Compared to the well-equipped arsenal of surface modification methods for flat surfaces, techniques that are applicable to curved, colloidal surfaces are still in their infancies. This technological gap exists, because spin-coating techniques used in traditional photolithographic processes are not applicable to curved surfaces of spherical objects. To generate microstructured colloidal particles we pursued a route that uses (i) Coating of the colloids with a photodefinable polymer, poly[4-benzoyl-p-xylylene- co-p-xylylene], via chemical vapor deposition polymerization; and (ii) spatially controlled surface reaction of the photoreactive coatings using a highly parallel projection lithographic patterning step. The rationale for selecting poly[4-benzoyl-p- xylylene-co-p-xylylene] as base coating was that this CVD-based reactive polymer coating forms homogeneous interlayers on curved surfaces while providing photo-reactive chemical groups for further surface modification (1-2). By replacing spin-coated photoresist with a vapor-deposited, photodefinable polymer coating, we were able to fabricate microstructured colloids with a wide range of surface patterns - including asymmetric and chiral surface structures - that so far were typically reserved for flat substrates. This high-throughput method can yield surface-structured colloidal particles at a rate of about 107 to 108 particles per operator per 1 day. In addition to the controlled fabrication of a series of identical colloids with multiple, biologically distinct binding patches, parallel fabrication of multiple types of distinct colloids is of specific interest to a range of different applications, such as biosensors . High pattern fidelity and excellent contrast are observed suggesting efficient conversion of the photoactive groups in the exposed areas only. In addition, a range of different patterns has been created demonstrating that patterns can be selected with high flexibility. This is in clear contrast to the currently existing methods for patterning of colloids, which are all subject to constrains imposed by the patterning technique itself. Finally, high-resolution patterns can be created on spheres with different radii. Equipped with spatially defined binding pockets, microstructured colloids can engage in programmable interactions, which can lead to directed self-assembly. The ability to create a wide range of colloids with both, simple and complex surface patterns may contribute to the genesis of previously unknown colloidal structures and may have important technological implications in a range of different applications including photonic and phononic materials or chemical sensors.

(1) Suh, K. Y., Langer, R. & Lahann, J. (2004) Advanced Materials 16, 1401-1405. (2) Chen, H.-Y. & Lahann, J. (2005) Analytical Chemistry 77, 6909-6914.

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