Abstract
The biophysical properties of DNA-modified Au nanoparticles (AuNPs) have attracted a great deal of research interest for various applications in biosensing. AuNPs have strong binding capability to the phosphate and sugar groups in DNA, rendering unique physicochemical properties for detection of metal ions. The formation of Au–DNA nanocomposites is evident from the observed changes in the optical absorption, plasmon band, zeta potential, DLS particle size distribution, as well as TEM and AFM surface morphology analysis. Circular dichroism studies also revealed that DNA-functionalized AuNP binding caused a conformational change in the DNA structure. Due to the size and shape dependent plasmonic interactions of AuNPs (33–78 nm) with DNA, the resultant Au–DNA nanocomposites (NCs) exhibit superior fluorescence emission due to chemical binding with Ca2+, Fe2+ and Mg2+ ions. A significant increase in fluorescence emission (λex = 260 nm) of Au–DNA NCs was observed after selectively binding with Mg2+ ions (20–800 ppm) in an aqueous solution where a minimum of 100 ppm Mg2+ ions was detected based on the linearity of concentration versus fluorescence intensity curve (λem = 400 nm). The effectiveness of Au–DNA nanocomposites was further verified by comparing the known concentration (50–120 ppm) of Mg2+ ions in synthetic tap water and a real life sample of Gelusil (300–360 ppm Mg2+), a widely used antacid medicine. Therefore, this method could be a sensitive tool for the estimation of water hardness after careful preparation of a suitably designed Au–DNA nanostructure.
Highlights
The interactions between Au nanoparticles (AuNPs) and DNA are essential to classify and expand upon, given the potential applications for NP–DNA complexes such as gene therapy, drug delivery, and DNA decoding
The loading of DNA could be maximized along the longitudinal cross-section of the Au nanorods (AuNRs), the major red shift was observed in this region, probably due to the close contact of dispersed AuNPs with the addition of DNA [25]
The free DNA showed a negative peak at 247 nm and a positive peak at approximately 278 nm in the circular dichroism (CD) spectrum, which corresponds to B-DNA
Summary
The interactions between Au nanoparticles (AuNPs) and DNA are essential to classify and expand upon, given the potential applications for NP–DNA complexes such as gene therapy, drug delivery, and DNA decoding. The importance of AuNPs is due to their unique optical properties related to the collective oscillation of the surface electrons, called surface plasmonic resonance (SPR) [1]. Since the frequency of this SPR band depends on the size, shape and chemical environment of the AuNP, any change in the environment of these particles, such as adsorption, desorption or aggregation, will shift the SPR band. Au nanostructures can act as signal intensifiers and lead to enhancement of the fluorescence and scattering response in various DNA detection schemes. The high sensitivity of the plasmon spectra towards the particle size and the local dielectric environment offers new methods for the detection of free DNA or other biomolecules [2], where the detection signal is exclusively based on the color changes during assay or modifications in the plasmonic spectra
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