Journal of Material Sciences & Engineering

What controls the unusual melting profiles of small AuNPs/DNA complexes

Abstract

Elia Grueso

In this work is studied the effect of addition of low NaClconcentrations on ds-DNA and ss-DNA conformational changes induced by smalltioproningold nanoparticles (AuNPs). For this purpose, fluorescence, UV-visible, CD,AFM, DLS and zeta potential techniques were used.The high affinity of ssDNA to AuNPs compared with ds-DNA is easily demonstrated by the results of competitive binding with SG. Additionally, it is proven that at 298 K, AuNPs/ds-DNA and AuNPs/ss-DNA complexes undergo a transition from extended-coil to more compact structures when the AuNPs concentration (CAuNPs) is increased, which for the ds-DNA system is accompanied by partial  denaturation.Particularly, for the AuNPs/ss-DNA system all of these techniques confirm that at a high CAuNPs, the compaction process is followed by a discrete transition to aggregation and an increase in structure size. A thorough conformational changes analysis indicates that these processes are larger in low CNaCland at high temperature. Remarkable is the abnormal melting temperature profiles (Tm) registered at high R = CAuNPs/CDNA ratios.At a suitable R ratio, which varies depending on CNaCl, a complex melting profile for the AuNPs/ds-DNA system was registered with two characteristic transitions: Tm,1= 338 K and Tm,2 = 368 K.The AFM technique performed at 298 K and 338 K also showed a different behaviour in both DNA-based systemsSpecifically, for the AuNPs/ss-DNA system, AFM at 298 K revealed the formation of large-sized aggregates formed by AuNPs/ss-DNA compact structures linked by AuNPs, which explains the characteristic melting curves.However, when both complexes were incubated at 338 K, the formation of highly stable ordered structures was always visualized at high R.These results constitute a significant difference in the use of small gold nanoparticles in comparison fluorescence biomarkers as a detection system of DNA structures providing both challenges and opportunities for improving sensing applications.