Failure progression and toughening mechanism of 3D-printed nacre-like structures under in-plane compression.

Nacre (also called mother-of-pearl) is known to have a delicate balance of stiffness, strength, and toughness, which originates from its 'brick-and-mortar' structure. In this study, nacre-like structures are fabricated using a high-resolution, multi-material 3D printer, where two different polyurethane acrylates (one that is hard and another that is soft) are used to represent the tablets and matrix. Six nacre-like structures are designed and fabricated to explore the influence of geometric parameters on the mechanical behaviors. Quasi-static in-plane compression tests and simulations are carried out to explore the failure mechanism of the nacre-like structures. The results show that the quasi-static compression responses of nacre-like structures have four stages: elastic, plateau, fragmentation, and densification. It is found that tuning the nacre architecture can optimize the mechanical performance of the specimen, including the peak load, ductility and stress reduction behavior et al. As the results of the numerical model show good agreement with the stress-strain response observed in the experiments, the model is applied to further investigate the strain distributions of the nacre-like structures. The patterns of the strain distribution suggest that synergistic deformation is the key toughening mechanism for the nacre-like structures.

Cerium oxide-graphene as the matrix for cholesterol sensor.

A simple and sensitive electrogenerated chemiluminescence (ECL) cholesterol biosensor was prepared based on cerium oxide-graphene (CeO(2)-graphene) composites as an efficient matrix. CeO(2)-graphene composites were prepared by depositing CeO(2) onto graphene and were characterized by scanning electron microscopy. The experimental results demonstrated that CeO(2)-graphene could catalyze the ECL of a luminol-H(2)O(2) (hydrogen peroxide) system to amplify the luminol ECL signal greatly. In addition, the use of CeO(2)-graphene provided a better biocompatible microenvironment for the immobilized enzyme, resulting in excellent stability and a long lifetime of the ECL biosensor. The surface assembly process, ECL behaviors, and electrochemistry of the biosensor were investigated in detail. The quantity of cholesterol was in the linear range from 12 µM to 7.2 mM with a detection limit of 4.0 µM (signal/noise = 3). In addition, the biosensor exhibited outstanding reproducibility, long-term stability, and selectivity. Moreover, this cholesterol biosensor offers an alternative analytical method with low cost and high speed.

Simultaneous determination of ascorbic acid, dopamine, uric acid and tryptophan on gold nanoparticles/overoxidized-polyimidazole composite modified glassy carbon electrode.

A novel electrode was developed through electrodepositing gold nanoparticles (GNPs) on overoxidized-polyimidazole (PImox) film modified glassy carbon electrode (GCE). The combination of GNPs and the PImox film endowed the GNPs/PImox/GCE with good biological compatibility, high selectivity and sensitivity and excellent electrochemical catalytic activities towards ascorbic acid (AA), dopamine (DA), uric acid (UA) and tryptophan (Trp). In the fourfold co-existence system, the peak separations between AA-DA, DA-UA and UA-Trp were large up to 186, 165 and 285 mV, respectively. The calibration curves for AA, DA and UA were obtained in the range of 210.0-1010.0 µM, 5.0-268.0 µM and 6.0-486.0 µM with detection limits (S/N=3) of 2.0 µM, 0.08 µM and 0.5 µM, respectively. Two linear calibrations for Trp were obtained over ranges of 3.0-34.0 µM and 84.0-464.0 µM with detection limit (S/N=3) of 0.7 µM. In addition, the modified electrode was applied to detect AA, DA, UA and Trp in samples using standard addition method with satisfactory results.

A biosensor for cholesterol based on gold nanoparticles-catalyzed luminol electrogenerated chemiluminescence.

A novel cholesterol biosensor was prepared based on gold nanoparticles-catalyzed luminol electrogenerated chemiluminescence (ECL). Firstly, l-cysteine-reduced graphene oxide composites were modified on the surface of a glassy carbon electrode. Then, gold nanoparticles (AuNPs) were self-assembled on it. Subsequently, cholesterol oxidase (ChOx) was adsorbed on the surface of AuNPs to construct a cholesterol biosensor. The stepwise fabrication processes were characterized with cyclic voltammetry and atomic force microscopy. The ECL behaviors of the biosensor were also investigated. It was found that AuNPs not only provided larger surface area for higher ChOx loading but also formed the nano-structured interface on the electrode surface to improve the analytical performance of the ECL biosensor for cholesterol. Besides, based on the efficient catalytic ability of AuNPs to luminol ECL, the response of the biosensor to cholesterol was linear range from 3.3 µM to 1.0 mM with a detection limit of 1.1 µM (S/N=3). In addition, the prepared ECL biosensor exhibited satisfying reproducibility, stability and selectivity. Taking into account the advantages of ECL, we confidently expect that ECL would have potential applications in biotechnology and clinical diagnosis.

Au-nanoclusters incorporated 3-amino-5-mercapto-1,2,4-triazole film modified electrode for the simultaneous determination of ascorbic acid, dopamine, uric acid and nitrite.

A novel biosensor has been constructed by the electrodeposition of Au-nanoclusters (nano-Au) on poly(3-amino-5-mercapto-1,2,4-triazole) (p-TA) film modified glassy carbon electrode (GCE) and employed for the simultaneous determination of dopamine (DA), ascorbic acid (AA), uric acid (UA) and nitrite (NO(2)(-)). NH(2) and SH groups exposed to the p-TA layer are helpful for the electrodeposition of nano-Au. The combination of nano-Au and p-TA endow the biosensor with large surface area, good biological compatibility, electricity and stability, high selectivity and sensitivity and flexible and controllable electrodeposition process. In the fourfold co-existence system, the linear calibration plots for AA, DA, UA and NO(2)(-) were obtained over the range of 2.1-50.1 µM, 0.6-340.0 µM, 1.6-110.0 µM and 15.9-277.0 µM with detection limits of 1.1×10(-6) M, 5.0×10(-8) M, 8.0×10(-8) M and 8.9×10(-7) M, respectively. In addition, the modified biosensor was applied to the determination of AA, DA, UA and NO(2)(-) in urine and serum samples by using standard adding method with satisfactory results.

Glucose biosensor based on titanium dioxide-multiwall carbon nanotubes-chitosan composite and functionalized gold nanoparticles.

In this paper, a new glucose biosensor was prepared. At first, Prussian blue (PB) was electrodeposited on a glassy carbon electrode (GCE) modified by titanium dioxide-multiwall carbon nanotubes-chitosan (TiO(2)-MWNTs-CS) composite, and then gold nanoparticles functionalized by poly(diallyldimethylammonium chloride) (PDDA-Au) were adsorbed on the PB film. Finally, the negatively charged glucose oxidase (GOD) was self-assembled on to the positively charged PDDA-Au. The electrochemical performances of the modified electrodes had been studied by cyclic voltammetry (CV) and amperometric methods, respectively. In addition, the stepwise fabrication process of the as-prepared biosensor was characterized by scanning electron microscopy. PDDA-Au nanoparticles were characterized by ultraviolet-vis absorption spectroscopy and transmission electron microscopy. Under the optimal conditions, the as-prepared biosensor exhibited a good response performance to glucose with a linear range from 6 µM to 1.2 mM with a detection limit of 0.1 µM glucose (S/N = 3). In addition, this work indicated that TiO(2)-MWNTs-CS composite and PDDA-Au nanoparticles held great potential for constructing biosensors.