Edgar Diessel

Glucose Quantification in Dried-down Nanoliter Samples Using Mid-Infrared Attenuated Total Reflection Spectroscopy

The aim of this study was to determine the feasibility of minimally invasive glucose concentration measurement of a body fluid within the physiologically important range below 100 nL with a number of samples such as interstitial fluid, plasma, or whole blood using mid-infrared spectroscopy, but starting with preliminary measurements on samples of simple aqueous glucose solutions. The Fourier transform infrared spectrometer was equipped with a Golden Gate® single reflection diamond attenuated total reflection (ATR) accessory and a room-temperature pyroelectric detector. As the necessary detection limits can be achieved only for dried samples within the spectrometric conditions realized by a commercial instrument, the work focused on the optimization of such ATR measurements. We achieved quantification of samples with volumes as low as 7 nL between 10 and 600 mg/dL. The standard error of prediction (SEP) for the concentration range 10–100 mg/dL is 3.2 mg/dL with full interval data between 1180 and 940 cm−1. The performance of the prediction is given by a coefficient of variation of prediction (CVpred) of 6.2%. When all samples within the whole concentration range are included, the SEP increases to 20.2 mg/dL, and hence the CVpred to 10.6% due to a nonlinear signal dependence on glucose concentration. A detection limit for glucose of 0.7 ng with a signal-to-noise ratio of 10 was obtained.

Novel laser-based technology for cell separation

A UV laser-based separation technique for biological cells is presented. This method refers to the separation of cells that adhere to a special UV absorptive polymer foil. To separate a cell the UV microbeam excises a disc with the attached cell out of the foil. Then, the beam transfers this complex to a separate substrate. This principle allows a rapid separation of adherent cells without the risk of contamination. The operating conditions of the separation scheme were examined. The laser separation scheme was applied to the separation of human embryonic kidney (HEK- 293) cells. The viability tests revealed that these cells survived the procedure. Therefore, the laser separation method is considered a useful tool for separating biological cells.