Compaction of Calf Thymus DNA by a Potential One-Head-Two-Tail Surfactant: Properties of Nanomaterials and Biological Testing for Gene Delivery.

A one-head-two-tail cationic surfactant, Dilauryldimethylammonium bromide (DDAB) has shown a great extent of calf thymus DNA (ct-DNA) compaction being adsorbed on the surfaces of negatively charged SiO2 nanoparticles (NPs). DDAB molecules show high adsorption efficiency and induce many positive surface charges per-unit surface area of the SiO2 NPs compared to cationic Gemini (12-6-12) and conventional (DTAB) surfactants in an aqueous medium at pH 7.4, as evident from zeta potential and EDAX data. Transmission electron microscopy and field emission scanning electron microscopy images, along with ethidium bromide exclusion assay and DLS data support the compaction of ct-DNA. Fluorescence microscopic images show that in the presence of SiO2 NPs, DDAB can perform 50% compaction of ct-DNA at a concentration ∼58% and ∼99% lower than that of 12-6-12 and DTAB, respectively. Better ct-DNA compaction by DDAB is evident compared to other Gemini surfactants (12-4-12 and 12-8-12) as well reported before. Time-correlated single photon counting fluorescence intensity decay measurements of a probe DAPI in ct-DNA have revealed the average lifetime value that is decreased by ∼61% at 2.5 µM of DDAB in the presence of SiO2 NPs as compared to a decrease by only ∼29% in its absence, supporting NPs-induced stronger surfactant binding with ct-DNA. Fluorescence lifetime data have also demonstrated the crowding effect of NPs. At 2.5 µM of DDAB, both fast and slow rotational relaxation components of DAPI contribute almost equally to depolarization with the absence of NPs; however, with the presence of NPs, ∼96% weightage of the anisotropy decay is for the fast component. The present DDAB-SiO2 NPs combination has proved to be an excellent gene delivery system based on the cell viability in the mouse mammary gland adenocarcinoma cells (4T1) and human embryonic kidney (HEK) 293 cell lines, and in vitro and in vivo studies.

Role of Gemini Surfactants with Variable Spacers and SiO2 Nanoparticles in ct-DNA Compaction and Applications toward In Vitro/In Vivo Gene Delivery.

Compaction of calf thymus DNA (ct-DNA) by two cationic gemini surfactants, 12-4-12 and 12-8-12, in the absence and presence of negatively charged SiO2 nanoparticles (NPs) (∼100 nm) has been explored using various techniques. 12-8-12 having a longer hydrophobic spacer induces a greater extent of ct-DNA compaction than 12-4-12, which becomes more efficient with SiO2 NPs. While 50% ct-DNA compaction in the presence of SiO2 NPs occurs at ∼77 nM of 12-8-12 and ∼130 nM of 12-4-12, but a conventional counterpart surfactant, DTAB, does it at its concentration as high as ∼7 µM. Time-resolved fluorescence anisotropy measurements show changes in the rotational dynamics of a fluorescent probe, DAPI, and helix segments in the condensed DNA. Fluorescence lifetime data and ethidium bromide exclusion assays reveal the binding sites of surfactants to ct-DNA. 12-8-12 with SiO2 NPs has shown the highest cell viability (≥90%) and least cell death in the human embryonic kidney (HEK) 293 cell lines in contrast to the cell viability of ≤80% for DTAB. These results show that 12-8-12 with SiO2 NPs has the highest time and dose-dependent cytotoxicity compared to 12-8-12 and 12-4-12 in the murine breast cancer 4T1 cell line. Fluorescence microscopy and flow cytometry are performed for in vitro cellular uptake of YOYO-1-labeled ct-DNA with surfactants and SiO2 NPs using 4T1 cells after 3 and 6 h incubations. The in vivo tumor accumulation studies are carried out using a real-time in vivo imaging system after intravenous injection of the samples into 4T1 tumor-bearing mice. 12-8-12 with SiO2 has delivered the highest amount of ct-DNA in cells and tumors in a time-dependent manner. Thus, the application of a gemini surfactant with a hydrophobic spacer and SiO2 NPs in compacting and delivering ct-DNA to the tumor is proven, warranting its further exploration in nucleic acid therapy for cancer treatment.

Refolding of denatured gold nanoparticles-conjugated bovine serum albumin through formation of catanions between gemini surfactant and sodium dodecyl sulphate.

The present work elucidates binding interactions of sodium dodecyl sulphate (SDS) with the conjugated gold nanoparticles (AuNPs)-bovine serum albumin (BSA), unfolded by each of two gemini surfactants, 1,4-bis(dodecyl-N,N-dimethylammonium bromide)-butane (12-4-12,2Br-) or 1,8-bis(dodecyl-N,N-dimethylammonium bromide)-octane (12-8-12,2Br-). Initially, at a low concentration of SDS there is a relaxation of bioconjugates from their compressed form due to the formation of catanions between SDS and gemini surfactants. On moving towards higher concentrations of SDS, these relaxed unfolded bioconjugates renature by removal of residual bound gemini surfactants. Mixed assemblies of SDS and gemini surfactants formed during refolding of bioconjugates are characterized by DLS and FESEM measurements. A step-by-step process of refolding observed for these denatured protein bioconjugates is exactly the inverse of their unfolding phenomenon. Parameters concerning nanometal surface energy transfer (NSET) and Förster's resonance energy transfer (FRET) phenomenon were employed to develop a binding isotherm. Moreover, there remains an inverse relationship between α-helix and ß-turns of bioconjugates during the refolding process. Significantly, in the presence of 12-8-12,2Br-, SDS induces more refolding as compared to that for 12-4-12,2Br-. Bioconjugation shows an effect on the secondary structures of refolded BSA, which has been explored in detail through various studies such as Fourier transform infrared spectroscopy, fluorescence, and circular dichroism (CD). Therefore, this approach vividly describes the refolding of denatured bioconjugates, exploring structural information regarding various catanions formed during the process that would help in understanding distance-dependent optical biomolecular detection methodologies and physicochemical properties.