The detection of thrombin based on aptamer binding is studied using two different optical fiber-based configurations: long period gratings coated with a thin layer of titanium dioxide and surface plasmon resonance devices in optical fibers coated with a multilayer of gold and titanium dioxide. These structures are functionalized and the performance to detect thrombin in the range 10 to 100 nM is compared in transmission mode. The sensitivity to the surrounding refractive index (RI) of the plasmonic device is higher than 3100 nm RIU−1 in the RI range 1.335 to 1.355, a factor of 20 greater than the sensitivity of the coated grating. The detection of 10 nM of thrombin was accomplished with a wavelength shift of 3.5 nm and a resolution of 0.54 nM.
This work reports a new type of optical fiber tweezers based on polymeric micro-lenses. The lenses are achieved by means of an economical and fast fabrication process, using an in-fiber photo-polymerization technique. The polymerization radiation is guided towards the fiber tip creating a polymeric waveguide. The method allows tailoring the geometry of the tip by adjusting the fabrication parameters. Furthermore, more complex shapes can be fabricated by exploring modal effects at the polymerization/trapping wavelengths, which can be used for different applications such as trapping, beam shaping and patterned illumination.
A method to control the output intensity profile of optical fibers is presented. Using guided wave photopolymerization in multimode structures the fabrication with modal assisted shaping of polymeric micro lenses is demonstrated. Results showing that a given linear polarized mode can be selectively excited controlling the intensity distribution at the fiber tip are presented. This pattern is then reproduced in the polymeric micro structure fabricated at the fiber tip thus modulating its output intensity distribution. Such structures can therefore be used to obtain at the fiber tip predetermined intensity patterns for attaining optical trapping or patterned illumination.
Surface Plasmon Resonance (SPR) is the base for some of the most sensitive label free optical fiber biosensors. However, most solutions presented to date require the use of fragile fiber optic structure such as adiabatic tapers or side polished fibers. On the other hand, long-period fiber gratings (LPG) present themselves as an interesting solution to attain an evanescent wave refractive index sensor platform while preserving the optical fiber integrity. The combination of these two approaches constitute a powerful platform that can potentially reach the highest sensitivities as it was recently demonstrated by detailed theoretical study [1, 2]. In this work, a LPG-SPR platform is explored in different configurations (metal coating between two LPG – symmetric and asymmetric) operating in the telecom band (around 1550 nm). For this purpose LPGs with period of 396 μm are combined with tailor made metallic thin films. In particular, the sensing regions were coated with 2 nm of chromium to improve the adhesion to the fiber and 16 nm of gold followed by a 100 nm thick layer of TiO2 dielectric material strategically chosen to attain plasmon resonance in the desired wavelength range. The obtained refractometric platforms were then validated as a biosensor. For this purpose the detection of thrombin using an aptamer based probe was used as a model system for protein detection. The surface of the sensing fibers were cleaned with isopropanol and dried with N2 and then the aminated thrombin aptamer (5’-[NH2]- GGTTGGTGTGGTTGG-3’) was immobilized by physisorption using Poly-L-Lysine (PLL) as cationic polymer. Preliminary results indicate the viability of the LPFG-SPR-APTAMER as a flexible platforms point of care diagnostic biosensors.
The measurement of refractive index (RI) is an important tool for label free biosensing in biomedical applications [1,2]. In
this work, a LPG based fiber optic interferometric probe is used for thrombin detection. The aptamer raised against the
thrombin was immobilized through an electrostatic immobilization method, using poly-L-lysine as cationic polymer. The
functionalized probe was characterized and tested against thrombin. The system was validated with the detection of
thrombin using an aptamer based probe (5’-[amine]GGTTGGTGTGGTTGG-3’) as a model system for protein detection.
The shift corresponding to the affinity-assay between TBA and the thrombin was of about 56 pm. A differential readout
interferometer based on a white light Mach-Zehnder configuration, with pseudo-heterodyne phase modulation is described.
The system can be used to interrogate two similar LPGs based interferometers in a differential scheme. Considering the
configuration where both devices are functionalized being one active (sensor) and the other one passive (reference) it is
possible to accurately measure the behavior of the analyte of interest independent of non-specific binding events, bulk
refractive index changes and temperature. Signal processing with low cost digital instrumentation developed in Labview
environment allows a detectable change in refractive index of Δn ≈ 2x10-6 [3]. Coupling the sensing probe together with a
passively functionalized reference probe in a differential system will enable pseudo-heterodyne interrogation and
extremely sensitive phase detection of biological species.
A Long Period Grating (LPG)-based platform for the detection of E. coli outer membranes proteins (EcOMPs) is presented. The sensing probe is achieved by the functionalization of a LPG inscribed in a single mode fiber (SMF28) with a DNA-aptamer resulting in a label-free configuration capable of specific recognize EcOMPs in waters. Measurement takes place by tracking the variations induced in the resonance wavelength by the refractive index changes at the fiber surface (≈100 nm/RIU). The sensing head was characterized and tested against EcOMPs and applied to spiked environmental water samples. The sensor displayed logarithmic responses in the range of 0.1 nM to 10 nM EcOMPs and is regenerated (under low pH conditions) and the deviation of the subsequent detection was less than 0.1 %.
An evanescent wave fiber optic sensor for detection of E. coli outer membranes proteins (EcOMPs) is presented. The sensing probe is achieved by the functionalization of a Long Period Grating (LPG) inscribed in a single mode fiber (SMF28) with poly-L-lysine (PLL) resulting in a label-free configuration capable of specific recognition of EcOMPs in waters due to the resonance wavelength shift variation owing to refractive index changes of the medium (≈100 nm/RIU). The sensing head was characterized and tested against EcOMP and applied to spiked environmental water samples. The sensor displayed linear responses in the range of 1×10-10 M to 1×10-8 M EcOMP and is regenerated (under low pH conditions) and the deviation of the subsequent detection was less than 0.1 %.
The deterioration of water quality by Cyanobacteria causes outbreaks and epidemics associated with harmful diseases in
Humans and animals because of the released toxins. Microcystin-LR (mcyst) is one of the most widely studied
hepatotoxin and World Health Organization recommends a maximum value of 1 μg L-1 of mcyst in drinking-water.
Therefore, there is a great demand for remote, real-time sensing techniques to detect and quantify the presence of mcyst.
In this work a Fabry-Perot sensing probe based on a fibre tip coated with a mcyst sensitive thin film is presented. Highly
specific recognition membranes, using sol-gel based Molecular Imprinted Polymers (MIPs), were developed to quantify
microcystins in water, showing great potential in the analysis of this kind of samples. The fibre Fabry-Perot MIP sensor
shows a linear response to mcyst concentration with a sensitivity of -13.2 ±} 0.4 nm L μg-1.
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