Bovine serum albumin (BSA) conjugated gold (Au) nanoparticles (NPs) were synthesized to explore their applications as drug delivery vehicles in systemic circulation. They showed little hemolysis and cytotoxic responses essentially required for such applications. This study shows some of the important physiochemical aspects needed for an appropriate synthesis of BSA-conjugated NPs where unfolded BSA is an essential reaction component. Unfolding of BSA was carried out under different experimental conditions in the presence of different ionic/ zwitterionic surfactants and monitored simultaneously by UV−visible studies. Cationic surfactants induced unfolding at relatively lower temperatures than anionic and zwitterionic surfactants due to stronger electrostatic interactions with BSA. TEM analysis revealed the presence of NPs with almost similar shapes and sizes for different samples, and all NPs were stabilized by a coating of unfolded BSA. Isoelectric point of unfolded BSA coating on NP surface was close to 4.7 in all cases, which was similar to that of unconjugated BSA. BSA free and cationic surfactant coated Au NPs were used as controls. They showed high hemolytic activity and very low cell viability under identical conditions. Thus, BSA coated NPs were considered to be the best vehicles for drug release and other possible biomedical applications.

Aqueous micellar solutions of F68 (PEO(78)-PPO(30)-PEO(78)) and P103 (PEO(17)-PPO(60)-PEO(17)) triblock polymers were used to synthesize gold (Au) nanoparticles (NPs) at different temperatures. All reactions were monitored with respect to reaction time and temperature by using UV-visible studies to understand the growth kinetics of NPs and the influence of different micellar states on the synthesis of NPs. The shape, size, and locations of NPs in the micellar assemblies were determined with the help of TEM, SEM, and EDS analyses. The results explained that all reactions were carried out with the PEO-PPO-PEO micellar surface cavities present at the micelle-solution interface and were precisely controlled by the micellar assemblies. Marked differences were detected when predominantly hydrophilic F68 and hydrophobic P103 micelles were employed to conduct the reactions. The UV-visible results demonstrated that the reduction of gold ions into nucleating centers was channeled through the ligand-metal charge-transfer complex (LMCT) and carried out by the surface cavities. Excessive hydration of the surface cavities in the case of F68 micelles produced a few small NPs, but their yield and size increased as the micelles were dehydrated under the effect of increasing temperature. The results concluded that the presence of well-defined predominantly hydrophobic micelles with a compact micelle-solution interfacial arrangement of surface cavities ultimately controlled the reaction.

Green chemistry of industrially important zein protein was explored in aqueous phase toward the synthesis of bioconjugated gold (Au) nanoparticles (NPs), which allowed us to simultaneously understand the unfolding behavior of zein with respect to temperature and time. Synthesis of Au NPs was monitored with simultaneous measurements of UV–visible absorbance due to the surface plasmon resonance (SPR) of Au NPs that triggered the adsorption of zein on the NP surface and thus resulted in its unfolding. Surface adsorption of zein further controlled the crystal growth of Au NPs, which relied on the degree of unfolding and fusogenic behavior of zein due to its predominant hydrophobic nature. The latter property induced a marked blue shift in the SPR rarely observed in the growing NPs during the nucleation process. A greater unfolding of zein in fact was instrumental in generating zein-coated faceted NPs that were subjected to their hemolytic response for their possible use as drug release vehicles. Zein coating significantly reduced the hemolysis and made bioconjugated Au NPs the best models for biomedical applications in nanotechnology.

Three block polymers, viz., L31, L64, and P123, were used as reducing agents for the synthesis of gold (Au) nanoparticles (NPs) to determine the effect of their micelle size, structure transitions, and environments on the mechanism of the reduction process leading to the overall morphology of Au NPs. Aqueous phase reduction was monitored with time at constant temperature and under the effect of temperature variation from 20 to 70 °C by simultaneous measurement of UV–visible spectra. The ligand to metal charge transfer (LMCT) band around 300 nm, due to a charge transfer complex formation between the micelle surface cavities and AuCl4 – ions, and Au NP absorbance around 550 nm, due to the surface plasmon resonance, were simultaneously measured to understand the mechanism of the reduction process and its dependence on the micelle structure transitions and environment of TBPs micelles. L64 micelles showed dramatic shift in the LMCT band from lower to higher wavelength due to an increase in the reduction potential of surface cavities induced by the structure transitions under the effect of temperature variations. This effect was not observed for micelles of either L31 or P123 and is explained on the basis of a difference in their micelle environments. The morphology of Au NPs thus evolved from the reduction process was studied with the help of TEM and SEM studies. Smaller micelle size with few surface cavities, as in L31, produced small NPs in comparison to large micelles with several surface cavities as in P123. Structure transitions of L64 demonstrated direct influence on the final morphology of NPs, and stronger transitions produced fused and deformed NPs in comparison to weaker transitions. The results showed that efficient reduction by the surface cavities and uninterrupted nucleation without structure transitions lead to well-defined morphologies in the presence of P123 micelles.

Self-assembled gold (Au) nanoparticles (NPs) were synthesized in micelle surface cavities of a L121 block polymer in the presence of zwitterionic (viz. DPS, TPS, and HPS) and sugar surfactants (OG and DDM) in aqueous phase at 70 °C by using the surface cavities of L121 as reducing sites for converting Au(III) into Au(0). All reactions were monitored simultaneously by UV-visible spectroscopy to determine the growth kinetics in gold nucleating centers on the basis of surface plasmon resonance that also helped in tracing the structure micelle transitions over a wide temperature range of 10-70 °C. The surfactant/L121 mole ratio was changed systematically from 0.5 to 2.5 by keeping L121 and HAuCl4 concentrations constant at 10 and 0.25 mM, respectively, to determine the shape and size of the micelles and their relation to the self-assembled behavior of Au NPs. TEM studies were used to have a direct insight into the morphology of micelle templates and their shape and size for self-assembled NPs. L121 along with DPS (C12 carbon chain) produced well-defined micelles loaded with tiny NPs of 3-6 nm in the L121-rich region of the mixture, while large flower-like compound micelles with a clear core-shell morphology were produced in the DPS-rich region. TPS and HPS (C14 and C16 hydrocarbon chains, respectively) with stronger hydrophobicity than DPS also produced almost similar micelles loaded with tiny NPs in the L121-rich region, but they disappear in the surfactant-rich region. Replacement of zwitterionic with ionic surfactants did not yield micelle templates for self-assembled NPs. Results conclude that well-defined micelles of L121 are the fine templates for self-assembled NPs that can only be achieved in the presence of a neutral surfactant with low concentration and low hydrophobicity.

Industrially important zein protein has been employed to understand its interactions with two model proteins bovine serum albumin (BSA) and cytochrome c (Cyc,c) following the in vitro synthesis of Au NPs so as to expand its applicability for biological applications. Interactions were studied under the effect of temperature variation by UV-visible and fluorescence emission studies. Temperature induced unfolding in the protein mixtures indicated their degree of mutual interactions through simultaneous nucleation of gold nanoparticles (Au NPs) and their subsequent shape control effects. Zein + BSA mixtures showed favorable protein-protein interactions over the entire mole fraction range with maximum close to x(BSA) = 0.24, whereas zein + Cyc,c showed such interactions only in the zein rich region with significant demixing in the Cyc,c rich region of the mixtures. Both hydrophobic as well as hydrophilic domains in the unfolded states were driving such interactions in the case of zein + BSA mixtures while demixing was the result of the predominant hydrophilic nature of Cyc,c and its self-aggregation behavior in the Cyc,c rich region in contrast to the predominant hydrophobic nature of zein. Zein + BSA mixtures produced small roughly spherical Au NPs fully coated with protein, whereas the demixing zone of zein + Cyc,c mixtures generated highly anisotropic NPs with little protein coating. To explore their biological applications, protein conjugated NPs of both mixtures were subjected to hemolysis where NPs coated with the former mixture showed little hemolysis and may act as drug delivery vehicles in systemic circulation in comparison to the latter. Both kinds of NPs further demonstrated their extraordinary antimicrobial activities with different kinds of strains and proved to be highly important environmentally friendly biomaterials.

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We demonstrate the potential use of 1,1′-bis(2-(cyclo­hexyloxy)-2-oxoethyl)-[4,4′-bipyridin]-1,1′-diium bromide (BP) and 1-ethyl-3-methyl­imidazolium chloride (EMI) ionic liquids (ILs) in in situ synthesis of gold nanoparticles (Au NPs) without using any external reducing or stabilizing agents. Both ILs produced nearly monodisperse NPs of 4–8 nm which were present in the form of self-assembled states. BP coated NPs formed self-assembled sheets and easily transferred to the organic phase by employing the water insoluble IL as a phase transfer agent. The efficiency of the phase transfer process was related to the extent of aggregation as well as functional groups. Both IL coated NPs were further used to extract the proteins from the complex biological mixtures. EMI coated NPs extracted proteins of large molar masses whereas BP coated NPs were good for the extraction of low molecular mass proteins. This disparity was controlled by the substituted functional groups of ILs. Bulky cyclohexyloxy functional groups of BP did not allow extraction of large molar mass proteins. Such a wide applicability of ILs in nanomaterials synthesis opens several new applications in the field of nanomedicine and nanobiotechnology where IL coated NPs can be used for diverse protein complexation.