Arrays and Cascades of Fluorescent Liquid−Liquid Waveguides: Broadband Light Sources for Spectroscopy in Microchannels (original) (raw)
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Applied Physics Letters, 2005
This letter describes a simple fluidic light source for use "on-chip" in integrated microsystems. It demonstrates the feasibility of light sources based on liquid-core, liquid-cladding ͑L 2 ͒ microchannel waveguides, with liquid cores containing fluorescent dyes. These fluorescent light sources, using both miscible and two-phase systems, are tunable in terms of the beam size, intensity and spectral content. The observed output intensity from fluorescent L 2 light sources is comparable to standard fiber optic spectrophotometer light sources. Integration of fluorescent light sources during device fabrication removes both the need for insertion and alignment of conventional, optical-fiber light sources and the constraints on channel size imposed by fiber optics, albeit at the cost of establishing a microfluidic infrastructure.
Microlens systems for fluorescence detection in chemical microsystems
Optical Engineering, 2001
Micro-optical systems based on refractive microlenses are investigated. These systems are integrated on a chemical chip. They focus an excitation beam into the detection volume (microliter or even submicroliter scale) and collect the emitted light from fluorescent molecules. The fluorescence must be carefully separated by spatial and spectral filtering from the excitation. This paper presents the ray tracing simulation, fabrication, and measurement of three illumination systems. The measurements show that an adroit placement and combination of microfabricated lenses and stops can increase the separation between the excitation light and the fluorescence light. Moreover we present the successful detection of a 20 nM Cy5™ (Amersham Life Science Ltd.) solution in a 100-m-wide and 50-m-deep microchannel (excitation volume Ϸ250 pL) using one of these illumination systems. The microchemical chip with the micro-optical system has a thickness of less than 2 mm.
Microfluidic chip for spectroscopic and refractometric analysis
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Performance of an Integrated Microoptical System for Fluorescence Detection in Microfluidic Systems
Analytical Chemistry, 2002
This article presents a new integrated microfluidic/microoptic device designed for basic biochemical analysis. The microfluidic network is wet-etched in a Borofloat 33 (Pyrex) glass wafer and sealed by means of a second wafer. Unlike other similar microfluidic systems, elements of the detection system are realized with the help of microfabrication techniques and directly deposited on both sides of the microchemical chip. The detection system is composed of the combination of refractive circular or elliptical microlens arrays and chromium aperture arrays. The microfluidic channels are 60 µm wide and 25 µm deep. The elliptical microlenses have a major axis of 400 µm and a minor axis of 350 µm. The circular microlens diameters range from 280 µm to 350 µm. The apertures deposited on the outer chip surfaces are etched in a 3000-Å-thick chromium layer. The overall thickness of this microchemical system is <1.6 mm. A limit of detection of 3.3 nM for a Cy5 solution in phosphate buffer (pH 7.4) was demonstrated. The crosstalk signal measured between two adjacent microchannels with 1 mm pitch was <1:5600, meaning that e1.8 × 10-4 % of the fluorescence light power emitted from one microchannel filled with a 50 µM Cy5 solution reaches the photodetector at the adjacent microchannel. This performance compares very well with that obtainable in microchemical chips using confocal fluorescence systems, taking differences in parameters, such as excitation power into microchannels, data acquisition rates, and signal filtering into account.
Journal of Chromatography A, 1995
Simultaneous measurements of absorbance and fluorescence are possible with axial-illuminated flow cells, fashioned with a unique bend geometry. The optical properties of these flow cells have been studied. Effects of variations in lumen refractive index, capillary wall thickness and physical pathlength have been examined. A theoretical understanding of the various light propagation modes and of light intensity distributions in these modes, based upon lumen refractive index, has been attained. Of more practical significance, optical pathlengths from < 1 cm to 6 cm are simply attained by positioning the inlet optical fiber along the capillary axis with respect to the bend. The flow cell volumes obtained with different combinations of capillary I.D. and optical pathlength make the flow cell and resulting detector compatible with conventional HPLC and microscale separations. Also, studies have been performed to determine the effects of increased optical pathlength on overall analytical separation efficiency and detectability in the analysis of polynuclear aromatic hydrocarbons using laser-induced fluorescence micro-LC.
Journal of Microelectromechanical Systems, 2001
This paper presents the fabrication of a microchemical chip for the detection of fluorescence species in microfluidics. The microfluidic network is wet-etched in a Borofloat 33 (Pyrex) glass wafer and sealed by means of a second wafer. Unlike other similar chemical systems, the detection system is realized with the help of microfabrication techniques and directly deposited on both sides of the microchemical chip. The detection system is composed of the combination of refractive microlens arrays and chromium aperture arrays. The microfluidic channels are 60 m wide and 25 m deep. The utilization of elliptical microlens arrays to reduce aberration effects and the integration of an intermediate (between the two bonded wafers) aluminum aperture array are also presented. The elliptical microlenses have a major axis of 400 m and a minor axis of 350 m. The circular microlens diameters range from 280 to 300 m. The apertures deposited on the outer chip surfaces are etched in a 3000-A-thick chromium layer, whereas the intermediate aperture layer is etched in a 1000-A-thick aluminum layer. The overall thickness of this microchemical system is less than 1.6 mm. The wet-etching process and new bonding procedures are discussed. Moreover, we present the successful detection of a 10-nM Cy5 solution with a signal-to-noise ratio (SNR) of 21 dB by means of this system.
Simultaneous absorbance, fluorescence and refractive index (SAFRIN) detection for Micro LC
Analytica Chimica Acta, 1999
Absorbance, fluorescence and refractive index detection are simultaneously accomplished in a Micro LC system. A unique double eccentric-bend fused silica capillary is employed with axial illumination to achieve a long path length, multisensing flow cell. Two different optical sources, one that excites fluorescence through absorption and one that is not absorbed by eluting analytes, are imaged into the bends with optical fibers, placed within the capillary lumen in separate legs of the device. Axially-propagating light exits at each bend where photodetectors simultaneously collect attenuated light, one signal based on absorption and the other signal based on refractive index. A nearby cylindrical lens, optical filter and photomultiplier tube collect fluorescence in the 'absorption' leg of the capillary. Thus, trifunctional detection is achieved in microscale liquid chromatography.
The next major challenges for lab-on-a-chip (LoC) technology are 1) the integration of microfluidics with optical detection technologies and 2) the large-scale production of devices at a low cost. In this paper the fabrication and characterisation of a simple optical LoC platform comprising integrated multimode waveguides and microfluidic channels based on a photo-patternable acrylate based polymer is reported. The polymer can be patterned into both waveguides and microfluidic channels using photolithography. Devices are therefore both quick and cost-effective to fabricate, resulting in chips that are potentially disposable. The devices are designed to be highly sensitive, using an in-plane direct excitation configuration in which waveguides intersect the microfluidic channel orthogonally. The waveguides are used both to guide the excitation light and to collect the fluorescence signal from the analyte. The potential of the device to be used for fluorescence measurements is demonstrated using an aqueous solution of sodium fluorescein. A detection limit of 7 nM is achieved. The possibilities offered by such a device design, in providing a cost-effective and disposable measurement system based on the integration of optical waveguides with LoC technology is discussed.
Talanta, 2008
A versatile, simple, liquid core waveguide (LCW)-based fluorescence detector design is described for capillary systems. A Teflon AF coated fused silica capillary serves as the LCW. The LCW is transversely excited. The light source can be a conventional or high power (HP) light emitting diode (LED) or a laser diode (LD). The source can be coupled to the LCW directly or via an optical fiber. Fiber coupling is convenient if a high power (necessarily heat sink mounted) emitter is used. The LCW is concentrically placed within a slightly larger opaque jacket tube and the LCW terminates just short of the jacket terminus, which is sealed with an optical window. The influent liquid thus exits the LCW tip, flows back around the LCW through the jacket annulus to exit via an aperture on the jacket tube. The problem of coupling the emitted light efficiently to the photodetector is thus solved by placing the tip of the annular tubular assembly directly on the detector. For excitation wavelengths of 365 nm (LED/HPLED) and 405 nm (LD), the tris(8-hydroxyquinoline-5sulfonic acid (sulfoxine)) chelate of aluminum (em,max ∼ 500 nm) and Coumarin 30 were respectively used as the model analyte. For source-detector combinations comprising (a) a UV LED (∼1.5 mW @ 15 mA) and a photodiode, (b) a LD (∼5 mW, abstracted from a "Blu-Ray" recorder) and a miniature photomultiplier tube (mPMT), and (c) a high power (210 mW @ 500 mA) surface-mount HPLED-mPMT, the S/N = 3 LODs were, respectively, 1.7 pmol Al, 3-100 fmol Coumarin 30 (depending on laser intensity and integration time), and 4 fmol Al. In the last case, the relative standard derivation (R.S.D.) at the 20 fmol level was 1.5% (n = 10).