Identifying Single Particles in Air Using a 3D-Integrated Solid-State Pore

Nanopore Environmental Analysis

As global pollution continues to escalate, timely and accurate monitoring is essential for guiding pollution governance and safeguarding public health. The increasing diversity of pollutants across environmental matrices poses a significant challenge for instrumental analysis methods, which often require labor-intensive and time-consuming sample pretreatment. Nanopore technology, an emerging single-molecule technique, presents a promising solution by enabling the rapid identification of multiple targets within complex mixtures with minimal sample preparation. A wide range of pollutants have been characterized using natural biological nanopores or artificial solid-state nanopores, and their distinct advantages include simple sample preparation, high sensitivity, and rapid onsite analysis. In particular, long-read nanopore sequencing has led to dramatic improvements in the analyses of environmental microbial communities, allows species-level taxonomic assignment using amplicon sequencing, and simplifies the assembly of metagenomes. In this Perspective, we review the latest advancements in analyzing chemical and biological pollutants through nanopore sensing and sequencing techniques. We also explore the challenges that remain in this rapidly evolving field and provide an outlook on the potential for nanopore environmental analysis to transform pollution monitoring, risk assessment, and public health protection.

Single-Molecule Bioelectronic Sensors with AI-Aided Data Analysis: Convergence and Challenges

Single-molecule bioelectronic sensing, a groundbreaking domain in biological research, has revolutionized our understanding of molecules by revealing deep insights into fundamental biological processes. The advent of emergent technologies, such as nanogapped electrodes and nanopores, has greatly enhanced this field, providing exceptional sensitivity, resolution, and integration capabilities. However, challenges persist, such as complex data sets with high noise levels and stochastic molecular dynamics. Artificial intelligence (AI) has stepped in to address these issues with its powerful data processing capabilities. AI algorithms effectively extract meaningful features, detect subtle changes, improve signal-to-noise ratios, and uncover hidden patterns in massive data. This review explores the synergy between AI and single-molecule bioelectronic sensing, focusing on how AI enhances signal processing and data analysis to boost accuracy and reliability. We also discuss current limitations and future directions for integrating AI, highlighting its potential to advance biological research and technological innovation.

Direct Determination of the Structure of Single Biopolymer Molecules Using Nanopore Sequencing

This review highlights operational principles, features, and modern aspects of the development of third-generation sequencing technology of biopolymers focusing on the nucleic acids analysis, namely the nanopore sequencing system. Basics of the method and technical solutions used for its realization are considered, from the first works showing the possibility of creation of these systems to the easy-to-handle procedure developed by Oxford Nanopore Technologies company. Moreover, this review focuses on applications, which were developed and realized using equipment developed by the Oxford Nanopore Technologies, including assembly of whole genomes, methagenomics, direct analysis of the presence of modified bases.

Hydrophobic Gating and Spatial Confinement in Hierarchically Organized Block Copolymer-Nanopore Electrode Arrays for Electrochemical Biosensing of 4-Ethyl Phenol

Hydrophobic gating in biological transport proteins is regulated by stimulus-specific switching between filled and empty nanocavities, endowing them with selective mass transport capabilities. Inspired by these, solid-state nanochannels have been integrated into functional materials for a broad range of applications, such as energy conversion, filtration, and nanoelectronics, and here we extend these to electrochemical biosensors coupled to mass transport control elements. Specifically, we report hierarchically organized structures with block copolymers on tyrosinase-modified two-electrode nanopore electrode arrays (BCP@NEAs) as stimulus-controlled electrochemical biosensors for alkylphenols. A polystyrene-b-poly(4-vinyl)pyridine (PS-b-P4VP) membrane placed atop the NEA endows the system with potential-responsive gating properties, where water transport is spatially and temporarily gated through hydrophobic P4VP nanochannels by the application of appropriate potentials. The reversibility of hydrophobic voltage-gating makes it possible to capture and confine analyte species in the attoliter-volume vestibule of cylindrical nanopore electrodes, enabling redox cycling and yielding enhanced currents with amplification factors >100× when operated in a generator-collector mode. The enzyme-coupled sensing capabilities are demonstrated using nonelectroactive 4-ethyl phenol, exploiting the tyrosinase-catalyzed turnover into reversibly redox-active quinones, then using the quinone-catechol redox reaction to achieve ultrasensitive cycling currents in confined BCP@NEA sensors giving a limit-of-detection of ∼120 nM. The mass transport controlled sensing platform described here is relevant to the development of enzyme-coupled multiplex biosensors for sensitive and selective detection of biomarkers and metabolites in next-generation point-of-care devices.

Focus on using nanopore technology for societal health, environmental, and energy challenges

With an increasing global population that is rapidly ageing, our society faces challenges that impact health, environment, and energy demand. With this ageing comes an accumulation of cellular changes that lead to the development of diseases and susceptibility to infections. This impacts not only the health system, but also the global economy. As the population increases, so does the demand for energy and the emission of pollutants, leading to a progressive degradation of our environment. This in turn impacts health through reduced access to arable land, clean water, and breathable air. New monitoring approaches to assist in environmental control and minimize the impact on health are urgently needed, leading to the development of new sensor technologies that are highly sensitive, rapid, and low-cost. Nanopore sensing is a new technology that helps to meet this purpose, with the potential to provide rapid point-of-care medical diagnosis, real-time on-site pollutant monitoring systems to manage environmental health, as well as integrated sensors to increase the efficiency and storage capacity of renewable energy sources. In this review we discuss how the powerful approach of nanopore based single-molecule, or particle, electrical promises to overcome existing and emerging societal challenges, providing new opportunities and tools for personalized medicine, localized environmental monitoring, and improved energy production and storage systems.

Nanodevices for Biological and Medical Applications: Development of Single-Molecule Electrical Measurement Method

A comprehensive detection of a wide variety of diagnostic markers is required for the realization of personalized medicine. As a sensor to realize such personalized medicine, a single molecule electrical measurement method using nanodevices is currently attracting interest for its comprehensive simultaneous detection of various target markers for use in biological and medical application. Single-molecule electrical measurement using nanodevices, such as nanopore, nanogap, or nanopipette devices, has the following features:; high sensitivity, low-cost, high-throughput detection, easy-portability, low-cost availability by mass production technologies, and the possibility of integration of various functions and multiple sensors. In this review, I focus on the medical applications of single- molecule electrical measurement using nanodevices. This review provides information on the current status and future prospects of nanodevice-based single-molecule electrical measurement technology, which is making a full-scale contribution to realizing personalized medicine in the future. Future prospects include some discussion on of the current issues on the expansion of the application requirements for single-mole-cule measurement.

Synchronized resistive-pulse analysis with flow visualization for single micro- and nanoscale objects driven by optical vortex in double orifice

Resistive-pulse analysis is a powerful tool for identifying micro- and nanoscale objects. For low-concentration specimens, the pulse responses are rare, and it is difficult to obtain a sufficient number of electrical waveforms to clearly characterize the targets and reduce noise. In this study, we conducted a periodic resistive-pulse analysis using an optical vortex and a double orifice, which repetitively senses a single micro- or nanoscale target particle with a diameter ranging from 700 nm to 2 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mu$$\end{document}μm. The periodic motion results in the accumulation of a sufficient number of waveforms within a short period. Acquired pulses show periodic ionic-current drops associated with the translocation events through each orifice. Furthermore, a transparent fluidic device allows us to synchronously average the waveforms by the microscopic observation of the translocation events and improve the signal-to-noise ratio. By this method, we succeed in distinguishing single particle diameters. Additionally, the results of measured signals and the simultaneous high-speed observations are used to quantitatively and systematically discuss the effect of the complex fluid flow in the orifices on the amplitude of the resistive pulse. The synchronized resistive-pulse analysis by the optical vortex with the flow visualization improves the pulse-acquisition rate for a single specific particle and accuracy of the analysis, refining the micro- and nanoscale object identification.

Rapid Discrimination of Extracellular Vesicles by Shape Distribution Analysis

A rapid and simple cancer detection method independent of cancer type is an important technology for cancer diagnosis. Although the expression profiles of biological molecules contained in cancer cell-derived extracellular vesicles (EVs) are considered candidates for discrimination indexes to identify any cancerous cells in the body, it takes a certain amount of time to examine these expression profiles. Here, we report the shape distributions of EVs suspended in a solution and the potential of these distributions as a discrimination index to discriminate cancer cells. Distribution analysis is achieved by low-aspect-ratio nanopore devices that enable us to rapidly analyze EV shapes individually in solution, and the present results reveal a dependence of EV shape distribution on the type of cells (cultured liver, breast, and colorectal cancer cells and cultured normal breast cells) secreting EVs. The findings in this study provide realizability and experimental basis for a simple method to discriminate several types of cancerous cells based on rapid analyses of EV shape distributions.

Monitoring the Effective Density of Airborne Nanoparticles in Real Time Using a Microfluidic Nanoparticle Analysis Chip

Determining the effective density of airborne nanoparticles (NPs; particles smaller than 100 nm in diameter) at a point of interest is essential for toxicology and environmental studies, but it currently requires complex analysis systems comprising several high-precision instruments as well as a specially trained operator. To address these limitations, a field-portable and cost-efficient microfluidic NP analysis device is presented, which provides quantitative information on the effective density and size distribution of NPs in real time. Unlike conventional analysis systems, the device can operate in a standalone mode because of the chip operating principle based on the electrostatic/inertial classification and electrical detection methods. Moreover, the device is both compact (16.0 × 10.9 × 8.6 cm³) and light (950 g) owing to the hardware strip down enabled by integrating the essential functions for effective density analysis on a single chip. Quantitative experiments performed to simulate real-life applications utilizing effective density (i.e., effective density-based morphology analysis on engineered NPs and multi-parametric NP monitoring in ambient air) demonstrate that the developed device can be used as an analysis tool in toxicological studies as an on-site sensor for the monitoring of individual NP exposure and environments, for quality monitoring of engineered NPs via aerosol synthesis, and other applications.

Current and Perspective Diagnostic Techniques for COVID-19

Since late December 2019, the coronavirus pandemic (COVID-19; previously known as 2019-nCoV) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been surging rapidly around the world. With more than 1,700,000 confirmed cases, the world faces an unprecedented economic, social, and health impact. The early, rapid, sensitive, and accurate diagnosis of viral infection provides rapid responses for public health surveillance, prevention, and control of contagious diffusion. More than 30% of the confirmed cases are asymptomatic, and the high false-negative rate (FNR) of a single assay requires the development of novel diagnostic techniques, combinative approaches, sampling from different locations, and consecutive detection. The recurrence of discharged patients indicates the need for long-term monitoring and tracking. Diagnostic and therapeutic methods are evolving with a deeper understanding of virus pathology and the potential for relapse. In this Review, a comprehensive summary and comparison of different SARS-CoV-2 diagnostic methods are provided for researchers and clinicians to develop appropriate strategies for the timely and effective detection of SARS-CoV-2. The survey of current biosensors and diagnostic devices for viral nucleic acids, proteins, and particles and chest tomography will provide insight into the development of novel perspective techniques for the diagnosis of COVID-19.

Back-Side Polymer-Coated Solid-State Nanopore Sensors

We systematically investigated the influence of polymer coating on temporal resolution of solid-state nanopores. We fabricated a Si₃N₄ nanopore integrated with a polyimide sheet partially covering the substrate surface. Upon detecting the nanoparticles dispersed in an electrolyte buffer by ionic current measurements, we observed a larger resistive pulse height along with a faster current decay at the tails under larger coverage of the polymeric layer, thereby suggesting a prominent role of the water-touching Si₃N₄ thin film as a significant capacitor serving to retard the ionic current response to the ion blockade by fast translocation of particles through the nanopores. From this, we came up with back-side polymer-coated chip designs and demonstrated improved pore sensor temporal resolution by developing a nanopore with a thick polymethyl-methacrylate layer laminated on the bottom surface. The present findings may be useful in developing integrated solid-state nanopore sensors with embedded nanochannels and nanoelectrodes.