Refined Cumulative Risk Assessment of Pb, Cd, and as in TCM Decoction Based on Bioavailability through In Vitro Digestion/MDCK Cells.

In this study, the oral bioavailability of Pb, Cd, and As in three types of traditional Chinese medicines (TCMs) and TCM decoctions were investigated through in vitro PBET digestion/MDKC cell model. Furthermore, a novel cumulative risk assessment model associated with co-exposure of heavy metal(loid)s in TCM and TCM decoction based on bioavailability was developed using hazard index (HI) for rapid screening and target organ toxicity dose modification of the HI (TTD) method for precise assessment. The results revealed that the bioavailability of Pb, Cd, and As in three types of TCM and TCM decoction was 5.32-72.49% and 4.98-51.97%, respectively. After rapid screening of the co-exposure health risks of heavy metal(loid)s by the HI method, cumulative risk assessment results acquired by TTD method based on total metal contents in TCMs indicated that potential health risks associated with the co-exposure of Pb, Cd, and As in Pheretima aspergillum (E. Perrier) and Oldenlandia diffusa (Willd.) Roxb were of concern. However, considering both the factors of decoction and bioavailability, TTD-adjusted HI outcomes for TCMs in this study were <1, indicating acceptable health risks. Collectively, our innovation on cumulative risk assessment of TCM and TCM decoction provides a novel strategy with the main purpose of improving population health.

Negative Differential Resistance in Conical Nanopore Iontronic Memristors.

Emerging ion transport dynamics with memory effects at nanoscale solution-substrate interfaces offers a unique opportunity to overcome the bottlenecks in traditional computational architectures, trade-offs in selectivity and throughput in separation, and electrochemical energy conversions. Negative differential resistance (NDR), a decrease in conductance with increasing potential, constitutes a new function from the perspective of time-dependent instead of steady-state nanoscale electrokinetic ion transport but remains unexplored in ionotronics to develop higher-order complexity and advanced capabilities. Herein, NDR is introduced in hysteretic and rectified ion transport through single conical nanopipettes (NPs) as ionic memristors. Deterministic and chaotic behaviors are controlled via an electric field as the sole stimulus. The NDR arises fundamentally from the availability and redistribution of the ionic charges during the hysteretic and rectified transport at asymmetric nanointerfaces. The elucidated mechanism is generalizable, and the drastically simplified operations enable tunable state-switching dynamics with higher-order complexity besides the first-order synaptic functions in multiple excitatory and inhibitory states.

Covalently-Bonded Laminar Assembly of Van der Waals Semiconductors with Polymers: Toward High-Performance Flexible Devices.

Van der Waals semiconductors (vdWS) offer superior mechanical and electrical properties and are promising for flexible microelectronics when combined with polymer substrates. However, the self-passivated vdWS surfaces and their weak adhesion to polymers tend to cause interfacial sliding and wrinkling, and thus, are still challenging the reliability of vdWS-based flexible devices. Here, an effective covalent vdWS-polymer lamination method with high stretch tolerance and excellent electronic performance is reported. Using molybdenum disulfide (MoS2 )and polydimethylsiloxane (PDMS) as a case study, gold-chalcogen bonding and mercapto silane bridges are leveraged. The resulting composite structures exhibit more uniform and stronger interfacial adhesion. This enhanced coupling also enables the observation of a theoretically predicted tension-induced band structure transition in MoS2 . Moreover, no obvious degradation in the devices' structural and electrical properties is identified after numerous mechanical cycle tests. This high-quality lamination enhances the reliability of vdWS-based flexible microelectronics, accelerating their practical applications in biomedical research and consumer electronics.

A Single-Entity Method for Actively Controlled Nucleation and High-Quality Protein Crystal Synthesis.

Lack of controls and understanding in nucleation, which proceeds crystal growth and other phase transitions, has been a bottleneck challenge in chemistry, materials, biology, and other fields. The exemplary needs for better methods for biomacromolecule crystallization include (1) synthesizing crystals for high-resolution structure determinations in fundamental research and (2) tuning the crystal habit and thus the corresponding properties in materials and pharmaceutical applications. Herein, a deterministic method is established capable of sustaining the nucleation and growth of a single crystal using the protein lysozyme as a prototype. The supersaturation is localized at the interface between a sample and a precipitant solution, spatially confined by the tip of a single nanopipette. The exchange of matter between the two solutions determines the supersaturation, which is controlled by electrokinetic ion transport driven by an external potential waveform. Nucleation and subsequent crystal growth disrupt the ionic current limited by the nanotip and are detected. The nucleation and growth of individual single crystals are measured in real time. Electroanalytical and optical signatures are elucidated as feedbacks with which active controls in crystal quality and method consistency are achieved: five out of five crystals diffract at a true atomic resolution of up to 1.2 Å. As controls, those synthesized under less optimized conditions diffract poorly. The crystal habits during the growth process are tuned successfully by adjusting the flux. The universal mechanism of nano-transport kinetics, together with the correlations of the diffraction quality and crystal habit with the crystallization control parameters, lay the foundation for the generalization to other materials systems.

Quantification of MicroRNAs or Viral RNAs with Microelectrode Sensors Enabled by Electrochemical Signal Amplification.

Quantification of circulating microRNAs (miRNAs) or viral RNAs is of great significance because of their broad relevance to human health. Currently, quantitative reverse transcription polymerase chain reaction (qRT-PCR), as well as microarray and gene sequencing, are considered mainstream techniques for miRNA identification and quantitation and the gold standard for SARS-CoV2 detection in the COVID-19 pandemic. However, these laboratory techniques are challenged by the low levels and wide dynamic range (from aM to nM) of miRNAs in a physiological sample, as well as the difficulty in the implementation in point-of-care settings. Here, we describe a one-step label-free electrochemical sensing technique by assembling self-folded multi-stem DNA-redox probe structure on gold microelectrodes and introducing a reductant, tris(2-carboxyethyl) phosphine hydrochloride (TCEP), in the detection buffer solution to achieve ultrasensitive detection with a detection limit of 0.1 fM that can be further improved if needed.

Kinetics-Based Ratiometric Electrochemiluminescence Analysis for Signal Specificity: Case Studies of Piperazine Drug Discrimination with Au Nanoclusters.

A multi-parameter calibration and analysis strategy has been developed based on the kinetics of charge transfer reactions. Absolute and ratiometric electrochemiluminescence signals are elucidated from single measurements for the detection of hydroxyzine and cetirizine as prototype drugs which greatly enhance the near-infrared electrochemiluminescence from atomically precise Au22 nanoclusters stabilized with lipoic acid ligands on ITO electrodes. The signal-on sensing mechanism eliminates the need for recognition elements and highly excess co-reactants in conventional electrochemiluminescence practice. The rates of sequential charge transfer reactions render specificity in electrochemiluminescence intensity and kinetics toward the target molecular/electronic structures and are conveniently controlled/optimized by operation parameters. Signal kinetic profiles, in stark contrast to steady-state or single-point recordings, not only improve the signal/noise ratio but also offer greater resolving power to differentiate analogue species and nonspecific interference. The fundamental kinetics-based ratiometric concept/strategy is not limited to a specific luminophore or a co-reactant and is thus generalizable. The case studies successfully detect and discriminate drug compounds at sub-nanomolar physiological ranges, with efficacy validated using synthetic urine toward point-of-care applications in therapeutic/abuse drug monitoring.

[Identification of geographical origins of Cordyceps based on data of amino acids with self-organizing map neural network].

In this study, data of amino acids of Cordyceps samples from Qinghai and Tibet was analyzed with self-organizing map neural network. A model of XY-Fused network was established with the content of 8 major amino acids and total amino acids for the identification of geographical origins of Cordyceps from Qinghai and Tibet. It had the prediction accuracy of 83.3% for the test set. In addition, data mining indicated that methionine was a special kind of amino acid in Cordyceps which could serve as a marker to identify its geographical origins. On this basis, the content ratio of methionine to total amino acids was proposed to be a quantifiable indicator to distinguish Cordyceps from Qinghai and Tibet.

Inhomogeneous Quantized Single-Electron Charging and Electrochemical-Optical Insights on Transition-Sized Atomically Precise Gold Nanoclusters.

Small differences in electronic structures, such as an emerging energy band gaps or the splitting of degenerated orbitals, are very challenging to resolve but important for nanomaterials properties. A signature electrochemical property called quantized double layer charging, i.e., "continuous" one-electron transfers (1e, ETs), in atomically precise Au133(TBBT)52, Au144(BM)60, and Au279(TBBT)84 is analyzed to reveal the nonmetallic to metallic transitions (whereas TBBT is 4-tert-butylbenzenethiol and BM is benzyl mercaptan; abbreviated as Au133, Au144, and Au279). Subhundred milli-eV energy differences are resolved among the "often-approximated uniform" peak spacings from multipairs of reversible redox peaks in voltammetric analysis, with single ETs as internal standards for calibration and under temperature variations. Cyclic and differential pulse voltammetry experiments reveal a 0.15 eV energy gap for Au133 and a 0.17 eV gap for Au144 at 298 K. Au279 is confirmed metallic, displaying a "bulk-continuum" charging response without an energy gap. The energy gaps and double layer capacitances of Au133 and Au144 increase as the temperature decreases. The temperature dependences of charging energies and HOMO-LUMO gaps of Au133 and Au144 are attributed to the counterion permeation and the steric hindrance of ligand, as well as their molecular compositions. With the subtle energy differences resolved, spectroelectrochemistry features of Au133 and Au144 are compared with ultrafast spectroscopy to demonstrate a generalizable analysis approach to correlate steady-state and transient energy diagram for the energy-in processes. Electrochemiluminescence (ECL), one of the energy-out processes after the charge transfer reactions, is reported for the three samples. The ECL intensity of Au279 is negligible, whereas the ECLs of Au133 and Au144 are relatively stronger and observable (but orders of magnitudes weaker than our recently reported bimetallic Au12Ag13). Results from these atomically precise nanoclusters also demonstrate that the combined voltammetric and spectroscopic analyses, together with temperature variations, are powerful tools to reveal subtle differences and gain insights otherwise inaccessible in other nanomaterials.

Deconvolution of electroosmotic flow in hysteresis ion transport through single asymmetric nanopipettes.

Unveiling the contributions of electroosmotic flow (EOF) in the electrokinetic transport through structurally-defined nanoscale pores and channels is challenging but fundamentally significant because of the broad relevance of charge transport in energy conversion, desalination and analyte mixing, micro and nano-fluidics, single entity analysis, capillary electrophoresis etc. This report establishes a universal method to diagnose and deconvolute EOF in the nanoscale transport processes through current-potential measurements and analysis without simulation. By solving Poisson, Nernst-Planck (PNP) with and without Navier-Stokes (NS) equations, the impacts of EOF on the time-dependent ion transport through asymmetric nanopores are unequivocally revealed. A sigmoidal shape in the I-V curves indicate the EOF impacts which further deviate from the well-known non-linear rectified transport features. Two conductance signatures, an absolute change in conductance and a 'normalized' one relative to ion migration, are proposed as EOF impact (factor). The EOF impacts can be directly elucidated from current-potential experimental results from the two analytical parameters without simulation. The EOF impact is found more significant in intermediate ionic strength, and potential and pore size dependent. The less-intuitive ionic strength and size dependence is explained by the combined effects of electrostatic screening and non-homogeneous charge distribution/transport at nanoscale interface. The time-dependent conductivity and optical imaging experiments using single nanopipettes validate the proposed method which is applicable to other channel type nanodevices and membranes. The generalizable approach eliminates the need of simulation/fitting of specific experiments and offers previously inaccessible insights into the nanoscale EOF impacts under various experimental conditions for the improvement of separation, energy conversions, high spatial and temporal control in single entity sensing/manipulation, and other related applications.

Near Infrared Electrochemiluminescence of Rod-Shape 25-Atom AuAg Nanoclusters That Is Hundreds-Fold Stronger Than That of Ru(bpy)3 Standard.

Near infrared (near-IR) electrogenerated chemiluminescence (ECL) from rod-shape bimetallic Au12Ag13 nanoclusters is reported. With ECL standard tris(bipyridine)ruthenium(II) complex (Ru(bpy)3) as reference, the self-annihilation ECL of the Au12Ag13 nanoclusters is about 10 times higher. The coreactant ECL of Au12Ag13 is about 400 times stronger than that of Ru(bpy)3 with 1 mM tripropylamine as coreactants. Voltammetric analysis reveals both oxidative and reductive ECLs under scanning electrode potentials. Transient ECL signals (tens of milliseconds) and decay profiles are captured by potential step experiments. An extremely strong and transient self-annihilation ECL is detected by activating LUMO and HOMO states sequentially via electrode reactions. The ECL generation pathways and mechanism are proposed based on the key anodic and cathodic activities arising from the energetics of this unique atomic-precision bimetallic nanocluster. Successes in the generation of the unprecedented strong near-IR ECL strongly support our prediction and choice of this nanocluster based on its record-high 40% quantum efficiency of near-IR photoluminescence. Correlation of the properties to the atomic/electronic structures has been a long-pursued goal particularly in the fast growing atomic-precision nanoclusters field. The mechanistic insights provided in this fundamental study could guide the design and syntheses of other nanoclusters or materials in general to achieve improved properties and further affirm the structure-function correlations. The high ECL signal in the less interfered near-infrared spectrum window offers combined merits of high-signal-low-noise/interference or high contrast for broad analytical sensing and immunoassays and other relevant applications.

[Determination of 42 veterinary drug residues in common animal derived food by dispersive solid phase extraction coupled with liquid chromatography-tandem mass spectrometry].

A liquid chromatography-tandem mass spectrometry method, coupled with a dispersive solid phase extraction (DSPE) procedure for sample preparation, was developed to determine 13 classes of 42 veterinary drugs in four representative animal-derived foods. The analytes were dispersed with water, extracted with acetonitrile containing 5% (v/v) formic acid, salted out by salts, and purified by DSPE. The analytes were separated on a C18 column (100 mm×2.1 mm, 2 µ m) with gradient elution using the mobile phase containing methanol and 0.1% (v/v) formic acid aqueous solution. Electrospray ionization-mass spectrometry was performed in multiple reaction monitoring mode for analysis of the 42 compounds. The correlation coefficients of the standard calibration curves for the 42 veterinary drugs were all above 0.995. Most recoveries at three spiked levels in the four representative matrixes ranged from 65.8% to 135.5%, with relative standard deviations of 0.5%-14.2% (n=6). The limits of detection (LODs, S/N=3) and the limits of quantification (LOQs, S/N=10) were 0.01-1.68 µ g/kg and 0.01-5.62 µ g/kg, respectively. The method is simple, rapid, sensitive, and suitable for the simultaneous determination of the 42 veterinary drugs in animal-derived food.

International regulatory requirements for skin sensitization testing.

Skin sensitization test data are required or considered by chemical regulation authorities around the world. These data are used to develop product hazard labeling for the protection of consumers or workers and to assess risks from exposure to skin-sensitizing chemicals. To identify opportunities for regulatory uses of non-animal replacements for skin sensitization tests, the needs and uses for skin sensitization test data must first be clarified. Thus, we reviewed skin sensitization testing requirements for seven countries or regions that are represented in the International Cooperation on Alternative Test Methods (ICATM). We noted the type of skin sensitization data required for each chemical sector and whether these data were used in a hazard classification, potency classification, or risk assessment context; the preferred tests; and whether alternative non-animal tests were acceptable. An understanding of national and regional regulatory requirements for skin sensitization testing will inform the development of ICATM's international strategy for the acceptance and implementation of non-animal alternatives to assess the health hazards and risks associated with potential skin sensitizers.

On the Non-Metallicity of 2.2†nm Au246 (SR)80 Nanoclusters.

The transition from molecular to plasmonic behaviour in metal nanoparticles with increasing size remains a central question in nanoscience. We report that the giant 246-gold-atom nanocluster (2.2 nm in gold core diameter) protected by 80 thiolate ligands is surprisingly non-metallic based on UV/Vis and femtosecond transient absorption spectroscopy as well as electrochemical measurements. Specifically, the Au246 nanocluster exhibits multiple excitonic peaks in transient absorption spectra and electron dynamics independent of the pump power, which are in contrast to the behaviour of metallic gold nanoparticles. Moreover, a prominent oscillatory feature with frequency of 0.5 THz can be observed in almost all the probe wavelengths. The phase and amplitude analysis of the oscillation suggests that it arises from the wavepacket motion on the ground state potential energy surface, which also indicates the presence of a small band-gap and thus non-metallic or molecular-like behaviour.

Correlation of Ion Transport Hysteresis with the Nanogeometry and Surface Factors in Single Conical Nanopores.

Better understanding in the dynamics of ion transport through nanopores or nanochannels is important for sensing, nucleic acid sequencing and energy technology. In this paper, the intriguing nonzero cross point, resolved from the pinched hysteresis current-potential (i-V) curves in conical nanopore electrokinetic measurements, is quantitatively correlated to the surface and geometric properties by simulation studies. The analytical descriptions of the conductance and potential at the cross point are developed: the cross-point conductance includes both the surface and volumetric conductance; the cross-point potential represent the overall/averaged surface potential difference across the nanopore. The impacts by individual parameter such as pore radius, half cone angle, and surface charges are systematically studied in the simulation that would be convoluted and challenging in experiments. The elucidated correlation is supported by and offer predictive guidance for experimental studies. The results also offer more quantitative and systematic insights in the physical origins of the concentration polarization dynamics in addition to ionic current rectification inside conical nanopores and other asymmetric nanostructures. Overall, the cross point serves as a simple yet informative analytical parameter to analyze the electrokinetic transport through broadly defined nanopore-type devices.

MiRNA Quantitation with Microelectrode Sensors Enabled by Enzymeless Electrochemical Signal Amplification.

Quantification of circulating microRNAs (miRNAs) is of great interest because of their potentials as disease biomarkers. Currently, quantitative reverse transcription polymerase chain reaction (qRT-PCR) and microarray are considered mainstream techniques for miRNA identification and quantitation. However, these techniques are challenged by the low levels and wide dynamic range (from aM to nM) of miRNAs in a physiological sample, as well as the difficulty in the implementation in point-of-care settings. Here, we describe a one-step label-free electrochemical sensing technique by assembling a triple-stem DNA-redox probe structure on a gold microelectrode and introducing a reductant, tris(2-carboxyethyl) phosphine hydrochloride (TCEP) in the detection buffer solution to achieve ultrasensitive miRNAs detection with a detection limit of 0.1 fM.

Near-Infrared Electrogenerated Chemiluminescence from Aqueous Soluble Lipoic Acid Au Nanoclusters.

Strong electrogenerated chemiluminescence (ECL) is detected from dithiolate Au nanoclusters (AuNCs) in aqueous solution under ambient conditions. A novel mechanism to drastically enhance the ECL is established by covalent attachment of coreactants N,N-diethylethylenediamine (DEDA) onto lipoic acid stabilized Au (Au-LA) clusters with matching redox activities. The materials design reduces the complication of mass transport between the reactants during the lifetime of radical intermediates involved in conventional ECL generation pathway. The intracluster reactions are highly advantageous for applications by eliminating additional and high excess coreactants otherwise needed. The enhanced ECL efficiency also benefits uniquely from the multiple energy states per Au cluster and multiple DEDA ligands in the monolayer. Potential step and sweeping experiments reveal an onset potential of 0.78 V for oxidative-reduction ECL generation. Multifolds higher efficiency is found for the Au clusters alone in reference to the standard Rubpy with high excess TPrA. The ECL in near-IR region (beyond 700 nm) is highly advantageous with drastically reduced interference signals over visible ones. The features of ECL intensity responsive to electrode potential and solution pH under ambient conditions make Au-LA-DEDA clusters promising ECL reagents for broad applications. The strategy to attach coreactants on Au clusters is generalizable for other nanomaterials.

Microelectrode miRNA sensors enabled by enzymeless electrochemical signal amplification.

Better detections of circulating microRNAs (miRNAs) as disease biomarkers could advance diseases diagnosis and treatment. Current analysis methods or sensors for research and applications are challenged by the low concentrations and wide dynamic range (from aM to nM) of miRNAs in a physiological sample. Here, we report a one-step label-free electrochemical sensor comprising a triple-stem DNA-redox probe structure on a gold microelectrode. A new signal amplification mechanism without the need of a redox enzyme is introduced. The novel strategy overcomes the fundamental limitations of microelectrode DNA sensors that fail to generate detectable current, which is primarily due to the limited amount of redox probes in response to the target analyte binding. By employing a reductant, tris(2-carboxyethyl) phosphine hydrochloride (TCEP) in the detection buffer solution, each redox molecule on the detection probe is cyclically oxidized at the electrode and reduced by the reductant; thus, the signal is amplified in situ during the detection period. The combined merits in the diagnosis power of cyclic voltammetry and the high sensitivity of pulse voltammetry enable parallel analysis for method validation and optimization previously inaccessible. As such, the detection limit of miRNA-122 was 0.1 fM via direct readout, with a wide detection range from sub fM to nM. The detection time is within minutes, which is a significant improvement over other macroscopic sensors and other relevant techniques such as quantitative reverse transcription polymerase chain reaction (qRT-PCR). The high selectivity of the developed sensors is demonstrated by the discrimination against two most similar family sequences: miR-122-3p present in serum and 2-mismatch synthetic RNA sequence. Interference such as nonspecific adsorption, a common concern in sensor development, is reduced to a negligible amount by adopting a multistep surface modification strategy. Importantly, unlike qRT-PCR, the microelectrochemical sensor offers direct absolute quantitative readout that is amenable to clinical and in-home point-of-care (POC) applications. The sensor design is flexible, capable of being tailored for detection of different miRNAs of interest. Combined with the fact that the sensor was constructed at microscale, the method can be generalized for high throughput detection of miRNA signatures as disease biomarkers.

Electronic coupling between ligand and core energy states in dithiolate-monothiolate stabilized Au clusters.

Electron transfer activities of metal clusters are fundamentally significant and have promising potential in catalysis, charge or energy storage, sensing, biomedicine and other applications. Strong resonance coupling between the metal core energy states and the ligand molecular orbitals has not been established experimentally, albeit exciting progress has been achieved in the composition and structure determination of these types of nanomaterials recently. In this report, the coupling between core and ligand energy states is demonstrated by the rich electron transfer activities of Au130 clusters. Quantized electron transfers to the core and multi-electron transfers involving the durene-dithiolate ligands were observed at lower and higher potentials, respectively, in voltammetric studies. After a facile multi-electron oxidation from +1.34 to +1.40 V, several reversal reduction processes at more negative potentials, i.e. +0.91 V, +0.18 V and -0.34 V, were observed in an electrochemically irreversible fashion or with sluggish kinetics. The number of electrons and the shifts of the respective reduction potentials in the reversal process were attributed to the electronic coupling or energy relaxation processes. The electron transfer activities and subsequent relaxation processes are drastically reduced at lower temperatures. The time- and temperature-dependent relaxation, involving multiple energy states in the reversal reduction processes upon the oxidation of ligands, reveals the coupling between core and ligand energy states.

Transitions in Discrete Absorption Bands of Au130 Clusters upon Stepwise Charging by Spectroelectrochemistry.

Rich and tunable physicochemical properties make noble metal clusters promising candidates as novel nanomolecules for a variety of applications. Spectroelectrochemistry analysis is employed to resolve previously inaccessible electronic transitions in Au130 clusters stabilized by a monolayer of di- and monothiolate ligands. Well-defined quantized double-layer charging of the Au core and oxidizable ligands make this Au130 nanocluster unique among others and enable selective electrolysis to different core and ligand charge states. Subsequent analysis of the corresponding absorption changes reveals that different absorption bands originate from different electronic transitions involving both metal core energy states and ligand molecular orbitals. Besides the four discrete absorption bands in the steady-state UV-visible-near-IR absorption spectrum, additional transitions otherwise not detectable are resolved upon selective addition/removal of electrons at cores and ligand energy states, respectively, upon electrolysis. An energy diagram is proposed that successfully explains the major features observed in electrochemistry and absorption spectroscopy. Those assignments are believed applicable and effective to explain similar transitions observed in some other Au thiolate clusters.