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Wet granular materials are three-dimensionally simulated by the discrete element method with water bridges incorporated between particles. The water bridges are simplified as toroidal shapes, and the matric suction is constantly maintained in the material. A comparison with experimental tests in the literature indicates that the toroidal shape approximation may be one of the best choices with high practicability and decent accuracy. Mechanical behaviours of wet granular materials are studied by triaxial tests. Effects of particle size distributions and void ratios are investigated systematically in this study. The hydraulic limit of the pendular state is also discussed. It gives the capillary cohesion function which is not only determined by the degree of saturation but also positively correlated to relative density and particle size polydispersity and inversely proportional to mean particle size. Furthermore, the capillary strengthening effect is also analysed microscopically in aid of the Stress–Force–Fabric relationship, mainly in fabric anisotropy, coordination number and stress transmission pattern, which revealed the micro-mechanisms of the additional effective stress induced by capillary effect.

Capillarity in wet granular materials induces cohesion and increases the material strength due to the attractive forces acting on capillary bridges. In the funicular state, water bridges may be not only formed between two grains but also binding three or more particles, which breaks the axial symmetry of the liquid bridge. This work presents a fundamental study on capillary forces and rupture behaviours of funicular water bridges between three spherical bodies at equilibrium (or static) configurations. Funicular water clusters are numerically solved by an energy minimization approach. Experimental comparisons are made by measuring capillary forces and these confirm the validity of the numerical solutions. Evolutions of capillary forces and rupture distances are investigated systematically by moving two spheres away from the centre. The fixed water volume condition and the constant mean curvature condition are studied respectively. Comparisons are made between the un-coalesced pendular liquid rings and the coalesced funicular bridge. For a same fixed total water volume, the capillary force is weakened by water bridge coalescence to a funicular bridge when the spheres are packed together, but the situation may vary for different contact angles and inter-particle distances. For the constant mean curvature condition, water bridge coalescence does not alter capillary force significantly when particles are packed closely, but the discrepancy is larger by increasing the gap. Funicular water bridge rupture criteria are also proposed based on the studied configurations. It is observed that in general the transmission from pendular to funicular state extends the rupture distance when it has a relatively high water volume or low air-water pressure difference.

Herein, a new electrochemiluminescence (ECL) strategy for enzyme-free microRNA-21 (miR-21) amplified detection was designed based on target-catalyzed hairpin assembly by combining the signal-amplification capability of both intramolecular and intermolecular ECL co-reaction. In this strategy, two hairpin DNA probes of H1 and H2 were designed as capture probes and detection probes, respectively. To be specific, the capture probes of H1 were immobilized on the multilayer interface of AuNPs and thiosemicarbazide (TSC) assembly on the single-walled carbon nanohorns decorated electrode, while the detection probes of H2 was anchored on the nanocarriers of gold nanoparticals functionalized reduced graphene oxide (Au-rGO) which were tagged with the self-enhanced ruthenium complex (PEI-Ru(ΙΙ)) in advance. Based on the target-catalyzed hairpin assembly, target miR-21 could trigger the hybridization of H1 and H2 to further be released for initiating the next hybridization process to capture a large number of H2 bioconjugates on the sensing surface. Herein, the TSC was used not only as a coupling reagent to attach the AuNPs via Au-S and Au-N bonds but also as a novel intermolecular coreactant to enhance the ECL intensity, and the PEI-Ru(ΙΙ) as emitters exhibited enhanced ECL efficiency. Therefore, a strong ECL signal was achieved by the dual amplification strategies of target recycle and the intramolecular/intermolecular co-reaction of PEI-Ru(ΙΙ) and TSC. The designed protocol provided an ultrasensitive ECL detection of miR-21 down to the sub-femtomolar level with a linear response about 6 orders of magnitude (from 1.0 × 10(-16)M to 1.0 × 10(-11)M) with a relatively low detection limit of 0.03 fM (S/N=3).