Sprecher
Beschreibung
Abstract:
Colloidal DNA-labelled magnetic nanoparticles (MNPs) enable enzyme-free biosensing and molecular recognition of nucleic acids and proteins, with their inherent magnetic properties being minimally interfered by background signals[1]. Upon a successful molecular recognition between capture ssDNA strands on MNPs and target strands in solution, the particle hydrodynamic size increases, thus slowing down the Brownian relaxation dynamics of MNPs that can be detected using magnetic particle spectroscopy (MPS). However, the interaction between DNA strands on MNPs and how their grafting density influences their molecular recognition towards targets remain poorly understood[1].
Here, we encapsulate single-core custom MNPs inside a thin polymeric shell, enabling their assembling with ssDNA strands of different lengths at various grafting densities through copper-free click chemistry conjugation (Fig. 1a). To investigate the interaction between ssDNA strands on MNPs, we conducted titration assays at four distinct DNA grafting densities by adding complementary strands to DNA-labelled MNPs over a broad concentration range (Fig. 1b). We then measured changes in magnetic relaxation dynamics by recording MPS harmonics spectra. As a complementary technique, we applied dynamic light scattering (DLS) to measure changes in particle hydrodynamic size upon binding to target and established a correlation between MPS and DLS results.
To characterize the titration curves, we fitted a Hill-like function to the data (Fig. 1b and c) and extracted two characteristic parameters K1/2 and n, which represent the target concentration where half of the capture strands are hybridized, and the extent of cooperativity, respectively. The titration experiments indicate that low DNA grafting density yields a Hill coefficient n < 1, indicating minimal cooperativity between ssDNA strands, thereby resulting in a shallower response to target DNA and benefiting a broader dynamic range for detection. While at high DNA grafting densities, the dense packing of ssDNA strands promotes their cooperativity on the MNPs, as indicated by n > 1, resulting in a sharper response to target binding but a narrower response window. We therefore propose that DNA strands are coiled on MNPs at low grafting densities, whereas at high grafting densities they adopt a brush-like conformation (Fig. 1b, inset). Our atomic force microscopy studies reveal a transition of ssDNA from being coiled to forming brushes as their grafting density increases. We will further discuss what is the length of the brushed shell and how this influences the multiplexed target detection.
References:
[1] A. Lak, Y. Wang, et al. Cooperative dynamics of DNA-grafted magnetic nanoparticles optimize magnetic biosensing and coupling to DNA origami. Nanoscale 16, (2024): 7678-7689.
