Microdroplet-Based Potentiometric Redox Measurements on Gold Nanoporous Electrodes

Environmental aspect and applications of nanotechnology to eliminate COVID-19 epidemiology risk

Herein, we discuss fast development of the new coronavirus disease COVID-19, emerged in late 2019 in Wuhan, Hubei Province, China, the ground zero of the coronavirus pandemic, and associated with relatively high mortality rate. COVID-19 risk originates from its ability to transmit easily from person to person through the respiratory droplets released during sneezing, breathing, talking, singing, or coughing within a range of nearly 1.5–2 m. The review begins with an overview of COVID-19 origin and symptoms that range from common cold to severe respiratory illnesses and death. Then, it sheds light on the role of nanotechnology as an effective tool for fighting COVID-19 via contributions in diagnosis, treatment, and manufacture of protective equipment for people and healthcare workers. Emergency-approved therapeutics for clinical trial and prospective vaccines are discussed. Additionally, the present work addresses the risk of severe acute respiratory syndrome coronavirus transmission via wastewater and means of wastewater treatment and disinfection via nanoscale materials. The review concludes with a brief assessment of the government's efforts and contemporary propositions to minimize COVID-19 hazard and spreading.

Nanobiotechnology as a platform for the diagnosis of COVID-19: a review

A sensitive method for diagnosing coronavirus disease 2019 (COVID-19) is highly required to fight the current and future global health threats due to severe acute respiratory syndrome coronavirus 2 (SARS-CoV 2). However, most of the current methods exhibited high false‐negative rates, resulting in patient misdiagnosis and impeding early treatment. Nanoparticles show promising performance and great potential to serve as a platform for diagnosing viral infection in a short time and with high sensitivity. This review highlighted the potential of nanoparticles as platforms for the diagnosis of COVID-19. Nanoparticles such as gold nanoparticles, magnetic nanoparticles, and graphene (G) were applied to detect SARS-CoV 2. They have been used for molecular-based diagnosis methods and serological methods. Nanoparticles improved specificity and shorten the time required for the diagnosis. They may be implemented into small devices that facilitate the self-diagnosis at home or in places such as airports and shops. Nanoparticles-based methods can be used for the analysis of virus-contaminated samples from a patient, surface, and air. The advantages and challenges were discussed to introduce useful information for designing a sensitive, fast, and low-cost diagnostic method. This review aims to present a helpful survey for the lesson learned from handling this outbreak to prepare ourself for future  pandemic.

Potentiometric Biosensing of Ascorbic Acid, Uric Acid, and Cysteine in Microliter Volumes Using Miniaturized Nanoporous Gold Electrodes

Potentiometric redox sensing is a relatively inexpensive and passive approach to evaluate the overall redox state of complex biological and environmental solutions. The ability to make such measurements in ultra-small volumes using high surface area, nanoporous electrodes is of particular importance as such electrodes can improve the rates of electron transfer and reduce the effects of biofouling on the electrochemical signal. This work focuses on the fabrication of miniaturized nanoporous gold (NPG) electrodes with a high surface area and a small footprint for the potentiometric redox sensing of three biologically relevant redox molecules (ascorbic acid, uric acid, and cysteine) in microliter volumes. The NPG electrodes were inexpensively made by attaching a nanoporous gold leaf prepared by dealloying 12K gold in nitric acid to a modified glass capillary (1.5 mm id) and establishing an electrode connection with copper tape. The surface area of the electrodes was ~1.5 cm², providing a roughness factor of ~16 relative to the geometric area of 0.09 cm². Scanning electron microscopy confirmed the nanoporous framework. A linear dependence between the open-circuit potential (OCP) and the logarithm of concentration (e.g., Nernstian-like behavior) was obtained for all three redox molecules in 100 μL buffered solutions. As a first step towards understanding a real system, the response associated with changing the concentration of one redox species in the presence of the other two was examined. These results show that at NPG, the redox potential of a solution containing biologically relevant concentrations of ascorbic acid, uric acid, and cysteine is strongly influenced by ascorbic acid. Such information is important for the measurement of redox potentials in complex biological solutions.

Enzyme Kinetics via Open Circuit Potentiometry

We demonstrate the application of open circuit potentiometry (OCP) to measure enzyme turnover kinetics, k_turn. The electrode surface will become poised by the addition of a well-behaved redox pair, such as ferrocenemethanol/ferrocenium methanol (FcMeOH/FcMeOH⁺), which acts as the cosubstrate for the enzymatic process. A measurable change in potential results when an enzyme consumes the one-electron transfer mediator. Glucose oxidase was studied as a test-case, but the method is generalizable across oxidoreductase enzymes that rely on electron transfer mediators. In the presence of glucose and FcMeOH⁺, glucose oxidase delivers electrons to FcMeOH⁺, and the potential changes with respect to the Nernst equation. A theoretical model incorporating enzymatic rate expressions into the Nernst equation was derived to explain the observed potential transients, and experimental data fit theory well. A similar experiment was performed using amperometry on ultramicroelectrodes (UMEs). Here, the same enzymatic rate expression may be incorporated into the equation for steady-state flux to an UME to obtain k_turn. While similar kinetic information was obtained from the potentiometric and amperometric responses, potentiometry is independent of electrode size and mass transfer effects. Finally, we show how k_turn changes as a function of one-electron mediator. Our results may eventually find applications to biosensors, where electrode fouling plagues long-term sensor performance.

Biofouling-Resistant Platinum Bimetallic Alloys

A new electrosynthetic approach for the fabrication of three-dimensional bicontinuous nanoporous platinum-based (3D-BC-NP-Pt(Au)) electrodes is described. Binary Pt-Ag alloys are first electrodeposited on gold substrates from appropriately formulated plating solutions. Following annealing and dealloying, a new family of nanoporous platinum-based electrodes emerges whose morphology, porosity, and chemical compositions depend on electrodeposition parameters and plating solution composition. Scanning electron microscopy images reveal an interesting and distinctive nanoporous gold-like microstructure with pores and ligaments in the 10-30 nm range arranged in a bicontinuous fashion throughout the thickness of the film. X-ray photoelectron spectroscopy (XPS) confirms that the as-formed electrodeposited films are silver-rich platinum binary alloys. Interestingly, XPS also reveals that after annealing and dealloying, the electrodes are actually ternary alloys containing platinum, gold, and a small amount of residual silver that remains after dealloying. Electrochemical measurements are consistent with this result and disclose a high surface area with roughness factors of 15-24. The ability to successfully conduct electrochemical measurements in biofouling solutions via a unique biosieving-like mechanism is demonstrated by exposure of the unique 3D bicontinuous nanoporous platinum-based electrode to fibrinogen in phosphate buffer and in a solution containing red blood cells. The work described herein has the potential to enrich the fields of electrochemical sensing and biosensing via the introduction of new 3D bicontinuous nanostructured porous platinum-based electrodes that can be easily and reliably fabricated.