Research
Current Projects:
1. Polymeric lithography editor: Editing submicron scale lithographic errors with nanoporous polymeric probes. We have developed a new lithographic editing system that has ability to erase and rectify errors in sub-micron scale. The erasing probe is either a conically shaped hydrogel (tip size ranges from submicron to multi-micron) template-synthesized from track-etched conical glass wafers or photolithographic patterned silicon wafers. A large range of probes, including “nanosponge” hydrogel-based probes (agarose, polyacrylamide, chitosan etc.) and non-porous polymer probes (polydimethylsiloxane, SU-8 etc.), “erases” patterns by hydrating and absorbing molecules into the probe matrix via diffusion mechanism. The presence of an interfacial liquid water layer between the tip and the substrate during erasing enables fast, uninterrupted translation of the eraser on the substrate. The erasing capacity of the hydrogel-based probes is extremely high because of the large free volume of the hydrogel matrix. The fast frictionless translocation and interfacial hydration resulted in an extremely high erasing rate (many hundreds to thousands of mm2 s-1), which is two to three orders of magnitude higher in comparison with the atomic force microscopy–based erasing (~0.1 mm2 s-1) experiments. The high precision and accuracy of the polymeric lithography editor (PLE) system stemmed from coupling piezoelectric actuators to an inverted optical microscope. Subsequently after erasing, “correct” patterns are precisely printed using at the “error” spots. PLE also provides a continuous optical feedback throughout the entire molecular editing process—writing, erasing, and rewriting. The device fabrication were demonstrated both on hard and soft substrates using PLE. For example, electrochemically erasing of metallic copper thin film using PLE allowed interdigitated array of microelectrodes for the fabrication of a functional microphotodetector devices. High-throughput dot and line erasing, writing with the conical “wet nanosponge,” and continuous optical feedback make PLE complementary to the existing catalog of nanolithographic/microlithographic and three-dimensional printing techniques. This new PLE technique will potentially open up many new and exciting avenues in lithography, which remain unexplored due to the inherent limitations in error rectification capabilities of the existing lithographic techniques.
Students involved: Nathalie Mora, Md. Ali Aswad, Annie Vargas and Miroslava Zaborska
Funding: NSF
2. Super-high resolution optical nanoscopy based on microlenses. Optical microscopy is an invaluable characterization tool in biological, chemical, and materials sciences from both fundamental studies and applied viewpoints. There is a physical limitation imposed on the spatial resolution of an optical microscope (through Abbe’s law) below which the optical features cannot be resolved. Recently, there are some optical microscopic techniques available that can significantly enhance spatial resolution. These imaging methods may require sophisticated hardware/software or special fluorophores to achieve resolution below diffraction limit. We demonstrate here the use of microlenses composed of high-refractive index (h, 1.47<n<1.73) materials greatly enhances the spatial resolution of images acquired using a conventional microscope. The proposed imaging technique can resolve features below 100 nm and provides magnification between ×2 and ×6 using a low intensity broad band white light illumination source. We utilize salt-based plano-convex microlenses (MLs) kept in-between a specimen and an objective of an inverted microscope. High-resolution images can be acquired in atmospheric conditions where biological samples are active. The proposed method is inexpensive, easy to use, and does not require extensive sample preparation. Any conventional optical microscope can be converted into a super-resolution nanoscope by incorporating MLs in the system. The fabrication of MLs is extremely simple, highly reproducible with high yield, and an array of MLs can be self-assembled in a wet-lab without any need for clean-room facilities. Our proposed ML-based nanoscope can be used for bright- and dark-fields, phase-contrast, and fluorescence imaging of biological specimens under atmospheric conditions.
Students involved: Rajesh Balaraman, Nathalie Mora, Katie Flynn and Jared Fiske
Funding: NIH
3. Bio-molecule and -particle sensing based on fluorescence resonance energy transfer (FRET). To date, little research work has addressed the use of the other factors than donor-acceptor inter-distance (r) in the Förster equation for sensing mechanism. We propose a novel FRET system that utilizes primarily changes in spectral overlap (J) between donor emission and acceptor absorption, and acceptor quantum yield (Qy) to modulate the rate of energy transfer between donor and acceptor molecules. Our probe is derived from fluorophore tagged conjugated polydiacetylene (PDA) bilayer liposomes, and the receptors are attached to the liposomes. By taking advantage of ligand-receptor interactions that resulted in changes in J values, we have developed FRET based biological sensors with sensitivity superior to colorimetric sensors. The sensing probes proposed here are expected to have detection limit in nanomolar, and with careful optimization picomolar detection limit is possible.
Students involved: Nathalie Mora, Jared Fiske
Funding: NIH
4. Antimicrobial and antioxidant functionalized nanoparticles for enhancing food safety and quality. The proposed research aimed at testing an innovative concept of preventing cross-contamination of food and controlling its microbial and oxidative spoilage by developing active antimicrobial and antioxidant food-contact surfaces. The examples of relevant surfaces are: parts of industrial equipment (e.g. conveyors, cutting organs, pipes and filters), kitchen utensils (cutting boards, knives) and packaging materials, primarily for liquid foods (bottles, plastic bags, laminated carton containers). The core idea of the proposal is building bio-compatible nanoparticles possessing antimicrobial and antioxidant properties due to the natural bioactive phenolic compounds covalently bound to their surface. These nanoparticles may be used as active coatings on food-contact surfaces. In this study we propose to check a hypothesis that antimicrobial and antioxidant properties of the phenolics are retained and even enhanced after binding to nanoparticles.
Students involved: Nathalie Becerra, Annie Vargas, Arosha Hemantha Loku Umagiliyage and Jim Thomson
Collaborators: Ruplal Choudhary (Plant, Soil, and Agricultural Systems, SIUC), Derek Fisher Microbiology, SIUC), Victor Rodov (Post Harvest and Food Sciences, ARO, Volcani Center, Israel), Eva Almenar (Michigan State University), Lilia Fernando (BIOTECH-UP Los Banos Laguna, Philippines), Jonna Atienza (BIOTECH-UP Los Banos Laguna, Philippines)
Funding: USDA/BARD