Fernando Benito-Lopez

Smartphone-Based Simultaneous pH and Nitrite Colorimetric Determination for Paper Microfluidic Devices

In this work, an Android application for measurement of nitrite concentration and pH determination in combination with a low-cost paper-based microfluidic device is presented. The application uses seven sensing areas, containing the corresponding immobilized reagents, to produce selective color changes when a sample solution is placed in the sampling area. Under controlled conditions of light, using the flash of the smartphone as a light source, the image captured with the built-in camera is processed using a customized algorithm for multidetection of the colored sensing areas. The developed image-processing allows reducing the influence of the light source and the positioning of the microfluidic device in the picture. Then, the H (hue) and S (saturation) coordinates of the HSV color space are extracted and related to pH and nitrite concentration, respectively. A complete characterization of the sensing elements has been carried out as well as a full description of the image analysis for detection. The results show good use of a mobile phone as an analytical instrument. For the pH, the resolution obtained is 0.04 units of pH, 0.09 of accuracy, and a mean squared error of 0.167. With regard to nitrite, 0.51% at 4.0 mg L(-1) of resolution and 0.52 mg L(-1) as the limit of detection was achieved.

Organic electrochemical transistor incorporating an ionogel as a solid state electrolyte for lactate sensing

Room temperature Ionic liquids (RTILs) have evolved as a new type of solvent for biocatalysis, mainly due to their unique and tunable physical properties.[1] In addition, within the family of organic semiconductor-based sensors, organic electrochemical transistors (OECTs) have attracted particular interest.[2] Here, we present a simple and robust biosensor, based on a OECT, capable of measuring lactic acid using a gel-like polymeric materials that endow RTIL (ionogel)[3] as solid-state electrolyte both to immobilise the enzyme and to serve as a supporting electrolyte.[4] This represents the first step towards the achievement of a fast, flexible, miniaturised and cheap way of measuring lactate concentration in sweat.

Substantial rate enhancements of the esterification reaction of phthalic anhydride with methanol at high pressure and using supercritical CO2 as a co-solvent in a glass microreactor

The esterification reaction of phthalic anhydride with methanol was performed at different temperatures in a continuous flow glass microreactor at pressures up to 110 bar and using supercritical CO(2) as a co-solvent. The design is such that supercritical CO(2) can be generated inside the microreactor. Substantial rate enhancements were obtained, viz. a 53-fold increase was obtained at 110 bar and 60 degrees C. Supercritical CO(2) as a co-solvent gave rise to a 5400-fold increase (both with respect to batch experiments at 1 bar at the same temperature).

Self-protonating spiropyran-co-NIPAM-co-acrylic acid hydrogel photoactuators

Up to now, photoresponsive hydrogels and ionogels based on poly(N-isopropylacrylamide) copolymerised with pendant spiropyran groups require exposure to external acidic solution (usually milimolar HCl) to generate the swollen gel prior to photo-triggered contraction. This serious functional limitation has been solved by copolymerising acrylic acid into the gel matrix, to provide an internal source of protons. Due to the relative pKa values of acrylic acid and the spiropyran and merocyanine isomers, the protonation and deprotonation occurs internally within the gel and there is no need for an external source of protons. Furthermore, the shrinking–expansion cycles of these gels in deionised water are repeatable, as protonation throughout the gel does not rely on movement of protons from an external acidic solution into the bulk gel. In contrast to previous formulations, these gels do not show degradation of their photo-induced shrinking ability after multiple washings in deionised water and repeated switching over a 2 month period.

Materials science and the sensor revolution

For the past decade, we have been investigating strategies to develop ways to provide chemical sensing platforms capable of long-term deployment in remote locations 1 , 2 , 3 . This key objective has been driven by the emergence of ubiquitous digital communications and the associated potential for widely deployed wireless sensor networks (WSNs). Understandably, in these early days of WSNs, deployments have been based on very reliable sensors, such as thermistors, accelerometers, flow meters, photodetectors, and digital cameras. Biosensors and chemical sensors (bio/chemo-sensors) are largely missing from this rapidly developing field, despite the obvious value offered by an ability to measure molecular targets at multiple locations in real-time. Interestingly, while this paper is focused on the issues with respect to wide area sensing of the environment, the core challenge is essentially the same for long-term implantable bio/chemo-sensors 4 , i.e.; how to maintain the integrity of the analytical method at a remote, inaccessible location?

Spiropyran polymeric microcapillary coatings for photodetection of solvent polarity.

Fused silica microcapillaries were functionalized with spiropyran-polymer brushes using surface-initiated ring-opening metathesis polymerization. Based on the inherited spiropyran properties, the functionalized capillaries were successfully used to photoidentify solvents of different polarity when passing through the microcapillary in continuous flow. In the present study, six different solvents (toluene, tetrahydrofuran, acetone, acetonitrile, ethanol, and methanol) can be easily detected while passing through the modified microcapillary by simply irradiating a portion of it with UV light (365 nm). This converts the closed spiropyran moiety to the open merocyanine form, and as a consequence, the microcapillary gains a distinct color and spectral response depending on the polarity of the solvent. The rate of ring-opening of the spiropyran-polymer brushes coatings has been determined in situ in the presence of different solvents, showing that the coloration rate is also influenced by the solvent polarity and therefore can be used as an additional parameter for solvent sensing.

A new light emitting diode-light emitting diode portable carbon dioxide gas sensor based on an interchangeable membrane system for industrial applications.

A new system for CO(2) measurement (0-100%) based on a paired emitter-detector diode arrangement as a colorimetric detection system is described. Two different configurations were tested: configuration 1 (an opposite side configuration) where a secondary inner-filter effect accounts for CO(2) sensitivity. This configuration involves the absorption of the phosphorescence emitted from a CO(2)-insensitive luminophore by an acid-base indicator and configuration 2 wherein the membrane containing the luminophore is removed, simplifying the sensing membrane that now only contains the acid-base indicator. In addition, two different instrumental configurations have been studied, using a paired emitter-detector diode system, consisting of two LEDs wherein one is used as the light source (emitter) and the other is used in reverse bias mode as the light detector. The first configuration uses a green LED as emitter and a red LED as detector, whereas in the second case two identical red LEDs are used as emitter and detector. The system was characterised in terms of sensitivity, dynamic response, reproducibility, stability and temperature influence. We found that configuration 2 presented a better CO(2) response in terms of sensitivity.

Fast prototyping of paper-based microfluidic devices by contact stamping using indelible ink

Here we present a fast and cheap prototyping technique for the realisation of paper-based microfluidic devices simply by using a stamp and indelible ink. The proposed mechanism involves contact stamping of indelible ink to laboratory filter paper using a PDMS stamp, which defines the microfluidic structure. It is a cleanroom and washing steps-free method which provides a reproducible method for the production of functional paper-based microfluidic devices in a single step in less than 10 s. The method is fully characterised and the concept has been applied, as a proof-of-principle, for the realisation of a low-cost colorimetric glucose sensor.

Portable integrated microfluidic analytical platform for the monitoring and detection of nitrite.

A wireless, portable, fully-integrated microfluidic analytical platform has been developed and applied to the monitoring and determination of nitrite anions in water, using the Griess method. The colour intensity of the Griess reagent nitrite complex is detected using a low cost Paired Emitter Detector Diode, while on-chip fluid manipulation is performed using a biomimetic photoresponsive ionogel microvalve, controlled by a white light LED. The microfluidic analytical platform exhibited very low limits of detection (34.0±0.1 μg L(-1) of NO2(-)). Results obtained with split freshwater samples showed good agreement between the microfluidic chip platform and a conventional UV-vis spectrophotometer (R(2)=0.98, RSD=1.93% and R(2)=0.99, RSD=1.57%, respectively). The small size, low weight, and low cost of the proposed microfluidic platform coupled with integrated wireless communications capabilities make it ideal for in situ environmental monitoring. The prototype device allows instrument operational parameters to be controlled and analytical data to be downloaded from remote locations. To our knowledge, this is the first demonstration of a fully functional microfluidic platform with integrated photo-based valving and photo-detection.

CMAS: fully integrated portable centrifugal microfluidic analysis system for on-site colorimetric analysis

A portable, wireless system capable of in situ reagent-based colorimetric analysis is demonstrated. The system is based on a reconfigurable low cost optical detection method employing a paired emitter detector diode device, which allows a wide range of centrifugal microfluidic layouts to be implemented. Due to the wireless communication, acquisition parameters can be controlled remotely and results can be downloaded in distant locations and displayed in real time. The stand-alone capabilities of the system, combined with the portability and wireless communication, provide the flexibility crucial for on-site water monitoring. The centrifugal microfluidic disc presented here is designed for nitrite detection in water samples, as a proof of principle. A limit of detection of 9.31 ppb, along with similar coefficients of correlation and precision, were obtained from the Centrifugal Microfluidic Analysis System compared with the same parameters measured using a UV-Vis spectrophotometer.