Nanopipettes provide a promising confined space that enables advances in electrochemical, optical, and mass spectrometric measurements at the nanoscale. They have been employed to reveal the hidden ...population properties and dynamics of single molecules and single particles. Moreover, new detection mechanisms based on nanopipettes have led to detailed information on single cells at high spatial and temporal resolution. In this Minireview, we focus on the fabrication and characterization of nanopipettes, summarize their wide applications for the analysis of single entities, and conclude with an outlook for advanced practical sensing.
The preparation and characterization of nanopipettes—promising devices for electrochemical, optical, and mass spectrometric measurements at the nanoscale—are the themes of this Minireview. Their application enables the dynamics and properties of single molecules and particles to be uncovered. Furthermore, new detection mechanisms based on nanopipettes have led to detailed information on single cells at high resolution.
Arrestins recognize different receptor phosphorylation patterns and convert this information to selective arrestin functions to expand the functional diversity of the G protein-coupled receptor ...(GPCR) superfamilies. However, the principles governing arrestin-phospho-receptor interactions, as well as the contribution of each single phospho-interaction to selective arrestin structural and functional states, are undefined. Here, we determined the crystal structures of arrestin2 in complex with four different phosphopeptides derived from the vasopressin receptor-2 (V2R) C-tail. A comparison of these four crystal structures with previously solved Arrestin2 structures demonstrated that a single phospho-interaction change results in measurable conformational changes at remote sites in the complex. This conformational bias introduced by specific phosphorylation patterns was further inspected by FRET and
H NMR spectrum analysis facilitated via genetic code expansion. Moreover, an interdependent phospho-binding mechanism of phospho-receptor-arrestin interactions between different phospho-interaction sites was unexpectedly revealed. Taken together, our results provide evidence showing that phospho-interaction changes at different arrestin sites can elicit changes in affinity and structural states at remote sites, which correlate with selective arrestin functions.
Capturing real-time electron transfer, enzyme activity, molecular dynamics, and biochemical messengers in living cells is essential for understanding the signaling pathways and cellular ...communications. However, there is no generalizable method for characterizing a broad range of redox-active species in a single living cell at the resolution of cellular compartments. Although nanoelectrodes have been applied in the intracellular detection of redox-active species, the fabrication of nanoelectrodes to maximize the signal-to-noise ratio of the probe remains challenging because of the stringent requirements of 3D fabrication. Here, we report an asymmetric nanopore electrode-based amplification mechanism for the real-time monitoring of NADH in a living cell. We used a two-step 3D fabrication process to develop a modified asymmetric nanopore electrode with a diameter down to 90 nm, which allowed for the detection of redox metabolism in living cells. Taking advantage of the asymmetric geometry, the above 90% potential drop at the two terminals of the nanopore electrode converts the faradaic current response into an easily distinguishable bubble-induced transient ionic current pattern. Therefore, the current signal was amplified by at least 3 orders of magnitude, which was dynamically linked to the presence of trace redox-active species. Compared to traditional wire electrodes, this wireless asymmetric nanopore electrode exhibits a high signal-to-noise ratio by increasing the current resolution from nanoamperes to picoamperes. The asymmetric nanopore electrode achieves the highly sensitive and selective probing of NADH concentrations as low as 1 pM. Moreover, it enables the real-time nanopore monitoring of the respiration chain (i.e., NADH) in a living cell and the evaluation of the effects of anticancer drugs in an MCF-7 cell. We believe that this integrated wireless asymmetric nanopore electrode provides promising building blocks for the future imaging of electron transfer dynamics in live cells.
The role of corticosteroids in acute lung injury (ALI) remains uncertain. This study aims to determine the underlying mechanisms of corticosteroid treatment for lipopolysaccharide (LPS)‐induced ...inflammation and ALI. We used corticosteroid treatment for LPS‐induced murine ALI model to investigate the effect of corticosteroid on ALI in vivo. Moreover, LPS‐stimulated macrophages were used to explore the specific anti‐inflammatory effects of corticosteroids on NLRP3‐inflammasome in vitro. We found corticosteroids attenuated LPS‐induced ALI, which manifested in reduction of the alveolar structure destruction, the infiltration of neutrophils and the inflammatory cytokines release of interleukin‐1β (IL‐1β) and interleukin‐18 (IL‐18) in Lung. In vitro, when NLRP3‐inflammasome was knocked out, inflammatory response of caspase‐1 activation and IL‐1β secretion was obviously declined. Further exploration, our results showed that when corticosteroid preprocessed macrophages before LPS primed, it obviously inhibited the activation of caspase‐1 and the maturation of IL‐1β, which depended on inhibiting the nuclear factor‐κB (NF‐κB) signal pathway activation. However, when corticosteroids intervened the LPS‐primed macrophages, it also negatively regulated NLRP3‐inflammasome activation through suppressing mitochondrial reactive oxygen species (mtROS) production. Our results revealed that corticosteroids played a protection role in LPS‐induced inflammation and ALI by suppressing both NF‐κB signal pathway and mtROS‐dependent NLRP3 inflammasome activation.
Single‐entity electrochemistry is a powerful tool that enables the study of electrochemical processes at interfaces and provides insights into the intrinsic chemical and structural heterogeneities of ...individual entities. Signal processing is a critical aspect of single‐entity electrochemical measurements and can be used for data recognition, classification, and interpretation. In this review, we summarize the recent five‐year advances in signal processing techniques for single‐entity electrochemistry and highlight their importance in obtaining high‐quality data and extracting effective features from electrochemical signals, which are generally applicable in single‐entity electrochemistry. Moreover, we shed light on electrochemical noise analysis to obtain single‐molecule frequency fingerprint spectra that can provide rich information about the ion networks at the interface. By incorporating advanced data analysis tools and artificial intelligence algorithms, single‐entity electrochemical measurements would revolutionize the field of single‐entity analysis, leading to new fundamental discoveries.
This Minireview summarizes the latest advances in data processing techniques for single‐entity electrochemistry towards achieving automation, real‐time monitoring, increased sensitivity, as well as improved temporal and current resolution.
Disulfide bonds play an important role in thiol‐based redox regulation. However, owing to the lack of analytical tools, little is known about how local O2 mediates the reversible thiol/disulfide ...cycle under protein confinement. In this study, a protein‐nanopore inside a glove box is used to control local O2 for single‐molecule reaction, as well as a single‐molecule sensor for real‐time monitoring of the reversible thiol/disulfide cycle. The results demonstrate that the local O2 molecules in protein nanopores could facilitate the redox cycle of disulfide formation and cleavage by promoting a higher fraction of effective reactant collisions owing to nanoconfinement. Further kinetic calculations indicate that the negatively charged residues near reactive sites facilitate proton‐involved oxygen‐induced disulfide cleavage under protein confinement. The unexpectedly strong oxidation ability of confined local O2 may play an essential role in cellular redox signaling and enzyme reactions.
The reversible thiol/disulfide cycle under protein confinement was monitored in real‐time using a mutant aerolysin nanopore. Experiments combined with kinetic calculations revealed that confined local O2 can lead to proton‐involved, oxygen‐induced disulfide bond cleavage. The negatively charged neighboring microenvironment facilitates disulfide bond cleavage, which plays a vital role in redox signaling and reactions.
Clarifying the hidden but intrinsic feature of single nanoparticles by nanoelectrochemistry could help understand its potential for diverse applications. The uncontrolled interface and bandwidth ...limitation in the electrochemical measurement put the obstacle in single particle collision. Here, we demonstrate a well‐defined 30 nm nanopore electrode with a rapid chemical‐electrochemical fabrication method which provides a high reproducibility in both size and performance. A capacitance‐based detection mechanism is demonstrated to achieve a high current resolution of 0.6 pA ±0.1 pA (RMS) and a high the temporal resolution of 0.01 ms. By utilizing this electrode, the dynamic interactions of every single particle in the mixture could be directly read during the collision process. The collision frequency is two orders of magnitude higher than previous reports, which helps reveal the hidden features of nanoparticles during the complex and multidimensional interaction processes.
Probing for nanoparticles: A 30 nm confined nanopore electrode (CNE) was fabricated to directly recognize intrinsic collision information of single nanoparticles of different sizes. The rapid method and controlled nanopore dimensions enable a high reproducibility. A new detection mechanism enables 0.01 ms ultrasensitive collision detection with high current resolution and collision frequency.
We have developed a glass nanopore based single molecule tool to investigate the dynamic oligomerization and aggregation process of Aβ1-42 peptides. The intrinsic differences in the molecular size ...and surface charge of amyloid aggregated states could be distinguished through single molecule induced characteristic current fluctuation. More importantly, our results reveal that the neurotoxic Aβ1-42 oligomer tends to adsorb onto the solid surface of nanopores, which may explain its instability and highly neurotoxic features.
We have employed glass nanopore as a single molecule technique for direct sensing amyloidosis process of Aβ1-42 peptide, which of great significance in Alzheimer's disease.
Real-time monitoring of chemical reactions is still challenging as well as important to study reaction mechanisms and reaction kinetics. Herein, we demonstrated the real-time monitoring of ...o-phenylenediamine (OPD) oxidation on the surface of gold nanoparticles by surface-enhanced Raman spectroscopy (SERS). The oxidation mechanism and the reaction kinetics were investigated on the basis of the SERS spectrum variation and the related density functionalized theory calculation. It was shown that the oxidation of OPD in the presence of copper ions was a two-step process of the deprotonation of the amino group on the aromatic rings and the rearrangement of the electron cloud to a π-conjugated system, which may open a new door to comprehensively understand the reaction process.
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