skip to main content

Title: Chemical Detection by Analyte-Induced Change in Electrophoretic Deposition of Gold Nanoparticles
The electrophoretic deposition (EPD) of citrate-stabilized Au nanoparticles (cit-Au NPs) occurs on indium tin oxide (ITO)-coated glass electrodes upon electrochemical oxidation of hydroquinone (HQ) due to the release of hydronium ions. Anodic stripping voltammetry (ASV) for Au oxidation allows the determination of the amount of Au NP deposition under a specific EPD potential and time. The binding of Cr 3+ to the cit-Au NPs inhibits the EPD by inducing aggregation and/or reducing the negative charge, which could lower the effective NP concentration of the cit-Au NPs and/or lower the electrophoretic mobility. This lowers the Au oxidation charge in the ASV, which acts as an indirect signal for Cr 3+ . The binding of melamine to cit-Au NPs similarly leads to aggregation and/or lowers the negative charge, also resulting in reduction of the ASV Au oxidation peak. The decrease in Au oxidation charge measured by ASV increases linearly with increasing Cr 3+ and melamine concentration. The limit of detection (LOD) for Cr 3+ is 21.1 ppb and 16.0 ppb for 15.1 and 4.1 nm diameter cit-Au NPs, respectively. Improving the sensing conditions allows for as low as 1 ppb detection of Cr 3+ . The LOD for melamine is 45.7 ppb for 4.1 nm Au NPs.  more » « less
Award ID(s):
Author(s) / Creator(s):
Date Published:
Journal Name:
Journal of The Electrochemical Society
Page Range / eLocation ID:
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. A chip-based electrochemical biosensor is developed herein for the detection of organophosphate (OP) in food materials. The principle of the sensing platform is based on the inhibition of dimethoate (DMT), a typical OP that specifically inhibits acetylcholinesterase (AChE) activity. Carbon nanotube-modified gold electrodes functionalized with polydiallyldimethylammonium chloride (PDDA) and oxidized nanocellulose (NC) were investigated for the sensing of OP, yielding high sensitivity. Compared with noncovalent adsorption and deposition in bovine serum albumin, bioconjugation with lysine side chain activation allowed the enzyme to be stable over three weeks at room temperature. The total amount of AChE was quantified, whose activity inhibition was highly linear with respect to DMT concentration. Increased incubation times and/or DMT concentration decreased current flow. The composite electrode showed a sensitivity 4.8-times higher than that of the bare gold electrode. The biosensor was challenged with organophosphate-spiked food samples and showed a limit of detection (LOD) of DMT at 4.1 nM, with a limit of quantification (LOQ) at 12.6 nM, in the linear range of 10 nM to 1000 nM. Such performance infers significant potential for the use of this system in the detection of organophosphates in real samples. 
    more » « less
  2. null (Ed.)
    Engineered nanoparticle (NP) size and natural organic matter (NOM) composition play important roles in determining NP environmental behaviors. The aim of this work was to investigate how NP size and NOM composition influence the colloidal stability of polyvinylpyrrolidone coated platinum engineered nanoparticles (PVP-PtNPs). We evaluated PVP-PtNP aggregation as a function of the NP size (20, 30, 50, 75, and 95 nm, denoted as PVP-PtNP 20–95 ) in moderately hard water (MHW). Further, we quantified the effect of the hydrophobic organic acid (HPOA) fraction of NOM on the aggregation of PVP-PtNP 20 and PVP-PtNP 95 using 6 NOM samples from various surface waters, representing a range of NOM compositions and properties. NOM samples were characterized for bulk elemental composition ( e.g. , C, H, O, N, and S), specific ultraviolet absorbance at 254 nm (SUVA 254 ), and molecular level composition ( e.g. , compound classes) using ultrahigh resolution mass spectrometry. Single particle-inductively coupled plasma-mass spectrometry (sp-ICP-MS) was employed to monitor the aggregation of PVP-PtNPs at 1 μg PVP-PtNP per L and 1 mg NOM per L concentrations. PVP-PtNP aggregate size increased with decreasing primary PVP-PtNP size, likely due to the lower zeta potential, the higher number concentration, and the higher specific surface area of smaller NPs compared to larger NPs at the same mass concentration. No aggregation was observed for PVP-PtNP 95 in MHW in the presence and absence of the different NOM samples. PVP-PtNP 20 formed aggregates in MHW in the presence and absence of the six NOM samples, and aggregate size increased in the presence of NOM likely due to interparticle bridging of NOM-coated PVP-PtNPs by divalent counterions. PVP-PtNP 20 aggregate size increased with the increase in NOM elemental ratio of H to C and the relative abundance of lignin-like/carboxyl rich-alicyclic molecules (CRAM)-like compounds. However, the aggregate size of PVP-PtNP 20 decreased with the increase in NOM molecular weight, NOM SUVA 254 , elemental ratio of O to C, and the relative abundance of condensed hydrocarbons and tannin-like compounds. Overall, the results of this study suggest that the composition and sources of NOM are key factors that contribute to the stability of PVP-PtNPs in the aquatic environment. 
    more » « less
  3. Abstract

    Phase‐pure [NiO]0.5[Al2O3]0.5spinel nanoparticles (NPs) with limited aggregation were obtained via liquid‐feed flame spray pyrolysis (LF‐FSP) by combusting metalloorganic precursor solutions. Thereafter “chocolate chip‐like” Nix[NiO0.5‐x][Al2O3]0.5nanoparticles consisting of primary [NiO0.5‐x][Al2O3]0.5particles with average particle sizes of 40‐60 nm decorated with Ni metal particles (<10 nm in diameter) dispersed on the surface were synthesized by heat treating the spinel NPs at 800°C/7 h in flowing 5% H2:N2100 mL/min in a fluidized bed reactor. The synthesized materials were characterized using TEM, XRD, FTIR, and TGA/DTA. The Ni depleted areas consist primarily of γ‐Al2O3. The Ni content (800°C) was determined by TGA to be ≈11.3 wt.% based on TGA oxidation behavior. The successful synthesis of such nanocomposites with limited aggregation on a high temperature support provides a facile route to synthesize well‐defined NP catalysts. This work serves as a baseline study for an accompanying paper, wherein thin, flexible, dense films made from these same NPs are used as regenerable catalysts for carbon nanotube syntheses.

    more » « less
  4. Here we report measurements of the oxygen reduction reaction (ORR) at single Pt nanoparticles (NPs) through their collision with a Au microdisk electrode of lower electrocatalytic activity. Performing measurements at an elevated pressure (10-atm, pure O2) raises the O2concentration ∼50-fold over air-saturated measurements, allowing the ORR activity of smaller Pt NPs to be resolved and quantified, compared to measurements taken at atmospheric pressure. Single-NP ORR current vs potential measurements for 2.6, 16, and 24 nm radius citrate-capped Pt NPs, show the catalytic activity of the smallest Pt NPs to be roughly one order of magnitude greater than the activity of the larger NPs. The particle-by-particle nature of our measurement quantifies the distribution of electrocatalytic activities of individual particles, which we determine to be larger than can be explained by the distribution of particle sizes. Additionally, we report that some of the observed ORR current transients contain multiple sharp peaks per single-NP measurement, indicating multiple collisions of a single Pt NP at the electrode surface.

    more » « less
  5. Abstract

    Electrophoretic deposition (EPD) of colloidal particles is a practical system for the study of crystallization and related physical phenomena. The aggregation is driven by the electroosmotic flow fields and induced dipole moments generated by the polarization of the electrode‐particle‐electrolyte interface. Here, the electrochemical control of aggregation and repulsion in the electrophoretic deposition of colloidal microspheres is reported. The nature of the observed transition depended on the composition of the solvent, switching from electrode‐driven aggregation in water to electrical field‐driven repulsion in ethanol for otherwise identical systems of colloidal microspheres. This work uses optical microscopy‐derived particles and a recently developed particle insertion method approach to extract model‐free, effective interparticle potentials to describe the ensemble behavior of the particles as a function of the solvent and electrode potential at the electrode interface. This approach can be used to understand the phase behavior of these systems based on the observable particle positions rather than a detailed understanding of the electrode‐electrolyte microphysics. This approach enables simple predictability of the static and dynamic behaviors of functional colloid‐electrode interfaces.

    more » « less