Ultrasound supported Infrared Sensors

Ultrasound Supported MIR Fiber Optic Probes for In-Line Bioprocess Monitoring is a proposal presented by the Institutes Chemical Technology and Analytics and General Physics at the Vienna University of Technology to make successful chemical measurement principles based on FTIR spectroskopy available especially in the regime of (bio)process technology. Measurement cells and probes shall be developed in which suspended matter such as biological cells can be moved almost at will by forces exerted on particles in standing ultrasonic wave fields. To accomplish this the measurement cells and probes will be equipped with piezo-elements irradiating the liquid to be measured with ultrasonic waves of typically 2 MHz. At the opposite wall this wave gets reflected and by superimposition with the incident wave the mentioned ultrasonic standing wave is built. Both the chemical compounds of the host liquid and substances which are enriched or consumed during the process in the microorganism (biocatalyst) are of interest in industrial applications. In addition to bioprocess also crystallization processes will be studied. During the FTIR measurement it is planned to push the microorganisms by ultrasonic means onto the sensorelement and to avoid contamination of it, to lift them immidiately after the spectroscopic measurement. The combination of infrared spectroscpy with a possibility to control the spatial residue of the biological cells could be capable to assess the chemical composition of the host liquid as well as chemical contents of the biomass. This is true for on-line and in-line measurement respectively and for stable repititions over longer time-periods.

The motivation for this project is the need for novel, powerful sensors for the biotechnology industry, particularly in relation to the collection of the actual state of a biochemical process. Of special interest in regard to product safety, as well as to productivity, is not only the chemical composition of the cells, but also which substances are enriched in the growth medium. In this context, infrared spectroscopy is a promising measurement method as it delivers a vast amount of information about substances particularly relevant in fermentation processes directly and in a destruction free manner. The project target, to translate the first experience with the combination of ultrasonic particle manipulation and infrared spectroscopy towards industrial applicability has been achieved. As a result, we present the prototype of a mid-IR sensor probe capable of assessing the individual infrared spectra of a carrier liquid and, therein suspended, i.e. freely distributed particles within a reaction vessel. This is possible because the spatial distribution of the particles can be controlled by means of an ultrasonic standing wave. In particular, the particles can either be kept away from the infrared sensor - then only the liquid is measured - or can be pushed towards the surface sensitive optical cell - then the measured spectrum is determined to a large extent by composition of the particles. The mid-IR sensor probe is coupled via optical fibres to the spectrometer which result in great flexibility in terms of the spatial arrangement of the components, without affecting the quality of the measurement. The prototype meets biotechnological standards in terms of materials and dimensions, to enable the mentioned application of the observation of cell cultures in a bioreactor. Biochemical processes in cells can change within a few minutes. Therefore, measurement times need to be significantly lower than this to be able to facilitate control of a process. Experiments with suspended yeast cells were successful, spectra could be recorded within three minutes or less. Also of particular importance for the envisaged field of exploitation are also robustness and long-term stability. In this context, the prototype delivered satisfying results: the formation of bio-film on the mid-IR sensor probe, which had proved to be a limiting factor in the preliminary tests, was only observed to a small extent, possibly due to the fact that a sound field was always present. In the rare cases where contaminations were present, they could be removed by the application of an appropriate ultrasound field. The feasibility of the concept was demonstrated beforehand in an experimental setup, a dummy reactor, for different suspensions. Resin particles, in which chemical reactions can take place were also present in such suspensions and it was possible to observe the progress of these reactions by infrared spectroscopy.