Maria Tenje

Drift study of SU8 cantilevers in liquid and gaseous environments

We present a study of the drift, in terms of cantilever deflections without probe/target interactions, of polymeric SU8 cantilevers. The drift is measured in PBS buffer (pH 7.4) and under vacuum (1mbar) conditions. We see that the cantilevers display a large drift in both environments. We believe this is because the polymer matrix absorbs liquid in one situation whereas it is being degassed in the other. An inhomogeneous expansion/contraction of the cantilever is seen because one surface of the cantilever may still have remains of the release layer from the fabrication. To further study the effect, we coat the cantilevers with a hydrophobic coating, perfluorodecyltrichlorosilane (FDTS). Fully encapsulating the SU8 cantilever greatly reduces the drift in liquid whereas a less significant change is seen in vacuum.

Monolithic single-mode SU-8 waveguides for integrated optics

We present the fabrication and characterization of single mode waveguides fabricated monolithically in SU-8. SU-8 is a negative resist, which can be structured by UV lithography followed by a baking step to induce cross-linking. As a material platform, SU-8 is well suited for systems used for biochemical analysis, as it possesses very high chemical resistance and good mechanical stability. Here we show that single mode embedded waveguides can be fabricated using SU-8 as core material and the modified SU-8, mr-L 6050XP, as cladding material. The refractive index difference between the two materials of the final waveguides is around 0.004. All waveguides fabricated in this work have a height of 4.5 μm and their widths are 3, 5 or 10 μm. We have characterized the losses of these waveguides with the cut-back method both at 635 nm and 1535 nm. We have furthermore studied changes in the refractive index of the material with changes in the processing of the SU-8 material. Finally, absorption measurements in the visible spectral range and mode profile analysis have also been performed. Because of the low optical absorption at wavelengths above 700 nm in combination with the fast, simple and cost-efficient fabrication process, we show that SU-8 is well suited as structuring material for waveguides for integrated optics.

An electrochemical-cantilever platform for hybrid sensing applications

This work presents a fully-functional, microfabricated electrochemical-cantilever hybrid platform with flow control. A new cantilever chip format is designed, fabricated, and mounted in a custom polymer flow cell. Issues such as leakage and optical/electrical access are addressed, and combined mechanical and electrochemical performance is investigated. Lastly, a cantilever is “defunctionalized” in situ to create a reference cantilever for differential measurements in detection of Cu2+ ions at concentrations of 10 µM and 100 nM.

An electrochemical-cantilever hybrid sensor for metal ions

In this work we have demonstrated a peptide-functionalized cantilever sensor with integrated electrochemical capabilities. Silicon nitride cantilevers with gold electrodes are functionalized with the chelating peptide Cys-Gly-Gly-His (CGGH) to capture Cu2+ ions from solution. Upon binding the copper ion the peptide folds, creating steric hindrance and causing compressive stress in the monolayer, deflecting the cantilever downward. Ethylenediaminetetraacetic acid (EDTA) was used to remove the copper ions from the peptide, regenerating the layer. A Cysteine monolayer deflected the cantilever upward with Cu2+ ions, indicating tensile stress in the layer, suggesting a different coordination scheme than the CGGH peptide layer.