Alicia Johansson

Polymeric cantilever-based biosensors with integrated readout

The authors present an SU-8 cantilever chip with integrated piezoresistors for detection of surface stress changes due to adsorption of biomolecules on the cantilever surface. Mercaptohexanol is used as a model biomolecule to study molecular interactions with Au-coated SU-8 cantilevers and surface stress changes of about 0.1N∕m are observed. The measurements indicate that the SU-8 surface is inert to mercaptohexanol molecules, which enables the use of a bare SU-8 cantilever as a reference. Moreover, the sensitivity of the cantilevers to pH changes is presented. The results demonstrate that SU-8 cantilevers are a promising alternative to Si-based cantilevers.

Miniature sensor suitable for electronic nose applications

A major research effort has been devoted over the years for the development of chemical sensors for the detection of chemical and explosive vapors. However, the deployment of such chemical sensors will require the use of multiple sensors (probably tens of sensors) in a sensor package to achieve selective detection. In order to keep the overall detector unit small, miniature sensors with sufficient sensitivity of detection will be needed. We report sensitive detection of dimethyl methylphosphonate (DMMP), a stimulant for the nerve agents, using a miniature sensor unit based on piezoresistive microcantilevers. The sensor can detect parts-per-trillion concentrations of DMMP within 10 s exposure times. The small size of the sensor makes it ideally suited for electronic nose applications.

Polymeric mechanical sensors with integrated readout in a microfluidic system

Micrometer sized cantilevers can be used as highly sensitive bio/chemical sensors and are usually fabricated in silicon. Here, we demonstrate the integration of an array of polymeric cantilever sensors into a microfluidic system designed for bio/chemical detection. The cantilever-sensors as well as the microfluidic system are fabricated in the polymer SU-8. Gold strain gauge resistors are incorporated in the cantilevers in order to make them sensitive to changes in surface stress. The cantilever device is fabricated as two separate parts, which are subsequently bonded together using SU-8 as glue. The sensitivity and noise response of the polymeric cantilevers are measured. The measured noise level indicates that the device is suitable for molecular recognition measurements.

SU-8 cantilever chip interconnection

The polymer SU-8 is becoming widely used for all kinds of micromechanical and microfluidic devices, not only as a photoresist but also as the constitutional material of the devices. Many of these polymeric devices need to include a microfluidic system as well as electrical connection from the electrodes on the SU-8 chip to a printed circuit board. Here, we present two different methods of electrically connecting an SU-8 chip, which contains a microfluidic network and free-hanging mechanical parts. The tested electrical interconnection techniques are flip chip bonding using underfill or flip chip bonding using an anisotropic conductive film (ACF). These are both widely used in the Si industry and might also be used for the large scale interconnection of SU-8 chips. The SU-8 chip, to which the interconnections are made, has a microfluidic channel with integrated micrometer-sized cantilevers that can be used for label-free biochemical detection. All the bonding tests are compared with results obtained using similar Si chips. It is found that it is significantly more complicated to interconnect SU-8 than Si cantilever chips primarily due to the softness of SU-8.

Smart plastic functionalization by nanoimprint and injection molding

In this paper, we present a route for making smart functionalized plastic parts by injection molding with sub-micrometer surface structures. The method is based on combining planar processes well known and established within silicon micro and sub-micro fabrication with proven high resolution and high fidelity with truly freeform injection molding inserts. The link between the planar processes and the freeform shaped injection molding inserts is enabled by the use of nanoimprint with flexible molds for the pattern definition combined with unidirectional sputter etching for transferring the pattern. With this approach, we demonstrate the transfer of down to 140 nm wide holes on large areas with good structure fidelity on an injection molding steel insert. The durability of the sub-micrometer structures on the inserts have been investigated by running two production series of 102,000 and 73,000 injection molded parts, respectively, on two different inserts and inspecting the inserts before and after the production series and the molded parts during the production series.

Temperature effects in Au piezoresistors integrated in SU-8 cantilever chips

We present a cantilever-based biosensor chip made for the detection of biochemical molecules. The device is fabricated entirely in the photosensitive polymer SU-8 except for integrated piezoresistors made of Au. The integrated piezoresistors are used to monitor the surface stress changes due to binding of biomolecules on the surface of the cantilever. Here we present the characterization of the chip with respect to temperature changes in the surrounding environment. Furthermore, self-heating of the piezoresistors due to the applied voltage over the resistors is investigated including the temperature increase of the cantilever surfaces. The obtained results indicate that although low voltages of about 0.5–1 V are required to avoid self-heating of the cantilevers, surface stress changes below 1 mN m−1 can still be detected. The results are compared to previously presented results for Si-based cantilevers.