Integrated fluorescence sensing in a lab-on-a-chip for DNA analysis

We report on monolithic optical sensor integration in a lab-on-a-chip toward onchip diagnosis of all kinds of genetic diseases, e.g. breast cancer. Such an analysis of genetic diseases is based on the capillary electrophoresis separation of DNA fragments amplified from diagnostically relevant regions of the concerned gene. This paper presents a proof of principle, demonstrating real time integrated fluorescence monitoring during the capillary electrophoresis separation of fluorescent dyes as well as fluorescently labeled DNA molecules in an on-chip microfluidic channel. To this end, sensing waveguides were integrated monolithically by means of femtosecond laser irradiation, in a commercial fused silica lab-on-a-chip, to perpendicularly intersect the microfluidic separation channel. Laser excitation through these waveguides induces fluorescence in the flowing microfluidic plugs. Depending on the number of species present, and the difference between their mobility, a corresponding number of electropherogram peaks are detected. Detection has been performed by a CCD camera in order to visualize the on-chip events and to provide access to spatial information, as well as by a photomultiplier tube in order to detect low values of fluorescence signal. The present limit of detection is estimated to be approximately 6 nM. The presented setup achieves high spatial resolution due to the small cross section of the waveguides, ~12 μm. This is an improvement over the conventional approach to place a pinhole in the path of the fluorescence output signal generated by a broadband background illumination, e.g. with an Hg or a Xe lamp. Future work will focus on extension of this principle to real world diagnostic samples for development of a fast and compact point of care optical biosensing device. During the conference we will present the latest results in wavelengthmultiplexed fluorescence monitoring of DNA separation at low limits of detection.