Selected Publications

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By Robert Davis (et al.)
Abstract: An optical detector has been fabricated that is specific for targeted bacterial cells, by stamping an antibody grating pattern on a silicon surface. The antibody grating alone produces insignificant optical diffraction, but upon immunocapture of cells, the optical phase change produces a diffraction pattern. This technique eliminates much of the surface modifications and the secondary immunochemical or enzyme-linked steps that are common in immunoassays. Microcontact printing provides an alternative to previously reported photolithographic-mediated antibody patterning processes and uses a photolithographic process simply to produce the elastomeric stamp. We have stamped antibodies directly onto clean native oxide silicon substrates with no other chemical surface treatments. Direct binding of the antibodies to the silicon occurs in a way that still allows them to function and selectively bind antigen. The performance of the sensor was evaluated by capturing Escherichia coli O157:H7 cells on the antibody-stamped lines and measuring the intensity of the first-order diffraction beam resulting from the attachment of cells. The diffraction intensity increases in proportion to the cell density bound on the surface.
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By R. C. Davis (et al.)
Abstract: Microcontact printing (μCP) is a new method of molecularly patterning surfaces on a micrometer scale. In this paper, we present the extension of microcontact printing to producing patterned layers of proteins on solid substrates. μCP avoids the use of strong acids and bases necessary in photolithographic patterning, allowing its use for patterning of proteins and other biological layers. We also describe the methods of thin stamp microcontact printing that allow printing of isolated features previously unattainable by microcontact printing. A solution of polylysine in borate-buffered saline was printed onto a glass coverslip, yielding micrometer scale features over an area of 4 cm2.
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By R. C. Davis (et al.)
Abstract: Near-field photodetection optical microscopy (NPOM) is a fundamentally new approach to near-field optical microscopy. This scanning probe technique uses a nanometer-scale photodiode detector which absorbs optical power directly as it is scanned in the near held of an illuminated sample surface. We have applied NPOM to measure the visible absorption spectrum of. dye molecules embedded in a single 300 nm polystyrene sphere. The near-held absorption spectrum is obtained by measuring the NPOM probe photocurrent while the wavelength of the illumination pump beam is scanned from 450 to 800 nm. Peaks-are identified at 567, 608, and 657 nn in the near-field spectrum of the single-dyed polystyrene sphere. These peak. positions are in good agreement with far-field absorption measurements performed on many dyed polystyrene spheres. (C) 1996 American Institute of Physics.
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By R. C. Davis (et al.)
Abstract: Near-field photodetection optical microscopy (NPOM) is a fundamentally new approach to near-field optical microscopy. This scanning-probe technique uses a nanometer-scale photodiode detector as a near-field optical probe. We have fabricated probes for NPOM that have optically sensitive areas as small as 100 nm x 100 nm. These new NPOM probes have been employed to image light transmitted through holes in an aluminum film. Near-surface optical interference is observed near defects and edges of the aluminum film. The optical edge response is shown to be of the order of 100 nm. (C) 1996 Optical Society of America
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By R. C. Davis (et al.)
Abstract: A submicrometer photodiode probe with a sub‐50 nanometer tip radius has been developed for optical surface characterization on a nanometer scale. The nanoprobe is built to detect subwavelength optical intensity variations in the near field of an illuminated surface. The probe consists of an Al–Si Schottky diode constructed near the end of a micromachined pyramidal silicon tip. The process for batch fabrication of the nanoprobes is described. Electrical and optical characterization measurements of the nanoprobe are presented. The diode has a submicrometer optically sensitive area with a 150 fW sensitivity.