Sulfur dots and iron co-doped nickel-based metal-organic frameworks with high nanozyme activity for the colorimetric determination of α-glucosidase activity.

Alpha-glucosidase (α-Glu) plays a crucial role in regulating the normal physiological function of the body; therefore, α-Glu activity detection is crucial in clinical studies. In this study, a nickel-based metal-organic framework (Ni-MOF) co-doped with sulfur dots (SDs) and iron (Fe) was designed and constructed for the colorimetric detection of α-Glu. The SDs/Fe/Ni-MOF shows a very low Michaelis-Menten constant (0.0466 mM) for H2O2, suggesting a very high affinity for H2O2. Additionally, the free radicals generated by the nanozyme-catalyzed reaction were analyzed, and the feasibility of the nanozyme-catalyzed process was further verified using density functional theory. The bimetallic (Fe and Ni) can improve the catalytic activity of the material, and sulfur can improve the affinity with the substrate to further enhance the catalytic performance. Notably, hydroquinone (HQ) inhibits nanozyme activity, whereas α-Glu hydrolyzes alpha-arbutin (α-Arb) and subsequently produces HQ. Therefore, this study developed a method for detecting α-Glu activity using α-Arb as a substrate. This method has high selectivity, a wide detection range (1.00-100 U L-1), and a low detection limit (0.525 U L-1). Finally, the method was used to α-Glu activity detected in serum samples with good accuracy. This study provides a new method for the detection of α-Glu.

Design and fabrication of Zn@ZnO@Ag chip for Raman scattering analysis of norfloxacin in liquid milk, fish and animal feeds.

A novel and easy-to-prepare plasmonic nanoparticles doped semiconductor substrate-Zn@ZnO@Ag chip with ultra-high surface-enhanced Raman scattering (SERS) activity was fabricated for label-free, rapid and sensitive analysis of norfloxacin. The Zn@ZnO array was synthesized by surface oxidation at low temperature, followed by in-situ reduction to form leaf-like AgNPs on Zn@ZnO array without extra reducing agent, thus fabricating a Zn@ZnO@Ag chip. The ultra-high SERS activity is attributed to the synergistic effect of semiconductor characteristics of ZnO and surface plasmon resonance properties of leaf-like AgNPs. The possible enhancement mechanism was verified by density functional theory simulations. The proposed SERS method showed a wide linear range (3.0-500.0 µg/L) and low limit of detection (0.8 µg/L) for norfloxacin analysis. High sensitivity, good selectivity and acceptable recoveries (82.7-113.6%) in real sample analysis were obtained. This study offers a promising SERS chip-based platform for norfloxacin detection in the field.

Fabrication of hierarchical ß-Bi2O3/AuAg microspheres for sensitive, selective and rapid detection of environment pollutants by surface-enhanced Raman spectroscopy.

In this paper, we report a novel surface-enhanced Raman spectroscopy (SERS) substrate based on hierarchical ß-Bi2O3/Au2Ag2 microspheres for rapid, sensitive and selective detection of environment pollutants including o-dianisidine (o-diASD) and Hg2+ in environmental samples. The sheet-like ß-Bi2O3 not only provides large specific surface areas for adsorption of molecules and AuAg, but also emerges as semiconductor matrix with chemical enhancement combined with AuAg with electromagnetic enhancement, making promising SERS activity. Particularly, the ß-Bi2O3/Au2Ag2 shows high SERS performance for 4-mercaptobenzoic acid and TMB with minimum detectable concentration of 0.1 µg/L with enhancement factor of 3.1 × 107 and 6.3 × 107, respectively. The density functional theory simulations were further adopted to explain the high SERS activity and selectivity for o-diASD and TMB. Finally, the ß-Bi2O3/Au2Ag2 was applied to direct detection of o-diASD, and indirect detection of Hg2+ by TMB marking in environmental samples. The linearity range of 0.5-200.0 and 0.2-500.0 µg/L with limit of detection of 0.2 and 0.07 µg/L for o-diASD and Hg2+ ions can be achieved, respectively. This method provides a novel strategy in designing and fabricating SERS substrates with high performance for rapid, sensitive and accurate analysis of environmental pollutants.

Smart Lattice Structures with Self-Sensing Functionalities via Hybrid Additive Manufacturing Technology.

Lattice structures are a group of cellular materials composed of regular repeating unit cells. Due to their extraordinary mechanical properties, such as specific mechanical strength, ultra-low density, negative Poisson's ratio, etc., lattice structures have been widely applied in the fields of aviation and aerospace, medical devices, architecture, and automobiles. Hybrid additive manufacturing (HAM), an integrated manufacturing technology of 3D printing processes and other complementary processes, is becoming a competent candidate for conveniently delivering lattice structures with multifunctionalities, not just mechanical aspects. This work proposes a HAM technology that combines vat photopolymerization (VPP) and electroless plating process to fabricate smart metal-coated lattice structures. VPP 3D printing process is applied to create a highly precise polymer lattice structure, and thereafter electroless plating is conducted to deposit a thin layer of metal, which could be used as a resistive sensor for monitoring the mechanical loading on the structure. Ni-P layer and copper layer were successfully obtained with the resistivity of 8.2×10-7Ω⋅m and 2.0 ×10-8 Ω⋅m, respectively. Smart lattice structures with force-loading self-sensing functionality are fabricated to prove the feasibility of this HAM technology for fabricating multifunctional polymer-metal lattice composites.

A ratiometric fluorescence and colorimetric dual-mode sensing platform based on sulfur quantum dots and carbon quantum dots for selective detection of Cu2.

A new dual-mode ratiometric fluorescence and colorimetric probe for selective determination of Cu2+ was developed based on blue-emission sulfur quantum dots (SQDs) and yellow-emission carbon quantum dots (CQDs). The fluorescence and absorbance of CQDs increased in the presence of Cu2+ due to the Cu2+ -oxidized o-phenylenediamine group on the surface of the CQDs. Because of the inner filter effect between SQDs and CQDs-Cu2+, the fluorescence response of SQDs decreased following the introduction of Cu2+. Furthermore, in the presence of Cu2+, the dual-mode SQD-CQD probe showed visible color changes under both ultraviolet light and sunlight. Under optimal conditions, the dual-mode probe was used to quantitatively detect Cu2+ with a linear range of 0.1-5.0 µM for ratiometric fluorescence and colorimetry, with a limit of detection of about 31 nM and 47 nM, respectively. Finally, the dual-mode probe was used for the determination of Cu2+ in practical samples to expand the practical application, and the difference between ratiometric fluorescence and colorimetric methods was compared. The recovery results confirmed the high accuracy of the dual-mode probe, showing that it has immense potential for sensitive and selective detection of Cu2+ in practical samples.

Investigation of Surface Acoustic Wave Propagation Characteristics in New Multilayer Structure: SiO2/IDT/LiNbO3/Diamond/Si.

Surface acoustic wave (SAW) devices are widely used in many fields such as mobile communication, phased array radar, and wireless passive sensor systems. With the upgrade of mobile networks, the requirements for the performance of SAW devices have also increased, and high-frequency wideband SAW devices have become an important research topic in communication systems and other application fields. In this paper, a theoretical study for the realization of a layered SAW filter based on a new SiO2/IDT/128°YX-LiNbO3/diamond/silicon layered structure using the modeling software COMSOL Multiphysics is presented. The effects of lithium niobate (LiNbO3), an interdigital transducer (IDT), and SiO2 thin films on the evolution of the phase velocity, electromechanical coupling coefficient (k2), and temperature coefficient of frequency were studied by employing a finite element method simulation. Furthermore, a longitudinal coupling resonator filter was designed. To investigate the SAW characteristics of the filter, a transient analysis was conducted to calculate the electrical potential and particle displacement under the resonance condition and to analyze the frequency response. The study concluded that this new multilayer structure can be applied to design and manufacture a variety of high-frequency and wideband SAW filters with a temperature compensation function, for operation above the GHz range.

Research on Novel CMUTs for Detecting Micro-Pressure with Ultra-High Sensitivity and Linearity.

Capacitive micromachined ultrasonic transducers (CMUTs) have been indispensable owing to their resonance characteristics in the MHz frequency range. However, the inferior pressure sensitivity and linearity of traditional CMUTs themselves cannot meet the actual demands of micro-pressure measurements. In this paper, two novel CMUTs are proposed for the first time to improve the measuring performance of micro-pressure in the range of 0-10 kPa. The core concept of the enhancement is strengthening membrane deformability by partly adjusting the CMUT framework under the combined action of electrostatic force and uniform pressure. Two modified structures of an inverted frustum cone-like cavity and slotted membrane are presented, respectively, and a finite element model (FEM) of CMUT was constructed and analyzed using COMSOL Multiphysics 5.5. The results demonstrate that the maximum displacement and pressure sensitivity are improved by 16.01% and 30.79% for the frustum cone-like cavity and 104.22% and 1861.31% for the slotted membrane, respectively. Furthermore, the results show that the width uniformity of the grooves does not influence the characteristics of the membrane, which mainly depend on the total width of the grooves, greatly enriching design flexibility. In brief, the proposed structural designs can significantly improve the micro-pressure measurement performance of the CMUT, which will accelerate the rapid breakthrough of technical barriers in the fields of aerospace, industry control, and other sensing domains.

Hybrid Cell Structure for Wideband CMUT: Design Method and Characteristic Analysis.

Capacitive micromachined ultrasonic transducer (CMUT) is an ultrasonic transducer based on the microelectromechanical system (MEMS). Wideband CMUT has good application prospects in ultrasonic imaging, ultrasonic identification, flow measurement, and nondestructive testing due to its excellent characteristics. This paper studies the method of increasing the bandwidth of the CMUT, proposes the structure of the wideband CMUT with a hybrid cell structure, and analyzes the design principles and characteristics of the wideband CMUT structure. By changing the cell spacing and the number of cells of different sizes composing the CMUT, we analyze the simulation of the effect of the spacing and number on the CMUT bandwidth, thereby optimizing the bandwidth characteristics of the CMUT. Next, the selection principle of the main structural parameters of the wideband CMUT is analyzed. According to the proposed principle, the CMUT in the air and water are designed and simulated. The results prove that both the air and water CMUT meet the design requirements. The design rules obtained in this paper can provide theoretical guidance for the selection of the main structural parameters of the wideband CMUT.

Highly Accurate Digital Processing of Large Stroke Guideway with an Optical Material-Corning Code 7972.

Currently, meter-long guideways rarely achieve an accuracy of dozens of nanometers due to processing difficulties such as the material and the edge effect. In this paper, we focus on this problem and propose a set of optimization processing methods to cope with it. In the grinding stage, a grinding tool is designed to improve the reciprocating processing and address the problem of warping; in the polishing stage, three different processes are compared, and the combination of magnetorheological finishing technology and the polyurethane disc technology process is purposed to reduce the polishing cycle and improve the surface figure accuracy. Moreover, through the combined process of magnetorheological finishing and smoothing, the edge effect and medium- and high-frequency error are essentially suppressed. The meter-long guideway is achieved with an accuracy of dozens of nanometers. Although the sizes of surface A/C and B/D are 1000 mm × 240 mm and 1000 mm × 160 mm, the surface figures are 20.33 nm, 22.78 nm, 39.23 nm and 26.58 nm RMS (Root Mean Square), respectively. The nanometer accuracy guideway is critical to an ultra-precision machine tool. Finally, the X-axis straightness of the profile measurement system formed by the guideway reaches 200 nm/600 mm.

Sensitive and selective determination of tetracycline in milk based on sulfur quantum dot probes.

A novel fluorescent probe based on sulfur quantum dots (SQDs) was fabricated for sensitive and selective detection of tetracycline (TC) in milk samples. The blue emitting SQDs were synthesized via a top-down method with assistance of H2O2. The synthesized SQDs showed excellent monodispersity, water solubility and fluorescence stability, with a quantum yield (QY) of 6.30%. Furthermore, the blue fluorescence of the obtained SQDs could be effectively quenched in the presence of TC through the static quenching effect (SQE) and inner filter effect (IFE) between TC and SQDs. Under the optimum conditions, a rapid detection of TC could be accomplished within 1 min and a wide linear range could be obtained from 0.1 to 50.0 µM with a limit of detection (LOD) of 28.0 nM at a signal-to-noise ratio of 3. Finally, the SQD-based fluorescent probe was successfully applied for TC determination in milk samples with satisfactory recovery and good relative standard deviation (RSD). These results indicate that the SQD-based fluorescent probe shows great potential in practical analysis of TC in real samples with high rapidity, selectivity, and sensitivity.

Fluorescence covalent interaction enhanced sensor for lead ion based on novel graphitic carbon nitride nanocones.

Novel graphitic carbon nitride nanocones (g-CNNCs) were synthesized for the first time in this study. The SEM, TEM, XPS and FT-IR were used to research the structure of the g-CNNCs. We found that the g-CNNCs showed high selective and sensitive for fluorescence enhancement detection of Pb2+ ion via covalent interaction. In addition, the g-CNNCs exhibit stable and specific concentration-dependent fluorescence intensity in the presence of Pb2+ ion in the range of 1-200 µmol·dm-3, and the limit of detection was estimated to be 0.0438 µmol·dm-3 (3S/k). More importantly, the g-CNNCs were used to detect practical samples with satisfactory results.

Fast synthesis of porous copper nanoclusters for fluorescence detection of iron ions in water samples.

Copper nanoclusters (Cu NCs) have attracted great research interest in recent years owing to its unique physical, electrical and optical properties. Macromolecules have been widely used as templates to synthesize fluorescent Cu NCs. In this study, a simple method for synthesis of albumin chicken egg capped porous copper nanoclusters (p-Cu NCs) was developed for the first time. The obtained p-Cu NCs exhibited intense emission and excitation peaks at 280 nm and 340 nm, respectively. Besides, the p-Cu NCs fluorescence probe could be quenched by Fe3+ ions in aqueous solutions. Therefore, the p-Cu NCs can be excellently candidated as fluorescent probe for the detection of Fe3+ ions. Under optimized conditions, this fluorescent probe exhibited a wide linear response concentration range (0.2 to 100 µM) to Fe3+ with a detection limit of 0.0234 µM. In addition, the fluorescent probe has been successfully used for the detection of Fe3+ in natural water samples with satisfactory result.

Nafion covered core-shell structured Fe3O4@graphene nanospheres modified electrode for highly selective detection of dopamine.

Nafion covered core-shell structured Fe3O4@graphene nanospheres (GNs) modified glassy carbon electrode (GCE) was successfully prepared and used for selective detection dopamine. Firstly, the characterizations of hydro-thermal synthesized Fe3O4@GNs were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. Then Fe3O4@GNs/Nafion modified electrode exhibited excellent electrocatalytic activity toward the oxidations of dopamine (DA). The interference test showed that the coexisted ascorbic acid (AA) and uric acid (UA) had no electrochemical interference toward DA. Under the optimum conditions, the broad linear relationship was obtained in the experimental concentration from 0.020 µM to 130.0 µM with the detection limit (S/N=3) of 0.007 µM. Furthermore, the core-shell structured Fe3O4@GNs/Nafion/GCE was applied to the determination of DA in real samples and satisfactory results were got, which could provide a promising platform to develop excellent biosensor for detecting DA.

A sensitive and reliable dopamine biosensor was developed based on the Au@carbon dots-chitosan composite film.

A novel composite film of Au@carbon dots (Au@CDs)-chitosan (CS) modified glassy carbon electrode (Au@CDs-CS/GCE) was prepared in a simple manner and applied in the sensitive and reliable determination of dopamine (DA). The CDs had carboxyl groups with negative charge, which not only gave it have good stability but also enabled interaction with amine functional groups in DA through electrostatic interaction to multiply recognize DA with high specificity, and the Au nanoparticle could make the surface of the electrode more conductive. Compared with the bare GCE, CS/GCE, and CDs-CS/GCE electrodes, the Au@CDs-CS/GCE had higher catalytic activity toward the oxidation of DA. Furthermore, Au@CDs-CS/GCE exhibited good ability to suppress the background current from large excess ascorbic acid (AA) and uric acid (UA). Under the optimal conditions, selective detection of DA in a linear concentration range of 0.01-100.0 µM was obtained with the limit of 0.001 µM (3S/N). At the same time, the Au@CDs-CS/GCE was also applied to the detection of DA content in DA's injection with satisfactory results, and the biosensor could keep its activity for at least 2 weeks.

Carbon dots and chitosan composite film based biosensor for the sensitive and selective determination of dopamine.

A simple, sensitive and reliable dopamine (DA) biosensor was developed based on a carbon dots (CDs) and chitosan (CS) composite film modified glassy carbon electrode (CDs-CS/GCE). Under optimal conditions, the CDs-CS/GCE showed a better electrochemical response for the detection of DA than that of the glassy carbon electrode (GCE). The oxidation peak current (Ipa) of DA was linear with the concentration of DA in the range from 0.1 µM to 30.0 µM with the limit of detection as 11.2 nM (3S/N). The CDs-CS/GCE was applied to the detection of DA content in an injection solution of DA with satisfactory results.