Smartphone-Based Whole-Cell Biosensor Platform Utilizing an Immobilization Approach on a Filter Membrane Disk for the Monitoring of Water Toxicants

Bioluminescent bacteria whole-cell biosensors (WCBs) have been widely used in a range of sensing applications in environmental monitoring and medical diagnostics. However, most of them use planktonic bacteria cells that require complicated signal measurement processes and therefore limit the portability of the biosensor device. In this study, a simple and low-cost immobilization method was examined. The bioluminescent bioreporter bacteria was absorbed on a filter membrane disk. Further optimization of the immobilization process was conducted by comparing different surface materials (polyester and parafilm) or by adding glucose and ampicillin. The filter membrane disks with immobilized bacteria cells were stored at −20 °C for three weeks without a compromise in the stability of its biosensing functionality for water toxicants monitoring. Also, the bacterial immobilized disks were integrated with smartphones-based signal detection. Then, they were exposed to water samples with ethanol, chloroform, and H2O2, as common toxicants. The sensitivity of the smartphone-based WCB for the detection of ethanol, chloroform, and H2O2 was 1% (v/v), 0.02% (v/v), and 0.0006% (v/v), respectively. To conclude, this bacterial immobilization approach demonstrated higher sensitivity, portability, and improved storability than the planktonic counterpart. The developed smartphone-based WCB establishes a model for future applications in the detection of environmental water toxicants.

Solid phase extraction of zinc with octadecyl silica membrane disks modified by N,N’-disalicylidene-1,2-phenylendiamine and determination by flame atomic absorption spectrometry

A procedure for separation and preconcentration of trace amounts of Zn(II) from aqueous media is proposed. The procedure is based on the adsorption of Zn2+ on octadecyl bonded silica membrane disk modified with N,N’-disalicylidene-1,2-phenylendiamine at pH 7. The retained zinc ions were then stripped from the disk with a minimal amount of 1.5 mol L-1 hydrochloric acid solution as eluent, and determined by flame atomic absorption spectrometry. Maximum capacity of the membrane disk modified with 5 mg of the ligand was found to be 226 μg Zn2+. The relative standard deviation of zinc for ten replicate extraction of 10 μg zinc from 1000 mL samples was 1.2%. The limit of detection of the proposed method was 14 ng of Zn2+ per 1000 mL. The method was successfully applied to the determination of zinc in natural water samples and accuracy was examined by recovery experiments and independent analysis by graphite furnace atomic absorption spectrometry (GFAAS).

C18 Bonded Silica Membrane Disk Modified with Cyanex 302 for Cr(III) and Cr(VI) Speciation and Flame Atomic Absorption Spectrometric Determination

A new SPE method for speciation of Cr(III) andCr(VI) has been developed using a Cyanex 302-impregnated C18 bonded silica membrane disk followed by flame atomic absorption spectrometric determination. The influence of various parameters, such as pH, flow rate, volume of sample solution, amount of Cyanex 302, and eluent type, concentration,and flow rate, on Cr(III) retention, were systematically studied. Cr(III) was quantitatively recovered from the modified sorbent at pH 4.5, while the recovery of Cr(VI) was negligible (0.5 ± 0.5 μg) throughout the pH range studied for its sorption, thus facilitating their separation and speciation. Most of the elements associated with Cr(III) did not show strong interference during its sorption. The sorption capacity of modified disk for Cr(III) was 117.6 ± 0.8 μg, and its enrichment factor for Cr(III) was 37. The LOD and LOQ of the method for Cr(III) were 0.88 and 2.93 μg/L, respectively. The efficiency of the disk for Cr(III) recovery remained unchanged up to 24 cycles. A certified reference material (BCR-701) was analyzed to validate theaccuracy of method developed for Cr(III). The method was applied to the determination of Cr(III) and Cr(VI) species in tap water and an industrialeffluent sample, with RSD ≤1.0%.

Octadecyl-Bonded Silica Membrane Disk Modified with Cyanex302 for Pre-Concentration and Determination of Iron in Food Products

A simple and rapid method using an octadecyl-bonded silica membrane disk impregnated with Cyanex302 is described for the pre-concentration and determination of iron. The influence of various parameters on sorption and elution of Fe(III) were systematically investigated. The sorption of Fe(III) at pH 3.2 was quantitative (99.3 ± 1.1%). It was completely recovered using 20 mL 5.0 M HCl and determined by flame atomic absorption spectrometry. Breakthrough volume of the modified disk for Fe(III) was >2000 mL, pre-concentration factor was >100, and reusability up to 28 cycles. The LOD and LOQ for Fe(III) were 0.45 μg/L and 1.51 μg/L, respectively, while precision for its determination in terms of RSD was ≤ 2.1%. This method was applied for Fe(III) determination in milk, fortified flour, cocoa powder, tea, and black pepper. To validate the procedure, EPA Method Standard (QC standard 21) was analyzed for Fe(III).

Solid-Phase Extraction and Atomic Absorption Spectrometric Determination of Cobalt Using an Octadecyl Bonded Silica Membrane Disk Modified with Cyanex 272

A simple SPE method for determination of cobalt(II) using a C18 bonded silica membrane disk impregnated with Cyanex 272 has been developed. Cobalt(II) was quantitatively sorbed at pH 6.0 from a sample solution and eluted using 10.0 mL 1.0 M HNO3 prior to its flame atomic absorption spectrometric determination. The influence of eluting agents, the minimum volume and maximum flow rate of the eluent, and interfering ions on cobalt(II) was studied. The method developed for cobalt(II) had an LOD of 1.4 g/L, and a preconcentration factor >200 with an RSD of 0.6. The reusability of the modified disk was for 40 cycles. The method was applied for the determination of cobalt in certified samples, urine, and industrial sludge samples.

Chip Formation of Highly Efficient Cutting Titanium Alloy Membrane Disk

Titanium alloy membrane disk is a typical part in aerial engine and it belongs to variable cross-section thin-wall part, which is apt to change its nature and difficult to machine. Serrated chip is prone to create in the machining process. A periodic serrated chip will cause high frequency undulation of the cutting force, and further leads to the cutting tool wear and affect the surface’s integrity. Based on the turning of titanium membrane disk, this paper used metallographic microscope and SEM to observe the morphology and micro shape of the chip, and analyzed the influence of cutting conditions on chip formation and the reason for serrated chip. Finally, a FEM analysis on the chip formation process is completed. Analysis results show that under all the set cutting conditions the serrated chip was formed in the machining process. The shearing slippage and fracture caused by dislocation movement can better explain the formation mechanism of serrated chip. The feed rate has great effect on the chip formation and the forming frequency of serrated chip. The FEM analysis results primly consistent with the experiment results, which can accurately forecast the cutting force, the distribution of temperature and the surface quality.