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.

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.

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.

Bovine serum albumen (BSA) conjugated gold (Au) nanoparticles (NPs) were directly synthesized by using BSA as a weak reducing agent against HAuCl4 in aqueous phase. A systematic variation in Au/BSA mole ratio showed a dramatic change in the size and shape of NPs which was very much dependent on the physical state of BSA. The nature of both colloidal NPs (due to surface plasmon resonance) and BSA (due to tryptophan residues) was monitored simultaneously by UV−visible measurements during the course of the reaction. A systematic variation in the reaction temperature from 20 to 70 °C demonstrated a clear denaturation process of BSA and how it influenced the synthesis of Au NPs. A predominantly native state of BSA that existed up to 40 °C proved to be a very mild reducing agent to convert Au(III) into Au(0). However, the reducing potential increased with unfolding of BSA beyond 40 °C and became maximum in the denaturation temperature range (i.e., 52−58 °C). Unfolded BSA conjugated NPs thus produced then started a seeding process with other similar NPs or free BSA to produce self-assembled colloidal assemblies in the form of soft film of BSA bearing NPs. SEM, TEM, and AFM studies were used to characterize the BSA conjugated NPs in the form of soft film. The soft film was used with water insoluble zein protein to produce very robust biodegradable protein films suitable for various food and pharmaceutical applications. Tensile strength and strain at failure measurements of zein protein films demonstrated that the film made with BSA conjugated NPs existed in the form of a soft film was much stronger and flexible in comparison to that made with nonaggregated NPs.