A Flexible Approach to the Fabrication of Chemical Gradients

Abstract

In this Communication, we demonstrate a novel approach to the fabrication of chemical gradients on the basis of self-assembled monolayers (SAMs). [1][2][3] The key idea of the approach is a tuning of the extent and rate of the exchange reaction between the primary SAM and a potential molecular substituent by electron or X-ray irradiation with a variable dose. Note that chemical gradients are extensively used for numerous practical applications, such as the investigation of biomolecular interactions, cell-mobility studies, diagnostics, nanotribology, microfluidics, et cetera. [4,5] A number of methods are available for the preparation of chemical gradients on various substrates. Most of these methods involve the use of alkanethiolate (AT) SAMs, as, for example, a cross-diffusion of two different AT solutions through a polysaccharide matrix, application of an electrochemical potential to the substrate during adsorption, the use of microfluidic devices, scanning-tunneling-microscopy-based replacement lithography, a gradual dipping of the substrate into solution of target molecules by computerized linear-motion drive, and using a masstransfer limited microcontact printing . [4][5][6][7][8][9][10][11] However, the chemical gradients prepared by using the above methods are mostly limited in their size, given by the dimensions of the device or equipment used (see above), and form, which, in most cases, is just a narrow rectangular stripe. In addition, the procedures needed for their fabrication are quite complex. Our aim was to develop a simple and flexible method to prepare chemical gradients of a variable form and on different length scales. Such method is a tuning of the exchange reaction between the primary SAM and a potential molecular substituent by electron-irradiation. We found that the extent and rate of these reactions, which at normal conditions have a limited extent and are very slow (days), [12][13][14] can be considerably influenced by electron-irradiation. Within a test experiment, we irradiated a SAM of nonsubstituted ATs (dodecanethiol, CH 3 (CH 2 ) 11 SH: DT) on gold by low-energy electrons with a variable dose and subsequently immersed the irradiated film into the solution of an x-substituted AT (mercaptoundecanoic acid, COOH(CH 2 ) 10 SH: MUDA) in ethanol (EtOH) for a variable time to perform the exchange reaction. The effect of irradiation and extent of the exchange reaction were monitored by the measurement of the advancing and receding water contact angles (h a and h r , respectively), which are very sensitive to the chemical composition of the SAMambient interface, including the portions of the CH 3 -(DT) and COOH-(MUDA) tail groups after the exchange reaction.As shown in inset of Figure 1, in the case of irradiation only, h a and h r decreased exponentially with increasing irradiation dose and exhibited a saturation behavior at high doses (ca. 7 mC cm -2 ). Thus, a contact-angle variation, which one can achieve by electron irradiation only, is quite small-about ) and subsequently immersed into ...

Herstellung von Proteinmustern durch Schreiben in proteinabweisende Matrizen

“…Die EBL ermöglicht die Erstellung von Mustern im cmbis nm-Bereich. [11,20,23] Hinsichtlich der Form der Muster gibt keine Einschränkungen; auch komplexe Gradientenmuster für Assays [20] sind herstellbar. Solche Muster können zur Simulation natürlicher biologischer Grenzflächen dienen, denn diese Grenzflächen weisen oft Gradienten auf, um gerichtete biologische Informationen zu codieren und zu vermitteln.…”

A New Approach for the Fabrication of Strongly Heterogeneous Mixed Self‐Assembled Monolayers

“…The applicability of this approach for mixed SAMs consisting of similar molecules, for example, alkanethiols (ATs) with different w-substitutions, has been demonstrated. [5,6] Herein, we show that IPER is quite versatile; it is applicable to the fabrication of strongly heterogeneous mixed SAMs consisting of molecules not only with different tail groups (substituents), but with different molecular chains as well. In particular, monomolecular templates, which contain device molecules incorporated into a passive aliphatic matrix, could be easily fabricated by IPER.…”

“…Recently, we developed a new approach for the fabrication of mixed SAMs of desired composition, the irradiation-promoted exchange reaction (IPER). [5,6] This method combines exchange reactions between a target SAM and potential molecular substituents with preliminary electron irradiation, which promotes the exchange process. The applicability of this approach for mixed SAMs consisting of similar molecules, for example, alkanethiols (ATs) with different w-substitutions, has been demonstrated.…”

Herstellung mikroskaliger Proteinresistenzgradienten durch Elektronenstrahl‐Lithographie

“…Diese Methode beruht auf der strahlungsinduzierten Austauschreaktion (irradiation-promoted exchange reaction, IPER) an selbstorganisierenden Monoschichten. [17][18][19] Wie wir und andere zuvor demonstriert haben, werden Thiolat-basierte SAMs auf Gold durch Röntgenstrahlung, [20,21] UVLicht [22,23] oder Elektronenbeschuss [18,[24][25][26] …”