Biocompatible and colloidally stable gold nanorods (GNRs) with well-defined plasmonic properties are essential for biomedical and theranostic applications. The as-synthesized GNRs using the seed-mediated method are stabilized by the surfactant, cetyltrimethylammonium bromide (CTAB), which is known for its cytotoxicity in many cell lines. Biocompatible GNRs synthesized using known protocols exhibit some extent of cytotoxicity and colloidal instability because of the incomplete removal of CTAB. We report a facile method for the efficient removal of CTAB molecules with 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) phospholipid molecules, which are naturally present in cell membranes. The kinetics of the ligand exchange process is studied using surface-enhanced Raman scattering (SERS) and corroborated with matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. From colloidal stability studies using dynamic light scattering (DLS) and UV-Vis spectroscopy, the optimal lipid concentration and duration required for the successful ligand exchange of CTAB by DMPC are reported. Using thermogravimetric analysis, the surface concentration of DMPC on colloidally stable GNRs is found to be approximately 9 molecules per nm. The 3-(4,5-dimethylthiozol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) and lactate dehydrogenase (LDH) assays show that the surface-modified DMPC-GNRs have significantly better biocompatibility than those of CTAB-GNRs. Studies on the ligand exchange, colloidal stability and biocompatibility of DMPC-GNRs with aspect ratios ranging from 2.2 to 4.2 demonstrate the robustness of the proposed method. The results provide insights into the important factors to be considered while designing biocompatible GNRs suitable for applications in nanomedicine.

An analytical solution of a mathematical model is reported to explain the growth kinetics of gold nanorods grown via seed mediated synthesis.

Silver triangular nanoplates (AgTNP) present unique surface plasmonic and catalytic properties depending upon the thickness and edge length. AgTNP are synthesized in a kinetically controlled growth process, by and large, using the polymer poly-vinylpyrrolidone (PVP) as a reductant. In this work, we present a systematic study to uncover the effect of the molecular weight (MW) of PVP and the PVP to silver salt (AgNO3) molar ratio ([P : S]) on the physical dimensions of AgTNP. The edge length of AgTNP shows a non-monotonic variation with respect to [P : S] for all MWs. Based on several control experiments, a kinetic mechanism is proposed and a mathematical model is developed to explain the formation of AgTNP. The elementary processes of the model include the reduction of Ag+ by the -OH group in PVP, followed by instantaneous nucleation. This phase is then followed by a slow reduction of Ag+ and growth of the nuclei to AgTNP. The model shows a reasonable agreement with experiments on the non-monotonic variation of edge length of AgTNP with respect to [P : S], as well as on the temporal evolution of the edge length.

Copper nanowires (Cu NWs) are a promising alternative to silver NWs to develop transparent conducting films (TCFs) due to their comparable electrical conductivity and relative abundance. Postsynthetic modifications of the ink and high-temperature postannealing processes for obtaining conducting films are significant challenges that need to be addressed before commercial deployment of these materials. In this work, we have developed an annealing-free (room temperature curable) TCF with Cu NW ink that requires minimal postsynthetic modifications. Organic acid pretreated Cu NW ink is used for spin-coating to obtain a TCF with a sheet resistance of 9.4 Ω/sq. and optical transparency of 67.4% at 550 nm. For oxidation protection, the Cu NW TCF is encapsulated with polydimethylsiloxane (PDMS). The encapsulated film is tested as a transparent heater at various voltages and shows good repeatability. These results demonstrate the potential of Cu NW-based TCFs as a replacement for Ag-NW based TCFs for a variety of optoelectronic applications, such as transparent heaters, touch screens, and photovoltaics.

Interfacial self-assembly of nanoparticles on curved substrates.