Nickel contamination analysis at cost-effective silver printed paper-based electrodes based on carbon black dimethylglyoxime ink as electrode modifier

Electrochemical detection of metal cations at paper-based sensors has been suggested as an attractive alternative to current spectroscopic and chromatographic detection techniques due to the ease of fabrication, disposable nature, and low cost. Herein, a novel carbon black (CB), dimethylglyoxime (DMG) ink is designed as an electrode modifier in conjunction with 3-electrode inkjet-printed paper substrates for use in the adsorptive stripping voltammetric electroanalysis of nickel cations in water samples. The developed method provides a novel, low-cost, rapid, and portable adsorptive stripping detection approach towards metal analysis in the absence of the commonly used toxic metallic films. The study demonstrated a novel approach to nickel detection at paper-based sensors and builds on previous work in the field of paper-based metal analysis by limiting the use of toxic metal films. The device sensitivity is improved by increasing the active surface area, electron transfer kinetics, and catalytic effects associated with non-conductive dimethylglyoxime films through CB nanoparticles for the first time and confirmed by electroanalysis. The first use of the CB-DMG ink allows for the selective preconcentration of analyte at the electrode surface without the use of toxic Mercury or Bismuth metallic films. Compared to similarly reported paper-based sensors, improved limits of detection (48 µg L-1), selectivity, and intermetallic interferences were achieved. The method was applied to the detection of nickel in water samples well below World Health Organization (WHO) standards.

Fabrication of Antibacterial Metal Surfaces Using Magnetron-Sputtering Method

One-hundred-nanometer films consisting of silver, copper, and gold nanocrystallites were prepared, and their antibacterial properties were quantitatively measured. The magnetron-sputtering method was used for the preparation of the metallic films over the glass plate. Single- and double-layer films were manufactured. The films were thoroughly characterized with the XRD, SEM, EDS, and XPS methods. The antibacterial activity of the samples was investigated. Gram-negative Escherichia coli, strain K12 ATCC 25922 (E. coli), and Gram-positive Staphylococcus epidermidis, ATCC 49461 (S. epidermidis), were used in the microbial tests. The crystallite size was about 30 nm in the cases of silver and gold and a few nanometers in the case of copper. Significant oxidation of the copper films was proven. The antibacterial efficacy of the tested samples followed the order: Ag/Cu > Au/Cu > Cu. It was concluded that such metallic surfaces may be applied as contact-killing materials for a more effective fight against bacteria and viruses.

Extraordinary optical transmission in silicon nanoholes

In this work, for the first time, a study was conducted of the existence of Extraordinary Optical Transmission (EOT) in Silicon (Si) thin films with subwavelength holes array and high excess carrier concentration. Typically EOT is studied in opaque perforated metal films. Using Si would bring EOT and its many applications to the silicon photonics realm and the mid-IR range. Since Si thin film is a semi-transparent film in mid-IR, a generalization was proposed of the normalized transmission metric used in literature for EOT studies in opaque films. The plasma dispersion effect was introduced into the studied perforated Si film through either doping or carriers’ generation. Careful consideration for the differences in optical response modeling in both cases was given. Full-wave simulation and analysis showed an enhanced transmission when using Si with excess carriers, mimicking the enhancement reported in perforated metallic films. EOT was found in the mid-IR instead of the visible range which is the case in metallic films. The case of Si with generated excess carriers showed a mid-IR EOT peak reaching 157% around 6.68 µm, while the phosphorus-doped Si case showed a transmission enhancement of 152% around 8.6 µm. The effect of varying the holes’ dimensions and generated carriers’ concentration on the transmission was studied. The analogy of the relation between the fundamental mode cutoff and the EOT peak wavelength in the case of Si to the case of metal such as silver was studied and verified. The perforated Si thin film transmission sensitivity for a change in the refractive index of the holes and surroundings material was investigated. Also, a study of the device potential in sensing the hole and surroundings materials that have almost the same refractive index yet with different absorption fingerprints was performed as well.

Nanoporous Metallic Films

Nanoporous metallic films are known to have high surface to volume ratio due to the presence of pores. The presence of pores and ligaments make them suitable for various critical applications like sensing, catalysis, electrodes for energy applications etc. Additionally, they also combine properties of metals like good electrical and thermal conductivity and ductility. They can be fabricated using top-down or bottom-up approaches also known as dealloying and templating which give the fabricator room to tailor properties according to need. In addition, they could find potential applications in many relevant fields in current scenario like drug delivery vehicles. However, there is a long way to go to extract its whole potential.

Nanophotonic biosensors harnessing van der Waals materials

Low-dimensional van der Waals (vdW) materials can harness tightly confined polaritonic waves to deliver unique advantages for nanophotonic biosensing. The reduced dimensionality of vdW materials, as in the case of two-dimensional graphene, can greatly enhance plasmonic field confinement, boosting sensitivity and efficiency compared to conventional nanophotonic devices that rely on surface plasmon resonance in metallic films. Furthermore, the reduction of dielectric screening in vdW materials enables electrostatic tunability of different polariton modes, including plasmons, excitons, and phonons. One-dimensional vdW materials, particularly single-walled carbon nanotubes, possess unique form factors with confined excitons to enable single-molecule detection as well as in vivo biosensing. We discuss basic sensing principles based on vdW materials, followed by technological challenges such as surface chemistry, integration, and toxicity. Finally, we highlight progress in harnessing vdW materials to demonstrate new sensing functionalities that are difficult to perform with conventional metal/dielectric sensors.