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While self-assembly is relatively well-known and widely used to form hierarchical structures and thin film coatings, controlled assembly is less known and utilized. Our prior work has demonstrated the concept of controlled assembly of macromolecules such as star polymers (MW ~383 kDa, hydrodynamic radius R ~ 13.8 nm) in droplets. The present work extends this concept to smaller molecules, in this case, poly(ethylene glycol) bis-tetrazine (PEG-bisTz, Mn 8.1 kDa, R ~1.5 nm). The key to control molecular assembly is to first deliver ultrasmall volumes (sub-fL) of solution containing PEG-bisTz to a substrate. The solvent evaporates rapidly due to the minute volume, thus forcing the assembly of solute, whose overall size and dimension are dictated by the initial liquid geometry and size. Using pre-patterned surfaces, this work revealed that the initial liquid shape can be further tuned, and as such we could control the final assembly of solute such as PEG-bisTz molecules. The degree of control is demonstrated by varying the micropatterns and delivery conditions. This work demonstrates the validity of controlled assembly for PEG-bisTz, and as such enables 3D nanoprinting of functional materials. The technology has promising applications in nanophotonics, nanoelectronics, nanocomposite materials, and tissue engineering. 

Antimicrobial and antiviral materials have attracted significant interest in recent years due to increasing occurrences of nosocomial infections and pathogenic microbial contamination. One method to address this is the combination of photoactive compounds that can produce reactive oxygen species (ROS), such as hydrogen peroxide and hydroxyl radicals to disinfect microbes, with carrier materials that meet the application requirements. Using anthraquinone (AQ) and cellulose nanocrystals (CNCs) as the photoactive and carrier components, respectively, this work demonstrated the first covalent incorporation of AQ onto CNCs. The morphology and the photoactive properties were investigated, revealing the structural integrity of the CNCs and the high degree of photoactivity of the AQ-CNC materials upon UVA exposure. The AQ-CNCs also exhibited an unexpected persistent generation of ROS under darkness, which adds advantages for antimicrobial applications.