Monitoring of biologically active agents such as bacteria, viruses, proteins and small molecules in environmental samples poses complex analytical problems. The particulate nature of the analytes and potential interferents is of particular concern for microfluidic systems in which the channels may not be much larger than the particles themselves. For this reason, sample preconditioning upstream of a chemical analytical device will usually be required. However, the small dimensions of microfluidic devices also allow unique methods of sample purification, concentration, and detection. In our laboratory we have developed a series of microfluidic chemical analytical devices for such purposes. These devices rely on the low Reynolds number flow conditions. In such conditions field flow fractionation based on sedimentation, diffusion and electrophoresis perpendicular to the flow direction can be profitably harnessed to precondition samples. The H-filter is one such device in which a simple 4-port device that allows two fluids to be brought into adjacent flow, and then separated downstream into two (or more) flow streams after exchange of material under the influence of one or more fields. It can be fabricated using anodically bonded silicon and Pyrex channels, or using polymeric devices formed using `soft lithography' techniques. We have tested the ability of this device to be used for purification of bacteria and their spores from complex samples containing silica and other interferent particles. We will present results of our tests of this device, as well as initial attempts to integrate the H-filter into a sample preconditioning system that includes on-chip pumps.
The spectroscopy and dynamics of highly excited vibrational levels of the a1A1 and b1B1 states of CH2 were studied using time-resolved Fourier transform emission spectroscopy. The use of a Fourier transform spectrometer allows efficient acquisition of dispersed fluorescence spectra over several thousand cm-1 range in the visible, with better than 1 cm-1 resolution, from this short lived and low concentration species. Furthermore, the temporal evolution of the dispersed fluorescence spectra due to collisional relaxation can be monitored with 50 ns time-resolution. The results presented and discussed in this paper are: (1) the state-to-state rotational energy transfer and reactive cross- sections for b1B1 (0, 16O, 0) CH2; and (2) rotational analysis of several previously unobserved high vibrational levels of the CH2 a1A1 state.