A micro-scale universal detector based on backscattering interferometry



Journal Title

Journal ISSN

Volume Title


Texas Tech University


As the current trend in miniaturization of analytical instrument continues, there is an urgent requirement for sensitive, small volume detection methodologies. Refractive index (Rl) detection, affords the generation of a signal for essentially all analyses, further more, the analytical signal is concentration rather than mass sensitive, and the technique is nondestructive. In the first part of this thesis, a universal detector based on backscatter interferometry has been developed to perform nanoliter volume refractive index measurements for on-chip SDS gel electrophoresis of proteins. The on-chip backscattering interferometry (OCIBD) detection system consists of a simple, folded optical train, it is based on the interaction of a laser beam and an etched channel in the shape of half cylinder in a silica plate. The backscattered light from the channel takes on the form of a high contrast interference pattern that contains information related to the bulk properties of the fluid located within the detection volume of 2.32 x 10"^ L. Depending on CE injection method, the positional changes of the interference fringes allow for the quantification of unlabeled proteins at the levels ranging from 17 to 310 attomoles. Separation and detection of 5 label-free proteins was achieved in less than 100 seconds with detection limits ranging from 0.95 picograms (1.1 x 10^-16mol) of Calmodulin to 7.0 picograms (1.0 x 10^-16) of BSA without signal filtering or active thermal control.

In the second part of this thesis, an ultra sensitive Dual capillary-Dual bicell (DCDB) MIBD system was also developed. DCDB MIBD system focuses a He-Ne laser through a half wave plate onto the cross section of two capillaries, one for reference and another for sensing analyte. The backscatering fringe patterns were detected with hwo bicell photodetectors. Because the two capillaries are located in identical thermal environment, the difference of the two bicell signals which represent the reference and probing capillary respectively, can cancel out the errors from the thermal drift, which is the major error in MIBD system. Thus gives an accurate detection of the specific signal of analyte without preciously controlling of the environment temperature. The characteristic of this system has been demonstrated by measuring glycerol concentration and real time monitoring protein folding/unfolding when temperature changed in a wild range. It has potential use as a real time nanoliter detector in |j,-HPLC, CE, FIA and scanning micro-calorimetry.



Refractive index -- Measurement, Interferometry, Electrophoresis, Backscattering -- Measurement -- Design and construction