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This report presents an investigation into the use of carbon paper electrodes prepared from chitosan-adhered graphene magnetite nanoparticles for the analysis of Cr(VI). The preparation and storage of carbon paper electrodes is a simple process, and these electrodes are easier to replace than electrodes modified by more conventional methods. The electrochemical detection of Cr(VI) using square wave adsorption cathodic dissolution voltammetry (SWAdCSV) with high selectivity and sensitivity, as well as the optimum conditions for the preparation of the electrodes and the electrode parameters affecting the SWAdCSV signal, were the main points of focus of the investigation. Cr(VI) was detected linearly in the range of 4-40 μg L-1 with a detection limit of 2.84 μg L-1. The electrode output precision, calculated as %RSD, was 7.16% (n = 6), and this was the measurement used for the detection of Cr(VI) in standard and test samples with recoveries between 89% and 114%. The results were consistent with those obtained using the standard UV-Vis spectrophotometric method with a paired t-test at 95% confidence level. [ABSTRACT FROM AUTHOR]

As a kind of organic basic compound containing nitrogen, biogenic amine is released from food spoilage and considered as an indicator for monitoring food freshness. Herein, an excellent dual-emission ratiometric fluorescent sensor for eight kinds of biogenic amines was established via the facile mixing of pH-responsive carbon dots and Rhodamine B. The developed sensor shows a rapid response (10 s), low limit of detection (0.733–3.943 μM) and a wide linear range (0–150 μM). More importantly, a portable fluorescent filter paper was prepared by simple dispersing the filter paper in a solution mixture of carbon dots and Rhodamine B. The obtained fluorescent filter paper based sensor showed an obvious color change in the presence of biogenic amine vapor derived from shrimp and mushroom. The results revealed that this sensor could realize the on-site and visual detection of biogenic amines in real food samples, making it suitable for potential application in food safety monitoring. [ABSTRACT FROM AUTHOR]

Selective enrichment of La(III) by green material as an industrial raw material is of great research interest. In this study, the selective interaction between P and La(III) was utilized, and waste paper (WP) modified with phytic acid (PA) was used to adsorb La(III) from water using a simple one-pot method. The adsorption capacity was 237.23 mg g−1 (30 °C, pH = 5, initial concentration of 200 mg L−1). The equilibrium isotherm fitted the Langmuir isotherm model well. The adsorption equilibrium was reached after 15 min. The adsorption kinetics followed the pseudo-second-order kinetic model, indicating that the adsorption mechanism of the material towards La(III) is single-layer chemisorption. It selectively adsorbed La(III) from four coexisting substances (Pb, Ni, Cu, and Co). After six cycles, the adsorption efficiency of the adsorbent material remained at 60%. [ABSTRACT FROM AUTHOR]

Naphthalenediimide derivative-absorbed papers, which were prepared by dropping chloroform solution, showed fluorescence under photoirradiation after exposure to vapors of small aromatic guests. The fluorescence intensity and maximum wavelength depended on the type of guest aromatic molecules, similar to the crystal. The naphthalenediimide derivative-absorbed papers showed vapochromic and mechanochromic properties. [ABSTRACT FROM AUTHOR]

Developing new forms of flexible zinc–air (Zn–air) batteries is crucial to economic growth. Nevertheless, the absence of an oxygen evolution reaction catalyst with high catalytic efficiency and low-cost causes instability of Zn–air battery cycling and economic unviability, respectively. In this paper, a leaf-like N-doped carbon structure with CoS2 nanoparticles self-supported on carbon fiber paper (CoS2-CZ@CFP) was developed as an air electrode for Zn–air batteries, which not only uses nonprecious metal elements, but also has a self-supporting configuration, enhancing the contact between the catalyst and electrode while facilitating the transfer of electrons. Sulfur as the source gas was introduced into Co-doped metal–organic skeletons (Co-ZIFs) anchored on carbon fiber paper (CFP) for in situ vulcanizing transition metal Co, which successfully ensures the uniform distribution of sulfide particles in the carbon matrix, hence enriching active catalyst sites. The CoS2-CZ@CFP demonstrated an overpotential of 1.611 V at J = 50 mA cm−2, superior to RuO2@CFP (1.814 V). A Zn–air battery fabricated using the synthesized CoS2-CZ@CFP exhibited an extended life cycle of 117 h. This research paves the way for a novel method of designing self-supporting configurations of sulfides and carbon matrix composites as promising air electrodes applicable to Zn–air batteries. [ABSTRACT FROM AUTHOR]

A simple, portable and cost-effective paper-based analysis device is developed for quantitative determination of ascorbic acid (AA) based on the UV-induced oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB). The method does not involve the introduction of any enzyme or external oxidants. More importantly, large equipment is not needed and only a 20 μL sample is needed for each analysis which only takes 8 min. The filter paper is pre-treated with TMB and it turns blue upon UV irradiation because TMB is a self-photosensitizer. The phenol hydroxyl groups of AA can inhibit photo-triggered oxidation resulting in a lighter blue color. The color signal is captured using a smartphone and analyzed using color analysis software. A series of factors that affect the performance of the device are investigated, including the concentration of TMB, buffer pH, channel selection, and irradiation time. The analytical performance is evaluated, and the results show that the method has a wide detection range of 0.05–1.0 mmol L−1 as well as a high selectivity and reproducibility. The proposed method is applied for assaying AA in beverage samples and a VC tablet, and the results correspond to those obtained using the UV method. The results of the recovery test of human serum indicate that the proposed method is feasible in biological samples. This device is easy to fabricate, and convenient to store and transport. It is a truly portable device which has great potential in the on-site assay. [ABSTRACT FROM AUTHOR]

A robust superhydrophobic filter paper was developed through a coating technique, simple and facile, cost-effective, eco-friendly, and defensible, for wide portfolio applications. To develop super hydrophobic filter papers, the paper was coated with inorganic–organic hybrid nanocomposites comprising zinc oxide, chitin, and polycaprolactone (chitin–ZnO–PCL) and zinc oxide, chitosan, and polycaprolactone (chitosan–ZnO–PCL) hybrids through the grafting method. The preparation of a superhydrophobic surface by dip-coating deposition is a facile process. Zinc oxide nanoparticles grafted with chitin–PCL and chitosan–PCL hybrids coated on paper exhibit superhydrophobic properties. Water contact angle measurement carried out using a goniometer showed the average static water angle values of 145° and 160° for the chitin–ZnO–PCL and chitosan–ZnO–PCL grafted hybrid coated surfaces, respectively. The surface morphology of the coating was studied using scanning electron microscopy, X-ray powder diffraction, UV radiation, and Fourier transform infrared spectroscopy. In addition, durability, oil/water separation, bio-degradability, and self-cleaning ability through water flush-out were also studied and reported. The results show that the coated filter papers possess excellent superhydrophobic properties for real-time applications. [ABSTRACT FROM AUTHOR]

Employing a one-pot Schiff-base condensation approach, the derivative "cholyl hydrazide Schiff base of phenothiazine" (ChHSB-PTZ) based on cholic acid has been synthesized and characterized via standard procedures. ChHSB-PTZ demonstrates exceptional sensitivity towards Sn(II) metal ion detection through fluorescence "turn-off" behavior based on chelation-enhanced fluorescence quenching (CHEQ) even in the presence of various cations and anions. Through modified Stern–Volmer and Stern–Volmer graph analyses, the binding constant (Ka) and limit of detection (LOD) were found to be 2.8 × 1010 M−1 and 2.2 nM, respectively. A 1 : 1 stoichiometry between ChHSB-PTZ and the Sn(II) metal ion was found via Job's plot. Moreover, the distribution of electronic states in the ChHSB-PTZ Schiff base and the sensing mechanism (CHEQ) were clarified through the use of 1H NMR titration spectroscopy and density functional theory (DFT) calculations. ChHSB-PTZ test paper strips are developed as an essential tool to improve the analytical applicability of the device and enable the rapid, accurate, and affordable detection of Sn(II) metal ions in environmental analysis. [ABSTRACT FROM AUTHOR]

Sulphur doped graphitic carbon nitride (SGCN) was effectively prepared and comprehensively described. A straightforward synthetic process based on thermal condensation was reported for the synthesis of SGCN using thiourea as a precursor. Cyclic voltammetry (CV) and differential pulse voltammetry were used to evaluate the electrochemical performance of cortisol. SGCN sheets were used to boost the electro-catalytic activity, exhibiting very exceptional electrochemical behaviour towards cortisol. As a result, we obtained a broad linear response range of 0.1–100 μM, as well as a comparatively low detection limit (15.8 × 10−8 M). Furthermore, the fabricated SGCN/CFP electrode shows excellent selectivity in the presence of a large number of possible interfering species. SGCN comprises (C with N and S) heteroatoms, which most likely would have led to a better current response towards cortisol detection. Furthermore, the structural defects that generate additional active sites on the surface of SGCN may enhance the quick electron transfer that occurs during the oxidation of cortisol. [ABSTRACT FROM AUTHOR]

We report the results of studies relating to the development of a conductive ink-coated, paper-based electrochemical DNA hybridization assay for the detection of the porA pseudogene of Neisseria gonorrhoeae (gonococcal DNA), the causative agent of gonorrhoea. Briefly, a conductive and highly homogenous ink was prepared by dispersing carboxylated MWCNTs (cMWCNTs) in a stable emulsion consisting of terpineol as solvent, carboxymethyl cellulose (CMC) as binder and polysorbate 80 (PS80) as the stabilizing agent. This cMWCNT-based ink was coated onto paper substrates to obtain cMWCNT@paper electrodes with a mean (± standard deviation, SD) resistivity of 1.066 (± 0.33) Ω cm. Furthermore, a magnetic bead (MB)-mediated hybridization assay comprising a specific 5′-biotinylated capture DNA probe (C) and 3′-methylene blue (MetB)-tagged detector DNA probe (D) was designed. These probes hybridized specifically with a porA target DNA sequence (T) forming a sandwich hybridization complex (C-T-D) at the MB surface. Thus formed C-T-D/Av/MB samples with different T concentrations were drop cast and adsorbed onto the cMWCNT@paper for electrochemical detection. The linear detection range and sensitivity of the electrochemical biosensing assay were found to be 100 fM–100 nM and 5.09 μA (log[concentration])−1, respectively. The biosensing assay was further shown to detect the target genomic gonococcal DNA in a mixture consisting of different DNA and protein interferents indicating its clinical viability. The results of rheological studies reveal that this thixotropic cMWCNT ink can be utilized for screen printing. These studies demonstrate the utilization of a conductive ink formulation for the fabrication of paper-based electrochemical sensing electrodes having high potential for cost-effective batch production and application in point-of-care (PoC) clinical diagnostics. [ABSTRACT FROM AUTHOR]

Electrochemical oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) has received increasing attention as it is an eco-friendly strategy for synthesizing a key monomer for the production of bio-based plastics. Developing efficient, low-cost and stable electrocatalysts is crucial for this electrochemical reaction. In this work, we have reported a facile process for the synthesis of hybrid nanosheet-structured NiCo2O4 on carbon fiber paper (NiCo2O4-CFP) for the efficient electrochemical conversion of HMF into FDCA. As a non-noble binary metal-based catalyst, NiCo2O4-CFP featured a nanosheet network and 3D nanosheet flower-like microspheres, showing 94.3% selectivity and 89.6% faradaic efficiency (FE) for FDCA, which outperformed its single component metal oxides NiO-CFP and Co3O4-CFP. And it also exhibited relatively high stability by maintaining over 80% FE after four successive cycles. The proposed mechanism suggested that the synergistic effect of Ni and Co elements in NiCo2O4 could facilitate HMF oxidation. [ABSTRACT FROM AUTHOR]

The water-soluble bromophenoxy-substituted naphthalimide derivative 1 and its copolymer P1 with acrylamide were synthesized and the photophysical properties of their host–guest complexes with cucurbit[8]uril (CB[8]) were studied. Notably, the host–guest complex CB[8]·1 showed long-lived RTP on filter paper and demonstrated a humidity response, making it suitable for use as an encryption ink. Furthermore, the solid powder of the host–guest complex between P1 and CB[8] exhibited a 4 s afterglow emission. [ABSTRACT FROM AUTHOR]

Viologens exhibit excellent color responses to external stimuli owing to their desirable redox properties. They have been widely studied in electrochromic and photoluminescent materials. Generally, polymeric materials have better processing properties and longer service life than small organic molecules. Herein, a viologen-containing polyurethane was synthesized and used to prepare an electrochromic device and a paper-based amine detector. The obtained electrochromic device displayed an excellent electrochromic behavior when subjected to an external voltage as low as 1.0 V. Moreover, the designed paper-based amine detector exhibits a highly sensitive color-change response when exposed to liquid amine solutions (down to 1 ppm concentration) or gaseous ammonia. The results of this study demonstrated that the developed viologen-containing polyurethane exhibits excellent electrochromic performance and the designed amine-detecting paper chips are an excellent tool for amine detection. [ABSTRACT FROM AUTHOR]

Pesticide residues are a serious problem towards agriculture, environment and food safety, so it is highly desirable to develop a swift, efficient and portable pesticide detection method. A fluorescence visual sensing method for glyphosine based on a nitrogen-doped biomass carbon quantum dot (N-CQD) paper-based sensor was developed. The fluorescence signal was quenched by Fe3+ in a static quenching process, and then the fluorescence of N-CQDs was recovered after adding glyphosine. Under the optimal experimental conditions and when tested with a fluorescence spectrofluorometer, the detection of glyphosine showed a two-stage linear pattern in the range of 0.1–0.6 μM and 0.6–1.6 μM with a detection limit of 0.075 μM. Then, the RGB values of different concentrations of glyphosine on the filter paper chip were detected by the software of the smartphone-color identifier. The logarithm of the glyphosine concentration was linearly related to the G value of RGB in the range of 0.25–10.00 mM and with a detection limit of 0.15 mM. The method was applied to measuring glyphosine-spiked juice and flour samples, and the recovery rates were 87.60–112.69% and 93.27–105.83%, respectively. The proposed N-CQDs/Fe3+ system had wide applications, and it was expected to be fast and effective at detecting pesticide residues. [ABSTRACT FROM AUTHOR]

Multilayer graphene (MLG) is in situ formed in a matrix of amorphous carbon prepared from carbonized waste paper at 750 °C. The resulting samples are systematically characterized by morphology, spectroscopy, diffractometry, nitrogen adsorption–desorption and electrochemistry. The carbon structure with six layered graphene can be formed in a matrix of amorphous carbon at such a low temperature. The resulting sample displays a specific surface area of 862 m2 g−1, a meso-pore volume of 0.55 cm3 g−1 and a capacitance of 214 F g−1, which are correspondingly 2.16, 2.29 and 2.14 times higher than those of the sample prepared directly from carbonized waste paper. Although the sample displays the basic characteristics of amorphous carbon, MLG is mostly found to be formed around the regular nickel crystal face in the amorphous carbon matrix. It is also found that the formation of MLG can be affected by the coexistence of nickel crystals and sodium metal. The optimized porous structural characteristics, including the specific surface area, and the micro- and meso-pore volumes, result from the rearrangement of graphite microcrystallites, giving an improved capacitive performance. [ABSTRACT FROM AUTHOR]

Bimodal NiCo2O4·MnO2 (NCM) nanorods were grown on carbon fiber paper (CFP) using a hydrothermal process. The structural and morphological studies were performed via powder X-ray diffraction and field-emission scanning electron microscopy, respectively. The aspect ratio of the developed electrode significantly improved up to a threshold concentration of manganese in the Ni/Co binary oxide, and thereafter decreased. The capacitive performance and electrochemical parameters of the developed NCM nanorods were analyzed using cyclic voltammetry, galvanostatic charge–discharge, and impedance spectroscopy. The maximum specific capacitance of the developed NCM nanorods was found to be 2575 F g−1 (305 mA h g−1) at a current density of 5 A g−1. Additionally, the excellent cyclic retention of nearly 92.5% was achieved for the NCM nanocomposite even after 5000 cycles. Also, the response time (τo) calculated from the Bode plot was found to be ∼22 s, which validated the fast charging of the developed electrode material. Furthermore, an asymmetric solid-state supercapacitor (ASC) device was successfully assembled utilizing NCM (1 : 2 : 2) nanorods and activated carbon as positive and negative electrodes, respectively. The developed device achieved a capacitance of 130 F g−1 (176.1 mA h g−1) with an energy density and power density of 138 W h kg−1 and 722 W kg−1, respectively, which could illuminate an LED bulb (1.8 V) for 50 min. [ABSTRACT FROM AUTHOR]

Valproic acid (VPA) is mainly used in the clinic to treat epilepsy, for which the therapeutic window is narrow to avoid causing adverse reactions such as hepatotoxicity and teratogenicity. Therefore, timely therapeutic drug monitoring is needed. A hapten containing a benzene ring and an amino group was designed and used to screen a monoclonal antibody (mAb) 3G10 with high specificity and sensitivity. The IC50 value of mAb 3G10 was ascertained as 68.13 ng mL−1 through an indirect competitive enzyme-linked immunosorbent assay. A colloidal gold-based immunochromatographic strip (CG-ICS) for the detection of free VPA in human serum was developed with gold-labeled mAb 3G10. Qualitative analysis of human serum samples can be conducted through visual observation. The visual limit of detection (vLOD) was 2 μg mL−1, and the cut-off value was 100 μg mL−1. A standard curve for quantitative detection was generated using a portable scanner, with a calculated LOD (cLOD) value of 0.144 μg mL−1 and a linear range of 0.565–48.385 μg mL−1. Comparing the results of CG-ICS for actual positive samples with those of a direct chemiluminescence kit, there was a good correlation between the two methods. Therefore, our CG-ICS can be applied to the rapid clinical monitoring of free VPA. [ABSTRACT FROM AUTHOR]

In this study, the rational preparation of Kevlar fiber (KF)-reinforced eco-friendly paper based on ultralong hydroxyapatite nanowires (HAPNWs) is reported. The ultralong HAPNWs were used to constitute the paper skeleton, and KF was used to further enhance the mechanical properties of the paper. The KF and ultralong HAPNWs interweaved with each other to form a three-dimensional porous structure and immobilize TiO2 nanoparticles, resulting in high flexibility and mechanical strength of the paper; in particular, the writable paper exhibited superhydrophobic, anti-fouling, self-cleaning and oil/water separation properties after being modified with fluorine-free stearic acid (STA). Owing to the photo-induced hydrophilicity and photocatalysis of TiO2, the surface wettability could be tuned by UV light. Moreover, the as-prepared paper possessed promising thermal stability, and the weight percentage was maintained above 90% even when it was heated to 800 °C. Unlike traditional paper, the as-prepared paper manifested favorable fire-retardant properties even when it was directly exposed to fire for 5 minutes. Furthermore, the soft paper was utilized to efficiently separate an oil/water mixed solution; moreover, it was used to transport water and various organic liquids when lubricant oil was infused into the porous structure. The present study is propitious for the fabrication of multifunctional inorganic paper, which will find practical applications in the fields of paper making, liquid transportation, oil–water separation, fire-retardants, and waterproofing. [ABSTRACT FROM AUTHOR]

Metabolic alkalosis, the most common acid–base disorder, is related to significantly increased mortality in hospitalized patients. Hunting for pH sensors lying in the neutral to alkaline pH range still remains challenging and in demand. Herein, we engineered a colorimetric/fluorescent method for monitoring alkalic pH based on a phenylboronic acid-containing probe (DDPB). In this approach, the dicyanoisophorone group of DDPB acted as an optical signal moiety, while the boronic acid acted as the latent pH response site. It was exactly deciphered that the reversible pH monitoring principle is based on the deprotonation/protonation mechanism and intramolecular charge transfer (ICT) strategy via1H NMR and DFT calculations. This approach presented a pH-sensitive response over pH values ranging from 7.00 to 10.23 (pKa = 9.33) with excellent reversibility. We further explored its application in sensing pH on a paper substrate for visual and rapid detection. In addition, it was successfully applied to measure pH variations in HK-2 cells when the cells underwent alkalosis. This work extends the application of optical probes based on boronic acid under alkaline pH conditions, and provides a new strategy for the design of alkaline pH probes. [ABSTRACT FROM AUTHOR]

In this work, Au nanoparticle (AuNP)-modified filter paper as a highly sensitive mercury extractant was successfully prepared in situ and applied in the head-space solid phase extraction (HS-SPE) of Hg(II) in water. The microstructure of the modified filter paper was characterized by using X-ray diffraction and scanning electron microscopy (XRD/SEM), and the results showed that AuNPs were well distributed on the fiber surface of the filter paper. Combined with portable Zeeman atomic absorption spectroscopy (ZAAS), the modified filter paper was successfully applied to Hg detection in water samples. Specifically, it can easily achieve in situ sample collection and detection under negative pressure in the field, which was reported for the first time. Several influencing factors such as extraction temperature, time, stirring speed, pH value, reductants, inorganic ions, and organic interfering and complexing agents were all investigated thoroughly. The limit of detection (LOD) for Hg(II) was 0.09 μg L−1, with linearity ranging from 0.09 to 50 μg L−1. Good recoveries were also obtained between 82 and 106% with RSDs below 7% in real water samples. The established method provided a convenient route for mercury detection in environmental water with a low amount of sample required (1 mL) and good detection performance, which is comparable to that of ICP-MS. [ABSTRACT FROM AUTHOR]

A new fluorescent probe (T2) containing pyrene-hydrazone furan moieties was developed and synthesized through a two-step process and then coated onto filter paper to form a paper-based sensor for TNT detection. The T2 sensor uses photoinduced electron transfer (PET) induced fluorescence quenching to detect TNT. The sensor properties were studied using fluorescence spectra, 1H-NMR titration and density functional theory (DFT) calculations. The reaction time of the T2 paper-based sensor for TNT detection was only five minutes. A smartphone was used as an alternative instrument to detect fluorescence signals and a typical image J-processing application was employed to evaluate the grayscale values of the smartphone-captured photographs. The sensor showed a linear concentration range for TNT detection of between 30–500 μM and a detection limit of 30 μM. The T2 paper-based sensor was found to have high selectivity and sensitivity, and it can successfully detect and image TNT in actual samples. This research demonstrates that a T2 paper-based sensor is a promising alternative for TNT detection owing to its short reaction time, high selectivity, sensitivity, and easy applicability. [ABSTRACT FROM AUTHOR]

Plasmonic paper has received attention as a surface-enhanced Raman scattering (SERS) substrate due to several advantages. These include low cost, high rates of sample collection, high physical flexibility and relative ease of fabrication. Here, we report the development of a plasmonic paper based on a combination of graphene oxide (GO) and gold nanorods (AuNRs) on cellulose substrates using a simple layer-by-layer immersion method. Rhodamine 6G (R6G) was selected as the probe molecule to determine the SERS efficiency. The GO–AuNR plasmonic paper composite demonstrated superior signal intensity compared to that of the paper substrate coated only with AuNRs. The signal enhancement was due to synergism between the electromagnetic enhancement (EM) originating from the AuNRs and the chemical enhancement effect (CE) originating from GO. To optimize the fabrication process, the first step was accomplished by varying the GO concentration during the paper pretreatment step. This was followed by determining the number of immersion cycles required for optimal absorption of AuNRs. The highest SERS signals derived from R6G molecules indicated that the 2 mg mL−1 GO pretreatment condition followed by two immersion cycles into the AuNR solution proved to be the best condition for plasmonic paper fabrication. The enhancement factor (EF) of the plasmonic paper was calculated to be 4.56 × 107 and the limit of detection (LOD) for R6G analysis was as low as 0.1 nM. Moreover, the plasmonic paper was tested in the detection of Mitoxantrone (MTX), an anti-cancer drug. We found that the LOD for detection of MTX was on the order of 5 μM. This simple and cost effective plasmonic paper offers an alternative SERS substrate which has potential in trace analysis and drug monitoring. [ABSTRACT FROM AUTHOR]

The design and preparation of a reduced graphene oxide (rGO) paper electrode with a reinforced concrete structure is an effective strategy to improve the mechanical properties of flexible electrodes. Therefore, PEDOT:PSS is added as a binder, toughening and conductive agent. CNTs, with good mechanical properties, are added to enhance the strength. Fe2O3 nanoparticles are added to increase the energy storage. According to these assumptions, we successfully prepared a flexible hydrophilic paper electrode with rGO nanosheets, PEDOT:PSS, CNTs and Fe2O3 nanoparticles by a constant temperature vacuum drying method. In addition, the assembled symmetrical supercapacitor exhibits a high capacitance of 1924 mF cm−3 at 1 mA cm−3, an excellent energy density of 35.6 W h kg−1 (at 166 W kg−1) and a remarkable cycle stability of 98.2% retention over 10 000 cycles at 1 mA cm−2. [ABSTRACT FROM AUTHOR]

As a part of our ongoing research, we have synthesized a new fluorescence probe, p-C4A, based on a calix[4]arene substituted with 4-aminoquinoline moieties with amide linkages. p-C4A can selectively recognize Li+ and PO43− ions and has been characterized via an emission study, an absorption study, ESI-MS spectroscopy, a 1H NMR study and cyclic voltammetry. The fluorescence sensor p-C4A can operate over a concentration range of 5–170 nM for Li+ sensing and 5–80 nM for PO43− sensing. The R2 values obtained for the sensing of Li+ and PO43− ions are 0.9962 and 0.9911, respectively. p-C4A demonstrates a minimum detection limit of 6.15 nM for Li+ and 9.0 nM for PO43−. The quantum yields of p-C4A as its Li+ and PO43− ion complexes were found to be 0.014 and 0.27, respectively. Herein, we report an easy-to-use, low-cost, disposable, paper-based, fluorescent, wax-printed device for the rapid chemical screening of Li+ and PO43−. This device can be used as a quick, portable, multiple-test panel that is simple, lightweight, and disposable. Moreover, in order to assess its analytical applicability, the prepared sensor was successfully used for the determination of Li+ and PO43− from wastewater samples, validating the proposed ion recovery method with 96–99% recovery rates. [ABSTRACT FROM AUTHOR]

The sustainable goal of technological advancement is to go from lab to site through the development of a sensitive, specific and portable sensor for pollution monitoring. Herein, we report a completely portable colorimetric prototype device for the selective monitoring of lead (Pb) pollution, mainly in air, which relies on a new aspect of analysing the colorimetric assays on paper strips by the direct measurement of the retroreflective information, other than the available tedious image analysis methods. Our indigenously developed citrate-functionalized silver nanoparticles (AgNPs) embedded in cellulose paper strips showed significant localized surface plasmonic resonance (LSPR) peaks in the blue region and with the increase in the Pb concentration, the LSPR band in the blue region decreased and a new peak appeared in the green region of the electromagnetic spectrum due to the formation of larger aggregates. The prototype device monitored these spectral changes and accordingly gave the Pb content present in the sample. In this work, we made the sample under study by the acid digestion of one of the widely present air-suspended particulates, i.e., PbO2. The prototype device is a suitable fielddeployable technique for environmental Pb sensing and will open up new perspectives for future advancement in low-cost paper-based sensing. [ABSTRACT FROM AUTHOR]

The integration of smartphones with visual-based paper strips has gained great attention because of the rapid, low-cost, and relible analysis. Herein, we report on the synthesis of a red luminescent europiumbased metal organic framework (Eu-MOF) for the detection of folic acid in pharmaceutical formulations. The Eu-MOF showed strong and stable red emission fluorescence (excited at 270 nm), and the emission was significantly quenched upon exposure to folic acid due to the inner filter effect. A fluorometric assay in solution and visual detection based on fluorescence on a paper strip were used independently to quantify folic acid. The paper strips were prepared using chromatography paper and with the aid of a smartphone, folic acid was visually detected. In solution, the calculated LOD was 0.3 mM with a dynamic linearity range from 1.0 to 12.50 mM. Meanwhile, in the visual detection based on a smartphone integrated with a paper test strip, the linearity was from 1.0 to 9.0 mM with 0.12 mM as the LOD. Color analysis, from the photographs taken with a smartphone, was performed via analyzing the RGB coordinates using the Image-J program. The luminescent probe was applicable to detect folic acid in various drug tablets with recovery data ranging from 95 to 103%. The application of smartphones and fluorescent paper strips provides reliable detection of folic acid for on-site analysis, particularly in remote rural areas. [ABSTRACT FROM AUTHOR]

Herein, a simple approach is demonstrated for the fabrication of a paper-based flexible symmetrical supercapacitor as an energy saving device with composite functional materials of nickel nanoparticles (Ni NPs) and polypyrrole (PPy). Specifically, an Ni@PPy nanocomposite was synthesized through a two-step process involving the growth of Ni NPs, followed by pyrrole polymerization on a paper substrate. The paper fabricated with Ni@PPy showed an electrical conductivity of 105 S cm−1. The paper-based flexible supercapacitor device configured with Ni@PPy/electrolyte/Ni@PPy was evaluated for electrochemical performance, and it showed a good specific capacitance of 544 F g−1 at 1 A g−1. A better specific energy of 48 W h kg−1, specific power of 400 W kg−1, and good cycling stability (68.3% capacitance retention after 3000 cycles at 5 A g−1) were obtained for the paper-based flexible supercapacitor compared with other reported polymer-based nanocomposite materials. The obtained results suggest that the fabricated paper-based supercapacitor is inexpensive, sustainable, highly efficient, portable and flexible for a wide range of electronic applications. [ABSTRACT FROM AUTHOR]

This work presents the development of a green paper-based analytical device (Green-PAD) array for pH detection. The array was obtained with natural dyes extracted from red cabbage (Brassica oleracea) and butterfly pea flower (Clitoria ternatea); a filter paper was used as a substrate. The RGB indexes of the PADs' colors were extracted from the pictures taken using a smartphone or using a specifically developed RGB detector (Arduino-based) to obtain RGB indexes not affected by the light and the photocamera sensitivity. Multi-technique chemometric models were developed for calculating the pH value, starting from the RGB triplet of each sensing PAD. A preliminary and explorative chemometric analysis with PCA (partial component analysis) and TWPCA (3-way PCA) was carried out. Partial least square regression, PLS, was then applied to correlate the color of the PAD's picture with the solutions' pH. Different solutions at various pHs, ranging from 1 to 13, were obtained by titrating orthophosphoric acid with standardized NaOH, and they were used to create PLS models. Some real samples were examined as a test set, and the results were validated with pH-meter measurements. The ability of the PLS to model the experimental data was satisfactory since a good agreement between the experimental and fitted pH values was obtained. The proposed PADs were prepared with natural dyes and filter papers, so they are completely biodegradable and eco-friendly. Their fabrication does not require toxic or expensive reagents and sophisticated equipment. Also, the developed RGB detector, built-up with low-cost components and recycled batteries, adds value making the measurement cheap, easy and feasible also by non-expert people. [ABSTRACT FROM AUTHOR]

A chromone-based symmetrical dipodal Schiff base probe L was designed and synthesized for multi-analyte detection in both aqueous and organic media. L displayed a prominent 'turn-on' fluorescence response with Al3+ (LOD = 6.9 μM) via the chelation-enhanced fluorescence (CHEF) process in a fully aqueous medium based on the inhibition of the photoinduced electron transfer (PET) process. Moreover, the in situ generated [L-Al3+] system was able to detect pyrophosphate (PPi) under identical experimental conditions. The proposed sensing pathway is believed to be the complexation with aluminium, followed by the subsequent decomplexation of the system by PPi. Furthermore, as the probe was decorated with –NH functionalities, it attained fluorescence indications upon binding with a basic anion. The detection ability of the probe for fluoride ions (LOD = 6.8 × 10−8 M) in the organic medium was studied using the 'turn-off' emission change based on the formation of a N–H⋯F hydrogen bond and subsequent deprotonation, as well as a visual change in color from yellow to reddish-yellow under UV light. The in situ prepared [L-F−] adducts could potentially sense Zn2+ ions with a 'turn-on' response via the metal-induced release of the free probe. All of the spectroscopic analyses were recorded to support the recognition mechanism of the aforementioned analytes by the reported probe molecule L. The probe also found applications in testing real water samples. [ABSTRACT FROM AUTHOR]

Recently, hydrogen peroxide (H2O2) has been used as a disinfectant in sanitizers for cleaning hands, and solid surfaces of hospitals, offices and homes to prevent the spread of the COVID-19 virus. The effluents from domestic, hospital and municipal waste should be monitored for their H2O2 content to avoid the entry of this toxic pollutant into the ecosystem. Therefore, we developed a low-cost graphene (Gr)-printed paper electrode for determination of H2O2 using cyclic voltammetry (CV). An office inkjet-printer and Gr nano-ink stabilized with ethyl cellulose (EC) were used for the fabrication of printed paper electrodes (PPEs) to determine H2O2 quantitatively. A stable Gr–EC nano-ink (2%) with viscosity and surface tension values of 12 mPa S−1 and 35 mN M−1, respectively, was formulated to obtain conductive electrodes. A wide linear range (2 μM–25 mM) with a better limit of detection (0.28 μM) for the determination of H2O2 was obtained when the Gr–EC/PPE was used as a working electrode. Further, the Gr–EC/PPE was successfully employed for analysis of H2O2 in wastewater. The electrochemical determination of H2O2 using the Gr–EC/PPE as an electrode in CV is rapid, economical, flexible and eco-friendly when compared with previously reported methods. [ABSTRACT FROM AUTHOR]

The integration of paper-based devices with fluorescent nanomaterials as recognition elements has offered novel opportunities for biosensing with enhanced sensitivity and selectivity, as well as stable signals. This work innovatively designed a fluorescent paper-based device for enantioselective sensing of D -alanine (D -Ala), where carbon dots (CDs) grafted cellulose paper (PCD) was used as the fluorophore and the in situ generated gold nanoparticles (AuNPs) were used as quenchers. D -α-Amino acid oxidase (DAAO) stereo-selectively catalyzed D -Ala to produce hydrogen peroxide (H2O2), which mediated the in situ formation of PCD/AuNPs composites and quenched the fluorescence of PCD based on fluorescence resonance energy transfer (FRET). Under optimal conditions, the designed PCD/AuNPs demonstrated a reliable quenching response to D -Ala in the range of 1–100 μM and the limit of detection was 0.55 μM. Moreover, the platform was applied to detect D -Ala in serum, simulated gastric fluid samples, and was further employed to determine D -Ala in BGC-823 gastric cancer cells with satisfactory results. Ultimately, the PCD/AuNPs platform provided a novel strategy for the development of reliable and sensitive assays based on paper-based devices. It has great potential to be utilized in enantioselective sensing and clinical early diagnosis. [ABSTRACT FROM AUTHOR]

The practicality of portable fluorescent detectors has attracted widespread attention. Herein, a series of luminogens was obtained via integrating pyrrole/fluorinated-pyrrole with triphenylamine in high yield. The emission performance was modified via varying the F and CN substituents on the pyrrole ring. The compounds TPACHO and TPAFCHO, with aldehyde-group-substituted pyrrole, exhibit significant mechanochromic luminescence (MCL) behavior and typical AIEE properties. The compounds TPA2CN and TPA2FCN can efficiently detect liquid and gaseous hydrazine hydrate, and they can achieve paper-based detection through visually clear emission color switching from yellow/orange to blue. The minimum detectable concentration of hydrazine was 10 mM. Moreover, TPA2CN exhibits good inhibitory activity toward human nasopharyngeal tumor cells (CNE1) and it has application prospects in tumor cell detection and biological cell monitoring. Thus, such functionalized paper can be applied as highly selective discriminating test strips for hydrazine hydrate. [ABSTRACT FROM AUTHOR]

Cellulose is a kind of low-cost, widely-sourced and environmentally friendly material. In this paper, a cellulose acetate/cellulose fiber paper composite membrane was prepared through a phase inversion process. Combining the advantages of these two materials, the composite membrane has good antifouling performance and excellent wear resistance. [ABSTRACT FROM AUTHOR]

The effective incorporation of novel and highly conductive hybrid functional nanomaterials onto flexible and porous substrates is extremely desirable to develop flexible supercapacitors. Herein, a novel 2D/0D-MoS2/SnS2 on a flexible cellulose paper substrate has been demonstrated for its utilization in flexible supercapacitors. The surface morphology and particle size of the MoS2 and SnS2 QDs, elemental composition, absorption spectra, and crystallinity have been analyzed thoroughly. Further, to explore the supercapacitor applications, the electrochemical response has been studied. The obtained results demonstrate that both the pristine MoS2 and MoS2/SnS2 QDs composites on cellulose paper exhibited excellent electrochemical performance. The specific capacitance for the pristine MoS2 and MoS2/SnS2 QDs displayed 422.2 F g−1 and 277.1 F g−1 at 0.5 A g−1 current density using a conventional two-electrode system. The drop-casting of SnS2 QDs provides better electrochemical active sites, which contributed to the enhanced specific capacitance of the composite structure. Moreover, it is shown that cellulose paper as an electrode material, using MoS2 and MoS2/SnS2 QDs, is applied as a supercapacitor for potential utilization in wearable electronics applications. [ABSTRACT FROM AUTHOR]

Herein, an inkjet-printed paper electrode (PPE) with gold nanoparticle (AuNP)-ink as a non-enzymatic electrochemical sensor for detection of glucose in blood serum is reported. In this work, a green method is used for the synthesis of the aqueous AuNP-ink and the electrode is fabricated on a paper substrate using an office desktop inkjet-printer. The developed AuNP-ink is stable and has a surface tension and viscosity of 70.2 mN m−1 and 2.1 mPa s (2% aqueous AuNP ink). The PPE with AuNPs is sintered at 100 °C for 30 min to obtain a conductive film for electrochemical sensing. The prepared AuNP-PPE is employed as a working electrode in cyclic voltammetry (CV) for the sensitive measurement of glucose in blood serum. The fabricated AuNP-PPE demonstrated excellent electrochemical activity and rapid electron transfer kinetics towards the oxidation of glucose. A wide linear range, 0.05–35 mM, with a limit of detection of 10 μM is observed for the determination of glucose. The advantages of using the AuNP-PPE in electrochemical measurements are that it is flexible, user-friendly, biodegradable, economic and enzyme-free with respect to the commercially available electrochemical sensors. [ABSTRACT FROM AUTHOR]

Paper-based sensors open a new avenue to produce easy-to-handle, inexpensive and simple-use analytical devices for widespread application fields in biological systems involving diagnosis, drug discovery and biosensing. In this manuscript, we constructed a fluorescence sensor based on functionalized paper coupled with silver nanoparticles (AgNPs) etching for hydrogen peroxide (H2O2) determination in biological systems. A significant fluorescence signal was achieved by immobilizing CDs onto the surface of cellulose filter paper by covalent bonds. The CDs functionalized paper coupled with AgNPs composites platform (PCD/AgNPs) consisted of CDs functionalized paper (PCD) and a AgNPs layer which acted as a fluorescence quencher of CDs via a physical adsorption mechanism. With the introduction of H2O2, the AgNPs were etched accompanied by the fluorescence recovery. As the target, a good linear relationship of a fluorescence turn-on response toward H2O2 between 10 and 120 μM was obtained with a limit of detection of 1.38 μM in our sensor. The designed sensor demonstrated good specificity and would have broad application prospects in the detection of milk samples and determination of H2O2 released from cancer cells. [ABSTRACT FROM AUTHOR]

One of the primary challenges for the development of electrochemical sensors for dopamine (DA) is the lack of selectivity due to the major interference from ascorbic acid (AA) which is oxidized at a potential close to the working potential of DA. In this work, we present a means for simple and cost-effective electrochemical detection of DA in the presence of interference using a microfluidic paper-based analytical device (eμPAD) to improve the selectivity and sensitivity. The device was made by incorporating the sample separation and the electrochemical detection elements into a single device, which required a single drop of the sample solution. For sample separation, Nafion was cast on the sample zone and microfluidic channel to block AA, before the solution was allowed to continuously flow to the detection zone. A multilayered eμPAD was fabricated by placing a round cotton pad on the detection zone to enable the generation of a quasi-steady flow rate. Thereafter, a packing tape was used to seal the top part of the device to increase the flow rate and prevent volatilization of the sample on the eμPAD. The concentration of DA that could be measured by the poly(glutamic acid) modified screen-printed graphene electrode was in the range of 1–200 μM, and the limit of detection (LOD) was 0.41 μM (3SD/slope). The proposed platform provides an accurate and satisfactory method for the detection of DA in real samples compared with UV-Vis spectroscopy. [ABSTRACT FROM AUTHOR]

Paper degradation by iron gall ink is a challenging issue for the conservation of ancient manuscripts. It is usually attributed to both FeII catalyzed oxidation and acid catalyzed hydrolysis of cellulose, yet the dominant degradation pathway remains an open question. In this work, electron spin resonance spectroscopy (ESR) was used to identify radicals involved in cellulose degradation. Papers impregnated with iron salts were put in contact with an aqueous solution of DMPO (spin-trap) and analyzed by ESR. No DMPO–OHṖ adducts were detected while the addition of formate, an intermediary target molecule, led on the contrary to the detection of a significant amount of DMPO–CO2Ṗ− adducts. This reveals the predominant occurrence of reactive oxygen species (ROS) other than hydroxyl radicals (most likely superoxide or hydroperoxyl radicals). The production of DMPO–CO2Ṗ− adducts was found to be oxygen dependent and to originate mainly from ferrous ions lixiviated from the impregnated papers. At high iron loads (above 1 mmol L−1), it was shown that quantification of these adducts should be done with great care because of a competing formation of hydroxylamine that jeopardizes the ESR signal. Complementary TPA hydroxylation measurements performed by HPLC on ink and iron sulfate impregnated papers revealed some production of hydroxyl radicals but at a concentration several orders of magnitude below that of the ROS detected with formation of DMPO–CO2Ṗ− adducts. This HOṖ production was moreover not correlated with cellulose chain scissions, indicating that autooxidation by these radicals is not the main mechanism of cellulose depolymerisation in presence of iron gall ink. [ABSTRACT FROM AUTHOR]

Human papillomavirus (HPV) is one of the most common sexually transmitted infections which causes cervical cancer in women. In order to avoid the development of cancer and the onset of the disease, a reliable and on-site diagnosis for early screening of HPV is still required. To achieve this goal, a smartphone-assisted paper-based colorimetric assay using pyrrolidinyl peptide nucleic acid (acpcPNA) as a probe for the detection of HPV DNA was developed. Dextrin-stabilized gold nanoparticles (d-AuNPs) were used as the colorimetric reagent. The aggregation of the d-AuNPs can be induced by the outstanding properties of the positively charged acpcPNA, generating a distinctive color change. After the duplex formation between the acpcPNA probe and the HPV DNA target, the acpcPNA probe was depleted and the residual probe can cause different degrees of d-AuNPs aggregation, resulting in a detectable color change. The different color change before and after the introduction of the DNA target as a function of the DNA concentration was quantified by analyzing the color intensity through a smartphone application. Under the optimal conditions, the linearity in the range from 1 to 1000 nM with a correlation coefficient of 0.9996 and an experimental limit of detection of 1 nM was obtained. In addition, the acpcPNA probe exhibited high selectivity for the DNA target over single-base-mismatch, two-base-mismatch, and non-complementary DNA. Moreover, this DNA sensor was successfully applied for the detection of HPV DNA from cell line samples. The proposed smartphone-based colorimetric DNA sensor offers a simple, sensitive, and selective way of detecting HPV DNA. Therefore, this DNA sensing device can be utilized as an alternative tool for the point-of-care (POC) screening of HPV. [ABSTRACT FROM AUTHOR]

In this work, a 3,4-ethylenedioxythiophene and tetrahydrophenazine based donor–acceptor–donor-type conjugated molecule was used for the first time as a turn-off fluorescence sensor for the detection of mercury (Hg2+) ions. Eleven metal ions (As3+, Cd2+, Cu2+, Fe2+, Fe3+, Hg+, Hg2+, K+, Ni2+, Se4+ and Zn2+) were tested and the proposed sensor exhibited almost 100% quenching in the fluorescence emission only when interacting with Hg2+ ions. Moreover, the sensor changed its color from yellow to blue upon Hg2+ addition, which indicates that the sensor is not only a fluorescence sensor but also a chromogenic sensor for Hg2+ detection. The solid state behavior was tested by preparing a simple paper-based sensor, and complete fluorescence quenching in the presence of Hg2+ was successfully obtained. The stoichiometry between the sensor and Hg2+ was found to be 1 : 1. The limit of detection (LOD) and the practical quantitation limit (PQL) were calculated to be 8.0 ppm and 26.3 ppm, respectively. The sensor was found to be more sensitive under acidic conditions, and the LOD decreased up to 3.0 ppm in the pH range of 1.6–2.3. [ABSTRACT FROM AUTHOR]

In the current study, noble metal nanoparticle functionalized MoS2 coated biodegradable low-cost paper sensors were fabricated for the selective detection of low concentrations of volatile organic compounds (VOCs). A MoS2 layer was grown on flexible cellulose paper by a two-step hydrothermal route and functionalized further by using noble metal nanoparticles like Au, Pd and Pt by a spray coating technique. MoS2 nanoflakes aggregating into a micro-flower morphology was confirmed by field emission scanning electron microscopy. X-ray photoelectron spectroscopy authenticated the existence of noble metal nanoparticles on the MoS2 surface. Sensors were then tested with seven different VOCs (≤100 ppm) of ketones, alcohols and aromatic hydrocarbon groups. Au–MoS2 and Pd–MoS2 showed inherent acetone and benzene selectivity with 50.5% and 45.7% responses, respectively, after exposure to 100 ppm concentrations at 50 °C. Paper sensors exhibited highly stable baseline resistances, less sensitivity towards humidity (∼75% RH) and an acceptable response/recovery time within 3–6 min at low temperature (50 °C). An additional effort was devoted to discriminating and recognizing different VOCs by using suitable classification algorithms utilizing four types of paper sensors, i.e. pure, Au, Pd and Pt MoS2. Principal component analysis and logistic regression schemes successfully classified five VOCs among the seven. Moreover, the sensing mechanism of the noble metal modified MoS2 paper sensor is discussed in light of the Schottky barrier model. [ABSTRACT FROM AUTHOR]

An optimized structure design of three-dimensional (3D) net-like carbon based Mn3O4 (Mn3O4/CP) composites was realized based on the theory of explosive nucleation and in situ growth. Mn3O4/CP composites have been successfully prepared on a large scale with filter paper adsorbed with manganese(II) oleate as the raw materials using a facile thermal decomposition route. The obtained Mn3O4/CP composite shows a reversible capacity of 1005 mA h g−1 after 90 cycles at a current density of 100 mA g−1, with a remarkably enhanced rate performance and excellent cycling stability compared to the pure Mn3O4 nanostructure which loses most of its capacity within 10 cycles. Even at a current density of 2000 mA g−1, the specific capacity of the Mn3O4/CP composite was still as high as 486 mA h g−1, which is much higher than that of pure Mn3O4 (38 mA h g−1) and the carbon materials (111 mA h g−1). The enhancement of the electrochemical performance could be attributed to the synergy of Mn3O4 enwrapped with the 3D conductive carbon network, thus making it a promising anode material for large-scale energy storage applications. Moreover, this facile and effective synthetic strategy can be further explored as a universal approach for the rapid synthesis of other transition metal oxides and carbon hybrids with subtle structure engineering. [ABSTRACT FROM AUTHOR]

Water-soluble, fluorescent carbon dots (CDs) have been successfully synthesized from waste paper. The as-prepared CDs, with an amorphous structure and small particle size, exhibit good photostability, high photoluminescence quantum yields (PLQYs) and fairly low toxicity, which indicate potential applications in the field of biolabelling. [ABSTRACT FROM AUTHOR]

Berberine (BBR) is a highly effective animal feed additive, but it also has adverse side effects on animals and causes potential food safety issues. Here, based on the preparation of a BBR monoclonal antibody, we developed a rapid, simple and sensitive lateral flow immunoassay (LFIA) using gold nanoparticle (GNP)- and fluorescent microsphere (FM)-labelled BBR antibodies for quantitative detection of BBR in feed samples. Under a hand-held optical scanner, the limits of detection of the GNP-LFIA and FM-LFIA were found to be 4.40 μg kg−1 and 2.00 μg kg−1, respectively, in feed samples. The spiked feed samples had acceptable recovery rates using the LFIAs, and the results were further confirmed by liquid chromatography/mass spectrometry. The actual feed sample test results by GNP-LFIA and FM-LFIA also showed good consistency. These two LFIAs provide a good option for fast screening of BBR on-site in feed samples. [ABSTRACT FROM AUTHOR]

A microfluidic paper-based analytical method is developed for determination of Hg(II) using gold nanoparticles functionalized with N,N′-bis(2-hydroxyethyl)dithiooxamide. Fabrication of the μPAD in this work is free of any expensive equipment and could be performed by untrained personnel. The color of modified AuNPs in the test zone instantly changes after addition of Hg(II), and this color change can be detected by the naked eye, or a digital camera. Under optimized experimental conditions, the linear range is 0.020–8.0 μM of Hg(II) with 12.5 nM (2.5 ppb) detection limit in aqueous solution. In the case of the μPAD, the linear concentration range is 0.025–2.0 μM Hg(II) with a detection limit of 15 nM (3.0 ppb). This method is used for the determination of mercury in real samples such as salmon fish and dusty days in Sanandaj, Iran. The results determined by this method agreed well with those determined according to the ASTM standard method. [ABSTRACT FROM AUTHOR]

Developing high-efficiency electrocatalysts for the hydrogen evolution reaction (HER) is of great importance. In this paper, dendrite-free Ni–Cu catalysts were synthesised via one-step pulse electrodeposition under a weak magnetic field (0.5 T). Regardless of the direction of the magnetic field, the ions were affected by the magnetohydrodynamic (MHD) effect, which greatly promoted the mass transfer and dispersion uniformity, and suppressed the uncontrollable agglomeration by electrodeposition. It was found that the nucleation mechanism changed from progressive nucleation under a 0 T magnetic field to instantaneous nucleation under a 0.5 T magnetic field. Large-scale (325 nm, 0 T) dendrite growth on the single-sided plane was successfully suppressed, and replaced by smaller (90 nm, 0.5 T) and uniformly distributed cluster growth around the carbon paper. In addition, the (111) plane was strengthened by the magnetic field. Electrochemical analysis showed that the Ni–Cu catalysts exposed more surface area and exhibited greatly enhanced catalytic activity, which only needed −57.3 mV to deliver the current density of 10 mA cm−2 with a small Tafel slope of 99.4 mV dec−1 in 1 M KOH. Overall, magneto-electrodeposition, especially under weak magnetic field conditions, provides great promise for the preparation of HER catalysts. [ABSTRACT FROM AUTHOR]

In this study, we report for the first time few-layered MoS2 nanosheets grown onto graphene dipped cellulose filter paper (M-G-CFP) using a simple hydrothermal method towards efficient adsorption of cationic methylene blue (MB) dye. Detailed morphological and chemical characterization studies of M-G-CFP are performed using FESEM, TEM, XRD and Raman spectroscopy that reveal micro flower-like MoS2 grown onto graphene modified paper with few layers of MoS2 nanosheets and its high purity nature. Due to electrostatic interactions between cationic dye and the anionic adsorbent surface, the hybrid M-G-CFP exhibits ultrafast removal of MB within 2 min with a maximum adsorption capacity of 485.4 mg g−1 which is superior in comparison to other reported MoS2 based adsorbents. This high adsorption capacity is attributed to large accessible active sites on the surface of the hybrid M-G-CFP structure. The adsorption mechanism of MB dye on the MoS2 nanosheets are well described using kinetic and isotherm models with the effects of parameters like pH, contact time and temperature. The kinetic and isotherm study reveals that the adsorption of MB dye follows a pseudo-second order model, indicating the chemisorption and Langmuir model of monolayer adsorption, respectively. Furthermore, this hybrid structure can be efficiently reused for subsequent dye adsorption without compromising on its dye removal efficiency suggesting it is a feasible and promising material towards wastewater treatment applications. [ABSTRACT FROM AUTHOR]

Herein, natural celery leaves and glutathione were used as the precursors to prepare carbon dots (CDs) as novel fluorescent paper sensors, which exhibited high sensitivity and selectivity for the detection of explosive nitrophenols (including 2-nitrophenol (2-NP), 3-nitrophenol (3-NP) and 4-nitrophenol (4-NP)). The prepared CDs featured blue fluorescence emission under irradiation using an UV lamp, and the fluorescence quantum yield was as high as 53%. As fluorescent probes, the CDs showed a particular response to 2-NP, 3-NP and 4-NP, and the detection limits of 2-NP, 3-NP and 4-NP were determined to be 39 nM, 43 nM and 26 nM, respectively. Due to the multiple advantages including good water solubility, low toxicity and excellent stability, CDs are expected to be widely used. Meanwhile, a CD-based test paper was exploited and it displayed a distinctive quenching response when exposed to 3-NP and 4-NP, with the visual detection limits of 0.5 μM and 0.1 μM, respectively. Furthermore, the low toxicity and biocompatibility of CDs were also demonstrated by evaluating cell culture experiments, and CDs showed good potential applications in imaging. In summary, the prepared CDs are promising for fluorescent paper sensors and bioimaging. [ABSTRACT FROM AUTHOR]

In this work, we developed pillar[5]arene-functionalized paper as a fluorescent sensor for cyanide ions in water. The pillar[5]arene bearing a mono-amine substituent was anchored covalently on paper by the sequence (i) oxidization of hydroxyl groups of glucoses in the cellulose, (ii) condensation with the amino group in the pillar[5]arene and (iii) reduction of the Schiff base obtained. Next, 10-methylacridinium iodide as a fluorescent indicator was introduced onto the paper by non-covalent interactions. Using a simple ultraviolet lamp, this functionalized paper could detect cyanide ions of concentration ranging from 10−7 to 10−3 M by the naked eye. [ABSTRACT FROM AUTHOR]

In this study, we describe the design and successful synthesis of a new hapten, which we used to prepare an anti-zilpaterol mouse monoclonal antibody (mAb) with an IC50 of 0.31 ng mL−1 and a limit of detection (LOD) of 0.02 ng mL−1. A colloidal gold immunochromatographic test strip was further developed and optimized using the antibody, and cross-reactivity experiments were carried out to prove its good specificity. Semi-quantitative and quantitative detections of zilpaterol were evaluated in swine urine and pork samples using the test strips. For semi-quantitative detection in swine urine and pork samples, the visual limit of detection values were 0.5 μg kg−1 and 0.5 μg kg−1, and the cut-off values were 5 μg kg−1 and 5 μg kg−1, respectively. For quantitative detection, the calculated limit of detection values were 0.08 μg kg−1 and 0.12 μg kg−1, and the remaining values were 10 μg kg−1 and 10 μg kg−1. The developed gold nanoparticle-based immunochromatographic assay is highly suitable for on-site detection and rapid preliminary screening of zilpaterol in swine urine and pork samples. [ABSTRACT FROM AUTHOR]