Slotted photonic crystal cavities with integrated microfluidics for biosensing applications

School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, Fife, Scotland, UK.
Biosensors & Bioelectronics (Impact Factor: 6.41). 09/2011; 27(1):101-5. DOI: 10.1016/j.bios.2011.06.023
Source: PubMed


We demonstrate the detection of dissolved avidin concentrations as low as 15 nM or 1 μg/ml using functionalized slotted photonic crystal cavities with integrated microfluidics. With a cavity sensing surface area of approximately 2.2 μm(2), we are able to detect surface mass densities of order 60 pg/mm(2) corresponding to a bound mass of approximately 100 ag. The ultra-compact size of the sensors makes them attractive for lab-on-a-chip applications where high densities of independent sensing elements are desired within a small area. The high sensitivity over an extremely small area is due to the strong modal overlap with the analyte enabled by the slotted waveguide cavity geometry that we employ. This strong overlap results in larger shifts in the cavity peak wavelength when compared to competing approaches.

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    • "from 1.33 for water based solutions to 1.5 for silica oil matching liquids and to above 1.8 for cargille liquids, is especially effective in tuning photonic structures beyond that accessible through solid species. In this case, the infiltration of fluid into the air holes of PC has been popularly investigated and demonstrated [74]–[77]. Both the theoretical and experimental results have demonstrated that the PCW can be optimized by selective fluid infiltration, and the low dispersion slow light over wide bandwidth has been achieved by choosing one kind of infiltration fluid with suitable refractive index into a certain infiltrated area [28], [78]–[80]. "
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    ABSTRACT: Slow light in photonic crystal waveguide (PCW) is now being heavily investigated for applications in optical devices. However, slow light with high group index in perfect PCW is usually accompanied by large group velocity dispersion (GVD), which would severely limit the bandwidth of slow light, deform optical pulses, and disturb its practical applications. In this review, various optimization methods that are proposed to overcome these drawbacks are introduced and compared. These methods rely largely on the ability to modify the slow light properties of PCWs with a change in their structural parameters or a change in their effective refractive indexes through external agents. For each optimization method, the corresponding group index, GVD, bandwidth, and normalized delay-bandwidth product are all presented along with the physical parameters, the potential advantages, and the fabrication complexity of PCW that enable them. Finally, the key problems and future development directions of slow light in PCW are discussed.
    Full-text · Article · May 2015 · IEEE Transactions on Nanotechnology
    • "This property enhances the light-matter interaction and results in a high sensitivity towards the local change of the environment. Through the resonant wavelength shift induced by the change of the RI in the slot, high Q PhC microcavities are widely utilized as chemical and biological sensors to detect gases [11], [12], solutions [13]– [17], and bio-molecules [18]. Compared to other types of RI sensors, such as multiple optical mode waveguides [19], Mach-Zehnder interferometers [20] and Young Interferometers [21], slot PhC bio-chemical sensors have advantages of small size, high sensitivity, and CMOS compatibility. "
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    ABSTRACT: We propose and experimentally demonstrate a series of L-n slot photonic crystal (PhC) microcavities, which operate as refractive index (RI) gas sensors. The cavities are simply composed of a silicon slab triangular photonic crystal with n holes replaced by a slot, which do not require sophisticated design or high fabrication resolution. With the increase in n, the quality factor of the cavity exponentially increases, which is explained by the envelope of electric field approaching a Gaussian profile. An L-9 slot PhC microcavity with a quality factor exceeding 30 000, sensitivity of 421 nm per RI unit (RIU), and detection limit down to 1 x 10(-5) RIU was experimentally demonstrated. The performance of the device is comparable with other fine-tuned PhC microcavity structures. Due to its simple structure and high fabrication tolerance, it could have wide applications in optical sensors.
    No preview · Article · Oct 2014 · IEEE Photonics Journal
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    • "Thus, during the last decades, many PhC sensors for different sensing application have been demonstrated, such as stress sensing, humidity sensing, refractive index sensing, and biochemical sensing [16] [17] [18] [19] [20] [21] [22] [23]. With the extensive research about photonic crystal sensors, ultra-high quality factor (Q) and high sensitivity can be achieved by using different kinds of structure such as microcavities [24] [25], resonant rings and disks [26], slot waveguides [27] [28], and heterostructures [29]. Photonic crystal biosensors detect analyte attached to the surface (surface-based sensing) or liquids filled into the holes around the PhC (bulk index sensing) via modulation of microcavity resonant wavelength. "
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    ABSTRACT: In this work, we propose radius-graded photonic crystal sensor arrays applied on nano-scale optical platform for label-free biosensing. Two L3 cavities and two H1 cavities are multiplexed and interlaced on both sides of a photonic crystal W1 waveguide on the radius-graded photonic crystal slab. The optical sensing characteristics of the nanocavity structure are predicted by three-dimensional finite difference time domain (3D-FDTD) simulation. In response to the refractive index change of air holes surrounding the cavities, four interlaced and symmetrical cavities are shown to independently shift their resonant wavelength without crosstalk. The simulation results demonstrate the refractive index sensitivity of sensor array varies from 66.67 to 136.67 nm/RIU corresponding to the number of functionalized air holes ranged from 4 to 21. This design makes different cavities multiplexed on both sides of waveguide possible. Meanwhile, the radius-graded photonic crystal with more symmetrical and interlaced cavities is better for large integration in the sensor arrays.
    Full-text · Article · Sep 2014 · Sensors and Actuators A Physical
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