Comparative assembly of colloidal quantum dots on surface templates patterned by plasma lithography

Plasma lithography is a template-guided self-assembly nanomanufacturing strategy for creating functional engineering devices using nanoscale and molecular building blocks. To elucidate the plasma lithography manufacturing process, the comparative binding of colloidal quantum dots on plasma patterned surface templates is investigated. In particular, fluorescence microscopy and scanning electron microscopy were performed to characterize the pH-dependent assembly of quantum dots at equilibrium conditions. Remarkably, the amino-modified quantum dots adhere favorably to plasma treated, hydrophilic areas at low pH and to untreated, hydrophobic areas at high pH. The crossover pH for this transition occurs at approximately pH 9. Similar transitions can also be observed in other molecules, including bovine serum albumin, fluorescein isothiocyanate, and poly-L-lysine. Examining the crossover pH values for different building blocks reveals that the assembly process is a result of the competition between electrostatic and van der Waals interactions. The ‘‘image reversal’’ by adjusting the pH provides a simple and effective approach for manipulating the amount and location of nanoscale building blocks assembled on plasma lithography patterned surface templates.