A flow-through microfluidic chip for continuous dielectrophoretic separation of viable and non-viable human T-cells

Effective methods for rapid sorting of cells according to their viability are critical in T cells based therapies to prevent any risk to patients. In this context, we present a novel microfluidic device that continuously separates viable and non-viable T-cells according to their dielectric properties. A dielectrophoresis (DEP) force is generated by an array of castellated microelectrodes embedded into a microfluidic channel with a single inlet and two outlets; cells subjected to positive DEP forces are drawn toward the electrodes array and leave from the top outlet, those subjected to negative DEP forces are repelled away from the electrodes and leave from the bottom outlet. Computational fluid dynamics is used to predict the device separation efficacy, according to the applied alternative current (AC) frequency, at which the cells move from/to a negative/positive DEP region and the ionic strength of the suspension medium. The model is used to support the design of the operational conditions, confirming a separation efficiency, in terms of purity, of 96% under an applied AC frequency of 1.5 × 10⁶ Hz and a flow rate of 20 μl/h. This work represents the first example of effective continuous sorting of viable and non-viable human T-cells in a single-inlet microfluidic chip, paving the way for lab-on-a-chip applications at the point of need.     

Secondary ion yields produced by keV atomic and polyatomic ion impacts on a self-assembled monolayer surface

A suite of keV polyatomic or 'cluster' projectiles was used to bombard unoxidized and oxidized self-assembled monolayer surfaces. Negative secondary ion yields, collected at the limit of single ion impacts, were measured and compared for both molecular and fragment ions. In contrast to targets that are orders of magnitude thicker than the penetration range of the primary ions, secondary ion yields from polyatomic projectile impacts on self-assembled monolayers show little to no enhancement when compared with monatomic projectiles at the same velocity. This unusual trend is most likely due to the structural arrangement and bonding characteristics of the monolayer molecules with the Au(111). Copyright 1999 John Wiley & Sons, Ltd.     

Chemfet Based Microsensors Covered with Ion-Partitioning Polymeric Membranes

 The development of a new type of microsensors based on chemically sensitive field-effect transistors (CHEMFETs) covered with polymeric bulk ion-partitioning membranes is presented. For the construction of the microsensor, a PVC plasticized membrane containing two ionophores, one selective to protons and the other to the analyte cation of interest, is placed on the gate of a pH sensitive field-effect transistor which acts as the transducer. With the use of thin (5–10 μm) ion-partitioning membranes onto the pH-sensitive ISFET gate, the proton displacement out of the membrane and to the pH sensitive gate is fast and reversible. This displacement generates a signal that is directly related to the analyte concentration found in the test solution. Comparing the performance of CHEMFETs and ISEs selective to the monovalent potassium cation and the divalent calcium ion validates this novel CHEMFET response mechanism.