Until now, spatially resolved Raman Spectroscopy has required to scan a sample under investigation in a time-consuming step-by-step procedure. Here, we present a technique that allows the capture of an entire Raman image with only one single exposure. The Raman scattering arising from the sample was collected with a fiber-coupled high-performance astronomy spectrograph. The probe head consisting of an array of 20 × 20 multimode fibers was linked to the camera port of a microscope. To demonstrate the high potential of this new concept, Raman images of reference samples were recorded. Entire chemical maps were received without the need for a scanning procedure.
Abstract. In this paper, we demonstrate the integration of a 3D hydrogel matrix within a hollow core Photonic Crystal Fibre (HC-PCF). In addition we also show the fluorescence of Cy5-labelled DNA molecules immobilised within the hydrogel formed in two different types of HC-PCF. The 3D hydrogel matrix is designed to bind with the amino-groups of biomolecules using an appropriate cross-linker, providing higher sensitivity and selectivity than the standard 2D coverage, enabling a greater number of probe molecules to be available per unit area. The HC-PCFs, on the other hand, can be designed to maximise the capture of fluorescence to improve sensitivity and provide longer interaction lengths.This could enable the development of fibre-based point-of-care and remote systems, where the enhanced sensitivity would relax the constraints placed on sources and detectors. In this paper, we will discuss the formation of such polyethylene glycol diacrylate (PEGDA) hydrogels within a HC-PCF, including their optical properties such as light-propagation and auto-fluorescence.
We present a miniaturized waveguide-based absorption measurement system operating at a wavelength of 635 nm, based on a silicon nitride integrated photonic platform, suitable for lab-on-chip applications. We experimentally demonstrate a high correlation between the bulk dye concentration and the measured absorption loss levels in the waveguides. We explain a photonic design process for choosing the ideal waveguide to minimize the coefficient of variation on the analyte concentration. The approach is designed for camera readout, allowing multiple readouts and easy integration for lab-on chip cartridge approach.
In recent years, numerous researchers have introduced liquids into the capillaries of Photonic Crystal Fibres (PCF), and more specifically hollow core PCFs (HC-PFC), to investigate new applications ranging from biosensing to liquid crystal switching. Clearly the main advantages of this technique are the strong interaction between the optical field and samples in the capillaries (e.g. [1]), and the possibility of long interaction lengths. There are several methods of filling PCFs, but the one that has received most attention relies on capillary action with or without overpressure. Therefore, flow-rate equations can be used to determine whether a specified length of PCF will be completely filled, assuming a laminar flow [2]. In this paper, we show experimentally that significant delays beyond the predicted filling times occur in HC-PCFs, when filling their capillaries with pure water.Experimentally, we used short pieces of commercially available HC-PCFs, with core diameter of approximately 11µm. These samples were cleaved and held vertically; allowing only capillary action to take place, i.e. no overpressure, and filling times were measured with assistance of a microscope (5 frames/s). A fusion splicer was used to collapse the cladding capillaries at the tip of the fibre so that the hollow core alone would be filled. Figure 1a shows the experimental results obtained for samples with different lengths of HC-PCF filled with pure water, for both collapsed (closed symbols) and non-collapsed (open symbols) cladding capillaries. The line on this figure represents the theoretically modelled time for our samples, as predicted by [2]. After each filling, water was pushed out of the capillaries, and the process was repeated a number of times. Figure 1b shows the times taken for consecutive fillings of the same samples. Our results clearly show that the initial filling of each piece of HC-PCFs took 5 to 10 seconds longer than theoretically predicted. Subsequent filling times approached the values given by the flow-rate equations. The change in filling rates for dry capillaries have been noted previously [3], due to variations in the contact angle between the fluid and the silica walls, affecting the flow-rate equations. Therefore we suggest that during the first exposures of the fibre to the liquid, an absorbing film is formed on the silica walls, reaching an equilibrium after few runs, probably because the contact angle becomes constant, as per [3]. We also found that the maximum number of fillings must be limited with the setup used here, because further fillings can damage the fibre facets, and re-cleaving becomes necessary. 0 20 40 60 80 100 0 10 20 30 40 collapsed: 51mm collapsed: 42 mm not collapsed: 64 mm not collapsed: 43 mm theory Filling Time (s) Fibre Length (mm) (a) 0 1 2 3 4 5 6 7 0 10 20 30 40 42 mm 43 mm 51mm collapsed: 51mm collapsed: 42 mm not collapsed: 64 mm not collapsed: 43 mm theory (b) Filling Time (s) Filling Number 64 mm Fig. 1 (a) Measurements of time of filling (symbols) and theoretical laminar flow...
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