Revealing Ionic Signal Enhancement with Probe Grafting Density on the Outer Surface of Nanochannels

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Surface charge effects in nanoconfines is one of the fundamentals in the ion current rectification (ICR) of nanofluidics, which provides entropic driving force by asymmetric surface charges and causes ion enrichment/depletion by the electrostatic interaction of fixed surface charges. However, the surface charge effect causes a significant electrostatic repulsion in nanoconfines, restricting additional like charge or elaborate chemistry on the highly charged confined surface, which limits ICR manipulation. Here, we use polydopamine (PDA), a nearly universal adhesive, that adheres to the highly positive-charged poly(ethyleneimine) (PEI) gel network in a nanochannel array. PDA enhances the ICR effect from a low rectification ratio of 9.5 to 92.6 by increasing the surface charge and hydrophobicity of the PEI gel network and, meanwhile, shrinking its gap spacing. Theoretical and experimental results demonstrate the determinants of the fixed surface charge in the enrichment/depletion region on ICR properties, which is adjustable by PDA-induced change in a nanoconfined environment. Chemically active PDA brings Au nanoparticles by chloroauric reduction for further hydrophobization and the modification of negative-charged DNA complexes in nanochannels, whereby ICR effects can be manipulated in versatile means. The results describe an adjustable and versatile strategy for adjusting the ICR behaviors of nanofluidics by manipulating local surface charge effects using PDA.

Section: ■ Results and Discussionmentioning

confidence: 97%

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

Lin

et al. 2022

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“…The grafting density of FE OS is related to the ionic signal enhancement. 15 The experimental results show that, when the same amount of analytes is added, the change ratio of the ionic signal increases with the increase of grafting density of FE OS . The numerical simulations show that, with the increase of grafting density of FE OS , the decrease of background current and the aggregation of analytes at the entrance of the pore contribute to ionic signal enhancement.…”

Section: ■ Outer Surface Modified Nanoporesmentioning

confidence: 94%

“…The conformational change of FE OS induced by an applied electric field can control the transport of analytes larger than ions, such as proteins and nanoparticles. The grafting density of FE OS is related to the ionic signal enhancement . The experimental results show that, when the same amount of analytes is added, the change ratio of the ionic signal increases with the increase of grafting density of FE OS .…”

Section: Outer Surface Modified Nanoporesmentioning

confidence: 94%

“…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 .…”

mentioning

confidence: 99%

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

Dai

Zhang

et al. 2022

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Solid-state nanopores, inspired by biological nanopores, have the advantages of good mechanical properties, stability, and easy modification. They have attracted wide attention in the fields of sequencing, sensing, molecular sieving, nanofluidic devices, nanoelectrochemistry, and energy conversion. Because of the ion/molecule transport characteristic of the pore, the research on solid-state nanopores mainly focuses on the functional modification of its inner wall. In recent years, the outer surface of nanopores has also attracted the attention of researchers, and the functional elements on the outer surface have the functions of anti-interference and ionic signal enhancement. In this perspective, we review research progress of inner wall and outer surface distinguished solid-state nanopores, highlight their processing and advantages, summarize their functions and applications in sensing, and give insight into further research.

“…Nanofluidic-based biochemical sensing is a promising approach for high-throughput, high-sensitive, and label-free detection of a wide range of targets, relying on the change of ion transport signals across the nanofluidic membrane. − Generally, the ion transport signal through nanofluidic membranes is governed by strong interactions between ion species and membrane surfaces, presenting very different behaviors from those of macroscopic fluids. , In order to realize selective ion/molecule transport, the nanofluidic membrane modified with an ion/molecule recognition agent (ionophores, aptamers, antibodies, etc.) that can selectively bind the target ion/molecule are commonly used. − Furthermore, precise regulation of membrane surface properties including surface charge and surface wettability has been demonstrated to be vital for the regulation of ionic signals of biological ion channels and commonly introduced into artificial nanofluidic systems. − For example, electrostatic interactions have been widely investigated for the regulation of the nanofluidic ion transport signal and applied in nanofluidic-based biochemical sensing. Our group systematically investigated the critical role of surface charge in ionic signals of nanofluidic-based chemical sensors by precisely adjusting the grafting density of DNA probes in nanoconfinements and found that the enhanced sensing performance can be realized with the tailoring surface and space charge density .…”

Section: Introductionmentioning

confidence: 99%

Revealing the Role of Surface Wettability in Ionic Detection Signals of Nanofluidic-Based Chemical Sensors

Wang

Gao

et al. 2022

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The nanofluidic ionic signal is governed by the interactions between ion species and the surface charge, surface wettability, and pore diameter of nanofluidic membranes. However, the effect of surface wettability on the ionic detection signal across the nanofluidic membrane remains poorly explored, limited nanofluidic applications in biochemical sensing. Here, we investigate the effect of surface wettability of the nanofluidic membrane on the ionic signal for the detection of hydrophobic drug molecules using a heterogeneous nanofluidic system. This ionic signal can be tuned by light or the presence of certain ions due to the tailoring of hydrophobic interactions between the ion species and membrane surface. Compared with traditional nanofluidic membranes whose ionic signal is governed by surface charge, the regulation mechanism reported here mainly dependents on specific hydrophobic interactions, which shows a more sensitive ionic signal to environments. By virtue of the mechanism, the selective detection of the three drug molecules was realized owing to their different hydrophobic interactions with membrane surfaces. These findings have implications for understanding mass transport in nanofluidic devices and biological components and porous media involving surface wettability in nanofluidic systems.