Search

An innovative modular approach for facile design and construction of flexible microfluidic biosensor platforms based on a dry manufacturing “craft-and-stick” approach is developed. The design and fabrication of the flexible graphene paper electrode (GPE) unit and polyethylene tetraphthalate sheet (PET)6/adhesive fluidic unit are completed by an economic and generic xurographic craft approach. The GPE widths and the microfluidic channels can be constructed down to 300 μm and 200 μm, respectively. Both units were assembled by simple double-sided adhesive tapes into a microfluidic integrated GPE (MF-iGPE) that are flexible, thin (−1 glucose. The MF-iGPE showed good reproducibility for glucose detection (RSD < 6.1%, n = 6) and required only 10 μL of the analyte. This modular craft-and-stick manufacturing approach could potentially further develop along the concept of paper-crafted model assembly kits suitable for low-resource laboratories or classroom settings.

Early detection is key to prevent health problems and could be performed by biosensors and chemical sensors. However, a lot of them still need bulky benchtop equipment. This work presents a portable device for measuring fluorescence and light absorption that can be used with optical biosensors or chemical sensors. It uses a small laser diode as a light source and three filter-mounted photodiodes as detectors, all of which are inexpensive, customizable and widely available commercially. The results from our device show good correlation with that from commercial instruments. Therefore, it could be beneficial for early or on-site detection.

Multichannel graphite electrodes (MGrEs) have been designed and fabricated in this study. A template was cut from an adhesive plastic sheet using a desktop cutting device. The template was placed on a polypropylene substrate, and carbon graphite ink was applied with a squeegee to the template. The size of the auxiliary electrode (AE) as well as the location of the reference electrode (RE) of MGrEs design were investigated. Scanning electron microscopy was used to determine the thickness of the ink on the four working electrodes (WEs), which was 21.9 ± 1.8 µm. Cyclic voltammetry with a redox probe solution was used to assess the precision of the four WEs. The intra-electrode repeatability and inter-electrode reproducibility of the MGrEs production were satisfied by low RSD (

A 3D porous graphene structure was directly induced by CO2 laser from the surface of Kapton tape (carbon source) supported by polyethylene terephthalate (PET) laminating film. A highly flexible laser-induced porous graphene (LI-PGr) electrode was then fabricated via a facile one-step method without reagent and solvent in a procedure that required no stencil mask. The method makes pattern design easy, and production cost-effective and scalable. We investigated the performance of the LI-PGr electrode for the detection of methamphetamine (MA) on household surfaces and in biological fluids. The material properties and morphology of LI-PGr were analysed by scanning electron microscopy (SEM), energy dispersive x-ray (EDX) and Raman spectroscopy. The LI-PGr electrode was used as the detector in a portable electrochemical sensor, which exhibited a linear range from 1.00 to 30.0 µg mL−1 and a detection limit of 0.31 µg mL−1. Reproducibility was good (relative standard deviation of 2.50% at 10.0 µg mL−1; n = 10) and anti-interference was excellent. The sensor showed good precision and successfully determined MA on household surfaces and in saliva samples.

Simple, robust, and low-cost nitrate- and ammonium-selective electrodes were made using substrate prepared from household materials. We explored phosphonium-based ILs and poly (methyl methacrylate)/poly(decyl methacrylate)(MMA-DMA) copolymer as matrix materials alternative to classical PVC-based membranes. IL-based membranes showed suitability only for nitrate-selective electrode exhibiting linear concentration range between 5.0 × 10−6 and 2.5 × 10−3 M with a detection limit of 5.5 × 10−7 M. On the other hand, MMA-DMA—based membranes showed suitability for both ammonium- and nitrate-selective electrodes, and were successfully applied to detect NO3− and NH4+ in water and soil samples. The proposed ISEs exhibited near-Nernstian potentiometric responses to NO3− and NH4+ with the linear range concentration between 5.0 × 10−5 and 5.0 × 10−2 M (LOD = 11.3 µM) and 5.0 × 10−6 and 1.0 × 10−3 M (LOD = 1.2 µM), respectively. The power of ISEs to detect NO3− and NH4+ in water and soils was tested by comparison with traditional, portable colorimetric techniques. Procedures required for analysis by each technique from the perspective of a non-trained person (e.g., farmer) and the convenience of the use on the field are compared and contrasted.

Laboratory-built passive samplers were used for monitoring of trace benzene, toluene and xylene (BTX) in Hat Yai from 28 July to 12 August, 2003. Sampler bottles contained activated Tenax TA 60/80 meshand a lab-built thermal well were developed and evaluated for the sampling and analysis of BTX. The sampling was carried out for two weeks before the passive samplers were thermally desorbed, trapped ina sampling loop by a laboratory built purge and trap system and analysed by gas chromatography (GC) equipped with a flame ionization detector. After optimization and calibration, the developed method showed high selectivity, a good sensitivity with detection limits for BTX of 0.8, 1.1 and 13.0 µg/m3 respectively and an acceptable precision. Ambient BTX measurements were conducted at many monitoring site i.e. hot spots (high exposure), residential areas/work places (common exposure) and park (low exposure). The concentration at hot spots range from 3.2 to 5.4 µg/m3 for benzene, 38.0 to 80.3 µg/m3 for toluene and 29.7 to 66.7 µg/m3 for xylene.The low BTX were found at the city periphery (Tesco-Lotus billboard sampling stations, roof level) and in Hat Yai Municipal Park but no absolute background concentration could be defined. The monitoring results showed that at higher level from the street surface, the level of BTX tended to decrease and the BTX pollution built up along a street canyon (Sanehanuson Road) according to the wind direction. The highest BTX were found at the underground parking, 23.5 725.1 and 267.9 µg/m3 respectively where both WHO guideline for Benzene (16.3 µg/m3) and Toluene (260 µg/m3) were exceeded.

Block copolymer E64B20E64, where E denotes oxyethylene, OCH2CH2, B denotes oxybutylene, OCH2CH (C2H5), and the subscripts denote number-average block lengths in repeat units, was synthesized by sequential anionic polymerization. Characterization was by gel permeation chromatography (for molar mass distribution) and 13C-NMR spectroscopy (for absolute molar mass and conformation of block architecture). Dynamic and static light scattering were used to study micellization and micelle properties of this copolymer in dilute aqueous solution and in the presence of naphthalene. Dynamic light scattering was used to analyze hydrodynamic radius, rh and hydrodynamic expansion factor, δh. Static light scattering was used to study micelle association number, Nw, thermodynamic expansion factor, δt, and thermodynamic radius, rt. The presence of naphthalene in micellar core increased Nw by 50% and increased micellar size.

This work presents a square-wave adsorptive stripping voltammetric sensor for the determination of chloramphenicol (CAP) using a glassy carbon electrode modified with branch-like poly (eriochrome black T) film (P(EBT)/GCE). Branch-like P(EBT) film on the GCE was prepared by electropolymerization using cyclic voltammetry. The morphology of the P(EBT)/GCE was characterized by scanning electron microscopy. The concentration of eriochrome black T monomer and the number of electropolymerization cycles used in the fabrication process were optimized. Operational conditions, such as accumulation potential and accumulation time were also optimized. Sensitive determinations were achieved from controlled adsorption at the P(EBT)/GCE. The P(EBT)/ GCE exhibited two linear ranges, 0.01 to 0.10 and 0.10 to 4.0 μmol L-1, with high sensitivity (5.2 μAμM-1). The limit of detection and quantitation were 3 and 11 nmol L-1, respectively. Repeatability (RSD < 2.7%, n = 18), reproducibility (RSD < 2.8%, n = 6) and anti-interference were good. The sensor determined CAP in eye drops and ointment with recoveries between 96 ± 3% and 102 ± 1% (n = 3). [ABSTRACT FROM AUTHOR]

An electrochemical sensor consisting of a screen-printed carbon electrode (SPCE) modified with graphene oxide-poly(acrylic acid)- palladium nanoparticles (GO-PAA-PdNPs) was developed for the nonenzymatic determination of glucose by flow injection amperometry (FI-Amp). PdNPs were synthesized on GO-PAA by electroless deposition. The surface morphology of the modified electrode was characterized by transmission electron microscopy (TEM) and Fourier transform infrared (FT-IR) spectroscopy. The electrochemical behavior of glucose on the different modified surfaces was studied by cyclic voltammetry and amperometry. The GO-PAA-PdNPs-modified SPCE showed excellent electrocatalytic performance for the oxidation of glucose. To achieve the optimal electrocatalytic oxidation of glucose by the GO-PAA-PdNPs/SPCE, the applied potential, sample volume and flow rate of the FIAmp system were optimized. Under the optimal conditions, the current response when the glucose standard was injected provided a detection limit of 22 μmol L-1, a limit of quantitation of 76 μmol L-1 and two linear ranges, 50 to 15,000 μmol L-1 and 15,000 to 60,000 μmol L-1. This sensor had excellent sensitivity as well as good repeatability and selectivity. The sensor was applied to detect glucose in biological fluid samples, and the results were in good agreement with those obtained by the standard hexokinasespectrophotometric method. [ABSTRACT FROM AUTHOR]

This work reports the development of a non-enzymatic electrochemical sensor for hydrogen peroxide based on a glassy carbon electrode modified with glassy carbon spherical powder carrying silver particles (AgPs-GCS/GCE). In this work, AgPs were synthesized on GCS by electroless deposition. The surface morphology and electrochemical behavior of the AgPs-GCS/GCE were characterized by scanning electron microscopy (SEM) and cyclic voltammetry, respectively. The average diameter of the AgPs on GCS was 673 ± 89 nm. The AgPs-GCS/GCE exhibited excellent electrocatalytic activity for the reduction of hydrogen peroxide. The proposed modified electrode was incorporated in a flow injection amperometry system (FI-Amp). The optimized fabrication and operational conditions included the amount of AgPs-GCS covering the GCE, and the applied potential, flow rate and sample volume. Under optimal conditions, the proposed method provided a wide linear range (0.25-350 µg mL-1) (r = 0.999) with high sensitivity (5.75 µA mg L-1 cm-2). The limit of detection (LOD) and limit of quantitation (LOQ) were 0.12 µg mL-1 and of 0.38 µg mL-1, respectively. This sensor exhibited good repeatability (RSD < 5.7%), good stability (RSD = 1.98%, n = 170), and high sample throughput (90 samples h-1) and the developed method successfully detected hydrogen peroxide in hair dyes and cotton samples with good recoveries (90 ± 2% to 106 ± 2%). [ABSTRACT FROM AUTHOR]