Integrated fiber optic incoherent broadband cavity enhanced absorption spectroscopy detector for near-IR absorption measurements of nanoliter samples

Abstract

An integrated fiber-optic sensor is described that uses incoherent broadband cavity enhanced absorption spectroscopy for sensitive detection of aqueous samples in nanoliter volumes. Absorption was measured in a 100 µm gap between the ends of two short segments of multimode graded-index fiber that were integrated into a capillary using a precision machined V-grooved fixture that allowed for passive fiber alignment. The other ends of the fibers were coated with dielectric mirrors to form a 9.5 cm optical resonator. Light from a fiber-coupled superluminescent diode was directly coupled into one end of the cavity, and transmission was measured using a fiber-coupled silicon photodiode. Dilute aqueous solutions of near infrared dye were used to determine the minimum detectable absorption change of 2.4×10(-4) under experimental conditions in which pressure fluctuations limited performance. We also determined that the absolute minimum detectable absorption change would be 1.6×10(-5) for conditions of constant pressure in which absorption measurement is limited by electronic and optical noise. Tolerance requirements for alignment are also presented.

Fiber-Optic Chemical Sensors and Biosensors (2008–2012)

“…However, the probe works far in the UV, where many other species cause absorption, and it will be selective only if appropriate antibodies are being applied. An integrated fiberoptic sensor was reported 225 that uses incoherent broadband cavity-enhanced absorption spectroscopy for the detection of NIR absorbing dyes in nanoliter volumes. Absorption was measured in a 100-μm gap between the ends of two short segments of multimode graded-index fiber that were integrated into a capillary to form a 9.5-cm optical resonator.…”

Cavity-based absorption spectroscopy techniques

“…Such evanescentwave CRDS and CEAS/ICOS detection can be performed by sampling liquid-or solution-phase species that are in contact with either an intracavity optical prism or an exposed portion of a fi bre-optical cavity; in the latter case, fi bre-loop CRDS and CEAS/ICOS techniques are of special interest. Apart from the review articles cited above, a selection of additional research papers provides a representative sample of the burgeoning literature in this area (Hallock et al , 2002(Hallock et al , , 2003a(Hallock et al , , 2003bvon Lerber and Sigrist, 2002;Tarsa et al , 2004aTarsa et al , , 2004bBechtel et al , 2005;Fiedler et al , 2005;Mazurenka et al , 2006;Fisk et al , 2007;Islam et al , 2007;Schnippering et al , 2008Schnippering et al , , 2009Seetohul et al , 2009aSeetohul et al , , 2009bPu and Gu, 2009;Kiwanuka et al , 2010;van der Sneppen et al , 2010;Wang and Herath, 2010;Gomez et al , 2012). Finally, in the context of cavity-based absorption spectroscopy in the liquid phase, we note that surface tension enables liquids to form droplets with intrinsic optical cavity properties (such as whispering-gallery modes, cavity-ringdown effects and interesting dynamical phenomena) and leading to 'cavity enhanced droplet spectroscopy' (Nockel and Chang, 2002;Symes et al , 2004).…”

Broadband cavity enhanced UV-VIS absorption spectroscopy for picolitre liquid samples

“…2 Measuring small volumes is particularly important for applications such as nanoparticle synthesis and characterisation, drug development, and single cell omics. 4,[9][10][11][12] The sensitivity required for measuring small volumes or low concentrations with traditional absorption spectroscopy has been beyond capabilities. 13 The limiting factor for a sample of concentration C is the pathlength, l, of light through the sample, which is directly related to the sample volume.…”

“…Optical fibres have been employed to act as a waveguide between the cavity mirrors and the sample to generate a CEAS with an enhancement factor of 9× in volumes ∼200 pl. 9,10 Using a plano-convex cavity configuration with volumes down to 50 fl an increased cavity enhancement factor of 266× was achieved. 4 However, the plano-convex geometry is tuned for a single resonant wavelength at ∼640 nm and measurements over a broad spectral range are difficult to achieve as they require the adjustment of the cavity geometry via a piezo actuator.…”