Temperature-dependent structural change of D-penicillamine-capped chiral gold nanoparticles investigated by infrared spectroscopy.

The structure and stability of D-penicillamine-capped gold nanoparticles (d-Pen Au NPs) were studied using spectroscopic tools. The synthesis of d-Pen Au NPs was examined using high-resolution transmission electron microscopy (HR-TEM), UV-vis absorption spectroscopy, and circular dichroism (CD). Temperature-dependent reversible structural changes of d-Pen Au NPs were observed using infrared spectroscopic tools. The three thiol, carboxyl, and amino binding groups of d-Pen were presumed to interact with Au NP surfaces on the basis of the infrared spectral features. d-Pen appeared to form quite a stable structure and desorb at a high temperature above 453 K on Au NPs. Our deconvolution analysis indicated the ν(s)(COO(-)) and ν(as)(COO(-)) carboxylate bands at ∼1,392 and ∼1,560 cm(-1) appeared to be weakened, whereas the amino band at ∼1,595 cm(-1) remained strong in increasing the temperature from 293 to 373 K. On the other hand, the intensities of the zwitter ionic bands at ∼999, ∼1,117, and ∼1,631 cm(-1) for NH(3)(+) appeared to decrease presumably due to the deprotonation process at 373 K. Our infrared spectroscopic study suggests that the deprotonated amino groups bind stronger, whereas the intra-carboxylate bonds become weaker as the temperature increase. Such structural changes of d-Pen Au NPs appeared to be reversible between 293 and 373 K.

Label-free Raman spectroscopy for accessing intracellular anticancer drug release on gold nanoparticles.

We investigated glutathione (GSH)-induced purine or pyrimidine anticancer drug release on gold nanoparticle (AuNP) surfaces by means of label-free Raman spectroscopy. GSH-triggered releases of 6-thioguanine (6TG), gemcitabine (GEM), acycloguanosine (ACY), and fadrozole (FAD) were examined in a comparative way by means of surface-enhanced Raman scattering (SERS). The GSH-induced dissociation constant of GEM (or ACY/FAD) from AuNPs was estimated to be larger by more than 38 times than that of 6TG from the kinetic relationship. Tripeptide control experiments were presented to check the turn-off Raman signalling mechanism. Dark-field microscopy (DFM) and transmission electron microscopy (TEM) indicated the intracellular AuNP loads. After their cellular uptake, GEM, ACY, and FAD would not show SERS intensities as strong as 6TG. This may be due to easier release of GEM, ACY, and FAD than 6TG by intracellular reducing species including GSH. We observed fairly strong SERS signals of GEM and 6TG in cell culture media solution. Our CCK-8 cytotoxicity assay data support that 6TG-AuNPs did not exhibit a substantial decrease in cell viability presumably due to strong binding. Label-free confocal Raman spectroscopy can be utilized as an effective tool to access intracellular anticancer drug release.

Confocal Raman microspectroscopic study of folate receptor-targeted delivery of 6-mercaptopurine-embedded gold nanoparticles in a single cell.

We investigate the cellular uptake behaviors and efficacy of folate-coated gold nanoparticles (AuNPs) for the targeted drug delivery system in human cancer cells. Folate-conjugated AuNPs embedded with a purine analogue cancer drug of 6-mercaptopurine (6MP) were assembled via a 1-ethyl-3-[3-dimethylaminopropyl] carbodiimide hydrochloride (EDC) coupling reaction between the amino group of 4-aminobenzenethiol (ABT) and the carboxyl group of folic acid. The assembly of folate and 6MP on AuNPs has been examined by absorption spectroscopy, transmission electron microscopy (TEM), and confocal Raman spectroscopy. The internalization of the conjugated AuNPs inside the folate receptor-positive HeLa and KB cells was checked by TEM and dark-field microscopy (DFM) combined with label-free confocal spectroscopy over the depth variable z at a micrometer resolution. DFM live cell imaging of folate-conjugated AuNPs in HeLa cells indicated that the targeted AuNPs appeared to attach on the cell surfaces and enter into the cell with an hour. The cell viability was also compared to estimate the efficacy of folate-conjugated AuNP delivery systems. Folate receptor-targeted AuNP systems appeared to decrease cancer cell viability both in vitro and in vivo more than did the use of the 6MP-coated AuNPs drug without any targeting systems.

In vitro toxicity of serum protein-adsorbed citrate-reduced gold nanoparticles in human lung adenocarcinoma cells.

We examined the cytotoxicity effect of the serum protein coated gold nanoparticles (AuNPs) in the A549 cells. Negatively charged AuNPs were prepared by chemical reduction using citrate. The dimension and surface charge of AuNPs were characterized using transmission electron microscopy (TEM), dynamic light scattering (DLS), and zeta potential measurements. The AuNPs modified by the citrate anion were presumed to adsorb the serum proteins as indicated from the visible absorption spectroscopy, DLS, and quartz crystal microbalance (QCM) data. The QCM results indicated that among the constituents, fetal bovine serum (FBS) should be the major adsorbate species on the AuNPs incubated in the RPMI medium. The internalization of AuNPs into the A549 cells was also monitored using TEM and dark-field microscopy (DFM). Both methylthiazol tetrazolium (MTT) and lactate dehydrogenase (LDH) assays revealed that AuNPs were toxic as determined by their half-maximal inhibitory concentration. A flow cytometric and real-time PCR analysis of apoptotic genes along with the ATP depletion measurements suggested that AuNPs induce cell damages through extrinsic and intrinsic apoptotic pathways.

Preferential adsorption of fetal bovine serum on bare and aromatic thiol-functionalized gold surfaces in cell culture media.

Intracellular uptake of serum-coated gold nanoparticles (AuNPs) in a single mammalian cell was examined in order to investigate the interactions of cell culture media and aromatic thiol-functionalized gold surfaces using micro-spectroscopic tools. The AuNPs modified by the aromatic thiols of para-aminobenzenethiol (ABT), para-hydroxy benzenethiol (HBT), and para-carboxylic benzenethiol (CBT, para-mercaptobenzoic acid) bearing NH(2), OH, and COOH surface functional groups are presumed to adsorb the serum proteins as indicated from the compiled quartz crystal microbalance (QCM) data. The QCM results indicate that among the constituents, fetal bovine serum (FBS) should be the major adsorbate species on AuNPs incubated in Roswell Park Memorial Institute (RPMI) medium. The functionalized AuNPs were found to be internalized as an aggregation state in mammalian cells as evidenced by transmission electron microscopy (TEM) images. We monitored such cellular uptake behaviors of aromatic thiol-modified AuNPs using dark-field microscopy (DFM)-guided confocal surface-enhanced Raman scattering techniques in order to identify the three-dimensional localization inside the single cell. We found that the uptake amounts of ABT, HBT, and CBT were similar by counting up to 70 particles inside the cells incubated in the solution mixture of the aromatic thiol and 1,4-phenylenediisocyanide (PDIC) as a reference. This result indicates for the short aromatic thiol compounds, the AuNPs should enter the cell after the serum-coating regardless of the surface functional groups. Considering that the aromatic thiols have little effect on the serum coating, the DFM/SERS method is an effective tool for monitoring the localization of AuNPs inside a single cell.