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1. Electrochemistry at a single nanoparticle: from bipolar regime to tunnelling

   https://doi.org/10.1039/c8fd00041g  

   Sun, Tong; Wang, Dengchao; Mirkin, Michael V. (October 2018, Faraday Discussions)

   This paper is concerned with long-distance interactions between an unbiased metal nanoparticle (NP) and a nanoelectrode employed as a tip in the scanning electrochemical microscope (SECM). A NP immobilized on the inert substrate acts as a bipolar electrode, producing positive SECM feedback. The tip current magnitude depends strongly on the ratio of the particle and tip radii and the heterogeneous charge-transfer kinetics. The onset of electron tunneling was observed at very short separation distances (<2–3 nm) at which the NP behaves as a part of the tip electrode. The rate constant of the electron-transfer (ET) or electrocatalytic reaction at the NP can be extracted from either feedback or tunneling current. The tunneling mode of SECM can be used to investigate heterogeneous reactions occurring at a single NP without making an ohmic contact with it. This technique can also help elucidate nanoparticle/electrode interactions in various electrochemical systems ranging from NPs immobilized on the electrode surface to nanoimpact collision events. 

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2. Electrospray deposition for single nanoparticle studies

   https://doi.org/10.1039/d1ay01295a  

   Jagdale, Gargi S.; Choi, Myung-Hoon; Siepser, Natasha P.; Jeong, Soojin; Wang, Yi; Skalla, Rebecca X.; Huang, Kaixiang; Ye, Xingchen; Baker, Lane A. (August 2021, Analytical Methods)

   null (Ed.)

   Single entity electrochemical (SEE) studies that can probe activities and heterogeneity in activities at nanoscale require samples that contain single and isolated particles. Single, isolated nanoparticles are achieved here with electrospray deposition of colloidal nanoparticle solutions, with simple instrumentation. Role of three electrospray (ES) parameters, viz. spray distance (emitter tip-to-substrate distance), ES current and emitter tip diameter, in the ES deposition of single Au nano-octahedra (Au ODs) is examined. The ES deposition of single, isolated Au ODs are analyzed in terms of percentage of single NPs and local surface density of deposition. The local surface density of ES deposition of single Au ODs was found to increase with decrease in spray distance and emitter tip diameter, and increase in ES current. While the percentage of single particle ES deposition increased with increase in spray distance and decrease in emitter tip size. No significant change in the single Au ODs ES deposition percentage was observed with change in ES current values included in this study. The most favourable conditions in the ES deposition of Au ODs in this study resulted in the local surface density of 0.26 ± 0.05 single particles per μm 2 and observation of 96.3% single Au OD deposition. 

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3. Temperature-dependent mechanical and phase behavior of pulmonary surfactant monolayers studied by dissipative particle dynamics modeling and experiments

   https://doi.org/10.1016/j.colsurfa.2025.137623  

   Santo, Kolattukudy P; Iepure, Monica; Arrendondo, Jonanthan; Min, Younjin; Neimark, Alexander V (November 2025, Colloids and Surfaces A: Physicochemical and Engineering Aspects)

   Interaction of nanoparticles (NP) with the lungs is an important field of study for controlling and understanding airborne nanotoxicity, as well as for advancing pulmonary drug delivery. In particular, NP interactions with lung surfactant (LS) films have been studied using experimental and computational means for particles of various physicochemical characteristics such as size, shape, and hydrophobicity. However, the dynamics of adhesion and encapsulation of heterogeneous NPs by biointerfaces remain poorly understood. In this work, we explore the effects of amphiphilic Janus NPs (JNPs) on lung surfactant films using dissipative particle dynamics (DPD) simulations. With a specially parametrized DPD model (Santo et al., Colloids and Surfaces A, 725, 137623 (2025)), we investigate the interfacial dynamics and interaction mechanisms of JNPs with model lung surfactant monolayers consisting of dipalmitoylphosphatidyl choline (DPPC) lipids. We find that the interaction of JNP with DPPC monolayers at a given surface density depends on the particle hydrophobic coverage and its initial orientation, resulting in three distinct scenarios: translocation, monolayer coating, and intercalation between the lipids as another amphiphilic entity. The surface pressure of the monolayer is found to increase nonmonotonically with JNP hydrophobic coverage, reaching a maximum at about 50% coverage. Interestingly, the surface pressure of a JNP−monolayer system is found to be similar to that of a pure monolayer at an effective area that excludes the JNP at the interface. Our simulation results elucidate the dynamics of JNP−lipid monolayer interactions and provide quantitative insights into how NPs of different surface chemistries could affect the functionality of LS films. 

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4. Detecting bound polymer layers in attractive polymer–nanoparticle hybrids

   https://doi.org/10.1039/D1NR02395K  

   Emamy, Hamed; Starr, Francis W.; Kumar, Sanat K. (August 2021, Nanoscale)

   When polymer–nanoparticle (NP) attractions are sufficiently strong, a bound polymer layer with a distinct dynamic signature spontaneously forms at the NP interface. A similar phenomenon occurs near a fixed attractive substrate for thin polymer films. While our previous simulations fixed the NPs to examine the dilute limit, here, we allow the NP to move. Our goal is to investigate how NP mobility affects the signature of the bound layer. For small NPs that are relatively mobile, the bound layer is slaved to the motion of the NP, and the signature of the bound layer relaxation in the intermediate scattering function essentially disappears. The slow relaxation of the bound layer can be recovered when the scattering function is measured in the NP reference frame, but this process would be challenging to implement in experimental systems with multiple NPs. Instead, we use the counterintuitive result that the NP mass affects its mobility in the nanoscale limit, along with the more expected result that the bound layer increases the effective NP mass, to suggest that the signature of the bound polymer manifests as a change in NP diffusivity. These findings allow us to rationalize and quantitatively understand the results of recent experiments focused on measuring NP diffusivity with either physically adsorbed or chemically end-grafted chains. 

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5. Pb ²⁺ -Selective Nanoemulsion-Integrated Single-Entity Electrochemistry for Ultrasensitive Sensing of Blood Lead

   https://doi.org/10.1021/acs.langmuir.3c03138  

   Madawala, Hiranya; Puri, Surendra Raj; Weaver, Delaney; Kim, Jiyeon (February 2024, Langmuir)

   Gilbert C. Walker (Ed.)

   Unequivocally, Pb2+ as a harmful substance damaging children’s brain and nerve systems, thereby causing behavior and learning disabilities, should be detected much lower than the elevated blood lead for children, 240 nM, endorsed by US CDC considering the unknown neurotoxic effects, yet the ultralow detection limit up to sub-ppb level remains a challenge due to the intrinsically insufficient sensitivity in the current analytical techniques. Here, we present nanoemulsion (NE)-integrated single-entity electrochemistry (NI-SEE) toward ultrasensitive sensing of blood lead using Pb-ion-selective ionophores inside a NE, i.e., Pb2+-selective NE. Through the high thermodynamic selectivity between Pb2+ and Pb–ionophore IV, and the extremely large partition coefficient for the Pb2+–Pb–ionophore complex inside NEs, we modulate the selectivity and sensitivity of NI-SEE for Pb2+ sensing up to an unprecedentedly low detection limit, 20 ppt in aqueous solutions, and lower limit of quantitation, 40 ppb in blood serums. This observation is supported by molecular dynamics simulations, which clearly corroborate intermolecular interactions, e.g., H-bonding and π*–n, between the aromatic rings of Pb–ionophore and lone pair electrons of oxygen in dioctyl sebacate (DOS), plasticizers of NEs, subsequently enhancing the current intensity in NI-SEE. Moreover, the highly sensitive sensing of Pb2+ is enabled by the appropriate suppression of hydroxyl radical formation during NI-SEE under a cathodic potential applied to a Pt electrode. Overall, the experimentally demonstrated NI-SEE approach and the results position our new sensing technology as potential sensors for practical environmental and biomedical applications as well as a platform to interrogate the stoichiometry of target ion–ionophore recognition inside a NE as nanoreactors. 

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