This results in a modulated fluorescence intensity that is composed of first, second and third harmonic signals which were found to strongly depend on the hybrization state of the DNA SAM, the DNA packing density on the surface, and the surface crystallography.
There, a 'fluctuating filament model' was introduced in which the chromosome is approximated as a confined elastic filament with constant DNA packing density.
DNA packing density on AuNPs influenced the thermal stability of DNA-AuNPs at 37 °C, but this effect was minimum as temperature increased to 85 °C.
DNA packing densities on AuNPs can influence the stability of DNA-AuNPs, as a result of the strong intermolecular repulsions among the largely negatively charged phosphodiester backbones of DNA molecules.
To examine the underlying mechanisms, we administered 0.2 or 0.8 mg/kg of dexamethasone to pregnant rats on gestational days 17, 18, and 19 and assessed brain region cell development with indices of DNA content (total cell numbers), DNA concentration (cell packing density), and protein/DNA ratio (relative cell size).
These results were obtained under the same experimental conditions, including DNA sequences, packing densities (Table 1), buffer conditions, and incubation temperatures.
The rate of DNA release from DNA-AuNPs with a packing density of 90 DNA molecules per AuNP was 3.4-fold slower than that of 190 DNA molecules per AuNP (Table 2).
Indices of cell packing density (DNA per gram of tissue) and cell number (DNA content) similarly showed effects only on the liver; however, there were significant changes in the protein/DNA ratio, an index of cell size, in fetal brain regions at doses as low as 1 mg/kg, below the threshold for inhibition of fetal brain cholinesterase (2 mg/kg).
In the occipital cortex and midbrain, there were smaller cells (reduced total protein/DNA ratio) and a corresponding increase in cell packing density (DNA concentration), features that are likely to reflect neuronal damage and "reactive gliosis," that is, replacement with smaller, glial cells (O'Callaghan 1988 , 1993 Roy et al. 1998, 2002; Roy and Sabherwal 1994, 1998).
The accessibility of DNA is dependent on the packing density of chromatin fibers, which plays a critical role in transcriptional regulation and all other DNA-related biological processes.
In addition, the increased local concentration of DNA molecules on AuNPs and the consequently decreased interaction between the surface of AuNPs and DNA molecules at a higher packing density could also contribute to the observed effect.
