Understanding of chiral site-dependent enantioselective identification on a plasmon-free semiconductor based SERS substrate

A photothermal effect-based chiral sensor for chiral discrimination and sensitive detection

Chiral analysis with simple devices is of great importance for analytical chemistry. Based on the photothermal (PT) effect, a simple chiral sensor with a portable laser device as the light source and a thermometer as the detection tool was developed for the chiral recognition of tryptophan (Trp) isomers and the sensitive sensing of one isomer (L-Trp). Gold nanorods (GNRs), which have outstanding photo-thermal conversion ability due to their localized surface plasma resonance (LSPR) effect, are used as PT reagents, and biomacromolecules bovine serum albumin (BSA) are used as natural chiral sources, and thus, GNRs@BSA was obtained through Au-S bonds. The resultant GNRs@BSA displays higher affinity toward L-Trp than D-Trp owing to the inherent chirality of BSA. Under the irradiation of near-infrared (NIR) light, the temperature of GNRs@BSA//L-Trp is greatly lower than that of GNRs@BSA//D-Trp due to its greatly decreased thermal conductivity, and thus chiral discrimination of Trp isomers can be achieved. In addition, the developed PT effect-based chiral sensor can be used for sensitive detection of L-Trp, and the linear range and limit of detection (LOD) are 1 μM-10 mM and 0.43 μM, respectively.

Electrochemical identification of reductive enantiomers in wood channels: A low-cost and scalable platform for chiral sensing

Chirality, an inherent characteristic of natural substances (such as sugars, peptides, proteins, and nucleic acid), plays a vital role in human metabolism and exerts substantial impacts. In general, chiral drugs can display diverse pharmacological and pharmacokinetic properties. One enantiomer may exhibit therapeutic effects, while the other could cause adverse reactions. Selective recognition of enantiomers is thus a significant task in the biomolecular and pharmaceutical fields. Despite the development of several chiral identification techniques, low-cost enantioselective sensing methods remain highly desirable. Here, we designed and developed an electrochemical sensing device for reductive enantiomer identification using natural wood channels as the substrate. The wood channels were endowed with oxidase-like activity through the in-situ growth of cerium oxide nanoparticles (CeO2). Chiral recognition capability was further introduced by incorporating a layer of chiral ZIF-8 (L-ZIF) as the chiral selector. To demonstrate the enantioselective sensing performance, 3,4-dihydroxyphenylalanine (DOPA) enantiomers were employed as model analytes. Due to the oxidase-like activity and the confinement effect of the proposed channels, the captured DOPA enantiomers were effectively oxidized to their quinone structure, and the Ce(IV) in CeO2 was reduced to Ce(III). These changes led to alterations in the surface charge of the channels, thereby modulating their ionic transport properties. This sensing mechanism also proved useful for the identification of other reductive enantiomers. The limits of detection for l-DOPA and d-DOPA were determined as 2.41 nM and 1.56 nM, respectively. The resulting wood channel-based sensing device not only can be used for the recognition and detection of reductive enantiomers, but also is expected to be applied to the non-electochemically active substances. Moreover, this study offers a novel type of solid-state channel material with low cost, reproducibility, and easy accessibility for electrochemical chiral sensing.

Reaction-Modulated Surface-Enhanced Raman Scattering Strategy for Stereoselective Differentiation and Identification of Amino Acids

Surface-enhanced Raman scattering (SERS) sensing of racemates is a remarkably fascinating yet very sophisticated objective because of similar physicochemical features of enantiomers. Inspired by the enantiomeric selectivity of nucleophilic addition reaction (NAR) toward amino acids, we herein propose highly effective, robust SERS discrimination of d- and l-valine by synergizing asymmetric gold nanorods-embedded ZIF-8 nanoparticles (AGNZ) with NAR to engender stereoselective molecular fingerprint. Experimental and chemometric analyses disclose that enantioselectivity lies in dual aspects: (i) abundant interfacial cavities and 3D hot-spots in AGNZ offer necessary confined asymmetrical surroundings to trigger enantiospecific molecular adsorption and interaction affinity, and (ii) the specified NAR drags the racemates adjacent to the interfacial area of AGNZ for maximum analytes-substrate interaction. This strategy is universal and can be utilized for the recognition of different amino acid enantiomers. Importantly, multiple quantifications of the racemic ratio can be realized with superior prognostic performances. This synergizing strategy therefore provides a significant paradigm shift from traditional methods to realize highly effective SERS discrimination of racemates.

Direct Readout of Homo- vs Heterochiral Ligand Shell of Quantum Dots

The chiroptical activity of various semiconductor inorganic nanocrystalline materials has typically been tested using circular dichroism or circularly polarized luminescence. Herein, we report on a high-throughput screening method for identifying and differentiating chiroptically active quantum-sized ZnO crystals using Raman spectroscopy combined with principal component analysis. ZnO quantum dots (QDs) coated by structurally diverse homo- and heterochiral aminoalcoholate ligands (cis- and trans-1-amino-2-indanolate, 2-amino-1-phenylethanolate, and diphenyl-2-pyrrolidinemethanolate) were prepared using the one-pot self-supporting organometallic procedure and then extensively studied toward the identification of specific Raman fingerprints and spectral variations. The direct comparison between the spectra demonstrates that it is very difficult to make definite recognition and identification between QDs coated with enantiomers based only on the differences in the respective Raman bands' position shifts and their intensities. However, the applied approach involving the principal component analysis performed on the Raman spectra allows the simultaneous differentiation and identification of the studied QDs. The first and second principal components explain 98, 97, 97, and 87% of the variability among the studied families of QDs and demonstrate the possibility of using the presented method as a qualitative assay. Thus, the reported multivariate approach paves the way for simultaneous differentiation and identification of chirotopically active semiconductor nanocrystals.

Flexible, scalable and simple-fabricated silver nanorod-decorated bacterial nanocellulose SERS substrates cooperated with portable Raman spectrometer for on-site detection of pesticide residues

Owing to good flexibility, prominent mechanical properties, three-dimensional (3D) nanofibrous structure and low background interference, sustainable bacterial nanocellulose (BNC) is a highly attractive matrix material for surface-enhanced Raman scattering (SERS) sensor. Herein, a highly sensitive, flexible and scalable silver nanorod-decorated BNC (AgNRs@BNC) SERS sensor is developed by a simple vacuum-assisted filtration. The AgNRs were firmly locked in the 3D nanofibrous network of cellulose nanofibers upon vacuum drying process, resulting in the formation of 3D SERS hotspots with a depth of more than 10 μm on the sensor. With 4-aminothiophenol (4-ATP) as a target molecule, a lowest distinguishable level of 10-12 M and a high enhancement factor of 1.1 × 109 were realized by the optimal AgNRs1.5@BNC SERS sensor. Moreover, the AgNRs@BNC SERS sensor exhibits high detectable level of 10-9 M for thiram molecules by integrating with a portable Raman spectrometer. Besides, toxic thiram residues on grape surface could be directly on-site identified by the combination of AgNRs@BNC SERS sensors and a portable Raman spectrometer through a feasible press-and-peel method. The flexible AgNRs@BNC SERS sensor cooperated with portable Raman system demonstrates great potential for on-site detection of pesticide residues on irregular food surfaces.

Circular Polarization-Resolved Raman Optical Activity: A Perspective on Chiral Spectroscopies of Vibrational States

Circular polarization-resolved Raman scattering methods include Raman optical activity (ROA) and its derivative─surface-enhanced Raman optical activity (SEROA). These spectroscopic modalities are rapidly developing due to their high information content, stand-off capabilities, and rapid development of Raman-active chiral nanostructures. These methods enable a direct readout of the vibrational energy levels of chiral molecules, crystals, and nanostructured materials, making it possible to study complex interactions and the dynamic interfaces between them. They were shown to be particularly valuable for nano- and biotechnological fields encompassing complex particles with nanoscale chirality that combine strong scattering and intense polarization rotation. This perspective dives into recent advancements in ROA and SEROA, their distinction from surface-enhanced Raman scattering, and the potential of these information-rich label-free spectroscopies for the detection of chiral biomolecules.

Structure-regulated enhanced Raman scattering on a semiconductor to study temperature-influenced enantioselective identification

Surface-enhanced Raman scattering (SERS) spectroscopy is an effective technique that can reveal molecular structure and molecular interaction details. Semiconductor-based SERS platforms exhibit multifaceted tunability and unique selectivity to target molecules as well as high spectral reproducibility. However, the detection sensitivity of semiconductors is impeded by inferior SERS enhancement. Herein, a surface and interference co-enhanced Raman scattering (SICERS) platform based on corrugated TiO2 nanotube arrays (c-TiO2 NTs) was developed, and the coupling of structural regulation and photo-induced charge transfer (PICT) effectively optimized the SERS performance of the semiconductor substrate. Due to the regularly oscillating optical properties of the c-TiO2 NTs, well-defined interference patterns were generated and the local electric field was significantly increased, which greatly promoted both the electromagnetic mechanism and PICT processes. The c-TiO2 NTs were subsequently applied as a highly sensitive SICERS substrate to investigate the mechanism of temperature influence on enantioselective identification. This identification process is related to the existence of temperature-sensitive hydrogen bonds and π-π interaction. This work demonstrates a simply prepared, low-cost, and sensitive SERS substrate that enables better investigation into molecular identification.

π-π+ Interaction Promoting the Absorption of Electroactive Chiral Selectors into the Cavity of Conductive Covalent Organic Framework for Enantioselective Sensing of Electrochemically Silent Molecules

To date, achieving enantioselective electroanalysis for electrochemically silent chiral molecules is still highly desired. Here, an ionic covalent organic framework (COF) consisting of the pyridinium cation was derived from the tripyridinium Zincke salt and 1,4-phenylenediamine in a one-pot reaction. The electrochemical measurements revealed that the ionic backbone contributed to the electron transfer with a low charge transfer resistance. Besides, the π-π+ interaction between the pyridinium cation and ferrocenyl unit can promote the absorption of electroactive chiral ferrocenyl reagents into the hole of COF, so as to afford the electrochemical signals by themselves, replacing the testing enantiomers. As a result, the electroactive complex used as an electrochemical platform was highly effective at enantiomerically recognizing amino alcohols (prolinol, valinol, leucinol, and alaninol) and amino acids (methionine, serine, and penicillamine), giving the ratios of current intensity between l- and d-enantiomers in the range of 1.46-1.72. Moreover, the density functional theory calculations determined the possible intermolecular interactions between the testing enantiomers and chiral selector: namely, hydrogen bonds and electrostatic attractions. Overall, the present work offers an effective strategy to enlarge the electrochemical scope for chiral recognition based on electroactive chiral COFs.

Hydrogen Bonding-Induced Aggregation of Chiral Functionalized AuNS@Ag NPs for Photothermal Enantioanalysis

Toward the challenges of signaling transduction amplified in enantioselective recognition, we herein devised an innovative strategy for highly selective recognition of amino acids and their derivatives, leveraging photothermal effects. In this approach, bifunctional l-ascorbic acid is employed to reduce silver ions in situ on Au nanostars. Simultaneously, its oxidate (l-dehydroascorbic acid) is bonded to the silver shell as a chiral selector to prepare chiral nanoparticles (C-AuNS@Ag NPs) with the ability to recognize stereoisomers and sensitively modulate the photothermal effect. l-Dehydroascorbic acid can selectively capture one of the enantiomers of the two forms through hydrogen bonding and drive aggregation of the nanoparticles, which sharply enhances the photothermal effect. Consequently, the two forms of the system exhibit a significant temperature difference, which enables the discrimination and quantification of enantiomers. Our strategy verifies that six chiral amino acids and their derivatives can be discriminated with enantioselective response values of up to 79. Additionally, the chiral recognition mechanism was revealed through density functional theory (DFT) calculations, providing a paradigm shift in the development of enantiomeric recognition strategies.

Quantitative Analysis of Trace Analytes with Highly Sensitive SERS Tags on Hydrophobic Interface

Surface-enhanced Raman scattering (SERS) presents a promising avenue for trace matter detection by using plasmonic nanostructures. To tackle the challenges of quantitatively analyzing trace substances in SERS, such as poor enrichment efficiency and signal reproducibility, this study proposes a novel approach using Au@internal standard@Au nanospheres (Au@IS@Au NSs) for realizing the high sensitivity and stability in SERS substrates. To verify the feasibility and stability of the SERS performances, the SERS substrates have exhibited exceptional sensitivity for detecting methyl blue molecules in aqueous solutions within the concentration range from 10-4 M to 10-13 M. Additionally, this strategy also provides a feasible way of quantitative detection of antibiotic in the range of 10-4 M to 10-10 M. Trace antibiotic residue on the surface of shrimp in aquaculture waters was successfully conducted, achieving a remarkably low detection limit of 10-9 M. The innovative approach has great potential for the rapid and quantitative detection of trace substances, which marks a noteworthy step forward in environmental detection and analytical methods by SERS.

Preparation of cellular membrane-mimicking glycopolymer interfaces by a solvent-assisted method on QCM-D sensor chips and their molecular recognition

Carbohydrate-based membranes that show molecular recognition ability are interesting mimics of biointerfaces. Herein, we prepared glycopolymer membranes on QCM-D sensor chips using a solvent-assisted method and investigated their interactions with a target lectin. The membrane containing the glycopolymer with a random arrangement of the carbohydrate units adsorbed more lectin than that containing the glycopolymer with an organized block of carbohydrate units.

MoO2 Pump-Enhanced Flexible TiO2 Nanojungle-Based Chemiresistors for Rapid Room-Temperature Detection of H2S at Parts-per-Billion Levels

In this study, we developed a gas sensing platform that can sensitively and specifically detect trace H2S in a high-humidity atmosphere at RT. Upon integrating a carbon nitride (C3N4) nanofilm and molybdenum dioxide (MoO2) nanosheets onto nanojungle-like TiO2 nanotube arrays (TiNTs), the fabricated chemiresistor showed rapid response (38 s)/recovery (58 s) abilities and remarkable detection sensitivity for H2S at concentrations down to 2 ppb, with an estimated detection limit of 1.13 ppb at RT and room-environmental light (REL). Importantly, the gas sensor exhibited satisfactory H2S sensing performance even in dark conditions with a response of 1.9 at 200 ppb. In this design, apart from the architectural advantages of the nanojungle-like TiNTs for accelerating the gas flow efficiency and the abundant sensing sites provided by the C3N4 film, the MoO2 nanosheets act as the essential electron pump not only for the H2S response but also for the subsequent recovery process in air. After employing the MoO2 pump onto C3N4/TiNTs, the response time and recovery time of the system are shortened to ∼35 and ∼11%, respectively. Moreover, we demonstrated the good performance of the flexible gas sensor in detecting trace H2S in human exhaled breath with good humidity resistance. These results highlight the possibility of designing chemiresistors operating in RT and REL conditions and to use these environmentally friendly TiO2-based sensors in real applications.

Enantioselective and Chemoselective Optical Detection of Chiral Organic Compounds without Resorting to Chromatography

Enantiorecognition and resolution are of essential importance in many diverse areas of science. Whenever there arises a need to analyze/investigate enantiomers in different situations chromatography stands up in our minds immediately. Nevertheless, chemoselective and enantioselective recognition/discrimination (without going for separation) constitutes a different perception and requirement. The techniques using chiroptical sensing cause detection based on molecular interactions induced in different manners. Enantioselective sensing of monosaccharides in γ-cyclodextrin assembly and by diboronic acid based fluorescent sensors, application of bi-naphthol and H8 BINOL based sensors and dendrimers, metal-to-ligand charge transfer transitions in CD, exciton-coupled circular dichroism, surface enhanced Raman spectroscopy, and enantioselective indicator displacement sensor arrays for enantioselective recognition/detection of chiral organic compounds, such as amines, amino acids/alcohols, and hydroxycarboxylic acids have been discussed in progressive manner with mechanistic explanations, wherever available. Besides, the chiroptical vs LC approach has been discussed. The present paper is focused on certain different non-chromatographic optical techniques and aims to extend an understanding and a view to consider such techniques which have been successful in selective detection, and determination of absolute configuration and enantiomeric excess, (without resorting to separation vis-à-vis LC) and that have potential use in high-throughput chiral assay and combinatorial search for asymmetric catalysts and reagents.

Construction of High-Active SERS Cavities in a TiO2 Nanochannels-Based Membrane: A Selective Device for Identifying Volatile Aldehyde Biomarkers

The accurate, sensitive, and selective on-site screening of volatile aldehyde biomarkers for lung cancer is of utmost significance for preclinical cancer diagnosis and treatment. Applying surface-enhanced Raman scattering (SERS) for gas sensing remains difficult due to the small Raman cross section of most gaseous molecules and interference from other components in exhaled breath. Using an Au asymmetrically coated TiO2 nanochannel membrane (Au/TiO2 NM) as the substrate, a ZIF-8-covered Au/TiO2 NM SERS sensing substrate is designed for the detection of exhaled volatile organic compounds (VOCs). Au/TiO2 NM provides uniformly amplified Raman signals for trace measurements in this design. Importantly, the interfacial nanocavities between Au nanoparticles (NPs) and metal-organic frameworks (MOFs) served as gaseous confinement cavities, which is the key to enhancing the capture and adsorption ability toward gaseous analytes. Both ends of the membrane are left open, allowing gas molecules to pass through. This facilitates the diffusion of gaseous molecules and efficient capture of the target analyte. Using benzaldehyde as a typical gas marker model of lung cancer, the Schiff base reaction with a Raman-active probe molecule 4-aminothiophene (4-ATP) pregrafted on Au NPs enabled trace and multicomponent detection. Moreover, the combination of machine learning (ML) and Raman spectroscopy eliminates subjective assessments of gaseous aldehyde species with the use of a single feature peak, allowing for more accurate identification. This membrane sensing device offers a promising design for the development of a desktop SERS analysis system for lung cancer point-of-care testing (POCT).

Single-Nanoparticle-Level Understanding of Oxidase-like Activity of Au Nanoparticles on Polymer Nanobrush-Based Proton Reservoirs

Enzyme-mimicking nanoparticles play a key role in important catalytic processes, from biosensing to energy conversion. Therefore, understanding and tuning their performance is crucial for making further progress in biological applications. We developed an efficient and sensitive electrochemical method for the real-time monitoring of the glucose oxidase (GOD)-like activity of single nanoparticle through collision events. Using brush-like sulfonate (-SO3-)-doped polyaniline (PANI) decorated on TiO2 nanotube arrays (TiNTs-SPANI) as the electrode, we fabricated a proton reservoir with excellent response and high proton-storage capacity for evaluating the oxidase-like activity of individual Au nanoparticles (AuNPs) via instantaneous collision processes. Using glucose electrocatalysis as a model reaction system, the GOD-like activity of individual AuNPs could be directly monitored via electrochemical tests through the nanoparticle collision-induced proton generation. Furthermore, based on the perturbation of the electrical double layer of SPANI induced by proton injection, we investigated the relationship between the measured GOD-like activities of the plasmonic nanoparticles (NPs) and the localized surface plasmon resonance (LSPR) as well as the environment temperature. This work introduces an efficient platform for understanding and characterizing the catalytic activities of nanozymes at the single-nanoparticle level.

Target-Driven Z-Scheme Heterojunction Formation for ppb H2S Detection from Exhaled Breath at Room Temperature

As a biomarker of periodontitis, sensitive and timely monitoring of hydrogen sulfide (H2S) in exhaled breath at room temperature (RT) is important for the early intervention of oral diseases. However, the required high operation temperature to achieve high sensitivity is still a technical challenge for directly monitoring exhaled breath. In this study, by integrating metal-organic frameworks (MOFs) into self-aligned TiO2 nanotube arrays (NTs), a chemiresistor gas sensor with outstanding sensitivity and selectivity was constructed for the detection of H2S at RT. The precise regulation of a Co(III)-based MOF CoBDC-NH2 (BDC-NH2 = 2-aminoterephthalic acid) not only induced more active surface for the preconcentration of the target gas but also caused a buildup of Z-scheme heterojunctions in the H2S atmosphere that induced an ultrahigh sensitivity at RT via 365 nm light-emitting diode irradiation. The response and recovery times decreased to ∼50 and ∼28%, respectively, when this system was exposed to UV light. The sensing chips based on the as-prepared TiO2/CoBDC-NH2 NTs exhibited the highest-ranking H2S sensing performance, i.e., a limit of detection of 1.3 ppb and excellent selectivity even to 100 times high concentration of interference gases, owing to the synergistic chemical environment provided by NH2-functionalized Co-MOFs and abundant photogenerated electrons provided by Z-scheme heterojunctions. This sensing chip was also used in a practical application for the timely monitoring of halitosis from direct exhaled breath. This study provides a reliable and sensitive design for clinically aiding the timely detection of H2S in a complex oral environment.

A review on current progress of Raman-based techniques in food safety: From normal Raman spectroscopy to SESORS

Frequently occurrence of food safety incidents has induced global concern over food safety. To ensure food quality and safety, an increasing number of rapid and sensitive analytical methods have been developed for analysis of all kinds of food composition and contaminants. As one of the high-profile analytical techniques, Raman spectroscopy has been widely applied in food analysis with simple, rapid, sensitive, and nondestructive detection performance. Research on Raman techniques is a direction of great interest to many fields, especially in food safety. Hence, it is crucial to gain insight into recent advances on the use of Raman-based techniques in food safety applications. In this review, we introduce Raman techniques from normal Raman spectroscopy to developed ones (e.g., surface enhanced Raman scattering (SERS), spatially offset Raman spectroscopy (SORS), surface-enhanced spatially offset Raman spectroscopy (SESORS)), in view of their history and development, principles, design, and applications. In addition, future challenges and trends of these techniques are discussed regarding to food safety.

Metal organic frameworks-in-nanochannels: A tailorable chromatography membrane for isolation of target protein

Metal-organic frameworks (MOFs) demonstrate strong potential in biosample separation. However, the obtained MOFs powders are unsuitable for recovery techniques in an aqueous solution, especially the challenges of withdrawing MOFs particles and expanding their functions for specific applications. Herein, a general strategy is designed utilizing metal oxide-nanochannel arrays as precursors and templates for in-situ selective growth of MOFs structures. The exemplary MOFs (Ni-bipy) with tailored composition are selectively grown in NiO/TiO₂ nanochannel membrane (NM) using NiO as the sacrificial precursor, which enables one to achieve a ∼262 times concentration of histidine-tagged proteins within 100 min. The significantly improved adsorption efficiency in a wide pH range and the effective enrichment from a complex matrix as a nanofilter illustrate the great potential of MOFs in nanochannels membranes for the high-efficiency recovery of essential proteins in complex biological samples. The porous self-aligned Ni-MOFs/TiO₂ NM exhibits biocompatibility and flexible functionalities, which is desirable for the generation of multifunctional nanofilter devices and developing biomacromolecule delivery vehicles.

Target Recognition-Triggered Peroxidase-Mimicking Activity Depression in Homochiral Nanochannels for Identifying Cystine Enantiomers

Enantioselective identification of chiral molecules is of paramount importance in medical science, biochemistry, and pharmaceutics owing to the configuration-dependent activities of enantiomers. However, the identical physicochemical properties of enantiomers remain challenging in chiral sensing. In this study, inspired by the peroxidase-mimicking activity of Fe(III)-based nanomaterials, an enantioselective artificial architecture is constructed on TiO₂ nanochannels. Homochiral Ti-based metal-organic frameworks (MOFs) use a 2,2'-bipyridine-5,5'-dicarboxylic acid ligand as the artificial enzyme skeleton, Fe(III) as peroxidase-mimicking centers, and l-tartaric acid (TA) as a chiral recognition selector. Using l-/d-cystine as model enantiomers, the chiral moieties of l-TA on Ti-MOFs allow stereoselective recognition of guest molecules through hydrogen bonds formed between chiral cystine and the host. In a tris(2-carboxyethyl)phosphine hydrochloride-containing environment, the disulfide bonds in cystine molecules are further cleaved, and the HS-tails react with Fe(III) active sites, causing the loss of peroxidase-like performance of nanochannels. Benefitting from the nanochannel architecture's current-potential (I-V) properties, the selective recognition of cystine enantiomers is directly monitored through the peroxidase-like activity change-induced ionic current signatures. This study provides a new and universal strategy for distinguishing disulfide- and thiol-containing chiral molecules.

Chiral plasmonic Au-Ag core shell nanobipyramid for SERS enantiomeric discrimination of biologically relevant small molecules

The identification of enantiomers is of great importance in chiral separations and medicinal chemistry. While Surface-enhanced Raman spectroscopy (SERS) is a technique that provides vibrational fingerprints of analytes. The enantiomers identification relies on the SERS difference between left and right-handed circularly polarized light or additional selectors for indirect distinction. In this work, Au-Ag core shell nanobipyramid (L/D-Au@Ag BPs) were synthesized guiding by chiral encoder of L/D-cysteine. L/D-Au@Ag BPs produced plasmon-induced circular dichroism signals in the plasmon resonance absorption band, which can be tuned by modulation the amount of cysteine. Moreover, the chiral anisotropy factor of L/D-Au@Ag BPs at 532 nm can reach 5.11 × 10^-3. Due to the selective resonance coupling between L/D-Au@Ag BPs and different enantiomers, L/D-Au@Ag BPs were further used as SERS substrates for efficient discrimination of biologically relevant small molecules. Chiral Au@Ag BPs display the potential for chiral drug identification.

An H2S-Regulated Artificial Nanochannel Fabricated by a Supramolecular Coordination Strategy

Hydrogen sulfide (H₂S), as the third gasotransmitter, has an important impact on physiological and pathological activities. Herein, we fabricated an artificial nanochannel with a conductance value of 2.01 nS via a supramolecular coordination strategy. Benefiting from the unique H₂S-mediated covalent reaction, the nanochannel biosensor could change from ON to OFF states with the addition of H₂S. Furthermore, this nanochannel directed the ion transport, showing a high rectification ratio as well as gating ratio. Subsequently, theoretical simulations were conducted to help to reveal the possible mechanism of the functionalized nanochannel. This study can provide insights for better understanding the process of H₂S-regulated biological channels and fabricating gas gated nanofluids.

Engineering hierarchical FeS2/TiO2 nanotubes on Ti mesh as a tailorable flow-through catalyst belt for all-day-active degradation of organic pollutants and pathogens

The increasing organic and microbiological pollutions in fresh water caused by human activities and industrial development have become a global concern nowadays. In this study, three-dimensional (3D) hierarchical FeS₂/TiO₂ structures with nanotube geometries were grown on a Ti mesh (M-TNTAs-FeS₂). Benefitting from the abundant available reactive sites on the open 3D micro/nanoporous structures, excellent photocatalytic activity of FeS₂/TiO₂ heterostructure in solar light, and satisfactory Fenton activity of FeS₂, the obtained M-TNTAs-FeS₂ exhibits outstanding performance as an all-day-active catalyst. Importantly, flexible meshes can be easily tailored and enveloped into fluorinated ethylene propylene (FEP) pockets in a series as a flow-through belt for large-capacitance applications (998 L m^-2 at a flow rate of 417 L m^-2 h^-1 for a four-pockets belt), as indicated by the degradation of azo dyes, antibiotics, pesticides, and pathogens. This study may inspire a new tailorable catalyst design for a promising point-of-use purification device.

Tuning the fast generation of luminescent silver nanodots on a surface

Silver nanodots, predominantly a near-IR emitter, can be instantly generated on a surface by silver cluster transfer. Kinetic trapping of ssDNA molecules on the surface limits the reorganization of the resulting silver nanodots for other silver nanodot emitters. Adjusting the freedom of the adsorbed ssDNA can tune the generation of various silver nanodots on the surface.