Microwave synthesis of blue emissive N-doped carbon quantum dots as a fluorescent probe for free chlorine detection

Blue emissive N-doped carbon quantum dots (N-CQDs) were prepared through a convenient and sustainable microwave synthesis method using citric acid monohydrate (CA) and urea as carbon and nitrogen sources, respectively, with an optimum molar ratio of 1:3 (CA:Urea). The surface functional groups, morphology, and hydrodynamic characteristics of N-CQDs were analysed with Fourier-transform infrared (FTIR) spectroscopy, high-resolution transmission electron microscopy (HRTEM) and dynamic light scattering (DLS), respectively. The as-synthesised N-CQDs with a quantum yield of 14.8%, exhibited excitation-independent fluorescence emission at 443 nm due to surface-state-induced fluorescence, with an optimum excitation wavelength at 360 nm. The N-CQDs were spherical, with an average particle size of 7.29 ± 3.91 nm based on HRTEM analysis. However, DLS analysis showed that the hydrodynamic size (293.0 ± 110.8 nm) was larger than the average particle size due to the presence of hydrophilic polymer chains and abundant surface groups on the N-CQDs. The free chorine-induced fluorescence quenching of N-CQDs at pH 9 denotes the sensitivity of N-CQDs towards detection of free chlorine in the form of hypochlorite (ClO-) ion, providing the limit of detection (LOD) of 0.4 mM and limit of quantification (LOQ) of 1.2 mM. The fluorescence quenching effect in the N-CQDs caused by the quencher (ClO-) is attributed to the dynamic quenching mechanism, via an intersystem crossing. The low selectivity of N-CQDs towards various ions justified N-CQDs’ selectivity as a free chlorine fluorescent probe that can be used for wastewater testing due to its high range sensitivity

Chitosan-modified cotton thread for the preconcentration and colorimetric trace determination of Co(II)

In this work we propose a thread-based microfluidic device (μTAD) for the preconcentration and colorimetric determination of Co(II) in water using a digital image. The reaction is based on complexation of Co(II) by 4-(2- pyridylazo) resorcinol (PAR), which changes the detection zone from yellow to red. PAR is immobilized in a chitosan membrane to retain the complex in the detection zone. The designed μTAD makes it possible to pre- concentrate and determine cobalt between 25 and 600 µg·L−1 with a relative standard deviation of 4% (n = 5), and a detection limit of 6.5 µg·L−1. The device permits an enhancement factor of 11 by combining the use of a chitosan retention membrane and a sample volume of 50 µL. Recovery experiments were performed in tap water to evaluate the accuracy of the method, and the results obtained compared to a reference method presents an error no higher than 5.7%This work was founded by Spanish “Ministerio de Economía y Competitividad” under Project CTQ2016-78754-C2-1-R and Junta de Andalucía under Projects B-FQM-243-UGR18 and P18-RT-2961. The project was partially supported by European Regional Development Funds (ERDF). Supporting Research in the State of Minas Gerais (Fapemig) (CEX-APQ-02436-15)

Cellulose: from biocompatible to bioactive material

International audienceSince the papyri, cellulose has played a significant role in human culture, especially as paper. Nowadays, this ancient product has found new scientific applications in the expanding sector of paper-based technology. Among paper-based devices, paper-based biosensors raise a special interest. The high selectivity of biomolecules for target analytes makes these sensors efficient. Moreover, simple paper-based detection devices do not require hardware or specific technical skill. They are inexpensive, rapid, user-friendly and therefore highly promising for providing resource-limited settings with point-of-care diagnostics. The immobilization of biomolecules onto cellulose is a key step in the development of these sensing devices. Following an overview of cellulose structural features and physicochemical properties, this article reviews current techniques for the immobilization of biomolecules on paper membranes. These procedures are categorized into physical, biological and chemical approaches. There is no universal method for biomolecule immobilization. Thus, for a given paper-based biochip, each strategy can be considered

Classification of alcohols obtained by QCM sensors with different characteristics using ABC based neural network

Alcohols with different structures are used frequently in hygiene products and cosmetics. It is desirable to classify these alcohols to evaluate their potential harmful effects using less costly methods. In this study, five different types of alcohol are classified using five QCM sensors with different structures. The main idea of the study is to determine the QCM sensor that makes the most successful classification. All the five of the QCM sensors gave successful results, but QCM12-constructed using only NP-was the most successful. ABC-based ANN is used for the classification, and the lowest MSE value in test dataset is obtained as 1.41E-16. The results of 300 different scenarios showed that different alcohols can be classified successfully by using ANN-ABC on the sensor data from QCM12. (C) 2019 Karabuk University. Publishing services by Elsevier B.V

Strategy to enhance the wettability of bioacive paper-based sensors

This paper reports a potential method that can restore the wettability of bioactive paper-based sensors while maintaining their bioactivity. This study is driven by the need to increase the wettability of the antibody-loaded blood typing paper devices in order to increase the blood typing assaying speed using such paper devices. Plasma treatment is used to improve the wettability of bioactive paper; the protective effect of bovine serum albumin (BSA) to biomolecules against plasma deactivation is investigated. In the first stage, horseradish peroxidase (HRP) was used as a model biomolecule, because of the convenience of its quantifiable colorimetric reaction with a substrate. By using this protection approach, the inactivation of biomolecules on paper during the plasma treatment is significantly slowed down. This approach enables plasma treatment to be used for fabricating paper-based bioactive sensors to achieve strong wettability for rapid penetration of liquid samples or reagents. Finally, we demonstrate the use of plasma treatment to increase the wettability of antibody treated blood typing paper. After the treatment, the blood typing paper becomes highly wettable; it allows much faster penetration of blood samples into the plasma treated testing paper. Antibodies on the paper are still sufficiently active for blood typing and can report patients' blood type accurately

Portable multispectral fluorometer for determination of formalin in food samples using nitrogen-doped carbon dots as the fluorescence probe

In this work, we developed a portable multispectral fluorometer for determining formalin (FA). We used nitrogen-doped carbon dots (N-CDs) as the fluorescence probe, based on right-angle fluorescence spectrometry with twin excitation high-power light emitting diode sources. The multispectral spectroscopy sensor was used as a detector for fluorescence intensity. The fluorescence intensity values were displayed from 0 to 65535 a.u. The FA determination results show a linear relationship in the FA concentration range of 10-75 mg L−1 with r2 = 0.9908. The limit of detection (LOD) was 2.09 mg L−1 (calculated from 3SDblank/slope (n = 3)). In addition, the percentage of relative errors compared with the standard method and standard instrument shows less than 10 percent. The performance of a portable multispectral fluorometer in actual samples exhibited no significant difference compared to the validation instrument results. Therefore, the development of a portable multispectral fluorometer can be used as a fluorometer, and the measurement performance is comparable to a standard fluorescence spectrometer

Poly(m-ferrocenylaniline) modified carbon nanotubes-paste electrode encapsulated in nafion film for selective and sensitive determination of dopamine and uric acid in the presence of ascorbic acid

A nafion covered carbon nanotubes-paste electrode modified with poly(m-ferrocenylaniline), (Nf/p(FcAni)-CNTsPE), provides a novel voltammetric sensor for the selective determination of dopamine (DA) and uric acid (UA) in the presence of ascorbic acid (AA). We studied the electrochemical activity of Nf/p(FcAni)-CNTsPE toward DA, UA, and AA by differential pulse voltammetry (DPV). DA and UA anodic peaks appear at 0.30 and 0.45 V, respectively while an anodic peak for AA was not observed. DPV oxidation peak values are linearly dependent on DA concentration over the range 1–150 μM (r2 = 0.992), and on UA concentration over the range 5–250 μM (r2 = 0.997). DA and UA detection limits are estimated to be 0.21 and 0.58 μM, respectively. The modified electrode shows both good selectivity and reproducibility for the selective determination of DA and UA in real samples. Finally, the modified electrode was successfully applied for the determination of DA and UA in pharmaceutical or biological sample fluids