Resonance Raman study of the oxygenation cycle of optically trapped singel red blood cells in a microfluidic system

Paper in proceeding, 2004

The average environmental response of red blood cells (RBCs) is routinely measured in ensemble studies, but in such investigations valuable information on the single cell level is obscured. In order to elucidate this hidden information is is important to enable the selection of single cells with certain properties while subsequent dynamics triggered by environmental stimulation are recorded in real time. It is also desirable to manipulate and control the cells under phsyiological conditions. As shown here, this can be achieved by combining optical tweezers with a confocal Raman set-up equipped with a microfluidic system. A micro-Raman set-up is combined with an optical trap with separate optical paths, lasers and objectives, which enables the acquisition of resonance Raman profils of single RBCs. The microfluidic system, giving full control over the media surrounding the cell, consists of a pattern of channels and reservoirs produced by electron beam lithography and moulded in PDMS. Fresh Hepes buffer or buffer containing sodium dithionite are transported through the channels using electro-osmotic flow, while the direct Raman response of the single optically trapped RBC is registered in another reservoir in the middle of the channel. Thus, it is possible to monitor the oxygenation cycle in a single cell and to study photo-induced chemistry. This experimental set-up has high potential for monitoring the drug response or conformational changes caused by other environmental stimuli for many types of single functional cells since "in vivo" conditions can be created.