Silicon Chemical Vapor Infiltration

CdSe nanocrystals in solution and films can enter a metastable state in which the highly luminescent nanocrystals become dark. This change, which we attribute to a surface transformation, can be caused by heating or by changing the environment of the nanocrystals at room temperature. The metastable transformation is reversed upon illumination of above-band-gap light, at which point the nanocrystals are again highly luminescent.

We describe a method for producing high-resolution chemical patterns on surfaces to control the attachment and growth of cultured neurons. Microcontact printing has been extended to allow the printing of μm-scale protein lines aligned to an underlying pattern of planar microelectrodes. Poly-L-lysine (PL) lines have been printed on the electrode array for electrical studies on cultured neural networks. Rat hippocampal neurons showed degree of attachment selectivity to the PL and produced neurites that faithfully grew onto the electrode recording sites.

We describe methods of fine scale chemical and topographical patterning of silicon substrates and the selected attachment and growth of central nervous system cells in culture. We have used lithography and microcontact printing to pattern surfaces with self-assembled monolayers and proteins. Chemical patterns can be created that localize and guide the growth of cells on the surfaces. Self-assembled surface texturing with structures at the tens of nanometers scale and lithographic based methods at the micrometer scale have been used to produce a variety of surface topographical features. These experiments suggest that surface texture at the scale of tens of nanometers to micrometers can influence the attachment of these cells to a surface and can be used as a mechanism of isolating cells to a particular area on a silicon substrate.

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.

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.

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.