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ABSTRACT: An optofluidic platform for real-time monitoring of live cell secretory activities is constructed via Fano resonance in a gold nanoslit array. Large-area and highly sensitive gold nanoslits with a period of 500 nm are fabricated on polycarbonate films using the thermal-annealed template-stripping method. The coupling between gap plasmon resonance in the slits and surface plasmon polariton Bloch waves forms a sharp Fano resonance with intensity sensitivity greater than 11 000% per refractive index unit. The nanoslit array is integrated with a cell-trapping microfluidic device to monitor dynamic secretion of matrix metalloproteinase 9 (MMP-9) from human acute monocytic leukemia cells in situ. Upon continuous lipopolysaccharide (LPS) stimulation, MMP-9 secretion is detected within 2 h due to ultrahigh surface sensitivity and close proximity of the sensor to the target cells. In addition to the advantage of detecting early cell responses, the sensor also allows interrogation of cell secretion dynamics. Furthermore, the average secretion per cell measured using our system well matches previous reports while it requires orders of magnitude less cells. The optofluidic platform may find applications in fundamental studies of cell functions and diagnostics based on secretion signals.
Small 04/2013; · 8.35 Impact Factor
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ABSTRACT: A precisely controlled metallic nanomesh was fabricated by using nanosphere lithography to pattern the silver thin film to form hexagonal nanohole arrays with excellent uniformity, high conductivity and good transparency. An Alq<sub>3</sub> based OLED, with the silver nanomesh electrode of high ðll factor of 70.2% demonstrated a considerable luminous efðciency of 4.8 cd/A, which is 60.9% higher than the referenced device with ITO anode. The periodical nanohole array not only increased the transparency but also helped extracting surface plasmonic wave in organic layers. By attaching the microlens array to further extract the trapped light in substrate, the extraction efficiency enhancement of device with nanomesh anode was 73.8% higher than 50.2% of the referenced device with ITO anode. And the overall current efficiency of device with nanomesh anode was 87.7% higher than traditional ITO based device.
Optics Express 04/2013; 21(7):8535-43. · 3.59 Impact Factor
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ABSTRACT: We have demonstrated a detection method for the ultra-sensitive detection of an mRNA biomarker. The method utilizes functionalized magnetic nanoparticles (MNPs) for signal enhancement in conjunction with surface plasmon resonance (SPR) on gold nanoslits. The approach for detection includes double hybridization at two different specific locations in two steps. First, the biomarker target molecule is captured with MNPs, and second, MNPs carrying the target molecule are introduced to the SPR chip to hybridize with probes immobilized on the gold nanoslits. In this work, MNPs were applied for a dual purpose: to isolate the target molecule from the sample matrix to prevent non-specific binding and to enhance the SPR response. Gold nanoslits that provide SPR sensing were fabricated by nanoimprinting lithography on polycarbonate (PC) film. The film was integrated with a microliter volume microfluidic chip to form the SPR detection chip. This detection method was used to detect mRNA heterogeneous nuclear ribonucleoproteins (hnRNP B1) in two cancer cell lines, CL1-0 and CL1-5. hnRNP B1 is an mRNA biomarker that is overexpressed in lung cancer tissue in the early stage of cancer and can be found in the serum and plasma of lung cancer patients. A synthetic target molecule and extracted total RNA from the cell lines were used as samples. Without amplification and labeling of the target molecule, the SPR results demonstrate a specific and sensitive method for the detection of hnRNP B1 mRNA in extracted RNA from the two selected cell lines. The method is capable of measuring down to 30 fM of the target molecule in a 7 μl sample (corresponding to 1.26 × 10(5) molecules) without amplification and labeling of the target molecule.
The Analyst 03/2013; · 4.23 Impact Factor
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ABSTRACT: A near-field coupling method for studying propagation properties of surface plasmon polariton (SPP) in subwavelength dielectric-loaded
SPP waveguides (DLSPPWs) is presented. In this method, a tapered fiber probe is employed to generate a nanometer optical spot.
When this spot is near the entrance of the DLSPPW with its polarization parallel to the waveguide, a strong guiding wave is
observed by a leakage radiation microscope. For DLSPPWs with a dielectric height of about 600nm, we observed SPP waves with
zigzag propagation patterns at 650nm wavelength. Such zigzag propagation results in a great reduction of propagation loss.
In addition, the zigzag wave has a strong optical confinement. The bending loss for an L-bend DLSPPW is only about 0.4dB.
KeywordSurface plasmon polariton–Waveguide–Near-field
Plasmonics 04/2012; 6(3):557-563. · 2.99 Impact Factor
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ABSTRACT: Gold nanoslit arrays have multiple resonances due to localized plasmons, Bloch wave surface plasmon polaritons, and Wood’s
anomaly. Different structures result in different resonances and affect the detection sensitivity of the nanoslits. We systematically
compared different structure parameters such as period, slit widths, and gold film thickness by using a spectral integration
method. The experimental results show the detection sensitivity had an optimal value for a 500-nm period and 130-nm-thick
nanoslits. Moreover, the sensitivity increases with the decrease of the slit widths. It was improved about three times when
the size was reduced from 230 to 56nm. The optimized structure can achieve a detection limit of 5 × 10−6 refractive index unit when the stability is 0.2%. Combining multispectral images and the spectral integration method, we
demonstrate real-time and multiple detections of antigen–antibody interactions.
KeywordsMultispectral imaging–Surface plasmons–Optical sensing and sensors–Nanostructures
Plasmonics 04/2012; 6(3):483-490. · 2.99 Impact Factor
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ABSTRACT: Nanostructure-based sensors are capable of sensitive and label-free detection for biomedical applications. However, high-throughput and low-cost fabrication techniques are the main issues which should be addressed. In this study, chip-based nanostructures for intensity-sensitive detection were fabricated and tested using a thermal-annealing-assisted template-stripping method. Large-area uniform nanoslit arrays with a 500 nm period and various slit widths, from 30 to 165 nm, were made on plastic films. A transverse magnetic-polarized wave in these gold nanostructures generated sharp and asymmetric Fano resonances in transmission spectra. The full width at half-maximum bandwidth decreased with the decrease of the slit width. The narrowest bandwidth was smaller than 10 nm. Compared to nanoslit arrays on glass substrates using electron-beam lithography, the proposed chip has a higher intensity sensitivity up to 10367%/RIU (refractive index unit) and reaches a figure of merit up to 55. The higher intensity sensitivity for the template-stripped nanostructure is attributed to a smoother gold surface and larger grain sizes on the plastic film, which reduces the surface plasmon propagation loss.
ACS Nano 03/2012; 6(4):2931-9. · 10.77 Impact Factor
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ABSTRACT: The authors demonstrated an efficient color conversion layer (CCL) by using nanosphere arrays in down-converted white organic light-emitting diodes (WOLEDs). The introduced periodical nanospheres not only helped extract the confined light in devices, but also increased the effective light path to achieve high-efficiency color conversion. By applying a CCL with red phosphor on a 400-nm-period nanosphere array, we achieved 137% color conversion ratio for blue OLEDs, which was 2.68 times higher than conventional flat CCL. The resulting luminous efficiency of WOLEDs with patterned CCLs (20.97 cd/A, 1000 cd/m2) was two times higher than the efficiency of the flat device (10.26 cd/A, 1000 cd/m2).
Optics Express 01/2012; 20(3):3005-14. · 3.59 Impact Factor
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ABSTRACT: Chip-based biosensors for sensitive label-free detection were fabricated and tested by using Fano-type resonant nanostructures. The sensor was composed of a 190 nm-thick gold nanoslit surrounded by 600-nm-period grooves. Transverse-magnetic polarized wave in these gold nanostructures generated asymmetrical resonant spectra due to the interference of broad-band cavity resonance in the single slit and narrow-band surface plasmon resonance on the periodic grooves. Compared to nanoslit arrays, such Fano-type sensor has a sharper resonance which yields a figure of merit up to 48. In addition, the crossed talk between sensing elements is reduced due to the Bragg reflection of the periodic grooves. A smaller detection separation down to 10 μm width was achieved. An antigen-antibody interaction experiment in aqueous environment verified the detection sensitivity in surface binding event.
Optics Express 11/2011; 19(24):24530-9. · 3.59 Impact Factor
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ABSTRACT: We present an antireflection structure consisted of irregular nanopillars to increase light extraction efficiency of flexible organic light-emitting devices. The nanopillars were made by imprinting the anodized aluminum oxide on polycarbonate substrates. The thermal viscosity effect formed the nanopillars with tapered shapes. Such nanopillars show excellent antireflection properties for a wide range of incident angles and wavelengths. The normal transmittance was improved from 85.5% to 95.9% for 150-nm-height nanopillars. The transmittance was greatly improved from 52.8% to 89.1% at 60° incident angle. With this antireflection structure, the device efficiency was improved 69% as compared to devices with flat substrates. Due to wide-angle antireflection, the image contrast ratio was also significantly improved.
Optics Express 05/2011; 19 Suppl 3:A295-302. · 3.59 Impact Factor
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ABSTRACT: Surface-enhanced Raman scattering (SERS) with enormous enhancements has been applied for ultra-sensitive detection in various fields, but the fabrication of large-scale, controllable and cost-effective substrates is a major challenge. We propose a novel fabrication process with a gas-assisted hot embossing process and an anodic aluminum oxide template to obtain the SERS substrate on a 1 × 1 cm polycarbonate film. The SERS spectra of 4-mercaptobenzoic acid (PMBA) on the gold substrate have been measured. The enhancement factors are between 3.99 × 107 and 4.92 × 107, depending on the heights of nanocones, which can be controlled by the embossing temperature and pressure. The simple and inexpensive SERS substrate has potential for wide application in SERS-based sensors.
Journal of Micromechanics and Microengineering 02/2011; 21(3):035023. · 2.11 Impact Factor
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ABSTRACT: We herein describe an integrated system for the high-throughput analysis of splicing events and the identification of transcript variants. The system resolves individual splicing events and elucidates transcript variants via a pipeline that combines aspects such as bioinformatic analysis, high-throughput transcript variant amplification, and high-resolution capillary electrophoresis. For the 14 369 human genes known to have transcript variants, minimal primer sets were designed to amplify all transcript variants and examine all splicing events; these have been archived in the ASprimerDB database, which is newly described herein. A high-throughput thermocycler, dubbed GenTank, was developed to simultaneously perform thousands of PCR amplifications. Following the resolution of the various amplicons by capillary gel electrophoresis, two new computer programs, AmpliconViewer and VariantAssembler, may be used to analyze the splicing events, assemble the consecutive exons embodied by the PCR amplicons, and distinguish expressed versus putative transcript variants. This novel system not only facilitates the validation of putative transcript variants and the detection of novel transcript variants, it also semi-quantitatively measures the transcript variant expression levels of each gene. To demonstrate the system's capability, we used it to resolve transcript variants yielded by single and multiple splicing events, and to decipher the exon connectivity of long transcripts.
Nucleic Acids Research 11/2010; 38(20):e187. · 8.03 Impact Factor
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ABSTRACT: A multispectral integration method to increase the detection limit of gold nanostructures is presented. This method considers all the resonances due to localized surface plasmons, Bloch wave surface plasmons, and Wood's anomalies. By integrating the wavelength shifts together with intensity changes over these resonances, the detection resolution is increased to about six times larger than that of commonly used wavelength or intensity methods. Further studies with different nanostructures show the detection sensitivity is increased with the decrease of aperture size. The detection limit for 40-nm nanoslits is improved by about seven times relative to that for 300-nm nanoslits. For sub-100-nm apertures, the detection resolution for nanoslits is better than that for nanoholes due to its non-cutoff transmission. The advantage of using the multispectral integration method in biosensing is verified by antigen-antibody interaction experiments.
Small 09/2010; 6(17):1900-7. · 8.35 Impact Factor
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ABSTRACT: An optical fiber sensor based on the change of optical confinement in a subwavelength tip is presented. The optical spot is substantially increased when the environmental refractive index (RI) increases from 1.3 to 1.4. By measuring the intensity of low angular spectral components, an intensity sensitivity up to 8000% per RI unit is achieved. The fiber tip sensors take advantage of the small detection volume and real-time responses. We demonstrate the application of the nanofiber sensors for measuring concentrations of acids and evaporation rates of aqueous mixtures.
Optics Letters 04/2010; 35(7):944-6. · 3.40 Impact Factor
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ABSTRACT: This paper proposes a novel nanosensing platform for protein fluorescence enhancement by nano ring gap (NRG) induced localized surface plasma resonance (LSPR). On this platform, gold nanoparticles (GNPs) surrounded by silver sheathes with a nanosized gap were designed and successfully fabricated for protein immobilization/detection. Through simulation, when the nano ring gap between silver sheath and gold nanoparticle reduced to 15 nm, the light intensity can be enhanced by around 8.5 folds of magnitude than that of the 5 nm gap sensor. Experiment result has also verified the fluorescence enhancement by 7 fold for bound protein on GNPs. This platform will be further tailored for single protein molecule detection in the future.
Micro Electro Mechanical Systems (MEMS), 2010 IEEE 23rd International Conference on; 02/2010
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ABSTRACT: Understanding the endocytosis process of gold nanoparticles (AuNPs) is important for the drug delivery and photodynamic therapy applications. The endocytosis in living cells is usually studied by fluorescent microscopy. The fluorescent labeling suffers from photobleaching. Besides, quantitative estimation of the cellular uptake is not easy. In this paper, the size-dependent endocytosis of AuNPs was investigated by using plasmonic scattering images without any labeling.
The scattering images of AuNPs and the vesicles were mapped by using an optical sectioning microscopy with dark-field illumination. AuNPs have large optical scatterings at 550-600 nm wavelengths due to localized surface plasmon resonances. Using an enhanced contrast between yellow and blue CCD images, AuNPs can be well distinguished from cellular organelles. The tracking of AuNPs coated with aptamers for surface mucin glycoprotein shows that AuNPs attached to extracellular matrix and moved towards center of the cell. Most 75-nm-AuNPs moved to the top of cells, while many 45-nm-AuNPs entered cells through endocytosis and accumulated in endocytic vesicles. The amounts of cellular uptake decreased with the increase of particle size.
We quantitatively studied the endocytosis of AuNPs with different sizes in various cancer cells. The plasmonic scattering images confirm the size-dependent endocytosis of AuNPs. The 45-nm-AuNP is better for drug delivery due to its higher uptake rate. On the other hand, large AuNPs are immobilized on the cell membrane. They can be used to reconstruct the cell morphology.
Journal of Nanobiotechnology 01/2010; 8:33. · 5.09 Impact Factor
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ABSTRACT: A new microarray for dynamical studies of surface biomolecular interactions without fluorescent labeling is proposed. We employed gold nanostructures to excite surface plasmons on the microarray surface and detected the intensity changes in the extraordinary transmission. The calculation and measurement results indicate that the nanoslit array has an intensity sensitivity much higher than the nanohole array due to its narrower resonant bandwidth. In addition, the sensitivity is increased as the slit width decreases. For 35 nm slit width, the intensity sensitivity reaches to approximately 4000%/RIU, two times larger than the slit width larger than 150 nm. Using the intensity changes, we demonstrate a 10 x 10 microarray for real-time measurements of antigen-antibody and DNA-DNA interactions.
Optics Express 12/2009; 17(25):23104-13. · 3.59 Impact Factor
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ABSTRACT: Large phase differences between transverse electric (TE) and transverse magnetic (TM) waves were investigated in plasmonic nanoslit arrays. The phase of the TE wave shifts ahead because of its low propagation constant. On the other hand, the phase of the TM wave is retarded due to the propagation of surface plasmons. The opposite phase shift forms a giant birefringence. Its magnitude was dependent on the width of nanoslits. The birefringence magnitude was ∼ 1 for 300-nm-wide nanoslits and up to ∼ 2.7 for 100 nm ones. The spectroscopic measurements indicate that waveplates made of gold nanoslits have large bandwidths.
Applied Physics Letters 07/2009; 95(1):013105-013105-3. · 3.84 Impact Factor
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ABSTRACT: A circle of planar nanoholes in a dielectric thin film can focus light into a sub-half-wavelength spot. The nanostructure with higher rotational symmetry shows better focusing properties. From finite-difference time-domain calculations, we verified such a focusing spot coming from the constructive interference of diffraction beams near the nanoholes. For a 1 microm size lens with eight 200 nm diameter holes, we achieved an optical spot smaller than 250 nm measured at 650 nm wavelength. This nanostructure provides a simple way to massively fabricate a planar lens array with a scale down to the submicrometer level.
Optics Letters 07/2009; 34(12):1867-9. · 3.40 Impact Factor
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ABSTRACT: The wavelength sensitivities of three kinds of nanostructures (nanoslits, nanoholes, and concentric circles) with various
aperture sizes were compared in water environment. These nanostructures were made on a 110-nm-thick gold film with a period
of 600nm. Surface plasmon resonances in these nanostructures produce transmission dips near the phase-matching conditions
while peaks at longer wavelengths. The wavelength sensitivities measured at dips are close to theoretical predictions and
about 1.5 times larger than those measured at peaks. Such sensitivity difference is attributed to various surface plasmon
distributions, as illustrated by the finite-difference time-domain calculations. In addition, the sensitivity decreases with
the increase of aperture size. The nanoslit array and concentric circles have better sensitivities than the nanohole array
due to the no cut-off transmission.
Plasmonics 11/2008; 3(4):119-125. · 2.99 Impact Factor
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ABSTRACT: We present a nano-optical probe for real-time refractive index measurement of single live cell. The probe was made of a tapered fiber tip coated with 13 nm diameter gold nanoparticles. The evanescent wave near the tip excited localized surface plasmon resonance of gold nanoparticles. By measuring the optical intensity scattered from the nanoparticles, the probe showed an intensity sensitivity up to ∼5400% per refractive index unit. The 3T3 fibroblast cell was tested by inserting the probe into the cytoplasm. Refractive index as measured by the localized plasmonic effect was 1.3506, consistent with the results measured by holographic methods.
Applied Physics Letters 11/2008; · 3.84 Impact Factor
