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In this paper, the bifurcation and chaotic behaviors of a Duffing oscillator with delayed displacement and velocity feedbacks under harmonic excitation are investigated. The analytically necessary condition for the chaos in the sense of Smale horseshoes is established based on Melnikov method. It could be found that the delayed displacement and velocity feedbacks affect the necessary condition respectively, so that the analysis on the effects of the two kinds of feedbacks is presented individually. The effects of displacement feedback coefficient, velocity feedback coefficient and their time delays on the analytically necessary condition are analytically discussed. Furthermore, some typical numerical results, including the bifurcation diagrams, Poincare maps and the largest Lyapunov exponents of the delayed oscillator are also presented and compared. The satisfactory qualitative agreement between the analytical and numerical results verify the correctness of the analytically necessary condition.

A label-free and sensitive electrochemiluminescence (ECL) aptasensor for thrombin (TB) was developed using three-layer porous nanoparticles of Au nanoparticles (Au NPs) decorated ferroferric oxide@stannic oxide (Fe 3 O 4 @SnO 2 @Au NPs) as multifunctional matrix for signal amplification. This system consists of Fe 3 O 4 @SnO 2 @Au NPs enhanced Ru(bpy) 3 2+ as efficient luminophore and two ferrocene (Fc) molecules labeled thrombin binding aptamer (TBA) as quenching probe. Briefly, Ru(bpy) 3 2+ was doped into a cation-exchange polymer of nafion (Ru-nafion), which was coated on bare glass carbon electrode (GCE). Then three-layer porous Fe 3 O 4 @SnO 2 @Au NPs were absorbed on the resultant GCE via electrostatic interaction. Subsequently, abundant amino-group functionalized assisted probes (NH 2 -APs) were loaded on the modified electrode based on Au-N bonding. With the base-pairing interaction, a quenching probe of two Fc molecules TBA could hybridize with NH 2 -APs to obtain a low background signal based on the quenching effect of Fc. In the presence of TB, the formed double-stranded DNA was dissociated and the obtained the structure of TB/Fc-TBA-Fc complex was released from the electrode surface, resulting in a proportional increase in ECL response with TB. As a result, the label-free and sensitive “signal-on” aptasensor displayed a wide linear range response for TB from 1 × 10 −5 to 10 nM with a low detection limit of 3.0 fM.

A regenerable electrochemiluminescence aptasensor for thrombin (TB) has been developed using dual co-reactants of poly(ethylenimine) (PEI) and thiosemicarbazide (TSC) for signal amplification. Herein, Au nanoparticle (AuNPs) were in-situ electrodeposited on glassy carbon electrode (GCE) in advance, and then the colloidal gold nanoparticle (nano-Au) and TSC were alternately self-assembled on AuNPs/GCE to obtain nano-Au/TSC/AuNPs multi-layers for 5’-thiolated partly complementary strand (PCS) immobilization. Subsequently, the multifunctional binding aptamer (MBA), consisted of an adenosine triphosphate (ATP) binding aptamer (ABA) and a thrombin binding aptamer (TBA), was hybridized with PCS to generate double-strands DNA (PCS/MBA). Meanwhile, the signal probe was fabricated by immobilizing detection thrombin aptamer (TBA 2) on the surface of PEI enhanced Ru(bpy)32+ doped nanospheres. On the basis of sandwich-type tactics, TB was measured quantitatively in the range from 1 × 10−5 nM to 0.1 nM. More importantly, the aptasensor could regenerate by treating with ATP to take off MBA based on ATP-induced conformation change, leaving only PCS onto the modified electrode to re-hybridize with MBA. The proposed aptasensor exhibited good selectivity, acceptable stability and satisfactory regenerability.

A one-dimensional overdamped system consisting of a symmetric periodic potential, a constant bias force and a trichotomous noise was investigated. In the frame of master equations, we derived analytical expression of its current. By means of numerical calculations, the results indicate that the current first increases, then decreases and finally increases with the bias force increasing, i.e., an absolute negative mobility (ANM) phenomenon. Our further investigations presented dependence of the ANM phenomenon on parameters of the noise. Its intrinsic physical mechanism was also open up, and a minimal model with ANM phenomenon is demonstrated.

In this work, a new signal amplified strategy based on the quenching effect of hemin and Au nanoparticles decorated CeO2 nanoparticles (Au@CeO2 NPs) for ultrasensitive detection of thrombin (TB) is reported for the first time. Herein, the poly(ethylenimine) (PEI) enhanced Ru(bpy)3(2+) nanocomposite was implemented by direct chemical polymerization, which could provide the desirable enhanced initial ECL signal. Furthermore, the detection aptamer of thrombin (TBA 2) was immobilized on Au@CeO2 NPs to form TBA 2/Au@CeO2 conjugates. Then, the G-rich DNA of TBA 2 sequence could fold into a G-quadruplex structure to embed hemin to obtain the quenching probe of hemin/TBA 2/Au@CeO2 conjugates. In the presence of target TB, the sandwiched structure could be formed between capture aptamer (TBA 1), TB and hemin/TBA 2/Au@CeO2 conjugates, thereby resulting in a proportional quenching in ECL response with TB, due to the quenching of both hemin and Au@CeO2 NPs. As a result, the signal-off aptasensor showed a wider linear range response from 10(-13) to 10(-8) M with lower detection limit of 0.03 pM.

Using immuno-fluorescent probing and Western blotting analysis, we reveal the exclusive cytoplasm nature of the small subunit ribosomal protein S20. To illustrate the importance of the cellular compartmentation of S20 to the function of small subunit 40S, we created a nuclear resident S20NLS mutant gene and examined polysome profile of cells that had been transfected with the S20NLS gene. As a result, we observed the formation of recombinant 40S carried S20NLS but this recombinant 40S was never found in the polysome, suggesting such a recombinant 40S was translation incompetent. Moreover, by the tactic of the energy depletion and restoration, we were able to restrain the nuclear-resided S20NLS in the cytoplasm. Yet, along a progressive energy restoration, we observed the presence of recombinant 40S subunits carrying the S20NLS in the polysome. This proves that S20 needs to be cytoplasmic in order to make a functional 40S subunit. Furthermore, it also implies that the assembly order of ribosomal protein in eukaryote is orderly regulated.

The simplified incidence function model with cross-correlated noises was employed to study the stability of a metapopulation perturbed by environments. Through numerically computing the stationary probability distribution function (PDF) and stochastically simulating the extinction time of a metapopulation, we found that: (i) The multiplicative noise intensity D inhibits the fluctuation of dynamic variable while the additive noise intensity α intensifies it, whether there is a correlation between the multiplicative noise and the additive noise; (ii) As the correlation strength (λ) between them is greater than zero, there is an optimal D in which the PDF curve deviates furthest from the extinction position, and another optimal D which maximally delays the extinction time of a metapopulation; (iii) For the constant D and α, the increment of λ not only upgrades the probability that patches are occupied by a metapopulation, but also delays the time that a metapopulation goes to extinction.

Electrochemical redox reactions in a twin-electrode (TE) type cell composed of a couple of Nafions®-coated indium tin oxide (ITO) electrodes each incorporating Ru(bpy)32+ and methylviologen (MV2+) were analyzed by in-situ spectrocyclic voltammetry. The cell system, ITO/Nafion®[Ru(bpy)32+]/aqueous electrolyte/Nafion[MV2+]/ITO, showed changes in visible absorption spectra induced by cyclic scanning of the potential difference between the two ITO electrodes. The spectral changes were attributed to the redox reactions of Ru(bpy)33+/2+ and MV2+/+· showing a multicolor electrochromism. The potential difference (+ 1.73 V) of the major redox wave in the cyclic voltammogram (CV) of the TE cell were close to the values (+ 1.76 V) calculated from the redox potentials of each species. Small peaks in the TE-CV suggested side reactions with H2O and O2, as well as migrations of the redox compounds into the opposite membranes. When each redox membrane was precycled repeatedly in an aqueous electrolyte solution, before fabricating a TE cell, the cell showed very stable behavior after repeated cyclic scanning. It has been shown that the present in-situ TE spectrocyclic voltammetry is useful for studying reactions occurring in practical devices.