A cone-shaped dendron called NanoCone has a well-defined three-dimensional structure and its size can be changed precisely. When this monodisperse molecule is coated on a surface, branches of the NanoCone form stable chemical bonds with the surface of a substrate, and a functional group at its apex is utilized for immobilization of a bioactive molecule. In addition, these molecules are located on the surface having the regular lateral spacing between them which was directly observed by using a high resolution scanning electron microscope (HRSEM). The average spacing was 3.2 ± 0.4 nm and density 0.05 – 0.06 ea/nm2. Also, in all of the cases, the spacing was larger than 2 nm. Topographical images obtained by atomic force microscopy (AFM) also showed that the resulting layer was smooth and homogeneous without any aggregates or holes in macroscopic scale.
Therefore, the particular topological structure of the employed NanoCone surface allows the optimal spacing between biomolecules on the surface for diagnosis or bioassay. By choosing appropriate size and degree of branching of the NB, the spacing can be precisely controlled from 3 up to more than10 nanometers. Also, a stringent choice of chemical structure of its backbone and organic sublayer effectively suppresses undesirable nonspecific binding of various biomolecules.
SEM image of surface and different sizes of NanoCones
– NanoCones Technology Allows Gold Standard Surface for Bioassay
NanoCones technology makes possible the following main features that, when combined, offer significant advantages over existing technologies.
a) Exact control of probe spacing/density
The dendron-modified substrate offers regular spacing between probes. Well-defined assembly of dendrons over the entire plate assures homogeneity and constant probe density.
b) Mimic of solution-phase behavior
Due to minimized steric hindrance between double helixes formed upon hybridization, very high hybridization efficiency and mimicry of solution phase behavior were observed. For example, oligomeric probe DNA discriminates a single base mismatched counterpart so effectively that contrast ratio is higher than 100. Also, SPR study showed that biotin on the dendron-modified surface captures Streptavidin more effectively than any other mixed monolayer.
c) Very low nonspecific binding
The dendron-modified layer shows very low nonspecific binding of various biomolecules on surface. This feature combined with spacing ensures high sensitivity of DNA microarrays. These outstanding factors allow DNA microarrays to be fabricated on a NanoCones surface to detect complementary DNA at low concentration (50 fM) for genetic mutation, and as little as 1 μg total RNA can be assayed successfully without any amplification for gene expression profiling research.
d) Absolute monolayer
Unlike a biochip plate having 3-dimensional complexity, the self-assembly approach of the NanoCones surface produces an absolute monolayer that ensures a well-defined immobilization of biomolecules of interest.