Microcontact printing in bioanalysis: where are we and where shall we be?

Since the inception of microcontact printing (μCP) in early 1990s by Whitesides and coworkers [1,2] to control protein adsorption on cell culture surfaces, it has nowadays covered the widest picture and area of protein analysis research field. Basically, μCP is the transferring of the ‘ink’ pattern from the surface of a relief elastomeric stamp to a substrate through contact. The stamp is usually made of polydimethylsiloxane (PDMS) or its structured forms due to its low Young’s modulus and high hydrophobicity (a contact angle of ∼110° with water), while the ‘ink’ is usually made of molecules, such as alkanethiols or proteins/enzymes type biomolecules. Complete transfer of these biomolecules from the stamp to a substrate has been observed (almost 100% efficiency) just after a few seconds of contact, without any loss of biological activity. In this way, μCP has simply fabricated functional patterns of proteins up to a scale where less than 0.1k molecules were placed in the sharp spots of the surface. Additionally, it has been suitable for fabrication of various biomolecules onto both the hydrophobic and hydrophilic substrates, such as various monolayers on gold, glass, poly(methylmethacrylate), silicon, silicon oxide or polystyrene. The reason behind the high resolution and contrast of the patterns fabricated by μCP of biomolecules, documented by atomic force microscopy, is the nondiffused behavior of adsorbed biomolecules’ surfaces and the mechanical stability of the patterns of the stamp [3]. The success of μCP of biomolecules in bioanalysis lies in how much we can reduce the time between drying of ‘inked’ stamp and printing of the biomolecules because even 1 min delay may decrease the success of transfer substantially.