Electrochemical stability of carbon-supported gold nanoparticles in acidic electrolyte during cyclic voltammetry

Enhanced sensitivity in electrochemical detection of ochratoxin A within food samples using ferrocene- and aptamer-tethered gold nanoparticles on disposable electrodes

Ensuring food security is crucial for public health, and the presence of mycotoxins, produced by fungi in improperly stored processed or unprocessed food, poses a significant threat. This research introduces a novel approach - a disposable aptasensing platform designed for the detection of ochratoxin A (OTA). The platform employs gold-nanostructured screen-printed carbon electrodes functionalized with a ferrocene derivative, serving as an integrated faradaic transducing system, and an anti-OTA aptamer as a bioreceptor site. Detection relies on the ferrocene electrochemical signal changes induced by the aptamer folding in the presence of the target molecule. Remarkably sensitive, the platform detects OTA within the range of 0.5 to 70 ng mL-1 and a detection limit of 11 pg mL-1. This limit is approximately 200 times below the levels stipulated by the European Commission for agricultural commodities. Notably, the sensing device exhibits efficacy in detecting OTA in complex media, such as roasted coffee beans and wine, without the need for sample pretreatment, yielding accurate recoveries. Furthermore, while label-free electrochemical aptasensors have proliferated, this study addresses a gap in understanding the binding mechanisms of some aptasensors. To enhance the experimental findings, a theoretical study was conducted to underscore the specificity of the anti-OTA aptamer as a donor for OTA detection. The molecular docking technique was employed to unveil the key binding region of the aptamer, providing valuable insights into the aptasensor specificity.

Antioxidative Impact of Phenolics-Loaded Nanocarriers on Cytoskeletal Network Remodeling of Invasive Cancer Cells

Natural phenolic compounds have antioxidant properties owing to their free radical-scavenging capability. The combined effect of a mixture of phenolic compounds has been studied; however, the detailed investigation for finding a correlation between single phenolic molecules and antioxidant activity has not been explored. Herein, we revealed that the number of phenolic hydroxyl groups in phenolics played a central role in their antioxidant capacity. Based on the finding, tannic acid showed the most effective antioxidant potential, e.g., 76% in tannic acid versus 22% in vitamin C as a standard antioxidant component. Because cancer progression is closely related to oxidative processes at the cellular level, we further applied the surface treatment of tannic acid drug-delivery nanocarriers. Tannic acid-loaded nanocarriers reduced reactive oxygen species of cancer cells as much as 41% of vehicle treatment and remodeled cytoskeletal network. By a gelatin degradation study, TA-loaded nanocarrier-treated cells induced 44.6% reduction of degraded area than vehicle-treated cells, implying a potential of blocking invasiveness of cancer cells.

Quantifying the removal of stabilizing thiolates from gold nanoparticles on different carbon supports and the effect on their electrochemical properties

Gold nanoparticles <10 nm in size are typically prepared using stabilizing agents, e.g. thiolates. Often standard recipes from literature are used to presumably remove these stabilisers to liberate the surface, e.g. for catalytic or electrocatalytic applications, however the success of these procedures is often not verified. In this work, thiolate-stabilised AuNPs of ca. 2 nm in size were synthesized and supported onto three different carbon supports, resulting in loadings from 15 to 25 wt% Au. These materials were post treated using three different methods in varying gas atmospheres to remove the stabilizing agent and to liberate the surface for electrochemical applications. Using thermogravimetry - mass spectroscopy (TG-MS), the amount of removed stabilizer was determined to be up to 95%. Identical location scanning transmission electron microscopy (il-(S)TEM) measurments revealed moderate particle growth but a stable support during the treatments, the latter was also confirmed by Raman spectroscopy. All treatments significantly improved the electrochemically accessible gold surface. In general, the results presented here point out the importance of quantitatively verifying the success of any catalyst post treatment with the aim of stabilizer removal.

Surface Effect on Young's Modulus of Sub-Two-Nanometer Gold [111] Nanocontacts

The surface bond nature of face centered cubic metals has been controversial between hardening and softening theoretically because of the lack of precise measurement. Here, we precisely measured the size dependence of Young's modulus of gold [111] nanocontacts with a clean surface by our in situ TEM-frequency modulation force sensing method in ultrahigh vacuum at room temperature. Young's modulus gradually decreased from ca. 80 to 30 GPa, as the nanocontact width decreased below 2 nm, which could be explained by surface softening; Young's modulus of the outermost atomic layer was estimated to be approximately 22 GPa, while that of the other part was almost the same with the bulk.

Electrochemical Stability and Degradation Mechanisms of Commercial Carbon-Supported Gold Nanoparticles in Acidic Media

Electrochemical stability of a commercial Au/C catalyst in an acidic electrolyte has been investigated by an accelerated stress test (AST), which consisted of 10,000 voltammetric scans (1 V/s) in the potential range between 0.58 and 1.41 V_RHE. Loss of Au electrochemical surface area (ESA) during the AST pointed out to the degradation of Au/C. Coupling of an electrochemical flow cell with ICP-MS showed that only a minor amount of gold is dissolved despite the substantial loss of gold ESA during the AST (∼35% of initial value remains at the end of the AST). According to the electrochemical mass spectrometry experiments, carbon corrosion occurs during the AST but to a minor extent. By using identical location scanning electron microscopy and identical location transmission electron microscopy, it was possible to discern that the dissolution of small Au particles (<5 nm) within the polydisperse Au/C sample is the main degradation mechanism. The mass of such particles gives only a minor contribution to the overall Au mass of the polydisperse sample while giving a major contribution to the overall ESA, which explains a significant loss of ESA and minor loss of mass during the AST. The addition of low amounts of chloride anions (10^-4 M) substantially promoted the degradation of gold nanoparticles. At an even higher concentration of chlorides (10^-2 M), the dissolution of gold was rather effective, which is useful from the recycling point of view when rapid leaching of gold is desirable.