With present trends towards size reduction of fluid handling systems and the use of micro-fabricated devices in chemical and biochemical analysis comes the need for alternate, non-conventional ultra-sensitive detection schemes, particularly those which can be miniaturized to the size of a chip to perform accurate analysis whether it is by FIA, CE, HPLC, or PCR. Unfortunately, with this system miniaturization the volumes of manipulated fluids are on the order of picoliters, which renders use of conventional detection useless. To overcome this limitation a unique universal Refractive index (RI) detector based on backscatter interferometry has been developed in our lab, the Micro-Interferometric Backscatter Detector (MIBD). MIBD is well-suited for small volume optical detection that employs a simple optical train, is relatively pathlength insensitive, probes ultra-small volumes, and can be used for “on-chip” detection with no modifications to the channel. This technique employs a laser, a capillary tube or a micro channel and a phototransducer. MIBD facilitates RI measurements at the level of 7 X 10-8 RIU within a 40 nL probe volume. It has been shown that micro-interferometry can be successfully employed in polarimetry at the 10 m-degree level in 1.0 nL probe volume and in calorimetry at the milli-degree level in a 350 pL probe volume. The fluid flow measurements performed in the capillaries with MIBD were done in the probe volume of 40nL with accuracy of 42.8 nL/min. Furthermore, applications for micro-interferometry that have been demonstrated or are under investigation include refractometry, polarimetry and thermometry or calorimetry that are being performed in picoliter volumes and on-chip to allow peptide sequencing, nano-scale polarimetry for pharmaceutical characterization and non-invasive thermometry for cold denaturation (protein folding) investigations and fundamental studies in on-chip CE. Finally, the use of micro-fluidics, special immobilization chemistry and unique detection methodologies are facilitating the preparation of patterns or arrays for high-throughput screening, DNA hybridization and proteomics research (Figure 1).
Darryl Bornhop (website)