Microfabricated tools for manipulation of small samples

Abstract

Microfabricated tools useful for manipulating small, delicate samples are formed from thin plastic films. The films have a small thickness (preferably 5 to 50 micrometers and typically 10 micrometers) and small lateral dimensions (preferably 2 mm or less and typically 0.1 to 1 mm) so that they are reasonably flexible, but are preferably curved by being wrapped around a cylindrical or flat post to give them some rigidity. The softness and thinness of the plastic reduce risk of sample damage during incidental contact with the tool. Its thinness makes it optically and X-ray transparent, so that the samples can be clearly visualized during manipulations and so that the tools can be used to collect X-ray data from samples. As an option, an X-ray sensitive phosphor is incorporated in the film at low concentration. This allows the X-ray beam to be visually located on the mount or tool. The plastic can also be treated to obtain a desired hydrophobicity or hydrophilicity, mechanically embossed or abraded, or coated with films (for example, of polyethylene glycol via pegylation procedures or of PDMS) that promote or inhibit sample adhesion.

Description

CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application claims the benefit under 35 U.S.C. 119(e) of U.S. application Ser. No. 60 / 762,118, filed Jan. 26, 2006, which is herby incorporated by reference.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates in general to a variety of microfabricated tools that can be employed for manipulating and measuring small (1 mm to 1 micrometer), delicate samples. These samples include macromolecular crystals, small molecule crystals, cells, tissues and cellular organelles. Examples of operations to be performed include measuring sample dimensions and sample temperature, retrieving samples from a solution or growth medium and transferring them from one solution to another, removing samples that are adhered to substrate surfaces, delicately but rigidly gripping and holding the samples, and mounting samples for optical or X-ray examination. [0004] 2. Description of the Background Art [0005] Sample...

AI Technical Summary

Benefits of technology

[0008] With specific reference to the various embodiments of the present invention, a first embodiment includes tools for sample measurements in which the optical transparency of the polymer film enables the sample being measured to be visualized through the film. The increased rigidity provided by the slight film curvature induced by wrapping the base of the film around the post allows easier measurements in, e.g., viscous liquids. The thinness of the film also allows it to be bent flat if it is pushed down against a flat surface. The softness and flexibility of the tool allow it to be used to push or dislodge from a substrate many soft, delicate, fragile samples like protein crystals, cells, tissues, etc. without damaging them. This softness and flexibility also minimizes the chance of sample damage during incidental contact with the tool. The measuring tool can be placed right next to the sample being measured, for example, within the solution in which it resides, and with its orientation matching the orientation of the sample dimension to be measured. Consequently, the tool can provide accurate measurements under a much wider variety of sample conditions than a microscope reticle, for example, which accurately measures dimensions only of surfaces perpendicular to the optical axis and in the same medium as the outer surface of the lens.

[0018] Another embodiment of the invention comprises tools for sample temperature measurement. In many applications one wants to know the sample's temperature. For example, in cryocrystallography, the sample is placed in a cold gas (nitrogen or helium) stream to keep it cold during X-ray data collection. The sample's temperature varies with how the gas flows are adjusted, with ambient conditions, and with the sample's position in the gas stream. In this embodiment, the sample holders disclosed in the ‘315 application’ as well as any of the tools described here can be formed with an integral thermocouple. The tool is again microfabricated from a polymer like polyimide or mylar. Two different metal layers are patterned and deposited, so that they overlap at the tip, forming a thermocouple junction. The metals may be deposited onto the polymer film by, e.g., sputtering (to reduce heating of the film). Conventional photoresist patterning and wet or dry etching can be used to remove metal to form the final pattern. The extremely small size (10-20 micrometers) of the thermocouple junction, the small cross-sectional area and therefore low thermal conductance of its leads, and the proximity of the junction to sample ensure accurate temperature measurements. The extremely low thermal mass of the junction plus sample holder and the thin film design also ensures a very rapid response in time to changes in temperature. In an alternative design, a thermistor is employed instead of a thermocouple for the temperature sensor. The thermistor can be fabricated by depositing and patterning on the polyimide an amorphous silicon layer. Provided that its lateral dimensions are small, the thermistor can be made quite thin and thus have a small thermal mass, without risk of breakage due to bending.

Problems solved by technology

Samples such as protein and virus crystals, cells and tissues are extremely fragile and can easily be damaged by incidental contact with hard (e.g., metal) objects.

They often adhere to glass slides or glass, plastic or metal containers in which they are grown and are difficult to remove.

However, because of their hardness and stiffness and the inevitable imprecision and vibrations associated with manual movement, they often damage or destroy the samples of interest even with only incidental contact, and they are too large for the smaller samples (100 micrometers or smaller) of increasing interest in, for example, protein crystallography.

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