Single-Molecule Nanotechnologies: An Evolution in Biological Dynamics Detection

Amorphous Co-Mo-S nanospheres fabricated via room-temperature vulcanization for asymmetric supercapacitors

Ternary metal sulfides employed in supercapacitors exhibit better electrochemical performances than their counterpart oxides due to their superior conductivity. However, the insertion/extraction of electrolyte ions can lead to a significant volume change in electrode materials, which can result in poor cycling stability. Herein, novel amorphous Co-Mo-S nanospheres were fabricated through a facile room-temperature vulcanization method. It involves the conversion of crystalline CoMoO4 by reacting it with Na2S at room temperature. In addition to the conversion of the crystalline state into an amorphous structure with more grain boundaries, which is beneficial for the transport of electron/ion and can accommodate the volume change generated by the insertion/extraction of electrolyte ions, the production of more pores led to an increased specific surface area. The electrochemical results indicate that the as-prepared amorphous Co-Mo-S nanospheres had a specific capacitance of up to 2049.7F/g@1 A/g together with good rate capability. The amorphous Co-Mo-S nanospheres can be used as the cathode of supercapacitors and assembled with an activated carbon anode into an asymmetric supercapacitor possessing a satisfactory energy density of 47.6 Wh kg-1@1012.9 W kg-1. One of the prominent features exhibited by this asymmetric device is its remarkable cyclic stability, with a capacitance retention of 107% after 10,000 cycles.

Nanofluidic Aptamer Nanoarray to Enable Stochastic Capture of Single Proteins at Normal Concentrations

Single-molecule experiments allow understanding of the diversity, stochasticity, and heterogeneity of molecular behaviors and properties hidden by conventional ensemble-averaged measurements. They hence have great importance and significant impacts in a wide range of fields. Despite significant advances in single-molecule experiments at ultralow concentrations, the capture of single molecules in solution at normal concentrations within natural biomolecular processes remains a formidable challenge. Here, a high-density, well-defined nanofluidic aptamer nanoarray (NANa) formed via site-specific self-assembly of well-designed aptamer molecules in nanochannels with nano-in-nano gold nanopatterns is presented. The nanofluidic aptamer nanoarray exhibits a high capability to specifically capture target proteins (e.g., platelet-derived growth factor BB; PDGF-BB) to form uniform protein nanoarrays under optimized nanofluidic conditions. Owing to these fundamental features, the nanofluidic aptamer nanoarray enables the stochastic capture of single PDGF-BB molecules at a normal concentration from a sample with an ultrasmall volume equivalent to a single cell by following Poisson statistics, forming a readily addressable single-protein nanoarray. This approach offers a methodology and device to surpass both the concentration and volume limits of single-protein capture in most conventional methodologies of single-molecule experiments, thus opening an avenue to explore the behavior of individual biomolecules in a manner close to their natural forms, which remains largely unexplored to date.

Single-molecular protein-based bioelectronics via electronic transport: fundamentals, devices and applications

Biomolecular electronics is a rapidly growing multidisciplinary field that combines biology, nanoscience, and engineering to bridge the two important fields of life sciences and molecular electronics. Proteins are remarkable for their ability to recognize molecules and transport electrons, making the integration of proteins into electronic devices a long sought-after goal and leading to the emergence of the field of protein-based bioelectronics, also known as proteotronics. This field seeks to design and create new biomolecular electronic platforms that allow for the understanding and manipulation of protein-mediated electronic charge transport and related functional applications. In recent decades, there have been numerous reports on protein-based bioelectronics using a variety of nano-gapped electrical devices and techniques at the single molecular level, which are not achievable with conventional ensemble approaches. This review focuses on recent advances in physical electron transport mechanisms, device fabrication methodologies, and various applications in protein-based bioelectronics. We discuss the most recent progress of the single or few protein-bridged electrical junction fabrication strategies, summarise the work on fundamental and functional applications of protein bioelectronics that enable high and dynamic electron transport, and highlight future perspectives and challenges that still need to be addressed. We believe that this specific review will stimulate the interdisciplinary research of topics related to protein-related bioelectronics, and open up new possibilities for single-molecule biophysics and biomedicine.

Molecular Electronics: Creating and Bridging Molecular Junctions and Promoting Its Commercialization

Molecular electronics is driven by the dream of expanding Moore's law to the molecular level for next-generation electronics through incorporating individual or ensemble molecules into electronic circuits. For nearly 50 years, numerous efforts have been made to explore the intrinsic properties of molecules and develop diverse fascinating molecular electronic devices with the desired functionalities. The flourishing of molecular electronics is inseparable from the development of various elegant methodologies for creating nanogap electrodes and bridging the nanogap with molecules. This review first focuses on the techniques for making lateral and vertical nanogap electrodes by breaking, narrowing, and fixed modes, and highlights their capabilities, applications, merits, and shortcomings. After summarizing the approaches of growing single molecules or molecular layers on the electrodes, the methods of constructing a complete molecular circuit are comprehensively grouped into three categories: 1) directly bridging one-molecule-electrode component with another electrode, 2) physically bridging two-molecule-electrode components, and 3) chemically bridging two-molecule-electrode components. Finally, the current state of molecular circuit integration and commercialization is discussed and perspectives are provided, hoping to encourage the community to accelerate the realization of fully scalable molecular electronics for a new era of integrated microsystems and applications.

Detecting nanoparticles by "listening"

In the macroscopic world, we can obtain some important information through the vibration of objects, that is, listening to the sound. Likewise, we can also get some information of the nanoparticles that we want to know by the means of "listening" in the microscopic world. In this review, we will introduce two sensing methods (cavity optomechanical sensing and surface-enhanced Raman scattering sensing) which can be used to detect the nanoparticles. The cavity optomechanical systems are mainly used to detect sub-gigahertz nanoparticle or cavity vibrations, while surface-enhanced Raman scattering is a well-known technique to detect molecular vibrations whose frequency generally exceeds terahertz. Therefore, the vibrational information of nanoparticles from low-frequency to high-frequency could be obtained by these two methods. The size of the viruses is at the nanoscale and we can regard it as a kind of nanoparticles. Rapid and ultrasensitive detection of the viruses is the key strategies to break the spread of the viruses in the community. Cavity optomechanical sensing enables rapid, ultrasensitive detection of nanoparticles through the interaction of light and mechanical oscillators and surface-enhanced Raman scattering is an attractive qualitatively analytical technique for chemical sensing and biomedical applications, which has been used to detect the SARS-CoV-2 infected. Hence, investigation in these two fields is of vital importance in preventing the spread of the virus from affecting human's life and health.

Design of Pyrrole-Based Gate-Controlled Molecular Junctions Optimized for Single-Molecule Aflatoxin B1 Detection

Food contamination by aflatoxins is an urgent global issue due to its high level of toxicity and the difficulties in limiting the diffusion. Unfortunately, current detection techniques, which mainly use biosensing, prevent the pervasive monitoring of aflatoxins throughout the agri-food chain. In this work, we investigate, through ab initio atomistic calculations, a pyrrole-based Molecular Field Effect Transistor (MolFET) as a single-molecule sensor for the amperometric detection of aflatoxins. In particular, we theoretically explain the gate-tuned current modulation from a chemical-physical perspective, and we support our insights through simulations. In addition, this work demonstrates that, for the case under consideration, the use of a suitable gate voltage permits a considerable enhancement in the sensor performance. The gating effect raises the current modulation due to aflatoxin from 100% to more than 103÷104%. In particular, the current is diminished by two orders of magnitude from the μA range to the nA range due to the presence of aflatoxin B1. Our work motivates future research efforts in miniaturized FET electrical detection for future pervasive electrical measurement of aflatoxins.

Nanopore Detection Assisted DNA Information Processing

The deoxyribonucleotide (DNA) molecule is a stable carrier for large amounts of genetic information and provides an ideal storage medium for next-generation information processing technologies. Technologies that process DNA information, representing a cross-disciplinary integration of biology and computer techniques, have become attractive substitutes for technologies that process electronic information alone. The detailed applications of DNA technologies can be divided into three components: storage, computing, and self-assembly. The quality of DNA information processing relies on the accuracy of DNA reading. Nanopore detection allows researchers to accurately sequence nucleotides and is thus widely used to read DNA. In this paper, we introduce the principles and development history of nanopore detection and conduct a systematic review of recent developments and specific applications in DNA information processing involving nanopore detection and nanopore-based storage. We also discuss the potential of artificial intelligence in nanopore detection and DNA information processing. This work not only provides new avenues for future nanopore detection development, but also offers a foundation for the construction of more advanced DNA information processing technologies.

A Critical Review on the Sensing, Control, and Manipulation of Single Molecules on Optofluidic Devices

Single-molecule techniques have shifted the paradigm of biological measurements from ensemble measurements to probing individual molecules and propelled a rapid revolution in related fields. Compared to ensemble measurements of biomolecules, single-molecule techniques provide a breadth of information with a high spatial and temporal resolution at the molecular level. Usually, optical and electrical methods are two commonly employed methods for probing single molecules, and some platforms even offer the integration of these two methods such as optofluidics. The recent spark in technological advancement and the tremendous leap in fabrication techniques, microfluidics, and integrated optofluidics are paving the way toward low cost, chip-scale, portable, and point-of-care diagnostic and single-molecule analysis tools. This review provides the fundamentals and overview of commonly employed single-molecule methods including optical methods, electrical methods, force-based methods, combinatorial integrated methods, etc. In most single-molecule experiments, the ability to manipulate and exercise precise control over individual molecules plays a vital role, which sometimes defines the capabilities and limits of the operation. This review discusses different manipulation techniques including sorting and trapping individual particles. An insight into the control of single molecules is provided that mainly discusses the recent development of electrical control over single molecules. Overall, this review is designed to provide the fundamentals and recent advancements in different single-molecule techniques and their applications, with a special focus on the detection, manipulation, and control of single molecules on chip-scale devices.

Single-Molecule Junction: A Reliable Platform for Monitoring Molecular Physical and Chemical Processes

Monitoring and manipulating the physical and chemical behavior of single molecules is an important development direction of molecular electronics that aids in understanding the molecular world at the single-molecule level. The electrical detection platform based on single-molecule junctions can monitor physical and chemical processes at the single-molecule level with a high temporal resolution, stability, and signal-to-noise ratio. Recently, the combination of single-molecule junctions with different multimodal control systems has been widely used to explore significant physical and chemical phenomena because of its powerful monitoring and control capabilities. In this review, we focus on the applications of single-molecule junctions in monitoring molecular physical and chemical processes. The methods developed for characterizing single-molecule charge transfer and spin characteristics as well as revealing the corresponding intrinsic mechanisms are introduced. Dynamic detection and regulation of single-molecule conformational isomerization, intermolecular interactions, and chemical reactions are also discussed in detail. In addition to these dynamic investigations, this review discusses the open challenges of single-molecule detection in the fields of physics and chemistry and proposes some potential applications in this field.

Preparation and characterization of a novel composite membrane of natural silk fiber/nano-hydroxyapatite/chitosan for guided bone tissue regeneration

Natural silk fiber (SF) was introduced into the chitosan/nano-hydroxyapatite (CS/n-HA) system to fabricate a novel guided bone tissue regeneration (GBR) membrane. The effect of different treatment methods (degummed, un-degummed, or dissolved SF) and different contents of SF on the properties of the CS/n-HA composite membrane was investigated. Results demonstrated that the degummed SF/CS/n-HA composite membrane with a weight ratio of 2:6:2 possessed the highest mechanical strength, where SF supported the composite membrane as a skeleton frame in the form of primeval state, while the un-degummed SF and dissolved SF had weaker reinforce effect due to the poor interface or poor interaction between SF and CS, and the dissolved SF/CS/n-HA composite membrane displayed the fastest degradation. However, the three SF could all improve the cell biocompatibility of the CS/n-HA composite membrane. Conclusively, the study revealed that degummed SF could in situ reinforce the CS/n-HA composite membrane with a simple and green processing method, which would provide an important guidance significant to develop a novel GBR membrane.

Anisotropic acoustic phonon polariton-enhanced infrared spectroscopy for single molecule detection

Nanoscale Fourier transform infrared spectroscopy (nano-FTIR) based on scanning probe microscopy enables the identification of the chemical composition and structure of surface species with a high spatial resolution (∼10 nm), which is crucial for exploring catalytic reaction processes, cellular processes, virus detection, etc. However, the characterization of a single molecule with nano-FTIR is still challenging due to the weak coupling between the molecule and infrared light due to a large size mismatch. Here, we propose a novel structure (monolayer α-MoO₃/air nanogap/Au) to excite anisotropic acoustic phonon polaritons (APhPs) with ultra-high field confinement (mode volume, V_APhPs∼ 10^-11V₀) and electromagnetic energy enhancement (>10⁷), which largely enhance the interaction of single molecules with infrared light. In addition, the anisotropic APhP-assisted nano-FTIR can detect single molecular dipoles in directions both along and perpendicular to the probe axis, while pristine nano-FTIR mainly detects molecular dipoles along the probe axis. The proposed structure provides a way to detect a single molecule, which will impact the fields of biology, chemistry, energy, and environment through fundamental research and applications.

Nanomechanics of self-assembled DNA building blocks

DNA has become a powerful platform to design functional nanodevices. DNA nanodevices are often composed of self-assembled DNA building blocks that differ significantly from the structure of native DNA. In this study, we present Flow Force Microscopy as a massively parallel approach to study the nanomechanics of DNA self-assemblies on the single-molecular level. The high-throughput experiments performed in a simple microfluidic channel enable statistically meaningful studies with nanometer scale precision in a time frame of several minutes. A surprisingly high flexibility was observed for a typical construct used in DNA origami, reflected in a persistence length of 10.2 nm, a factor of five smaller than for native DNA. The enhanced flexibility is attributed to the discontinuous backbone of DNA self-assemblies that facilitate base pair opening by thermal fluctuations at the end of hybridized oligomers. We believe that the results will contribute to the fundamental understanding of DNA nanomechanics and help to improve the design of DNA nanodevices with applications in biological analysis and clinical research.

A single-molecule electrical approach for amino acid detection and chirality recognition

One of the ultimate goals of analytic chemistry is to efficiently discriminate between amino acids. Here we demonstrate this ability using a single-molecule electrical methodology based on molecular nanocircuits formed from stable graphene-molecule-graphene single-molecule junctions. These molecular junctions are fabricated by covalently bonding a molecular machine featuring a permethylated-β-cyclodextrin between a pair of graphene point contacts. Using pH to vary the type and charge of the amino acids, we find distinct multimodal current fluctuations originating from the different host-guest interactions, consistent with theoretical calculations. These conductance data produce characteristic dwell times and shuttling rates for each amino acid, and allow accurate, statistical real-time, in situ measurements. Testing four amino acids and their enantiomers shows the ability to distinguish between them within a few microseconds, thus paving a facile and precise way to amino acid identification and even single-molecule protein sequencing.