Sensors and Actuators B 161 (2012) 1135–1138 Contents lists available at SciVerse ScienceDirect Sensors and Actuators B: Chemical journa l h o mepage: www.elsevier.com/locate/snb Short communication Biological functionalization of massively parallel arrays of nanocantilevers using microcontact printing S. Guillon, S. Salomon, F. Seichepine, D. Dezest, F. Mathieu, A. Bouchier, L. Mazenq, C. Thibault, C. Vieu, T. Leïchlé ∗ , L. Nicu LAAS-CNRS, Université de Toulouse, 7 Avenue du Colonel Roche, Toulouse, France a r t i c l e i n f o Article history: Received 23 August 2011 Received in revised form 30 October 2011 Accepted 31 October 2011 Available online 12 November 2011 Keywords: Nanoelectromechanical systems Nanocantilevers Biofunctionalization Biosensing Microcontact printing a b s t r a c t In this paper, we present a back-end method for biofunctionalizing a large-scale array of nanocantilevers. Our method relies on the use of a modified microcontact printing process where molecules are delivered onto the fragile structures from the grooves of the stamp while its base sits on the chip, thus provid- ing mechanical stability. We have used this method to print antibodies onto fabricated chips containing up to 10 5 nanostructures/cm 2 and the presence of antibodies was validated by fluorescent microscopy. Furthermore, measurement of the nanocantilever resonant frequency shifts provoked by a mean added mass of ∼140 fg/cantilever demonstrated that the cantilevers retained their mechanical integrity. Hence, the method presented here aims at providing an answer to the biofunctionalization of freestanding nanostructures for their use as biosensors. © 2011 Elsevier B.V. All rights reserved. 1. Introduction One of the most promising applications of nanoelectrome- chanical systems (NEMS) is foreseen in the field of ultrasensitive mechanical biosensing [1–4]. For this to become reality, a major challenge is the functionalization of closely packed nanostructures [5] in such a way that biological receptors are precisely located solely onto the active biosensing areas, thus preventing the waste of biological matter and enabling the subsequent biological blocking of the passive parts of the chip. So far, the issue of the freestand- ing nanostructures functionalization has been seldom addressed because of the absence of generic tools or techniques allowing large-scale molecular delivery at the nanoscale. One way to circum- vent this difficulty is to perform the functionalization step before completing the fabrication of the NEMS. This strategy can typi- cally be used in a top-down NEMS fabrication process by protecting the biological layer during the subsequent NEMS fabrication steps, that consists in placing the functionalized nanostructures at spe- cific locations on a substrate and releasing them [6,7]. The main limitation of this strategy is the tradeoff between the choice of the post-functionalization processing steps and the resilience of the chosen biological receptors to such technological constraints, which for most of them are biologically unfriendly. ∗ Corresponding author. Tel.: +33 5 6133 7993; fax: +33 5 6133 6208. E-mail address: tleichle@laas.fr (T. Leïchlé). In this paper, we report on the use of a corrugated polymer stamps technique [8] for the post-process biological function- alization of large arrays of freestanding nanocantilevers while preserving their mechanical integrity. Thermally oxidized silicon nanocantilevers are fabricated and then functionalized with fluo- rescently labeled immunoglobulin (IgG) using a specially designed microcontact printing (CP) stamp. The presence of IgG onto the desired locations is validated both by fluorescent microscopy and measurement of nanocantilevers quality factor and resonant fre- quency shifts provoked by the corresponding added mass. 2. Materials and methods Arrays of nanocantilevers were fabricated using silicon-on- insulator (SOI) substrates and a UV stepper photo repeater. The use of SOI wafers (340 nm P-type Si/1 m SiO 2 /525 m Si from Soitec, France) ensured the production of cantilevers with a con- trollable thickness (since fabricated in the top silicon layer) and the release of the cantilevers in aqueous solution without structure collapsing and sticking issues (by using the 1 m-thick buried SiO 2 as a sacrificial layer). A UV stepper photo repeater (I Line CANON FPA 3000 i4/i5, N.A. 0.63) was used to pattern the shape of the nanocantilevers via a 600 nm thick positive photoresist layer (ECI). After developing the photoresist, the top silicon layer was verti- cally etched by reactive ion etching (RIE, Alcatel AMS4200) until the intermediate SiO 2 layer appeared. The sacrificial SiO 2 was then etched by dipping the entire wafer in a buffered hydrofluoric acid 0925-4005/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2011.10.084