51 research outputs found
Portable capillary-based (non-chip) capillary electrophoresis
Miniaturized, portable instrumentation has been gaining popularity in all areas of analytical chemistry. Capillary electrophoresis (CE), due to its main strengths of high separation efficiency, relatively short analysis time and low consumption of chemicals, is a particularly suitable technique for use in portable analytical instrumentation. In line with the general trend in miniaturization in chemistry utilizing microfluidic chips, the main thrust of portable CE (PâCE) systems development is towards chip-based miniaturized CE. Despite this, capillary-based (non-chip) PâCE systems have certain unmatched advantages, especially in the relative simplicity of the regular cylindrical geometry of the CE capillary, maximal volume-to-surface ratio, no need to design and to fabricate a chip, the low costs of capillary compared to chip, and better performance with some detection techniques. This review presents an overview of the state of the art of PâCE and literature relevant to futuredevelopments. We pay particular attention to the development and the potential of miniaturization of functional parts for PâCE. These include components related to sample introduction, separation and detection, which are the key elements in PâCE design. The future of PâCE may be in relatively simple, rugged designs (e.g., using a short piece of capillary fixed to a chip-sized platform on which injection and detection parts can be mounted). Electrochemical detection is well suited for miniaturization, so is probably the most suitable detection technique for PâCE, but optical detection is gaining interest, especially due to miniaturized light sources (e.g., light-emitting diodes)
Effect of laser processing parameters and glass type on topology of micro-channels
Traditional processes to manufacture micro-fluidic
devices include standard lithography, electron beam writing
and photo-patterning. These techniques are well established
but most are limited to surface micro-fabrication. Laser
micro-machining provides an alternative for microfabrication
of devices. This paper presents Design of
Experiment models for the fabrication of micro-channel
structures with four different types of glass, soda-lime,
fused-silica, borosilicate and quartz. A 1.5kW CO2 laser
with 90 ÎŒm spot size was used to fabricate micro-channels
on the surface of glass sheets. Power, P, pulse repetition
frequency, PRF, and translation speed, U, were set as
control parameters. The resulting geometry of the channel
(depth and width) and transmission capabilities were
measured and analyzed. A comparison of the results of this
experimental testing with the four glass types showed that
quartz and fused-silica glasses would have better channel
topologies for chemical sensing applications
Numerical model for light propagation and light intensity distribution inside coated fused silica capillaries
Numerical simulations of light propagation through capillaries have been reported to a limited extent in the literature for uses such as flow-cell design. These have been restricted to prediction of light path for very specific cases to date. In this paper, a new numerical model of light propagation through multi-walled cylindrical systems, to represent coated and uncoated capillaries is presented. This model allows for light ray paths and light intensity distribution within the capillary to be predicted. Macro-scale (using PMMA and PC cylinders) and micro-scale (using PTFE coated fused silica capillaries) experiments were conducted to validate the model's accuracy. These experimental validations have shown encouragingly good agreement between theoretical predictions and measured results, which could allow for optimisation of associated regions for monolith synthesis and use in fluidic chromatography, optical detection systems and flow cells for capillary electrophoresis and flow injection analysis
Spiropyran modified microfluidic chip channels for photonically controlled sensor array detection of metal ions
Microfluidic chips are particularly attractive for analytical purposes because they provide a convenient small platform for rapid analysis and detection.1 Furthermore, spiropyrans dyes can be used as photonically controlled, self-indicating molecular recognition agents for the fabrication of sensors.2 Here, we show how through integrating the beneficial characteristics of microfluidic devices and spiropyrans dyes, a simple and very innovative chip for on-line metal ion sensor array can be realised.
The chip (4x3cm) consists of four independent 180m depth, polydimethylsiloxane (PDMS) channels. 1â-(3-Carboxypropyl)-3,3â-dimethyl-6-nitrospiro-[2H-1]-benzopyran-2,2â-indoline is covalently immobilised on the ozone plasma activated PDMS microchannel surfaces.
Upon exposure to UV light, the transparent PDMS channels change to light purple colour because the spiropyran molecules of the surface undergo a heterocyclic ring cleavage that result in the formation of the highly conjugated merocyanine form. When stock solutions of several ion metals (Ca2+,Zn2+,Hg2+,Cu2+) are pumped independently through the four channels, different optical responses were observed for each metal.
1-L.Basabe-Desmonts et al. Anal.Bioanal.Chem.(2008)390:307â315.
2-R.J.Byrne et al. J.Mat.Chem.(2006)16:1332-1337
Spiropyran modified PDMS micro-fluidic chip device for photonically controlled sensor array detection of metal ions
Microâfluidic chips are particularly attractive in biological and life sciences for analytical purposes
because they provide a convenient small platform for rapid analysis and detection [1]. Using
microâfluidic devices for the determination of ions emerges as a potential solution to some of the
challenges not overtaken by conventional techniques e.g. atomic absorption, inductivelyâcoupled
plasmaâoptical emission, mass spectrometry and ionâselective electrodes [2]. For example, these
devices can integrate complex sample handling processes, calibration, and detection steps into a
compact, portable system. Moreover they require small sample volumes (low ÎŒl or nl), consume
little power, and are easily constructed for multiâanalyte detection, either through multiple
parallel fluidic architectures or by using arrays of detection elements.
Organic photochromic compounds like spiropyrans are particularly interesting targets for the
development of new approaches to sensing since they offer new routes to multiâfunctional
materials that take advantage of their photoâreversible interconversion between two
thermodynamically stable states (a spiropyran (SP) form, and a merocyanine (MC) form), which
have dramatically different charge, polarity and molecular conformations. Furthermore, they can
be easily incorporated into membranes for improved robustness and ease of handling [3], but
from our perspective, most interesting of all, they have metal ionâbinding and molecular
recognition properties which are only manifested by the MC form. Based on the coordinationinduced
photochromism characteristic of the MC form, spiropyrans have been employed as
molecular probes for metal ions and organic molecules [4].
In this abstract, we show how through integrating the beneficial characteristics of microâfluidic
devices and spiropyrans photoswitches, a simple and very innovative chip configured as an onâline
metal ion sensor array can be realised (Figure 1). The microâfluidic device consists of five
independent 94 ÎŒm depth, 150 ÎŒm width channels fabricated in polydimethylsiloxane. The
spiropyran 1ââ(3âcarboxypropyl)â3,3ââdimethylâ6ânitrospiroâ1âbenzopyranâ2,2ââindoline (SPâCOOH)
is immobilised by physical adsorption directly on ozone plasma activated PDMS microâchannel
walls. When the colourless, inactive, spiropyran coating absorbs UV light it switches to the highly
coloured merocyanine form (MCâCOOH), which also has an active binding site for certain metal
ions. Therefore metal ion uptake can be triggered using UV light and subsequently reversed on
demand by shining white light on the coloured complex, which regenerates the inactive spiropyran
form, and releases the metal ion. When stock solutions of several metal ions (Ca2+, Zn2+, Hg2+, Cu2+,
Co2+) are pumped independently through the five channels, different optical responses were
observed for each metal (Figure 2), (i.e. complex formation with metal ions is associated with
characteristic shifts in the visible spectrum), and the platform can therefore be regarded as a
microâstructured device for online multiâcomponent monitoring of metal cations
Immobilisation and incorporation of photochromic spiropyran dyes in polymeric substrates for metal ion sensing and micro-fluidics
The use of scanning contactless conductivity detection for the characterisation of stationary phases in micro-fluidic chips
The use of scanning capacitively coupled contactless conductivity detection for the evaluation of the structural homogeneity and density of both packed and monolithic stationary phases in microfluidic chips is presented here for the first time
Fibre coupled micro-light emitting diode array light source with integrated band-pass filter for fluorescence detection in miniaturised analytical systems
In this work, a new type of miniaturized fibre-coupled solid-state light source is demonstrated as an excitation source for fluorescence detection in capillary electrophoresis. It is based on a parabolically shaped micro- light emitting diode (”-LED) array with a custom band-pass optical interference filter (IF) deposited at the back of the LED substrate. The GaN ”-LED array consisted of 270 individual ”-LED elements with peak emission at 470nm, each about 14”m in diameter and operated as a single unit. Light was extracted through the transparent substrate material, and coupled to an optical fibre (400”m in diameter, numerical aperture NA = 0.37), to form an integrated ”-LED-IF-OF light source component. This packaged ”-LED-IFOF light source emitted approximately 225”W of optical power at a bias current of 20mA. The bandpass IF filter was designed to reduce undesirable LED light emissions in the wavelength range above 490 nm . Devices with and without IF were compared in terms of optical power output, spectral characteristics as well as LOD values. While the IF consisted of only 7.5 pairs (15 layers) of SiO2/HfO2 layers it resulted in an improvement of the baseline noise as well as the detection limit measured using fluorescein as test analyte, both by approximately one order of magnitude, with a LOD of 1Ă10-8 mol/L obtained under optimised conditions. The ”-LED-IF-OF light source was then demonstrated for use in capillary electrophoresis with fluorimetric detection. Limits of detection obtained by this device were compared to those obtained with a commercial fibre coupled LED device
Numerical Modelling of Light Propagation for Development of Capillary Electrophoretic and Photochemical Detection Systems
Versatile capillary column temperature control using a thermoelectric array based platform
A new direct contact platform for capillary column precise temperature control based upon the use of individually controlled sequentially aligned Peltier thermoelectric units is presented. The platform provides rapid temperature control for capillary and microbore liquid chromatography columns and allows simultaneous temporal and spatial temperature programming. The operating temperature range of the platform was between 15 and 200 0C for each of 10 aligned Peltier units, with a ramp rate of approximately 400 0C/min. The system was evaluated for a number of nonstandard capillary based applications, such as the direct application of temperature gradients with both linear and nonlinear profiles, including both static column temperature gradients and temporal temperature gradients, and the formation of in-capillary monolithic stationary phases with gradient polymerization through precise temperature control
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