High-Precision Single-Cell microRNA Therapy by a Functional Nanopipette with Sensitive Photoelectrochemical Feedback

This work proposes the concept of single-cell microRNA (miR) therapy and proof-of-concept by engineering a nanopipette for high-precision miR-21-targeted therapy in a single HeLa cell with sensitive photoelectrochemical (PEC) feedback. Targeting the representative oncogenic miR-21, the as-functionalized nanopipette permits direct intracellular drug administration with precisely controllable dosages, and the corresponding therapeutic effects can be sensitively transduced by a PEC sensing interface that selectively responds to the indicator level of cytosolic caspase-3. The experimental results reveal that injection of ca. 4.4 × 10-20  mol miR-21 inhibitor, i.e., 26488 copies, can cause the obvious therapeutic action in the targeted cell. This work features a solution to obtain the accurate knowledge of how a certain miR-drug with specific dosages treats the cells and thus provides an insight into futuristic high-precision clinical miR therapy using personalized medicine, provided that the prerequisite single-cell experiments are courses of personalized customization.

A Fast and Reversible Responsive Bionic Transmembrane Nanochannel for Dynamic Single-Cell Quantification of Glutathione

Biological channels can rapidly and continuously modulate ion transport behaviors in response to external stimuli, which play essential roles in manipulating physiological and pathological processes in cells. Here, to mimic the biological channels, a bionic nanochannel is developed by synergizing a cationic silicon-substituted rhodamine (SiRh) with a glass nanopipette for transmembrane single-cell quantification. Taking the fast and reversible nucleophilic addition reaction between glutathione (GSH) and SiRh, the bionic nanochannel shows a fast and reversible response to GSH, with its inner-surface charges changing between positive and negative charges, leading to a distinct and reversible switch in ionic current rectification (ICR). With the bionic nanochannel, spatiotemporal-resolved operation is performed to quantify endogenous GSH in a single cell, allowing for monitoring of intracellular GSH fluctuation in tumor cells upon photodynamic therapy and ferroptosis. Our results demonstrate that it is a feasible tool for in situ quantification of the endogenous GSH in single cells, which may be adapted to addressing other endogenous biomolecules in single cells by usage of other stimuli-responsive probes.

The Modification and Applications of Nanopipettes in Electrochemical Analysis

Nanopipette, which is fabricated by glasses and possesses a nanoscale pore in the tip, has been proven to be immensely useful in electrochemical analysis. Numerous nanopipette-based sensors have emerged with improved sensitivity, selectivity, ease of use, and miniaturization. In this minireview, we provide an overview of the recent developments of nanopipette-based electrochemical sensors based on different types of nanopipettes, including single-nanopipettes, self-referenced nanopipettes, dual-nanopipettes, and double-barrel nanopipettes. Several important modification materials for nanopipette functionalization are highlighted, such as conductive materials, macromolecular materials, and functional molecules. These materials can improve the sensing performance and targeting specificities of nanopipettes. We also discuss examples of related applications and the future development of nanopipette-based strategies.

Artificial Synapse: Spatiotemporal Heterogeneities in Dopamine Electrochemistry at a Carbon Fiber Ultramicroelectrode

An artificial synapse is developed that mimics ultramicroelectrode (UME) amperometric detection of single cell exocytosis. It comprises the nanopipette of a scanning ion conductance microscope (SICM), which delivers rapid pulses of neurotransmitter (dopamine) locally and on demand at >1000 defined locations of a carbon fiber (CF) UME in each experiment. Analysis of the resulting UME current-space-time data reveals spatiotemporal heterogeneous electrode activity on the nanoscale and submillisecond time scale for dopamine electrooxidation at typical UME detection potentials. Through complementary surface charge mapping and finite element method (FEM) simulations, these previously unseen variations in electrochemical activity are related to heterogeneities in the surface chemistry of the CF UME.

A Practical Electrochemical Nanotool for Facile Quantification of Amino Acids in Single Cell

Though significant advances are made in the arena of single-cell electroanalysis, quantification of intracellular amino acids of human cells remains unsolved. Exemplified by l-histidine (l-His), this issue is addressed by a practical electrochemical nanotool synergizing the highly accessible nanopipette with commercially available synthetic DNAzyme. The fabricated nanotools are screened before operation of a single-use manner, and the l-His-provoked cleavage of the DNA molecules can be sensibly transduced by the ionic current rectification response, the intrinsic property of nanopipette governed by its interior surface charges. Regional distribution of cytosolic l-His level in human cells is electrochemically quantified for the first time, and time-dependent drug treatment effects are further revealed. This work unveils the possibility of electrochemistry for quantification of cytosolic amino acids of a spatial- and time-based manner and ultimately enables a better understanding of amino acid-involved events in living cells.

Electric Field-Controlled Synthesis and Characterisation of Single Metal-Organic-Framework (MOF) Nanoparticles

Achieving control over the size distribution of metal-organic-framework (MOF) nanoparticles is key to biomedical applications and seeding techniques. Electrochemical control over the nanoparticle synthesis of the MOF, HKUST-1, is achieved using a nanopipette injection method to locally mix Cu²⁺ salt precursor and benzene-1,3,5-tricarboxylate (BTC^3- ) ligand reagents, to form MOF nanocrystals, and collect and characterise them on a TEM grid. In situ analysis of the size and translocation frequency of HKUST-1 nanoparticles is demonstrated, using the nanopipette to detect resistive pulses as nanoparticles form. Complementary modelling of mass transport in the electric field, enables particle size to be estimated and explains the feasibility of particular reaction conditions, including inhibitory effects of excess BTC^3- . These new methods should be applicable to a variety of MOFs, and scaling up synthesis possible via arrays of nanoscale reaction centres, for example using nanopore membranes.

Nanofountain Probe Electroporation Enables Versatile Single-Cell Intracellular Delivery and Investigation of Postpulse Electropore Dynamics

Introducing exogenous molecules into cells with high efficiency and dosage control is a crucial step in basic research as well as clinical applications. Here, the capability of the nanofountain probe electroporation (NFP-E) system to deliver proteins and plasmids in a variety of continuous and primary cell types with appropriate dosage control is reported. It is shown that the NFP-E can achieve fine control over the relative expression of two cotransfected plasmids. Finally, the dynamics of electropore closure after the pulsing ends with the NFP-E is investigated. Localized electroporation has recently been utilized to demonstrate the converse process of delivery (sampling), in which a small volume of the cytosol is retrieved during electroporation without causing cell lysis. Single-cell temporal sampling confers the benefit of monitoring the same cell over time and can provide valuable insights into the mechanisms underlying processes such as stem cell differentiation and disease progression. NFP-E parameters that maximize the membrane resealing time, which is essential for increasing the sampled volume and in meeting the challenge of monitoring low copy number biomarkers, are identified. Its application in CRISPR/Cas9 gene editing, stem cell reprogramming, and single-cell sampling studies is envisioned.

Sensing with Nanopores and Aptamers: A Way Forward

In the 90s, the development of a novel single molecule technique based on nanopore sensing emerged. Preliminary improvements were based on the molecular or biological engineering of protein nanopores along with the use of nanotechnologies developed in the context of microelectronics. Since the last decade, the convergence between those two worlds has allowed for biomimetic approaches. In this respect, the combination of nanopores with aptamers, single-stranded oligonucleotides specifically selected towards molecular or cellular targets from an in vitro method, gained a lot of interest with potential applications for the single molecule detection and recognition in various domains like health, environment or security. The recent developments performed by combining nanopores and aptamers are highlighted in this review and some perspectives are drawn.

Probing the Membrane Vibration of Single Living Cells by Using Nanopipettes

The vibration of a cell membrane plays a key role in the regulation of cell shape and the behavior of cells. However, most existing approaches for the measurement of cell vibration require either exogenous modification or sophisticated techniques, and the main challenge lies in developing methods that can monitor membrane vibration of living cells directly. Herein, a noninvasive strategy based on ultrasmall quartz nanopipettes is introduced. With a tip size of less than 100 nm, nanopipettes can be spatially controlled for precision targeting of a specific location on the membrane of single living cells. Surprisingly, by employing a constant voltage, stable cyclic oscillations are observed from the continuous current versus time traces. The time-domain current can be decomposed into two basic waves: the high-frequency one indicates the local membrane vibration driven by the electro-osmotic flow from the nanopipette, whereas the low-frequency one indicates the natural frequency of the whole cell. This provides a simple but reliable method to test local and global membrane vibration of single living cells simultaneously with little damage, which provides a tool for the quantification of drugs, disease, or mutations of the cell structure.

Scanning MWCNT-Nanopipette and Probe Microscopy: Li Patterning and Transport Studies

A carbon-nanotube-enabling scanning probe technique/nanotechnology for manipulating and measuring lithium at the nano/mesoscale is introduced. Scanning Li-nanopipette and probe microscopy (SLi-NPM) is based on a conductive atomic force microscope (AFM) cantilever with an open-ended multi-walled carbon nanotube (MWCNT) affixed to its apex. SLi-NPM operation is demonstrated with a model system consisting of a Li thin film on a Si(111) substrate. By control of bias, separation distance, and contact time, attograms of Li can be controllably pipetted to or from the MWCNT tip. Patterned surface Li features are then directly probed via noncontact AFM measurements with the MWCNT tip. The subsequent decay of Li features is simulated with a mesoscale continuum model, developed here. The Li surface diffusion coefficient for a four (two) Li layer thick film is measured as D=8(±1.2)×10(-15) cm(2) s(-1) (D=1.75(±0.15)×10(-15) cm(2) s(-1)). Dual-Li pipetting/measuring with SLi-NPM enables a broad range of time-dependent Li and nanoelectrode characterization studies of fundamental importance to energy-storage research.