Open Access

Hydrophilic surface-enhanced Raman spectroscopy (SERS) substrates were prepared by a combination of TiO2-coatings of aluminium plates through a direct titanium tetraisopropoxide (TTIP) coating and drop coated by synthesised gold nanoparticles (AuNPs). Differences between the wettability of the untreated substrates, the slowly dried Ti(OH)4 substrates and calcinated as well as plasma treated TiO2 substrates were analysed by water contact angle (WCA) measurements. The hydrophilic behaviour of the developed substrates helped to improve the distribution of the AuNPs, which reflects in overall higher lateral SERS enhancement. Surface enhancement of the substrates was tested with target molecule rhodamine 6G (R6G) and a fibre-coupled 638 nm Raman spectrometer. Additionally, the morphology of the substrates was characterised using scanning electron microscopy (SEM) and Raman microscopy. The studies showed a reduced influence of the coffee ring effect on the particle distribution, resulting in a more broadly distributed edge region, which increased the spatial reproducibility of the measured SERS signal in the surface-enhanced Raman mapping measurements on mm scale.

Surface-enhanced Raman spectroscopy (SERS) with subsequent chemometric evaluation was performed for the rapid and non-destructive differentiation of seven important meat-associated microorganisms, namely Brochothrix thermosphacta DSM 20171, Pseudomonas fluorescens DSM 4358, Salmonella enterica subsp. enterica sv. Enteritidis DSM 14221, Listeria monocytogenes DSM 19094, Micrococcus luteus DSM 20030, Escherichia coli HB101 and Bacillus thuringiensis sv. israelensis DSM 5724. A simple method for collecting spectra from commercial paper-based SERS substrates without any laborious pre-treatments was used. In order to prepare the spectroscopic data for classification at genera level with a subsequent chemometric evaluation consisting of principal component analysis and discriminant analysis, a pre-processing method with spike correction and sum normalisation was performed. Because of the spike correction rather than exclusion, and therefore the use of a balanced data set, the multivariate analysis of the data is significantly resilient and meaningful. The analysis showed that the differentiation of meat-associated microorganisms and thereby the detection of important meat-related pathogenic bacteria was successful on genera level and a cross-validation as well as a classification of ungrouped data showed promising results, with 99.5 % and 97.5 %, respectively.

Due to the toxicity and negative environmental impact of lead- and chromate(IV and VI)-based delay compositions, alternative substance mixtures are required to be investigated as possible substitutes for pyrotechnic materials. Therefore, the Mg/ CaO2 and Mg/Li2O2 delay compositions were subject of this work. These mixtures were processed into pellets with the aid of the dry binders HPMC, MgSt, PEG1, PEG2 and PVP and used in delay elements. The binder content used for all the composition was 5wt%. Burning rates were investigated while taking the influence of oxidizer particle size and the effect of different binders into account. The results show that the combustion rate can be adjusted both via the grain size and by means of the various binders. Further, the impact of the different binders on the ignition temperature of the Mg/Li2O2 and Mg/CaO2 compositions was measured. The compositions were also classified as insensitive to impact and friction. However, during preparation of delay pallets, unintended ignition of pellets occurred while using the HPMC, PEG1, PEG2 and PVP binders. For this reason, safety measures should be followed and special care should be taken while preparing delay pellets. While the peroxides could be identified with Raman spectroscopy, no peroxide residue was found in the reaction products of both peroxide magnesia mixtures.