Detection of small molecules and microbial cells by surface-enhanced Raman spectroscopy using roll-toroll produced substrates:Dissertation

The objective of this thesis was to study patterned substrates and gold nanoparticles as surface-enhanced Raman spectroscopy tools for label-free detection of biological analytes with high sensitivity and easy sample handling. There are many fields, such as environmental monitoring, medical analysis, food safety and national security, which currently lack a rapid analysis tool for bioanalyte recognition. This thesis concentrated on applying disposable singleuse surface-enhanced Raman scattering (SERS) substrates for the detection of microbial cells and small molecules. The substrates were patterned with roll-toroll (R2R) UV replication. R2R fabrication of the SERS substrates enables industrial scale manufacturing of large sensor areas in a repeatable manner. SERS detection is based on the recording of inelastically scattered photons. The scattering is enhanced locally by a resonance effect of the surface plasmons of noble metal surfaces. SERS can achieve sensitive detection of low analyte volumes, even in the range of a few particles. In addition, it has the advantage of label-free detection due to the fingerprint spectrum, in which the signal reveals information concerning the composition of the molecules forming the analyte. In this study the SERS substrates were combined with metal nanoparticles and the samples were concentrated with hydrophobic materials. The sample intake to the chip was developed for the detection of rhodamine 6G inside an optofluidic SERS chip. The behaviour of small molecules in the flow was studied through a polymer lid with microfluidic circuits attached to SERS substrates. The second topic concentrated on detection of Listeria innocua ATCC 33090 bacterial cells with SERS substrates and gold nanoparticles. The limit of detection (LOD) was found to be approx. 2·104 CFU/ml. In the third topic, the effect of the shape and composition of the nanoparticles on the SERS detection of yeast was studied with three yeast strains originating from the beverage industry: Wickerhamomyces anomalus, Brettanomyces bruxellensis and Rhodotorula mucilaginous. A specific Raman spectrum was detected for all of the strains