Ultra-low Concentration Research Articles

Highly sensitive Fe3+ luminescence detection via single-ion adsorption

To achieve a lower detection limit has always been a goal of analytical chemists. Herein, we demonstrate the first picomolar level detection capability for Fe3+ ion via luminescence detection technology. The results of structural analysis and theoretical calculation show that Fe3+ ions are adsorbed on the central node of Eu-DBM (DBM = dibenzoylmethane) sensor in the form of single ion at ultralow concentration. Subsequently, the pathways of photo-induced charge and energy transfer of the obtained Eu-DBM@Fe3+ material have been changed, from the initial DBM-to-Eu3+ before Fe3+ adsorption to the ultimate DBM-to-Fe3+ after adsorption process, which quenches the luminescence of Eu3+ ion. This work not only obtains the highly sensitive luminescence detection ability, but also innovatively proposes the single-ion adsorption mechanism, both of which have important scientific and application values for the development of more efficient detection agents in the future.

Efficient SO2 capture at ultra-low concentration using a hybrid absorbent of deep eutectic solvent and ethylene glycol

Deep eutectic solvents (DESs) are considered as the highly effective absorbents for sulfur dioxide (SO2) capture. However, the high viscosity of DESs and the resulting slow absorption rate as well as low absorption capacity at low SO2 concentration seriously hinder their industrial application. In this study, DES of N-methyldiethanolamine (MDEA) and imidazole (Im) is simply blended with ethylene glycol (EG) forming a hybrid absorbent, namely MDEA/Im-EG, which exhibits extremely high SO2 capture capacity at low concentration. In particular, SO2 capture capacity in MDEA/Im-EG (molar ratio = 1:1) reaches 0.446 g SO2/g absorbent at 293.2 K with SO2 concentration of 2000 ppm. Moreover, the corresponding desorption enthalpy is only −40.67 kJ/mol. To well understand the results, thermodynamic analysis of SO2 capture is performed and the SO2 capture mechanism is speculated by nuclear magnetic resonance and Fourier transform infrared spectroscopy.

Long‐lasting chemiluminescence by aggregation‐induced emission surfactant with ultralow critical micelle concentration

AbstractThe development of green and simple chemiluminescence (CL) systems with intensive and long‐lasting emission is highly desirable in lighting and extension of their applications. In this study, it is found that the involvement of aggregation‐induced emission (AIE) surfactant could greatly enhance the CL of luminol–H2O2–Co2+ system. The inserted hydrophobic tetraphenylethylene fluorophore in AIE is able to increase the hydrophobicity of alkyl chain and decrease the critical micelle concentration (CMC) of surfactant. The synergistic effect of micelle‐improved enrichment and CL resonance energy transfer endows luminol–H2O2–Co2+ system intensive and long‐lasting emission under neutral pH conditions (pH 7.4). The visible emission is still observed even after 60 min. Our study has opened a new avenue for exploring green and simple effective CL systems through AIE surfactant with unltralow CMC toward various applications in lighting, optical sensing, and photocatalysis, etc.

Ultra-low concentration terbium (Tb) adsorption on garlic peels biosorbent and its application for Nd-Fe-B scraps recovery

Motivated by the strategic value of middle-heavy rare earth elements (MHREEs), we proposed a bio-adsorption method to recover ultra-low concentration terbium (Tb(Ⅲ)) from industrial wastewater that originated from the Nd-Fe-B scraps recovery process. It could be found that Tb(Ⅲ) ions as low as 5.34 ng·mL−1(ppb) could be adsorbed onto Ca(Ⅱ)-modified garlic peels (Ca-GP) within 10 min with the adsorption efficiency of 99.2% at pH 3.5. The adsorption behavior of Tb(Ⅲ) onto Ca-GP conformed the Langmuir isotherm model and pseudo-second-order kinetic model. ATR-FTIR, XPS and density-functional theory (DFT) calculations results showed that Tb(Ⅲ) ions could be ion-exchanged with cations in Ca-GP such as Ca(Ⅱ) and -COOH. In application, column experiment results showed that the maximum bed adsorption capacity for Tb, praseodymium (Pr), neodymium (Nd), dysprosium (Dy), and Total rare earth elements (REEs) ions calculated by the Thomas model was 0.06, 3.50, 9.65, 7.34, and 27.37 μg·g−1, respectively, with the initial concentration of 0.37 ng·mL−1 Tb, 20 ng·mL−1 Pr, 44 ng·mL−1 Nd, 67 ng·mL−1 Dy and 170 ng·mL−1 total REEs ions of actual solutions (below the solubility of rare-earth hydroxide). This manuscript thus provided a novel cost-effective and efficient approach to the enrichment and recovery of MHREEs from ultra-low concentration REEs ions-containing solutions.

Pt-functionalized Amorphous RuOx as Excellent Stability and High-activity Catalysts for Low Temperature MEMS Sensors.

The unsaturated coordination and abundant active sites endow amorphous metals with tremendous potential in improving metal oxide semiconductors' gas-sensing properties. However, the amorphous materials maintain the metastable status and easily transfer into the lower-active crystals during the gas-sensing process at high working temperatures, significantly limiting their further applications. Here, a bimetal amorphous PtRu catalyst is developed by accurately regulating the introduction of Pt species into amorphous RuOx supports to realize the highly active and stable H2 S gas-sensing detection. It is found that incorporation of low-concentration Pt species can effectively maintain the amorphous state of initial RuOx and delay the crystallization temperature as high as 100°C. Further, ex situ XPS and in situ Raman spectroscopy analysis confirm that active Pt species can facilitate H2 S adsorption by strong Pt-S coordination and dissociate the sulfur species to the surrounding support, which contribute to the chemisorption and sensitization of H2 S. Meanwhile, electron transport at the interface between Pt, RuOx and ZnO further activates the reaction process at the surface of the gas-sensitive material. The final PtRu-modified ZnO (PtRu/ZnO) sensor enables the detection of H2 S in the ultra-low concentration range of 15-2000 ppb with remarkable stability.

Review on Multidimensional Adsorbents for CO2 Capture from Ambient Air: Recent Advances and Future Perspectives

The urgency of curbing global warming triggered by growing CO2 emissions has generated significant attention. Direct air capture (DAC) is a crucial and feasible technology to cut CO2 emissions at nonpoint sources, therefore achieving negative emissions. Solid porous sorbents have drawn increasing attention for CO2 capture from the atmosphere with ultralow CO2 concentration (ca. 400 ppm). However, most related studies focus on nanoparticle-based adsorbents and their functionalized counterparts, which are more prone to lose weight in the atmosphere. In this context, we summarize nanoparticle composite adsorbents, including zero-dimensional powders, one-dimensional fibers, two-dimensional membranes, and three-dimensional aerogels, and assess the physicochemical properties and typical applications of major types of nanoporous adsorbents in the field of CO2 adsorption and separation with emphasis on DAC. The multidimensions of emerging adsorbents versus CO2 uptake are discussed and compared separately. Combined with recent reported advances, we provide deep insights for the design and synthesis of multifunctional materials for efficient CO2 adsorption. Moreover, life cycle and techno-economic assessments of DAC using different materials are briefly estimated. Finally, challenges and current trends in the DAC system for commercialization have been put forward.

Analyte enrichment and sensitive detection over nanosecond laser textured stainless steel superhydrophobic surfaces

In this report, we have investigated the use of nanosecond laser texturing produced superhydrophobic surfaces for enrichment and sensitive detection of analytes. We have shown that by carefully choosing the laser processing parameters, the superhydrophobic surfaces capable of maintaining a small (5 μL) aqueous droplet in spherical shape till the last stage of evaporation and hence enabling the droplet to deposit its entire content over ∼80–100 μm size residual spot upon complete evaporation, can be prepared. The spot was found to get formed by bridging over the micro structures suggesting that the droplet remained suspended over the structures i.e. did not penetrate the structures till the very end of the evaporation process. By performing fluorescence spectroscopy of the residual spot, Rhodamine 6G could be detected at an ultra-low concentration of 10−18 molL−1 in a 5 μL water droplet. When compared with the results obtained on unprocessed stainless steel substrate, these superhydrophobic steel surfaces were found to provide four orders of magnitude enhancement in the lowest detectable concentration of Rhodamine 6G.

Construction of layered double hydroxides on wood surfaces for wood coloring

Wood dyeing usually requires a large concentration of metal solution, which when released to the atmosphere as waste liquid, causes pollution. In this study, a metal-organic framework (MOF) with micron-size structure was in-situ grown on a wood surface as a template and precursor for a layered double hydroxide (LDH). The LDH had a nanoscale structure and was generated on the wood surface from ultra-low concentration NiCl2 solution. The generation was based on a hydrolytically induced exchange process between the MOF and hydroxide ions. The results of following this procedure showed that petal-like Co/Ni-LDH with micro-nano composite structure was formed on the wood surface. Due to the LDH, a uniform light green color was formed on the wood surface at a reaction temperature and time of 60 ℃ in 34 min, respectively. To improve the hydrophobicity of the LDH layer, a long chain alkyl with low surface energy was introduced into the lamellae from a sodium stearate solution, constructing a superhydrophobic layer on the wood surface. The modified wood surface showed excellent UV light aging and water resistances. Moreover, Ni2+ was replaced with Mn2+, Fe3+, Cu2+, and Zn2+ ions and dark brown, yellow, blue, and white colors, respectively, were formed on wood. The present method is also suitable for other wood. Wood surface color adjusted by LDH uses low concentration of metal salt solution and proved to be a mild and green wood color toning method.

Retarding the diffusion rate of piperazine through the interface of aqueous/organic phase: Bis-tris propane tuned the trans-state of ultra-low concentration piperazine

An urgent challenge during the preparation of polyamide thin film composite membrane via the interfacial polymerization method was excessive diffusion rate of piperazine to form uncontrollable polyamide layer thickness, ultimately leaded to low water permeability to increase the operating cost. Herein, a uniquely new method, which brought down one order of magnitude of piperazine concentration to ultra-low grade (0.01% w·v−1) to retard the diffusion rate, was utilized to avoid the problem. However, the ultra-low concentration of piperazine could not easily react with trimesoyl chloride, bis-tris propane as conditioning agent was needed to overcame the trouble. The kinetics diffusion process of piperazine under the function of bis-tris propane was intensively studied by molecular dynamics simulation and other characterizations. Bis-tris propane could combine with piperazine to generate intermolecular force and then carry piperazine molecules moving toward the interface of aqueous/organic phase, which tuned the trans-state of piperazine to the benefit of rection. This work offered a novelty insight to surmount the problem of the excessive diffusion rate, which could promote the development of membrane technology.

Immuno-Sensing at Ultra-Low Concentration of TG2 Protein by Organic Electrochemical Transistors.

Transglutaminase 2 (TG2) is a ubiquitously expressed member of the transglutaminase family with Ca2+-dependent protein crosslinking activity. Its subcellular localization is crucial in determining its function, and indeed, TG2 is found in the extracellular matrix, mitochondria, recycling endosomes, plasma membrane, cytosol, and nucleus because it is associated with cell growth, differentiation, and apoptosis. It is involved in several pathologies, such as celiac disease, cardiovascular, hepatic, renal, and fibrosis diseases, carrying out opposite functions of up and down regulation in the progression of the same pathology. Therefore, this fine regulation requires a very sensitive and specific method of identification of TG2, which is to be detected in very small quantities in a deregulated condition. Here, we demonstrate the possibility of detecting TG2 down to attomolar concentration by using organic electrochemical transistors driven by gold electrodes functionalized with anti-TG2 antibodies. In particular, a direct correlation between the TG2 concentration and the transistor transconductance values, as extracted from typical transfer curves, was found. Overall, our findings highlight the potentialities of this new biosensing approach for the detection of TG2 in the context of pathological diseases, offering a rapid and cost-effective alternative to traditional methods.

Austenite Formation and Manganese Partitioning during Double Soaking of an Ultralow Carbon Medium‐Manganese Steel

Double soaking (DS) is a thermal processing route intended to produce austenite–martensite microstructures in steels containing austenite‐stabilizing additions and consists of intercritical annealing (primary soaking), followed by heating and brief isothermal holding at an increased temperature (secondary soaking), and quenching. Herein, experimental dilatometry during DS of a medium‐manganese (Mn) steel with nominally 7 wt% Mn and an ultralow residual carbon concentration, in combination with phase‐field simulations of austenite formation during secondary soaking, is presented. The feasibility of maintaining heterogeneous Mn distributions during DS is demonstrated and insight is provided on the effects of the secondary soaking temperature and prior Mn distribution on the ferrite‐to‐austenite phase transformation during the secondary soaking portion of the DS treatment.

An ultrasonically catalyzed conductometric metal oxide gas sensor system with machine learning-based ambient temperature compensation

The ultrasonic catalysis method provides a new means of enhancing sensing performance of some types of gas sensors. But generating the ultrasound consumes electric energy and increases the system mass. Thus, it is significant to lower the energy consumption and mass of the ultrasonic excitation structure as much as possible, while enhancing the sensing performance. In this work, a thin conical metal shell excited by a piezoelectric disk has been proposed, serving as the focusing ultrasonic transducer and protection case for a SnO2 gas sensor. The ultrasonic transducer’s total mass is only 11 g. The experiments show that the ultrasonic transducer can significantly reduce the low detection limit (LDL), and measured LDL of the sonicated sensor for H2 can be as low as 107 ppb (1/3 of the same sensing element not sonicated) with a response of 4.6%. In this case, the ultrasonic transducer’s power consumption and temperature rise is 146 mW and 3 ℃, respectively. The low temperature rise indicates that the LDL may be further decreased by increasing the ultrasonic vibration. The effect of ambient temperature change on predicted H2 concentration is compensated by two convolutional neural networks for the low (1–100 ppm) and ultralow (≤ 1 ppm) concentration ranges, and the relative error of concentration prediction in these two concentration ranges is 5.7% and 12.3%, respectively.

Sunlight propelled two-dimensional nanorobots with enhanced mechanical damage of bacterial membrane

Bacterial pollution in water sources poses a serious threat to human health and causes a water crisis. To treat it efficiently and ecologically, many studies have explored the antibacterial properties of two-dimensional nanomaterials in water, but their static antibacterial modes limit their effectiveness. In this work, we designed a facile and effective antibacterial nanorobots by loading super small gold nanorods (sAuNR) onto the surface of MXene nanosheets (MXene@sAuNR). The plasmon resonance effect of sAuNR can enhance the optical absorption cross section of the nanorobots, thereby improving their motion ability under irradiation and then causing cell membrane mechanical damage to bacteria. Our research proved that nanorobots with good optical driving characteristics displayed gratifying antibacterial properties even at ultra-low concentration as 5 µg/mL within 30 min. Furthermore, the nanorobots showed satisfactory antibacterial efficiency in real river samples under sunlight irradiation. These nanorobots presented in this study provides valuable insights towards designing self-energy collection and self-driving antibacterial materials that overcome the shortcomings of conventional static antibacterial methods. As sunlight is the cheapest and natural light source, these nanorobots have opened an effective and sustainable way for large-scale treatment of bacterial pollution in water.

Vat Photopolymerization of Nanocellulose-Reinforced Vegetable Oil-Based Resins: Synergy in Morphology and Functionalization

With the advancement of additive manufacturing (AM) and the mass adoption of 3D printing technology, it is essential to shift focus to environmentally and economically sustainable materials. As the utilization of renewable feedstocks is quite limited in this context, the utilization of more bio-based raw materials in the ongoing development of AM represents an essential means of achieving this shift. In this work, vat photopolymerization 3D printing has been used to process vegetable oil-based (VO) resins with an ultralow concentration of 0.07 vol % nanocellulose fibrils (NFC) and crystals (NCC). The developed nanocellulose containing bio-based vat photopolymerization resin shows excellent shelf stability, enabling high-resolution printing. Compatibilization of the nanocellulose with the polymer matrix was achieved through the introduction of isocyanate or acrylate groups via reactions of acryloyl chloride (AC) and hexamethylene diisocyanate (HMDI) with cellulose surface hydroxyls. Surface functionalization results in ∼20–30% increases in interfacial adhesion and stress transfer, yielding significant improvements in mechanical performance (4× higher toughness, 2.4× higher tensile strength, and 2× higher tensile strain) in 3D-printed specimens. Fourier-transformation infrared (FTIR) spectroscopy complemented by solid-state nuclear magnetic resonance (NMR) techniques enabled a more detailed study of the chemical structure of these materials as well. Tensile performance comparison with literature data on VO-based natural fiber-reinforced resins showed that this work brought bio-based resins one step closer to competing with petroleum-based resins. The prepared VO/nanocellulose resins are promising candidates for high-performance bio-based resins derived from completely renewable feedstocks.

PH and non-enzymatic glucose response at ultra-low concentration using submicrochannel heterogeneous membrane

The construction of solid nanochannel-based biosensor with submicron pore size has great significance to the analysis of biomolecule with high sensitivity and low detection limit. In this paper, a submicrochannel heterogeneous membrane with asymmetric geometry is prepared as the base by combining thermo-crosslinked hydrophobic conducting polymer and porous anodic aluminium oxide channel (AAO) with submicron pore size (269 nm). After the polydopamine-Au multilayer assembly, a large number of Au nanoparticles with adjustable size (∼10 and 89 nm) and density are in situ generated and fixed on the inner wall of AAO. Then 4-mercapto phenylboric acid with high density is grafted through Au-S bond to construct the submicrochannel heterogeneous membrane with the characteristic of ion current rectification in response to pH and saccharide. Benefit from the blocking effect of hydrophobic conducting polymer and the multilayer assembly of polydopamine-Au, the current of background response by the membrane device is effectively reduced, the ion current rectification strength can be effectively regulated in the range of pH 3–9, and the response to ultra-low glucose concentration without enzyme is achieved in the linear range of 1 pM-0.1 μM. A universal substrate platform is provided for the construction of solid nanochannel-based biosensor with submicron pore size.

Ultrasensitive detection and distinction of pollutants based on SERS assisted by machine learning algorithms

SERS as a promising sensing technique still faces challenges in the precise identification of trace-amount molecules due to the limitation of sensitivity and cleanliness of SERS substrate. Here, we report a precise and ultrasensitive identification of multiple pollutants via 3D clean cascade-enhanced nanosensor assisted by machine learning algorithms. This SERS substrate could achieve cascading electromagnetic energy with a remarkable enhancement factor as high as 8.35 × 109, which is attributed to the combination of micro-level polystyrene sphere (PS) porous array and nano-level Au-Ag clusters of this substrate. Benefitting from high cleanliness and ultra-sensitivity, multiple hazardous pollutants with similar geometry and Raman peaks at ultra-low concentration were successfully distinguished assisted by principal component analysis (PCA). As a result, this efficient and clean SERS substrate together with artificial intelligence could promote the application of SERS technology in the accurate identification of trace contaminants. Data AvailabilityData will be made available on request.

An ultrasensitive electrochemical aptasensor using Tyramide-assisted enzyme multiplication for the detection of Staphylococcus aureus

In this study, we aimed to introduce a new electrochemical aptasensor based on the tyramide signal amplification (TSA) technology for a highly-sensitive detection of the pathogenic bacterium, Staphylococcus aureus, as a model of foodborne pathogens. In this aptasensor, the primary aptamer, SA37, was used to specifically capture bacterial cells; the secondary aptamer, SA81@HRP, was used as the catalytic probe; and a TSA-based signal enhancement system comprising of biotinyl-tyramide and streptavidin-HRP as electrocatalytic signal tags was adopted to fabricate the sensor and improve the detection sensitivity. S. aureus cells were selected as the pathogenic bacteria to verify the analytical performance of this TSA-based signal-enhancement electrochemical aptasensor platform. After the simultaneous binding of SA37-S. aureus-SA81@HRP formed on the gold electrode, thousands of @HRP molecules could be bound onto the biotynyl tyramide (TB) displayed on the bacterial cell surface through a catalytic reaction between HRP and H2O2, resulting in the generation of the highly amplified signals mediated by HRP reactions. This developed aptasensor could detect S. aureus bacterial cells at an ultra-low concentration, with a limit of detection (LOD) of 3 CFU/mL in buffer. Furthermore, this chronoamperometry aptasensor successfully detected target cells in both tap water and beef broth with LOD to be 8 CFU/mL, which are very high sensitivity and specificity. Overall, this electrochemical aptasensor using TSA-based signal-enhancement could be a very useful tool for the ultrasensitive detection of foodborne pathogens in food and water safety and environmental monitoring.

Free-standing membrane incorporating single-atom catalysts for ultrafast electroreduction of low-concentration nitrate

The release of wastewaters containing relatively low levels of nitrate (NO3-) results in sufficient contamination to induce harmful algal blooms and to elevate drinking water NO3- concentrations to potentially hazardous levels. In particular, the facile triggering of algal blooms by ultra-low concentrations of NO3- necessitates the development of efficient methods for NO3- destruction. However, promising electrochemical methods suffer from weak mass transport under low reactant concentrations, resulting in long treatment times (on the order of hours) for complete NO3- destruction. In this study, we present flow-through electrofiltration via an electrified membrane incorporating nonprecious metal single-atom catalysts for NO3- reduction activity enhancement and selectivity modification, achieving near-complete removal of ultra-low concentration NO3- (10 mg-N L-1) with a residence time of only a few seconds (10 s). By anchoring Cu single atoms supported on N-doped carbon in a carbon nanotube interwoven framework, we fabricate a free-standing carbonaceous membrane featuring high conductivity, permeability, and flexibility. The membrane achieves over 97% NO3- removal with high N2 selectivity of 86% in a single-pass electrofiltration, which is a significant improvement over flow-by operation (30% NO3- removal with 7% N2 selectivity). This high NO3- reduction performance is attributed to the greater adsorption and transport of nitric oxide under high molecular collision frequency coupled with a balanced supply of atomic hydrogen through H2 dissociation during electrofiltration. Overall, our findings provide a paradigm of applying a flow-through electrified membrane incorporating single-atom catalysts to improve the rate and selectivity of NO3- reduction for efficient water purification.

Atomically Dispersed ZnN5 Sites Immobilized on g-C3 N4 Nanosheets for Ultrasensitive Selective Detection of Phenanthrene by Dual Ratiometric Fluorescence.

Ultrasensitively selective detection of trace polycyclic aromatic hydrocarbons (PAHs) like phenanthrene (PHE) is critical but remains challenging. Herein, atomically dispersed Zn sites on g-C3 N4 nanosheets (sZn-CN) are constructed by thermal polymerization of a Zn-cyanuric acid-melamine supramolecular precursor for the fluorescence detection of PHE. A high amount (1.6 wt%) of sZn is grafted in the cave of CN with one N vacancy in the form of unique Zn(II)N5 coordination. The optimized sZn-CN achieves a wide detection range (1 ng L-1 to 5 mg L-1 ), ultralow detection limit (0.35 ng L-1 , with 5-order magnitude improvement over CN), and ultrahigh selectivity toward PHE even among typical PAHs based on the built PHE-CN dual ratiometric fluorescence method. By means of in situ Fourier transform infrared spectroscopy, time-resolved absorptionand fluorescence spectroscopy, and theoretical calculations, the resulting superior detection performance is attributed to the favorable selective adsorption of PHE on as-constructed atomic Zn(II)N5 sites via the ionic cation-π interactions (Znδ+ C2 δ- type), and the fluorescence quenching is dominated by the inner filter effect (IFE) from the multilayer adsorption of PHE at low concentrations, while it is done by the protruded photogenerated electron-transfer process, as well as IFE from the monolayer adsorption of PHE at ultralow concentration.

Preparation of two-component polyacrylamide inverse emulsion drag reducer for slick water and investigation of its rheological and drag reduction properties

In this paper, a slick water drag reducer with excellent drag reduction and a simple molecular structure, called QIE-0, was prepared by inverse emulsion copolymerization. QIE-0 is a copolymer emulsion of acrylamide and 2-acrylamide-2-methylpropyl sulfonic acid with an average molecular weight of 5.17 × 106 Da. QIE-0 has excellent thermal stability, and the temperature resistance can reach 220 °C. Prolonged static storage (180 days) did not change the viscosity-increasing properties, and the viscosity of 0.1% QIE-0 solution is 5.2 mPa s. QIE-0 presents a three-dimensional network structure in an aqueous solution and the structure changes with concentration. QIE-0 has special fluidity and a linear viscoelastic domain from 0.1% to 100%. QIE-0 solution has no thixotropy and is a stable structure. The drag reduction rate of ultra-low concentration (0.01%) slick water systems reaches 82.10%. The drag reduction rates of different systems are fitted by the established exponential function model and the power function model, and the correlation coefficient between the predicted values and the experimental values is greater than 0.999. QIE-0 meets the needs of slick water fracturing fluid applications and has huge potential applications in unconventional oil and gas production.