The ability of ten polyphenolic antioxidants to prevent CuO nanoparticle ((CuO)-Cu-NP) and H2O2-mediated DNA damage and cytotoxicity was investigated. Five of the polyphenols (MEPCA, PREGA, MEGA, ECG, and EGCG) prevent (CuO)-Cu-NP/H2O2-mediated DNA damage (IC50 values of 7.5-800 mu M), three have no effect (PCA, VA, and EC), and two (GA and EGC) result in increased DNA damage. Most polyphenols had similar antioxidant/ prooxidant activity in the presence of (CuO)-Cu-NP or free copper ions. Electron paramagnetic resonance (EPR) spectroscopy of reactive oxygen species (ROS) generated by (CuO)-Cu-NP/H2O2 in the presence of representative polyphenols correlate with results of DNA damage studies: in the presence of (CuO)-Cu-NP/H2O2, MEPCA prevents ROS formation, VA has no effect on ROS levels, and EGC increases ROS levels. EPR results with CuO nanoparticles washed to remove dissolved copper in solution (wCuO) in the presence of H2O2/ascorbate suggest that MEPCA prevents ROS formation on the nanoparticle surface in addition to preventing ROS formation from dissolved copper. In mouse fibroblast (L929) cells, combining (CuO)-Cu-NP with H2O2 results in significantly greater cytotoxicity than observed for either component alone. After 3 h incubation with MEPCA or MEGA, the viability loss in L929 cells induced by (CuO)-Cu-NP/H2O2 challenge was significantly rescued at physiologically relevant polyphenol levels (1 mu M). These studies show that polyphenols can protect DNA and inhibit cytotoxicity generated by (CuO)-Cu-NP under oxidative stress conditions.

The optical and chemical properties of gold and silver nanoparticles make them useful for many applications, including surface enhanced spectroscopy-based biosensors, photostable colorants, enhanced photovoltaics, and nanoscale optical elements. We report a simple technique to generate patterns of gold and silver nanoparticles with controlled shape and shape-dependent optical properties using metal stamps to impress them onto a glass substrate or flexible polymers. The pressure flattens the nanoparticles, converting initially spherical nanoparticles into discs with reduced height and increased diameter. This deformation causes their localized surface plasmon resonance wavelength to red-shift. Nanoparticles were characterized by electron microscopy, atomic force microscopy, and dark field optical scattering spectroscopy. The deformed nanoparticle patterns had a lateral resolution limited by the nanoparticle diameter (single particles are partly flattened only where they contact the stamp). The method also (i) transfers the stamp's topography, with smooth stamps generating flattened nanoparticles with uniform height, and small changes in stamp height are evident in the nanoparticle height and scattering wavelength, and (ii) allows facile removal of undeformed nanoparticles using scotch tape, and patterns of deformed nanoparticles can be transferred to a thin polymer-film. The patterning process is simple and inexpensive. It can be performed by hand for demonstrations or artistic applications, with controlled force for plasmonics research, and potentially automated on reel-to-reel presses for large scale production.

Copper(II) oxide nanoparticles (NPCuO) have many industrial applications, but are highly cytotoxic because they generate reactive oxygen species (ROS). It is unknown whether the damaging ROS are generated primarily from copper leached from the nanoparticles, or whether the nanoparticle surface plays a significant role. To address this question, we separated nanoparticles from the supernatant containing dissolved copper, and measured their ability to damage plasmid DNA with addition of hydrogen peroxide, ascorbate, or both. While DNA damage from the supernatant (measured using an electrophoresis assay) can be explained solely by dissolved copper ions, damage by the nanoparticles in the presence of ascorbate is an order of magnitude higher than can be explained by dissolved copper and must, therefore, depend primarily upon the nanoparticle surface. DNA damage is time-dependent, with shorter incubation times resulting in higher EC50 values. Hydroxyl radical (•OH) is the main ROS generated by NPCuO/hydrogen peroxide as determined by EPR measurements; NPCuO/hydrogen peroxide/ascorbate conditions generate ascorbyl, hydroxyl, and superoxide radicals. Thus, NPCuO generate ROS through several mechanisms, likely including Fenton-like and Haber-Weiss reactions from the surface or dissolved copper ions. The same radical species were observed when NPCuO suspensions were replaced with the supernatant containing leached copper, washed NPCuO, or dissolved copper solutions. Overall, NPCuO generate significantly more ROS and DNA damage in the presence of ascorbate than can be explained simply from dissolved copper, and the NPCuO surface must play a large role.

We describe a simple technique to alter the shape of silver nanoparticles (AgNPs) by rolling a glass tube over them to mechanically compress them. The resulting shape change in turn induces a red-shift in the localized surface plasmon resonance scattering spectrum and exposes new surface area. The flattened particles were characterized by optical and electron microscopy, single-nanoparticle scattering spectroscopy, and surface-enhanced Raman spectroscopy (SERS). Atomic force microscopy and scanning electron microscopy images show that the AgNPs deform into discs; increasing the applied load from 0 to 100 N increases the AgNP diameter and decreases the height. This deformation caused a dramatic red shift in the nanoparticle scattering spectrum and also generated new surface area to which thiolated molecules could attach, as evident from SERS measurements. The simple technique employed here requires no lithographic templates and has potential for rapid, reproducible, inexpensive, and scalable tuning of nanoparticle shape, surface area, and resonance while preserving particle volume.

Three gold-nanoparticle (AuNP) undergraduate experiment modules that are focused on nanoparticles interfacial phenomena have been developed. Modules 1 and 2 explore the synthesis and characterization of AuNPs of different sizes but with the same total gold mass. These experiments enable students to determine how particle size affects the AuNP optical properties and ligand binding capacities. Module 3 investigates the fundamental mechanism governing organothiol self-assembly onto AuNPs and explores the fate of the sulfur-bounded hydrogen (RS–H) for organothiols on the AuNP surface. A benchtop centrifuge, a UV–vis spectrophotometer, and pH strips are needed. The depth of required chemistry knowledge is appropriate for upper-level chemistry students.

The wavelength-dependent correlations between UV-vis intensities and surface enhanced Raman spectroscopic (SERS) enhancement factors (EFs) of aggregated gold and silver nanoparticles (AgNPs and AuNPs) were investigated using two experimental approaches. The first is to study the time-resolved SERS EFs under three fixed excitation wavelengths (532, 632, and 785 am), each as a function of nanoparticle (NP) aggregation states. The second is to compare SERS EFs at these three excitation wavelengths for a series of protein-stabilized AuNP or AgNP aggregates. The SERS EFs were determined using a solvent internal reference method. The NP UV-vis intensity is an excellent indicator for identifying the optimal aggregation state for the AgNP-based SERS acquisitions under each of the three excitation wavelengths and for the AuNP-based SERS under 632 nm excitation. However, the NP UV-vis intensity is an unreliable predictor of the optimal excitation wavelength for either AuNPs or AgNPs. Computational simulations reveal that the NP SERS enhancement is much more sensitive than NP UV-vis intensity to small changes in the NP aggregation states. In addition to enhancing the understanding of the correlation among NP aggregation, UV-vis intensity, and SERS activity, the techniques and insights derived from this work should be important for developing sensitive and reproducible colloidal-NP-based SERS applications.

Recent research has demonstrated that the nanoparticle (NP) surface enhanced Raman spectroscopy (SERS) substrate modifies an analyte's Raman signal through two competitive mechanisms, SERS enhancement and NP inner filter effect, instead of SERS enhancement alone as commonly believed. Using a combination of time-resolved Raman spectroscopy and a solvent internal reference method, reported herein is a quantitative determination of the SERS enhancement factors (EFs) of mercaptobenzimidazole (MBI), a model organothiol, adsorbed onto gold and silver nanoparticles (AuNPs and AgNPs). The peak MBI SERS EF depends only on the type and size of NPs, but not analyte and NP concentrations, or the type (KF, KCl, KBr, and K2SO4) and concentrations of the electrolytic aggregation agents. The experimental SERS EFs of MBI on both AuNPs and AgNPs can be fully explained by the electromagnetic mechanism alone. This result, combined with our recent findings that a series of structurally diverse organothiols have similar SERS EFs, argues quite strongly against the possibility of large chemical enhancement (e.g., >10 times) for organothiols adsorbed onto colloidal AuNPs and AgNPs.

Organosulfur compounds are known to poison metallic nanoparticle catalysts. Herein NaBH4 is shown to desorb and desulfurize 2-mercaptobenzimidazole (2-MBI) and 6-thioguanine (6-TG) adsorbed on 10, 15, and 50 nm diameter gold nanoparticles (AuNPs). The desulfurization rates decrease significantly with increasing AuNP sizes. Isotope labeling experiments, conducted with NaBD4 in H2O, indicate that this desulfurization reaction proceeds through a pathway requiring hydrogen uptake onto AuNP surfaces prior to the 2-MBI or 6-TG desulfurization reaction, rather than direct hydride attack from BH4– on the sulfur-bearing carbon in 2-MBI or 6-TG, or H2 reaction with 2-MBI or 6-TG . In addition to serving as the hub for electron charge transfer between hydride and proton, AuNPs capture the cleaved sulfide, facilitating sulfur separation from the desulfurized products.

The resonance Raman (RR) enhancement factors of Rhodamine 6G (R6G) in water and on gold and silver nanoparticles (AuNPs and AgNPs) were determined using a double ratiometric method where adenine is used as the internal reference. The RR enhancement factor for R6G on AgNPs upon laser excitation at 532 nm is 537.6 +/- 214.8. This is similar to 5 times lower than the experimental (2.7 +/- 0.3) x 10(3) RR enhancement factor for R6G in water. These experimental RR enhancement factors for R6G in water and on AgNPs are 10(4) smaller than the 10(7) RR enhancement proposed in literature for R6G in water and on SERS substrates. In addition, a simple back-of-the-envelope calculation showed that even with this damped RR for R6G on AgNPs in comparison to R6G in water, a SERS enhancement factor of 10(6) is sufficient to explain the single-molecule resonance SERS activities reported for R6G located in nanoparticle junctions. This conclusion is deduced from fact that normal Raman spectrum could be readily obtained with 24 fmol of adenine at laser focal volume of similar to 150 fL at 532 nm excitation. This work provides the first direct experimental evidence for the recent theoretical predication that plasmonic nanoparticles quench the resonance Raman signal. In addition, the double ratiometric method reported in this work represents a significant technique development in Raman and SERS, which should pave the way for quantitative investigations of the RR for dye molecules dissolved in solution or adsorbed on plasmonic nanoparticles.

Presented herein is a combined experimental and computational study of the gold nanopartide (AuNP) inner filter effect on surface enhanced Raman spectroscopic (SERS) measurements. Using a bianalyte strategy in which dithiopurine (DTP) and ethanol were employed as the model analytes, we demonstrated that AuNPs enhance DTP's Raman signal but attenuate ethanol's Raman intensity. Combined time-resolved UV-vis and Raman measurements showed that AuNP aggregation has significant and an exactly opposite impact on the AuNP inner filter effect and SERS enhancement. This research provides critical new insights regarding SEAS signal variation and offers a simple methodology for reliable determination of the SERS enhancement factors.

The protein and gold nanoparticle (AuNP) interfacial interaction has broad implications for biological and biomedical applications of AuNPs. In situ characterization of the morphology and structural evolution of protein on AuNPs is difficult. We have found that the protein coating layer formed by bovine serum albumin (BSA) on AuNP is highly permeable to further organothiol adsorption. Using mercaptobenzimidazole (MBI) as a molecular probe, it is found that BSA interaction with AuNP is an exceedingly lengthy process. Structural modification of BSA coating layer on AuNP continues even after 2 days' aging of the (AuNP/BSA) mixture. While BSA is in a near full monolayer packing on the AuNPs, it passivates only up to 30% of the AuNP surfaces against MBI adsorption. Aging reduces the kinetics of the MBI adsorption. However, even in the most aged BSA-coated AuNP (3 days), 80% of the MBI adsorption occurs within the first 5 min of the MBI addition to the (AuNP/BSA) mixture. The possibility of MBI displacing the adsorbed BSA was excluded with quantitative BSA adsorption studies. Besides MET, other organothiols including endogenous amino acid thiols (cysteine, homocysteine, and glutathione) were also shown to penetrate through the protein coating layer and be adsorbed onto AuNPs. In addition to providing critical new understanding of the morphology and structural evolution of protein on AuNPs, this work also provides a new venue for preparation of multicomponent composite nanoparticle with applications in drug delivery, cancer imaging and therapy, and material sciences.