(121c) Fluorescence-Labelled Polymer Beads for Chemical Monitoring of Nanoliter Fluid Segments

Nanoliter fluid segments are under investigation for combinatorial chemical synthesis [1,2] and for miniaturized screening experiments [3]. Therefore, the exact control and the measurement of concentration of educts, dissolved catalysts and of effectors on biological processes is important. Particular, the cell activity, metabolism, cell division, growth, differentiation processes, embryonic development and cell-cell-communication are strongly effected by chemical conditions.

The application of conventional analytical tools is difficult for fluid segments due to their small size. There is a challenge for alternative read-out techniques of chemical information by non-invasive methods. Here, the introduction of core-shell micro particles carrying indicator molecules into fluid segments is reported. The polymer matrix of the core is inert and can be varied in composition in order to adapt approximately the density of the process liquids. The use of density-adapted particles is preferred for avoiding undesired sedimentation. The surface of the polymer core is covered by a polyelectrolyte multishell. Fluorescence dyes suited for indication of environmental conditions are immobilized inside this molecular multishell. The low thickness of about 10 nm of this surface films ensures, that the indicator beads respond very fast on chemical changes in the surrounding media.

The experiments showed, that sensor beads of three :m diameter can be introduced into the nanoliter fluid segments with different, but well-controlled concentrations. Homogenous distributions were achieved by injecting bead dispersions in aqueous carbohydrate solutions into perfluoroctane using PTFE tube and injector material. The obtained fluid segments of about 150 nL volume contained between about 1 and 1000 sensorbeads depending of original concentration in the particle suspension.

The read-out of optical information can occur either by microscopic imaging or by integrating measurement of fluorescence intensity in a certain spectral range. The first method is well applicable for the characterization of segments with sensor beads inside micro channels with coverchips with plane parallel optical transparent walls (Fig. a,b). The second method is well suited for the characterization of sequence segments flowing through micro tubes (Fig. c). The results demonstrate the applicability of polymer-based sensor micro particles with polyelectrolyte shells for monitoring purposes in nanoliter fluid segments.

Acknowledgement

We thank J. Albert (IPHT Jena), F. Möller and S. Schneider (Ilmenau) for technical assistance. Valuable discussion and support by A. Groß (Ilmenau) and financial support by the German Environmental Foundation (DBU) are gratefully acknowledged

References [1] A. Günther, K.F. Jensen, LabChip 6 (2006), 1487 [2] J.M. Köhler, Th. Henkel, A. Grodrian, Th. Kirner, M. Roth, K. Martin, J. Metze, Chem. Engin. J. 101 (2004), 201 [3] K. Martin, Th, Henkel, V. Baier, A. Grodrian, Th. Schön, M. Roth, J.M. Köhler, J. Metze, Lab Chip 3 (2003), 202

Figure a and b) Imaging of an aqueous fluid segment with polyelectroltye sensor beads inside a lithographically prepared micro channel (excitation: 450-490 nm, detection: 515 nm); bead density: 104 particles/:L (a); 250 particles/:L (b); c) Intensity-time plot for fluid segments with incorporated fluorescence-labelled micro beads flowing through a PTFE micro tube of 0.5 mm diameter segment volume: about 150 nl, (excitation: 450-490 nm, detection: .515 nm)