Miniature high speed label-free cell analysis systems have yet to be developed, but have the potential to deliver fast, inexpensive and simple full blood cell analysis systems that could be used routinely in clinical practice. We demonstrate a microfluidic single cell impedance cytometer that performs a white blood cell differential count. The device consists of a microfluidic chip with micro-electrodes that measure the impedance of single cells at two frequencies. Human blood, treated with saponin/formic acid to lyse erythrocytes, flows through the device and a complete blood count is performed in a few minutes. Verification of cell dielectric parameters was performed by simultaneously measuring fluorescence from CD antibody-conjugated cells. This enabled direct correlation of impedance signals from individual cells with phenotype. Tests with patient samples showed 95% correlation against commercial (optical/Coulter) blood analysis equipment, demonstrating the potential clinical utility of the impedance microcytometer for a point-of-care blood analysis system.

Counting the different subpopulations of cells in a fingerprick of human blood is important for a number of clinical point-of-care (PoC) applications. It is a challenge to demonstrate the integration of sample preparation and detection techniques in a single platform. In this paper we demonstrate a generic microfluidic platform that combines sample processing and characterisation and enumeration in a single, integrated system. Results of microfluidic 3-part differential leukocyte (granulocyte, lymphocyte and monocyte) counts, together with erythrocyte and thrombocyte (platelet) counts, in human blood are shown and corroborated with results from hospital clinical laboratory analysis.

Protein film voltammetry has been employed to define multiple catalytic consequences of proton coupled electron transfer (PCET) in a cytochrome c nitrite reductase. Current-potential profiles reflecting the steady-state rate of nitrite-limited reduction have been defined from pH 4 to 8. Lowering the electrode potential at pH 8 causes the catalytic current to increase and then decrease before it takes a value independent of any further lowering of electrode potential. By comparison, at pH 4, catalysis is initiated at more positive electrode potentials in an approximately sigmoidal fashion with no attenuation of the catalytic rate evident at more negative electrode potentials. The results show that activity is turned on by the coupled transfer of two electrons and one proton to the enzyme. The decreased rate of catalysis at lower electrode potentials under more alkaline conditions shows that this rate attenuation occurs only when reduction is not coupled to compensating protonation(s) of the enzyme. Sites within the enzyme whose reduction and/or protonation may contribute to the definition of these activities are discussed.

This paper demonstrates an integrated microfluidic system that performs a full blood count using impedance analysis. A microfluidic network design for red blood cell (RBC) lysis is presented, and the diffusive mixing processes are analyzed using experimental and simulated results. Healthy and clinical bloods analyzed with this system, and the data shows good correlation against data obtained from commercial hematology machines. The data from the microfluidic system was compared against hospital data for 18 clinical samples, giving R(2) (coefficient of determination) values of 0.99 for lymphocytes, 0.89 for monocytes, and 0.99 for granulocytes in terms of relative counts and 0.94 for lymphocytes, 0.91 for monocytes, and 0.95 for granulocytes in terms of absolute counts. This demonstrates the potential clinical utility of this new system for a point-of-care purpose.

The recent structural characterization of the NrfA from Escherichia coli provides a framework to rationalize the spectroscopic and functional properties of this enzyme. Analyses by EPR and magnetic CD spectroscopies have been complemented by protein-film voltammetry and these are discussed in relation to the essential structural features of the enzyme.