Surface Functionalization and Escherichia coli Detection Using Surface-Enhanced Raman Spectroscopy Driven by Functional Organic Polymer/Gold Nanofilm-Based Microfluidic Chip.

In this work, a microfluidic prototype based on polymeric materials was developed to monitor surface processes using surface-enhanced Raman spectroscopy (SERS), keeping the reagents free of environmental contamination. The prototype was fabricated on poly(methyl methacrylic acid) (PMMA). A micrometric membrane of a functional organic polymer (FOP) based on p-terphenyl and bromopyruvic acid monomers was formed on the PMMA surface to promote the formation of metal nanoclusters. Au nanosized film was deposited on the FOP membrane to give rise to the SERS effect. A microchannel was formed on another piece of PMMA using micromachining. A representative 3D model of the prototype layer arrangement was built and simulated in COMSOL Multiphysics® to approximate the electric field distribution and calculate the power enhancement factor as the Au film changes over time. The fabrication process was characterized using UV-visible and Raman spectroscopies and XPS. The prototype was tested using a Raman microscope and liquid solutions of cysteamine and Escherichia coli (E. coli). The simulation results demonstrated that the morphological characteristics of the Au layer give rise to the SERS effect, and the power enhancement factor reaches values as high as 8.8 × 105 on the FOP surface. The characterization results showed the formation of the FOP and the Au film on PMMA and the surface functionalization with amine groups. The Raman spectra of the prototype showed temporal evolution as different compounds were deposited on the upper wall of the microchannel. Characteristic peaks associated with these compounds were detected with continuous monitoring over time. This prototype offers many benefits for applications like monitoring biological processes. Some advantages include timely surface evaluation while avoiding environmental harm, decreased use of reagents and samples, minimal interference with the process by measuring, and detecting microorganisms in just 1 h, as demonstrated with the E. coli sample.

A Comparative and Critical Analysis for In Vitro Cytotoxic Evaluation of Magneto-Crystalline Zinc Ferrite Nanoparticles Using MTT, Crystal Violet, LDH, and Apoptosis Assay.

Zinc ferrite nanoparticles (ZFO NPs) are a promising magneto-crystalline platform for nanomedicine-based cancer theranostics. ZFO NPs synthesized using co-precipitation method are characterized using different techniques. UV-visible spectroscopy exhibits absorption peaks specific for ZFO. Raman spectroscopy identifies Raman active, infrared active, and silent vibrational modes while Fourier transforms infrared spectroscopic (FTIR) spectra display IR active modes that confirm the presence of ZFO. X-ray diffraction pattern (XRD) exhibits the crystalline planes of single-phase ZFO with a face-centered cubic structure that coincides with the selected area electron diffraction pattern (SAED). The average particle size according to high-resolution transmission electron microscopy (HR-TEM) is 5.6 nm. X-ray photoelectron spectroscopy (XPS) signals confirm the chemical states of Fe, Zn, and O. A superconducting quantum interference device (SQUID) displays the magnetic response of ZFO NPs, showing a magnetic moment of 45.5 emu/gm at 70 kOe. These ZFO NPs were then employed for comparative cytotoxicity evaluation using MTT, crystal violet, and LDH assays on breast adenocarcinoma epithelial cell (MCF-7), triple-negative breast cancer lines (MDA-MB 231), and human embryonic kidney cell lines (HEK-293). Flow cytometric analysis of all the three cell lines were performed in various concentrations of ZFO NPs for automated cell counting and sorting based on live cells, cells entering in early or late apoptotic phase, as well as in the necrotic phase. This analysis confirmed that ZFO NPs are more cytotoxic towards triple-negative breast cancer cells (MDA-MB-231) as compared to breast adenocarcinoma cells (MCF-7) and normal cell lines (HEK-293), thus corroborating that ZFO can be exploited for cancer therapeutics.

Three-Dimensional-Order Macroporous AB2O4 Spinels (A, B =Co and Mn) as Electrodes in Zn-Air Batteries.

In this work, atomically substituted three-dimensionally ordered macroporous (3DOM) spinels based on Co and Mn (MnCo2O4 and CoMn2O4) were synthetized and used as cathodic electrocatalysts in a primary Zn-air battery. Scanning/transmission electron microscopy images show a 3DOM structure for both materials. Skeleton sizes of 114.4 and 140.8 nm and surface areas of 65.3 and 74.6 m2 g-1 were found for MnCo2O4 and CoMn2O4, respectively. The increase in surface area and higher presence of Mn3+ and Mn4+ species in the CoMn2O4 3DOM material improved battery performance with a maximum power density of 101.6 mW cm-2 and a specific capacity of 1440 mA h g-1, which shows the highest battery performance reported to date using similar spinel materials. The stability performance of the electrocatalyst was evaluated in half-cell and battery cell systems, showing the higher durability of CoMn2O4, which was related to its better capability to perform the electrocatalytic process as adsorption, electron transfer, and desorption. It was found through density functional theory calculations that the CoMn2O4 spinel has a higher density of states in the Fermi level vicinity and better conductivity. Finally, the unique shape of 3DOM spinels promoted a high interaction between electroactive species and catalytic sites, making them suitable for oxygen reduction reaction applications.

A Flow-Through Membraneless Microfluidic Zinc-Air Cell.

In this work, the proof of concept of a functional membraneless microfluidic Zn-air cell (µZAC) that operates with a flow-through arrangement is presented for the first time, where the activity and durability can be modulated by electrodepositing Zn on porous carbon electrodes. For this purpose, Zn electrodes were obtained using chronoamperometry and varying the electrodeposition times (20, 40, and 60 min), resulting in porous electrodes with Zn thicknesses of 3.3 ± 0.3, 11.6 ± 2.4, and 34.8 ± 5.1 µm, respectively. Pt/C was initially used as the cathode to analyze variables, such as KOH concentration and flow rate, and then, two manganese-based materials were evaluated (α-MnO2 and MnMn2O4 spinel, labeled as Mn3O4) to determine the effect of inexpensive materials on the cell performance. According to the transmission electron microscopy (TEM) results, α-MnO2 has a nanorod-like shape with a diameter of 11 ± 1.5 nm, while Mn3O4 presented a hemispherical shape with an average particle size of 22 ± 1.8 nm. The use of α-MnO2 and Mn3O4 cathodic materials resulted in cell voltages of 1.39 and 1.35 V and maximum power densities of 308 and 317 mW cm-2, respectively. The activities of both materials were analyzed through density of state calculations; all manganese species in the α-material MnO2 presented an equivalent density of states with a reduced orbital occupation to the left of the Fermi energy, which allowed for better global performance above Mn3O4/C and Pt/C.