Current Research
Graphene Membranes for Energy Efficient Water Purification and Gas Separations
Direct synthesis of graphene with well‐defined nanoscale pores over large areas can transform the fabrication of nanoporous atomically thin membranes (NATMs) and greatly enhance their potential for practical applications. However, scalable bottom‐up synthesis of continuous sheets of nanoporous graphene that maintain integrity over large areas has not been demonstrated. Here, it is shown that a simple reduction in temperature during chemical vapor deposition (CVD) on Cu induces in‐situ formation of nanoscale defects (≤2–3 nm) in the graphene lattice, enabling direct and scalable synthesis of nanoporous monolayer graphene. By solution‐casting of hierarchically porous polyether sulfone supports on the as‐grown nanoporous CVD graphene, large‐area (>5 cm2) NATMs for dialysis applications are demonstrated. The synthesized NATMs show size‐selective diffusive transport and effective separation of small molecules and salts from a model protein, with ≈2–100× increase in permeance along with selectivity better than or comparable to state‐of‐the‐art commercially available polymeric dialysis membranes. The membranes constitute the largest fully functional NATMs fabricated via bottom‐up nanopore formation, and can be easily scaled up to larger sizes permitted by CVD synthesis. The results highlight synergistic benefits in blending traditional membrane casting with bottom‐up pore creation during graphene CVD for advancing NATMs toward practical applications.
Bacterial Isolation for Sepsis Detection
This research aims to improve diagnosis of bacterial infections implicated in sepsis by isolating and concentrating bacteria without performing blood cultures. Sepsis is when the immune response to infection becomes dysregulated and destructive. Current diagnostics rely on blood cultures, which can take days and often lack predictive value for sepsis patients. By using functionalized magnetic beads and centrifugal microfluidics, we can isolate and concentrate whole bacteria from blood in less than three hours.
Use of Plant Xylem for Development of Low-cost Water Filters
This research is to develop a low-cost, point-of-use water filter using sapwood xylem from coniferous trees to facilitate safe access to drinking water for rural communities in India that lack access to safe water supplies. Our research has shown how sapwood xylem could be repurposed into a water filter capable of meeting the drinking water requirement of an average household for nearly a week. The widespread availability of conifers in particular regions in India could allow for the manufacture of inexpensive, xylem-based filtration devices. If scaled up, this technology could support local economies across the globe as well as facilitate access to safe drinking water in regions that lack centralized water distribution systems.
Improved Point-of-use Water Sensors Based on User Preferences
Micropollutant “Dry Sampling” Technology for Water Quality Monitoring
This research aims to realize dry preservation of heavy metal contaminants in water samples using cation exchange resins for improved water quality monitoring.
Low-Cost Air Particulate Monitor Based on Particle Capture and Imaging
Particulate Matter (PM) pollution continues to be an important global environmental issue and raises increasing concerns for public health. The strong correlation between personal health impact and actual local exposure creates a huge demand for air particulate sensors meant for small-scale measurement. However, today’s air particulate monitoring technologies suffer from high cost, high power requirements, or large size, which presents an opportunity to create low-cost, compact, and low-power sensors that are desired for block-level, household, automobile, or even personal-level monitoring. This research aims to develop such sensors with the goals of low cost (<$5), ability to measure particulate counts PM10 and PM2.5 with sensitivity down to 200 nm particle size and dynamic range of 1-500 μg/m3, compact size (<2 cm x 2 cm). The power consumption should be low so as to enable autonomous operation for prolonged periods of time at the desired measurement frequency. We are developing methods to achieve these goals, the novel low-cost PM sensor design involves capture of particles from air on a substrate followed by detection of scattered light using an optical imaging system.
Past Research
Microfluidic Cell Sorting and Analysis
Separation and analysis of cells is important for biomedical research, diagnostics, and cell therapeutics. We are developing new technologies to analyze and sort cells that minimize sample processing and improve performance over existing methods. We have pioneered microlfuidic devices for sorting of cells in continuous flow based on transient cell-surface adhesion, called cell rolling. In this process, we use molecular-level cell-surface interactions to steer cells flowing in microlfuidic devices, resulting in separation with high purity and recovery. For example, we have demonstrated the ability to directly separate cells from blood without prior sample processing, which opens the possibility of monitoring the white blood cells at the point of care. We have also developed devices to analyze cells based on adhesion. The cell-surface interactions directly result in a visual readout by affecting the motion of cells flowing through the devices. These devices are being used to elucidate the adhesion behavior of mesenchymal stem cells, which are gaining increasing attention for cell therapies. Finally, we have also developed a microfluidic circuit with a feed-forward loop to sort particles based on size and deformability, and are studying the flow of cells through constrained microchannels.
People: Suman Bose, Chia-Hua Lee
Collaboration: Jeffrey Karp (BWH), Krystyn Van Vliet (MIT), Angela Belcher (MIT)
Nanoparticles for Drug Delivery
Biodegradable lipid and polymeric nanopoarticles with the ability to target diseased tissue and release drugs in a controlled manner are highly promising as carriers for drug therapy. We are using microfluidic devices for synthesis of polymeric nanoparticles with tunable properties and homogeneous distributions. Our aim is to control their properties such as size, charge, homogeneity, and drug loading by rapid mixing of precursors during nanoprecipitation. These devices are being used for understanding the role of nanoparticle properties on their in vitro and in vivo behavior to develop nanoparticles and to optimize them for different applications.
People: Jong-min Lim, Sunandini Chopra
Collaboration: Omid Farokhzad (BWH), Robert Langer (MIT)
Nanostructured Membranes for Water Purification and Gas Separations
Controlling the nanoscale structure of materials offers new avenues for advancing membrane technology. We are developing new membranes for water purification and gas separations. We have developed membranes that employ short hydrophobic nanopores to trap vapor, and enable practically isothermal vapor-phase transport across two liquid menisci separated by a sub-micron vapor gap. This membrane decouples the transport from membrane material, presenting opportunities to make them chlorine-resistant. It can potentially reject all non-volatile material such as boron that is otherwise difficult to remove using polymeric membranes. We are also developing graphene-based membranes that exploits flow through nanometer-scale pores in graphene. Theoretical studies have shown the potential of these membranes for high-flux water purification and gas separations. We are developing methods to fabricate such membranes and techniques to study mass transport through graphene.
People: Jongho Lee, Sean O’Hern, Tarun Jain, Michael Boutilier
Collaboration: Nicolas Hadjiconstantinou (MIT), Jing Kong (MIT), Evelyn Wang (MIT), Juan Carlos Idrobo (ORNL), Tahar Laoui and Faizur Rehman (KFUPM)
Nanofluidic Devices for DNA Analysis
Nanofluidic devices have unique capabilities for manipulation and sensing of DNA molecules at the single-molecule level. We have developed nanofluidic devices that employ multiple measurements on single molecules to enhance the ability to size DNA molecules. We have also developed a fabrication technique to integrate membranes containing nanopores into microfluidic devices, which decreases noise and enables the design of networks containing nanopores. Combined with active control of molecules, these devices can provide improved DNA analysis and sorting capabilities.
People: Tarun Jain
Collaboration: Carlos Aguilar (MIT Lincoln Labs), Pete Carr (MIT Lincoln Labs)
