Research

Photonic crystal biosensor

Novel optical methods for performing label-free detections have attracted growing attention driven by increasing demands for better understanding of specific interactions between biomolecules (such as protein binding and DNA hybridization), which provide a chemical foundation for all cellular processes. Although a number of label-free techniques exist, including surface plasmon resonance (SPR), interferometry, waveguides, ring resonators, and photonic crystals, they are limited in their ability to measure the binding kinetics of very small molecules (MW< 500 Da), to detect low concentrations (< 1 pg/mm2), or to detect low affinity interactions, which is of great importance to critical biological analysis, such as high-throughput screening of small molecules in drug discovery, or detecting very low concentration biomarkers in complex media.

        In this project, I developed a novel photonic crystal biosensor. This sensor uses a one-dimensional photonic crystal structure in a total-internal-reflection geometry (PC-TIR), which forms a high-finesse Fabry-Perot resonator with an open cavity (Fig. 1). It achieves a narrow resonance width (~ 1 nm) and high sensitivity (~1800 nm/RIU or 1 nm/nm), thus large figure of merit (FOM) value (~ 1500), more than 50 times larger than the widely-studied SPR based sensors. With a high resolution detection system, I demonstrated its ultralow detection limits (i.e., high performances) in a series of experiments: 1X10-8 RIU for bulk solvent refractive index, 2X10-5 nm for molecular layer thickness, and 6 fg/mm2 for surface mass density. Furthermore, I achieved ultrasensitive biomolecular detections ranging over three orders of magnitude in molecular weight, including very small molecules (<250 Da), DNA oligonucleotides (< 1 pM), proteins, and antibodies (Fig. 2).

       

          

Fig. 1. (a) Schematic of PC-TIR sensor; (b) intensity distribution within the sensor structure                         Fig. 2. Measurements of molecular binding

               

References:

  1. Y. Guo, J. Y. Ye, B. Huang, T. P. Thomas, J. R. Baker, Jr. and T. B. Norris, "Real-time biomolecular binding detection using a sensitive photonic crystal biosensor," Anal. Chem. 82, 5211-5218 (2010) [PDF & SI]

  2. Y. Guo, J. Y. Ye, C. Divin, T. P. Thomas, et al. "Label-free biosensing using a photonic crystal structure in a total-internal-reflection geometry," Proc. SPIE 7188, 71880B (2009) [PDF]

  3. Y. Guo, C. Divin, A. Myc, F. L. Terry, Jr., J. R. Baker, Jr., T. B. Norris and J. Y. Ye, "Sensitive bioassay using a photonic crystal structure in total internal reflection," Opt. Express 16, 11741-11749 (2008) [PDF]

  4. J. Y. Ye, Y. Guo, T. B. Norris, and J. R. Baker, Jr., "Photonic crystal sensor," US Patent 7,639,362 (2009)(issued)

Optofluidic multi-hole capillary

Optofluidics has emerged as a dynamic and rapidly developing research field over the past few years, in which optics and microfluidics are synergistically integrated to enhance the performance and function of the microsystems. In this project, I developed a novel optofluidic, multi-hole capillary for bio-chemical applications. It consists of a bundle of multiple flow-through micro/nano-sized holes (Fig.3), which provides a lot of unique features including 3-dimensional geometry for large surface-to-volume ratio, low sample volume (~ nL), inherent micro-/nano sized fluidic channels for convenient and efficient sample delivery, and light guiding properties for large signal accumulation. Combing with the state-of-the-art photonic technologies (such as Fabry-Perot resonator, SERS, and fluorescence spectroscopy), I have developed the corresponding optofluidic systems.

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           Fig.3 (a) Schematic of flow-through multi-hole capillary   (b) SEM images of multi-hole capillaries with different hole numbers and sizes

Sub-project 1. Optofluidic 3-D SERS biosensor

3-dimensional surface-enhanced Raman scattering (SERS) detection integrated with optofluidics offers many advantages over conventional SERS conducted under planar and static conditions. In this project, I developed a novel optofluidic SERS platform based on nanoparticle-functionalized flow-through multi-hole capillaries for rapid, reliable, and ultrasensitive analyte detection. It can be operated in both transverse and  longitudinal directions. A detection limit better than 100 fM for rhodamine 6G molecule was achieved with an enhancement factor exceeding 108.

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                        Fig.4 (a) Schematic of optofluidic 3-D SERS biosensor                                             (b) Ultrasensitive, highly-specific molecular detection

Sub-project 2. Optofluidic Fabry-Perot cavity biosensor

To date, most of the label-free sensors employ the flow-over scheme, which relies on the analytes in bulk solution to diffuse to the sensing surface. While simple, this approach suffers from mass transport problems that significantly slows down the detection speed, in particular, at low sample concentrations. Recently, the flow-through scheme has attracted great attention, which takes advantage of inherent micro/nano sized fluidic channels for high analyte capture efficiency. In this project, I develop a novel flow-through, label-free Fabry-Perot cavity sensor with fiber interferometry, which takes advantage of both micro/nanofluidics and Fabry-Perot resonator, and achieves rapid and sensitive biomolecular detection.

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                                      Fig.5 (a) Schematic of optofluidic FP biosensor                                        (b) Rapid and sensitive biodetection

Sub-project 3. Optofluidic fluorescence immunoassay

Fluorescence detection of biomolecules is currently one of the most widely used methods in the areas of basic biological research, medical diagnostics, and drug discovery. In this project, I am developing a novel optofluidic fluorescence immunoassay for ultrasensitive (< 1fM), rapid (<15 mins), and high-through (similar to ELISA) biomolecular detection.

References:

  1. Y. Guo+, M. K. K. Oo+, K. Reddy, and X. Fan, "Ultrasensitive optofluidic surface-enhanced Raman scattering detection based on flow-through multihole capillaries,"ACS Nano 6, 381-388 (2012) [PDF & SI] (+: Co-first author)

  2. M. K. K. Oo+, Y. Guo+, K. Reddy, J. Liu, and X. Fan, "Ultrasensitive vapor detection with SERS active gold nanoparticles immobilized flow-through multi-hole capillaries," Anal. Chem. 84, 3376-3381 (2012) [PDF & SI] (+: Co-first author)

  3. Y. Guo, H. Li, K. Reddy, H. S. Shelar, V. R. Nittoor, and X. Fan, "Optofluidic Fabry-Perot cavity biosensor with integrated flow-through micro/nano channels," Appl. Phys. Lett. 98, 041104 (2011) [PDF]

  4. X. Fan, Y. Guo, and M. K. K. Oo, "Flow-through multi-hole structures and their applications," U. S. Provisional Patent Application, serial No. 61/557,588 (2011)

  5. X. Fan, Y. Guo, "Fabry-Perot based optofluidic sensor," PCT International Patent Application, serial No. PCT/US2012/21499 (2012)

Optoacoustics

There is a strong demand for high-resolution imaging techniques to obtain comprehensive morphological and functional information of important biological samples. Compared to high-resolution tomography such as confocal microscopy, two-photon microscopy, and optical coherence tomography (OCT), ultrasound imaging can achieve a much deeper penetration depth into biological tissues, and provides an invaluable noninvasive imaging method. Currently, the unavailability of two-dimensional (2-D) high-frequency transducer arrays (> 50 MHz) is a major bottleneck preventing further development of real-time 3-D high-resolution imaging. Piezoelectric ultrasound transducers are mature for arrays operating at less than 10 MHz, but it is extremely difficult to produce 2-D arrays operating above 20 MHz. Using optical methods to generate and detect ultrasound is an attractive technology, however, most of optical methods could only generate or detect high frequency ultrasound on separate transducer elements, and currently there is no commercial product which can achieve high-resolution, all-optical, ultrasound imaging in one single device.

          In this project, I use an innovative photonic crystal-metallic (PCM) structure, which provides many unique advantages for making all-optical ultrasound transducer. It can act as an ideal ultrasound transmitter which absorbs 100% energy of the laser pulse to generate stronge broad-band ultrasound signal; at the same time, it can be used as a high-sensitivity optoacoustic receiver to the reflected ultrasound. Moreover, it has a simple configuration, which is very easy to fabricate with current fabrication technology and with low cost. The preliminary experimental results indicate that this structure is able to generate and detect broad-band (over 100 MHz) ultrasound signals. Further development with fiber technologies will enable to build a compact fiber tip-based ultrasound probe, and then to construct 2-D transducer arrays for real-time, 3-D high resolution imaging. This new imaging technology will open up possibilities unimaginable so far in noninvasive biological diagnosis and treatment, and has significant applications in ophthalmology, dermatology, intravascular imaging (IVUS), and small animal imaging.

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Fig.6 (a) Schematic of all-optical ultrasound transducer                   (b) Resonance modes for optoacoustics

References:

  1. Y. Guo, T. B. Norris, J. R. Baker, Jr., L. J. Guo, and N. G. Walter, "Photonic crystal - metallic structures and applications," PCT International Patent Application, serial No. PCT/US2011/38177 (2011)

  2. Y. Guo, H. W. Baac, S. L. Chen, T. B. Norris, L. J. Guo, "Broad-band, high-efficiency optoacoustic generation using a novel photonic crystal-metallic structure," Proc. SPIE 7899, 78992C (2011) [PDF]

  3. C. M. Chow, Y. Zhou, Y. Guo, T. B. Norris, X. Wang, C. X. Deng and J. Y. Ye, "Broadband optical ultrasound sensor with a unique open-cavity structure,"J. Biomed. Opt. 16, 017001 (2011) [PDF]

TIRFM

Total internal reflection fluorescence microscopy (TIRFM) is a powerful technique. It can excite and visualize fluorophores present in extremely thin axial sectioning (like the near-membrane region of live or fixed cells grown on coverslips), which allows wide-field imaging with very low background and minimal out-of-focus fluorescence. The unique features of TIRFM make it invaluable in biological studies, such as single molecule detection, single particle tracking and the observation of dynamic membrane events on live cell surfaces (signaling, endocytosis, and exocytosis).

        Conventional glass coverslip used in TIRFM has limited intensity enhancement within evanescent field, which disfavors fluorescence emission. In this project, I propose to use the photonic crystal-metallic (PCM) structure. It combines the properties of a photonic crystal structure with that of a metallic structure and provides many unique advantages in TIRFM, including large field enhancement for strong emission signal, distance-dependent coupling with surface plasmons for small detection volume, sensitivity only to p polarization for suppression of background noise, and control of vertical propagation length. Moreover, it has great potential to combine with nanostructured surface for single-molecule detection. 

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Fig.7 (a) Schematic of prism-based TIRFM with PCM structure; (b) intensity enhancement in PCM, pure metal and glass structures

References:

  1. Y. Guo, T. B. Norris, J. R. Baker, Jr., L. J. Guo, and N. G. Walter, "Photonic crystal - metallic structures and applications," PCT International Patent Application, serial No. PCT/US2011/38177 (2011)

More projects

           More interesting projects have been developed, in particular, a novel photodetector integrated photonic crystal structure has been developed for ultrahigh throughput label-free biosensor microarrays, 3D high resolution ultrasound imaging, acoustic transducer arrays, and high sensitivity pressure sensors. 

References:

  1. Y. Guo, H. Subbaraman, R. T. Chen, "Integrated photonic crystal structures and their applications"
    U. S. Provisional Patent Application #61/699,042, filed 09/10/2012