Aptamer-Gated Ion Channel for Ultrasensitive Mucin 1 Detection

Nanochannels with Varied Outer Surface Charges for Protein Discrimination

Solid-state nanochannels with probe modification demonstrate effective spontaneous charge modulation and selective ionic current regulation. Outer-surface functionalization of these nanochannels enables tunable ionic current signals before and after analyte detection. To modulate local charge distributions, we designed sensing nanochannels with significant ion rectification properties for protein detection. In this work, we utilized asymmetrically charged sensing nanochannels with DNA probe modifications to generate abundant ionic current information for multianalyte recognition. During protein detection, DNA probes on the outer surfaces of the nanochannels were competitively replaced by proteins, thereby modulating the local charge distribution. This modulation influences the ionic current through ion rectification, generating cross-reactive and differentiated signals for each target. As a result, the sensing nanochannels with asymmetry of the surface charge effectively discriminate 6 proteins using only one kind of probe. Furthermore, this system successfully distinguished proteins across various concentrations and within complex environments. This work represents a significant advancement in the development of differential sensors based on outer-surface-functionalized nanochannels for multianalyte discrimination.

Concentration Energy Ion Channels with Molecular-Structure Dual Recognition for Sustainable Environmental Monitoring

Pesticides are vital for crop and seafood production but leave persistent residues that pose risks to ecosystems and human health through bioaccumulation. The detection of pesticide residues requires highly sensitive and selective technologies. Herein, a nanochannel sensor capable of dual recognition of ionic charge and molecular conformation based on molecular imprinting technology (MIT) is presented, offering a significant improvement in selectivity and sensitivity over traditional nanopore sensors. The MIT-based nanochannels with imprinting sites tailored to pesticide molecules go beyond recognizing the molecular size and surface functional groups, enabling the detection of molecular configurations. In this research, the approach enables the detection of 10 pesticide molecules with detection limits (LODs) ranging from 12.9 to 26.9 pM, achieving two orders of magnitude lower than fluorescence-based methods. Density functional theory (DFT) and molecular dynamics (MD) simulations revealed hydrogen bonding as the dominant interaction in the imprinting process. This versatile nanochannel construction method, proposed for the first time, provides dual recognition capabilities and is expected to advance nanochannel sensing while promoting sustainable environmental development.

Multiplexed Detection of Pancreatic-Specific Nucleic Acids and Protein Biomarkers Using a Logic Nanofluidic Platform

Early detection of pancreatic cancer is vital for patient survival. However, current diagnostic approaches remain constrained by insufficient precision and specificity inherent to single-biomarker detection strategies. Herein, we develop a nanochannel biosensing platform implementing cooperative dual-signal detection of pancreatic-specific biomarkers CA19-9 and miRNA-196a. Using liquid-liquid interface self-assembly, we constructed anodic aluminum oxide (AAO)-Au hybrid nanochannels integrated with a surface-modified double-key DNA nanolock (DDN). The conformational switch of DDN logic gating triggered by miRNA-196a exposes the CA19-9-aptamer, enabling specific target recognition and consequent ion current signal attenuation. Simultaneously, released miRNA-196a is quantified by catalytic hairpin assembly and hybridization chain reaction-mediated cascade amplification. Experiments show that the present DDN-based logic nanofluidic platform could achieve an ultralow detection limit of 0.000027 U·mL-1 for CA19-9 and 4.74 aM for miRNA-196a, which is 2-3 orders of magnitude higher than traditional ELISA/qPCR methods. Finally, clinical sample analysis confirms the high specificity of this platform in distinguishing pancreatic cancer and acute pancreatitis from healthy individuals. This DDN-functionalized nanofluidic biosensor provides valuable insights into designing precision detection platforms for pancreatic cancer, highlighting its significant potential for clinical diagnostics.

Using Regular Porous Membrane-Based Blood-Brain Barrier Model to Screen Brain-Targeted Drugs with Nanochannel Electrochemistry

Constructing in vitro blood-brain barrier (BBB) model provides an innovative approach for studying the pathophysiology of the brain and screening drugs. Although commercial Transwell was the simplest and most widely utilized in vitro model, reasonably mimicking essential characteristics of human BBB and dynamic monitoring BBB function remain a challenge. Herein, inspired by the highly permeable extracellular matrix membrane in human BBB, a novel in vitro BBB model was established by combining functionalized anodic alumina oxide (AAO) membrane with nanochannel electrochemistry (ANE-BBB). Benefiting from the topographical nanostructures and modified cell-adhesive peptide on the AAO surface, a tight endothelial barrier was formed, which can be directly visualized by phase-contrast microscope, and the barrier function can be real time monitored by nanochannel electrochemistry. More importantly, according to the current signal induced by the diffusion of redox species through the nanochannels toward the underlying electrode surface, dynamic evaluation of BBB-crossing behavior and precise screening of brain-targeted nanodrugs can be achieved. The constructed ANE-BBB overcomes the shortcomings of invisible cell culture, low permeability, and inaccurate real-time monitoring of screening drugs in traditional Transwell and provides a reliable tool for the design of nanodrugs to the central nervous system.

Detection of Analytes with the Outer Surface of Solid-State Nanochannels: From pm to μm

Accurately simulating or sensitively monitoring specific substances, such as ions, molecules, and proteins in the life process, is essential for gaining a fundamental comprehension of the underlying biological mechanism, which has been a trending topic for many years. Solid-state nanochannels, inspired by biological ion channels, have been developed for decades and have achieved significant success, representing the forefront of the interdisciplinary fields of bioanalytical chemistry and nanotechnology. Typically, solid-state nanochannels with a pore size of less than 100 nm are selected to construct nanochannel-based biosensors, which can be an excellent platform to analyze small analytes, such as ions and small molecules, in a restricted space and simulate the intricate process of ion transport in living organisms. Furthermore, by integrating functional components that are termed probes into artificial devices, the nanochannel system has emerged as a remarkable tool for label-free and highly sensitive detection in practical applications. Nonetheless, the detection of large substances (more than nanoscale in size) has consistently posed a significant challenge, since previous research on solid-state nanochannels has mainly concentrated on the contribution of probes at the inner wall, which requires the biotargets to enter the nanochannel for successful detection. Moreover, the lack of testing techniques for the chemical and physical properties of probes anchored deep inside confined nanochannels results in an unclear working mechanism, which is another issue that cannot be ignored. The requirement for a more efficient and extensive detection platform has spurred an in-depth study of nanochannels, which provides innovative insight concentrating on the less restricted space on the outer surface (OS) of nanochannels and the probes at the OS (POS).In this Account, several approaches to constructing the OS and modifying POS are briefly summarized. Subsequently, ultrasensitive detection of analytes across a range of sizes, encompassing not only the ions and small molecules from ∼100 pm to ∼2 nm but also the large substances from ∼2 nm to ∼20 μm through the use of POS in the last five years, is introduced. Through the characterization of OS and the precise control of POS, the sensing mechanism, including surface charge and wettability, with POS is discussed unambiguously. Additionally, an intelligent model using dual-signal responses such as electrical and optical to enhance the responsiveness and accuracy of quantitative analysis is discussed, which can distinguish the conformation of an analyte by the exposed single cysteine thiol group. We expect that this timely Account will offer instructive insights into the development of a nanochannel-based platform to facilitate the analysis of biomolecules of varying sizes.

Machine Learning Assisted Nanofluidic Array for Multiprotein Detection

Solid-state nanopore and nanochannel biosensors have revolutionized protein detection by offering label-free, highly sensitive analyses. Traditional sensing systems (1st and 2nd stages) primarily focus on inner wall (IW) interactions, facing challenges such as complex preparation processes, variable protein entry angles, and conformational changes, leading to irregular detection events. To address these limitations, recent advancements (3rd stage) have shifted toward outer surface (OS) functionalization but are constrained by single-protein recognition models. Herein, we show a machine learning assisted nanofluidic array (MANY) sensing system (4th stage) that integrates a supervised dimensionality reduction strategy with photoresponsive MoS2 nanofluidic array functionalized with nonspecific functional elements (FEarray) at the OS. This approach serves as a proof-of-concept for label-free, probe-free detection of multiple proteins with 100% accuracy, highlighting its significant potential for rapid diagnostics in future disease detection applications.

Dual-functional probe for sensitive detection of MCF-7 cells and mendelian randomization analysis of MUC1 association with multiple cancers

The present study successfully developed a method based on a dual-functional probe for detecting breast cancer cells MCF-7 by recognizing the MUC1 protein on the cell surface. This method integrated inductively coupled plasma mass spectrometry (ICP-MS) and fluorescence imaging technology, enhancing the sensitivity, specificity, and accuracy of breast cancer cell detection. Additionally, through two-sample Mendelian randomization (MR) analysis, we verified a potential correlation between breast cancer and MUC1 (PIVW<0.05), while also proving no potential correlation between liver cancer and MUC1 (PIVW>0.05). Furthermore, this study explored the relationship between other cancers and MUC1, indicating a potential correlation between ovarian cancer and colorectal cancer with MUC1 (PIVW<0.05). In summary, this study provides new strategies for the early diagnosis and treatment of breast cancer and offers new insights into the potential of MUC1 as a biomarker for the detection of other cancers.

Influence of crosslinker on aptamer immobilization and aptasensor sensing response for non-metallic surfaces

Aptasensors transduce the specific binding of the target biomolecules with an aptamer into a measurable signal and enable rapid detection of biomolecules. Aptamer immobilization on the sensing surface through covalent bonding is preferred as it ensures stable and repeatable attachment of the aptamers in the desired configuration. Previous sensing reports have utilized homo-bifunctional crosslinkers like glutaraldehyde to immobilize aptamers to amine-terminated surfaces, but the efficacy of attachment chemistries and their influence on sensor response have not been evaluated. Here, we compare sensing and immobilization density results for four separate crosslinkers - one homo-bifunctional and three hetero-bifunctional - to immobilize the Ebola soluble Glycoprotein (sGP) binding DNA aptamer on the amine-terminated non-metallic surfaces - nanoporous anodized alumina oxide (NAAO) membranes and polystyrene beads. In each case, the aptamer-functionalized NAAO membranes were exposed to a range of Ebola virus sGP concentrations to obtain sensing responses. Measured sensing responses were fit to the Langmuir-Hill's equation. The maximum possible sensor response, Fmax, obtained for each attachment chemistry is compared to determine the effectiveness of the different attachment chemistries. We also used crosslinkers to attach radiolabeled aptamers to amine modified polystyrene particles to determine the attachment efficiency based on the acquired aptamer density on the particle for each crosslinker. Sensing and attachment efficiency results show that aptamer attachment on the sensor surface using a homo-bifunctional crosslinker led to inconsistent sensing response for sensing of sGP across experiments and lower aptamer densities on polystyrene particles. In contrast, the results from aptasensors with aptamers attached through hetero-bifunctional crosslinkers provided consistent sensing responses across experiments and higher aptamer densities on the surface.

In situ noninvasive monitoring of cell secretions based on MOFs/AAO hybrid membrane induced asymmetric ion transport

Nanofluidic hybrid membranes display distinct ionic current rectification (ICR) properties and provide high surface area for immobilizing probes on the outer surface, exhibiting great potential in detection of biomolecules. Herein, we fabricated MOFs/AAO hybrid membrane with aptamers functionalized on the outer surface for in situ detection of living cells released secretions. TNF-α (a small molecular protein secreted by macrophages) was used as a model. After TNF-α was specifically captured by aptamers on the membrane surface, the asymmetry of surface charge on the hybrid membrane was amplified, the ICR was increased from 3.89 to 18.85. According to the ICR change, TNF-α was sensitively measured with a detection limit of ∼0.49 pM, which was significantly lower than other reported methods. When the hybrid membrane was clamped in the middle of self-made device, PET membrane incubated macrophages was rolled up and inserted into the chamber to mimic cellular microenvironment. Macrophages released TNF-α could be real time monitored with ionic current, macrophages and normal cells could be effectively distinguished according to the released TNF-α level. Thus, we proposed a nanofluidic platform for accurately measuring cell secretions in an engineered cellular microenvironment with a direct manner, without the need for labels or amplification steps.

MicroRNA Triggered Dimerization of DNA Tetrahedron for Enhanced Biosensing Performance of Solid-State Nanochannels Functionalized with MoS2 Nanosheets

Solid-state nanochannels (SSN) have great development potential as a biosensing interface. The integration of two-dimensional nanomaterials with nanochannels endows SSN with diverse properties, including distinguishing DNA nanostructures. In this study, by modifying MoS2 nanosheets, the outer surface of SSN could be endowed with robust adsorption properties for single-stranded DNA. Therefore, DNA tetrahedrons connected with single-stranded DNA could remain on the SSN surface, whereas DNA tetrahedron dimers with full double-stranded structures formed by the presence of target microRNA cannot be retained on the surface of nanochannels. The change in the DNA nanostructure generated by the target recognition process could cause variations of steric hindrance and electrostatic repulsion on the surface of the SSN. The variations were reflected by the free diffusion flux of [Fe(CN)6]3-. Then, the sensitive electrochemical detection method for microRNA was established, and the detection limit of the method for microRNA-31 was as low as 0.5 fM. The study provided a promising approach for the ultrasensitive detection of biomarkers, thereby offering potential means for early diagnosis of the related diseases.

Superassembled Mesoporous Carbon-Fe2O3 Heterochannels for Photothermal-Enhanced Hyaluronidase Sensing

Developing an activity detection platform for hyaluronidase (HAase) is crucial for diagnosing and treating cancer. However, traditional detection of HAase is based on changes in the flow rate caused by viscosity or requires complex modifications and processing, which limits the detection accuracy and sensitivity. Herein, hyaluronic acid (HA)-modified mesoporous-based heterochannels (mesoporous carbon-doped γ-Fe2O3 nanoparticles/anodized aluminum oxide, MC-γ-Fe2O3/AAO) featuring ordered 3D transport frameworks and a photothermal property were developed for high performance HAase detection. The HA molecules on the surface of the mesoporous layer provide abundant active sites for HAase detection. An improved ionic current was realized after enzymatic hydrolysis reactions between HA and HAase due to enhanced surface charges and more hydrophilicity, leading to highly sensitive and accurate HAase detection. Notably, the detection performance can be further upgraded with the assistance of the photothermal property of γ-Fe2O3. An amplified detection current signal was achieved owing to a synergistic effect between ion currents and photoresponsive currents. A wide linear detection range from 1 to 50 U/mL and a low detection limit of 0.348 U/mL were obtained, achieving a 2% improvement under illumination. Importantly, the heterochannels have also been successfully applied for HAase detection in fetal bovine serum samples, manifesting considerable application prospects. This work provides a new strategy in constructing photoresponsive nanochannels with a photothermal property for a highly efficient biosensing platform.

Super-assembled periodic mesoporous organosilica membranes with hierarchical channels for efficient glutathione sensing

Bioinspired nanochannel-based sensors have elicited significant interest because of their excellent sensing performance, and robust mechanical and tunable chemical properties. However, the existing designs face limitations due to material constraints, which hamper broader application possibilities. Herein, a heteromembrane system composed of a periodic mesoporous organosilica (PMO) layer with three-dimensional (3D) network nanochannels is constructed for glutathione (GSH) detection. The unique hierarchical pore architecture provides a large surface area, abundant reaction sites and plentiful interconnected pathways for rapid ionic transport, contributing to efficient and sensitive detection. Moreover, the thioether groups in nanochannels can be selectively cleaved by GSH to generate hydrophilic thiol groups. Benefiting from the increased hydrophilic surface, the proposed sensor achieves efficient GSH detection with a detection limit of 1.2 μM by monitoring the transmembrane ionic current and shows good recovery ranges in fetal bovine serum sample detection. This work paves an avenue for designing and fabricating nanofluidic sensing systems for practical and biosensing applications.

Polyoxometalate-based plasmonic electron sponge membrane for nanofluidic osmotic energy conversion

Nanofluidic membranes have demonstrated great potential in harvesting osmotic energy. However, the output power densities are usually hampered by insufficient membrane permselectivity. Herein, we design a polyoxometalates (POMs)-based nanofluidic plasmonic electron sponge membrane (PESM) for highly efficient osmotic energy conversion. Under light irradiation, hot electrons are generated on Au NPs surface and then transferred and stored in POMs electron sponges, while hot holes are consumed by water. The stored hot electrons in POMs increase the charge density and hydrophilicity of PESM, resulting in significantly improved permselectivity for high-performance osmotic energy conversion. In addition, the unique ionic current rectification (ICR) property of the prepared nanofluidic PESM inhibits ion concentration polarization effectively, which could further improve its permselectivity. Under light with 500-fold NaCl gradient, the maximum output power density of the prepared PESM reaches 70.4 W m-2, which is further enhanced even to 102.1 W m-2 by changing the ligand to P5W30. This work highlights the crucial roles of plasmonic electron sponge for tailoring the surface charge, modulating ion transport dynamics, and improving the performance of nanofluidic osmotic energy conversion.

Pore-Size-Dependent Role of Functional Elements at the Outer Surface and Inner Wall in Single-Nanochannel Biosensors

Biological nanopores feature functional elements on the outer surfaces (FEOS) and inner walls (FEIW), enabling precise control over ions and molecules with exceptional sensitivity and specificity. This provides valuable inspiration to scientists for the development of intelligent artificial nanochannel-based platforms, with a wide range of potential applications, including biosensors. Much effort has been dedicated to investigating the distinct contribution of FEOS and FEIW of multichannel membrane biosensors. However, the intricate interactions among neighboring pores in multichannel biosensors have presented challenges. This underscores the untapped potential of single nanochannels as ideal candidates in this field. Here, we employed single nanochannel membranes with different pore sizes to investigate the distinct contributions of FEIW and FEOS to single-nanochannel biosensors, combined with numerical simulations. Our findings revealed that alterations in the negative charges of FEIW and FEOS, induced by target binding, have differential effects on ion transport, contingent upon the degree of nanoconfinement. In the case of smaller pores, such as 20 nm, the ion concentration polarization driven by FEIW can independently control ion transport through the surface's electric double layer. However, as the pore size increases to 40-60 nm, both FEIW and FEOS become essential for effective ion concentration polarization. When the pore size reaches 100 nm, both FEIW and FEOS are ineffective and thus unsuitable for biosensors. Simulations demonstrate that the observed phenomena can be attributed to the interactions between the charges of FEIW and FEOS within the overlapping electric double layer under confinement. These results underscore the critical role of pore size as a key parameter in governing the functionality of probes within or on nanopore-based biosensors as well as in the design of nanopore-based devices.

2,5-Thiophenedicarboxylic Acid Bridging Hexameric CeIII-Substituted Selenotungstate and Its Application for Detecting Mucin 1

The development of polyoxometalate chemistry not only is derived from the continuous discovery of novel polyoxometalates (POMs) but also stems from the exploitation of their new functionalities. In this work, we obtained a rigid sulfur-containing heterocyclic ligand-linking aggregate [N(CH3)4]10Na6H6[Ce8(H2O)26W8(HTDA)2(TDA)2O20][SeW4O18]2[SeW9O33]4·112H2O (1) (H2TDA = 2,5-thiophenedicarboxylic acid). Its polyanionic unit consists of one [Ce4(H2O)13W4O10(HTDA)(TDA)O10]18+ cluster and two kinds of Keggin-type [SeW4O18] and [SeW9O33] segments. It is noteworthy that H2TDA ligands not only work as connectors to link two symmetrical {[Ce4(H2O)13W4(HTDA)(TDA)O10][SeW4O18][SeW9O33]2}11- units but also function as ornaments to graft to the polyanionic backbone. Furthermore, 1 and 3,4-ethylenedioxythiophene (EDOT) were deposited on the glassy carbon electrode (GCE) by the electropolymerization (EPM) method, resulting in a 1-poly(3,4-ethylenedioxythiophene) (1-PEDOT) composite film, which can provide sufficient binding sites to immobilize Au nanoparticles (Au NPs). Hereafter, the Au NPs-immobilized 1-PEDOT modified electrode (Au/1-PEDOT/GCE) was used to construct an electrochemical aptasensor to detect mucin 1, showing a low detection limit of 29.5 fM in the Tris solution. This work not only demonstrates that rigid heterocyclic ligands are beneficial for the creation of novel rare-earth-substituted selenotungstate hybrids but also provides more enlightenment for POM-based materials used for electrochemical detection of cancer markers.

Aptamer-Functionalized Interface Nanopores Enable Amino Acid-Specific Peptide Detection

Single-molecule proteomics based on nanopore technology has made significant advances in recent years. However, to achieve nanopore sensing with single amino acid resolution, several bottlenecks must be tackled: controlling nanopore sizes with nanoscale precision and slowing molecular translocation events. Herein, we address these challenges by integrating amino acid-specific DNA aptamers into interface nanopores with dynamically tunable pore sizes. A phenylalanine aptamer was used as a proof-of-concept: aptamer recognition of phenylalanine moieties led to the retention of specific peptides, slowing translocation speeds. Importantly, while phenylalanine aptamers were isolated against the free amino acid, the aptamers were determined to recognize the combination of the benzyl or phenyl and the carbonyl group in the peptide backbone, enabling binding to specific phenylalanine-containing peptides. We decoupled specific binding between aptamers and phenylalanine-containing peptides from nonspecific interactions (e.g., electrostatics and hydrophobic interactions) using optical waveguide lightmode spectroscopy. Aptamer-modified interface nanopores differentiated peptides containing phenylalanine vs. control peptides with structurally similar amino acids (i.e., tyrosine and tryptophan). When the duration of aptamer-target interactions inside the nanopore were prolonged by lowering the applied voltage, discrete ionic current levels with repetitive motifs were observed. Such reoccurring signatures in the measured signal suggest that the proposed method has the possibility to resolve amino acid-specific aptamer recognition, a step toward single-molecule proteomics.

Diverse applications and development of aptamer detection technology

Aptamers have received extensive attention in recent years because of their advantages of high specificity, high sensitivity and low immunogenicity. Aptamers can perform almost all functions of antibodies through the combination of spatial structure and target, which are called "chemical antibodies". At present, aptamers have been widely used in cell imaging, new drug development, disease treatment, microbial detection and other fields. Due to the diversity of modifications, aptamers can be combined with different detection technologies to construct aptasensors. This review focuses on the diversity of aptamers in the field of detection and the development of aptamer-based detection technology and proposes new challenges for aptamers in this field.

Solid-state nanochannels for bio-marker analysis

Bio-markers, such as ions, small molecules, nucleic acids, peptides, proteins and cells, participate in the construction of living organisms and play important roles in biological processes. It is of great significance to accurately detect these bio-markers for studying their basic functions, the development of molecular diagnosis and to better understand life processes. Solid-state nanochannel-based sensing systems have been demonstrated for the detection of bio-markers, due to their rapid, label-free and high-throughput screening, with high sensitivity and specificity. Generally, studies on solid-state nanochannels have focused on probes on the inner-wall (PIW), ignoring probes on the outer-surface (POS). As a result, the direct detection of cells is difficult to realize by these inner-wall focused nanochannels. Moreover, the sensitivity for detecting ions, small molecules, nucleic acids, peptides and proteins requires further improvement. Recent research has focused on artificial solid-state nanochannels with POS, which have demonstrated the ability to independently regulate ion transport. This design not only contributes to the in situ detection of large analytes, such as cells, but also provides promising opportunities for ultra-high sensitivity detection with a clear mechanism. In this tutorial review, we present an overview of the detection principle used for solid-state nanochannels, inner-wall focused nanochannels and outer-surface focused nanochannels. Furthermore, we discuss the remaining challenges faced by current nanochannel technologies and provide insights into their prospects.

Modular DNA Tetrahedron Nanomachine-Guided Dual-Responsive Hybridization Chain Reactions for Discernible Bivariate Assay and Cell Imaging

Engineering of multivariate biosensing and imaging platforms involved in disease plays a vital role in effectively discerning cancer cells from normal cells and facilitating reliable targeted therapy. Multiple biomarkers such as mucin 1 (MUC1) and nucleolin are typically overexpressed in breast cancer cells compared to normal human breast epithelium cells. Motivated by this knowledge, a dual-responsive DNA tetrahedron nanomachine (drDT-NM) is constructed through immobilizing two recognition modules, MUC1 aptamer (MA) and a hairpin H1* encoding nucleolin-specific G-rich AS1411 aptamer, in two separate vertexes of a functional DT architecture tethering two localized pendants (P^M and P^N). When drDT-NM identifiably binds bivariate MUC1 and nucleolin, two independent hybridization chain reactions (HCR^M and HCR^N) as amplification modules are initiated with two sets of four functional hairpin reactants. Among them, one hairpin for HCR^M is dually ended by fluorescein and quencher BHQ1 to sense MUC1. The responsiveness of nucleolin is executed by operating HCR^N utilizing another two hairpins programmed with two pairs of AS1411 splits. In the shared HCR^N duplex products, the parent AS1411 aptamers are cooperatively merged and folded into G-quadruplex concatemers to embed Zn-protoporphyrin IX (ZnPPIX/G4) for fluorescence signaling readout, thereby achieving a highly sensitive intracellular assay and discernible cell imaging. The tandem ZnPPIX/G4 unities also act as imaging agents and therapeutic cargos for efficient photodynamic therapy of cancer cells. Based on drDT-NM to guide bispecific HCR amplifiers for adaptive bivariate detection, we present a paradigm of exquisitely integrating modular DNA nanostructures with nonenzymatic nucleic acid amplification, thus creating a versatile biosensing platform as a promising candidate for accurate assay, discernible cell imaging, and targeted therapy.

A multi-channel responsive AuNP@COF core-shell nanoprobe for simultaneous subcellular profiling of multiple cancer biomarkers

The abnormal change in the expression profile of multiple cancer biomarkers is closely related to tumor progression and therapeutic effect. Due to their low abundance in living cells and the limitations of existing imaging techniques, simultaneous imaging of multiple cancer biomarkers has remained a significant challenge. Here, we proposed a multi-modal imaging strategy to detect the correlated expression of multiple cancer biomarkers, MUC1, microRNA-21 (miRNA-21) and reactive oxygen (ROS) in living cells, based on a porous covalent organic framework (COF) wrapped gold nanoparticles (AuNPs) core-shell nanoprobe. The nanoprobe is functionalized with Cy5-labeled MUC1 aptamer, a ROS-responsive molecule (2-MHQ), and a miRNA-21-response hairpin DNA tagged by FITC as the reporters for different biomarkers. The target-specific recognition can induce the orthogonal molecular change of these reporters, producing fluorescence and Raman signals for imaging the expression profiles of membrane MUC1 (red fluorescence channel), intracellular miRNA-21 (green fluorescence channel), and intracellular ROS (SERS channel). We further demonstrate the capability of the cooperative expression of these biomarkers, along with the activation of NF-κB pathway. Our research provides a robust platform for imaging multiple cancer biomarkers, with broad potential applications in cancer clinical diagnosis and drug discovery.

Super-assembled mesoporous thin films with asymmetric nanofluidic channels for sensitive and reversible electrical sensing

Bioinspired artificial nanochannels have emerged as promising candidates for developing smart nanofluidic sensors due to their highly controllable size and surface functionality. However, little attention has been paid to the role of the outer surface of the nanochannels in enhancing the detection sensitivity. Herein, an asymmetric nanochannel-based responsive detection platform with ultrathin tannic acid modified mesoporous silica (TA-MS) layer and alumina oxide (AAO) thin film is prepared through super-assembly strategy. The functional TA-MS outer surface layer provides abundant phenolic groups on the nanochannels for ions and molecules transport, which paves the way for the development of heterochannels for label-free, reversible and highly sensitive dopamine (DA) detection based off of cation displacement effect. Notably, by engineering optimal thickness of the TA-MS, the sensing performance can be further improved. After optimization, the linear response ranges for DA detection are 0.001-1 μM, 1-10 μM and 10-200 μM with the detection limit of 0.1 nM. The prepared sensor exhibits stable reversibility after several detection cycles. In addition, this method was successfully applied for DA detection in fetal bovine serum sample. Theoretical calculations further prove the detection mechanism. This work opens a new horizon of using mesoporous materials to construct nanofluidic sensors for ultrasensitive small molecule detection and recognition.

Microstructured Optical Fiber-Enhanced Light-Matter Interaction Enables Highly Sensitive Exosome-Based Liquid Biopsy of Breast Cancer

Exosome-based liquid biopsies highlight potential utility in diagnosis and determining the prognosis of patients with cancer and other diseases. However, the existing techniques are severely limited for practical applications due to the complications of high cost, low sensitivity, tedious procedures, and large sample consumption. Herein, we report a microstructured optical fiber sensor for fast, sensitive, and accurate quantification of exosomes in blood samples of breast cancer patients. Numerical simulations are applied to demonstrate that hollow-core microstructured antiresonant fibers (HARFs) can stringently confine light in the fiber core, ensuring strong light-matter interaction and thus maximumly amplifying the signal. Taking this advantage, a AuNPs-dsDNA assembly containing gold nanoparticles, a recognizing DNA aptamer, and a fluorescent reporter DNA sequence is fabricated followed by immobilization on the fiber wall to form a AuNPs-dsDNA-HARF sensor. Cancer-derived exosomes can be recognized and captured in the fiber channel and generate dose-dependent fluorescent signals for quantification. The microfiber sensor demonstrates enhanced sensitivity and specificity, enabling the detection of single digits of exosome particles at the nanoliter sample level. In addition, by tracking exosome phenotypic changes, the proposed fiber sensor can facilitate precise drug treatment monitoring. This work provides a robust platform for exosome-based biopsy for cancer diagnosis and prediction of therapeutic outcomes.

Ultrasensitive dual-signal electrochemical ratiometric aptasensor based on Co-MOFs with intrinsic self-calibration property for Mucin 1

The concentration of tumor biomarker Mucin 1 (MUC 1) is highly related with many diseases, which can be employed for the early diagnosis of cancer. In this paper, an electrochemical ratiometric aptasensor with intrinsic self-calibration property for the detection of MUC 1 is presented. In this paper, Co-MOFs themselves were employed as signal substances. This strategy was fabricated by using gold nanoparticles@black phosphorus (BP) as the substrate on the electrode, followed by modification of DNA nanotetrahedrons (DTN) via Au-S bond. The terminal of DTN contains MUC 1 aptamer. In the presence of MUC 1, the signal of DNA-labeled Co-MOFs can be detected. The current signal of Co-MOFs increased and that of thionine (as reference) was unchanged upon the addition of MUC 1. Thus, an intrinsic self-calibration aptasensor was achieved. In order to simplify the modification procedure, the electrolyte solution thionine was employed as an inner reference probe. Moreover, coupling of the hybridization chain reaction (HCR) with these MOFs signal tags presents an enzyme-free method for signal amplification, endowing the proposed ratiometric biosensor detection with high reproducibility and high sensitivity. The current ratio (I_IR/I_SP) remained stable over 30 individual measurements performed on ten different working electrodes. Even ten repeated scans performed on a single electrode exhibited a constant current ratio. The electrochemical ratiometric aptasensor is highly sensitivity for MUC 1 with the detection limit of 1.34 fM. Our proposed ratiometric sensor has great potential for the detection of cancer-related biomarkers.

Electrostatic-Gated Kinetics of Rapid Ion Transfers at a Nano-liquid/Liquid Interface

Charge (ion and electron)-transfer reactions at a liquid/liquid interface are critical processes in many important biological and chemical systems. An ion-transfer (IT) process is usually very fast, making it difficult to accurately measure its kinetic parameters. Nano-liquid/liquid interfaces supported at nanopipettes are advantageous approaches to study the kinetics of such ultrafast IT processes due to their high mass transport rate. However, correct measurements of IT kinetic parameters at nanointerfaces supported at nanopipettes are inhibited by a lack of knowledge of the nanometer-sized interface geometry, influence of the electric double layer, wall charge polarity, etc. Herein, we propose a new electrochemical characterization equation for nanopipettes and make a suggestion on the shape of a nano-water/1,2-dichloroethane (nano-W/DCE) interface based on the characterization and calculation results. A theoretical model based on the Poisson-Nernst-Planck equation was applied to systematically study how the electric double layer influences the IT process of cations (TMA⁺, TEA⁺, TPrA⁺, ACh⁺) and anions (ClO₄^-, SCN^-, PF₆^-, BF₄^-) at the nano-W/DCE interface. The relationships between the wall charge conditions and distribution of concentration and potential inside the nanopipette revealed that the measured standard rate constant (k⁰) was enhanced when the polarity of the ionic species was opposite to the pipette wall charge and reduced when the same. This work lays the right foundation to obtain the kinetics at the nano-liquid/liquid interfaces.

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

Grafting specific recognition moieties onto solid-state nanofluidic channels is a promising way for selective and sensitive sensing of analytes. However, the time-consuming interaction between recognition moieties and analytes is the main hindrance to the application of nanofluidic channel-based sensors in rapid detection. Here, we show the integration of ordered two-dimensional covalent organic frameworks (2D COFs) to solid-state nanofluidic channels to achieve rapid, selective, and sensitive detection of contaminants. As a proof of concept, a thiourea-linked 2D COF (JNU-3) as the recognition unit is covalently bonded on the stable artificial anodic aluminum oxide nanochannels (AAO) to fabricate a JNU-3@AAO-based nanofluidic sensor. The rapid and selective interaction of Hg(II) with the highly ordered channels of JNU-3 allows the JNU-3@AAO-based nanofluidic sensor to realize ultrafast and precise determination of Hg(II) (90 s) with a low limit of detection (3.28 fg mL^-1), wide linear range (0.01-100 pg mL^-1), and good precision (relative standard deviation of 3.8% for 11 replicate determination of 10 pg mL^-1). The developed method was successfully applied to the determination of mercury in a certified reference material A072301c (rice powder), real water, and rice samples with recoveries of 90.4-99.8%. This work reveals the great potential of 2D COFs-modified solid-state nanofluidic channels as a sensor for the rapid and precise detection of contaminants in complicated samples.

Tetrahedral DNA Nanostructure with Multiple Target-Recognition Domains for Ultrasensitive Electrochemical Detection of Mucin 1

In this work, a tetrahedral DNA nanostructure (TDN) designed with multiple biomolecular recognition domains (m-TDN) was assembled to construct an ultrasensitive electrochemical biosensor for the quantitative detection of tumor-associated mucin 1 (MUC-1) protein. This new nanostructure not only effectively increased the capture efficiency of target proteins compared to the traditional TDN with a single recognition domain but also enhanced the sensitivity of the constructed electrochemical biosensors. Once the target MUC-1 was captured by the protein aptamers, the ferrocene-marked DNA strands as electrochemical signal probes at the vertices of m-TDN would be released away from the electrode surface, causing significant reduction of the electrochemical signal, thereby enhancing significantly the detection sensitivity. As a result, this well-designed biosensor achieved ultrasensitive detection of the biomolecule at a linear range from 1 fg mL^-1 to 1 ng mL^-1, with the limit of detection down to 0.31 fg mL^-1. This strategy provides a new approach to enhance the detection sensitivity for the diagnosis of diseases.

Cell Surface Transporters and Novel Drug Developments

Despite the numerous scientific and technological advances made within the last decade the attrition rates for new drug discovery remain as high as 95% for anticancer drugs. Recent drug development has been in part guided by Lipinski's Rule of 5 (Ro5) even though many approved drugs do not comply to these rules. With Covid-19 vaccine development strategy dramatically accelerating drug development perhaps it is timely to question the generic drug development process itself to find a more efficient, cost effective, and successful approach. It is widely believed that drugs permeate cells via two methods: phospholipid bilayer diffusion and carrier mediated transporters. However, emerging evidence suggests that carrier mediated transport may be the primary mechanism of drug uptake and not diffusion as long believed. Computational biology increasingly assists drug design to achieve desirable absorption, distribution, metabolism, elimination and toxicity (ADMET) properties. Perfecting drug entry into target cells as a prerequisite to intracellular drug action is a logical and compelling route and is expected to reduce drug attrition rates, particularly gaining favour amongst chronic lifelong therapeutics. Novel drug development is rapidly expanding from the utilisation of beyond the rule of five (bRo5) to pulsatile drug delivery systems and fragment based drug design. Utilising transporters as drug targets and advocating bRo5 molecules may be the solution to increasing drug specificity, reducing dosage and toxicity and thus revolutionising drug development. This review explores the development of cell surface transporter exploitation in drug development and the relationship with improved therapeutic index.

Ferrofluids transport in bioinspired nanochannels: Application to electrochemical biosensing with magnetic-controlled detection

Controllable transport of ions, molecules or fluids in bioinspired nanochannels is crucial to study biointeraction occurred in confined space and also develop biosensing platforms or devices. Herein, ferrofluids transport in biofunctionalized nanochannels was investigated and a novel electrochemical biosensing platform with the characteristic of label-free, high sensitivity and rapid response was constructed. The hydrophilic ferrofluids can flux swiftly through the antibody-immobilized nanochannels with the assistance of a permanent magnet. It was initially found that the presence of ferrofluids would depress the redox current of the electrochemical probe [Fe(CN)₆]^3-. The mechanism of the depressing effect was ascribed to the constrained diffusion of [Fe(CN)₆]^3- which lowered the concentration of it at the electrode surface and the weak adsorption of the ferrofluids which increased the charge transfer resistance of the interface. Therefore, redox current of the probe was applied to indicate the amount of the ferrofluids fluxing through the bioinspired nanochannels. The steric hindrance of the bioinspired nanochannels changed with the amount of the corresponding target being incubated, resulting in quantitative variation of the redox current. In this way, electrochemical biosensing platform based on ferrofluids transport was constructed. Using carbohydrate antigen 153 (CA153) as a model target, a low detection limit of 0.0013 U·mL^-1 was acquired. This magnetic-controlled bioelectrochemical platform was expected to be expanded to other applications such as genetic testing, drug analysis, and molecular identification.

Locally superengineered cascade recognition–quantification zones in nanochannels for sensitive enantiomer identification

As an intriguing and intrinsic feature of life, chirality is highly associated with many significant biological processes. Simultaneous recognition and quantification of enantiomers remains a major challenge. Here, a sensitive enantiomer identification device is developed on TiO₂ nanochannels via the design of cascade recognition–quantification zones along the nanochannels. In this system, β-cyclodextrin (β-CD) is self-assembled on one side of the nanochannels for the selective recognition of enantiomers; CuMOFs are designed as the target-responsive partners on the other side of the nanochannels for the quantification of enantiomers that pass through the nanochannels. As a proof-of-principle of the cascade design, arginine (Arg) enantiomers are tested as the identification targets. The l-Arg molecules selectively bind in the recognition zone; d-Arg molecules pass through the recognition zone and then interact with the quantification zone via a specialized reduction reaction. As verified by nanofluidic simulations, because of the confinement effect of nanoscale channels combined with the condensation effect of porous structure, the in situ reaction in the quantification zone contributes to an unprecedented variation in transmembrane K⁺ flux, leading to an improved identification signal. This novel cascade-zone nanochannel membrane provides a smart strategy to design multifunctional nanofluidic devices.

A design of the cascade recognition–quantification zone is developed along TiO₂ nanochannels. The asymmetric nanochannels exhibit a predominant sensitivity and selectivity for enantiomer discrimination.

Interfacially Super-Assembled Tyramine-Modified Mesoporous Silica-Alumina Oxide Heterochannels for Label-Free Tyrosinase Detection

Tyrosinase (TYR) is a multifunctional copper-containing enzyme that plays a critical role in the biosynthetic pathway of melanin. Thus, the detection of TYR activity possesses vast importance from clinical diagnosis to the food industry. However, most TYR detection methods are expensive, complicated, and time-consuming. Herein, a functional nanofluidic heterochannel composed of an ultrathin tyramine-modified mesoporous silica layer (Tyr-MS) and alumina oxide (AAO) arrays is constructed by an interfacial super-assembly method. The heterochannel with plenty of enzyme catalytic sites for TYR provides the response of the ion current signal against TYR concentrations. Introducing enzymatic reaction paves the way for the heterochannel to achieve label-free, selective, specific detection of TYR. Notably, a highly sensitive detection of TYR with a limit of 2 U mL^-1 was obtained by optimizing the modified conditions. Detailed investigations and theoretical calculations further reveal the mechanism for the detection performance. This work provides a simple, low-cost, quick response, and label-free platform based on functional nanofluidic devices for enzyme-sensing technologies.

MUC1 detection and in situ imaging method based on aptamer conformational switch and hybridization chain reaction

Mucin 1 (MUC1) overexpression in tumor cells is related to various cancers, including breast, stomach, and lung cancer. MUC1 detection and imaging are important for cancer localization in tissue sections to support histopathological diagnosis. In this study, we developed a simple, enzyme-free MUC1 detection and in situ imaging method. Three hairpin probes, Apt-trigger, HP1-FAM, and HP2, were designed for MUC1 recognition and hybridization chain reaction (HCR). The Apt-trigger probe was composed of two sequences: the MUC1 aptamer and HCR trigger sequence. The 5' end of the HP1-FAM probe was modified with a FAM signal molecule. In the presence of MUC1, the aptamer sequence is activated and bound to MUC1, which opens the hairpin structure. Then, the trigger sequence gets exposed and, complementary to HP1-FAM, triggers a continuous HCR process. This method was successfully used to detect MUC1 of 200 pM-25 nM and MUC1 in situ imaging in specific cells, such as human breast carcinoma (MCF-7) and human colon cancer (HT-29) cells.

Tailored Chiral Copper Selenide Nanochannels for Ultrasensitive Enantioselective Recognition and Detection

We constructed a tailorable membrane channel system consisting of penicillamine molecules intercalated in copper selenide nanoparticles (Cu_2-x Se NPs), which exhibited circular dichroism (CD) bands in the near infrared region (CD, 800-1600 nm) with a maximum intensity of 164.5 mdeg at 1440 nm. The chiral ligand hybridized to the surface of achiral Cu_2-x Se NPs by breaking the intrinsic symmetry of Cu_2-x Se NPs and further large-scale assembly induced strong optical activity. The fabricated multilayer chiral membrane achieved an increased rectification ratio (RR) up to 114. The integration of penicillamine allowed for high enantioselective recognition against naproxen,which displayed high sensitivity with a limit of detection (LOD) as low as 0.027 nM.

Aptamer Self-Assembly-Functionalized Nanochannels for Sensitive and Precise Detection of Chloramphenicol

Sensitive and precise determination of chloramphenicol (CAP) is of great significance for human health due to its high risk in trace amounts. Solid-state artificial nanochannels are expected to be highly promising sensing devices owing to single-molecule sensitivity, target-specific selectivity, and portability. Herein, we report an aptamer self-assembly-functionalized artificial nanochannel-based sensor for highly sensitive and precise determination of CAP. Aptamer self-assembly (AAs) served as the specific recognition component and were in situ grown on the surface of stable anodic aluminum oxide (AAO) nanochannels to develop an AAs@AAO nanochannel-based sensor. Selective interaction with CAP led to the disassembly of AAs and sensitive current change of AAs@AAO nanochannels, allowing sensitive and precise sensing of CAP in complex food samples. The developed AAs@AAO nanochannel-based sensor showed a wide linear range from 0.32 to 1600 pg. mL^-1, low limit of detection (LOD) of 0.1 pg. mL^-1, high precision with relative standard deviation of 2.9%, and quantitative recoveries of 93.4-102.2% for CAP in milk, milk powder, and honey samples. This work proposes a versatile nanochannel-based platform for facile, sensitive, and precise sensing of hazardous residues in food samples.

Highly Sensitive Colorimetric/Surface-Enhanced Raman Spectroscopy Immunoassay Relying on a Metallic Core-Shell Au/Au Nanostar with Clenbuterol as a Target Analyte

Lateral flow immunoassay (LFIA) has emerged as an effective technique in the field of food safety and environmental monitoring. However, sensitive and quantitative detection is still challenging for LFIAs in complex environments. In this work, a dual-model colorimetric/SERS lateral flow immunoassay for ultrasensitive determination of clenbuterol was constructed based on a metallic core-shell Au/Au nanostar acting as a multifunction tag. Raman reporter molecules are located between the core (AuNP) and shell (Au nanostar) to form a sandwich structure, which contributes to eliminate the environmental interference and improve the detection stability. In addition, the Au/Au nanostar provides a much higher Raman enhancement due to the presence of sharp tips and larger surface roughness in comparison with gold nanoparticles (AuNPs). Thus, on the basis of the antibody-antigen interaction, the dual-model immunoassay can produce strong colorimetric and surface-enhanced Raman spectroscopy (SERS) signals for highly sensitive detection of the target analyte, clenbuterol. Under optimal conditions, clenbuterol could be detected by the colorimetric model with a visual detection limit of 5 ng/mL. Meanwhile, the SERS signal of the Au/Au nanostar was accumulated on the test line for the SERS model detection with a quantitative detection limit as low as 0.05 ng/mL, which is at least 200-fold lower than that of the traditional AuNPs-based immunoassay. Furthermore, recovery rates of the proposed method in food samples were 86-110%. This dual-model immunoassay provides an effective tool for antibiotic residues analysis and demonstrates a broad potential for future applications in food safety monitoring.