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(a) Microfabrication scheme for MESDD: (i) photoexposure (ii) photoresist development, (iii) based reactive ion etching of hard mask, (iv) Bosch process for deep silicon etch, (v) hydrofluoric acid wet etch for removal of hard mask and back film; (b) Mask design for MESDD.
(a) Microhydrogel features of different sizes; (b) SEM image of hydrogel features.
(a) MESDD mounted in the operational configuration; (b) Circuit diagram of the electrospray protein dispensing unit.
Multiple biomolecules electrosprayed through alternate and parallel source tips of MESDD on a single substrate. (a) Biotin on hydrogel features; (b) Protein A on hydrogel features; (c) Protein A on hydrogel features. Biotin and Protein A were detected by a solution of streptavidin—Alexa 594 and rabbit antimouse IgG—Alexa 488 conjugates, respectively.
Fluorescently (Alexa 488) labeled rabbit anti-mouse IgG bound non-specifically to the silicon oxide background but not to the hydrogel. (a) Protein A did not bind non-specifically to hydrogel features that were not functionalized with aldehyde groups. (b) When Protein A was dispensed on the hydrogel features with aldehyde functionalization, the Protein A molecules bound through stable amide bonds as a result of Schiff base chemistry followed by reductive amination.
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