Marcus Lehto

On-chip liquid storage and dispensing for lab-on-a-chip applications

This work presents novel components for on-chip storage and dispensing inside a lab-on-a-chip (LOC) for applications in immunoassay point-of-care testing (POCT), where incubation and washing steps are essential. It involves easy-to-use on-chip solutions for the sequential thermo-hydraulic actuation of liquids. The novel concept of combining the use of a rubber plug, both as a non-return valve cap and as a liquid injection interface of a sealed reservoir, allows simple filling of a sterilized cavity, as well as the storage and dispensing of reagent and washing buffer liquids. Segmenting the flow with air spacers enables effective rinsing and the use of small volumes of on-chip stored liquids. The chip uses low-resistance resistors as heaters in the paraffin actuator, providing the low-voltage actuation that is preferred for handheld battery driven instruments.

A Polymeric Paraffin Microactuator

Paraffin wax is a promising material in microactuators not only because of its ability of producing large displacements and high forces at the same time but also because of the variety of manufacturing techniques available. In this paper, a simple actuator based on paraffin wax as the active material is fabricated and tested. Ultraviolet-curable epoxy is used in a technique combining simultaneous moulding and liquid-phase photopolymerization in a single-process step to build the stiff part of the actuator body. A heater is integrated in the paraffin reservoir, and a polyimide tape is used as the deflecting membrane. Thermomechanical analysis of the paraffin wax shows that it exhibits a volume expansion of 10%, including phase transitions and linear expansion. As for the actuator, a stroke of 90 mum is obtained for the unloaded device, whereas 37 mum is recorded with a 0.5-N contact load at a driving voltage of 0.71 V and a frequency of 1/32 Hz. The actuator can be used in microsystems, where both large strokes and forces are needed. The low-cost materials and low driving voltage also makes it suitable for disposable systems.

A polymeric paraffin micropump with active valves for high-pressure microfluidics

We present the potentially strongest micropump in sub-cm/sup 3/ size yet for microfluidics, using simple processes and materials such as epoxy, paraffin, and polyimide. Utilizing the large volume expansion associated with the melting of paraffin for actuation, a pump consisting of two active valves and one pumping chamber operated by three identical paraffin actuators has been realized. UV-curable epoxy, which encloses the paraffin, forms the channel structure and joins the glass cover, actuator membrane and resistive heaters for melting the paraffin, is the main construction material. With water as a pumping fluid and a 2 V drive voltage, the valves were subjected to pressures up to about 1 MPa without showing any leakage. A flow rate of 74 nl/min was obtained in normal operation.

Metallic High-Pressure Microfluidic Pump with Active Valves

We present for microfluidics the strongest yet mechanical micropump in sub-cm3 size, using simple processes and materials such as Parylene coated stainless steel stencils, paraffin, and copper clad polyimide. The pump consists of two active valves and one pumping chamber, each operated by a paraffin actuator. Each actuator is driven by a square pulse waveform with an amplitude of 1.8 V. The pump sequence has a period time of 14.4 s, resulting in the pumping of water up to 50 bar (5 MPa) back pressure without leakage and a flow rate of 0.75 muL/min.