In Situ Probing of Laser Annealing of Plasmonic Substrates with Surface-Enhanced Raman Spectroscopy.

In this work, we in situ monitor the laser annealing of template-fabricated silver substrates using surface-enhanced Raman scattering (SERS) and 4-mercaptobenzoic acid (4-MBA) as a molecular probe. The annealing process, which exhibits a strong dependence on the laser power, yields a large (>50×) increase in the SERS of the immobilized 4-MBA. This increased SERS response is correlated with the changing substrate morphology using optical and scanning electron microscope images.

A polysaccharide from Dictyophora indusiata inhibits the immunosuppressive function of cancer-associated fibroblasts.

Reversing the function of cancer-associated fibroblasts (CAFs) may improve the efficacy of cancer therapy. Here, we isolated a novel polysaccharide from Dictyophora indusiata (ZSP4) and examined its effects on the function of prostate CAFs. The supernatant of prostate CAFs can stimulate the proliferation of immune cells and inhibit the growth of CD4+/CD8+ T cells.

Ion selective redox cycling in zero-dimensional nanopore electrode arrays at low ionic strength.

Surface charge characteristics and the electrical double layer (EDL) effect govern the transport of ions into and out of nanopores, producing a permselective concentration polarization, which dominates the electrochemical response of nanoelectrodes in solutions of low ionic strength. In this study, highly ordered, zero-dimensional nanopore electrode arrays (NEAs), with each nanopore presenting a pair of recessed electrodes, were fabricated to couple EDL effects with redox cycling, thereby achieving electrochemical detection with improved sensitivity and selectivity. These NEAs exhibit current amplification as high as 55-fold due to the redox cycling effect, which can be further increased by ∼500-fold upon the removal of the supporting electrolyte.

Electrochemistry at single molecule occupancy in nanopore-confined recessed ring-disk electrode arrays.

Electrochemical reactions at nanoscale structures possess unique characteristics, e.g. fast mass transport, high signal-to-noise ratio at low concentration, and insignificant ohmic losses even at low electrolyte concentrations.

Closed bipolar electrode-enabled dual-cell electrochromic detectors for chemical sensing.

Bipolar electrodes (BPE) are electrically floating metallic elements placed in electrified fluids that enable the coupling of anodic and cathodic redox reactions at the opposite ends by electron transfer through the electrode. One particularly compelling application allows electron transfer reactions at one end of a closed BPE to be read out optically by inducing a redox-initiated change in the optical response function of a reporter system at the other end. Here, a BPE-enabled method for electrochemical sensing based on the electrochromic response of a methyl viologen (MV) reporter is developed, characterized, and rendered in a field-deployable format.

Polysaccharides from Polygonatum Inhibit the Proliferation of Prostate Cancer-Associated Fibroblasts.

Inhibition of cancer-associated broblasts (CAFs) may improve the efficacy of cancer therapy. Polysaccharide extracted from polygonatum can selectively inhibit the growth of prostate-CAFs (<.001) without inhibiting the growth of normal broblasts (NAFs).

Nanoporous Silver Film Fabricated by Oxygen Plasma: A Facile Approach for SERS Substrates.

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.

Ion Accumulation and Migration Effects on Redox Cycling in Nanopore Electrode Arrays at Low Ionic Strength.

Ion permselectivity can lead to accumulation in zero-dimensional nanopores, producing a significant increase in ion concentration, an effect which may be combined with unscreened ion migration to improve sensitivity in electrochemical measurements, as demonstrated by the enormous current amplification (∼2000-fold) previously observed in nanopore electrode arrays (NEA) in the absence of supporting electrolyte. Ionic strength is a key experimental factor that governs the magnitude of the additional current amplification (AFad) beyond simple redox cycling through both ion accumulation and ion migration effects. Separate contributions from ion accumulation and ion migration to the overall AFad were identified by studying NEAs with varying geometries, with larger AFad values being achieved in NEAs with smaller pores.

On-demand in situ generation of oxygen in a nanofluidic embedded planar microband electrochemical reactor.

In situ generation of reagents and their subsequent use downstream presents new opportunities to amplify the utility of nanofluidic devices by exploiting the confined geometry to address mass transport limitations on reaction kinetics and efficiency. Oxygen, an inherently valuable reactant, can be produced from electrolysis of water, a process that can be conveniently integrated within a nanofluidic system. Here, we construct and characterize a nanofluidic device consisting of a planar microband electrode embedded within a nanochannel for in situ electrochemical generation and optical monitoring of O.

Self-induced redox cycling coupled luminescence on nanopore recessed disk-multiscale bipolar electrodes.

We present a new configuration for coupling fluorescence microscopy and voltammetry using self-induced redox cycling for ultrasensitive electrochemical measurements. An array of nanopores, each supporting a recessed disk electrode separated by 100 nm in depth from a planar multiscale bipolar top electrode, was fabricated using multilayer deposition, nanosphere lithography, and reactive-ion etching. Self-induced redox cycling was induced on the disk electrode producing ∼30× current amplification, which was independently confirmed by measuring induced electrogenerated chemiluminescence from Ru(bpy)/tri--propylamine on the floating bipolar electrode.

Redox cycling on recessed ring-disk nanoelectrode arrays in the absence of supporting electrolyte.

In canonical electrochemical experiments, a high-concentration background electrolyte is used, carrying the vast majority of current between macroscopic electrodes, thus minimizing the contribution of electromigration transport of the redox-active species being studied. In contrast, here large current enhancements are achieved in the absence of supporting electrolyte during cyclic voltammetry at a recessed ring-disk nanoelectrode array (RRDE) by taking advantage of the redox cycling effect in combination with ion enrichment and an unshielded ion migration contribution to mass transport. Three distinct transport regimes are observed for the limiting current as a function of the concentration of redox species, Ru(NH3)6(2+/3+), revealed through the strong dependence of ion transport on ionic strength.

Recessed ring-disk nanoelectrode arrays integrated in nanofluidic structures for selective electrochemical detection.

Arrays of recessed ring-disk (RRD) electrodes with nanoscale spacing fabricated by multilayer deposition, nanosphere lithography, and multistep reactive ion etching were incorporated into nanofluidic channels. These arrays, which characteristically exhibit redox cycling leading to current amplification during cyclic voltammetry, can selectively analyze electroactive species based on differences in redox reversibility, redox potential, or both. Using Ru(NH3)6(3+) and ascorbic acid (AA) as model reversible and irreversible redox species, the selectivity for electrochemical measurement of Ru(NH3)6(3+) against a background of AA improves from ∼10, for an array operated in a fluidically unconstrained geometry, to ∼70 for an array integrated within nanofluidic channels.

Surface-enhanced Raman spectroscopy detection of ionic solutes by surfactant-mediated adsorption to a hydrophobic surface.

Chemical modification of the surfaces of surface-enhanced Raman spectroscopy (SERS)-active metals with thin molecular layers expands the variety of molecular species that can be attracted to the SERS surface from solution. This approach can provide selective detection of new classes of molecules that would not otherwise be detectable through direct interaction with a SERS-active metal. For example, polycyclic aromatic compounds can be attracted from aqueous solution to gold or silver SERS substrates that are modified with alkylsilanes or alkanethiols.

Redox cycling in nanoscale-recessed ring-disk electrode arrays for enhanced electrochemical sensitivity.

An array of nanoscale-recessed ring-disk electrodes was fabricated using layer-by-layer deposition, nanosphere lithography, and a multistep reactive ion etching process. The resulting device was operated in generator-collector mode by holding the ring electrodes at a constant potential and performing cyclic voltammetry by sweeping the disk potential in Fe(CN)6(3-/4-) solutions. Steady-state response and enhanced (~10×) limiting current were achieved by cycling the redox couple between ring and disk electrodes with high transfer/collection efficiency.

Confocal Raman microscopy probing of temperature-controlled release from individual, optically-trapped phospholipid vesicles.

Control of permeability of phospholipid vesicle (liposome) membranes is critical to their applications in analytical sensing, in fundamental studies of chemistry in small volumes, and in encapsulation and release of payloads for site-directed drug delivery. Applications of liposome formulations in drug delivery often take advantage of the enhanced permeability of phospholipid membranes at their gel-to-fluid phase transition, where the release of encapsulated molecules can be initiated by an increase in temperature. Despite numerous successful liposome formulations for encapsulation and release methods to study the kinetics, this process has been limited to investigations of bulk vesicle dispersions, which provide little or no information about the vesicle membrane structure and its relationship to the kinetics of trans-membrane transport.

Surface-enhanced Raman scattering study of the kinetics of self-assembly of carboxylate-terminated n-alkanethiols on silver.

Adsorption of 11-mercaptoundecanoic acid (MUA) on silver from methanol and aqueous solutions was monitored in situ by surface-enhanced Raman scattering (SRES) spectroscopy. While adsorption of MUA from methanol is a one-step formation of a thiol-bound monolayer, SERS spectra reveal that monolayer formation from aqueous solution involves interactions of both carboxylate and thiol groups of MUA with the silver surface. Several Raman scattering bands, including the ν(C-S), ν(s)(COO(-)), and ν(C-C), were used to investigate the evolution of the structure of adsorbed MUA on silver surfaces.

Surface-enhanced Raman spectroscopy investigation of the potential-dependent acid-base chemistry of silver-immobilized 2-mercaptobenzoic acid.

The acid-base chemistry of 2-mercaptobenzoic acid (2-MBA) immobilized on a polycrystalline silver surface was investigated by surface-enhanced Raman spectroscopy under potential control. The COO(-) bending mode of the benzoate form and the C-COOH stretching mode of the benzoic acid form of 2-MBA were used to determine the relative deprotonated and protonated populations of the bound ligand, respectively. In addition, shifts in the symmetric carboxylate stretching mode of 2-MBA reveal interactions between the benzoate group and the silver surface, interactions which could be displaced by acetate and other buffer anions from solution.

An improved transmutation method for quantitative determination of the components in multicomponent overlapping chromatograms.

An improved method is proposed for the quantitative determination of multicomponent overlapping chromatograms based on a known transmutation method. To overcome the main limitation of the transmutation method caused by the oscillation generated in the transmutation process, two techniques--wavelet transform smoothing and the cubic spline interpolation for reducing data points--were adopted, and a new criterion was also developed. By using the proposed algorithm, the oscillation can be suppressed effectively, and quantitative determination of the components in both the simulated and experimental overlapping chromatograms is successfully obtained.

Continuous wavelet transform applied to removing the fluctuating background in near-infrared spectra.

A novel method based on continuous wavelet transform (CWT) was proposed as a preprocessing tool for the near-infrared (NIR) spectra. Due to the property of the vanishing moments of the wavelet, the fluctuating background of the NIR spectra can be successfully removed through convolution of the spectra with an appropriate wavelet function. The vanishing moments of a wavelet and the scale parameter are two key factors that govern the result of the background elimination.