Single-cell ATP detection and content analyses in electrostimulus-induced apoptosis using functionalized glass nanopipettes

Glass nano/micron pipette-based ion current rectification sensing technology for single cell/in vivo analysis

Glass nano/micron pipettes, owing to their easy preparation, unique confined space at the tip, and modifiable inner surface of the tip, can capture the ion current signal caused by a single entity, making them widely used in the construction of highly sensitive and highly selective electrochemical sensors for single entity analysis. Compared with other solid-state nanopores, their conical nano-tip causes less damage to cells when inserted into them, thereby becoming a powerful tool for the in situ analysis of important substances in cells. However, glass nanopipettes have some shortcomings, such as poor mechanical properties, difficulty in precise preparation (aperture less than 50 nm), and easy blockage during complex real sample detection, limiting their practicability. Therefore, in recent years, researchers have conducted a series of studies on glass micropipettes. Ionic current rectification technology is a novel electrochemical analysis technique. Compared with traditional electrochemical analysis methods, it does not generate redox products during the detection process; therefore, it can not only be used for the determination of non-electrochemically active substances, but also causes less damage to the cell/living body in situ analysis, becoming a powerful analysis technology for the in situ analysis of cells/in vivo in recent years. In this review, we summarize the preparation and functionalization of glass nano/micron pipettes and introduce the sensing mechanisms of two electrochemical sensing platforms constructed using glass nano/micron pipette-based ion current rectification sensing technology as well as their applications in single cell/in vivo analysis, existing problems, and future prospects.

Electrostimulation Evokes Caspase-3-Activated Fast Cancer Cell Pyroptosis and Its Nuclear Stress Response Pathways

Pyroptosis of programmed cell death has been recognized as a more effective way to inhibit the occurrence and development of tumors than the better-studied apoptosis. However, it is still challenging to quickly and effectively trigger pyroptosis of cancer cells for high-efficacy cancer treatment. Here, we report on the first use of mild constant-potential electrostimulation (cp-ES) to quickly trigger cancer cell pyroptosis with a probability up to ∼91.4% and significantly shortened time (within 1 h), ∼3-6 times faster than typical drug stimulation to induce pyroptosis. We find that the ES-induced cancer cell pyroptosis is through the activated caspase-3 (pathway) cleavage of gasdermin E (GSDME) to form an N-terminal fragment (GSDME-N) and observe nuclear shrinkage and reduction of the number of nucleoli as well as down-/up-regulated expression of two important nucleoproteins of nucleolin and nucleophosmin (NPM1). The study enriches the basic understanding of pyroptosis and provides a new avenue for potential effective treatment of cancer.

CS/PVP Hydrogel-Based Nanocapillary for Monitoring Bacterial Growth and Rapid Antibiotic Susceptibility Testing

Infection with drug-resistant bacteria poses a significant threat to human health. Judicious use of antibiotics could reduce the likelihood of bacterial resistance, which can be evaluated through antibiotic susceptibility testing (AST). This paper focuses on the application of a needle-like nanocapillary tip filled with chitosan (CS)/polyethylene pyrrolidone (PVP) hydrogel based on its specific pH-sensitive properties. The gel-filled nanocapillary has the potential to be used for electrical pH detection with a sensitivity of 3.06 nA/pH and a linear range from 7.3 to 4.3. Such sensitivity for pH measurement could be extended for monitoring of bacterial (such as Escherichia coli and Streptococcus salivarius) growth because of the relationship between pH and bacterial growth. Bacterial growth curves obtained using the hydrogel-filled nanocapillary showed good agreement with the OD600 method. Moreover, this device could be applied for rapid AST for tetracycline and norfloxacin on E. coli with minimum inhibitory concentrations of 2 and 0.125 μg/mL, respectively. This study expands the application of the hydrogel-based nanocapillary for bacterial research by monitoring changes in pH values.

Solid-State Glass Nanopipettes: Functionalization and Applications

Solid-state glass nanopipettes provide a promising confined space that offers several advantages such as controllable size, simple preparation, low cost, good mechanical stability, and good thermal stability. These advantages make them an ideal choice for various applications such as biosensors, DNA sequencing, and drug delivery. In this review, we first delve into the functionalized nanopipettes for sensing various analytes and the methods used to develop detection means with them. Next, we provide an in-depth overview of the advanced functionalization methodologies of nanopipettes based on diversified chemical kinetics. After that, we present the latest state-of-the-art achievements and potential applications in detecting a wide range of targets, including ions, molecules, biological macromolecules, and single cells. We examine the various challenges that arise when working with these targets, as well as the innovative solutions developed to overcome them. The final section offers an in-depth overview of the current development status, newest trends, and application prospects of sensors. Overall, this review provides a comprehensive and detailed analysis of the current state-of-the-art functionalized nanopipette perception sensing and development of detection means and offers valuable insights into the prospects for this exciting field.

Detection of Glutamate Decarboxylase Antibodies and Simultaneous Multi-Molecular Translocation Exploration by Glass Nanopores

Glutamic acid decarboxylase antibody (GADAb) has emerged as a significant biomarker for clinical diagnosis and prognosis in type 1 diabetes (T1D). In this study, we investigated the potential utilization of glass capillary solid-state nanopores as a cost-effective and easily preparable platform for the detection of individual antigens, antibodies, and antigen-antibody complexes without necessitating any modifications to the nanopores. Our findings revealed notable characteristic variations in the translocation events of glutamic acid decarboxylase (GAD65) through nanopores under different voltage conditions, discovered that anomalous phenomenon of protein translocation events increasing with voltage may potentially be caused by the crowding of multiple proteins in the nanopores, and demonstrated that there are multiple components in the polyclonal antibodies (GADAb-poly). Furthermore, we achieved successful differentiation between GAD65, GADAb, and GADAb-GAD65 complexes. These results offer promising prospects for the development of a rapid and reliable GADAb detection method, which holds the potential to be applied in patient serum samples, thereby facilitating a label-free, cost-effective, and early diagnosis of type I diabetes.

Metal Ion-Regulated Fluorescent Sensor Array Based on Gold Nanoclusters for Physiological Phosphate Sensing

The detection of physiological phosphates (PPs) is of great importance due to their essential roles in numerous biological processes, but the efficient detection of different PPs simultaneously remains challenging. In this work, we propose a fluorescence sensor array for detecting PPs based on metal-ion-regulated gold nanoclusters (AuNCs) via an indicator-displacement assay. Zn2+ and Eu3+ are selected to assemble with two different AuNCs, resulting in quenching or enhancing their fluorescence. Based on the competitive interaction of metal ions with AuNCs and PPs, the fluorescence of AuNCs will be recovered owing to the disassembly of AuNC-metal ion ensembles. Depending on different PPs' distinct fluorescence responses, a four-channel sensor array was established. The array not only exhibits good discrimination capability for eight kinds of PPs (i.e., ATP, ADP, AMP, GTP, CTP, UTP, PPi, and Pi) via linear discriminant analysis but also enables quantitative detection of single phosphate (e.g., ATP) in the presence of interfering PPs mixtures. Moreover, potential application of the present sensor array for the discrimination of different PPs in real samples (e.g., cell lysates and serum) was successfully demonstrated with a good performance. This work illustrates the great potential of a metal ion-regulated sensor array as a new and efficient sensing platform for differential sensing of phosphates as well as other disease-related biomolecules.

Recent advances of nanopore technique in single cell analysis

Single cells and their dynamic behavior are closely related to biological research. Monitoring their dynamic behavior is of great significance for disease prevention. How to achieve rapid and non-destructive monitoring of single cells is a major issue that needs to be solved urgently. As an emerging technology, nanopores have been proven to enable non-destructive and label-free detection of single cells. The structural properties of nanopores enable a high degree of sensitivity and accuracy during analysis. In this article, we summarize and classify the different types of solid-state nanopores that can be used for single-cell detection and illustrate their specific applications depending on the size of the analyte. In addition, their research progress in material transport and microenvironment monitoring is also highlighted. Finally, a brief summary of existing research challenges and future trends in nanopore single-cell analysis is tentatively provided.

Difunctional Microelectrode Arrays for Single-Cell Electrical Stimulation and pH Detection

Due to its direct effect on biomolecules and cells, electrical stimulation (ES) is now widely used to regulate cell proliferation, differentiation, and neurostimulation and is even used in the clinic for pain relief, treatment of nerve damage, and muscle rehabilitation. Conventional ES is mostly studied on cell populations, but the heterogeneity of cancer cells results in the inability to access the response of individual cells to ES. Therefore, detecting the extracellular pH change (ΔpHe) after ES at the single-cell level is important for the application of ES in tumor therapy. In this study, cellular ΔpHe after periodic impulse electrostimulation (IES) was monitored in situ by using a polyaniline (PANI)-modified gold microelectrode array. The PANI sensor had excellent sensitivity (53.68 mV/pH) and linear correlation coefficient (R2 = 0.999) over the pH range of 5.55-7.41. The cells showed different degrees of ΔpHe after the IES with different intervals and stimulation potential. A shorter pulse interval and a higher stimulation potential could effectively enhance stimulation and increase cellular ΔpHe. At 0.5 V potential stimulation, the cellular ΔpHe increased with decreasing pulse interval. However, if the pulse interval was long enough, even at a higher potential of 0.7 V, there was no significant additional ΔpHe due to the insufficient stimulus strength. Based on the above conclusions, the prepared PANI microelectrode arrays (MEAs) were capable of stimulating and detecting single cells, which contributed to the deeper application of ES in tumor therapy.

Glass Nanopipette-Based Plasmonic SERS Platform for Single-Cell MicroRNA-21 Sensing during Apoptosis

As one of the most widely distributed microRNAs, microRNA-21 (miRNA-21) significantly regulates target genes' expression levels and participates in many cellular and intercellular activities, and its abnormal expression is always related to some diseases, especially cancer. Hence, detecting miRNA-21, as a biomarker, at the single-cell level helps us to reveal cell heterogeneity and expression level variation during the state change of cells. In this study, we constructed a gold nanoparticles nanomembrane (AuNPs-NM)-modified plasmonic glass nanopipette (P-nanopipette) surface-enhanced Raman scattering (SERS) sensing platform to sensitively detect content variation of the intracellular miRNA-21 during the electrostimulus (ES)-induced apoptosis process. The cytoplasm-located miRNA-21 was first extracted by using the extraction DNA (HP1)-modified P-nanopipette through a hybridization chain reaction (HCR). The nanopipette was then incubated with a labeling DNA (HP2) and reporter 4-MBA-modified Raman tag. The Raman signal (collected from the tip area near the orifice within 1 μm) showed a good response to the content variation of intracellular miRNA-21 under ES, and the proposed single-cell SERS detection platform provides a simple way to study intracellular substance change and evaluate cancer treatment outcomes.

Gold Nanocluster-Based Fluorescent Microneedle Platform toward Visual Detection of ATP

Adenosine triphosphate (ATP) participates in the regulation of most biological processes, and the ATP level is closely associated with many diseases. However, it still remains challenging to achieve on-site monitoring of ATP in an equipment-free and efficient way. Microneedles, a minimally invasive technology that can extract biomarkers from liquid biopsies, have recently emerged as useful tools for early diagnosis of a broad range of diseases. In this work, we developed hydrogel microneedles that are loaded with ATP-specific dual-emitting gold nanoclusters (RhE-AuNCs) for fast sampling and on-needle detection of ATP. These RhE-AuNCs were photo-crosslinked to the hydrogel matrix to form a fluorescent microneedle patch. Based on the ATP-induced Förster resonance energy transfer in RhE-AuNCs, a highly selective, sensitive, and reliable ATP sensor was developed. Moreover, simultaneous capture and visual detection of ATP was achieved by the AuNC-loaded microneedle sensing platform, which exhibits promising sensing performance. This work provides a new approach to design a point-of-care ATP sensing platform, which also holds great potential for the further development of microneedle-based analytical devices.

Universal Near-Infrared Fluorescent Nanoprobes for Detection and Real-Time Imaging of ATP in Real Food Samples, Living Cells, and Bacteria

Adenosine triphosphate (ATP), an essential metabolite for active microorganisms to maintain life activities, has been widely regarded as a marker of cell activity and an indicator of microbial contamination. Herein, we designed two near-infrared (NIR) fluorescent nanoprobes named CYA@ZIF-90 and CYQ@ZIF-90 by encapsulating the NIR dye CYA/CYQ in ZIF-90 for the rapid detection of ATP. Between them, nanoprobe CYA@ZIF-90 can achieve higher NIR emission (702 nm) and rapid detection (2 min). Based on the superior spatiotemporal resolution imaging of ATP fluctuations in living cells, the applicability of CYA@ZIF-90 for imaging and detection of ATP in living bacteria was explored for the first time. The nanoprobe indirectly realizes the quantitative detection of bacteria, and the detection limit can be as low as 74 CFU mL-1. Therefore, the prepared nanoprobe is expected to become a universal ATP sensing detection tool, which can be further applied to evaluate cell apoptosis, cell proliferation, and food-harmful microbial control.

Solid-State Nanopore/Nanochannel Sensing of Single Entities

Solid-state nanopores/nanochannels, with their high stability, tunable geometry, and controllable surface chemistry, have recently become an important tool for constructing biosensors. Compared with traditional biosensors, biosensors constructed with solid-state nanopores/nanochannels exhibit significant advantages of high sensitivity, high specificity, and high spatiotemporal resolution in the detection single entities (such as single molecules, single particles, and single cells) due to their unique nanoconfined space-induced target enrichment effect. Generally, the solid-state nanopore/nanochannel modification method is the inner wall modification, and the detection principles are the resistive pulse method and the steady-state ion current method. During the detection process, solid-state nanopore/nanochannel is easily blocked by single entities, and interfering substances easily enter the solid-state nanopore/nanochannel to generate interference signals, resulting in inaccurate measurement results. In addition, the problem of low flux in the detection process of solid-state nanopore/nanochannel, these defects limit the application of solid-state nanopore/nanochannel. In this review, we introduce the preparation and functionalization of solid-state nanopore/nanochannel, the research progress in the field of single entities sensing, and the novel sensing strategies on solving the above problems in solid-state nanopore/nanochannel single-entity sensing. At the same time, the challenges and prospects of solid-state nanopore/nanochannel for single-entity electrochemical sensing are also discussed.

Glass Capillary-Based Nanopores for Single Molecule/Single Cell Detection

A glass capillary-based nanopore (G-nanopore), due to its tapered tip, easy tunability in orifice size, and especially its flexible surface modifications that can be tailored to effectively capture and enhance the ionic current signal of single entities (single molecules, single cells, and single particles), offers a powerful and nanoconfined sensing platform for diverse biological measurements of single cells and single molecules. Compared with other artificial two-dimensional solid-state nanopores, its conical tip and high spatial and temporal resolution characteristics facilitate noninvasive single molecule and selected area (subcellular) single cell detections (e.g., DNA mutations, highly expressed proteins, and small molecule markers that reflect the change characteristics of the tumor), as a small G-nanopore (≤100 nm) does negligible damage to cell functions and cell membrane integrity when inserted through the cell membrane. In this brief review, we summarize the preparation of G-nanopores and discuss the advantages of them as solid-state sensing platforms for single molecule and single cell detection applications as well as for cancer diagnosis and treatment applications. We also describe the current bottlenecks that limit the widespread use of G-nanopores in clinical applications and provide an outlook on future developments. The brief review will provide the reader with a quick survey of this field and facilitate the rapid development of a G-nanopore sensing platform for future tumor diagnosis and personalized medicine based on single-molecule/single-cell bioassay.

Label-Free SERS Detection of Protein Damage in Organelles under Electrostimulation with 2D AuNPs-based Nanomembranes as Substrates

Proteins as the material basis of life are the main undertakers of life activities. However, it is difficult to identify the related proteins in organelles during stimuli-induced stress responses in cells and remains a great challenge in early diagnosis and treatment of disease. Here, proteins in the cell nucleus and mitochondria of cells under the electrical stimulation (ES) process were collected and sensitively detected based on label-free surface-enhanced Raman spectroscopy (SERS) by using AuNP-based nanomembranes as high-performance SERS substrates. Due to the existence of rich "hot spots" on the 2D plasmonic sensing platform, high-quality SERS spectra of proteins were obtained with superior sensitivity and repeatability. From the SERS analyses in vitro, it was found that the conformation of some proteins in the two kinds of organelles from cancerous HCT-116 cells (compared with normal NCM-460 cells) changed significantly and the expression levels of tyrosine, phenylalanine, and tryptophan were significantly promoted during the stimulation process. Although currently the exact proteins are still unknown, the damage of proteins in the organelles of cells at the amino acid level under ES can be revealed by the method. The developed plasmonic SERS sensing platform would be promising for bioassay and cell studies.

A perspective on astrocyte regulation of neural circuit function and animal behavior

Studies over the past two decades have demonstrated that astrocytes are tightly associated with neurons and play pivotal roles in neural circuit development, operation, and adaptation in health and disease. Nevertheless, precisely how astrocytes integrate diverse neuronal signals, modulate neural circuit structure and function at multiple temporal and spatial scales, and influence animal behavior or disease through aberrant excitation and molecular output remains unclear. This Perspective discusses how new and state-of-the-art approaches, including fluorescence indicators, opto- and chemogenetic actuators, genetic targeting tools, quantitative behavioral assays, and computational methods, might help resolve these longstanding questions. It also addresses complicating factors in interpreting astrocytes' role in neural circuit regulation and animal behavior, such as their heterogeneity, metabolism, and inter-glial communication. Research on these questions should provide a deeper mechanistic understanding of astrocyte-neuron assemblies' role in neural circuit function, complex behaviors, and disease.

Facile fabrication of highly sensitive and non-label aptasensors based on antifouling amyloid-like protein aggregates

In this paper, we present a robust and versatile method for developing non-label aptasensors with high sensitivity. Amyloid-like protein aggregates were facilely synthesized with the commonly used passivating agent bovine serum albumin (BSA) in developing biosensors, and the produced amyloid-like phase-transited BSA (PTB) exhibited excellent antifouling performances and robust interfacial adhesion with the electrode surface. In order to improve the detection sensitivity of electrochemical measurements, reduced graphene oxide was electrochemically deposited onto the electrode surface. Moreover, gold nanoparticles were introduced to enhance the conductivity of the PTB film and facilitate subsequent aptamer modification. Two common biological species, adenosine triphosphate (ATP) and cytochrome c (cyt c), were chosen as detection targets, and their corresponding aptasensors were successfully constructed and systematically evaluated. The proposed aptasensors based on the PTB-Au antifouling composite exhibited high sensitivity and specificity towards ATP and cyt c detection, and the detection limits were calculated to be 0.26 nM and 0.64 nM for ATP and cyt c, respectively. Hence, this work provides a simple approach to develop highly sensitive aptasensors without any labeling process, and thus promises its great application in biological analysis.

CRISPR/Cas-powered nanobiosensors for diagnostics

CRISPR diagnostics (CRISPR-Dx) offer a wide range of enhancements compared to traditional nanobiosensors by taking advantage of the excellent trans-cleavage activity of the CRISPR/Cas systems. However, the single-stranded DNA/RNA reporters of the current CRISPR-Dx suffer from poor stability and limited sensitivity, which make their application in complex biological environments difficult. In comparison, nanomaterials, especially metal nanoparticles, exhibits robust stability and desirable optical and electrocatalytical properties, which make them ideal as reporter molecules. Therefore, biosensing research is moving towards the use of the trans-cleavage activity of CRISPR/Cas effectors on metal nanoparticles and apply the new phenomenon to develop novel nanobiosensors to target various targets such as viral infections, genetic mutations and tumor biomarkers, by using different sensing methods, including, but not limited to fluorescence, luminescence resonance, colorimetric and electrochemical signal readout. In this review, we explore some of the most recent advances in the field of CRISPR-powered nanotechnological biosensors. Demonstrating high accuracy, sensitivity, selectivity and versatility, nanobiosensors along with CRISPR/Cas technology offer tremendous potential for next-generation diagnostics of multiple targets, especially at the point of care and without any target amplification.

Photoactivated Biosensing Process for Dictated ATP Detection in Single Living Cells

The subcellular distribution of adenosine 5'-triphosphate (ATP) and the concentration of ATP in living cells dynamically fluctuate with time during different cell cycles. The dictated activation of the biosensing process in living cells enables the spatiotemporal target detection in single living cells. Herein, a kind of o-nitrobenzylphosphate ester hairpin nucleic acid was introduced as a photoresponsive DNA probe for light-activated ATP detection in single living cells. Two methods to spatiotemporally activate the probe in single living cells were discussed. One method was the usage of the micrometer-sized optical fiber (about 5 μm) to guide the UV light (λ = 365 nm) to selectively activate the photoresponsive DNA probe in single living cells. The second method involved a two-photon laser confocal scanning microscope to selectively irradiate the photoresponsive DNA probes confined in single living cells via two-photon irradiation (λ = 740 nm). ATP aptamer integrated in the activated DNA probes selectively interacted with the target ATP, resulting in dictated signal generation. Furthermore, the photoactivated biosensing process enables dictated dual-model ATP detection in single living cells with "Signal-ON" fluorescence signal and "Signal-OFF" electrochemical signal outputs. The developed photoactivated biosensor for dictated ATP detection with high spatiotemporal resolution in single living cells at a desired time and desired place suggests the possibility to monitor biomarkers during different cell cycles.

Holographic Optical Tweezers and Boosting Upconversion Luminescent Resonance Energy Transfer Combined Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas12a Biosensors

Taking advantage of outstanding precision in target recognition and trans-cleavage ability, the recently discovered CRISPR/Cas12a system provides an alternative opportunity for designing fluorescence biosensors. To fully exploit the analytical potential, we introduce here some meaningful concepts. First, the collateral cleavage of CRISPR/Cas12a is efficiently activated in a functional DNA regulation manner and the bottleneck which largely applicable to nucleic acids detection is broken. After selection of a representative aptamer and DNAzyme as the transduction pathways, the sensing coverage is extended to a small organic compound (ATP) and a metal ion (Na⁺). The assay sensitivity is significantly improved by utilizing a bead-supported enrichment strategy wherein emerging holographic optical tweezers are used to enhance imaging stability and simultaneously achieve multiflux analysis. Last, a sandwich-structured energy-concentrating upconversion nanoparticle triggered boosting luminescent resonance energy transfer mode is comined to face with complicated biological samples by skillfully confining the emitters into a very limited inner shell. Following the above attempts, the developed CRISPR/Cas12a biosensors not only present an ultrasensitive assay behavior toward these model non-nucleic acid analytes but also can serve as a formidable toolbox for determining real samples including single cell lysates and human plasma, proving a good practical application capacity.

Photocontrolled Nanopipette Biosensor for ATP Gradient Electroanalysis of Single Living Cells

Emerging nanopipette tools have demonstrated substantial potential for advanced single-cell analysis, which plays vital roles from fundamental cellular biology to biomedical diagnostics. Highly recyclable nanopipettes with easy and quick regeneration are of special interest for precise and multiple measurements. However, existing recycle strategies are generally plagued by operational complexity and limited efficiency. Light, acting in a noncontact way, should be the ideal external stimulus to address this issue. Herein, we present the photocontrolled nanopipette capable of probing cellular adenosine triphosphate (ATP) gradient at single-cell level with good sensitivity, selectivity, and reversibility, which stems from the use of ATP-specific azobenzene (Azo)-incorporated DNA aptamer strands (AIDAS) and thereby the sensible transduction of variable nanopore size by the ionic currents passing through the aperture. Photoisomerized conformational change of the AIDAS by alternative UV/vis light stimulation ensures its noninvasive regeneration and repeated detection. Inducement and inhibition of the cellular ATP could also be probed by this nanosensor.

A nanofluidic device for ultrasensitive and label-free detection of tetracycline in association with γ-cyclodextrin and GO

Herein, an ultrasensitive and selective nanofluidic device for tetracycline (TC) was developed in association with γ-cyclodextrin and graphene oxide (GO). The assay was designed based on the change of the nanochannel surface charge due to the selective recognition ability of GO between aptamers and TC-aptamer complexes. And γ-cyclodextrin was utilized to eliminate the excess TC since the amine group molecules were inclined to be adsorbed onto the nanochannel surface and affected the adsorption efficiency of the nanochannel. In the presence of TC, TC specifically binded to the aptamer to form TC-aptamer and was separated from GO. The TC-aptamer complexes could be quantitated with conical nanochannels coated with polyethyleneimine (PEI)/Zr4+. The redundant TC was removed by γ-cyclodextrin. The detection limit of the nanofluidic device was as low as 2 ng L-1 (S/N = 3) and the linear range was 10 ng L-1 to 10 μg L-1. Moreover, the nanofluidic device provided high specificity and good recovery rates of 94.8-109.3% in natural river, tapwater and wastewater samples. The results revealed that our study provided a new rapid detection method for trace contaminant analysis.

Aptamer-Functionalized Microdevices for Bioanalysis

Aptamers have drawn great attention in the field of biological research and disease diagnosis for the remarkable advantages as recognition elements. They show unique superiority for facile selection, desirable thermal stability, flexible engineering, and low immunogenicity, complementing the use of conventional antibodies. Aptamer-functionalized microdevices offer promising properties for bioanalysis applications because of the compact sizes, minimal reaction volume, high throughput, operational feasibility, and controlled preciseness. In this review, we first introduce the innovative technologies in the selection of aptamers with microdevices and then highlight some advanced applications of aptamer-functionalized microdevices in bioanalysis field for diverse targets. Aptamer-functionalized microfluidic devices, microarrays, and paper-based and other interface-based microdevices are all bioanalysis platforms with huge potential in the near future. Finally, the major challenges of these microdevices applied in bioanalysis are discussed and future perspectives are also envisioned.

An Integrated Electrochemical Nanodevice for Intracellular RNA Collection and Detection in Single Living Cell

New tools for single-cell interrogation enable deeper understanding of cellular heterogeneity and associated cellular behaviors and functions. Information of RNA expression in single cell could contribute to our knowledge of the genetic regulatory circuits and molecular mechanism of disease development. Although significant progresses have been made for intracellular RNA analysis, existing methods have a trade-off between operational complexity and practical feasibility. We address this challenge by combining the ionic current rectification property of nanopipette reactor with duplex-specific nuclease-assisted hybridization chain reaction for signal amplification to realize a simple and practical intracellular nanosensor with minimal invasiveness, which enables single-cell collection and electrochemical detection of intracellular RNA with cell-context preservation. Systematic studies on differentiation of oncogenic miR-10b expression levels in non-malignant breast cells, metastatic breast cancer cells as well as non-metastatic breast cancer cells were then realized by this nanotool accompanied by assessment of different drugs effects. This work has unveiled the ability of electrochemistry to probe intracellular RNA and opened new opportunities to study the gene expression and heterogeneous complexity under physiological conditions down to single-cell level.

Target-Triggered Assembly in a Nanopipette for Electrochemical Single-Cell Analysis

Engineered nanopipette tools have recently emerged as a powerful approach for electrochemical nanosensing, which has major implications in both fundamental biological research and biomedical applications. Herein, we describe a generic method of target-triggered assembly of aptamers in a nanopipette for nanosensing, which is exemplified by sensitive and rapid electrochemical single-cell analysis of adenosine triphosphate (ATP), a ubiquitous energy source in life and important signaling molecules in many physiological processes. Specifically, a layer of thiolated aptamers is immobilized onto a Au-coated interior wall of a nanopipette tip. With backfilled pairing aptamers, the engineered nanopipette is then used for probing intracellular ATP via the ATP-dependent linkage of the split aptamers. Due to the higher surface charge density from the aptamer assembly, the nanosensor would exhibit an enhanced rectification signal. Besides, this ATP-responsive nanopipette tool possesses excellent selectivity and stability as well as high recyclability. This work provides a practical single-cell nanosensor capable of intracellular ATP analysis. More generally, integrated with other split recognition elements, the proposed mechanism could serve as a viable basis for addressing many other important biological species.

An electrochemical aptasensor for ATP based on a configuration-switchable tetrahedral DNA nanostructure

A novel electrochemical aptasensor for ATP was developed based on an aptamer-embedded configuration-switchable tetrahedral DNA nanostructure (TDN) and the formation of a G-quadruplex. This unique TDN was formed through the self-assembly of four specially designed single-stranded DNA (ssDNA) sequences (S1, S2, S3 and S4). The TDN was immobilized on the surface of a Au electrode through the thiol groups at the 5'-end of S1, S2 and S3. Five edges of the TDN were designed to form a double helix to preserve the structural robustness of the tetrahedron, while the ATP aptamer embedded sequence (S3) was designed to be located at the rest edge. The two terminals of S4 at the same edge were composed of two split G-quadruplex-forming sequences, which were non-complementary to the aptamer. This edge offered the configuration-switchable characteristic of the TDN. In the absence of ATP, the TDN remained in a relaxed state, and the G-quadruplex cannot form due to the large distance between the split G-quadruplex-forming sequences. However, in the presence of ATP, the aptamer combined with ATP and shortened the distance between the split sequences, resulting in the taut state of the TDN and the formation of a G-quadruplex at the edge. After the addition of hemin, the differential pulse voltammograms (DPVs) were used to quantify ATP. The sensor revealed a dynamic response range from 0.1 nM to 1 μM, with a detection limit of 50 pM. In addition, the specificity and practicability in real samples were also verified, indicating its potential applications.

Glucose level determination in single cells in their satiety and starvation states using an enzymatic functional glass nanopore

Enzymatic functional glass nanopipettes containing glucose oxidase (GOx) and cytochrome c (Cyt c) were developed for detecting glucose in single cells.