Dead volume free micro-machined electro-spray chip for mass spectrometry.

Design and fabrication themes of a dead volume free electro-spray chip for mass spectrometry based on mechanical micro-machining approach is discussed in this article. To implement the dead volume free concept, a cantilever needle is embedded inside the micro-channel of the spray-chip such that there is no connecting joint between the sample wall and the spray-tip. To ensure that the proposed spray-chip is able to produce efficient Taylor cone, embedded needles with different cone angles are fabricated to produce an efficient experiment. Experiments to distinguish amphetamine by a LCQ type mass spectrometry are conducted. Experimental results show that the proposed dead volume free electro-spray chip is able to reach the desired goal. It is also found from the experiments that the ringlike cross-section of the needle embedded micro-channel is critical to the stability of the Taylor cone at the spray-tip. To ensure a stable Taylor cone can be produced at the spray-tip, an embedded needle with a smaller diameter is desired.

Centrifugal and electric field forces dual-pumping CD-like microfluidic platform for biomedical separation.

In this article, we propose a versatile CD-like multi-channel electrophoresis-based biomedical separation system that is driven by the interactive forces between the centrifugal force and the electric field force. The centrifugal force control of this system is realized through the velocity control of a DC servo motor, while the electric field is governed through the concentric conducting circuits, which are suitably designed and fabricated by sputtering on metal mask method, and can be adjusted to provide multi-stage voltages. Experimental results demonstrate that the electro-osmotic flow (EOF) effect can be effectively reduced when the electric field force and centrifugal force are in the opposite direction. Benefits from this are that the electrophoresis separation time can be prolonged and the length of the microfluidic channels can be shortened; therefore, more effective separation efficiency can be obtained. Moreover, other advantages, such as lower joule-heat generation, low-chemistry reaction, and no variation on the ion concentration during processes, make this biomedical separation system more useful.