Compact Detection System Research Articles

A simple and compact fluorescence detection system for capillary electrophoresis and its application to food analysis

A novel fluorescence detection system for CE was described and evaluated. Two miniature laser pointers were used as the excitation source. A Y-style optical fiber was used to transmit the excitation light and a four-branch optical fiber was used to collect the fluorescence. The optical fiber and optical filter were imported into a photomultiplier tube without any extra fixing device. A simplified PDMS detection cell was designed with guide channels through which the optical fibers were easily aligned to the detection window of separation capillary. According to different requirements, laser pointers and different filters were selected by simple switching and replacement. The fluorescence from four different directions was collected at the same detecting point. Thus, the sensitivity was enhanced without peak broadening. The fluorescence detection system was simple, compact, low-cost, and highly sensitive, with its functionality demonstrated by the separation and determination of red dyes and fluorescent whitening agents. The detection limit of rhodamine 6G was 7.7 nM (S/N = 3). The system was further applied to determine illegal food dyes. The CE system is potentially eligible for food safety analysis.

Side-entry laser-beam zigzag irradiation of multiple channels in a microchip for simultaneous and highly sensitive detection of fluorescent analytes.

A simple and highly sensitive technique for laser-induced fluorescence detection on multiple channels in a plastic microchip was developed, and its effectiveness was demonstrated by laser-beam ray-trace simulations and experiments. In the microchip, with refractive index nC, A channels and B channels are arrayed alternately and respectively filled with materials with refractive indexes nA for electrophoresis analysis and nB for laser-beam control. It was shown that a laser beam entering from the side of the channel array traveled straight and irradiated all A channels simultaneously and effectively because the refractive actions by the A and B channels were counterbalanced according to the condition nA < nC < nB. This technique is thus called "side-entry laser-beam zigzag irradiation". As a demonstration of the technique, when nC = 1.53, nA = 1.41, nB = 1.66, and the cross sections of both eight A channels and seven B channels were the same isosceles trapezoids with 97° base angle, laser-beam irradiation efficiency on the eight A channels by the simulations was 89% on average and coefficient of variation was 4.4%. These results are far superior to those achieved by other conventional methods such as laser-beam expansion and scanning. Furthermore, fluorescence intensity on the eight A channels determined by the experiments agreed well with that determined by the simulations. Therefore, highly sensitive and uniform fluorescence detection on eight A channels was achieved. It is also possible to fabricate the microchips at low cost by plastic-injection molding and to make a simple and compact detection system, thereby promoting actual use of the proposed side-entry laser-beam zigzag irradiation in various fields.

Compact and modular multicolour fluorescence detector for droplet microfluidics.

Multicolour fluorescence detection is often necessary in droplet microfluidics, but typical detection systems are complex, bulky, and expensive. We present a compact and modular detection system capable of sub-nanomolar sensitivity utilizing an optical fibre array to encode spectral information recorded by a single photodetector.

Electrically pumped semiconductor laser with monolithic control of circular polarization

We demonstrate surface emission of terahertz (THz) frequency radiation from a monolithic quantum cascade laser with built-in control over the degree of circular polarization by "fishbone" gratings composed of orthogonally oriented aperture antennas. Different grating concepts for circularly polarized emission are introduced along with the presentation of simulations and experimental results. Fifth-order gratings achieve a degree of circular polarization of up to 86% within a 12°-wide core region of their emission lobes in the far field. For devices based on an alternative transverse grating design, degrees of circular polarization as high as 98% are demonstrated for selected far-field regions of the outcoupled THz radiation and within a collection half-angle of about 6°. Potential and limitations of integrated antenna gratings for polarization-controlled emission are discussed.

A compact high-resolution elastic recoil detection system for lithium depth profiling

A compact high-resolution elastic recoil detection analysis (ERDA) system was developed for precise Li analysis. 200–400keV He+ ions were used as primary ions and the energy spectra of recoiled Li ions were measured using a magnetic spectrometer. Due to its dispersion the background originating from the scattered primary ions is reduced. The recoiled ions of the substrate other than Li, which may also contribute to the background, were rejected by a thin mylar foil placed in front of a focal plane detector. An electrostatic quadrupole lens was installed at the entrance of the magnetic spectrometer to improve the depth resolution by correcting the effect of the kinematic broadening. The performance of the developed high-resolution ERDA was examined by measuring several samples. A thin Li layer (1.5×1015cm−2) deposited on a graphite surface was clearly observed and the detection limit was estimated to be less than 0.01ML under typical measurement conditions. The depth resolution was estimated to be 0.5nm at the surface and was better than 3nm in the surface region within 5nm from the surface.

Radiation characteristics of terahertz waveguide‐fed circularly polarised antipodal exponentially tapered slot antenna

A terahertz (THz) waveguide-fed circularly polarised (CP) antipodal exponentially tapered slot antenna (AETSA) is designed, fabricated and measured. This antenna is fed by a WR2.2 rectangular waveguide. The integrated AETSA is fabricated by deep reactive-ion etching on silicon wafers, gold-sputtering and gold–gold thermo-compression bonding. Optimised exponential curves are introduced to the profiles of tapered slots to realise the CP performance. The measured radiation patterns at 490 GHz show beamwidths of 42° and 39° in the 0°-plane and 90°-plane, with low sidelobes. Furthermore, the measured axial ratios (ARs) from 480 to 500 GHz are lower than 2 dB. The THz waveguide-fed CP AETSA has potential to be applied in compact THz imaging, detection and communication systems.

A Multichannel Integrated Readout Circuit for High Throughput X-Ray Spectroscopy With Silicon Drift Detectors

In this paper, we describe a front-end ASIC for the readout of multi-elements Silicon Drift Detectors (SDDs) specifically designed for high count-rate X-ray spectroscopy applications. In particular, the focus of this design is on the maximization of the event throughput and, at the same time, keeping a high energy resolution. The readout of a detector array by means of 8 separate channels allows increasing the maximum count-rate of the system. The use of one or more of these front-end ASICs allows the management of several readout channels required by a multi-SDD detector within a very compact detection system, as well as maintaining excellent noise performance. The use of a very-fast high-order processing filter and of an efficient pile-up rejection strategy allows minimizing the pile-up probability and maximizing the event throughput of the single channels for a given processing time. The use of a 3-phase peak-stretcher, together with a fast output multiplexer, permits to minimize the dead-time during the valid-data acquisition, practically to a value limited by the pure overlap of the shaped pulses. The ASIC is designed with the possibility of operating with the input JFET integrated on the detector itself as well as to operate in combination with an external preamplifier. The measured noise-contribution added by the front-end ASIC is only 2.9 electrons at 1.8 μs shaping time and just 4.1 electrons at the shortest 600 ns peaking time, exploiting at best the speed capability. In X-ray spectroscopy measurements, the ASIC connected to an SDD coupled to a CMOS preamplifier has allowed to achieve an energy resolution of 126 eV at 1.5 μs peaking time and 115 kcps/channel input rate, and 144 eV at 600 ns peaking time and 800 kcps/channel input rate.

A low-cost 2D fluorescence detection system for μm sized beads on-chip

In this paper we describe a compact fluorescence detection system for on-chip analysis of beads, comprising a low-cost optical HD-DVD pickup. The complete system consists of a fluorescence detection unit, a control unit and a microfluidic chip containing microchannels and optical markers. With these markers the laser beam of the optical pickup can be automatically focused at the centre of the microchannel. With the complete system a two-dimensional fluorescent profile across the channel width can be obtained such that there is no need for hydrodynamic or electrokinetic focusing of the particles in a specific part of the channel. Fluorescent μm sized beads suspended in medium have been detected with the system. Since on both sides of the main beam two additional laser beams at a known distance are generated, also the velocity of individual beads has been determined.

Multicolour LED in luminescence sensing application

Light emitting diodes (LEDs) are in general used as light sources with nearly monochromatic spectral characteristic. Beyond this typical application, they can work as light sensing devices. In this case, their spectral response has the property of an optical band pass filter. As an application we present a sensor for the measurement of environmental properties like temperature and pressure based on the temperature and oxygen dependent luminescence decay of some luminescence materials. Herein, a multicolour LED is used as a compact excitation and detection system. Furthermore, we have investigated the spectral absorption characteristics and the responsivity of standard LEDs working as light detectors and compared them with photodiode based detectors.

Highly sensitive fluorescence detection system for microfluidic lab-on-a-chip

We demonstrate a compact, low cost and practical fluorescence detection system for lab-on-a-chip applications. The system comprises a commercially available InGaN light emitting diode (501 nm) as light source, an organic or silicon photodiode detector, absorptive dye coated colour filters and linear and reflective polarisers. An injection moulded polystyrene microfluidic chip is used as the platform for fluorescence immunoassays for cardiac markers myoglobin and CK-MB. The optical limit of detection (LOD) is measured using a TransFluoSphere® suspension at 5.6 × 10(4) beads µl(-1) which can be equated to ∼3 nM fluorescein equivalent concentration. The LOD for the human plasma immunoassays is measured as 1.5 ng ml(-1) for both myoglobin and CK-MB.

Performance of a digital CdTe X-ray spectrometer in low and high counting rate environment

The high performances of CdTe detectors for X-ray and gamma ray spectroscopy are already well known. Among the traditional semiconductor spectrometers, CdTe detectors show high detection efficiency and good room temperature performance and are well suited for the development of compact detection systems. In this work, we investigated the performance of a CdTe detector coupled with a custom digital pulse processing (DPP) system for X-ray spectroscopy. The DPP method, implemented on a PC platform, performs a pile-up inspection and a pulse height analysis of the preamplifier output pulses, digitized by a 14-bit, 100MHz ADC. The spectroscopic results point out the excellent performance of the digital spectrometer both at low (150cps) and at high photon counting rate (up to 370kcps), confirming the high potentialities of CdTe detectors coupled with DPP systems. The detector and the DPP system were developed by our collaboration as a spectrometer prototype for direct measurement of diagnostic X-ray spectra in the 1–40keV energy range.

Thin-film organic photodiodes for integrated on-chip chemiluminescence detection – application to antioxidant capacity screening

We demonstrate that solution processed thin-film organic photodiodes (OPDs) can be used as compact and sensitive integrated detectors for antioxidant capacity screening. The OPDs were fabricated with blends of regioregular poly(3-hexylthiophene) (P3HT) and (6,6)-phenyl C 61 butyric-acid methyl-ester (PCBM). The devices had a broadband photoresponse from 350 nm to 650 nm with a peak responsivity of 0.25 A/W at 550 nm and a dark current density of 0.59 μA/cm 2 under 10 mV bias for a device area of 1 mm 2. The signal rise and fall times of the detectors were 0.51 μs and 0.66 μs, respectively. The detectors were applied to an on-chip peroxyoxalate chemiluminescence (PO-CL) assay for antioxidant capacity determination. Antioxidant standards were injected into a stream of PO-CL reagents, resulting in a CL emission decrease that correlated with the antioxidant capacity. For the encountered CL signals the OPDs provided a comparable response to photomultiplier tubes (PMTs) commonly used in analytical applications. Antioxidant capacity screening results showed excellent consistency between the two detection methods. The compact and portable detection system is suited not only to low-cost in-the-field antioxidant capacity screening, but could have wider applications for chemiluminescence based diagnostic tests at the point-of-care.

Progress in the Development of CdTe and CdZnTe Semiconductor Radiation Detectors for Astrophysical and Medical Applications

Over the last decade, cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe) wide band gap semiconductors have attracted increasing interest as X-ray and gamma ray detectors. Among the traditional high performance spectrometers based on silicon (Si) and germanium (Ge), CdTe and CdZnTe detectors show high detection efficiency and good room temperature performance and are well suited for the development of compact and reliable detection systems. In this paper, we review the current status of research in the development of CdTe and CdZnTe detectors by a comprehensive survey on the material properties, the device characteristics, the different techniques for improving the overall detector performance and some major applications. Astrophysical and medical applications are discussed, pointing out the ongoing Italian research activities on the development of these detectors.

A compact and portable laser-induced breakdown spectroscopy instrument for single and double pulse applications

We present LIBS experimental results that demonstrate the use of a newly developed, compact, versatile pulsed laser source in material analysis related to art and archaeological applications in view of research aiming at the development of portable LIBS instrumentation. LIBS qualitative analysis measurements were performed on various samples and objects, and the spectra were recorded in gated and non-gated modes. The latter is important because of advantages arising from size and cost reduction when using simple, compact spectrograph-CCD detection systems over the standard ICCD-based configurations. The new laser source exhibited a very reliable performance in terms of laser pulse repeatability, autonomy and interface. Having the ability to work in double pulse mode it provided versatility in the measurements leading to increased LIBS signal intensities, improved the signal-to-noise ratio and the RSD of the spectra. The first test results are encouraging and demonstrate that this new laser is suitable for integration in compact, portable LIBS sensors with a wide spectrum of materials analysis applications.

Analysis of Lead Ions in a Waste Solution Using Infrared Photo-Diode Electrode.

To detect lead ions using electrochemical voltammetric analysis, Infrared Photo-Diode Electrode (IPDE) was applied via cyclic and square wave stripping voltammetry. Lead ions were deposited at 0.5 V (versus Ag/AgCl) accumulation potential. Instrumental measurements systems were made based on a simple and compact detection system. The stripping voltammetric and cyclic voltammetric optimal parameters were searched. The results yielded a cyclic range of 40∼240 mgl−1 Pb(II) and a square wave stripping working range of 0.5∼5.00 mgl−1 Pb(II). The relative standard deviation at 2 and 4 mgl−1 Pb(II) was 0.04% and 0.02% (n = 15), respectively, using the stripping voltammetric conditions. The detection limit was found to be 0.05 mgl−1 with a 40 sec preconcentration time. Analytical interference ions were also evaluated. The proposed method was applied to determine lead ions in various samples.

Fibre-optic UV systems for gas and vapour analysis

The identification and quantification of compounds in the gas phase becomes of increasing interest in the context of environmental protection, as well as in the analytical field. In this respect, the high extinction coefficients of vapours and gases in the ultraviolet wavelength region allow a very sensitive measurement system. In addition, the increased performance of the components necessary for setting up a measurement system, such as fibres, light sources and detectors has been improved. In particular the light sources and detectors offer improved stability, and the deep UV performance and solarisation resistance of fused silica fibres allow have been significantly optimized in the past years. Therefore a compact and reliable detection system with high measuring accuracy is developed. Within this paper possible applications of the system under development and recent results will be discussed.

Measurement of pH and dissolved oxygen within cell culture media using a hydrogel microarray sensor

Abstract The sensing of analytes in cell culture media without the introduction of exogenous reagents proves difficult in today's cell culturing systems. In this paper, a completely embeddable microarray sensor that has been developed along with a compact fluorescent imaging system to sense oxygen and pH non-invasively is described. The compact detection system consists of an ultra-bright blue diode source, coupling optics, interference filters and a compact moisture resistant CCD camera. The microarray sensor was created by photoreaction injection molding and contains two separate sensing elements. The system was constructed and the array tested using simple spiked buffer solutions and complex cell media. In addition, the system was coupled to a bioreactor and tested over 2 weeks. The standard error of prediction during a bioprocess for both oxygen and pH detection was 0.75% and 0.092, respectively. The time response of the sensor in the designed flow-through arrangement was less than 90 s for both pH and oxygen, well within that needed for cell culture monitoring. Overall, this sensing approach has promise as a lab-on-a-chip type sensor for complete sensing of the culture environment and eventually may be used in a feedback system that allows monitoring and control without human intervention.

Integration of optical fiber light guide, fluorescence detection system, and multichannel disposable microfluidic chip

A combination of fluorescence detection and microfluidic technology provides promising applications in life sciences. A prototype of an integrated fluorescence detection system and optical fiber light guide on a laminate-based multichannel microfluidic chip has been developed and tested. A blue LED, plastic optical fiber, photodiode, Mylar and PMMA, and fluorescein and BSA-FITC were used as an excitation source, light coupler and guide, detector, microfluidic substrate and sample, respectively. The results show that the system is capable of detecting weak fluorescence emission from a fluorescein solution at concentration down to 0.01 ng/ml, and gives linear response. The results were also reproducible, and no cross-talk between adjacent channels was observed. The test using BSA as a model analyte demonstrates its feasibility for on-chip immunosensor applications. The performance and applications can be developed further. This prototype can be used as a platform to develop a simple and compact bio-fluorescence detection system integrated with an inexpensive and disposable multichannel microfluidic chip for biomedical devices.

Compact wavelength detection system incorporating a guided-mode resonance filter

The authors demonstrate a compact system for the detection of the peak wavelength value emitted by a light source. The system is composed of only two components, a graded-wavelength guided-mode resonance filter placed before a charge-coupled device sensor array. The filter provides a spatially resolved transmission minimum, the position of which is controlled by the wavelength of the incoming light. The sensor array collects the spatially resolved transmitted intensity and the wavelength is determined by recording the position of the transmission minimum along its length. Using this technique, wavelength changes as small as 0.011nm can be detected.

Parallel Detection of Si-Based Microcantilevers Resonant Frequencies Using Piezoresistive Signals Downmixing Scheme

Piezoresistive microcantilevers were developed to be used as displacement or force sensors associated with self-detection onboard electronic systems. The aim of this work was to realize a parallel integrated and compact detection system without the need for an optical readout scheme. The electronics developed specifically for this application, when dynamically operated, allows us to measure each piezoresistive microcantilever resonance frequency (by achieving at the same time an enhancement of the quality factor) with an accuracy of 0.1 Hz