Strongly fluorescent graphene quantum dots (GQDs) have been prepared by one-step solvothermal method with PL quantum yield as high as 11.4%. The GQDs have high stability and can be dissolved in most polar solvents. Because of fine biocompatibility and low toxicity, GQDs are demonstrated to be excellent bioimaging agents.

Many biological organisms with exceptional freezing tolerance can resist the damages to cells from extra-/intracellular ice crystals and thus maintain their mechanical stability at subzero temperatures. Inspired by the freezing tolerance mechanisms found in nature, here we report a strategy of combining hydrophilic/oleophilic heteronetworks to produce self-adaptive, freeze-tolerant and mechanically stable organohydrogels. The organohydrogels can simultaneously use water and oil as a dispersion medium, and quickly switch between hydrogel- and organogel-like behaviours in response to the nature of the surrounding phase. Accordingly, their surfaces display unusual adaptive dual superlyophobic in oil/water system (that is, they are superhydrophobic under oil and superoleophobic under water). Moreover, the organogel component can inhibit the ice crystallization of the hydrogel component, thus enhancing the mechanical stability of organohydrogel over a wide temperature range (−78 to 80 °C). The organohydrogels may have promising applications in complex and harsh environments.

A simple and novel method has been demonstrated for avoiding coffee ring structure based on hydrosoluble polymer additives during droplet evaporation. The polymer additives lead to the motion of the contact line (CL) resulted from the viscosity and Marangoni effect. The viscosity provides a large resistance to the radially outward flow. It results in a small amount of spheres deposited at droplet edge, which do not facilitate the pinning of the CL. The Marangoni effect resulted from the variation of polymer concentration at droplet edge during droplet evaporation contributes to the motion of the CL. Thus, uniform and ordered macroscale SiO(2) microspheres deposition is achieved. What's more, the coffee ring effect can be eliminated by different hydrosoluble polymer. This method will be applicable to a wide of aqueous system and will be of great significance for extensive applications of droplet deposition in biochemical assays and material deposition.

A simple and novel method for avoiding the coffee ring structure has been demonstrated based on hydrophobic silicon pillar arrays during single-drop evaporation. When a drop of a colloidal suspension of latex spheres is dropped onto hydrophobic silicon pillar arrays with high contact angle hysteresis, the latex spheres are deposited at the periphery to form a porous gel foot due to the Wenzel wetting state of the drop on the substrate, which results in an effective elimination of the coffee ring structure. The coffee ring effect is avoided by relying on radially inward mass transport: a circulatory fluid flow triggered by means of the gel foot growth. Thus, uniform and ordered macroscale colloidal photonic crystals are fabricated. In the meantime, the influences of some factors, such as concentration of latex spheres, evaporation temperature, periodicity of hydrophobic silicon pillar arrays and the distance between the top rims of adjacent silicon pillars on drop deposition are investigated. This facile approach to eliminating the coffee ring structure will be of great significance for extensive applications of drop deposition in biochemical assays and material deposition.

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