The Influence of Precipitated Particles on the Grain Size in Cold-Rolled Al-Mn Alloy Foils upon Annealing at 100-550 °C.

The Al-Mn alloy heat exchanger fin production process includes a brazing treatment at s high temperature of 600 °C, in which coarse grains are preferred for their high resistance to deformation at elevated temperatures by decreasing the grain boundary sliding. In this study, Al-1.57Mn-1.57Zn-0.58Si-0.17Fe alloy foils cold rolled by 81.7% (1.1 mm in thickness) and 96.5% (0.21 mm in thickness) were annealed at 100-550 °C for 1 h to investigate their recrystallization behavior, grain sizes, and precipitates by increasing the annealing temperature, using micro-hardness measurement, electron back-scattered diffraction (EBSD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. The micro-hardness results showed that the recrystallization finishing temperatures for the two samples were almost the same, 323 ± 2 °C. The EBSD results showed that when the annealing temperature decreased from 550 to 400 °C, the recrystallized grain sizes of the two samples were nearly identical-both increased slightly. Further decreasing the annealing temperature from 400 to 330 °C caused the grain sizes to increase more, with the thinner foil sample having a more significant increase. The SEM and TEM observations showed that the micron-sized primary-phase remained unchanged during the annealing process. The nano-sized secondary phase precipitates formed during the hot-rolling process experienced a coarsening and dissolving process upon annealing. The particle size of the secondary phase increased from 32 nm to 44 nm and the area fraction decreased from 4.2% to 3.8%. The nucleation analysis confirmed that the large primary-phase could act as a nucleation site through particle stimulated nucleation (PSN) mode. The relatively dense secondary phase precipitates with small sizes at lower temperatures could provide higher Zener drag to the grain boundaries, leading to fewer nuclei and thereafter coarser grains. The coarsening of the recrystallized grains in the foils could be implemented through thickness reduction and/or precipitation processes to form densely distributed nano-sized precipitates.

Effect of the Solid Solution and Aging Treatment on the Mechanical Properties and Microstructure of a Novel Al-Mg-Si Alloy.

A novel Al-Mg-Si aluminum alloy with the addition of the micro-alloying element Er and Zr that was promptly quenched after extrusion has been studied. The solid solution and aging treatment of the novel alloy are studied by observing the microstructure, mechanical properties, and strengthening mechanism. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques are employed to examine the changes in the microstructure resulting from various solid solution treatments and aging treatments. The best strengthening effect can be achieved when the solubility of the MgSi phase and precipitate ß″ (Mg2Si phase) is at their maximum. The addition of Er and Zr elements promotes the precipitation of the ß″ phase and makes the b″ phase more finely dispersed. The aging strengthening of alloys is a comprehensive effect of the dislocation cutting mechanism and bypass mechanism, the joint effect of diffusion strengthening of Al3(Er,Zr) particles and the addition of Er and Zr elements promoting the precipitation strengthening of ß″ phases. In this paper, by adding Er and Zr elements and exploring the optimal heat treatment system, the yield strength of the alloy reaches 437 MPa and the tensile strength reaches 453 MPa after solid solution treatment at 565 °C/30 min and aging at 175 °C/10 h.

Effect of Zr and Er Addition on the Microstructural Evolution of a Novel Al-Mg-Zn-Er-Zr Alloy during Hot Compression.

The hot compression experiment of homogenized Al-5.2Mg-0.6Mn-0.29Zn-0.16Er-0.12Zr alloy was carried out by the Gleeble-3500 thermal simulation testing system. The deformation behavior in temperatures of 350~500 ℃ and deformation rates of 0.01~10 s-1 was studied. The relationship between stress and strain rate and deformation temperature was analyzed. The constitutive equation of alloy high-temperature deformation was constructed by the Zener-Hollomon method, and the hot working diagram with the true strain of 0.2 and 0.5 was constructed according to the dynamic material model. The research results show that flow stress has a positive correlation with strain rate and a negative correlation with temperature. The steady flow stress during deformation can be described by a hyperbolic sinusoidal constitutive equation. Adding Er and Zr into Al-Mg alloy can not only refine grains and strengthen precipitation but also form a core-shell Al3(Er, Zr) phase. In the deformation process, Al3(Er, Zr) precipitates can pin dislocations and inhibit dynamic recrystallization (DRX). Dynamic recovery (DRV) is dominant during hot deformation. The mechanism of dynamic recovery is dislocation motion. At high temperatures, Al3(Er, Zr) can also inhibit grain coarsening. The average hot deformation activation energy of the alloy is 203.7 kJ/mol. This high activation energy can be due to the pinning effect of Er and Zr precipitates. The processing map of the alloy was analyzed and combined with the observation of microstructure, the hot deformation instability zone of the alloy was determined, and the suitable process parameters for hot deformation were obtained, which were 450~480 °C, and the strain rate is 0.01~0.09 s-1.

Effect of Aging Treatment on the Precipitation Behavior of a Novel Al-Cu-Zr Cast Alloy.

A novel Al-Cu-Zr alloy is designed in this paper, which provides a method for further improving the strength of Al-Cu alloys. In this paper, the addition of the micro-alloying element Zr in Al-Cu alloy was studied. The effect of aging treatment on the mechanical properties and precipitation behavior of the alloy was studied. With the addition of Zr, Al3Zr phases were formed in the alloy, which acts as obstacles to dislocation motion. In addition, Al3Zr phases can be used as the nucleation site of θ' phases to promote precipitation. All this can improve the strength of Al-Cu alloys. After one-step aging, corresponding to the highest hardness, the largest amount of θ' phases were observed in the alloy matrix. By contrast, after two-step aging, the θ' phases were finer, and a large amount of Guinier-Preston (GP) zones formed during the pre-aging step, which were transformed into denser and finer θ' phases in the secondary aging step. After the same solution treatment (540 °C/12 h), undergoing 120 °C/4 h + 175 °C/10 h two-step aging, the ultimate tensile strength, yield strength, and elongation of the Al-Cu-Zr alloy were 398.7 MPa, 313.3 MPa, and 7.9%, respectively.

Highly Biocompatible Plasmonically Encoded Raman Scattering Nanoparticles Aid Ultrabright and Accurate Bioimaging.

Plasmonically engineered nanomaterials based on Au-Ag for surface-enhanced Raman scattering (SERS)-based biomedicine is of great importance but is still far behind clinical needs because of the poor compatibility between sensitivity and safety. Here, robust plasmonically encoded Raman scattering nanoparticles, named Au core-Raman-active molecule-Ag shell-Au shell nanoparticles (CMSS NPs), were synthesized. The as-developed CMSS NPs possess a unique exterior ultrathin Au shell (∼2.2 nm thickness) that plays double key roles as an effective wrapping layer as well as a plasmonic enhancing layer, thereby showing not only extraordinary stability against oxidative damages and bioerosion but also outstanding SERS sensitivity because of the stronger in-built electromagnetic field, achieving a significant SERS enhancement factor of 3.3 × 108. The results confirm that the individual CMSS NPs show ultrahigh brightness, reproducibility, selectivity, and biocompatibility in single-cell Raman imaging. Moreover, ultrabright in vivo tumor imaging with 1 × 1 mm2 area can be quickly achieved within 35 s under open-air condition. Furthermore, by secondary plasmonic encoding, the CMSS NPs flexibly serve as nanobeacon to monitor single-cell autophagy with improved accuracy. The CMSS NPs are expected as versatile SERS probes that enable ultrabright, fast, and precise Raman-based bioimaging and clinical bioapplications.

Spatially Engineered Janus Hybrid Nanozyme toward SERS Liquid Biopsy at Nano/Microscales.

Nanomaterials with intrinsic enzyme-mimicking properties (nanozymes) have been widely considered as artificial enzymes in biomedicine. However, manipulating inorganic nanozymes for multivariant targeted bioanalysis is still challenging because of the insufficient catalytic efficiency and biological blocking effect. Here, we rationally designed a spatially engineered hollow Janus hybrid nanozyme vector (h-JHNzyme) based on the bifacial modulation of Ag-Au nanocages. The silver face inside the h-JHNzyme served as an interior gate to promote the enzymatic activity of the Ag-Au nanozyme, whereas two-dimensional DNAzyme-motif nanobrushes deposited on the exterior surface of the h-JHNzyme endowed it with the targeting function and tremendously enhanced the peroxidase-mimicking activity. We demonstrated that the spatially separated modulation of the h-JHNzyme propelled it as a powerful "all-in-one" enzymatic vector with excellent biocompatibility, specific vectorization, remarkable enzymatic performance, and clinical practicability. Further, we programmed it into a stringent catalytic surface-enhanced Raman scattering (SERS) liquid biopsy platform to trace multidimensional tumor-related biomarkers, such as microRNAs and circulating tumor cells, with a limit of detection of fM and single cell level, respectively. The developed enzymatic platform showed great potential in facilitating reliable quantitative SERS liquid biopsy for on-demand clinical diagnosis.

Plasmon Coupling-Enhanced Raman Sensing Platform Integrated with Exonuclease-Assisted Target Recycling Amplification for Ultrasensitive and Selective Detection of microRNA-21.

A "signal-off" surface-enhanced Raman scattering (SERS) platform has been constructed for ultrasensitive detection of miRNA-21 by integrating exonuclease-assisted target recycling amplification with a plasmon coupling enhancement effect. On this platform, Raman-labeled Au nanostar (AuNS) probes can be covalently linked with the thiolated aptamer (Apt) on the Au-decorated silicon nanowire arrays (SiNWAs/Au) substrate, creating a coupled electromagnetic field between the substrate and the probes to enhance Raman signal. In the presence of miRNA-21, T7 exonuclease specifically hydrolyzed Apt on Apt/miRNA duplex to release miRNA-21. The regenerated element could then initiate another cycle of Apt/miRNA duplex formation and Apt cleavage. Correspondingly, the capture ability of substrate toward probes and the plasmon coupling effect between them were both diminished, giving a prominent attenuation of Raman intensity that can work as the detection signal. Due to the cascading integration between the target cycle process and the plasmon coupling effect, the present platform displayed a very low detection limit (0.34 fM, 3σ) for miRNA-21 detection. Furthermore, it was proven to be effective for analyzing miRNA-21 in biological samples and distinguishing the expression levels of miRNA-21 in MCF-7 cells and NIH3T3 cells, which became a promising tool to monitor miRNA-21 in cancer auxiliary diagnosis and drug screening.

Graphene Quantum Dots Wrapped Gold Nanoparticles with Integrated Enhancement Mechanisms as Sensitive and Homogeneous Substrates for Surface-Enhanced Raman Spectroscopy.

Rational engineering of highly stable and Raman-active nanostructured substrates is still urgently in demand for achieving sensitive and reliable surface-enhanced Raman spectroscopy (SERS) analysis in solution phase. Herein, monodisperse N-doping graphene quantum dots wrapped Au nanoparticles (Au-NGQD NPs) were facilely prepared, and further their applications as substrates in SERS-based detection and cellular imaging have been explored. The as-prepared Au-NGQD NPs exhibit superior long-term stability and biocompatibility, as well as large enhancement capability due to the integration of electromagnetic and chemical enhancements. The practical applicability of the Au-NGQD NPs was verified via the direct SERS tests of several kinds of aromatics in solution phase. Finite-difference time-domain simulations in combination with density functional theory calculation were also successfully used to explain the enhancement mechanism. Furthermore, the Au-NGQD NPs were conjugated with 4-nitrobenzenethiol (4-NBT, as reporter) and 4-mercaptophenylboronic acid (MPBA, as targeting element) to construct the MPBA/4-NBT@Au-NGQD probes, which could specifically recognize glycan-overexpressed cancer cells through SERS imaging on a cell surface. The prepared Au-NGQDs show great potential as superior SERS substrates in solution phase for on-site Raman detection.

Aptamer-Conjugated Au Nanocage/SiO2 Core-Shell Bifunctional Nanoprobes with High Stability and Biocompatibility for Cellular SERS Imaging and Near-Infrared Photothermal Therapy.

The combination of surface-enhanced Raman scattering (SERS) imaging technology with near-infrared (NIR) light-triggered photothermal therapy is of utmost importance to develop novel theranostic platforms. Herein, an aptamer-conjugated Au nanocage/SiO2 (AuNC/SiO2/Apt) core-shell Raman nanoprobe has been rationally designed as the bifunctional theranostic platform to fulfill this task. In this theranostic system, the Raman-labeled Au nanocage (AuNC) was encapsulated into a bioinert shell of SiO2, followed by conjugating aptamer AS1411 as the target-recognition moiety. AuNC served as the SERS-active and photothermal substrate due to its large free volume, built-in plasmon effect, and NIR photothermal capacity, while the SiO2 coating endowed the nanoprobes with good stability and biocompatibility, as well as abundant anchoring sites for surface functionalization. Considering their prominent SERS and photothermal properties, the application potential of the AuNC/SiO2/Apt nanoprobes was investigated. The proposed nanoprobes could be applied to targeted detection and SERS imaging of nucleolin-overexpressing cancer cells (MCF-7 cells as the model) from normal cells and also exhibited acceptable photothermal efficacy without systematic toxicity. This theranostic nanoplatform provided a possible opportunity for in situ diagnosis and noninvasive treatment of cancer cells by SERS imaging-guided photothermal therapy.

Plasmonic Au nanostar Raman probes coupling with highly ordered TiO2/Au nanotube arrays as the reliable SERS sensing platform for chronic myeloid leukemia drug evaluation.

The accurate therapeutic evaluation for chronic myeloid leukemia (CML) drug is of great importance to minimize side effects and enhance efficacy. Herein, a facile and precise surface-enhanced scattering (SERS) approach based on coupled plasmonic field has been introduced to evaluate the therapeutic outcomes of antileukemia drug through ultrasensitive assay of caspase-3 activity in apoptotic cells. Caspase-3 as an apoptosis indicator could specifically cleave the N-terminus of biotinylated DEVD-peptide (biotin-Gly-Asp-Gly-Asp-Glu-Val-Asp-Gly-Cys) immobilized on the Au nanoparticle-decorated TiO2 nanotube arrays (TiO2/Au NTAs) substrate. After the enzyme cleavage with caspase-3, Raman-labelled Au nanostar (AuNS) probes captured the residual DEVD-peptides via the recognition between streptavidin and biotin, thus resulting in an enhanced Raman response on the SERS platform. The variation of Raman intensity revealed caspase-3 activity that reflected the chemotherapeutic effect. On this platform, AuNS nanoprobes offered a large number of binding sites and intrinsic "hot spots" for Raman reporters, while TiO2/Au NTAs rendered a homogenously coupled electromagnetic field between the adjacent repeated units over the large area. In particular, a spatially expanding plasmonic field formed by coupling AuNSs with TiO2/Au NTAs would further heighten Raman enhancement. Taking these advantages, the strong and uniform Raman signals were achieved. Furthermore, the practicability investigation witnessed that the proposed SERS strategy was available to evaluate the therapeutic effect of dasatinib on CML K562 cells. The developed method possesses fascinating advantages of cost-effectiveness, excellent reproducibility and high sensitivity, which endows it with promising potential in apoptosis monitoring and anticancer drug development.

Speciation of inorganic arsenic(III) and arsenic(V) by a facile dual-cloud point extraction coupled with inductively plasma-optical emission spectrometry.

A simple and efficient method using dual-cloud point extraction (dual-CPE) coupled with inductively coupled plasma-optical emission spectrometry (ICP-OES) was developed for the speciation of inorganic arsenic [As(III) and As(V)]. In first step of dual-CPE, As(III) formed a hydrophobic complex with ammonium pyrrolidine dithiocarbamate (As-APDC), and was subsequently entrapped by the Triton X-114 surfactant-rich phase at pH 5.0, whereas As(V) remained in the bulk supernatant. The surfactant-rich phase containing the As(III)-APDC complex was treated with a 2.0molL-1 of nitric acid, and As(III) was back extracted into the aqueous phase at the second cloud point extraction stage before ICP-OES detection. The As(V) concentration was calculated by subtracting the concentration of As(III) from the total inorganic arsenic concentration after reducing As(V) to As(III) by thiourea. Different factors affecting the extraction of As(III) were investigated in detail. Under the optimum conditions, the detection limit for As(III) was 0.72ngmL-1 along with the relative standard deviation of 3.5% (C = 10.0ngmL-1, n = 5). The calibration curve was linear in the range of 2.0-50.0ngmL-1. This method was validated against the certified reference material (GSBZ 50004-88), and applied for the speciation of inorganic As(III) and As(V) in the spiked snow water sample.

Speciation of antimony(III) and antimony(V) by electrothermal atomic absorption spectrometry after ultrasound-assisted emulsification of solidified floating organic drop microextraction.

A simple, sensitive and efficient method of ultrasound-assisted emulsification of solidified floating organic drop microextraction (USE-SFODME) coupled to electrothermal atomic absorption spectrometry for the speciation of antimony at different oxidation state Sb(III)/Sb(V) in environmental samples was established. In this method, the hydrophobic complex of Sb(III) with sodium diethyldithiocarbamate (DDTC) is extracted by 1-undecanol at pH 9.0, while Sb(V) remains in aqueous phase. Sb(V) content can be calculated by subtracting Sb(III) from the total antimony after reducing Sb(V) to Sb(III) by l-cysteine. Various factors affecting USE-SFODME including pH, extraction solvent and its volume, concentration of DDTC, sonication time, and extraction temperature were investigated. Under the optimized conditions, the calibration curve was linear in the range from 0.05 to 10.0 ng mL(-1), with the limit of detection (3σ) 9.89 ng L(-1) for Sb(III). The relative standard deviation for Sb(III) was 4.5% (n=9, c=1.0 ng mL(-1)). This method was validated against the certified reference materials (GSB 07-1376-2001, GBW07441), and applied to the speciation of antimony in environmental samples (soil and water samples) with satisfactory results.

Selective cloud point extraction for the determination of cadmium in food samples by flame atomic absorption spectrometry.

A new cloud point extraction (CPE) procedure for preconcentration of cadmium prior to the determination by flame atomic absorption spectrometry (FAAS) was developed. The method is based on the fact that cadmium could form hydrophobic ion-associated complex in the presence of iodide and methyl green (MG), and the hydrophobic ion-associated complex could be extracted into surfactant-rich phase. The main factors affecting CPE procedure, such as pH, concentration of KI, MG and surfactant, equilibrium temperature and incubation time, sample volume were investigated. Potential interference from co-existing ions was largely eliminated as most of co-existing ions can not form extractable ion-associated complex with iodide and MG. Under the optimum conditions, the limit of detection (3σ) and limit of quantity (10σ) were 0.90ngmL(-1) and 3.0ngmL(-1) for cadmium, respectively, and relative standard deviation was 4.2% (c=50ngmL(-1), n=7). The proposed method was successfully applied to determination of cadmium in the certified reference rice sample (GBW08510) and food samples with satisfactory results.

Cloud point extraction combined with electrothermal atomic absorption spectrometry for the speciation of antimony(III) and antimony(V) in food packaging materials.

A simple, sensitive method for the speciation of inorganic antimony by cloud point extraction combined with electrothermal atomic absorption spectrometry (ETAAS) is presented and evaluated. The method based on the fact that formation of a hydrophobic complex of antimony(III) with ammonium pyrrolidine dithiocarbamate (APDC) at pH 5.0 and subsequently the hydrophobic complex enter into surfactant-rich phase, whereas antimony(V) remained in aqueous solutions. Antimony(III) in surfactant-rich phase was analyzed by ETAAS after dilution by 0.2 mL nitric acid in methanol (0.1M), and antimony(V) was calculated by subtracting antimony(III) from the total antimony after reducing antimony(V) to antimony(III) by l-cysteine. The main factors affecting the cloud point extraction, such as pH, concentration of APDC and Triton X-114, equilibrium temperature and incubation time, sample volume were investigated in detail. Under the optimum conditions, the detection limit (3 sigma) of the proposed method was 0.02 ng mL(-1) for antimony(III), and the relative standard deviation was 7.8% (c=1.0 ng mL(-1), n=7). The proposed method was successfully applied to speciation of inorganic antimony in the leaching solutions of different food packaging materials with satisfactory results.