We demonstrated quantitative real-time label-free detection of DNA sequences using the liquid core optical ring resonator (LCORR) sensor. The LCORR is a recently developed sensing platform that integrates microfluidics and photonic sensing technology with low detection limit and sub-nanoliter detection volume. We analyzed experimentally and theoretically the LCORR response to a variety of DNA samples that had different strand lengths (25-100 bases), number of base- mismatches (1-5), and concentrations (10 pM to 10 microM) to evaluate the LCORR sequence detection capability. In particular, we established the linear correlation between the LCORR sensing signal and the molecule density, which allows us to accurately calculate the molecule density on the surface. It is found that the probe surface coverage was 26-51% and the extent of hybridization was 40-50%. The titration curve for 25-base probe and 25-base target DNA yields a dissociation constant of 2.9 nM. With a 37.1 nm/RIU LCORR, detection of 10 pM bulk DNA concentration was demonstrated. The mass detection limit was estimated to be 4 pg/mm(2), corresponding to a density of 10(10) molecules/cm(2) on the surface. We also showed that the LCORR was sensitive enough to differentiate DNA with only a few base-mismatches based on the raw sensing signal and kinetic analysis. Our work will provide important insight into the light-DNA interaction at the ring resonator surface and lay a foundation for future LCORR-based DNA label-free microarray development.
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"The accumulation of a biomolecule layer changes the neff, leading to measurable change in λ due to a WGM resonant wavelength shift. The OFRR has been used to detect protein , DNA , viral particle , and pesticide concentrations  with a RI detection limit on the order of 10−7 refractive index units (RIU) and mass detection on the order of pg mm−2 [16,18,20–22]. "
[Show abstract][Hide abstract] ABSTRACT: We have demonstrated label free detection of CD4+ and CD8+ T-Lymphocyte whole cells and CD4+ T-Lymphocyte cell lysis using the optofluidic ring resonator (OFRR) sensor. The OFRR sensing platform incorporates microfluidics and photonics in a setup that utilizes small sample volume and achieves a fast detection time. In this work, white blood cells were isolated from healthy blood and the concentrations were adjusted to match T-Lymphocyte levels of individuals infected with HIV. Detection was accomplished by immobilizing CD4 and CD8 antibodies on the inner surface of the OFRR. Sensing results show excellent detection of CD4+ and CD8+ T-Lymphocyte cells at medically significant concentrations with a detection time of approximately 30 minutes. This work will lead to a rapid and low-cost sensing device that can provide a CD4 and CD8 count as a measure of HIV progression.
"When analytes are captured on the OFRR inner surface (see Fig. 1(B)), the interaction of the WGM and the analyte results in a change in n eff and hence a spectral shift of the WGM. Due to its high Q-factor, the OFRR can achieve a RI detection limit of 10 −7 refractive index units (RIU) and a mass detection limit of sub-pg mm −2 , on par with the most sensitive biosensors   . The OFRR has been applied in many biomedical applications including CD4 and CD8 T-lymphocyte detection, viral particle detection, and DNA detection [27,28,30]. "
[Show abstract][Hide abstract] ABSTRACT: Protein biomarkers have recently been heavily researched in their roles in the detection, quantification, and monitoring of aggressive types of breast cancer. In this work, we describe a novel, label-free approach for detecting the HER2 extra-cellular domain breast cancer biomarker in human serum samples using the opto-fluidic ring resonator (OFRR). The OFRR incorporates microfluidics and optical ring resonator sensing technology to achieve rapid label-free detection in a small and low-cost platform. In this study, HER2 proteins were spiked in serum at varying concentrations. Results show that the OFRR is able to detect HER2 at medically relevant concentrations in serum ranging from 13 to 100 ng/mL in 30 min. Our work will lead to a device that can be used as a tool for monitoring disease progression in a low-cost sensing setup.
Preview · Article · Apr 2010 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: We developed a novel label-free opto-fluidic ring resonator (OFRR) biosensor for detection of an organophosphorus (OP) pesticide. The OFRR is based on a micro-sized glass capillary whose circular wall forms a ring resonator that supports the whispering gallery modes (WGMs). The WGMs has an evanescent field in the capillary core and interacts with the analyte flowing in the capillary. We used parathion-methyl as a model system to investigate the OFRR sensing performance in terms of bulk refractive index sensitivity, surface activation for affinity property, detection limit, and reproducibility. The performance of the OFRR was further compared with that of the Biacore 3000 SPR system. Our results show that the detection limit of 3.8 × 10−11 M for parathion-methyl was achieved with an analysis time of about 0.5 min, 10 times faster than the surface plasmon resonance (SPR) system. Furthermore, the OFRR biosensor demonstrated excellent reproducibility (R.S.D. = 3.5%, n = 5). The OFRR offers optical label-free detection mechanism with integrated microfluidics. It is a promising technology platform for development of portable multi-channel biosensors with high sensitivity, quick detection time, and sub-nanoliter detection volume.
Preview · Article · Jul 2008 · Sensors and Actuators B Chemical