Nanobioanalytics via on-chip infrared Mach-Zehnder interferometry

In the field of biofunctional structures and surfaces, nanostructured systems are of increasing importance. The proposed research approach uniquely combines biomolecular recognition, nanostructured surfaces, and novel on-chip mid-infrared sensor concepts.

The main aim is to facilitate trace analysis at the nano-scale concerning structural dimensions, molecular recognition interface, required reagents, determinable analyte concentrations, and fundamental understanding of molecular interaction processes. A particularly sensitive device configuration is a Mach-Zehnder interferometer, which has already been successfully established in the visible spectral range. Using mid-infrared radiation (MIR; 3 -15 μm), some significant benefits arise, which are utilized for the first time in the framework of this project: (i) At MIR wavelengths, tolerances within the nanostructuring process increase; (ii) evanescent fields in the MIR provide higher penetration depths into the medium adjacent to the waveguide leading to an increase in probed analytical volume providing for the determination of biomolecules at pico- to femtomolar levels; (iii) spectral ‘fingerprints’ of molecules in the MIR provide inherently selective and distinctive molecular identification; (iv) larger biomolecules up to entire organisms (e.g. bacteria) may take advantage of signal-enhancing nano-structured surfaces (surface enhanced infrared absorption; SEIRA).

Finally, gradients with respect to surface properties such as the type of molecular recognition or the surface (nano)architecture may be generated via spatially resolved surface modifications. Using appropriate multivariate data evaluation schemes along with intelligently designed arrays further enhances the accessible data space. Initial application scenarios target the identification of endocrine-active molecular contaminants, and the selective detection of strains of bacteria.

[1] M. Sieger, F. Balluff, X. Wang, S.-S. Kim, L. Leidner, G. Gauglitz, B. Mizaikoff: On-Chip Integrated Mid-Infrared GaAs/AlGaAs Mach-Zehnder Interferometer, Analytical Chemistry 85, 3050-3052 (2013)
[2] L. Leidner, M. Ewald, M. Sieger, B. Mizaikoff, G.Gauglitz: Migrating the Mach-Zehnder Chemical and Bio-Sensor to the Mid-Infrared Region, Proceedings SPIE Photonics Europe vol. 8774, 87740S-1-15 (2013)