioconjugates 1
Figure 2: Detection Carried Out With Kimialys Bioconjugates
Detection Carried Out With Kimialys Bioconjugates 2
  • Visual detection around 10 pg/mL
  • No false positive observed (no non-specific interaction) over 12 repetitions with 2 different lots
  • No background noise observed after 20 minutes of migration


This short study in dipstick format highlights the 3 main advantages of Kimialys’ K-One surface chemistry applied to LFA:

  • K-one coated gold nanoparticles generate an 8-fold gain in LoD compared to latex beads. This results from optimal orientation of the capture antibodies towards the solution, thereby maximising capture efficiency.
  • No background noise is observed on the strip after the migration of the K-One based bioconjugates, while latex bead migration leads to a feint pink staining. This showcases the optimal protection of the surface brought by K-One against non-specific interactions.
  • Changing from latex beads to K-One gold bio conjugates does not necessitate changes to any other experimental parameters.