A novel 3D-printed portable electroplating device enhances latent fingerprints on metal substrates

This work introduces a 3D-printed portable electroplating device for the visualization of latent fingerprints (LFPs) on metallic substrates. An electroplating solution of Ag+-Cu2+ in a deep eutectic solvent (DES) is used. The electroplating is performed by two electrodes equivalent to an anode (+) and a cathode (-). The cathode is connected to the metal surface with the magnetic or alligator clip for carrying the LFP. The anode is connected to cotton dipped in the electroplating solution. The device was optimized in terms of the electroplating solution composition, and electroplating potential, current, and time. The device produced images with good resolution, revealing LFP ridges in minute detail of more than 12 points. The device also exhibited good repeatability and images were assessed against guidelines from the Centre for Applied Science and Technology (CAST) and the International Fingerprint Research Group (IFRG). The developed device could be applied to visualize LFPs in forensic investigations.

Electrochemical investigations and antimicrobial activity of Au nanoparticles photodeposited on titania nanoparticles

Titanium oxide nanopowder (TiO2 NPs) was synthesized via anodization in 0.7 M perchloric acid then annealed in nitrogen at 450 °C for 3 h to prepared the Titanium Oxide Nitrogen annealed nanoparticles (TiO2 NPs-N2) powder as catalytic support. Using a photodeposition process, gold was added with isopropanol as a sacrificial donor and H[AuCl4] acid, producing gold nanoparticles on nitrogen-annealed titanium oxide nanoparticles (Au-NPs on TiO2-NPs-N2). The mass loading of Au NPs was 2.86 × 10-4 (g/cm2). TEM images of Au NPs on TiO2-NPs-N2 suggest circular particles with a tendency to agglomerate. Cyclic voltammetry (CV) was used to investigate the electrocatalytic performance of the Au NPs/TiO2-NPs-N2 catalysts in ferrocyanide, KOH, and H2SO4, and the results were compared to those of a polycrystalline Au electrode that is readily accessible in the market. In KOH, H2SO4, and (2 M KOH + 0.1 M glycerol) solutions, the Au NPs/TiO2-NPs-N2 electrode displayed a startlingly high electrocatalytic performance. Using CV, the electrocatalytic oxygen reduction reaction (ORR) of Au NPs/TiO2-NPs-N2 and Au-NPs against glycerol oxidation in basic media was studied. The results indicated that Au NPs/TiO2-NPs-N2 is a promising support material for improving the electrocatalytic activity for acidic and basic oxidation. The electrode made of Au NPs/TiO2-NTs-N2 has steady electrocatalytic activity and may be reused repeatedly. TiO2 NPs and Au NPs/TiO2NPs-N2 showed satisfactory antibacterial activity against some human pathogenic bacteria using the disc diffusion method.

Microbial Electrosynthesis Inoculated with Anaerobic Granular Sludge and Carbon Cloth Electrodes Functionalized with Copper Nanoparticles for Conversion of CO2 to CH4

Microbial electrosynthesis (MES) can sustainably convert CO₂ to products and significant research is currently being conducted towards this end, mainly in laboratory-scale studies. The high-cost ion exchange membrane, however, is one of the main reasons hindering the industrialization of MES. This study investigates the conversion of CO₂ (as a sole external carbon source) to CH₄ using membraneless MES inoculated with anaerobic granular sludge. Three types of electrodes were tested: carbon cloth (CC) and CC functionalized with Cu NPs, where Cu NPs were deposited for 15 and 45 min, respectively. During the MES experiment, which lasted for 144 days (six cycles), methane was consistently higher in the serum bottles with CC electrodes and applied voltage. The highest CH₄ (around 46%) was found in the second cycle after 16 days. The system’s performance declined during the following cycles; nevertheless, the CH₄ composition was twice as high compared to the serum bottles without voltage. The MES with Cu NPs functionalized CC electrodes had a higher performance than the MES with plain CC electrodes. Microbial profile analysis showed that the Methanobacterium was the most dominant genus in all samples and it was found in higher abundance on the cathodes, followed by the anodes, and then in the suspended biomass. The genus Geobacter was identified only on the anodes regarding relative bacterial abundance at around 6–10%. Desulfovibrio was the most dominant genus in the cathodes; however, its relative abundance was significantly higher for the cathodes with Cu NPs.

Electrochemical detection of selected heavy metals in water: a case study of African experiences

The safety of water resources throughout the globe has been compromised by various human activities and climate change over the last decades.

CoPtx/γ-Al2O3 bimetallic nanoalloys as promising catalysts for hydrazine electrooxidation

Stable bimetallic catalysts composed of CoPtx/γ-Al2O3 (x = Pt/Co molar ratio) were synthesized by wet impregnation method followed by calcination and the H2 reduction. The powders were characterized using XRD, AAS, BET, SEM, EDX, TPR, and TPO techniques. The prepared catalysts were drop casted on the glassy carbon electrode (GCE) and catalytic performance was examined for hydrazine electrooxidation in alkaline medium via cyclic voltammetry (CV). All the compositions in CoPtx/γ-Al2O3 series showed high responses towards hydrazine electrooxidation, however; high activity of CoPt0.034/γ-Al2O3 catalyst inferred it as a best material with an anodic peak current (iP) response of 200 μA at 0.86 V. The prominent electrochemical (EC) responses for this composition are attributed to better accessible surface area resulting in a fast electron transfer. The CoPtx/γ-Al2O3 catalysts are reported as the robust and superior prospective materials for extensive electroanalytical and catalytic studies.

Counting the number of enzymes immobilized onto a nanoparticle-coated electrode

To immobilize enzymes at the surface of a nanoparticle-based electrochemical sensor is a common method to construct biosensors for non-electroactive analytes. Studying the interactions between the enzymes and nanoparticle support is of great importance in optimizing the conditions for biosensor design. This can be achieved by using a combination of analytical methods to carefully characterize the enzyme nanoparticle coating at the sensor surface while studying the optimal conditions for enzyme immobilization. From this analytical approach, it was found that controlling the enzyme coverage to a monolayer was a key factor to significantly improve the temporal resolution of biosensors. However, these characterization methods involve both tedious methodologies and working with toxic cyanide solutions. Here we introduce a new analytical method that allows direct quantification of the number of immobilized enzymes (glucose oxidase) at the surface of a gold nanoparticle coated glassy carbon electrode. This was achieved by exploiting an electrochemical stripping method for the direct quantification of the density and size of gold nanoparticles coating the electrode surface and combining this information with quantification of fluorophore-labeled enzymes bound to the sensor surface after stripping off their nanoparticle support. This method is both significantly much faster compared to previously reported methods and with the advantage that this method presented is non-toxic.

Graphical abstract

Amalgam Electrode-Based Electrochemical Detector for On-Site Direct Determination of Cadmium(II) and Lead(II) from Soils

Toxic metal contamination of the environment is a global issue. In this paper, we present a low-cost and rapid production of amalgam electrodes used for determination of Cd(II) and Pb(II) in environmental samples (soils and wastewaters) by on-site analysis using difference pulse voltammetry. Changes in the electrochemical signals were recorded with a miniaturized potentiostat (width: 80 mm, depth: 54 mm, height: 23 mm) and a portable computer. The limit of detection (LOD) was calculated for the geometric surface of the working electrode 15 mm² that can be varied as required for analysis. The LODs were 80 ng·mL^-1 for Cd(II) and 50 ng·mL^-1 for Pb(II), relative standard deviation, RSD ≤ 8% (n = 3). The area of interest (Dolni Rozinka, Czech Republic) was selected because there is a deposit of uranium ore and extreme anthropogenic activity. Environmental samples were taken directly on-site and immediately analysed. Duration of a single analysis was approximately two minutes. The average concentrations of Cd(II) and Pb(II) in this area were below the global average. The obtained values were verified (correlated) by standard electrochemical methods based on hanging drop electrodes and were in good agreement. The advantages of this method are its cost and time effectivity (approximately two minutes per one sample) with direct analysis of turbid samples (soil leach) in a 2 M HNO₃ environment. This type of sample cannot be analyzed using the classical analytical methods without pretreatment.

Synthesis and characterization of porous carbon–MoS2 nanohybrid materials: electrocatalytic performance towards selected biomolecules

Porous carbon nanohybrids are promising materials as high-performance electrodes for both sensing and energy conversion applications.

Competitive Attachment of Gold Nanoparticles on an Indium Tin Oxide Electrode

Fundamental aspects of the attachment of gold nanoparticles (AuNPs) onto a 3-aminopropyltrimethoxysilane (APTMS) modified indium tin oxide (ITO) electrode were explored using commercially available Au colloid solutions of 5, 10 and 20 nm. In particular, competitive attachments of AuNPs were observed using mixed solutions of two Au colloids. Consequently, it was found that smaller AuNPs are easily attached on an APTMS modified ITO. On the other hand, the result of the stepwise attachments showed that after the surface was modified by the first AuNPs, the second AuNPs have difficulty attaching. This means, if surface connecting -NH2 terminals of APTMS are once occupied, further modification or exchange of the attached AuNPs would not be easy. From the present results, a contaminant amount of smaller AuNPs is considered to be a practical problem in modifying ITO surfaces by AuNPs.

Membrane-intercalating conjugated oligoelectrolytes: impact on bioelectrochemical systems

Conjugated oligoelectrolytes (COEs), molecules that are defined by a π-delocalized backbone and terminal ionic pendant groups, have been previously demonstrated to effectively reduce charge-injection/extraction barriers at metal/organic interfaces in thin-film organic-electronic devices. Recent studies demonstrate a spontaneous affinity of certain COEs to intercalate into, and align within, lipid bilayers in an ordered orientation, thereby allowing modification of membrane properties and the functions of microbes in bioelectrochemical and photosynthetic systems. Several reports have provided evidence of enhanced current generation and bioproduction. Mechanistic approaches suggest that COEs influence microbial extracellular electron transport to abiotic electrode surfaces via more than one proposed pathway, including direct electron transfer and meditated electron transfer. Molecular dynamics simulations as a function of molecular structure suggest that insertion of cationic COEs results in membrane thinning as the lipid phosphate head groups are drawn toward the center of the bilayer. Since variations in molecular structures, especially the length of the conjugated backbone, distribution of ionic groups, and hydrophobic substitutions, show an effect on their antimicrobial properties, preferential cell localization, and microbial selection, it is promising to further design novel membrane-intercalating molecules based on COEs for practical applications, including energy generation, environmental remediation, and antimicrobial treatment.

A joint experimental and computational search for authentic nano-electrocatalytic effects: electrooxidation of nitrite and L-ascorbate on gold nanoparticle-modified glassy carbon electrodes

The investigation of electrocatalytic nanoeffects is tackled via joint electrochemical measurements and computational simulations. The cyclic voltammetry of electrodes modified with metal nanoparticles is modeled considering the kinetics of the electrochemical process on the bulk materials of the different regions of the electrode, that is, the substrate (glassy carbon) and the nanoparticles (gold). Comparison of experimental and theoretical results enables the detection of changes in the electrode kinetics at the nanoscale due to structural and/or electronic effects. This approach is applied to the experimental assessment of electrocatalytic effects by gold nanoparticles (Au NPs) in the electrooxidation of nitrite and L-ascorbate. Glassy carbon electrode is modified with Au NPs via seed-mediated growth method. Divergence between the kinetics of these processes on gold macroelectrodes and gold nanoparticles is examined. Whereas claimed catalytic effects are not observed in the electrooxidation of nitrite, electrocatalytic nanoeffects are verified in the case of L-ascorbate. This is probably due to that the electron transfer process follows an adsorptive mechanism. The combination of simulation with experiments is commended as a general strategy of authentification, or not, of nanoelectrocatalytic effects.

Enzyme integrated silicate-Pt nanoparticle architecture: a versatile biosensing platform

A novel 3-D nanoarchitectured platform based on Pt nanoparticles (nPts) is developed for the sensing of sub-nanomolar levels of hydrogen peroxide and for the fabrication of amperometric biosensor for uric acid, cholesterol and glucose. The nPts have been immobilized on the thiol functional group containing sol-gel silicate 3-D network derived from 3-mercaptopropyltrimethoxysilane (MPTS). The nanoparticles on the 3-D architecture have size distribution between 7 and 10nm. The nPts on the platform efficiently catalyze the oxidation of H(2)O(2) at the potential of +0.45 V in the absence of enzymes and redox mediators. This nanoarchitectured platform is highly sensitive and can detect H(2)O(2) at sub-nanomolar levels (0.1 nM) in neutral solution. The nanoarchitectured platform does not suffer from interference due to other common easily oxidizable interfering agents. Excellent reproducibility, long-term storage and operational stability are observed. This platform is used to determine H(2)O(2) concentration in rainwater and for the fabrication of biosensors. Amperometric oxidase-based biosensing platforms are developed by integrating the enzymes and nPts with the silicate network for the sensing of uric acid cholesterol and glucose. The enzyme encapsulated 3-D architecture retains the enzymatic activity and efficiently detects enzymatically generated H(2)O(2) without any interference. These biosensors are stable and show excellent sensitivity and fast response time. A linear response was obtained for a wide concentration range of all analytes. The practical utilization of the biosensor for the measurement of uric acid, cholesterol and glucose in serum sample is demonstrated. The biological sample analysis was validated with clinical laboratory measurements.