Jessica Melin

Development of micromachined hollow tips for protein analysis based on nanoelectrospray ionization mass spectrometry

Two novel types of micromachined nanoelectrospray emitter tips have been designed, fabricated and tested. The fabrication method of the hollow tips is based on a self-aligning deep reactive ion etch process. The tips consist of either silicon dioxide or silicon and feature orifice diameters of 10 and 18 μm, respectively. The geometrical characteristics of both emitter types are favorable for the generation of stable electrospray ionization, i.e. wetting of the tip shaft is avoided and the base of the Taylor cone is limited to the diameter of the orifice. A silicon dioxide tip was operated in a bench top setup to visually evaluate the electrospray. Both types of tips were also successfully used for the analysis of an insulin sample in an ion trap mass spectrometer.

A Low-Temperature Thermopneumatic Actuation Principle for Gas Bubble Microvalves

We introduce a novel type of microfluidic actuator in which a trapped air bubble functions as the thermally controlled volume displacing element. The pressure of the trapped air pocket is controlled by the changing equilibrium gas composition for static operation and by thermal expansion for dynamic operation. The volume displacement is determined by the liquid surface tension and the valve geometry. A fully functional demonstrator device was successfully fabricated and tested. The absence of moving mechanical parts, the electrical control of the valve, and the limited required actuation temperature make the actuator suitable for control of large-scale integration fluidic networking in biotechnical applications.

A liquid-triggered liquid microvalve

This work introduces a novel surface tension and geometry based liquid-triggered liquid microvalve for on-chip liquid control. The simultaneous presence of two liquid plugs at the uncomplicated valve junction triggers the further movement of the liquids and overcomes the stop valve function of the device, thereby providing a precise means of timing liquid movement on-chip. The structure was shown to successfully function and forms the basis for several novel and useful functions, including fluidic AND gates, contactless on-chip liquid sample control, timing of independent processes on the same microchip, bubble-free joining of liquids, all of which pose great challenges in the area of microfluidics.

Single-use microfluidic pumps and valves based on a thermally responsive PDMS composite

In this work we present active microfluidic liquid handling integrated on-chip with no need for external actuators. The concept is based on a temperature sensitive silicone elastomer composite, consisting of PDMS and expandable microspheres. We successfully fabricated single-use microfluidic pumps and displaced liquids in the range of nanoliters even against counter pressures up to 100kPa. Moreover, liquid flow in a microchannel was entirely blocked by means of integrated valves. The valves could withstand pressures up to 140kPa. The devices were fabricated entirely from low cost materials and allow wafer-level processing to be used.

A Low-Temperature Thermopneumatic Gas Bubble Valve

We introduce a novel type of actuation for microvalves, in which a trapped air bubble functions as the thermally controlled volume displacing element. The pressure of the trapped air pocket is controlled thermally using a resistive heater. The volume displacement is determined by the liquid surface tension and the valve geometry. A fully functional demonstrator device was successfully fabricated and tested. The absence of moving mechanical parts, the electrical control of the valve, and the limited required actuation temperature make the actuator suitable for control of LSI fluidic networking in biotechnical applications.