The Fraunhofer Institute for Ceramic Technologies and Systems, Branch Materials Diagnostics (IKTS-MD) covers also some fields of biosensing and nanotechnology, from basic research towards applications. This talk will especially address optically based methods for sensing applications: starting from analysis of the fractal dimension of time-resolved auto-fluorescence spectroscopy, to time-resolved luminescence measurements on upconversion phosphors for electron beam monitoring and last a refractive index sensing with a CCD chip technology based on localized SPR sensing. For all discussed methods the possible application will be discussed on examples of demonstrators in the fields of cancer diagnostics, medical surface sterilization process and biosensing.
We present our recent investigations on time-resolved measurements of alterations in the temporal luminescence decay of upconversion phosphors induced by electron beam treatment. The latter is a promising alternative to low-temperature and dry sterilization of surfaces for sensitive packaging materials. Especially in the food and medical sector regulations concerning sterility are increasingly tightened. For this, a secure proof for electron-beam-assisted sterilization is required. However, no non-destructive and in situ method exists up to now. Our approach to provide a secure proof of sterilization is to place a suitable marker material based on rare-earth-doped phosphors inside or on top of the packaging material of the respective product. Upon electron irradiation the marker material changes its luminescent properties as a function of applied energy dose. We verified the energy dependence by means of time-resolved measurements of the luminescent decay of different upconversion materials. In our experimental realization short laser pulses in the near-infrared range excite the marker material. The emitted light is spectrally resolved in a monochromator, collected via a silicon photo diode, and analyzed with an oscilloscope. As the main results we observe a reduction of luminescence lifetime due to electron beam treatment dependent on the emission wavelength. Hence, the electron beam induces changes in the particles' up- and down-conversion properties from which the applied energy dose can be derived.
Driven by a demand for integrated optical sensors in structural health and environmental monitoring we present the application of plasmonic gradient structures as sensor substrate. Therefore, nanoparticle arrays of gold are fabricated by interference lithography, which exhibit localized surface plasmons (LSPs). The plasmonic properties of such nanoparticles can be tuned by altering their size. In our approach, an additional photochemical growth by exposure to HAuCl4 and light is used to manufacture gradients of nanoparticle sizes within the array. These gradients in turn induce different spectral responses depending on the illuminated region of the array gradient. To enable sensing applications, such plasmonic gradient structures are placed as a filter in front of a photodetector to allow detection of transmitted optical signals from different locations of the array. Different applications can be envisioned in this configuration: On the one hand, sensing of wavelength shifts of the illuminating light source can be enabled by comparing the photocurrents generated in adjacent sensor elements. Additionally the application of refractive index measurements is demonstrated with the same detector configuration. The change in extinction of the illuminating light at different wavelengths can be used to obtain an intensity shift at the detector elements. This shift correlates to the change of the spectral resonance conditions in the array gradient upon change of refractive index.