EBL-Based Fabrication and Different Modeling Approaches for Nanoporous Gold Nanodisks

We report electron beam lithography (EBL) based fabrication and different modeling techniques for disk-shaped nanoporous gold nanoparticles (NPG disk). The EBL technique can provide large area 2D patterns of regularly or randomly distributed nanodisks with narrow size distribution and flexible interdisk (center to center) distance. Such flexibility is essential to obtain quasi-single NPG disk response, which typically peaks in the near-infrared (NIR) spectrum beyond 1 μm, from ensemble measurements by common UV/vis/NIR spectrometers instead of a specialized NIR spectroscopic microscope. NPG disks of 200 to 500 nm diameter and 50 nm thickness have been fabricated and characterized. To model the NPG disk and calculate its plasmonic properties, two different modeling approaches have been developed. A model based on the Bruggeman effective medium theory (B-EMT model) requires little information about the nanoporous structure. In contrast, the nanoporous model (NP model) retains the essential nanoporous structural features of NPG disk. To evaluate the performance of these models, simulated extinction spectra have been compared to the experimental data. Both the B-EMT and NP models perform well to estimate the far-field plasmon resonance peak position. However, to obtain the accurate information about the plasmon peak width/plasmon lifetime and near-field plasmonic hot-spots formation within the nanopores, the NP model is essential since the B-EMT model lacks the nanoporous network

Nanoporous Gold Disks Functionalized with Stabilized G‑Quadruplex Moieties for Sensing Small Molecules

We report label-free small molecule sensing on nanoporous gold disks functionalized with stabilized Guanine-quadruplex (G4) moieties using surface-enhanced Raman spectroscopy (SERS). By utilizing the unique G4 topological structure, target molecules can be selectively captured onto nanoporous gold (NPG) disk surfaces via π–π stacking and electrostatic attractions. Together with high-density plasmonic “hot spots” of NPG disks, the captured molecules produce a remarkable SERS signal. Our strategy represents the first example of the detection of foreign molecules conjugated to nondouble helical DNA nanostructures using SERS while providing a new technique for studying the formation and evolution of G4 moieties. The molecular specificity of G4 is known to be controlled by its unit sequence. Without losing generality, we have selected d­(GGT)₇GG sequence for the sensing of malachite green (MG), a known carcinogen frequently abused illegally in aquaculture. The newly developed technique achieved a lowest detectable concentration at an impressive 50 pM, two orders of magnitude lower than the European Union (EU) regulatory requirement, with high specificity against potential interferents. To demonstrate the translational potential of this technology, we achieved a lowest detectable concentration of 5.0 nM, meeting the EU regulatory requirement, using a portable probe based detection system

Recordings of hypoglossal rootlets discharge in medullary slices.

<p>Typical recording of the discharge from the control group (A) and the CSE group (B), respectively. In each panel, the upper line indicates the compression format of activities of the hypoglossal rootlets throughout the experiment, and the middle and lower lines indicate the raw and integrated activities of the hypoglossal rootlets before, during and after acidification, respectively.</p

Changes in hypoglossal rootlets discharge in medullary slices induced by acidification.

<p>(A) and (B): Changes of burst frequency (BF) in the control (n = 13) and CSE groups (n = 15), respectively; (C) and (D): Changes of integrated amplitude (IA) in the control (n = 13) and CSE groups (n = 15), respectively. All data were normalized to the baseline value which was defined as the average BF and IA for 5min prior to acidic stimulation. *<i>P</i>< 0.05, **<i>P</i>< 0.01 vs. baseline.</p

Statistical comparison of basal discharge of hypoglossal rootlets in medullary slices.

<p>Comparison of the basal burst frequency (A) and integrated amplitude (B) of the hypoglossal rootlets activities of the medullary slices in neonatal rats between the control group (n = 13) and the CSE group (n = 15).</p

Comparison of changes in hypoglossal rootlets discharge in medullary slices induced by acidification.

<p>(A) Comparison of burst frequency (BF) of hypoglossal rootlets between the control (n = 13) and CSE (n = 15) groups; (B) Comparison of integrated amplitude (IA) of hypoglossal rootlets between the control (n = 13) and CSE (n = 15) groups. *<i>P</i>< 0.05, **<i>P</i>< 0.01 vs. CSE.</p