Synthesis of chiral graphene structures and their comprehensive applications: a critical review

From a molecular viewpoint, chirality is a crucial factor in biological processes. Enantiomers of a molecule have identical chemical and physical properties, but chiral molecules found in species exist in one enantiomer form throughout life, growth, and evolution. Chiral graphene materials have considerable potential for application in various domains because of their unique structural framework, properties, and controlled synthesis, including chiral creation, segregation, and transmission. This review article provides an in-depth analysis of the synthesis of chiral graphene materials reported over the past decade, including chiral nanoribbons, chiral tunneling, chiral dichroism, chiral recognition, and chiral transfer. The second segment focuses on the diverse applications of chiral graphene in biological engineering, electrochemical sensors, and photodetectors. Finally, we discuss research challenges and potential future uses, along with probable outcomes.

Ion transport in nanofluidics under external fields

Nanofluidic channels with tailored ion transport dynamics are usually used as channels for ion transport, to enable high-performance ion regulation behaviors. The rational construction of nanofluidics and the introduction of external fields are of vital significance to the advancement and development of these ion transport properties. Focusing on the recent advances of nanofluidics, in this review, various dimensional nanomaterials and their derived homogeneous/heterogeneous nanofluidics are first briefly introduced. Then we discuss the basic principles and properties of ion transport in nanofluidics. As the major part of this review, we focus on recent progress in ion transport in nanofluidics regulated by external physical fields (electric field, light, heat, pressure, etc.) and chemical fields (pH, concentration gradient, chemical reaction, etc.), and reveal the advantages and ion regulation mechanisms of each type. Moreover, the representative applications of these nanofluidic channels in sensing, ionic devices, energy conversion, and other areas are summarized. Finally, the major challenges that need to be addressed in this research field and the future perspective of nanofluidics development and practical applications are briefly illustrated.

Effects of Ionic Strength on the Morphology, Scattering, and Mechanical Response of Neurofilament-Derived Protein Brushes

Protein brushes not only play a key role in the functionality of neurofilaments but also have wide applications in biomedical materials. Here, we investigate the effect of ionic strength on the morphology of protein brushes using continuous-space self-consistent field theory. A coarse-grained multiblock charged macromolecular model is developed to capture the chemical identity of amino acid sequences. For neurofilament heavy (NFH) brushes at pH 2.4, we predict three morphological regimes: swollen brushes, condensed brushes, and coexisting brushes, which consist of both a dense inner layer and a diffuse outer layer. The brush height predicted by our theory is in good agreement with the experimental data for a wide range of ionic strengths. The dramatic height decrease is a result of the electrostatic screening-induced transition from the overlapping state to the isolated state of the coexisting brushes. We also studied the evolution of the scattering and mechanical responses accompanying the morphological change. The oscillation in the reflectivity spectra characterizes the existence and microstructure of the inner condensed layer, whereas the shoulder in the force spectra signifies a swollen morphology.

Homochiral Zeolitic Imidazolate Framework with Defined Chiral Microenvironment for Electrochemical Enantioselective Recognition

The recognition and separation of chiral molecules with similar structure are of great industrial and biological importance. Development of highly efficient chiral recognition systems is crucial for the precise application of these chiral molecules. Herein, a homochiral zeolitic imidazolate frameworks (c-ZIF) functionalized nanochannel device that exhibits an ideal platform for electrochemical enantioselective recognition is reported. Its distinct chiral binding cavity enables more sensitive discrimination of tryptophan (Trp) enantiomer pairs than other smaller chiral amino acids owing to its size matching to the target molecule. It is found that introducing neighboring aldehyde groups into the chiral cavity will result in an inferior chiral Trp recognition due to the decreased adsorption-energy difference of D- and L-Trp on the chiral sites. This study may provide an alternative strategy for designing efficient chiral recognition devices by utilizing the homochiral reticular materials and tailoring their chiral environments.

Chiral MOFs encapsulated by polymers with poly-metallic coordination as chiral biosensors

Chiral materials have drawn the widespread attention for their its chiral recognition ability. The design and synthesis of chiral material are of importance owing to the unpredictability in controlling chirality during the synthesis process. To circumvent problems, a chiral MOF (D-His-ZIF-8) was synthesized by ligand exchange of 2-methylimidazole (Hmim) on ZIF-8 by D-histidine (D-His), which can be treated as chiral host to distinguish amino acid enantiomers. The obtained D-His-ZIF-8 can provide chiral nanochannels for amino acid guests. Meanwhile, polynary transition-metal ion (Co²⁺ and Fe³⁺) coordinating with polydopamine (PDA) wrapped on the surface of D-His-ZIF-8 can increase the active sites. The electrochemical chiral recognition behavior showed that D-His-ZIF-8@CoFe-PDA exhibited good recognition of the tryptophan enantiomer (L/D-Trp) (working potential of -0.2 V vs. Hg/HgCl₂). The LOD and LOQ of L-Trp were 0.066 mM and 0.22 mM, respectively, while the LOD and LOQ of D-Trp were 0.15 mM and 0.50 mM, respectively. Finally, the usefulness of D-His-ZIF-8@CoFe-PDA/GCE was evaluated with a recovery of 94.4-103%. The analysis of real  samples shows that D-His-ZIF-8@CoFe-PDA/GCE is a feasible sensing platform for the detection of L-Trp and D-Trp.

Solid-state nanopore: chemical modifications, interactions, and functionalities

Nanopore technology is a burgeoning detection technology for single-molecular sensing and ion rectification. Solid-state nanopores have attracted more and more attention because of their higher stability and tunability than biological nanopores. However, solid-state nanopores still suffer the drawbacks of low signal-to-noise ratio and low resolution, which hinders their practical applications. Thus, developing operatical and useful methods to overcome the shortages of solid-state nanopores is urgently needed. Here, we summarize the recent research on nanopore modification to achieve this goal. Modifying solid-state nanopores with different coating molecules can improve the selectivity, sensitivity, and stability of nanopores. The modified molecules can introduce different functions into the nanopores, greatly expanding the applications of this novel detection technology. We hope that this review of nanopore modification will provide new ideas for this field.

Mechanisms of Enzymatic Transduction in Nanochannel Biosensors

The immobilization of enzymes in solid-state nanochannels is a new avenue for the design of biosensors with outstanding selectivity and sensitivity. This work reports the first theoretical model of an enzymatic nanochannel biosensor. The model is applied to the system previously experimentally studied by Lin, et al. (Anal. Chem. 2014, 86, 10546): a hourglass nanochannel modified by glucose oxidase for the detection of glucose. Our predictions are in good agreement with experimental observations as a function of the applied potential, pH and glucose concentration. The sensing mechanism results from the combination of three processes: i) the establishment of a steady-state proton concentration gradient due to a reaction-diffusion mechanism, ii) the effect of that gradient on the charge of the adsorbed enzymes and native surface groups, and iii) the effect of the resulting surface charge on the ionic current. Strategies to improve the sensor performance based on this mechanism are identified and discussed.

Multicharged cyclodextrin supramolecular assemblies

Multicharged cyclodextrin (CD) supramolecular assemblies, including those based on positively/negatively charged modified mono-6-deoxy-CDs, per-6-deoxy-CDs, and random 2,3,6-deoxy-CDs, as well as parent CDs binding positively/negatively charged guests, have been extensively applied in chemistry, materials science, medicine, biological science, catalysis, and other fields. In this review, we primarily focus on summarizing the recent advances in positively/negatively charged CDs and parent CDs encapsulating positively/negatively charged guests, especially the construction process of supramolecular assemblies and their applications. Compared with uncharged CDs, multicharged CDs display remarkably high antiviral and antibacterial activity as well as efficient protein fibrosis inhibition. Meanwhile, charged CDs can interact with oppositely charged dyes, drugs, polymers, and biomacromolecules to achieve effective encapsulation and aggregation. Consequently, multicharged CD supramolecular assemblies show great advantages in improving drug-delivery efficiency, the luminescence properties of materials, molecular recognition and imaging, and the toughness of supramolecular hydrogels, in addition to enabling the construction of multistimuli-responsive assemblies. These features are anticipated to not only promote the development of CD-based supramolecular chemistry but also contribute to the rapid exploitation of these assemblies in diverse interdisciplinary applications.

Biomimetic Nanochannels: From Fabrication Principles to Theoretical Insights

Biological nanochannels which can regulate ionic transport across cell membranes intelligently play a significant role in physiological functions. Inspired by these nanochannels, numerous artificial nanochannels have been developed during recent years. The exploration of smart solid-state nanochannels can lay a solid foundation, not only for fundamental studies of biological systems but also practical applications in various fields. The basic fabrication principles, functional materials, and diverse applications based on artificial nanochannels are summarized in this review. In addition, theoretical insights into transport mechanisms and structure-function relationships are discussed. Meanwhile, it is believed that improvements will be made via computer-guided strategy in designing more efficient devices with upgrading accuracy. Finally, some remaining challenges and perspectives for developments in both novel conceptions and technology of this inspiring research field are stated.

Biological nanopores for sensing applications

Biological nanopores are proteins with transmembrane pore that can be embedded in lipid bilayer. With the development of single-channel current measurement technologies, biological nanopores have been reconstituted into planar lipid bilayer and used for single-molecule sensing of various analytes and events such as single-molecule DNA sensing and sequencing. To improve the sensitivity for specific analytes, various engineered nanopore proteins and strategies are deployed. Here, we introduce the origin and principle of nanopore sensing technology as well as the structure and associated properties of frequently used protein nanopores. Furthermore, sensing strategies for different applications are reviewed, with focus on the alteration of buffer condition, protein engineering, and deployment of accessory proteins and adapter-assisted sensing. Finally, outlooks for de novo design of nanopore and nanopore beyond sensing are discussed.

A renewable electrochemical sensor based on a self-assembled framework of chiral molecules for efficient identification of tryptophan isomers

Molecular self-assembly provides a reasonably effective strategy for the design and construction of chiral sensors. Here, Cu²⁺ was connected to β-cyclodextrin (β-CD) through coordination to synthesize Cu₂-β-CD, subsequently assembled with ammoniated chitosan-MWCNTs (NH₂-CS-MWCNTs) by the effect of coordination driver to form a chiral sensing interface Cu₂-β-CD/NH₂-CS-MWCNTs. Using the electrochemical method, the valid recognition of tryptophan (Trp) isomers was achieved on the self-assembly interface. Under the optimal experimental conditions, the developed sensor exhibited good linearity and satisfactorily renewable ability. Cu₂-β-CD/NH₂-CS-MWCNTs/GCE showed the capacity to predict the ratio of D-Trp and L-Trp in racemic mixtures and the possibility of qualitative and quantitative determination for Trp isomers. Finally, the electrochemical sensor was used to detect the Trp enantiomers in rat serum, further verifying the feasibility of the sensor in the determination of actual samples. Therefore, the electrochemical chiral sensor not only is used for the recognition of Trp enantiomers but shows great potential in practical applications.

Bio-inspired Track-Etched Polymeric Nanochannels: Steady-State Biosensors for Detection of Analytes

Bio-inspired polymeric nanochannel (also referred as nanopore)-based biosensors have attracted considerable attention on account of their controllable channel size and shape, multi-functional surface chemistry, unique ionic transport properties, and good robustness for applications. There are already very informative reviews on the latest developments in solid-state artificial nanochannel-based biosensors, however, which concentrated on the resistive-pulse sensing-based sensors for practical applications. The steady-state sensing-based nanochannel biosensors, in principle, have significant advantages over their counterparts in term of high sensitivity, fast response, target analytes with no size limit, and extensive suitable range. Furthermore, among the diverse materials, nanochannels based on polymeric materials perform outstandingly, due to flexible fabrication and wide application. This compressive Review summarizes the recent advances in bio-inspired polymeric nanochannels as sensing platforms for detection of important analytes in living organisms, to meet the high demand for high-performance biosensors for analysis of target analytes, and the potential for development of smart sensing devices. In the future, research efforts can be focused on transport mechanisms in the field of steady-state or resistive-pulse nanochannel-based sensors and on developing precisely size-controlled, robust, miniature and reusable, multi-functional, and high-throughput biosensors for practical applications. Future efforts should aim at a deeper understanding of the principles at the molecular level and incorporating these diverse pore architectures into homogeneous and defect-free multi-channel membrane systems. With the rapid advancement of nanoscience and biotechnology, we believe that many more achievements in nanochannel-based biosensors could be achieved in the near future, serving people in a better way.

Construction of A High-Flux Protein Transport Channel Inspired by the Nuclear Pore Complex

Inspired by the nuclear pore complex (NPC), herein we have established a biomimetic high-flux protein delivery system via the ingenious introduction of pillar[5]arene-based host-guest system into one side of artificial hour-glass shaped nanochannel. With a transport flux of 660 lysozymes per minute, the system provides efficient high-flux protein transport at a rate which is significantly higher than that of an unmodified nanochannel and conventional bilateral symmetrical modified nanochannels. In view of these promising results, the use of artificial nanochannel to improve protein transport not only presents a new potential chemical model for biological research and better understanding of protein transport behavior in the living systems, but also provides a high-flux protein transporter device, which may have applications in the design of protein drug release systems, protein separation systems and microfluidics in the near future.

Bioinspired Solid-State Nanochannel Sensors: From Ionic Current Signals, Current, and Fluorescence Dual Signals to Faraday Current Signals

Inspired from bioprotein channels of living organisms, constructing "abiotic" analogues, solid-state nanochannels, to achieve "smart" sensing towards various targets, is highly seductive. When encountered with certain stimuli, dynamic switch of terminal modified probes in terms of surface charge, conformation, fluorescence property, electric potential as well as wettability can be monitored via transmembrane ionic current, fluorescence intensity, faraday current signals of nanochannels and so on. Herein, the modification methodologies of nanochannels and targets-detecting application are summarized in ions, small molecules, as well as biomolecules, and systematically reviewed are the nanochannel-based detection means including 1) by transmembrane current signals; 2) by the coordination of current- and fluorescence-dual signals; 3) by faraday current signals from nanochannel-based electrode. The coordination of current and fluorescence dual signals offers great benefits for synchronous temporal and spatial monitoring. Faraday signals enable the nanoelectrode to monitor both redox and non-redox components. Notably, by incorporation with confined effect of tip region of a needle-like nanopipette, glorious in-vivo monitoring is conferred on the nanopipette detector at high temporal-spatial resolution. In addition, some outlooks for future application in reliable practical samples analysis and leading research endeavors in the related fantastic fields are provided.

A Pseudorotaxane System Containing γ-Cyclodextrin Formed via Chiral Recognition with an AuI 6 AgI 3 CuII 3 Molecular Cap

Solvent-mediated crystal-to-crystal transformations of [Au₆ Ag₃ Cu₃ (H₂ O)₃ (d-pen)₆ (tdme)₂ ]³⁺ (d-[1(H₂ O)₃ ]³⁺ ; pen^2- =penicillaminate, tdme=1,1,1-tris(diphenylphosphinomethyl)ethane) to form unique supramolecular species are reported. Soaking crystals of d-[1(H₂ O)₃ ]³⁺ in aqueous Na₂ bdc (bdc^2- =1,4-benzenedicarboxylate) yielded crystals containing d-[1(bdc)(H₂ O)₂ ]⁺ due to the replacement of a terminal aqua ligand in d-[1(H₂ O)₃ ]³⁺ by a monodentate bdc^2- ligand. When γ-cyclodextrin (γ-CD) was added to aqueous Na₂ bdc, d-[1(H₂ O)₃ ]³⁺ was transformed to d-[1(bdc@γ-CD)(H₂ O)₂ ]⁺ , where a γ-CD ring was threaded by a bdc^2- molecule to construct a pseudorotaxane structure. While the use of dicarboxylates with an aliphatic carbon chain instead of bdc^2- afforded analogous pseudorotaxanes, such pseudorotaxane species were not formed when crystals of [Au₆ Ag₃ Cu₃ (H₂ O)₃ (l-pen)₆ (tdme)₂ ]³⁺ (l-[1(H₂ O)₃ ]³⁺ ) enantiomeric to d-[1(H₂ O)₃ ]³⁺ were soaked in aqueous Na₂ bdc and γ-CD, affording only crystals containing l-[1(bdc)(H₂ O)₂ ]⁺ .

Regional and functional division of functional elements of solid-state nanochannels for enhanced sensitivity and specificity of biosensing in complex matrices

Solid-state nanochannels (SSNs) provide a promising approach for biosensing due to the confinement of molecules inside, their great mechanical strength and diversified surface chemical properties; however, until now, their sensitivity and specificity have not satisfied the practical requirements of sensing applications, especially in complex matrices, i.e., media of diverse constitutions. Here, we report a protocol to achieve explicit regional and functional division of functional elements at the outer surface (FE_OS) and inner wall (FE_IW) of SSNs, which offers a nanochannel-based sensing platform with enhanced specificity and sensitivity. The protocol starts with the fabrication and characterization of the distribution of FE_OS and FE_IW. Then, the evaluation of the contributions of FE_OS and FE_IW to ionic gating is described; the FE_IW mainly regulate ionic gating, and the FE_OS can produce a synergistic effect. Finally, hydrophobic or highly charged FE_OS are applied to ward off interference molecules, non-target molecules that may affect the ionic signal of nanochannels, which decreases false signals and helps to achieve the highly specific ionic output in complex matrices. Compared with other methods currently available, this method will contribute to the fundamental understanding of substance transport in SSNs and provide high specificity and sensitivity in SSN-based analyses. The procedure takes 3-6 d to complete.

Recent advances in chiral discrimination on host-guest functionalized interfaces

Chiral discrimination has gained much focus in supramolecular chemistry, since it is one of the fundamental processes in biological systems, enantiomeric separation and biochemical sensors. Though most of the biochemical processes can routinely recognize biological enantiomers, enantioselective identification of chiral molecules in artificial systems is currently one of the challenging topics in the field of chiral discrimination. Inaccuracy, low separation efficiency and expensive instrumentation were considered typical problems in artificial systems. Recently, chiral recognition on the interfaces has been widely used in the fields of electrochemical detection and biochemical sensing. For the moment, a series of macrocyclic host functionalized interfaces have been developed for use as chiral catalysts or for enantiomeric separation. Here, we have briefly exposited the most recent advances in the fabrication of supramolecular functionalized interfaces and their application for chiral recognition.

Chiral Nanochannels of Ordered Mesoporous Silica Constructed by a Pillar[5]arene-Based Host-Guest System

The separation of racemic compounds by chiral nanochannels has attracted extensive attention. However, the fabrication of high-performance chiral nanochannels is still a challenge owing to the difficulty in magnifying the weak chiral interaction to macroscopic properties of materials. Herein, by introducing a l-alanine-pillar[5]arene host to achiral ordered mesoporous silica (OMS), chiral OMS nanochannels were fabricated, which exhibited excellent selectivity (ee value up to 90.2%) to separate racemic drugs with promising reusability and stability. Besides, it was identified that enantioselective separation took place through a molecular-recognition-adsorbed transport mechanism. This work highlights the great potential of chiral OMS nanochannels as a platform for enantioselective separation.

Effects of Chiral Molecule Modification on Surface Biosorption Behavior

Antifouling materials have many important applications in biomedical devices and marine coating. Oligo(ethylene glycol) (OEG) or poly(ethylene glycol) (PEG) exhibit promising antifouling properties and are widely used in biomedical engineering. Chiral selection is an important phenomenon in biological processes. Because of the influence of steric hindrance, the modification of chiral molecules with different chirality at interfaces will affect the intermolecular interaction at the interfaces and lead to different structures of interfacial molecules. The difference of surface structures such as surface hydration structure would impact the adsorption of biomolecules on the surface, thus causing different varieties of cell adhesion and cell growth. In this study, the influence on surface hydration and surface cell adhesion of OEG self-assembled monolayers (SAMs) modified with cysteine showing different chirality are explored. The water structure at the interfaces of OEG/water in different conditions was probed with sum frequency generation vibrational spectroscopy (SFG-VS). The results show that the interfacial water structure can change significantly with either d-cysteine or l-cysteine modification on OEG. Water molecules are more ordered at the OEG/water interface under the d-cysteine modification on OEG SAMs, which improves the protein adsorption resistance of the surface. In contrast, l-cysteine modification would make the water less ordered at the OEG/protein solution interface and enhance the protein adsorption. Additionally, optical micrographs indicate that l-cysteine can significantly promote the OEG SAMs cell adhesion and growth, while d-cysteine exhibits an inhibitory effect, which is consistent with the results of SFG-VS experiments.

Not by Serendipity: Rationally Designed Reversible Temperature-Responsive Circularly Polarized Luminescence Inversion by Coupling Two Scenarios of Harata-Kodaka's Rule

Intelligent control over the handedness of circularly polarized luminescence (CPL) is of special significance in smart optoelectronics, information storage, and data encryption; however, it still remains a great challenge to rationally design a CPL material that displays reversible handedness inversion without changing the system composition. Herein, we show this comes true by coupling the two scenarios of Harata-Kodaka's rule on the same supramolecular platform of crystalline microtubes self-assembled from surfactant-cyclodextrin host-guest complexes. Upon coassembling a linear dye with its electronic transition dipole moment outside of the cavity of β-CyD, the chirality transfer from the induced chirality of SDS in the SDS@2β-CyD microtubes to the dye generates left-handed CPL at room temperature. Upon elevating temperature, the dye forms inclusion complex with β-CyD, so that right-handed CPL is induced because the polar group of the dye is outside of the cavity of β-CyD. This process is completely reversible. We envision that host-guest chemistry would be very promising in creating smart CPL inversion materials for a vast number of applications.

Ionic Current Rectification Triggered Photoelectrochemical Chiral Sensing Platform for Recognition of Amino Acid Enantiomers on Self-Standing Nanochannel Arrays

Chirality is an intrinsic and essential property of nature, and the enantiomeric discrimination of chiral molecules can provide important information leading to a better understanding of chiral recognition in biological systems and furthering the development of useful molecular devices in biochemical and pharmaceutical studies. Therefore, the exploration of new detection techniques with high accuracy and reliability for high-throughput enantioselective detection is still highly desirable. Herein, a chiral enantiomers selective recognition platform based on self-standing titanium dioxide nanochannel arrays (TiO₂ NCAs) is proposed to implement the ionic current rectification triggered photoelectrochemical (PEC) detection, which provides a novel sensing platform to discriminate chiral amino acid through synchronous output dual response signals of ionic current and photocurrent. The utilization of nanochannel arrays guaranteed the high-throughput detection, and the dual signal model avoided a "false positive" detection. In addition, based on the fabricated detection platform, various chiral substances can be facilely detected through integrating different chiral regulation units, which shed light on the construction of reliable chiral sensors for practical applications in a biological environment.

Chiral drug fluorometry based on a calix[6]arene/molecularly imprinted polymer double recognition element grafted on nano-C-dots/Ir/Au

A luminescent double recognition nanoprobe is described as a new strategy for the selective determination of chiral molecules. C-dots/Ir/Au fluorescent nanoparticles, synthesised under hydrothermal conditions, are used as a high-performance probe in combination with a molecularly imprinted polymer (MIP) and calix[6]arene as a double recognition element. Thiolated calix[6]arene is grafted on C-dots/Ir/Au as the first recognition element, which then forms a host-guest complex with the target molecule levodopa (L-DOPA). Subsequently, an MIP is prepared on the C-dots/Ir/Au (MIP/C-dots/Ir/Au) by chemical polymerisation. After the removal of L-DOPA, double recognition imprinting cavities are formed. The fluorescence intensity at 478 nm of the nanoprobe is effectively quenched by adsorption of L-DOPA on MIP/C-dots/Ir/Au, which provides a method for L-DOPA determination. Owing to the double recognition strategy, this method has excellent selectivity which can effectively avoid interference from enantiomer D-DOPA, and a imprinting factor of 7.1 is obtained for L-DOPA. This accurate and reliable method, with a wide linear range (5 × 10^-10 to 1.2 × 10^-7 mol L^-1) and a low limit of detection (1.45 × 10^-10 mol L^-1), was successfully applied to the determination of L-DOPA in real samples, giving standard recoveries of 89.7-110.0%. Thus, the proposed sensing method provides a viable approach for the determination of a single enantiomer. Graphical abstract Schematic presentation of the MIP/C-dots/Ir/Au for L-DOPA detection. A fluorescence double chiral recognition nanoprobe is prepared of C-dots/Ir/Au nanoparticles as signal probe, and a molecularly imprinted polymer (MIP) and calix[6]arene as a double recognition element. Owing to the double recognition strategy, this method has strong specificity and can effectively avoid interference from enantiomers and racemates.

Nanochannel sensor for sensitive and selective adamantanamine detection based on host-guest competition

The abuse of adamantanamine (ADA) and its derivatives as veterinary drugs in the poultry industry could cause severe health problems for humans. It is of great need to develop a rapid, cheap and ultrasensitive method for ADA detection. In this study, a sensitive conical nanochannel sensor was established for the rapid quantitative detection of ADA with the distinctive design of the host-guest competition. The sensor was constructed by functionalizing the nanochannel surface with p-toluidine and was then assembled with Cucurbit [7]uril (CB [7]). When ADA is added, it could occupy the cavity of CB [7] due to the host-guest competition and makes CB [7] to release from the CB [7]-p-toluidine complex, resulting in a distinct change of hydrophobicity of the nanochannel, which could be determined by the ionic current. Under the optimal conditions, the strategy permitted sensitive detection of ADA in a linear range of 10-1000 nM. The nanochannel based ADA sensing platform showed both high sensitivity and excellent reproducibility and the limit of detection was 4.54 nM. For the first time, the rapid and sensitive recognition of an illegal medicine was realized based on the host-guest competition method with the nanochannel system and the principle and feasibility of this method were described at length. This strategy provides a simple, reliable, and effective way to apply host-guest system in the development of nanochannel sensor for small-molecule drug detection.

Enantioseparation processes and mechanisms in functionalized graphene membranes: Facilitated or retarded transport?

Up to date, functionalized graphene-based membranes have exhibited a promising potential in the enantioseparation. However, since precisely controlling the interlayer distance of two-dimensional materials is a great challenge in practical experiments, the transport mechanism of chiral guests in such membranes, together with various critical parameters that play a controlling role in the transport behaviors of the preferentially binding enantiomer in narrow channels, remains to be explored. The molecular dynamics (MD) simulation, especially using the steered MD (SMD) method, might be an alternative way to investigate the enantioseparation processes and mechanisms of layered membranes with different interlayer distances. In this work, D-alanine modified graphene sheets with different interlayer distances were built as membrane models, whereas D- and L-phenylalanine were selected as chiral probes. The effect of the interlayer distance and the applied external force on the enantioseparation performance was examined. Results show that such two parameters exert a significant influence on the enantioseparation performance: (a) Increasing the interlayer distance would result in a conversion from the retarded to the facilitated mechanism at a proper external force (medium); (b) both the large and small driving forces would only lead to the appearance of the retarded transport for the preferential enantiomer, unlike the moderate force; (c) the interaction energy of L-phenylalanine with D-isomer selector decreases with the rising interlayer distances studied in this work, regardless of what the external force is. Our findings can provide guidance on the practical applications in the membrane-based chiral separation.

Ionic current in nanochannels grafted with pH-responsive polyelectrolyte brushes modeled using augmented strong stretching theory

In this paper, we provide a theory to quantify the ionic current ( i ion ) in nanochannels grafted with pH-responsive polyelectrolyte (PE) brushes. We consider the PE brushes to be modeled by our recently proposed augmented strong stretching theory (SST) model that improves the existing SST models by incorporating the effects of excluded volume interactions and an extended mass action law. Use of such augmented SST for this problem implies that this is the first study on computing i ion in PE brush-grafted nanochannels accounting for the appropriate coupled configuration-electrostatic description of the PE brushes. i ion is obtained as functions of PE brush grafting density, medium pH and salt concentration ( c ∞ ), and the density of polyelectrolyte chargeable sites (PECS). For large c ∞ , i ion increases linearly with c ∞ (as for such c ∞ , i ion becomes independent of the PE charge and is dominated by the bulk mobility and number density of the electrolyte ions), whereas i ion is independent of c ∞ at small c ∞ (where the electric double layer electrostatics and the total number of ions in the system is dominated by the hydrogen ions). We further witness an enhancement of i ion for smaller pH and larger grafting density at low and moderate c ∞ , while there is little to no effect of the PECS density on the ionic current except for weakly grafted brushes at low c ∞ . We anticipate that this study will serve as a theoretical foundation for a large number of applications that are based on the brush-induced modification of the ionic current in a nanochannel.

Direct Nucleus-Targeted Drug Delivery Using Cascade pHe /Photo Dual-Sensitive Polymeric Nanocarrier for Cancer Therapy

The cell nucleus-targeted delivery of therapeutic agents plays a critical role in cancer therapy, since the biological target of many anticancer therapeutics is the cell nucleus. However, multiple physiological barriers limit the delivery efficiency of free drugs, resulting in unsatisfactory therapeutic effects. Herein, thioketal crosslinked polyphosphoester-based nanoparticles with a tumor acidity (pH_e )-sensitive transactivator of transcription (TAT) peptide (DA-masked TAT-decorating reactive oxygen species (ROS)-sensitive Ce6/DOX-loaded hyperbranched nanoparticles (^D TRCD)) are explored for cascade nucleus-targeted drug delivery. Following administration, ^D TRCD experiences prolonged circulation by masking the targeting effect of its TAT peptide and then achieves enhanced tumor cell uptake and improved translocation into the perinuclear region by reactivating the TAT targeting capability in tumor tissue. Subsequently, ROS generated by ^D TRCD under 660 nm laser not only disrupts the nuclear membrane to allow entry into the nuclei but also triggers intracellular release of the payload in the nuclei. As evidenced by in vivo experiments, such pH_e /photo dual-sensitive polymeric nanocarriers offer remarkable therapeutic effects, efficiently suppressing tumor growth. This multistage cascade nucleus-targeted drug delivery concept provides new avenues to develop nucleus-targeted drug delivery systems.

Biomolecule-Functionalized Solid-State Ion Nanochannels/Nanopores: Features and Techniques

Solid-state ion nanochannels/nanopores, the biomimetic products of biological ion channels, are promising materials in real-world applications due to their robust mechanical and controllable chemical properties. Functionalizations of solid-state ion nanochannels/nanopores by biomolecules pave a wide way for the introduction of varied properties from biomolecules to solid-state ion nanochannels/nanopores, making them smart in response to analytes or external stimuli and regulating the transport of ions/molecules. In this review, two features for nanochannels/nanopores functionalized by biomolecules are abstracted, i.e., specificity and signal amplification. Both of the two features are demonstrated from three kinds of nanochannels/nanopores: nucleic acid-functionalized nanochannels/nanopores, protein-functionalized nanochannels/nanopores, and small biomolecule-functionalized nanochannels/nanopores, respectively. Meanwhile, the fundamental mechanisms of these combinations between biomolecules and nanochannels/nanopores are explored, providing reasonable constructs for applications in sensing, transport, and energy conversion. And then, the techniques of functionalizations and the basic principle about biomolecules onto the solid-state ion nanochannels/nanopores are summarized. Finally, some views about the future developments of the biomolecule-functionalized nanochannels/nanopores are proposed.

Cell adhesion and proliferation in chiral pores triggered by polyoxometalates

The chirality of polyoxometalate anchoring in the cavity of pitted films was demonstrated to strongly influence the adhesion and proliferation of E. coli cells.

A chiral signal-amplified sensor for enantioselective discrimination of amino acids based on charge transfer-induced SERS

An ultra-high sensitivity enantioselective sensor with excellent discrimination performance for trace amino acids by using charge transfer-induced SERS.