Chemosensors, Volume 7, Issue 2 (June 2019) – 11 articles

In this work, we report on the development of an electrochemical biosensor for high selectivity and rapid detection of Hg²⁺ and Pb²⁺ ions using DNA-based specific aptamer probes labeled with ferrocene (or methylene blue) and thiol groups at their 5′ and 3′ termini, respectively. Aptamers were immobilized onto the surface of screen-printed gold electrodes via the SH (thiol) groups, and then cyclic voltammetry and impedance spectra measurements were performed in buffer solutions with the addition of HgCl₂ and PbCl₂ salts at different concentrations. Changes in 3D conformation of aptamers, caused by binding their respective targets, e.g., Hg²⁺ and Pb²⁺ ions, were accompanied by an increase in the electron transfer between the redox label and the electrode. Accordingly, the presence of the above ions can be detected electrochemically. The detection of Hg²⁺ and Pb²⁺ ions in a wide range of concentrations as low as 0.1 ng/mL (or 0.1 ppb) was achieved. The study of the kinetics of aptamer/heavy metal ions binding gave the values of the affinity constants of approximately 9.10⁻⁷ mol, which proved the high specificity of the aptamers used. Full article

Emissions from transportation sources can impact local air quality and contribute to adverse health effects. The Kansas City Transportation and Local-Scale Air Quality Study (KC-TRAQS), conducted over a 1-year period, researched emissions source characterization in the Argentine, Turner, and Armourdale, Kansas (KS) neighborhoods and the broader southeast Kansas City, KS area. This area is characterized as a near-source environment with impacts from large railyard operations, major roadways, and commercial and industrial facilities. The spatial and meteorological effects of particulate matter less than 2.5 µm (PM_2.5), and black carbon (BC) pollutants on potential population exposures were evaluated at multiple sites using a combination of regulatory grade methods and instrumentation, low-cost sensors, citizen science, and mobile monitoring. The initial analysis of a subset of these data showed that mean reference grade PM_2.5 concentrations (gravimetric) across all sites ranged from 7.92 to 9.34 µg/m³. Mean PM_2.5 concentrations from low-cost sensors ranged from 3.30 to 5.94 µg/m³ (raw, uncorrected data). Pollution wind rose plots suggest that the sites are impacted by higher PM_2.5 and BC concentrations when the winds originate near known source locations. Initial data analysis indicated that the observed PM_2.5 and BC concentrations are driven by multiple air pollutant sources and meteorological effects. The KC-TRAQS overview and preliminary data analysis presented will provide a framework for forthcoming papers that will further characterize emission source attributions and estimate near-source exposures. This information will ultimately inform and clarify the extent and impact of air pollutants in the Kansas City area. Full article

The rapid development of information and communication technology provides an opportunity for scientists to develop a quantitative analytical method that is built on a mobile gadget as a detector. In this paper, we report a low-cost, simple and portable analytical method for mercury ion quantification based on digital image colorimetry coupled with a smartphone application. A small amount of silver nanoparticles (AgNPs) was used as a colorimetric agent that is selective only to mercury ions. The yellowish brown color of AgNPs instantly changed to colorless after the addition of mercury ions due to a redox reaction. To increase the portability, we attached the AgNPs onto a medium to create a paper-based analytical device. The final data processing of the colorimetric analysis was conducted using an android application available on the Google Play Store, called “Mercury Detector”. The proposed method has good sensitivity, with a detection limit of 0.86 ppb, which is comparable to those of bulk and more expensive instruments. This allows for the detection of mercury ions as low as 2 ppb (10 nM), which is also the maximum contaminant level permitted in drinking water by the US Environmental Protection Agency. The proposed method was applied to real samples that provide satisfactory results on accuracy (2.4%) and precision (2.5%). Full article

Fabrication of biocompatible electrodes for the investigation of catecholamines is a known challenge. In this work, methionine was chosen as a modifier for fabrication of a biocompatible carbon paste electrode by electropolymerization, through cyclic voltammetry. The electrochemical behavior of the poly(methionine) modified carbon paste electrode was characterized by cyclic voltammetry for simultaneous determination of dopamine (DA) and uric acid (UA) in a phosphate-buffered solution at pH 7.0. In the absence of an amino acid methionine layer, the bare carbon paste electrode exhibits rather poor voltammetric signals in DA and UA in the binary mixture, with oxidation potentials of DA and UA overlapping with each other. The poly(methionine) modified carbon paste electrode exhibits good catalytic activity with noticeably different oxidation potentials of DA and UA. The experimental results closely agree with the theoretical prediction based on a Fukui function complementary to the simulated electrostatic potential maps. Full article

This work describes the use of a paper substrate for electro-optical detection of toxic hydrogen sulfide (H₂S) gas. For electrical detection, a chemiresistive type of gas sensor was developed. Ultrathin gold film electrodes (UTGFE) were produced by physical vapor deposition of gold on nanostructured latex-coated paper substrate. The gas-sensing film was deposited on the electrodes by inkjet printing. The sensing films were characterized by atomic force microscopy, X-ray photoelectron spectroscopy and conductometry. The sensing films showed more than seven orders of magnitude change in resistance when exposed to as low as 1 part per million (ppm) H₂S gas at room temperature. Besides resistive response, the change in color of the sensing films was studied on a paper substrate, both as a function of print density of the sensing material and H₂S concentration. For quantification of the analyte the red, green and blue color deconvolution was performed on the pictures of the paper strip indicator using an open source software. A clear response was obtained from the blue channel. The inexpensive disposable color strips produced on the paper substrate can be used for qualitative and quantitative detection (as low as 1.5 ppm) of H₂S gas. Full article

Fluorescence sensing, of d-block elements such as Cu²⁺, Fe³⁺, Fe²⁺, Cd²⁺, Hg²⁺, and Zn²⁺ has significantly increased since the beginning of the 21st century. These particular metal ions play essential roles in biological, industrial, and environmental applications, therefore, there has been a drive to measure, detect, and remediate these metal ions. We have chosen to highlight the low molecular weight fluorescent probes (LMFPs) that undergo an optical response upon coordination with the group 12 triad (Zn²⁺, Cd²⁺, and Hg²⁺), as these metals have similar chemical characteristics but behave differently in the environment. Full article

Bromide ions are present in many environments, such as sedative drugs, methyl-bromide-treated vegetables and seawater. Excess bromide in humans interferes with iodide metabolism and is considered toxic. The need for fast and inexpensive methods for bromide detection is of interest. Spectrophotometric detection methods provide accurate and sensitive results. The well-known ability of metalloporphyrins to bind anionic ligands to the central metal ion has been exploited. The changes in the optical properties of Pt(II) 5,10,15,20-tetra(4-methoxy-phenyl)-porphyrin (PtTMeOPP) under the influence of bromide ions allowed us to achieve a fast, simple and reliable UV-vis spectrophotometric method of detection with a detection limit of 2.5 × 10⁻⁸ M and a good confidence coefficient: 99.05%. The potential interfering ions, such as Cl⁻, I⁻, NO₂⁻, NO₃⁻, SCN⁻, SO₃²⁻, SO₄²⁻ and PO₄³⁻ of 100-fold higher and Cl⁻ and R-S⁻ of 1000-fold higher concentrations in the mixture as compared to the determined concentration of bromide ions (c = 10⁻⁵ M), were tested and did not influence the results. The behavior of the sensitive porphyrin in various pH media was investigated in order to determine their influence upon the bromide detection capacity. Full article

Vapors of volatile organic compounds such as benzene, toluene, and xylene (BTX) may cause health concerns. The sensitive detection of these compounds in air remains challenging. In this study, we reported on modification of the Quartz Crystal Microbalance (QCM) sensing chip using polyvinyl acetate (PVAc) film as active coating for the analysis of BTX vapors. The PVAc film was deposited on the QCM sensing chip surface by a spin coating technique. The morphology of the PVAc films was confirmed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The sensitivities of PVAc based QCM system for benzene, toluene, and xylene analyses were 0.018, 0.041, and 0.081 Hz/ppm, respectively. The high sensitivity of the proposed QCM system for analysis of BTX vapors is believed to be due to the effective interaction between the PVAc film and BTX molecules. The analyte vapor pressure appears to also affect the sensitivity. These data show that the prepared QCM sensor has a low time constant, good reproducibility, and excellent stability. It offers an alternative to the developed methods for detection of BTX and possibly other aromatic hydrocarbons in the air. Full article

The high toxicity of phosphine and the use of organophosphines as nerve agent precursors has provoked the requirement for a rapid and reliable detection methodology for their detection. Herein, we demonstrate that a ferrocene-derived molecular probe, armed with an azidobenzene trigger, delivers a ratiometric electrochemical signal selectively in response to organophosphorus(III) compounds and can be accurately measured with an inexpensive, handheld potentiostat. Through an intensive assay optimization process, conditions were found that could determine the presence of a model organophosphine(III) nerve agent precursor within minutes and achieved a limit of detection for triphenylphosphine of just 13 ppm. Due to the portability of the detection system and the excellent stability of the probe in solution, we envisaged that this proof-of-concept of work could easily be taken into the field to enable potentially toxic organophosphorus(III) compounds to be detected at the point-of-need. Full article

Zinc Oxide (ZnO) nanowalls (NWLs) are interesting nanostructures for sensing application. In order to push towards the realization of room-temperature operating sensors, a detailed investigation of the synthesis effect on the electrical and optical properties is needed. This work focuses on the low-cost synthesis of ZnO NWLs by means of chemical bath deposition (growth time of 5, 60, and 120 min) followed by annealing in inert ambient (temperature of 100, 200, and 300 °C). The as-grown NWLs show a typical intertwined network of vertical sheets whose features (thickness and height) stabilize after 60 min growth. During thermal annealing, NWLs are converted into ZnO. The electric transport across the ZnO NWL network radically changes after annealing. A higher resistivity was observed for longer deposition times and for higher annealing temperatures, at which the photoluminescence spectra resemble those obtained for ZnO material. A longer deposition time allows for a better transformation to ZnO during the annealing, thanks to the presence of ZnO seeds just after the growth. These findings can have a significant role in promoting the realization of room-temperature operating sensors based on ZnO NWLs. Full article

Poly(propylenimine) dendrimers from first and third generations modified with 1,8-naphthalimide units and their Zn(II) complexes have been investigated by absorption and fluorescence spectroscopy. These dendrimers have been deposited on a cotton cloth by the extraction method, producing yellow-colored textile materials. They have been characterized by defining their color coordinates L*a*b*, XYZ and xy. The antimicrobial activity of dendrimers has been investigated in vitro against model gram-positive and gram-negative bacteria and yeasts. Being deposited onto the surface of cotton fabric, the studied dendrimers reduced bacterial growth and prevented the formation of bacterial biofilm. Anticancer and cytotoxicity activities have also been performed against HeLa and Lep-3 human tumor cell lines as model systems. Full article