Particle Size Measurement and Detection of Bound Proteins of Non-Porous/Mesoporous Silica Microspheres by Single-Particle Inductively Coupled Plasma Mass Spectrometry

Single-particle inductively coupled plasma mass spectrometry (spICP-MS) has been used for particle size measurement of diverse types of individual nanoparticles and micrometer-sized carbon-based particles such as microplastics. However, its applicability to the measurement of micrometer-sized non-carbon-based particles such as silica (SiO2) particles is unclear. In this study, the applicability of spICP-MS to particle size measurement of non-porous/mesoporous SiO2 microspheres with a nominal diameter of 5.0 µm or smaller was investigated. Particle sizes of these microspheres were measured using both spICP-MS based on a conventional calibration approach using an ion standard solution and scanning electron microscopy as a reference technique, and the results were compared. The particle size distributions obtained using both techniques were in agreement within analytical uncertainty. The applicability of this technique to the detection of metal-containing protein-binding mesoporous SiO2 microspheres was also investigated. Bound iron (Fe)-containing proteins (i.e., lactoferrin and transferrin) of mesoporous SiO2 microspheres were detected using Fe as a presence marker for the proteins. Thus, spICP-MS is applicable to the particle size measurement of large-sized and non-porous/mesoporous SiO2 microspheres. It has considerable potential for element-based detection and qualification of bound proteins of mesoporous SiO2 microspheres in a variety of applications.

Single entity collision for inorganic water pollutants measurements: Insights and prospects

In the context of aquatic environmental issues, dynamic analysis of nano-sized inorganic water pollutants has been one of the key topics concerning their seriously amplified threat to natural ecosystems and life health. Its ultimate challenge is to reach a single-entity level of identification especially towards substantial amount of inorganic pollutants formed as natural or manufactured nanoparticles (NPs), which enter the water environments along with the potential release of constituents or other contaminating species that may have coprecipitated or adsorbed on the particles' surface. Here, we introduced a 'nano-impacts' approach-single entity collision electrochemistry (SECE) promising for in-situ characterization and quantification of nano-sized inorganic pollutants at single-entity level based on confinement-controlled electrochemistry. In comparison with ensemble analytical tools, advantages and features of SECE point at understanding 'individual' specific fate and effect under its free-motion condition, contributing to obtain more precise information for 'ensemble' nano-sized pollutants on assessing their mixture exposure and toxicity in the environment. This review gives a unique insight about the single-entity collision measurements of various inorganic water pollutants based on recent trends and directions of state-of-the-art single entity electrochemistry, the prospects for exploring nano-impacts in the field of inorganic water pollutants measurements were also put forward.

Voltammetry of Carbon Nanotubes and the Limitations of Particle-Modified Electrodes: Are Carbon Nanotubes Electrocatalytic?

The use of carbon nanotubes (CNTs) as electrocatalysts is summarized; the limitations of using voltammetry based on CNT-modified electrodes is explained; and the role of mass transport, as well as electrode kinetics, with respect to dictating the voltammetric responses is discussed. The use of single-entity electrochemistry to at least complement, if not replace, ensemble voltammetry is advocated along with other caveats, notably purity, with respect to CNT voltammetry.

Printable Nonenzymatic Glucose Biosensors Using Carbon Nanotube-PtNP Nanocomposites Modified with AuRu for Improved Selectivity

Nonenzymatic glucose biosensors have the potential for a more reliable in vivo functionality due to the reduced risk of biorecognition element degradation. However, these novel sensing mechanisms often are nanoparticle-based and have nonlinear responses, which makes it difficult to gauge their potential utility against more conventional enzymatic biosensors. Moreover, these nonenzymatic biosensors often suffer from poor selectivity that needs to be better addressed before being used in vivo. To address these problems, here we present an amperometric nonenzymatic glucose biosensor fabricated using one-step electrodeposition of Au and Ru nanoparticles on the surface of a carbon-nanotube-based platinum-nanoparticle hybrid in conductive polymer. Using benchtop evaluations, we demonstrate that the bimetallic catalyst of Au-Ru nanoparticles can enable the nonenzymatic detection of glucose with a superior performance and stability. Furthermore, our biosensor shows good selectivity against other interferents, with a nonlinear dynamic range of 1-19 mM glucose. The Au-Ru catalyst has a conventional linear range of 1-10 mM, with a sensitivity of 0.2347 nA/(μM mm²) ± 0.0198 (n = 3) and a limit of detection of 0.068 mM (signal-to-noise, S/N = 3). The biosensor also exhibits a good repeatability and stability at 37 °C over a 3 week incubation period. Finally, we use a modified Butler-Volmer nonlinear analytical model to evaluate the impact of geometrical and chemical design parameters on our nonenzymatic biosensor's performance, which may be used to help optimize the performance of this class of biosensors.

Porosity determination of nano- and sub-micron particles by single particle inductively coupled plasma mass spectrometry

By comparing the spICP-MS signal intensities of solid and porous nanoparticles of the same composition and size, the porosity of particles can be determined.

Single Particle Electrochemistry of Collision

A novel electrochemistry method using stochastic collision of particles at microelectrode to study their performance in single-particle scale has obtained remarkable development in recent years. This convenient and swift analytical method, which can be called "nanoimpact," is focused on the electrochemical process of the single particle rather than in complex ensemble systems. Many researchers have applied this nanoimpact method to investigate various kinds of materials in many research fields, including sensing, electrochemical catalysis, and energy storage. However, the ways how they utilize the method are quite different and the key points can be classified into four sorts: sensing particles at ultralow concentration, theory optimization, kinetics of mediated catalytic reaction, and redox electrochemistry of the particles. This review gives a brief overview of the development of the nanoimpact method from the four aspects in a new perspective.

Observing Single Hollow Porous Carbon Catalyst Collisions for Oxygen Reduction at Gold Nanoband Electrode

The evaluation of single carbon particle catalysts is critical to better understand the relationship between structure and properties. Here, we use an electrochemical collision method to study the electrocatalytic behaviour of single hollow porous carbon catalyst on gold nanoband electrodes (AuNBE). We observed the catalytic current of oxygen reduction of single carbon particle and quantified the contribution of the porous structure to the catalytic performance. We find that the meso/microporous and hollow structures contribute to the electrocatalytic current. Our research provides direct evidence that the hollow/porous structures improve the electrocatalytic performance.

Understanding nanoparticle porosity via nanoimpacts and XPS: electro-oxidation of platinum nanoparticle aggregates

The porosity of platinum nanoparticle aggregates (PtNPs) is investigated electrochemically via particle-electrode impacts and by XPS. The mean charge per oxidative transient is measured from nanoimpacts; XPS shows the formation of PtO and PtO₂ in relative amounts defined by the electrode potential and an average oxidation state is deduced as a function of potential. The number of platinum atoms oxidised per PtNP is calculated and compared with two models: solid and porous spheres, within which there are two cases: full and surface oxidation. This allows insight into extent to which the internal surface of the aggregate is 'seen' by the solution and is electrochemically active.

Simultaneous activity and surface area measurements on single mesoporous nanoparticle aggregates

The underpotential deposition of hydrogen and the hydrogen evolution reaction is studied at individual mesoporous nanoparticles. This work shows how the electroactive surface area and catalytic activity of these individual particles can be simultaneously measured.