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Nanomaterials with enzyme-like characteristics (also called nanozymes) have attracted increasing attention in the area of analytical chemistry. Nevertheless, most of the nanozymes used for analytical applications are oxidoreductase mimics, and their enzyme-like activities are usually demonstrated by using chromogenic and/or fluorogenic substrates. Herein, the phosphatase mimetic activity of cerium oxide nanoparticles (nanoceria) was investigated by using CDP-star as the chemiluminescent (CL) substrate. Interestingly, we found that the phosphatase mimetic activity of nanoceria can be remarkably inhibited by the addition of Al 3+ . Based on this finding, a highly sensitive and selective CL method for Al 3+ detection is proposed. The CL intensity of the nanoceria/CDP-star system decreased with the increasing Al 3+ concentrations in the range from 30 nM to 3.5 μM. A detection limit as low as 10 nM was obtained. Finally, the CL detection of intracellular Al 3+ was achieved, demonstrating the utility of the CL method in complex biological samples., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

We report on facile synthesis and characterization of phosphate-functionalized polymer dots (PDs) by doping tributyl phosphate (TBP) in a semiconducting polymer poly[9,9-dioctylfluorenyl-2,7-diyl)-co-1,4-benzo-{2,10-3}-thiadiazole)] (PFBT). Then, the prepared TBP@PFBT PDs were used to develop a very high sensitive probe for detection Fe 3+ , Cu 2+ ions and Cytochrome c based on aggregation induced fluorescence off mechanism. The PDs exhibited a linear dynamic range for Fe 3+ from 0.1 to 2 nM with a detection limit of 30 pM and for Cu 2+ from 2.0 to 50.0 nM with a detection limit of 0.35 nM. Meanwhile, this probe showed a linear dynamic range for Cyt c from 175 to 1750 pM with a detection limit of 32.7 pM. The TBP@PFBT PDs is a simple, one-step, fast, non-invasive, label-free, and inexpensive probe that is capable of online apoptosis monitoring response to drugs with an ever-present opportunity to contribute in a variety of in-vitro and in-vivo biological applications. We also obtained sharp, specific 2D and 3D imaging results for early stage apoptosis in breast cancer cells. Moreover, this technique possesses the advantage of rapid determination of Fe 3+ ion in biological or environmental samples. Importantly, this label-free assay provides short determination time of only a few min, easy operation and very low LOD allowing 100-4000 times increased in sensitivity over previously reported probes, together with high selectivity without need to using biorecognition elements like enzymes, antibodys and/or aptamers. Such excellent features make the TBP@PFBT PDs an excellent probe for successful apoptosis imaging in live cells., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Graphene quantum dot (GQD) has been attractive in analytical science field due to its low toxicity, stable photoluminescence. Herein, nitrogen-doped GQD (N-GQD) was prepared by a facile solvothermal treatment of GO using dimethylformamide, and exhibited a green emission with 23.1% quantum yield. The N-GQD probe showed a selective and sensitive fluorescence enhancement response to Al 3+ , the mechanism might be the formation of a complex between Al 3+ and N-GQD constrained the photo-induced electron transfer (PET) process of N-GQD itself. With Benesi-Hildebrand equation, the binding constant and molar ratio between N-GQD and Al 3+ was calculated to be 4.6 × 10 4 Lmol -1 and 1:1 respectively. The pK a value of N-GQD was also determined to be 4.4 by capillary electrophoresis. In pH 4.0 PBS solution, there was a good linear relation between the fluorescence intensity and the logarithm of concentration of Al 3+ in the range of 2.5-75μmolL -1 , the limit of detection (3σ) was 1.3μmolL -1 . This "Off - On" fluorescence method had been applied to accurate quantification of aluminum in hydrotalcite tablets. What's more, the fluorescence switch property of N-GQD was explored by alternate addition of Al 3+ and EDTA. The probe was also utilized for detection Al 3+ in living cells due to its excellent biocompatibility., (Copyright © 2017 Elsevier B.V. All rights reserved.)

This article aims to establish the judicious use of iron-binding chemistry of microbial chelators in order to functionalize the surface of iron nanoparticles to develop non-toxic nanobiosensor. Anchoring a simple siderophore 2,3-dihydroxybenzoylglycine (H 3 L), which bears catechol and carboxyl functionalities in tandem, on to the surface of Fe 3 O 4 nanoparticles has developed a unique nanobiosensor HL-FeNPs which showed highly selective and sensitive detection of Al 3+ in 100% water at physiological pH. The biosensor HL-FeNPs, with 20nM limit of detection, behaves reversibly and instantly. In-vivo bio-imaging in live brine shrimp Artemia confirmed that HL-FeNPs could be used as fluorescent biomarker for Al 3+ in live whole organisms. Magnetic nature of the nanosensor enabled HL-FeNPs to remove excess Al 3+ by using external magnet. To our knowledge, the possibility of microbial chelator in the practical development of Al 3+ selective nanobiosensor is unprecedented., (Copyright © 2017 Elsevier B.V. All rights reserved.)

In this paper, the cheap, easily obtained small antibiotic molecule of vancomycin was employed as reducer/stabilizer for facile one-pot synthesis of water exhibited a bluish fluorescence emission at 410nm within a short synthesis time about 50min. Based on the strong fluorescence quenching due to electron transfer mechanism by the introduction of ferric ions(Fe 3+ ), the Van-AuNCs were interestingly designed for sensitive and selective detecting Fe 3+ with a limit of 1.4μmol L -1 in the linear range of 2-100μmol L -1 within 20min. The Van-AuNCs based method was successfully applied to determine Fe 3+ in tap water, lake water, river water and sea water samples with the quantitative spike recoveries from 97.50-111.14% with low relative standard deviations ranging from 0.49-1.87%, indicating the potential application of this Van-AuNCs based fluorescent sensor for environmental sample analysis., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Heavy metal detection is a key topic in analytical chemistry. DNA-based metal recognition has advanced significantly producing many specific metal ligands, such as thymine for Hg 2+ and cytosine for Ag + . For practical applications, however, robust sensors that can work in a diverse range of salt concentrations need to be developed, while most current sensing strategies cannot meet this requirement. In this work, 2-aminopurine (2AP) is used as a fluorescence label embedded in the middle of four 10-mer DNA homopolymers. 2AP can be quenched up to 98% in these DNA without an external quencher. The interaction between 2AP and all common metal ions is studied systematically for both free 2AP base and 2AP embedded DNA homopolymers. With such low background, Hg 2+ induces up to 14-fold signal enhancement for the poly-T DNA, and Ag + enhances up to 10-fold for the poly-C DNA. A detection limit of 3nM is achieved for both metals. With these four probes, silver and mercury can be readily discriminated from the rest. A comparison with other signaling methods was made using fluorescence resonance energy transfer, graphene oxide, and SYBR Green I staining, respectively, confirming the robustness of the 2AP label. Detection of Hg 2+ in Lake Huron water was also achieved with a similar sensitivity. This work has provided a comprehensive fundamental understanding of using 2AP as a label for metal detection, and has achieved the highest fluorescence enhancement for non-protein targets., (Copyright © 2016 Elsevier B.V. All rights reserved.)

A novel fluorescent dendrimer PYTPAG2, with pyrene as the interior core and triphenylamine (TPA) as the exterior periphery, is studied as a fluorescence-quenching sensor for iron (ш) ions (Fe(3+)), both in solution and as a film. This dendrimer-based sensor possesses preferential detection of Fe(3+) by a very strong fluorescence quenching not found for other metal ions. The fluorescent detection limits of this PYTPAG2 sensor for Fe(3+) in solution and thin-film are 6.5×10(-7)M and 5.0×10(-7)M, respectively. The possible mechanism of this process is explained by the complexation between the peripheral TPA units of PYTPAG2 and Fe(3+) ions, which may disrupt the fluorescence resonance energy transfer (FRET) from the TPA groups to the pyrene core (intramolecular of PYTPAG2) and results in the fluorescence quenching. Moreover, this striking performance could not be disturbed by pH, the interference with other metal ions, counter anions, or surrounding environment. In addition, biological fluorescence imaging studies of Fe(3+) in living roundworms demonstrate its valuable practical application., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Developing fluorescent probes for monitoring intracellular Cu(+) is important for human health and disease, whereas a few types of their receptors showing a limited range of binding affinities for Cu(+) have been reported. In the present study, we first report a novel peptide receptor of a fluorescent probe for the detection of Cu(+). Dansyl-labeled tripeptide probe (Dns-LLC) formed a 1:1 complex with Cu(+) and showed a turn-on fluorescent response to Cu(+) in aqueous buffered solutions. The dissociation constant of Dns-LLC for Cu(+) was determined to be 12 fM, showing that Dns-LLC had more potent binding affinity for Cu(+) than those of previously reported chemical probes for Cu(+). The binding mode study showed that the thiol group of the peptide receptor plays a critical role in potent binding with Cu(+) and the sulfonamide and amide groups of the probe might cooperate to form a complex with Cu(+). Dns-LLC detected Cu(+) selectively by a turn-on response among various biologically relevant metal ions, including Cu(2+) and Zn(2+). The selectivity of the peptide-based probe for Cu(+) was strongly dependent on the position of the cysteine residue in the peptide receptor part. The fluorescent peptide-based probe penetrated the living RKO cells and successfully detected Cu(+) in the Golgi apparatus in live cells by a turn-on response. Given the growing interest in imaging Cu(+) in live cells, a novel peptide receptor of Cu(+) will offer the potential for developing a variety of fluorescent probes for Cu(+) in the field of copper biochemistry., (Copyright © 2016 Elsevier B.V. All rights reserved.)

The first example of droplet digital PCR logic gates ("YES", "OR" and "AND") for Hg (II) and Ag (I) ion detection has been constructed based on two amplification events triggered by a metal-ion-mediated base mispairing (T-Hg(II)-T and C-Ag(I)-C). In this work, Hg(II) and Ag(I) were used as the input, and the "true" hierarchical colors or "false" green were the output. Through accurate molecular recognition and high sensitivity amplification, positive droplets were generated by droplet digital PCR and viewed as the basis of hierarchical digital signals. Based on this principle, YES gate for Hg(II) (or Ag(I)) detection, OR gate for Hg(II) or Ag(I) detection and AND gate for Hg(II) and Ag(I) detection were developed, and their sensitively and selectivity were reported. The results indicate that the ddPCR logic system developed based on the different indicators for Hg(II) and Ag(I) ions provides a useful strategy for developing advanced detection methods, which are promising for multiplex metal ion analysis and intelligent DNA calculator design applications., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Highly blue luminescent nitrogen-doped carbon dots (N-CDs) with a fluorescence quantum yield of 42.3% were prepared by an efficient one-step pyrolytic route from ethylenediaminetetraacetic acid and urea. The as-synthesized N-CDs were demonstrated as an effective fluorescent probe for label-free, selective and sensitive recognition of Fe(3+) with a linear range of 0.5μM to 2mM and a detection limit of 13.6nM due to Fe(3+)-quenched fluorescence (turn-off). The quenched fluorescence could be turned on after the addition of apoferritin owing to the removal of ferric species from the surface of N-CDs by apoferritin, making complex N-CDs/Fe(3+) a selective apoferritin probe with a linear range of 0.1-25μM and a detection limit as low as 2.6nM. In addition, the application of this novel N-CDs-based probe for imaging Fe(3+) ions and apoferritin in living cells suggest that this sensing system has great potential applications in biosensing, bioimaging, and many other fields., (Copyright © 2016 Elsevier B.V. All rights reserved.)

The 4-N,N-dimethyl-1,8-naphthalimide based fluorescent probes have been explored for selective detection of Au(3+). Both probes show a pronounced fluorescence enhancement response to Au(3+). Hydroxy is introduced as ligand of Au(3+) for Probe 1 and the newly designed Probe 2 contains an alkyne moiety to recognize Au(3+) through an irreversible C≡C bond hydrolysis reaction. Probe 1 exhibits higher performance such as faster response, lower detection limit of 0.050μM and the better responsive effect in 99.5% water system compared with most of probes published. The Probe 2 displays high stability to pH, suitable water solubility, wider linear range (0-100μM) to Au(3+), and live-cells imaging with low cytotoxicity., (Copyright © 2016 Elsevier B.V. All rights reserved.)

In this paper, we present a class of bio-dots, polyepinephrine (PEP)-based fluorescent organic dots (PEP-FODs) for selective and sensitive detection of Fe(2+), Fe(3+), and Cu(2+). The PEP-FODs were derived from epinephrine via self-polymerization at relatively low temperature down to 60°C with low cytotoxicity and relative long lifetime (7.24ns). The surface morphology and optical properties of the synthesized PEP-FODs were characterized. We found that the diameters of PEP-FODs were mainly distributed in the narrow range of 2-4nm with an average diameter of 2.9nm. An optimal emission peak located at 490nm was observed when the green light-emitting PEP-FODs were excited at 400nm. It is discovered that Fe(2+), Fe(3+), and Cu(2+)can strongly quench the fluorescence of PEP-FODs through the nonradiative electron-transfer. The detection limit of 0.16, 0.67, and 0.15μM was obtained for Fe(2+), Fe(3+), and Cu(2+), respectively. The independent sensing platform of Fe(2+), Fe(3+), and Cu(2+)could be established by using NaF as a complexing agent and by regulating the reaction time between NaF and metal ions. Cell viability studies reveal that the as-prepared PEP-FODs possess good solubility and biocompatibility, making it as excellent imaging nanoprobes for intracellular Fe(2+), Fe(3+), and Cu(2+)sensing. The developed PEP-FODs might hold great promise to broaden applications in nanotechnology and bioanalysis., (Copyright © 2016 Elsevier B.V. All rights reserved.)

A diketopyrrolopyrrole-based probe DPP-PyR was able to recognize Fe(3+) and Au(3+) with fluorescent turn-on response via different emission modes with relatively low detection limit. Moreover, DPP-PyR exhibited preferential second mode of selectivity for Au(3+) as it ratiometrically displaced Fe(3+) from the [DPP-PyR+Fe(3+)] complex. Furthermore, the imaging experiments indicated that this probe was cell-permeable and could be used to detect Fe(3+) and Au(3+) ions within living cell. To the best of our knowledge, it was the first probe for detection Fe(3+) and Au (3+) at the same time ever reported., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Herein, the structure of two DNA strands which are complementary except fourteen T-T and C-C mismatches was programmed for the design of the combinatorial logic operation by utilizing the different protective capacities of single chain DNA, part-hybridized DNA and completed-hybridized DNA on unmodified gold nanoparticles. In the presence of either Hg(2+) or Ag(+), the T-Hg(2+)-T or C-Ag(+)-C coordination chemistry could lead to the formation of part-hybridized DNA which keeps gold nanoparticles from clumping after the addition of 40 μL 0.2M NaClO4 solution, but the protection would be screened by 120 μL 0.2M NaClO4 solution. While the coexistence of Hg(2+), Ag(+) caused the formation of completed-hybridized DNA and the protection for gold nanoparticles lost in either 40 μL or 120 μL NaClO4 solutions. Benefiting from sharing of the same inputs of Hg(2+) and Ag(+), OR and AND logic gates were easily integrated into a simple colorimetric combinatorial logic operation in one system, which make it possible to execute logic gates in parallel to mimic arithmetic calculations on a binary digit. Furthermore, two other logic gates including INHIBIT1 and INHIBIT2 were realized to integrated with OR logic gate both for simultaneous qualitative discrimination and quantitative determination of Hg(2+) and Ag(+). Results indicate that the developed logic system based on the different protective capacities of DNA structure on gold nanoparticles provides a new pathway for the design of the combinatorial logic operation in one system and presents a useful strategy for development of advanced sensors, which may have potential applications in multiplex chemical analysis and molecular-scale computer design., (Copyright © 2015 Elsevier B.V. All rights reserved.)

In this paper, a novel label-free fluorescent biosensor for terbium (ш) (Tb(3+)) was proposed based on structural conversion of G-quadruplex DNA mediated by Thioflavin T (ThT) and Tb(3+). In the presence of K(+), ThT could bind to K(+)-stabilized parallel G-quadruplex, giving rise to high fluorescence intensity. Upon the addition of Tb(3+), Tb(3+) could competitively bind to parallel G-quadruplex leading to the structural change, which resulted in fluorescence decrease. The change of fluorescence intensity (ΔF=F0-F) showed a good linear response toward the concentration of Tb(3+) over the range from 1.0 pM to 10.0 µM with a limit of detection of 0.55 pM. This proposed biosensor was simple and cost-effective in design and in operation with ultrahigh sensitivity and selectivity. Thus, the proposed biosensor could be a promising candidate for monitoring ultratrace Tb(3+) in environment., (Copyright © 2015 Elsevier B.V. All rights reserved.)

A salicylimine probe L with a simple structure has been researched more in-depth on fluorescence sensor properties based on two-photon (TP) absorption. L displays excellent selective turn-on fluorescence response for Al(3+) in hexamethylenetetramine-buffered (HMTA) aqueous solution (0.3M, pH=5.8) under one-photon (OP) excitation. With the help of OP fluorescence, TP fluorescence titration, UV-spectra titration and Job's plot, the stoichiometric ratio of L with Al(3+) was determined to be 1:1. The coordination sites and the coordination mechanism of L with Al(3+) were analyzed in detail through (1)H NMR data. Not only with a detection limit of 5.2×10(-9)M in vitro, but also the probe has been successfully used in the live cells and tissues for the imaging of Al(3+) with TP fluorescence microscopy due to the enlarged TP cross section, providing a novel testing method for measuring Al(3+) in solution or cell tissue with low autofluorescence and cytotoxicity., (Copyright © 2014 Elsevier B.V. All rights reserved.)

The integration of unique characteristics of nanomaterials with highly specific recognition elements, such as biomolecules and organic molecules, are the foundation of many novel nanoprobes for bio/chemical sensing and imaging. In the present report, branched polyethylenimine (PEI) was grafted with 8-chloroacetyl-aminoquinoline to synthesize a water-soluble and biocompatible quinoline-based Zn(2+) probe PEIQ. Then the PEIQ was covalently conjugated to [Ru(bpy)3](2+)-encapsulated SiNPs to obtain the ratiometric fluorescence nanoprobe which exhibits a strong fluorescence emission at 600 nm and a negligible fluorescence emission at 500 nm in the absence of Zn(2+) upon a single wavelength excitation. After the addition of different amounts of Zn(2+), the fluorescence intensity at 500 nm increased continuously while the fluorescence intensity at 600 nm remained stable, thus changing the dual emission intensity ratios and displaying continuous color changes from red to green which can be clearly observed by the naked eye. The nanoprobe exhibits good water dispersivity, biocompatibility and cell permeability, high selectivity over competing metal ions, and high sensitivity with a detection limit as low as 0.5 μM. Real-time imaging of Zn(2+) in A549 cells has also been realized using this novel nanoprobe., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Field effect transistors have risen as one of the most promising techniques in the development of biomedical diagnosis and monitoring. In such devices, the sensitivity and specificity of the sensor rely on the properties of the active sensing layer (gate dielectric and probe layer). We propose here a new type of transistor developed for the detection of Fe(3+) ions in which this sensing layer is made of a monolayer of lipids, engineered in such a way that it is not sensitive to pH in the acidic range, therefore making the device perfectly suitable for biomedical diagnosis. Probes are γ-pyrone derivatives that have been grafted to the lipid headgroups. Affinity constants derived for the chelator/Fe(3+) complexation as well as for other ions demonstrate very high sensitivity and specificity towards ferric ions with values as high as 5.10(10) M and a detected concentration as low as 50 fM., (© 2013 Published by Elsevier B.V.)

The 4-propargylamino-1,8-naphthalimide based fluorescent probe 1 has been explored as a sensor for selective detection of Au(3+). 4-Amino-1,8-naphthalimides, that possess typical intramolecular charge transfer (ICT) electronic characteristics, have been widely used as versatile platforms for fluorescent probes. The newly designed probe 1 contains a propargylamine moiety at C-4 of the naphthalimide chromophore that reacts with Au(3+) to generate a product that has distinctly different electronic properties from 1. Specifically, the probe undergoes a remarkable change in its absorption spectrum upon addition of Au(3+) that is associated with a distinct color change from yellow to light pink. In addition, a blue shift of ca. 56 nm also takes place in the emission spectra of the probe. Consequently, 1 serves as a reaction-based sensor or so called chemodosimeter for Au(3+). Importantly, surfactants enhance the rate of reaction of 1 with Au(3+), thus, enhancing its use as a real time sensor. Finally, the results of studies probing its application to bioimaging of Au(3+) in live cells show that the probe 1 has a unique ability to sense Au(3+) in cells and, in particular, in lipid droplets within cells., (Copyright © 2013 The Authors. Published by Elsevier B.V. All rights reserved.)

Gold nanoparticles-based colorimetric assay possesses several unique advantages, and has been applied for a wide range of targets, varying from nucleic acids to different metal ions. However, due to the lack of proper coordinating ligand, gold nanoparticles-based colorimetric sensing system for Au³⁺ has not been developed so far. It is well-known that Au³⁺ could induce the oxidation transition of thiol compounds to disulfide compounds. In this article, for the first time we converted such thiol masking reaction into colorimetric sensing system for label-free detection of Au³⁺ via a target-controlled aggregation of nanoparticles strategy. In the new proposed sensing system, fluorosurfactant-capped gold nanoparticles were chosen as signal reporter units, while an Au³⁺-triggered oxidation of cysteine (Cys), which inhibited the aggregation of gold nanoparticles, acted as the recognition unit. By varying the amount of Cys, a tunable response range accompanied with different windows of color change could be obtained for Au³⁺, illustrating the universality of the sensing system for Au³⁺ samples with different sensitivity requirements. Under optimized condition, the proposed sensing system exhibits a high sensitivity towards Au³⁺ with a detection limit of 50 nM, which is lower than previously reported spectroscopic methods. It has also been applied for detection of Au³⁺ in practical water samples with satisfactory result., (Copyright © 2013 Elsevier B.V. All rights reserved.)

A water-soluble biocompatible aziridine-based biosensor with pendant anthracene units was synthesized by radicalar polymerization of N-substituted aziridines in supercritical carbon dioxide. The binding ability of the sensor towards a series of metal ions was examined by comparing the fluorescence intensities of the solutions before and after the addition of 100 equivalents of a solution of the metal ion chloride salt. A fast, simple and highly optical sensitive dual behavior, "off-on" and "on-off" response, was observed after the biosensor was exposed to the metal cations in aqueous solution. Zinc presented the highest fluorescence enhancement (turn-on) and copper presented the highest fluorescence quenching (turn-off). The response time was found to be instantaneous and the detection limit was achieved even in the presence of excess metal cation competitors. By using immunofluorescence microscopy it was also shown that oligoaziridine acts as an "on-off" probe through highly sensitive (detection limit of 1.6nM), selective and reversible binding to copper anions under physiologic conditions using living Human Fibroblast cells. The stoichiometry for the reaction of the biosensor with Cu(2+) was determined by a Job plot and indicates the formation of an oligoaziridine-Cu(2+) 1:2 adduct., (Copyright © 2012 Elsevier B.V. All rights reserved.)

A bilayer amperometric nitrate biosensor with an integrated permselective layer has been developed for exclusion of inorganic anion and cation interferences. The inner PPy(polypyrrole)-NaR-NADH layer of the biosensor is formed by galvanostatic polymerization of pyrrole (Py) in presence of nitrate reductase (NaR) and nicotinamide adenine dinucleotide (NADH), followed by formation of the outer permselective poly-ortho-phenylenediamine (P-o-PDA) layer by potentiodynamic polymerization of ortho-phenylenediamine (o-PDA). The exclusion efficiency (E(eff)) of the outer layer in rejecting inorganic cation and anion interferences is evaluated by a new proposed relationship. 73-87% and 47-84% of anion and cation interferences, respectively, were efficiently rejected with the permselective layer. Further improvement in the exclusion efficiency for cations was accomplished by combining the use of the outer layer with the addition of 1mM EDTA into the measurement solution. The addition of EDTA improved the E(eff) achieved for cation rejection by 10-40% to give net E(eff) of 89-94%. The inclusion of the outer layer also aided the retention of NaR and NADH in the inner PPy-NaR-NADH layer and, hence, enabled improved amperometric detection of nitrate, achieving a detection limit of 0.20 μM and a linear concentration range of 10-500 μM with a 3.4%rsd (n=10)., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Urea biosensors based on urease covalently immobilized on to ammonium and hydrogen ion-selective electrodes were included in arrays together with ammonium, potassium, sodium, hydrogen and generic response to alkaline sensors. Response models based on artificial neural network (ANN) and partial least squares (PLS1) were built, tested and compared for the simultaneous determination of urea, ammonium, potassium and sodium. The results show that it is possible to obtain good ANN and PLS calibration models for simultaneous determination of these four species, but with better prediction capability when the ANN are used. The developed bioelectronic tongue was applied to multidetermination in urine samples. The ANN model showed again better agreement with reference methods, allowing a simple direct determination of urea in the real samples without the necessity of eliminating the alkaline interferences, or compensating endogenous ammonium.