253 research outputs found
Distance dependence of surface plasmon-coupled emission observed using Langmuir-Blodgett films
No full textSurface plasmon-coupled emission (SPCE) is a phenomenon in which fluorophores in the excited state couple with metallic structures resulting in surface plasmons that radiate into the substrate. The authors examined the dependence of SPCE on the distance and orientation of a fluorophore in the nanometric range of the Ag surface. The distance of the fluorophore from the Ag surface was controlled from 2 to 52 nm using Langmuir-Blodgett films. For a horizontally oriented cyanine dye, the experimental intensity and lifetime measurements are in excellent agreement with the detailed theoretical analysis of SPCE
An improved cerulean fluorescent protein with enhanced brightness and reduced reversible photoswitching
No full textCyan fluorescent proteins (CFPs), such as Cerulean, are widely used as donor fluorophores in Förster resonance energy transfer (FRET) experiments. Nonetheless, the most widely used variants suffer from drawbacks that include low quantum yields and unstable flurorescence. To improve the fluorescence properties of Cerulean, we used the X-ray structure to rationally target specific amino acids for optimization by site-directed mutagenesis. Optimization of residues in strands 7 and 8 of the β-barrel improved the quantum yield of Cerulean from 0.48 to 0.60. Further optimization by incorporating the wild-type T65S mutation in the chromophore improved the quantum yield to 0.87. This variant, mCerulean3, is 20% brighter and shows greatly reduced fluorescence photoswitching behavior compared to the recently described mTurquoise fluorescent protein in vitro and in living cells. The fluorescence lifetime of mCerulean3 also fits to a single exponential time constant, making mCerulean3 a suitable choice for fluorescence lifetime microscopy experiments. Furthermore, inclusion of mCerulean3 in a fusion protein with mVenus produced FRET ratios with less variance than mTurquoise-containing fusions in living cells. Thus, mCerulean3 is a bright, photostable cyan fluorescent protein which possesses several characteristics that are highly desirable for FRET experiments
Porous organic crystals crosslinked by free-radical reactions
No full textTwo hydrogen-bonded crosslinked organic frameworks (HCOFs) were synthesized via free radical reactions utilizing butadiene and isoprene as crosslinkers. These HCOFs exhibit high crystallinity, enabling detailed structural characterization via single-crystal X-ray diffraction analysis. Subsequently, one of the olefin-rich HCOFs was converted to a hydroxylated framework through hydroboration–oxidation while maintaining the high crystallinity.This article is published as Samanta, Krishanu, Jiashan Mi, Albert D. Chen, Fangzhou Li, Richard J. Staples, Aaron J. Rossini, and Chenfeng Ke. "Porous organic crystals crosslinked by free-radical reactions." Chemical Communications 60, no. 57 (2024): 7311-7314. doi: https://doi.org/10.1039/D4CC02454K
SPR-based sensing of physiological analytes using a tunable laser:Towards wearable applications
No full textIn stressful situations, concentrations of various molecules in the human body shift in response to the stressor. These molecules are measurable indicators of stress and are therefore called stress biomarkers. In many stress conditions, such as in overtraining syndrome, early detection of these biomarkers is highly important as the conditions are often not fully reversible. Early detection of the stress symptoms could be achieved with wearable sensors that would continuously monitor health information from different body fluids, such as sweat, urine, saliva, tears and blood. Compared to more conventional electrochemical or optical methods, plasmonic sensing could offer higher sensitivity, better stability and faster data collection while enabling implementation to compact devices. In this work, a sensor chip, based on grating-coupled surface plasmon resonance, is proposed for stress biomarker detection. In this work, we show a highly sensitive grating-based SPR sensor working in concert with a tunable laser within the wavelength range of 1528-1565 nm. The SPR sensor was designed using COMSOL Multiphysics software and was fabricated by means of UV nanoimprinting lithography. The implemented SPR sensor shows sensitivity close to 1200 nm/RIU, with a figure of merit (a ratio between the sensitivity and the full width at half maximum of the SPR dip) exceeding 400. The experimental results are strongly in agreement with COMSOL simulations. Such impressive characteristics of the fabricated sensor are among the best reported in the literature. The sensitivity of the chip was tested with two different stress-related biomarkers: glucose and lactate. With the tested range of 0 to 1.1 M, in the current version of the setup, without a receptor layer, the detection limits of glucose and lactate were 5.9 and 36.9 mM, respectively, which are close to the physiological ranges of these analytes in body fluids. The detection limit can be further improved with the sensor functionalization, thermal stabilization and mechanical isolation. When integrated into a wearable device, this approach has a potential in future healthcare applications, such as in continuous stress monitoring.</p
Scattering Field Enhanced Biosensing Based on Sub-wavelength Split-ring Plasmonic Cavity With High Q-factor
No full textPlasmonic structures are widely used in modern biosensor design. various plasmonic resonant cavities could efficiently achieve a high Q-factor, improving the local field intensity to enhance photoluminescence or SERS (Surface-Enhanced Raman Scattering) of small molecules. Also, the combination between virus-like particles and plasmonic structures could significantly influence the scattering spectrum and field, which is utilized as a method for biological particle detection. In this paper, we designed one kind of gold plasmonic cavity with the shape of a split-ring. An edge gap and a bonus center bulge are introduced in the split-ring structure. Our simulation is based on Finite Difference Time Domain (FDTD) method. Polarization Indirect Microscopic Imaging (PIMI) technique is used here to detect far-field mode distribution under the resonant wavelength. The simulation results demonstrate resonant peaks in the visible spectrum at about 600 nm with a Q-factor reaches to 74. Localized hot spots are generated by an edge dipole mode and a cavity hexapole mode at resonant wavelength, which is according to dark points in the PIMI sinδ image. Also, the split-ring cavity shows a sensitivity when combined with biological particles. The scattering distribution is evidently changed as a result of energy exchange between particles and split-ring cavity, indicating a promising possibility for biosensing
Surface plasmon enhanced upconversion luminescence for biosensing applications
No full textUpconversion (UC) luminescence sensing is a technique to improve the detection limit of conventional fluorescence in biosensing that is commonly limited by the autofluorescence-generated background signal. The main limitation of UC materials is their low wavelength conversion efficiency. Many studies have been made to enhance the efficiency of UC materials by optimizing light absorption and energy transfer processes. However, rather low efficiency remains an issue limiting the practical usage of UC materials in biosensors. Plasmon enhancement is a way to improve UC photoluminescence by enhancing the excitation and emission rates. In this study, we modeled and fabricated gold gratings for exciting surface plasmon polaritons (SPPs) at 976-nm wavelength. We aim at increasing the local optical intensity at the locations of UC nanoparticles on a nano-structured plasmonic surface. The UC nanoparticles were adsorbed on the gratings via biomolecule conjugation. UC photoluminescence on the gratings was compared with flat gold surfaces. Experimentally, we achieved UC enhancement up to 70, which is relatively high in comparison with other plasmon-enhanced UC techniques presented in the literature. The results of our work can be applied in various biosensing applications in which low excitation intensity is preferred
Enhanced X-ray emission from nano-particle doped bacteria
No full textRecently, it has been greatly appreciated that intense light matter interaction is modified due to the nano- and microstructures in the target by – surface plasmons, laser energy localization scattering etc. Extreme laser intensities produce dense plasmas and collective mechanisms generate energetic electrons, ions and hard X-rays. Recently, it is postulated that the anharmonic electron motion, driven by ultrashort, high-intensity laser pulses, provides a universal mechanism for the laser absorption. Here, we provide the first demonstration of anharmonic-resonance-aided high laser-absorption in a biological system. At intensities of ∼1016–18 W/cm2, 40 fs pulses excite a plasma formed with E. coli bacteria. The density-inhomogeneities due to the micro- and nanostructures in the bacterial target increase Anharmonic Resonance (AHR) heating and result in a 104-fold enhancement in the hard X-ray yield compared to plain solid targets. These observations lead to novel high-energy X-ray sources that have implications to lithography, imaging and medical applications
- …
