Diamine Oxidase-Conjugated Multiwalled Carbon Nanotubes to Facilitate Electrode Surface Homogeneity

Carbon nanomaterials have gained significant interest over recent years in the field of electrochemistry, and they may be limited in their use due to issues with their difficulty in dispersion. Enzymes are prime components for detecting biological molecules and enabling electrochemical interactions, but they may also enhance multiwalled carbon nanotube (MWCNT) dispersion. This study evaluated a MWCNT and diamine oxidase enzyme (DAO)-functionalised screen-printed electrode (SPE) to demonstrate improved methods of MWCNT functionalisation and dispersion. MWCNT morphology and dispersion was determined using UV-Vis spectroscopy (UV-Vis) and scanning electron microscopy (SEM). Carboxyl groups were introduced onto the MWCNT surfaces using acid etching. MWCNT functionalisation was carried out using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) and N-Hydroxysuccinimide (NHS), followed by DAO conjugation and glutaraldehyde (GA) crosslinking. Modified C-MWNCT/EDC-NHS/DAO/GA was drop cast onto SPEs. Modified and unmodified electrodes after MWCNT functionalisation were characterised using optical profilometry (roughness), water contact angle measurements (wettability), Raman spectroscopy and energy dispersive X-ray spectroscopy (EDX) (vibrational modes and elemental composition, respectively). The results demonstrated that the addition of the DAO improved MWCNT homogenous dispersion and the solution demonstrated enhanced stability which remained over two days. Drop casting of C-MWCNT/EDC-NHS/DAO/GA onto carbon screen-printed electrodes increased the surface roughness and wettability. UV-Vis, SEM, Raman and EDX analysis determined the presence of carboxylated MWCNT variants from their non-carboxylated counterparts. Electrochemical analysis demonstrated an efficient electron transfer rate process and a diffusion-controlled redox process. The modification of such electrodes may be utilised for the development of biosensors which could be utilised to support a range of healthcare related fields.

Molybdenum doped titanium dioxide photocatalytic coatings for use as hygienic surfaces: the effect of soiling on antimicrobial activity

Titanium dioxide (TiO2) surfaces doped with molybdenum (Mo) were investigated to determine if their photocatalytic ability could enhance process hygiene in the brewery industry. Doping TiO2 with Mo showed a 5-log reduction in bacterial counts within 4 to 24 h and a 1-log reduction in yeast numbers within 72 h. The presence of a dilute brewery soil on the surface did not interfere with antimicrobial activity. The TiO2-Mo surface was also active in the dark, showing a 5-log reduction in bacteria within 4 to 24 h and a 1-log reduction in yeast numbers within 72 h, suggesting it could have a novel dual function, being antimicrobial and photocatalytic. The study suggests the TiO2-Mo coating could act as a secondary barrier in helping prevent the build-up of microbial contamination on surfaces within the brewery industry, in particular in between cleaning/disinfection regimes during long production runs.

The detection of food soils on stainless steel using energy dispersive X-ray and Fourier transform infrared spectroscopy

Organic soiling is a major issue in the food processing industries, causing a range of biofouling and microbiological problems. Energy dispersive X-ray (EDX) and Fourier transform infra red spectroscopy (FT-IR) were used to quantify and determine the biochemical groups of food soils on stainless steel surfaces. EDX quantified organic material on surfaces where oily based residues predominated, but was limited in its usefulness since other food soils were difficult to detect. FT-IR provided spectral 'fingerprints' for each of the soils tested. Key soiling components were associated with specific peaks, viz. oils at 3025 cm(-1)-3011 cm(-1), proteins at 1698 cm(-1)-1636 cm(-1) and carbohydrates at 1658 cm(-1)-1596 cm(-1), 783 cm(-1)-742 cm(-1). High concentrations of some soils (10%) were needed for detection by both EDX and FT-IR. The two techniques may be of use for quantifying and identifying specific recalcitrant soils on surfaces to improve cleaning and hygiene regimes.

The influence of silver content on the tribological and antimicrobial properties of ZrN/Ag nanocomposite coatings

ZrN/Ag nanocomposite coatings with varying silver contents were produced by co-deposition in a dual pulsed magnetron sputtering system. The coatings were characterised using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), scratch adhesion testing, thrust washer wear testing and nanoindentation. The hardness of the ZrN/Ag coatings and the friction coefficient running unlubricated against a steel counterface decreased with increasing silver content, whereas the coating-to-substrate adhesion increased for coatings with higher silver contents, compared to a 'pure' ZrN coating. The antimicrobial properties of the coatings were investigated using two well established microbiological assay techniques: zones of inhibition and a NBT (nitro-blue tetrazolium) redox dye. Zones of inhibition were used to determine the extent of silver ion release from the nanocomposite materials, and a NBT (nitro-blue tetrazolium) redox dye was used to determine the antimicrobial effectiveness of the surfaces following incubation. The microorganisms tested were Pseudomonas aeruginosa (P. aeruginosa), Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Whilst no zones of inhibition were observed for S. aureus, on any of the surfaces, the diameter of the 'kill' zones generally increased with increasing silver content for the other microorganisms. For the NBT assays, after incubation, no P. aeruginosa colony forming units were observed on any surface and the number of viable cells of E. coli and S. aureus decreased with increasing silver content, compared to a 'pure' ZrN surface.

The use of physicochemical methods to detect organic food soils on stainless steel surfaces

Food processing surfaces fouled with organic material pose problems ranging from aesthetic appearance, equipment malfunction and product contamination. Despite the importance of organic soiling for subsequent product quality, little is known about the interaction between surfaces and organic soil components. A range of complex and defined food soils was applied to 304 stainless steel (SS) surfaces to determine the effect of type and concentration of soil on surface physicochemical parameters, viz surface hydrophobicity (DeltaG(iwi)), surface free energy (gamma(s)), Lifshitz van der Waals (gamma_LW(s)), Lewis acid base (gamma_AB(s)), electron acceptor (gamma_+(s) ) and electron donor (gamma_-(s) ) measurements. When compared to the control surface, changes in gamma_AB(s), gamma_+(s) and gamma_-(s) were indicative of surface soiling. However, soil composition and surface coverage were heterogeneous, resulting in complex data being generated from which trends could not be discerned. These results demonstrate that the retention of food soil produces changes in the physicochemical parameters of the surface that could be used to indicate the hygienic status of a surface.