A Practical Hydrazine-Carbothioamide-Based Fluorescent Probe for the Detection of Zn2+: Applications to Paper Strip, Zebrafish and Water Samples

A practical hydrazine-carbothioamide-based fluorescent chemosensor TCC (N-(4-chlorophenyl)-2-(thiophene-2-carbonyl)hydrazine-1-carbothioamide) was applied for Zn2+ detection. TCC exhibited selective fluorescence emission for Zn2+ and did not show any interference with other metal ions. In particular, TCC was utilized for the detection of Zn2+ in paper strips, zebrafish and real water samples. TCC could detect Zn2+ down to 0.39 μM in the solution phase and 51.13 μM in zebrafish. The association ratio between TCC and Zn2+ was determined to be 2:1 by ESI-mass and Job plot. The sensing mechanism of TCC for Zn2+ was illustrated to be a chelation-enhanced fluorescence process through spectroscopic experiments and theoretical calculations.

Energy harvesting through a piezoelectric sensor

Energy harvesting through motion caused by wind is a unique way of finding an alternative energy source for several electronic devices. Piezo-electronic sensors, which harvest energy from small vibrations and movements, are investigated by many researchers nowadays. This paper conducted an experimental study to find an alternative energy source for diverse electronics with forced oscillations from a fan. The relations between the force applied by wind and the oscillation of a paper strip were studied.

Novel Metallochromic Hydrazone-Based Chemosensor Toward Colorimetric Paper Strip For Selective Detection Cu2+

A solid-state sensor was developed for the determination of copper ions (Cu2+) in aqueous media using tricyanofuranhydrazone as a spectroscopic probe and a paper sheet as the hosting strip. A new tricyanofuranhydrazone-based colorimetric chemosensor (TCFH) was synthesized for selective detection of Cu2+ in aqueous environments. The synthesis strategy of TCFH involved an azo-coupling process between the diazonium salt of 8-aminoquinoline and an active methyl-bearing tricyanofuran (TCF) heterocyclic moiety. The molecular structure of the prepared TCFH chemical sensor was verified with FT-IR, 1H and 13C NMR, as well as elemental analysis. Due to intramolecular charge transfer, TCFH chromophore demonstrated pronounced solvatochromism depending on the solvent polarity. Changes in both color and UV-vis absorption spectra demonstrated by the developed chemosensor proved that TCFH can be utilized to detect Cu2+ in the presence of other competing metallic cations and anions. The synthesized TCFH probe, which contains a hydrazone recognition moiety, demonstrates dramatic solvatochromic activity and high selectivity at the microlevel of copper ions with a color shift from yellow to purple. Mechanisms accounting for both metallochromic and solvatochromic activities were explored. Moreover, test strips of TCFH were successfully developed and applied for the detection of copper ions at different concentrations in aqueous media. The colorimetric properties of the prepared TCFH-immobilized paper strips were investigated by CIE Lab chromogenic parameters, colorimetric strength (K/S) and UV-Vis absorbance spectra. The metallochromic paper strip exhibited a detection limit at the ppm range. The best detection of Cu2+ was achieved in the pH range of 6.6-7.4 demonstrating an immediate color switch from yellow to purple relying on the total content of Cu2+. Scanning electron microscopy (SEM) was applied to characterize the deposition of tricyanofuranhydrazone onto the surface of the paper strip.

A Handy and Accessible Tool for Identification of Sn(II) in Toothpaste: Inclination to an Eco-Friendly Environment

An easily accessible colorimetric probe, a carbazole-naphthaldehyde conjugate (CNP), was successfully prepared for the selective and sensitive recognition of Sn(II) in different commercially-available toothpaste and mouth wash samples. The binding mechanism of CNP for Sn2+ was confirmed by UV-Vis, 1H and 13C NMR titrations. The proposed sensing mechanism was supported by quantum chemical calculations. Selective detection of Sn(II) in the nanomolar range (85 nM), among other interfering metal ions, makes it exclusive. Moreover, Sn2+ can be detected with a simple paper strip from toothpaste, which makes this method handy and easy accessible. The potential application of this system for monitoring Sn2+ can be used as an expedient tool in environmental and industrial purpose.

Electrochemical studies of lateral flow assay test results for procalcitonin detection

In this study, the lateral flow assay (LFA) has been developed for the detection of bacterial infection (BI) by specific biomarker procalcitonin (PCT), without a need for complicated instrumentations and technical expertise. For the development of the assay, gold nanoparticles (AuNP) and their conjugates with antibodies specific to the model antigen PCT are assessed. Polyclonal antibody (pAb) labelled with gold nanoparticles (AuNP) to obtain the AuNP-pAb complex and the specific monoclonal antibody (mAb) have been dropped at the test zone. This complex is placed over the conjugate line of the LFA strip. In the absence of PCT or the presence of other biomarkers, the test line remained colourless, which revealed the specificity of assay towards PCT among a pool of various analytes. Herein, observations have been made through two different platforms for quantitative and qualitative analysis for the detection of PCT biomarker. The qualitative analysis has been performed on the basis of appearance red color in the test band, while for quantitative analysis, a novel approach has been adopted. Herein, the nitrocellulose membrane (paper strip) is cut out from the LFA strip and used for electrochemical studies under similar solution conditions. Different paper strips presented different cyclic voltammograms (CV) that could be correlated to varying PCT concentrations captured at the test line of the paper strip. The qualitative detection limit for PCT using this LFA was determined to be 2 ng/ml and the quantitative detection limit was 1 ng/ml. The electrochemical response studies of the paper strip by CV technique revealed the sensitivity value of 0.695 mA ng/ml.

Label-Free Surface Enhanced Raman Scattering (SERS) on Centrifugal Silver Plasmonic Paper (CSPP): A Novel Methodology for Unprocessed Biofluids Sampling and Analysis

Label-free SERS is a powerful bio-analytical technique in which molecular fingerprinting is combined with localized surface plasmons (LSPs) on metal surfaces to achieve high sensitivity. Silver and gold colloids are among the most common nanostructured substrates used in SERS, but since protein-rich samples such as serum or plasma can hinder the SERS effect due to protein–substrate interactions, they often require a deproteinization step. Moreover, SERS methods based on metal colloids often suffer from a poor reproducibility. Here, we propose a paper-based SERS sampling method in which unprocessed human serum samples are first soaked on paper strips (0.4 × 2 cm2), and then mixed with colloidal silver nanoparticles by centrifugation to obtain a Centrifugal Silver Plasmonic Paper (CSPP). The CSPP methodology has the potential to become a promising tool in bioanalytical SERS applications: it uses common colloidal substrates but without the need for sample deproteinization, while having a good reproducibility both in terms of overall spectral shape (r > 0.96) and absolute intensity (RSD < 10%). Moreover, this methodology allows SERS analysis more than one month after serum collection on the paper strip, facilitating storage and handling of clinical samples (including shipping from clinical sites to labs).

Reducing Unspecific Protein Adsorption in Microfluidic Papers Using Fiber-Attached Polymer Hydrogels

Microfluidic paper combines pump-free water transport at low cost with a high degree of sustainability, as well as good availability of the paper-forming cellulosic material, thus making it an attractive candidate for point-of-care (POC) analytics and diagnostics. Although a number of interesting demonstrators for such paper devices have been reported to date, a number of challenges still exist, which limit a successful transfer into marketable applications. A strong limitation in this respect is the (unspecific) adsorption of protein analytes to the paper fibers during the lateral flow assay. This interaction may significantly reduce the amount of analyte that reaches the detection zone of the microfluidic paper-based analytical device (µPAD), thereby reducing its overall sensitivity. Here, we introduce a novel approach on reducing the nonspecific adsorption of proteins to lab-made paper sheets for the use in µPADs. To this, cotton linter fibers in lab-formed additive-free paper sheets are modified with a surrounding thin hydrogel layer generated from photo-crosslinked, benzophenone functionalized copolymers based on poly-(oligo-ethylene glycol methacrylate) (POEGMA) and poly-dimethyl acrylamide (PDMAA). This, as we show in tests similar to lateral flow assays, significantly reduces unspecific binding of model proteins. Furthermore, by evaporating the transport fluid during the microfluidic run at the end of the paper strip through local heating, model proteins can almost quantitatively be accumulated in that zone. The possibility of complete, almost quantitative protein transport in a µPAD opens up new opportunities to significantly improve the signal-to-noise (S/N) ratio of paper-based lateral flow assays.

Rapid detection of pesticide in milk, cereal and cereal based food and fruit juices using paper strip-based sensor

The study was aimed to validate paper strip sensors for the detection of pesticide residues in milk, cereal-based food, and fruit juices in comparison with GC–MS/MS under field conditions. The detection limit of pesticide using rapid paper strip sensor for organophosphate, carbamate, organochlorine, fungicide, and herbicide group ranges from 1 to 10, 1–50, 250–500, 1–50, and 1 ppb, respectively in milk and milk product, cereal-based food and fruit juices. Among 125 samples of milk samples collected from the market 33 milk samples comprising 31 raw milk and 2 pasteurized milk found positive for pesticide using the strip-based sensor. In cereal based food and fruit juice samples, 6 cereal flours and 4 fruit juices were found positive for pesticide residues. The pesticide positive samples were further evaluated quantitatively using GC–MS/MS wherein 7 samples comprised of raw milk, pasteurized milk, rice flour, wheat flour, maize flour, apple juice, and pomegranate juice have shown the presence of chlorpyrifos, chlorpyrifos-methyl, α-endosulfan, β-endosulfan DDD and DDT at trace level as well as at above MRL level. It is envisaged that the developed paper strip sensor can be a potential tool in the rapid and cost-effective screening of a large number of food samples for pesticide residues.