Xin's Paper On Utilizing Light-Triggered Plasmon-Driven Catalysis Reactions as a Template for Molecular Delivery and Release Has Been Published In Chemical Science!


Due to the facile manipulation and non-invasive nature of light-triggered release, it is one of the most potent ways to selectively and remotely deliver a molecular target. Among the various carrier platforms, plasmonic nanoparticles possess advantages such as enhanced cellular uptake and easy loading of “cargo” molecules. Two general strategies are currently utilized to achieve light-induced molecule release from plasmonic nanoparticles. The first uses femtosecond laser pulses to directly break the bond between the nanoparticle and the loaded target. The other requires significant photo-thermal effects to weaken the interaction between the cargo molecules and nanoparticle-attached host molecules. Different from above mechanisms, herein, we introduce a new light-controlled molecular-release method by taking advantage of a plasmon-driven catalytic reaction at the particle surface. In this strategy, we link the target to a plasmon responsive molecule, 4-aminobenzenethiol (4-ABT), through the robust and simple EDC coupling reaction and subsequently load the complex onto the particles via the strong Au–thiol interaction. Upon continuous-wave (CW) laser illumination, the excited surface plasmon catalyzes the formation of 4,4′-dimercaptoazobenzenethiol (DMAB) and simultaneously releases the loaded molecules with high efficiency. This method does not require the use of high-power pulsed lasers, nor does it rely on photo-thermal effects. We believe that plasmon-driven release strategies open a new direction for the designing of next-generation light-triggered release processes.

DOI: 10.1039/C7SC02089A

Hobbie's paper on probing molecular orientation with surface-enhanced hyper-Raman scattering has been published in The Journal of Physical Chemistry Letters!


Herein, we utilize surface-enhanced hyper-Raman scattering (SEHRS) under resonance conditions to probe the adsorbate geometry of rhodamine 6G (R6G) on silver colloids. Our results show resonance SEHRS is highly sensitive to molecular orientation due to non-Condon effects, which do not appear in its linear counterpart surface-enhanced Raman scattering. Comparisons between simulated and measured SEHRS spectra reveal R6G adsorbs mostly perpendicular to the nanoparticle surface along the ethylamine groups with the xanthene ring oriented edgewise. Our results expand upon previous studies that rely on indirect, qualitative probes of R6G’s orientation on plasmonic substrates. More importantly, this work represents the first determination of adsorbate geometry by SEHRS and opens up the possibility to study the orientation of single molecules in complex, plasmonic environments.

DOI: 10.1021/acs.jpclett.7b00498

Mike's paper on uranium detection is published and will be featured on the cover of Analytical Methods!


A surface-enhanced Raman scattering (SERS) method, based on functionalized silver colloids, is developed for the detection of uranyl ions that yields a limit of detection of 24 ppb. The signal is obtained from functionalized colloids three months after preparation and in the presence of interferents likely to be present in groundwater. Additionally, our method is transferrable to a hand-held Raman spectrometer with comparable sensitivity, exhibiting potential for field analysis of uranium.


DOI: 10.1039/C7AY00183E

Sarah's paper on imaging energy transfer in decorated nanoparticles is published in The Journal of Physical Chemistry Letters!


Driven by the desire to understand energy transfer between plasmonic and catalytic metals for applications such as plasmon-mediated catalysis, we examine the spatially resolved electron energy-loss spectra (EELS) of both pure Au nanoprisms and Pt-decorated Au nanoprisms. The EEL spectra and the resulting surface-plasmon mode maps reveal detailed near-field information on the coupling and energy transfer in these systems, thereby elucidating the underlying mechanism of plasmon-driven chemical catalysis in mixed-metal nanostructures. Through a combination of experiment and theory we demonstrate that although the location of the Pt decoration greatly influences the plasmons of the nanoprism, simple spatial proximity is not enough to induce significant energy transfer from the Au to the Pt. What matters more is the spectral overlap between the intrinsic plasmon resonances of the Au nanoprism and Pt decoration, which can be tuned by changing the composition or morphology of either component.

Chaoxiong's paper on fabrication of nanoporous silver films is published in ACS Applied Materials and Interfaces!


Nanoporous metal films are promising substrates for surfaced-enhanced Raman scattering (SERS) measurement, owing to their homogeneity, large surface area, and abundant hot-spots. Herein, a facile procedure was developed to fabricate nanoporous Ag film on various substrate surfaces. Thermally deposited Ag film was first treated with O2 plasma, resulting in porous Ag/AgxO film (AgxO-NF) with nanoscale feature. Sodium citrate was then used to reduce AgxO to Ag, forming nanoporous Ag film (AgNF) with similar morphology. The AgNF substrate demonstrates 30-fold higher Raman intensity than Ag film over polystyrene nanospheres (d = 600 nm) using 4- mercaptobenzoic acid (4-MBA) as the sensing molecule. Comparing with ordinary Raman measurement on 4-MBA solution, an enhancement factor of ∼6 × 106 was determined for AgNF. The AgNF substrate was evaluated for benzoic acid, 4- nitrophenol, and 2-mercaptoethanesulfonate, showing high SERS sensitivity for chemicals that bind weakly to Ag surface and molecules with relatively small Raman cross section at micromolar concentration. In addition to its simplicity, the procedure can be applied to various materials such as transparency film, filter paper, hard polystyrene film, and aluminum foil, revealing similar Raman sensitivity. By testing the durability of the substrate, we found that the AgxO films can be stored in ambient conditions for more than 90 days and still deliver the same SERS intensity if the films are treated with sodium citrate before use. These results demonstrate the advantage of the proposed approach for mass production of low-cost, sensitive, and durable SERS substrates. The transferable nature of these AgNF to different flexible surfaces also allows their easy integration with other sensing schemes.

Xin's paper on sensing glucose and hydrogen peroxide in urine and serum is published in Analytical Chemistry!


Hydrogen peroxide (H2O2) is known as a key molecule in a variety of biological processes, as well as a crucial byproduct in many enzymatic reactions. Therefore, being able to selectively and sensitively detect H2O2 is not only important in monitoring, estimating, and decoding H2O2 relevant physiological pathways but also very helpful in developing enzymatic-based biosensors for other analytes of interest. Herein, we report a plasmonic probe for H2O2 based on 3- mercaptophenylboronic acid (3-MPBA) modified gold nanoparticles (AuNPs) which is coupled with surface-enhanced Raman scattering (SERS) to yield a limit of detection (LOD) of 70 nM. Our probe quantifies both exogenous and endogenous H2O2 levels in living cells and can further be coupled with glucose oxidase (GOx) to achieve quantitative and selective detection of glucose in artificial urine and human serum.

Hobbie's paper on probing two-photon molecular properties of crystal violet using surface-enhanced hyper-Raman scattering is published in The Journal of Physical Chemistry C!


The surface-enhanced hyper-Raman scattering spectra of crystal violet are experimentally measured and theoretically calculated for excitation energies spanning the two lowest-lying electronic states (12,700− 27,400 cm−1 ). The theory and experiment are in qualitative agreement over the measured energy range, indicating that first-principles calculations capture many of the complex resonance contributions in this prototypical octupolar system. The discrepancies between theory and experiment are investigated by comparing spectra obtained in different local environments as well as from higher-order surface-enhanced spectroscopies. A comparison between relative surface-enhanced hyper-Raman scattering band ratios plotted as a function of excitation wavelength and crystal violet’s absorption spectra elucidates correlations between groups of vibrations and the excitedelectronic states. Our results suggest that the spectral features across the range of resonance excitation energies (∼15,500−27,400 cm−1 ) are dominated by strong A-term scattering.

Yueying and Guoliang's paper on the study of the full plasmonic spectrum of self-assembled Au-Ag alloy nanoparticles is published in ACS Photonics!


We report the self-assembly of ultrasmooth AuxAg1−x nanoparticles with homogeneous composition via pulsed laser-induced dewetting (PLiD). The nanoparticles are truncated nanospheres that sustain unique plasmonic features. For the first time an electron energy loss spectroscopy (EELS) study elucidating the size and composition effects on the plasmonic modes of truncated AuxAg1−x nanospheres is carried out. EELS characterization captures a linear red-shift in both bright and dark modes as a function of the atomic fraction of Au and a progressive red-shift of all modes as the size increases. The results are interpreted in the context of Mie theory and electron beam simulations. Armed with the full plasmonic spectrum of the AuxAg1−x system, the truncated spheres and their ordered arrays synthesized via PLiD have promise as elements in advanced photonic devices.