Weinan Leng

Nanoclustered Gold Honeycombs for Surface-Enhanced Raman Scattering

A honeycomb-shaped gold substrate was developed for surface-enhanced Raman imaging (SERI). The honeycombs are composed of clusters of 50-70 nm gold nanoparticles and exhibit high Raman enhancement efficiency. An average surface enhancement factor (ASEF) of 1.7 × 10(6) was estimated for a monolayer of L-cysteine molecules adsorbed to gold via a thiol linkage. The presence of a linear relationship in the low concentration region was observed in SERI detection of malachite green isothiocyanate (MGITC). These results together with the high reproducibility and simple and cost-effective fabrication of this substrate suggest that it has utility for applications of surface-enhanced Raman scattering (SERS) in quantitative diagnoses and analyte detection.

Room temperature seed mediated growth of gold nanoparticles: mechanistic investigations and life cycle assesment

In this study, we report the first room temperature seed-mediated synthesis of gold nanoparticles (AuNPs) in the presence of citrate and a gold salt. In contrast to citrate-reduction in boiling water, these mild reaction conditions provide expanded capacity to probe the mechanism of seed-mediated growth following gold salt addition. Moreover, comparative life cycle assessment indicates significant reductions in the environmental impacts for the room temperature synthesis. For this study, highly uniform gold seeds with Z-average diameter of 17.7 ± 0.8 nm and a polydispersity index of 0.03 ± 0.01 were prepared by a pH controlled protocol. We investigated the AuNP growth mechanism via time resolved UV-vis spectroscopy, dynamic light scattering, and transmission electron microscopy. This study indicates that citrate and its oxidation byproduct acetone dicarboxylate serve to bridge and gather Au(III) ions around gold nanoparticle seeds in the initial growth step.

Differentiation of Microcystin, Nodularin, and Their Component Amino Acids by Drop-Coating Deposition Raman Spectroscopy

Raman spectra of microcystin-LR (MC-LR), MC-RR, MC-LA, MC-LF, MC-LY, MC-LW, MC-YR, and nodularin collected by drop-coating deposition Raman (DCDR) spectroscopy are sufficiently unique for variant identification. Amino acid spectra of L-phenylalanine, L-leucine, L-alanine, D-alanine, L-glutamic acid, L-arginine, L-tryptophan, L-tyrosine, and N-methyl-D-aspartic acid were collected in crystalline, DCDR, and aqueous forms to aid in cyanotoxin Raman peak assignments. Both peak ratio analysis and principal component analysis (PCA) properly classified 72 DCDR spectra belonging to the eight toxins. Loading plots for the first three principal components (PCs) most heavily weighted the peaks highlighted in the peak ratio analysis, specifically the 760 cm(-1) tryptophan peak, 853 cm(-1) tyrosine peak, and 1006 cm(-1) phenylalanine peak. Peak ratio analyses may be preferred under some circumstances because of the ease and speed with which the ratios can be computed, even by untrained lab technicians. A set of rules was created to mathematically classify toxins using the peak ratios. DCDR methods hold great potential for future application in routine monitoring because portable and hand-held Raman spectrometers are commercially available, DCDR spectra can be collected in seconds for biomolecule mixtures as well as samples containing impurities, and the method requires far fewer consumables than conventional cyanotoxin detection methods.

Protein-aided formation of triangular silver nanoprisms with enhanced SERS performance

In this work, we present a modified seed-mediated synthetic strategy for the growth of silver nanoprisms with low shape polydispersity, narrow size distribution and tailored plasmonic absorbance. During the seed nucleation step, consensus sequence tetratricopeptide repeat (CTPR) proteins are utilized as potent stabilizers to facilitate the formation of planar-twinned Ag seeds. Ag nanoprisms were produced in high yield in a growth solution containing ascorbic acid and CTPR-stabilized Ag seeds. From the time-course UV-Vis and transmission electron microscopy (TEM) studies, we postulate that the growth mechanism is the combination of facet selective lateral growth and thermodynamically driven Ostwald ripening. The resultant Ag nanotriangles (NTs) exhibit excellent surface enhanced Raman spectroscopy (SERS) performance. The enhancement factor (EF) measured for the 4-mercapto benzoic acid (4-MBA) reporter is estimated to be 3.37 × 105 in solution and 2.8 × 106 for the SERS substrate.

Facile, tunable, and SERS-enhanced HEPES gold nanostars

Gold nanoparticles have shown promise as effective tools in biomedicine for drug delivery, imaging, and photo thermal therapy. We present the preparation of gold nanostars (AuNSs) through a two-step approach utilizing a common Goods buffer, HEPES, as a weak reducing agent. AuNSs with tunable branch-lengths up to 30 nm in length were produced in a two-step synthesis. We have investigated the effect of the ionic strength on the AuNS growth and branch length. AuNSs were found to be near-infrared responsive and provide an augmented SERS signal, with an enhancement factor, defined as the magnitude of SERS signal amplification, of approximately 107. The unique branched morphology of the AuNSs confers optical properties advantageous for in vivo biomedical applications.

Controlled Evaluation of the Impacts of Surface Coatings on Silver Nanoparticle Dissolution Rates

Silver nanoparticles (AgNPs) are increasingly being incorporated into a range of consumer products and as such there is significant potential for the environmental release of either the AgNPs themselves or Ag+ ions. When AgNPs are exposed to environmental systems, the engineered surface coating can potentially be displaced or covered by naturally abundant macromolecules. These capping agents, either engineered or incidental, potentially block reactants from surface sites and can alter nanoparticle transformation rates. We studied how surface functionalization affects the dissolution of uniform arrays of AgNPs fabricated by nanosphere lithography (NSL). Bovine serum albumin (BSA) and two molecular weights of thiolated polyethylene glycol (PEG; 1000 and 5000 Da) were tested as model capping agents. Dissolution experiments were conducted in air-saturated phosphate buffer containing 550 mM NaCl. Tapping-mode atomic force microscopy (AFM) was used to measure changes in AgNP height over time. The measured dissolution rate for unfunctionalized AgNPs was 1.69 ± 0.23 nm/d, while the dissolution rates for BSA, PEG1000, and PEG5000 functionalized samples were 0.39 ± 0.05, 0.20 ± 0.10, and 0.14 ± 0.07 nm/d, respectively. PEG provides a steric barrier restricting mass transfer of reactants to sites on the AgNP surface and thus diminishes the dissolution rate. The effects of BSA, however, are more complicated with BSA initially enhancing dissolution, but providing protection against dissolution over extended time.

Aerosol Emissions from Fuse-Deposition Modeling 3D Printers in a Chamber and in Real Indoor Environments

Three-dimensional (3D) printers are known to emit aerosols, but questions remain about their composition and the fundamental processes driving emissions. The objective of this work was to characterize the aerosol emissions from the operation of a fuse-deposition modeling 3D printer. We modeled the time- and size-resolved emissions of submicrometer aerosols from the printer in a chamber study, gained insight into the chemical composition of emitted aerosols using Raman spectroscopy, and measured the potential for exposure to the aerosols generated by 3D printers under real-use conditions in a variety of indoor environments. The average aerosol emission rates ranged from ∼108 to ∼1011 particles min-1, and the rates varied over the course of a print job. Acrylonitrile butadiene styrene (ABS) filaments generated the largest number of aerosols, and wood-infused polylactic acid (PLA) filaments generated the smallest amount. The emission factors ranged from 6 × 108 to 6 × 1011 per gram of printed part, depending on the type of filament used. For ABS, the Raman spectra of the filament and the printed part were indistinguishable, while the aerosol spectra lacked important peaks corresponding to styrene and acrylonitrile, which are both present in ABS. This observation suggests that aerosols are not a result of volatilization and subsequent nucleation of ABS or direct release of ABS aerosols.

Aerosol microdroplets exhibit a stable pH gradient

Significance Aerosols with high water content (aerosol droplets) are ubiquitous and play a significant role in atmospheric chemistry and meteorology. However, directly measuring the pH of an individual aerosol droplet remains challenging due to its inaccessibility to pH electrodes. In this study, nanometer-sized pH probes were dispersed in droplets to report pH via surface-enhanced Raman spectroscopy. The droplet core exhibits higher pH than the bulk solution, suggesting the presence of a stable pH gradient. This in situ technique extends pH characterization to confined water environments and deepens our understanding of aerosol chemistry and the air/water interface. Suspended aqueous aerosol droplets (<50 µm) are microreactors for many important atmospheric reactions. In droplets and other aquatic environments, pH is arguably the key parameter dictating chemical and biological processes. The nature of the droplet air/water interface has the potential to significantly alter droplet pH relative to bulk water. Historically, it has been challenging to measure the pH of individual droplets because of their inaccessibility to conventional pH probes. In this study, we scanned droplets containing 4-mercaptobenzoic acid–functionalized gold nanoparticle pH nanoprobes by 2D and 3D laser confocal Raman microscopy. Using surface-enhanced Raman scattering, we acquired the pH distribution inside approximately 20-µm-diameter phosphate-buffered aerosol droplets and found that the pH in the core of a droplet is higher than that of bulk solution by up to 3.6 pH units. This finding suggests the accumulation of protons at the air/water interface and is consistent with recent thermodynamic model results. The existence of this pH shift was corroborated by the observation that a catalytic reaction that occurs only under basic conditions (i.e., dimerization of 4-aminothiophenol to produce dimercaptoazobenzene) occurs within the high pH core of a droplet, but not in bulk solution. Our nanoparticle probe enables pH quantification through the cross-section of an aerosol droplet, revealing a spatial gradient that has implications for acid-base–catalyzed atmospheric chemistry.

Gold nanospheres and gold nanostars immobilized onto thiolated eggshell membranes as highly robust and recyclable catalysts

This study describes a facile method for immobilizing nanoparticles with different morphologies onto a biopolymeric fibrous network – eggshell membranes (ESM). Solution processing of the ESM to liberate inherent thiols enabled efficient immobilization of gold nanoparticles without the use of additional, external crosslinkers. The catalytic activity of such prepared membranes was evaluated through the reduction of p-nitrophenol (PNP) to p-aminophenol (PAP). The resulting biohybrid materials exhibited enhanced stability and reusability over colloidal nanoparticle suspensions and retained their desirable catalytic activity even after ten reaction cycles and a period of one hundred days.

Stable oligonucleotide-functionalized gold nanosensors for environmental biocontaminant monitoring

The global propagation of environmental biocontaminants such as antibiotic resistant pathogens and their antibiotic resistance genes (ARGs) is a public health concern that highlights the need for improved monitoring strategies. Here, we demonstrate the environmental stability and applicability of an oligonucleotide-functionalized gold nanosensor. The mecA ARG was targeted as model biocontaminant due to its presence in clinically-relevant pathogens and to its emergence as an environmental contaminant. mecA-specific nanosensors were tested for antibiotic resistance gene (ARG) detection in ARG-spiked effluent from four wastewater treatment plants (WWTPs). The mecA-specific nanosensors showed stability in environmental conditions and in high ionic strength ([MgCl2]<50mM), and high selectivity against mismatched targets. Spectrophotometric detection was reproducible with an LOD of 70pM (≈4×107genes/μL), even in the presence of interferences associated with non-target genomic DNA and complex WWTP effluent. This contribution supports the environmental applicability of a new line of cost-effective, field-deployable tools needed for wide-scale biocontaminant monitoring.