Quantitative Analysis of Raman Signal Enhancement from Aqueous Samples in Liquid Core Optical Fibers

Abstract

Raman scattering from aqueous liquids can be collected with high efficiency by enclosing the liquid within a suitable waveguide, as several groups have reported. Here, we present a quantitative model that predicts the relative strength of signals collected from (a) a tubular waveguide and (b) a flat-walled cuvette. Experimental measurements of Raman scattering from aqueous ethanol are made using two geometries, a Teflon-AF waveguide and a standard quartz cuvette. The model correctly predicts the enhancements in several ethanol Raman bands provided by the waveguide geometry. This model should be useful in aligning and characterizing liquid core waveguides, whose manufacture is still undergoing refinements. In particular, the model shows that absorption and scattering losses affect the enhancement factor in different ways.

Review of optical fibre probes for enhanced Raman sensing

“…Apart from the influence of wavelength and waveguide length, optical fibre transmission characteristics can also be studied in greater detail by the effects of macro-bending, launch/acceptance angles, geometries and temperature on the evanescent field. [3,65,69,71,[73][74][75] Many methods of modelling and simulation, supported by wave theory, are known to evaluate the mode properties of guiding waves in Raman fibre probes, e.g. the beam-propagation method (BPM), MIT MEEP code, [26,76] the full vectorial finite element method (FEM) [77,78] and COMSOL Multiphysics software.…”

“…μg/ml level,~10 À8 M Micro-channel with AF 2400 SERS, micro-fluid [117] Urea~0.15 M Micro-channel with PDMS Microfluidic chip, Forward scattering [108] Methanol ND Teflon @ AF-2400 capillary tube Forward scattering [69] Trans-stilbene~0.25 M Quartz capillary tube Back-scattering [72] R6G~10 À9 M Hollow-core silica optical fibre SERS, Back-scattering [56] Adenosine 5 0 -monophosphate, Guanosine 5 0 -monophosphate, Uridine 5 0 -monophosphate 0.1 mg/ml, 0.1 mg/ml, 0.1 mg/ml Teflon @ AF-2400 Forward scattering [105] Methanol, ethanol, acetonitrile ND Teflon @ AF-2400 capillary tubing Forward scattering [118] 4-Nitroaniline, 4-nitrophenol, 2,4-dinitrophenol, nitrobenzene 10 μg/ml, 50 μg/ml, 250 μg/ml, 500 μg/ml, Teflon AF2400 capillary tube Forward scattering, Liquid chromatography [119] Ethanol water, KNO 3 0.022 ± 0.005%, 0.08 g/l Optofluidic jet waveguide Orthogonal excitation approach, fibre excitation/collection approach [120] Aqueous ethanol ND Teflon AF2400 waveguide Back-scattering [74] Biochemical creatinine dissolved in water and in urine mg/dl level Teflon @ -AF LCOFs geometry Back-scattering [121] β-carotene 2.5 × 10 À10 M Teflon AF2400 waveguide Back-scattering [122] Lysozyme~54 μM Teflon-AF capillary Back-scattering [10] Aqueous phenylalanine~6 × 10 À4 M T e f l o n @ AF-2400 capillary tubing Back-scattering [123] Mefloquine, Chloroquine 0.08 μM, 0.008 μM Teflon-AF capillary Back-scattering, UV Resonance Raman scatterers [33] 2-Propanol 5% Teflon AF2400 tube with a L-joint outlet 90°scattering [124] Carbon disulphide (CS2) influenced by β-carotene~1 0 À12 mol/l Hollow-core silica optical fibre Forward scattering, SRS [125,126] Carbon disulphide ND Multimode hollow-core optical fibre Stimulated Rayleigh-Kerr and Raman-Kerr scattering, Forward scattering [127] I 2 in benzene mg/l level Hollow-core quartz optical fibre Resonance Raman scatterers [128] Carbon disulphide ND Quartz-glass hollow fibre Stimulated Kerr scattering, Forward scattering [129] β-carotene molecule 10 À16 M Long-pathlength quartz glass tube Resonance Raman scattering, back-face collection geometry [130] 1,4-Bis(4-vinylpyridyl) phenylene (BVPP) 1 × 10 À8 mol/l U-shape microtube Back-scattering, SERS 1-Naphthalenethiol 10 μM HCPCFs MFC, BS, SF [66] Ethanol ND HCPCFs NSF, FS…”

Optofluidic Jet Waveguide Sensor for Raman Spectroscopy

“…Besides the background noise reduction attempts, as spontaneous Raman scattering is a weak optical effect, different methods in effective collection efficiency have been proposed as for instance the use of liquid core waveguides (LCWs) [1] or by means of hollow core photonic crystal fibers (HC-PCFs) [2].…”

Quantitative analysis of liquid formulations using FT-Raman spectroscopy and HPLC

“…[5][6][7]. There are also some scatter studies dealing with other materials, such as ethanol and water mixtures [8,9], rhodamine-6G and methanol mixtures [9]. Quantitative Raman spectroscopy has also been used for studying acid dissociation in solvents [10].…”