Rapid warning microanalyzer for heavy metals monitoring in natural waters

Acord transformatiu CRUE-CSICA warning microanalyzer for the rapid monitoring of different heavy metals in water using Carbon Dots (CDs) as selective optical reagents is presented. The synthesized CDs have different surface functionalization and exhibit selective fluorescence quenching by heavy metal ions, that combined with the use of microfluidics, provide sensitivity, ease of automation and reproducibility to the method. Moreover, they present maximum excitation wavelengths around 350 nm, allowing multiparametric analysis with a single light source. Although quantum yields range from 16 % to 78 % depending on the type of CDs, enough sensitivity is achieved for each heavy metal using the same measurement conditions of the optical detection system (lock-in modulating frequency, signal amplitude and measurement frequency). The microanalyzer is composed of a Cyclic Olefin Copolymer (COC) analytical microsystem, a flow management system, and a miniaturized customized optical detection system. In this paper, we demonstrate that our proposed system can be used as a toxicity control system by selectively measuring five different heavy metal ions (Co, Cu, Hg, Ni, and Pb) with detection limits ranging from 2 to 12 ppb. Spiked tap water samples were analyzed, giving recoveries from 98 % to 134 %. Polluted samples containing four of the five heavy metal ions studied (Co, Cu, Ni, and Pb) were also analyzed with no significant differences observed between both methods, the proposed microanalyzer and the reference method (ICP-OES)

LTCC microflow analyzers with monolithic integration of thersmal control

Recently, the low temperature co-fired ceramics technology has shown to be an excellent alternative to silicon-based microfabrication techniques for the production of three-dimensional structures using a multi-layer approach. This enables the integration of several unitary operations of a classical analytical process and also the integration of sensors, actuators and electronics in the same substrate. In this work, we show the integration of the actuators and the sensors needed for the control of temperature inside a miniaturized fluidic device. The proposed device presents enough thermal accuracy to be used in chemical systems where temperature control is a crucial factor, such as enzyme reactions or polymerase chain reaction systems.The authors would like to thank the Spanish MEC for its financial support through: Consolider-Ingenio 2010 (CSD2006-00012), TEC2006-13907-C04-04/MIC and CIT-310200-2007-29. CSM is also thankful to the Alban Program (High-level grants from the European Union to Latin America for its financial support (Grant number: E05D053315MX)

Microreactor with integrates temperature control for the synthesis of CdSe nanocrystals

The recent needs in the nanosciences field have promoted the interest towards the development of miniaturized and highly integrated devices able to improve and automate the current processes associated to the efficient nanomaterials production. Herein, a green tape based microfluidic system to perform high temperature controlled synthetic reactions of nanocrystals is presented. The device, which integrates both, the microfluidics and a thermally controlled platform, was applied to the automated and continuoussynthesis of CdSe quantum dots. Since temperature can be accurately regulated as required, sizecontrolled and reproducible quantum dots could be obtained by regulating this parameter and the molar ratio of precursors. The obtained nanocrystals were characterized by UV-Vis and fluorescencespectrophotometries. The band width of the emission peaks obtained indicates a narrow size distribution of the nanocrystals, which confirms the uniform temperature profile applied for each synthetic process, being the optimum temperature at 270° C (Full Width at Half Maximum = 40 nm). This approach allows a temperature controlled, easy, low cost and automated way to produce quantum dots in organic media, enhancing its application from laboratory-scale to pilot-line scale processes.This work has been supported by the Spanish Ministry of Science and Innovation (MICINN) through projects CTQ2009-12128 and the Consolider Ingenio 2010 project CSD2006 -12 and Catalonia 15 Government through SGR 2009 -0323

Serum/plasma potassium monitoring using potentiometric point-of-care microanalyzers with improved ion selective electrodes

Different causes can trigger imbalances on homeostatic mechanisms between intracellular and extracellular compartments resulting in abnormal blood potassium concentrations (hypo or hyperkalemia). This can lead to serious consequences, even a life-threatening situation. Early diagnosis, treatment and follow-up are essential to minimize critical impacts in patients. Bedside determination of blood potassium is not accessible in all health care centers or in all emergency departments and far less common in this kind of centers in emerging countries. We have therefore proposed a portable, economic and long-lifetime potentiometric point-of-care (POC) analytical microsystem to deal with this question. It is a continuous flow microfluidic platform, made of cyclic olefin copolymer (COC), which combines microfluidics and a detection system based on the potentiometric technique containing a potassium selective electrode with a novel composition of polymeric membrane, which improves lifetime. Its size is smaller than a credit card and shows a linear range of Nernst calibration equation from 1 to 26 mM K+, a detection limit of 0.16 mM K+, a satisfactory repeatability and reproducibility, and an analysis frequency of 20 samples h−1, requiring only 25 μL as sample volume. Moreover, lifetime is as long as 9 months by intensive use. All these features comply with medical requirements. Human serum samples were analyzed with the developed device and the obtained results were compared with those provided by two methods: ICP-OES and another using ion selective electrodes. No significant differences were observed, demonstrating the suitability of the developed POC microanalyzer for bedside health applications

Design, fabrication and characterization of microreactors for high temperature syntheses

Microfluidic reactors offer many potential advantages in several research and industrial fields such as processes intensification, which includes a better reaction control (kinetics and thermodynamics), a high throughput and a safer operational environment (reduced manipulation of dangerous reagents and low sub-products generation). Nevertheless, scaling-down limitations appear concerning the materials used in the fabrication of microreactors for most of the liquid-phase reactions, since they usually require high temperatures (up to 300 °C), solvents and organic reagents. In this work, the development of a set of modular and monolithic microreactors based on the integration of microfluidics and a thermal platform (sensor/high-temperature heater) is proposed to perform high temperature reactions. The reliability and performance of both configurations were evaluated through an exhaustive characterization process regarding their thermal and microfluidic performance. Obtained results make the devices viable for their application in controlled and reproducible synthetic processes occurring at high temperatures such as the synthesis of quantum dots. The proposed microfluidic approach emerge as an engaging tool for processes intensification, since it provides better mass and temperature transfer than conventional methods with a reduction not only of the size and energy consumption, but also of by-products and reagents consumption.This work has been supported by the Spanish Ministry of Science and Innovation (MICINN) through projects CTQ2009-12128 and the Consolider Ingenio 2010 project CSD2006 -12 and Catalonia Government through SGR 2009 -0323

Live synthesis of selective carbon dots as fluorescent probes for cobalt determination in water with an automatic microanalyzer

Altres ajuts: acords transformatius de la UABA new strategy integrating the straight synthesis of carbon dots (CDs) and their direct use for the determination of heavy metals by means of fuorescence quenching is presented. The proposal consists of a modular analyzer, which includes a low temperature co-fred ceramics (LTCC) microreactor for the synthesis of CDs and a cyclic olefn copolymer (COC) microfuidic platform, which automatically performs a reverse fow injection analysis (rFIA) protocol for the determination of heavy metal ions in water by CD fuorescence quenching. As a proof of concept, nitrogen-doped CDs were synthesized from acrylic acid and ethylenediamine (ED) with quantum yields (QYs) of up to 44%, which are selective to cobalt. With the described system, we synthesized homogeneous CDs without the need for further purifcation and with the minimum consumption of reagents, and optimized fuorescence measurements can be performed with freshly obtained luminescent nanomaterials that have not undergone decomposition processes. They have an averagehydrodynamic diameter of 4.2±0.9 nm and maximum excitation and emission wavelengths at 358 nm and 452 nm, respectively. The system allows the automatic dilution and bufering of the synthesized CDs and the sample prior to the determination of cobalt. The concentration of cobalt was determined with good sensitivity and a limit of detection of 7 μg·L−1 with a linear range of 0.02-1 mg·L−1 of Co2+. Spiked tap water and river water samples were analyzed, obtaining recovery from 98 to 104%. This demonstrates the potential of the equipment as an efcient on-site control system for heavy metal monitoring in water

Porosity enhancement by the utilization of screening patterns in electro-perforated paper webs

In this work, a technique to enhance the porosity of electro-perforated paper webs using screening matrices is described. The proposed approach relies on the confining effect that acts on a train of sparks when forced to pass through a small hole pierced through a ceramic substrate located in-between two needle-like electrodes. It is shown how the maximum porosity level achievable by the electro-perforation process depends on the drag distance parameter. Since the proposed method is aimed at reducing the latter, an eventual enhancement of the number of perforations per unit area can be obtained. The method has been experimentally tested. It is worth mentioning the suitability of the matrix-aided paper perforation process for its use in industrial environments.Publicad

Bidimensional planar micro-optics for optochemical absorbance sensing

A new approach for developing optochemical absorbance sensors is presented. The method is based on a planar micro-optic circuit in which an optochemically active membrane that responds to selective compounds is deposited in the device, yielding a part of the guiding planar structure. In this way the optical field is confined in the direction transverse to the substrate and controlled in the lateral direction by means of planar micro-optics components. High sensitivity of the device can be easily obtained because of the relatively long light paths through the membrane, and the response time is low because the analyte has to diffuse through a several-micrometer-thin membrane. Experimental results of measurements of the concentration of potassium are also presented to verify the possibilities of these devices as specific absorbance sensors

A monolithic continuous-flow microanalyzer with amperometric detection based on the green tape technology

The development of micro total analysis systems (muTAS) has become a growing research field. Devices that include not only the fluidics and the detection system but also the associated electronics are reported scarcely in the literature because of the complexity and the cost involved for their monolithic integration. Frequently, dedicated devices aimed at solving specific analytical problems are needed. In these cases, low-volume production processes are a better alternative to mass production technologies such as silicon and glass. In this work, the design, fabrication, and evaluation of a continuous-flow amperometric microanalyzer based on the green tape technology is presented. The device includes the microfluidics, a complete amperometric detection system, and the associated electronics. The operational lifetime of the working electrode constitutes a major weak point in electrochemical detection systems, especially when it is integrated in monolithic analytical devices. To increase the overall system reliability and its versatility, it was integrated following an exchangeable configuration. Using this approach, working electrodes can be readily exchanged, according to the analyte to be determined or when their surfaces become passivated or poisoned. Furthermore, the electronics of the system allow applying different voltamperometric techniques and provide four operational working ranges (125, 12.5, 1.25, and 0.375 muA) to do precise determinations at different levels of current intensity.The authors would like to thank the Spanish MEC for its financial support through: Consolider-Ingenio 2010 (CSD2006-00012), TEC2006-13907-C04-04/MIC and CIT- 310200-2007-29

Compact and autonomous multiwavelength microanalyzer for in-line and in-situ colorimetric determinations

Nowadays, the attainment of microsystems that integrate most of the stages involved in an analytical process has raised an enormous interest in several research fields. This approach provides experimental set-ups of increased robustness and reliability, which simplify their application to in-line and continuous biomedical and environmental monitoring. In this work, a novel, compact and autonomous 10 microanalyzer aimed at multiwavelength colorimetric determinations is presented. It integrates the microfluidics (a three-dimensional mixer and a 25 mm length "Z-shape" optical flow-cell), a highly versatile multiwavelength optical detection system and the associated electronics for signal processing and drive, all in the same device. The flexibility provided by its design allows the microanalyzer to be operated 15 either in single fixed mode to provide a dedicated photometer or in multiple wavelength mode to obtain discrete pseudospectra. To increase its reliability, automate its operation and allow it to work under unattended conditions, a multicommutation sub-system was developed and integrated to the experimentalset-up. The device was initially evaluated in the absence of chemical reactions using four acidochromic dyes and later applied to determine some key environmental parameters such as phenol index, chromium 20 (VI) and nitrite ions. Results were comparable with those obtained with commercial instrumentation and allowed to demonstrate the versatility of the proposed microanalyzer as an autonomous and portable device able to be applied to other analytical methodologies based on colorimetric determinations.The authors would like to acknowledge the Spanish, Brazilian and Mexican authorities and agencies for its financial support through projects CTQ2009-12128, CONSOLIDER INGENIO2010-CSD2006-12, PHB2010-0064-PC (MEC-50 CAPES) and P509AC0376 (CYTED). Z.M da Rocha would like to acknowledge FAPESP (Project 2009/08486-4) for their financial support