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1. Mechanistic Elucidation of Nanomaterial-Enhanced First-Generation Biosensors Using Probe Voltammetry of an Enzymatic Reaction

   https://doi.org/10.3390/bios13080798  

   Wemple, Ann H; Kaplan, Jamie S; Leopold, Michael C (August 2023, Biosensors)

   The incorporation of nanomaterials (NMs) into biosensing schemes is a well-established strategy for gaining signal enhancement. With electrochemical biosensors, the enhanced performance achieved from using NMs is often attributed to the specific physical properties of the chosen nanocomponents, such as their high electronic conductivity, size-dependent functionality, and/or higher effective surface-to-volume ratios. First generation amperometric biosensing schemes, typically utilizing NMs in conjunction with immobilized enzyme and semi-permeable membranes, can possess complex sensing mechanisms that are difficult to study and challenging to understand beyond the observable signal enhancement. This study shows the use of an enzymatic reaction between xanthine (XAN) and xanthine oxidase (XOx), involving multiple electroactive species, as an electrochemical redox probe tool for ascertaining mechanistic information at and within the modified electrodes used as biosensors. Redox probing using components of this enzymatic reaction are demonstrated on two oft-employed biosensing approaches and commonly used NMs for modified electrodes: gold nanoparticle doped films and carbon nanotube interfaces. In both situations, the XAN metabolism voltammetry allows for a greater understanding of the functionality of the semipermeable membranes, the role of the NMs, and how the interplay between the two components creates signal enhancement. 

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2. Green Synthesis of Gold Nanoparticles Using Upland Cress and Their Biochemical Characterization and Assessment

   https://doi.org/10.3390/nano12010028  

   Hutchinson, Noah; Wu, Yuelin; Wang, Yale; Kanungo, Muskan; DeBruine, Anna; Kroll, Emma; Gilmore, De’Jorra; Eckrose, Zachary; Gaston, Stephanie; Matel, Phoebe; et al (January 2022, Nanomaterials)

   This article belongs to the Special Issue Synthesis and Applications of Gold Nanoparticles) Rodolphe Antoine (Ed.)

   This research focuses on the plant-mediated green synthesis process to produce gold nanoparticles (Au NPs) using upland cress (Barbarea verna), as various biomolecules within the upland cress act as both reducing and capping agents. The synthesized gold nanoparticles were thoroughly characterized using UV-vis spectroscopy, surface charge (zeta potential) analysis, scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX), atomic force microscopy (AFM), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), and X-ray diffraction (XRD). The results indicated the synthesized Au NPs are spherical and well-dispersed with an average diameter ~11 nm and a characteristic absorbance peak at ~529 nm. EDX results showed an 11.13% gold content. Colloidal Au NP stability was confirmed with a zeta potential (ζ) value of −36.8 mV. X-ray diffraction analysis verified the production of crystalline face-centered cubic gold. Moreover, the antimicrobial activity of the Au NPs was evaluated using Gram-negative Escherichiacoli and Gram-positive Bacillus megaterium. Results demonstrated concentration-dependent antimicrobial properties. Lastly, applications of the Au NPs in catalysis and biomedicine were evaluated. The catalytic activity of Au NPs was demonstrated through the conversion of 4-nitrophenol to 4-aminophenol which followed first-order kinetics. Cellular uptake and cytotoxicity were evaluated using both BMSCs (stem) and HeLa (cancer) cells and the results were cell type dependent. The synthesized Au NPs show great potential for various applications such as catalysis, pharmaceutics, and biomedicine. 

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3. Tailoring carrier dynamics in perovskite solar cells via precise dimension and architecture control and interfacial positioning of plasmonic nanoparticles

   https://doi.org/10.1039/c9ee03937f  

   Cui, Xun; Chen, Yihuang; Zhang, Meng; Harn, Yeu Wei; Qi, Jiabin; Gao, Likun; Wang, Zhong Lin; Huang, Jinsong; Yang, Yingkui; Lin, Zhiqun (January 2020, Energy & Environmental Science)

   Placing plasmonic nanoparticles (NPs) in close proximity to semiconductor nanostructures renders effective tuning of the optoelectronic properties of semiconductors through the localized surface plasmon resonance (LSPR)-induced enhancement of light absorption and/or promotion of carrier transport. Herein, we report on, for the first time, the scrutiny of carrier dynamics of perovskite solar cells (PSCs) via sandwiching monodisperse plasmonic/dielectric core/shell NPs with systematically varied dielectric shell thickness yet fixed plasmonic core diameter within an electron transport layer (ETL). Specifically, a set of Au NPs with precisely controlled dimensions ( i.e. , fixed Au core diameter and tunable SiO 2 shell thickness) and architectures (plain Au NPs and plasmonic/dielectric Au/SiO 2 core/shell NPs) are first crafted by capitalizing on the star-like block copolymer nanoreactor strategy. Subsequently, these monodisperse NPs are sandwiched between the two consecutive TiO 2 ETLs. Intriguingly, there exists a critical dielectric SiO 2 shell thickness, below which hot electrons from the Au core are readily injected to TiO 2 ( i.e. , hot electron transfer (HET)); this promotes local electron mobility in the TiO 2 ETL, leading to improved charge transport and increased short-circuit current density ( J sc ). It is also notable that the HET effect moves up the Fermi level of TiO 2 , resulting in an enhanced built-in potential and open-circuit voltage ( V oc ). Taken together, the PSCs constructed by employing a sandwich-like TiO 2 /Au NPs/TiO 2 ETL exhibit both greatly enhanced J sc and V oc , delivering champion PCEs of 18.81% and 19.42% in planar and mesostructured PSCs, respectively. As such, the judicious positioning of rationally designed monodisperse plasmonic NPs in the ETL affords effective tailoring of carrier dynamics, thereby providing a unique platform for developing high-performance PSCs. 

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4. Optical properties of nanoporous gold foams

   https://doi.org/10.1063/1.5030128  

   Asane, J_K; Qi, Z.; Biener, M_M; Liberman, V.; Noginov, M_A (September 2018, AIP Advances)

   We fabricated and experimentally studied Au nano-foams and Al2O3 scaffolds filled with Au nanoparticles (NPs). We found that while the reflectance spectra of Au nano-foams depended very little on the 8-10 nm Al2O3 ALD coating, the spectra were highly sensitive to annealing, which increased the sizes of voids and ligaments from 50-100 nm to ∼300 nm. The effective dielectric permittivities of the Au nano-foams and Al2O3 scaffolds with Au NPs were extremely high, ∼50. At the same time, Au nano-foams covered with a dielectric (MgF2) featured bright structural colors, calling for the model, which extends beyond the effective medium approximation. 

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5. Surface‐Mediated Interconnections of Nanoparticles in Cellulosic Fibrous Materials toward 3D Sensors

   https://doi.org/10.1002/adma.202002171  

   Yan, Shan; Shan, Shiyao; Wen, Jianguo; Li, Jing; Kang, Ning; Wu, Zhipeng; Lombardi, Jack; Cheng, Han‐Wen; Wang, Jie; Luo, Jin; et al (July 2020, Advanced Materials)

   Abstract Fibrous materials serve as an intriguing class of 3D materials to meet the growing demands for flexible, foldable, biocompatible, biodegradable, disposable, inexpensive, and wearable sensors and the rising desires for higher sensitivity, greater miniaturization, lower cost, and better wearability. The use of such materials for the creation of a fibrous sensor substrate that interfaces with a sensing film in 3D with the transducing electronics is however difficult by conventional photolithographic methods. Here, a highly effective pathway featuring surface‐mediated interconnection (SMI) of metal nanoclusters (NCs) and nanoparticles (NPs) in fibrous materials at ambient conditions is demonstrated for fabricating fibrous sensor substrates or platforms. Bimodally distributed gold–copper alloy NCs and NPs are used as a model system to demonstrate the semiconductive‐to‐metallic conductivity transition, quantized capacitive charging, and anisotropic conductivity characteristics. Upon coupling SMI of NCs/NPs as electrically conductive microelectrodes and surface‐mediated assembly (SMA) of the NCs/NPs as chemically sensitive interfaces, the resulting fibrous chemiresistors function as sensitive and selective sensors for gaseous and vaporous analytes. This new SMI–SMA strategy has significant implications for manufacturing high‐performance fibrous platforms to meet the growing demands of the advanced multifunctional sensors and biosensors. 

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