Multianalyte imaging in one-shot format sensors for natural waters

Copper nanowire array as highly selective electrochemical sensor of nitrate ions in water

Contamination of water with nitrate ions is a significant problem that affects many areas of the world. For this reason, European legislation has set the maximum permissible concentration of nitrates in drinking water at 44 mg/L. Thus, it is clear that a continuous monitoring of nitrate ions is of high technological interest but it must be rapid, easy to perform and directly performable in situ. In this work we have developed a nanostructured sensor based on array of copper nanowires obtained with the simple method of galvanic deposition. The nanostructured sensors have a very short response time with a detection limit less than 10 μM. Different interfering species were tested finding a negligible effect except for the chloride ions. However, this problem has been solved by removing chloride ions from the water through a simple precipitation of chloride compounds with low solubility. Nanostructured sensors were also used to analyze real water samples (rain, river and drinking water). In the case of drinking water, we have measured a concentration of nitrate ions very close to the that measured by conventional laboratory techniques.

Optical Sensing with a Potentiometric Sensing Array by Prussian Blue Film Integrated Closed Bipolar Electrodes

The simultaneous optical readout of a potentiometric sensor array of ion-selective electrodes (ISEs) based on PVC membranes is described here for the first time. The optical array consists of electrochromic Prussian Blue (PB) films in multiple closed ion-selective bipolar electrodes (BPEs), which gives a physical separation between the optical detection and sample compartments. The potential-dependent turnover of PB generates Prussian White (PW). A near-Nernstian response of the PB film is confirmed by colorimetric absorbance experiments as a function of applied potential. In the combined bipolar electrode cell, the overall potential is kept constant with a single potentiostat over the entire array where each PB spot indicates the potential change of an individual connected potentiometric probe. For cation-selective electrodes, the absorbance or blue intensity of the connected PB film is enhanced with increasing target cation activity. The colorimetric absorbance changes are simultaneously followed by a digital camera and analyzed by Mathematica software. A multiple cation-BPE array allows one to achieve simultaneous quantitative analysis of potassium, sodium, and calcium ions, demonstrated here in highly colored fruit juices. Mass transport at the PB thin film is shown not to be rate-limiting. The measuring ranges can be tuned in a wide range by potential control. The PB film exhibits greatly improved reproducibility and stability as compared to previous work with a ferroin redox probe confined in a thin solution layer.

Printed disposable colorimetric array for metal ion discrimination

One of the main limiting factors in optical sensing arrays is the reproducibility in the preparation, typically by spin coating and drop casting techniques, which produce membranes that are not fully homogeneous. In this paper, we increase the discriminatory power of colorimetric arrays by increasing the reproducibility in the preparation by inkjet printing and measuring the color from the image of the array acquired by a digital camera, using the H coordinate of the HSV color space as the analytical parameter, which produces robust and precise measurements. A disposable 31 mm × 19 mm nylon membrane with 35 sensing areas with 7 commercial chromogenic reagents makes it possible to identify 13 metal ions and to determine mixtures with up to 5 ions using a two-stage neural network approach with higher accuracy than with previous approaches.

Fluorescent pH-sensitive nanoparticles in an agarose matrix for imaging of bacterial growth and metabolism

Living color: fluorescent pH-sensitive nanoparticles 12 nm in diameter were prepared and incorporated into agarose gel in a Petri dish to image pH changes during bacterial growth and metabolism.

State-of-the-art of (bio)chemical sensor developments in analytical Spanish groups

(Bio)chemical sensors are one of the most exciting fields in analytical chemistry today. The development of these analytical devices simplifies and miniaturizes the whole analytical process. Although the initial expectation of the massive incorporation of sensors in routine analytical work has been truncated to some extent, in many other cases analytical methods based on sensor technology have solved important analytical problems. Many research groups are working in this field world-wide, reporting interesting results so far. Modestly, Spanish researchers have contributed to these recent developments. In this review, we summarize the more representative achievements carried out for these groups. They cover a wide variety of sensors, including optical, electrochemical, piezoelectric or electro-mechanical devices, used for laboratory or field analyses. The capabilities to be used in different applied areas are also critically discussed.