Session J16: Focus Session: Biochip Physics II

Direct-Print Organic Photonics for Biodetection Chips

The development of commercial portable Biochip applications based on optical detection is hindered by the lack of imaging systems that can be directly integrated into the chip itself. Currently, fluorescence/luminescence signals are read out with power-hungry, bulky and expensive off-chip imaging systems, like CCD cameras or photomultiplier tubes. Here we present an enabling technology that for the first time allows cheap and easy integration of imaging systems directly into disposable Biochip systems. Our technology is based on organic semiconductor materials that can be processed in liquid form by inkjet and screen printing, in a process much faster and cheaper than the complicated fabrication of silicon-based imaging sensors. Organic photosensors can be printed on various substrate materials like plastic foil or glass or directly onto Biochip systems. The ultrathin photodiodes with an overall thickness of only 300 to 500 nm show quantum efficiencies better than 0.5 and linear light-response over 6 orders of magnitude. The pixel size can range from 50 to over 1000 $\mu $m and inkjet fabrication allows tailoring the sensor layout to the needs of the specific application. Single photodiodes, photodiode line-arrays or 2D arrays of photodiodes can be printed onto diverse materials. Besides the dramatically reduced production costs for printed photodiodes, the presented readout architecture allows detection of e.g. chemiluminescence signals with highest sensitivities and minimum crosstalk due to the close proximity of sample and printed photodiode.   

On-the-flow differentiation between cells based on native fluorescence spectroscopy on a chip

Native fluorescence spectroscopy is a promising approach for the detection of pathogens without specific binding or tagging of the analyte. The distinction between different species is possible with (multi-color) UV excitation together with the detection of several spectral bands. We have developed a compact platform that combines a microfluidic quartz channel with chip-size wavelength-selective detection of the fluorescence from particles traversing the channel. The interaction between the UV excitation light and the analyte is enhanced by anti-resonantly guiding the light within fluid. We have recorded the intrinsic fluorescence of single cells (e.g. yeast, e-coli, and BT) passing the detection area. Knowing the particle speed and the physical dimensions of the observation window, we are able to determine particle positions with microscopic ($\sim $10 microns) resolution. A special modulation technique allows us to achieve a high signal to noise ratio even for high particle speeds. Combining our technique with a cell sorting mechanism would allow for on-the-chip characterization and sorting of untagged cells.   

Design of a Molecular Diode: Nanoratchets

We use the concepts hydrodynamic flow in asymmetric structures and apply them to our own asymmetric bump array/diffusion array technology at the nanoscale. Our basic premise is that asymmetrically designed metamaterials at the nanoscale can act, under the influence of externally applied forces, as molecular ratchets which will sort molecules based on their size. At some nano length scale, we believe that the classical concepts of stick boundary conditions break down and a new regime of transport begins. We present computer simulations and experiments which show that at the nanoscale level we can efficiently separate objects the size of proteins.   

Toward on-chip directed evolution of unicellular organisms for efficient hydrogen production

To provide an energy resource alternative to fossil fuels, photosynthetic organisms must increase their energy conversion efficiency. The green algae \textit{C. reinhardtii} stores light energy in hydrogen gas at 0.1\% efficiency, less than the 10\% required to compete with established fuels. This work combines hydrogen sensing in liquid culture with micro habitat patch (MHP) chips for directing hydrogen-producing organisms to evolve improved energy conversion efficiency. A MHP chip contains 87 1 mm $\times$ 1 mm $\times$ 100~$\mu\mathrm{m}$ interconnected chambers. By measuring hydrogen output from different chambers, we will select less productive patches to annihilate. We microfabricated chips from poly(dimethylsiloxane). Color changes in fluorescence micrographs confirm that 254~nm radiation kills algae in MHPs, liberating nutrients and space for exploitation by adjacent populations. We demonstrated colorimetric detection of hydrogen gas production at a rate of $10^{-8}~\mathrm{mol~H_2~mL^{-1}~s^{-1}}$ using tungsten film on sub-mL liquid cultures of \textit{C. reinhardtii} during 2-hrs. of fermentation in darkness.   

Rapid Detection of Microorganisms--State of Art and Future Directions

For the last several decades, nutrient-based culture growth methods have been accepted as the standard for microorganism detection and identification. However, since the discovery of nucleic acids and molecular breakthrough technologies such as restriction enzymes and polymerase chain reactions, the detection and identification of microorganisms have advanced to culture-independent methods that fall under the category of rapid microbial detections. Here, we present an overview of major rapid microbial detection technologies. These technologies will include both amplification and non-amplification based methods for the detection and identification of target microorganisms. The technologies described can be applied to detecting a wide variety of microorganisms, including bacteria, viruses, mycoplasma, and fungi and have the potential sensitivity to detect a single microorganism. Also in this presentation, we will present examples of real-life applications as well as future challenges for the advancement of the field of rapid microbiology.   

Guidance and detection of neuronal cells using Si nanomembranes

"Lab-on-a-chip" microfluidic technology [1] has emerged as a powerful tool for studying biological systems. Unlike standard macro-scale systems used for decades, microfluidics allows the micro-environment of a neuronal cell culture to be finely regulated. The reduction in feature sizes gives control over fluid phenomena such as laminar flow, shear stresses, and velocity profiles. Here we present a new approach to ``lab-on-a-chip'' design for studying neuronal cells, integrating microfluidic systems with silicon nanomembrane-based microelectronics. We show that this technology permits rapid production of microchannels with a large variety of shapes/sizes, thereby allowing the exposure of neuronal cell cultures to multiple environments, both mechanical and chemical, simultaneously. In addition, these microfluidic channels can be easily integrated with silicon nanomembrane based electronics. [1] A.J.Blake, T.M.Pearce, N.S.Rao, S.M.Johnson and J. C. Williams, Lab Chip, 2007, 7, 842.   

Well-Oriented NanoWell Array Metrics for Digital NanoBioChip

Recently many researchers have sought new paradigm for nanobiochip that can be miniaturized and integrated to produce intelligent analysis systems in numerous biotechnology. We have been tried to develop biocompatible materials based nanopatterning, self-assembly array to address challenging problem in nanobioscience. In this time, we describe the nanometrics geometry of a well-oriented nanowell (ONW) array derived from nanofabrication technology which can easily be employed for digital detection with a high S/N ratio, miniaturization, integrated assays and single molecule analysis. We fabricated the self-organized nanopatterning of copolymer as a platform of biomolecular nanoarry using nanolithography. We also present a strong specific antibody-antigen interaction on lipid-membrane modified gold surface using ONW. We believe these findings can be related to various nanobiochip applications. References 1. H.Y. Lee, T. Kawai, K.Y.Suh et al, Advanced Materials, In press (2007). 2. H.Y. Lee, T. Kawai et al, Appl. Phys. Lett. 89, (2006) 113901.   

Magnetically Directed Cell Co-Localization for Cell-Cell Interaction Studies

The ability to create ordered patterns of cells has enabled new approaches to various areas of biological interest, such as tissue engineering, biosensing, and the study of interactions between cells. In this work, we apply forces to cells through binding with magnetic nanowires. The nanowires feature high remanent magnetization, allowing for effective manipulation in low-strength magnetic fields, and when used in conjunction with lithographically patterned magnetic microstructures can precisely position cells into predetermined locations. Chemical functionalization then confines the cells to these substrate areas. We have used this technique to create large numbers of isolated pairs of cells by magnetically guiding them to sites on cobalt and permalloy arrays. Further, the use of two different cell types leads to arrays with heterotypic cell pairs in numbers that exceed those attainable with random cell seeding. Initial experiments applying this magnetic cell trapping technique to perform biological studies of cell-cell interactions will also be described.   

Electromagnetic Sensors of Biological Motors

Biological motors operate on time scales that readily couple to oscillatory electric fields. Modest ac fields applied to cells in an aqueous medium lead to greatly enhanced fields across the plasma membrane or (at kHz frequencies) internal membranes. Membrane complexes thus contribute to both linear and nonlinear responses to sinusoidal fields. For example, activity of motors in mitochondrial and (for chloroplasts) photosynthetic electron transport chains correlate with frequency-dependent second and third harmonics. Our electrode-based biosensors are scalable for micro- and nano-fluidic biochips. At low frequencies (less than 100Hz) we find it advantageous to use SQUIDs, which reduce contact effects and could lead to clinical applications.   

Single-molecule stochastic sensors for proteins using engineered nanopores

We were able to design an unusual temperature-responsive pore-based nanostructure with a single movable elastin-like-polypeptide (ELP) loop. If a voltage bias was applied, the engineered pore exhibited transient current blockades, the nature of which depended on the length and sequence of the inserted ELP. These blockades are associated with the excursions of the ELP loop into the nanopore. At low temperatures, the ELP is fully expanded and blocks the pore completely, but reversibly. At high temperatures, the ELP is dehydrated and structurally collapsed, thus enabling a substantial ionic flow. Acidic binding sites comprised of negatively-charged aspartic acid residues, engineered within the pore lumen, produced dramatic changes in the functional properties of the nanopore, catalyzing the translocation of cationic polypeptides from one side of the membrane to the other. For example, when two electrostatic binding sites were introduced, at the entry and exit of the nanopore, both the rate constants of association and dissociation increased substantially, diminishing the free energy barrier for translocation.   

Imaging Protein-Functionalized Quantum Dot Diffusion and Binding at Surfaces

Understanding single biomolecule and nanoparticle interactions with surfaces at fluid-solid interfaces is a key to improving molecular transport and binding in many biotechnology applications. Biosensor sensitivity, for example, is typically limited by diffusion [2] and non-specific binding to analytical surfaces. We have assembled a Total Internal Reflectance Fluorescence (TIRF) microscopy system with single-photon-sensitive cameras to image diffusion and binding of fluorescently-labeled biomolecules on surfaces under both static and laminar flow conditions. We have acquired movies (57 frames/s) of streptavidin-functionalized CdSe quantum dots (QDs) diffusing, transiently attaching, and permanently immobilizing on repulsive, hydrophilic silica surfaces. From the single-particle trajectories we have extracted diffusion coefficients and transient attachment lifetimes. The binding of protein-functionalized QDs to our nominally repulsive surfaces can be attributed to surface defects, adsorbates, and protein conformational changes. In flow, the QD elevation above the no-slip surface can be approximated, giving a picture of elevated transport between transient attachments and QD departures to and from the surface. [2] Sheehan and Whitman, Nano Lett. 5, 803 (2005).