Carrier-based polymeric membrane potentiometric sensors have been widely used for determination of inorganic ions in clinical and environmental applications. In view of the need for a wider application scope of these sensors, the list of targets needs to be increased. Molecularly imprinted polymer (MIP)-based potentiometric sensors are ideal candidates for sensing of organic and biological species. The development of such sensors may open attractive horizons for potentiometric sensing and further expand the field. The past few decades have witnessed remarkable achievements in these sensors. This review summarizes recent advances in the MIP synthesis, the detection modes of these sensors and their applications for organic and biological species in environmental and biological analyses, and attempts to illustrate the research directions. We hope that this review will shed new light on the understanding of MIP-based potentiometric sensors and pave the way for the widespread applications of polymeric membrane potentiometric sensors.

Molecularly imprinted polymer-based potentiometric sensors

This study reports a new chemical sensor based on ion-imprinted polymer matrix using copper nanoparticles-polyaniline nanocomposite (IIP-Cu-NPs/PANI). This sensor was prepared by electropolymerization using aniline as a functional monomer and nitrate as template onto the copper nanoparticles-modified glassy carbon (GC) electrode surface. Both ion-imprinted (IIP) and nonimprinted (NIP) electrochemical sensor surfaces were evaluated using UV-Visible spectrometry and scanning electron microscopy (SEM). The electrochemical analysis was made via cyclic voltammetry (CV), linear sweep voltammetry (LSV), and impedance spectroscopy (IS). Throughout this study various analytical parameters, such as scan rate, pH value, concentration of monomer and template, and electropolymerization cycles, were optimized. Under the optimum conditions, the peaks current of nitrate was linear to its concentration in the range of 1μM-0.1M with a detection limit of 31μM and 5μM by EIS and LSV. The developed imprinted nitrate sensor was successfully applied for nitrate determination in different real water samples with acceptable recovery rates.

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Ion-Imprinted Electrochemical Sensor Based on Copper Nanoparticles-Polyaniline Matrix for Nitrate Detection

Development and deployment of sensing technologies is one of the main steps in achieving sustainability in crop production through precision agriculture. Key sensing methodologies developed for monitoring soil moisture and nutrients with recent advances in the sensing devices reported in literature using those techniques are overviewed in this article. The soil moisture determination has been divided into four main sections describing soil moisture measurement metrics and laboratory-based testing, followed by in-situ, remote and proximal sensing techniques. The application, advantages and limitations for each of the mentioned technologies are discussed. The nutrient monitoring methods are reviewed beginning with laboratory-based methods, ion-selective membrane based sensors, bio-sensors, spectroscopy-based methods, and capillary electrophoresis-based systems for inorganic ion detection. Attention has been given to the core principle of detection while reporting recent sensors developed using the mentioned concepts. The latest works reported on the different sensing methodologies point towards the trend of developing low-cost, easy to use, field-deployable or portable sensing systems aimed towards improving technology adoption in crop production leading to efficient site-specific soil and crop management which in turn will bring us closer to reaching sustainability in the practice of agriculture.

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Sensing Methodologies in Agriculture for Soil Moisture and Nutrient Monitoring

A facile co-precipitation technique is used in the synthesis of pure ZnO and Y-doped (5, 10 and 15 wt.%) ZnO nanostructures (YZO) and fabricated by using electron beam deposition over a glass substrate. The crystal morphological features of pure ZnO and YZO nanoparticles (NPs) were characterized by XRD (x-ray diffraction), CV (cyclic voltammetry), SEM (scanning electron microscopy), UV–visible spectroscopy and PL (photoluminescence) spectroscopic techniques. Drastic change in the crystalline phase and morphology is observed as a result of Y+3 doping. The polar surface area of Zn 2+ vanished due to charge compensation Y3+ which in turn responsible for transition in morphology of pure ZnO from hexagonal to spherical shape (YZO). In comparison with pure ZnO NPs, Y-doped ZnO exhibited better ammonia gas sensing properties. The selectivity and sensitivity of 150 ppm of ammonia gas at 250 °C for 15 wt.% of YZO were comparatively higher than pure ZnO nanostructures. The response and recovery time of 15 wt.% of YZO was 58 s and 87 s, respectively. The gas sensor YZO nanostructures exhibited better selectivity toward ammonia gas compared with the other volatile gases such as methane, hydrogen sulfide, ethylene, chloroform. The selectivity and sensor features of Y-doped ZnO were experimentally analyzed.

Synthesis and Fabrication of Y-Doped ZnO Nanoparticles and Their Application as a Gas Sensor for the Detection of Ammonia

Nutrients such as nitrogen and phosphorus are key indexes in evaluating water eutrophication. Electronic sensors, i.e., potentiometric sensors, voltammetric sensors, and field-effect transistor (FET) sensors, that rely on electrical signals (e.g., potential, current and resistance) have shown unique properties and capabilities in detecting nutrients. Compared with conventional methods, these electronic sensors enable a rapid and low-level detection of nitrogen salts and phosphates in water. Over the past decades various sensor designs and sensing elements have been studied and reported. With the development of nanomaterials, the performance of electronic sensors has been further improved, presenting tremendous opportunities for detecting nutrients and other water contaminants. This review article will introduce the recent progress of electronic sensors in detecting nitrogen salts and phosphates, and will discuss current limitations and future directions for these sensors.

Rapid detection of nutrients with electronic sensors: a review

A poly(N-methylpyrrole) based ion selective electrode (ISE) has been prepared by electro-polymerization of N-methylpyrrole using potassium nitrate as the supporting electrolyte. Electrochemical and chemical variables were used to optimize the potentiometric response of the electrodes and to maximize the selectivity for nitrate over potential interferences. The selectivity, longevity and stability of the ion-imprinted polymer give this electrode advantages over traditional nitrate ISEs. The best prototype electrode exhibits a linear potential response to nitrate ion within the concentration range of 5.0 × 10−6 to 0.1 M nitrate with a near Nernstian slope of −56.3 mV per decade (R2 = 0.9998) and a strong preference for the nitrate ion over other anions. The selectivity coefficients of the electrode were evaluated by the fixed interference method. The use of N-methylpyrrole has advantages over pyrrole in terms of selectivity and pH insensitivity.

Ellen M. Bomar

Papers

Nitrate Ion Selective Electrode Based on Ion Imprinted Poly(N-methylpyrrole)