Jay W. Grate

This report covers the topics of discussion and the recommendations of the panel members. On December 8 and 9, 2010, the Geochemistry, Biogeochemistry, and Subsurface Science (GBSS) Science Theme Advisory Panel (STAP) convened for a more in-depth exploration of the five Science Theme focus areas developed at a similar meeting held in 2009. The goal for the fiscal year (FY) 2011 meeting was to identify potential topical areas for science campaigns, necessary experimental development needs, and scientific members for potential research teams. After a review of the current science in each of the five focus areas, the 2010 STAP discussions successfully led to the identification of one well focused campaign idea in pore-scale modeling and five longer-term potential research campaign ideas that would likely require additional workshops to identify specific research thrusts. These five campaign areas can be grouped into two categories: (1) the application of advanced high-resolution, high mass accuracy experimental techniques to elucidate the interplay between geochemistry and microbial communities in terrestrial ecosystems and (2) coupled computation/experimental investigations of the electron transfer reactions either between mineral surfaces and outer membranes of microbial cells or between the outer and inner membranes of microbial cells.

Micromodel technologies are a useful and important method to study pore‐scale fluidic processes, using two‐dimensional formats that enable direct visualization of processes within patterned microstructures. In this technical note, Nile red, 9‐diethylamino‐5H‐benzo[alpha]phenoxazine‐5‐one, is demonstrated as a single dye whose solvatochromism enables selective visualization of two immiscible liquid fluids in a pore network micromodel containing a homogeneous array of pillars. Nile red dissolves in, and partitions between, hexadecane as a nonwetting fluid and polyethylene glycol 200 (PEG200) as a hydrophilic wetting fluid in a micromodel with silicon oxide surfaces. Both the absorption spectra and fluorescence emission spectra are sensitive to the solvent environment, such that the two phases can be distinguished by the observed color or the fluorescence emission band. Bright field, epifluorescence, confocal fluorescence, and hyperspectral microscopy methods were used to image the micromodel after displacing PEG200 in the model with hexadecane. Using a single solvatochromic dye facilitates direct visualization and identification of both phases anywhere in the micromodel on the basis of color and also enables collection of complementary fluorescent images for each phase. The use of Nile red with these imaging methods facilitates selective visualization of phase identity at specific locations; the interfaces between the two immiscible liquid phases; wetting behavior of the wetting phase within the pore network; and retention of the wetting phase as thin films around pillars and as bridges across the pore throats. The pillars and wetting phase bridges create a network of obstacles defining a tortuous flow path for the displacing nonwetting phase.

The potential for the use of biological agents by terrorists is a real threat. Two approaches for antibody-based detection of biological species are described in this paper: 1) The use of microbead arrays for multiplexed flow cytometry detection of cytokines and botulinum neurotoxin simulant, and 2) a microfluidic platform for capture and separation of different size superparamagnetic nanoparticles followed by on-chip fluorescence detection of the sandwich complex. These approaches both involve the use of automated fluidic systems for trapping antibody-functionalized microbeads, which allows sample, assay reagents, and wash solutions to be perfused over a micro-column of beads, resulting in faster and more sensitive immunoassays. The automated fluidic approach resulted in up to five-fold improvements in immunoassay sensitivity/speed as compared to identical immunoassays performed in a typical manual batch mode. A second approach for implementing multiplexed bead-based immunoassays without using flow cytometry detection is currently under development. The goal of the microfluidic-based approach is to achieve rapid (<20 minutes), multiplexed (≥ 3 bioagents) detection using a simple and low-cost, integrated microfluidic/optical detection platform. Using fiber-optic guided laser-induced fluorescence, assay detection limits were shown to be in the 100's of picomolar range (10's of micrograms per liter) for botulinum neurotoxin simulant without any optimization of the microfluidic device or optical detection approach.

The objectives of our research were to develop the first automated radiochemical process analyzer including sample pretreatment methodoology, and to initiate work on new detection approaches, especially using modified diode detectors.