Exponential Increase in an Ionic Signal: A Dominant Role of the Space Charge Effect on the Outer Surface of Nanochannels

Abstract

Nanochannels have advantage in sensitive analyses due to the confinement effects on ionic signal in nano-or subnanometric confines but could realize further gains by optimizing signal mechanism. Making target recognitions on the outer surface of nanochannels has been verified to improve target recognitions and signal conversions by maximizing surfaces accessible to targets and ions, but until recently, the signal mechanism has been still unclear. Using electroneutral peptide nucleic acid (PNA) and negative-charged DNA, we verified a dominant space charge effect on an ionic signal on the outer surface of nanochannels. A typical exponential increase of the ionic signal with the charge density on the outer surface has been demonstrated through the PNA−PNA, PNA−DNA, DNA−DNA hybrid, DNA cleavage, and hybridization chain reaction. These results challenge the essential role of steric hindrance on the ionic signal and describe a new ion passageway surrounded and accelerated by the stern layer of charged species on the nanochannel outer surface.

Polydopamine-Induced Modification on the Highly Charged Surface of Asymmetric Nanofluidics: A Strategy for Adjustable Ion Current Rectification Properties

“…Furthermore, the experimental results showed that the ICR ratio decreased with the pore size of the PET nanochannels (Figure S12), which stem from the space compression of the ion-enrichment/depletion region and the corresponding enhancement of the double-layer interaction. 73,74 Both the experimental and theoretical results demonstrated that the change in surface charge by modified PDA in the ion-depletion region leads to the fundamental change in the ICR effect.…”

Inner Wall and Outer Surface Distinguished Solid-State Nanopores for Sensing

“…For a long time, people ignored FE OS , so that its functions were not clear. We carried out research on the precise functional zoning of solid-state nanopores and focused on the role of FE OS in ion gating (Figure c). − By controllably depositing metal layers using an electron-beam evaporation technique, only the one outer surface of the nanopores was modified (Figure a). For example, a thick gold layer was sputtered onto one side of the anodic aluminum oxide nanopore membrane, and the capture probe was immobilized to the outer surface through Au–S chemistry for regulating ion gating after the formation of a self-assembled DNA monolayer .…”

“…FE OS such as negatively charged DNA causes an exponential increase in an ionic signal by the space charge effect. 16 DNA rolling circle amplification on the outer surface of nanopores achieves single-base mismatch detection of mRNA-21 with a sensitivity of 6 fM. 17 FE OS can effectively improve the ion selectivity and output power of nanopores without increasing the internal resistance.…”

“…These studies only focus on the functional elements modified on the inner wall (FE IW ) and ignore the role of functional elements modified on the outer surface (FE OS ) in sensing. To distinguish the functions of FE IW and FE OS , we carried out a series of studies on the impact of precise functional zoning of inner wall and outer surface on ion/molecule transport in solid-state nanopores and developed some highly sensitive and specific nanopore-based sensors. − Here, we review the research progress of inner wall and outer surface distinguished solid-state nanopores (Figure ) and discuss the development prospects and challenges. The nanopores discussed in this perspective are a broad concept, including nanochannels, mainly membrane materials such as silicon nitride, , two-dimensional materials, , aluminum oxide, and polymer films .…”

Integrating Ordered Two-Dimensional Covalent Organic Frameworks to Solid-State Nanofluidic Channels for Ultrafast and Sensitive Detection of Mercury

“…Specific recognition moiety-functionalized solid-state nanofluidic channels have been shown to be selective and sensitive sensors for various analytes. − Steady-state current change with chemical composition, surface charge, wettability, and the diameter of the nanofluidic channel caused by even a single molecule can be efficaciously recorded, endowing nanofluidic sensors with sensitivity down to aM levels. ,− The introduction of various specific recognition moieties including aptamer, phenylboronic acid, antibodies, and functional metal–organic frameworks brings the nanofluidic channel target-specific selectivity. , However, the time-consuming interaction of the recognition moieties and the targets is a great limitation for the application of nanofluidic channel-based sensors in rapid detection. ,− Thus, promoting the kinetics for the interaction between the analyte and the recognition moiety on the nanofluidic channels is the key to overcome the limitation.…”