Surface-enhanced Raman scattering (SERS)-active systems based on macroscopic Ag nanosponge aggregates as well as the conditions of SERS spectral measurements were optimized for selective and sensitive detection of a biomedically important, amphiphilic bile pigment bilirubin (BR) in alkaline aqueous solutions and in its solutions in a selected water miscible solvent, namely dimethylsulfoxide (DMSO) and/or water-immiscible solvent, namely CH2Cl2. Ag nanosponges assembled by using HCl as a pre-aggregation agent were found to be the optimal SERS-active systems for a reliable detection of BR in all the above-mentioned solvents. In all cases, the protonated form of adsorbed BR has been detected upon BR incorporation into Ag nanosponges, and its marker bands have been established by SERS spectral probing at excitation wavelengths in the 445-780 nm range. The sensitivity of SERS spectral detection was evaluated in terms of the concentration values of SERS spectral detection limits (SERS LODs) of BR incorporated into Ag nanosponges. In particular, the SERS LOD for BR incorporated from its alkaline aqueous solution is 1 x 10-8 M (at 532 nm excitation), for BR incorporated from its solution in DMSO, its value is also 1 x 10-8 M (at 532 and/or 633 nm excitations), and for incorporation from the solution of BR...

Plasmonic nanocrystals have a unique ability to support localized surface plasmon resonances and exhibit rich and intriguing optical properties. Engineering plasmonic nanocrystals can maximize their potentials for specific applications. In this dissertation, we developed three unprecedented Au nanorod-based plasmonic nanocrystals through rational design of the crystal shape and/or composition, and successfully demonstrated their applications in light condensation, photothermal conversion, and surface-enhanced Raman spectroscopy (SERS). The “Au nanorod-Au nanosphere dimer” nanocrystal was synthesized via the ligand-induced asymmetric growth of a Au nanosphere on a Au nanorod. This dimeric nanostructure features an extraordinary broadband optical absorption in the range of 400‒1400nm, and it proved to be an ideal black-body material for light condensation and an efficient solar-light harvester for photothermal conversion. The “Au nanorod (core) @ AuAg alloy (shell)” nanocrystal was built through the epitaxial growth of homogeneously alloyed AuAg shells on Au nanorods by precisely controlled synthesis. The resulting core-shell structured, bimetallic nanorods integrate the merits of the AuAg alloy with the advantages of anisotropic nanorods, exhibiting strong, stable and tunable surface plasmon resonances that are essential for SERS applications in a corrosive environment. The “high-index faceted Au nanorod (core) @ AuPd alloy (shell)” nanocrystal was produced via site-specific epitaxial growth of AuPd alloyed horns at the ends of Au nanorods. The AuPd alloyed horns are bound with high-index side facets, while the Au nanorod concentrates an intensive electric field at each end. This unique configuration unites highly active catalytic sites with strong SERS sites into a single entity and was demonstrated to be ideal for in situ monitoring of Pd-catalyzed reactions by SERS. The synthetic strategies developed here are promising towards the fabrication of novel plasmonic nanocrystals with fascinating properties for nanoplasmonics and nanophotonics.

Identifying and detecting health hazards in food products, especially contaminants and toxic substances such as allergens, food toxins and agricultural residues from pesticides, remains a challenge. Increasing demand for food products and growing health consciousness necessitate rapid and accurate measurements which can be easily conducted on-site without long measurement times and high costs. Due to their ease of use, accuracy sample preparation and rapidity, biosensors have started to outcompete time-consuming lab-scale analytical devices. However, as the use of biosensors increase, a concern of the amount of plastics and synthetic polymers used in the fabrication of these biosensors rises. In this dissertation, new ways to create biodegradable and eco-friendly plant-based SERS biosensor platforms from corn protein, zein, are presented. Its higher hydrophobicity and film forming capability make zein a very suitable biopolymer for fabricating biosensors. In the first part of this dissertation, chemical crosslinking was tested to improve the surface hydrophobicity, surface roughness (using AFM), mechanical properties, kinetics of gelation and film formation of zein films, and as a result zein-film based SERS platforms with fewer defects could be fabricated. In the second part, the detection sensitivity of the zein film-based SERS platforms was increased with metallic nanoparticle decoration (gold, silver or silver-shelled-gold). The addition of all three types of nanoparticles significantly increased the SERS enhancement factors of the platforms, with silver-shelled-gold nanoparticles giving the highest enhancement factor of 10⁵. In the last part of this thesis, a novel approach was tested, where electrospun zein nanofibers decorated with metallic nanoparticles were used as a SERS biosensor platform. Due to their higher surface area-to-volume ratios, electrospun zein nanofibers gave a higher SERS enhancement factor (10⁶). This enhancement factor enabled the detection of acrylamide, a food carcinogen, with a 10⁴ times lower detection limit than nanophotonic based nanoimprinted zein, acrylamide sensor platform. Overall, this dissertation successfully shows the fabrication of biodegradable and eco-friendly SERS sensor platforms that have comparable detection sensitivities to those of non-biodegradable ones.

This thesis explores the practical usefulness of surface enhanced Raman spectroscopy on a colloidal substrate for quantification of organic analytes in a water matrix. The method evaluated is very simple and accessible as it utilizes a commercially available hand held Raman spectrometer and citrate reduced silver colloid substrate. Spectra of 4-mercaptopyridine (Mpy) and riboflavin (Rf) samples in distilled water were recorded. A Raman enhancement factor on the order of 108 was achieved for Mpy and its limit of detection was 0.1 nM. The standard deviation of Mpy intensity was <10% for 25 nM samples recorded at the same point in time, but significantly higher for samples recorded at different times. Mpy and Rf could be detected in parallel and both analytes had a close to linear Raman intensity to concentration relationship over a 100 times relative concentration change. We conclude that with improved substrate stability, a similar method should be practically applicable for quantification of suitable analytes down to the nM-range in samples of well defined composition. Considering the method's simplicity and the limited optimization efforts it has a large room for improvement.

Chemical and topographic surface patterning for the preparation of functional surfaces and particle arrays has been intensively investigated and widely applied in sensor technology, engineering of adhesion and wetting, catalysis, as well as nanobioanalytics. However, the parallel high-throughput functionalization of surfaces with microparticle arrays under ambient conditions by state-of-the-art surface patterning methods has remained challenging. The aim of this thesis is the parallel generation of microparticle arrays on surfaces to tailor the surface properties. Two strategies are studied for this purpose. The first strategy, inspired by the functional principles of adhesive secretion of insect feet’s hairy contact elements yielding tiny droplets as footprints onto contact substrates, involves the formation of microdot arrays by capillary submicron stamping using spongy continuous nanoporous block copolymer stamps with regular hexagonal arrays of contact elements. After infiltration of AgNO3 solution from the stamps’ backside, arrays of discrete two-dimensional AgNO3 microdots with an average diameter ~ 730 nm on silicon wafers extending several square millimetres were generated, while under higher pressure holey AgNO3 films were obtained. Subsequently, the patterns were transferred into Si wafers by surface-limited metal-assisted chemical etching (MACE). Topographically patterned silicon (tpSi) characterized by hexagonal arrays of wells resulted from MACE of Si wafers patterned with AgNO3 microdots, while MACE of Si wafers patterned with holey AgNO3 films yielded ordered Si pillar arrays. H2PtCl6, PdCl2 and HAuCl4 aqueous solutions were also employed as inks for preparation of tpSi by insect-inspired capillary sub-microstamping and MACE. Exploratory experiments suggest that inkjet printing of polymeric inks onto tpSi could yield persistent and scratch-resistant polymer blot patterns without coffee ring-like features for potential utilization as permanent identity labels or quick response codes. Hexagonal arrays of Au microparticles were rationally positioned by solid-state dewetting of thin gold films on tpSi at an elevated temperature under Ar atmosphere. The rationally positioned Au microparticles subsequently acted as seeds for the growth of dense, homogeneous layers of overlapping three-dimensional (3D) gold nanodendrites by templated galvanic displacement reactions. The obtained 3D gold nanodendrite layers on tpSi featuring high specific surfaces as well as abundance of sharp edges and vertices showed promising performances in SERS-based sensing and the heterocatalytic reduction of 4-nitrophenol to 4-aminophenol. The second example involves the functionalization of polymer surfaces with arrays of inorganic lubricant microparticles for friction management and the tailoring of tribological properties based on an imprint lithographic approach. For example, the tailoring of the interfacial shear behavior of a movable polymer part might be customized in this way by functionalizing the polymeric parts’ surfaces with MoS2 microparticle arrays. Monodomain monolayers of MoS2 microparticles were prepared on SiO2-coated Si wafers via thermal sulfurization arrays of ammonium tetrathiomolybdate microparticles obtained by imprint lithography. After transfer of the MoS2 microparticle arrays to poly(methyl methacrylate) (PMMA) monoliths (PMMA_MoS2) under conservation of the array order in such a way that the MoS2 microparticles were partially embedded into the PMMA and partially exposed, the obtained PMMA_MoS2 exhibited modified mechanical properties characterized by low friction coefficients half as that of non-modified PMMA monoliths. Therefore, the functionalization of surfaces with microparticle arrays is a viable and promising strategy to generate unprecedented surface functionalities.

Surface enhanced Raman spectroscopy (SERS) has been widely applied for rapid and sensitive detection of various chemical and biological targets. Here, we incorporated a syringe filter system into the SERS method to detect pesticides, protein toxins and bacteria in water. For the detection of chemical and protein targets, silver nanoparticles (Ag NPs) were aggregated by sodium chloride (NaCl) to form nanoclusters that could be trapped in the pores of the filter membrane to from the SERS-active membrane. Then a coating of capture (e.g. aptamer) was integrated on the nanoparticle substrate if needed. Then samples were filtered through the membrane. After capturing the target, the membrane was taken out and air dried before measuring by a Raman instrument. The developed filter SERS method was able to detect fungicide ferbam as low as 2.5 ppb level and had a good quantitative capability, which could also be carried out on site using a portable Raman instrument. The aptamer integrated filter SERS was able to detect ricin b chain in water at 100 ppb level. The filter membrane was then applied to detect bacteria E.Coli with the integration of 4-mpba as a capture and indicator. With SERS mapping, we can detect E.Coli down to 101 CFU/ml and the viability of bacteria on the membrane could be confirmed by incubating the membrane on TS agar down to 102 CFU/ml. This study shows the filter based SERS methods improve the detection capability in water samples, with a great versatility for various types of assays.

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Adjuvants can enhance the performance of the pesticide active ingredients in many ways including decreasing surface tension and reducing evaporation. Understanding how adjuvants effect pesticide behavior (e.g., surface persistence) is crucial for developing effective pesticide formulations, as well as facilitating the development of effective approaches to reduce pesticide residues from the surface of fresh produce post-harvest. The objective of this study is to investigate the effect of a non-ionic surfactant, Surf-Ac 910, on the persistence of two model pesticides, thiabendazole and phosmet on apple surfaces. The result shows that the addition of Surf-Ac 910 increased both the maximum wetted area and evaporation rate of thiabendazole, a systemic pesticide, and phosmet, a non-systemic pesticide. Utilizing surface-enhanced Raman spectroscopy to explore the surface and penetrative behaviors of thiabendazole and phosmet revealed that the addition of Surf-Ac 910 influenced the Raman signal of pesticides as well. The addition of Surf-Ac 910 decreased the Raman signal intensity when added to phosmet but did not affect the Raman signal intensity when added to thiabendazole. In terms of penetration, the addition of Surf-Ac 910 did not affect the penetration depth of phosmet but slightly increased the penetration depth of thiabendazole. These findings were true for both short-term, 40 minutes, and long-term, 3 days, exposure. Next, the effects of adjuvants on the removal of pesticide residues were investigated. Common household materials, such as baking soda, were effective at removing surface pesticide residues. After testing a variety of baking soda concentrations and starch granules, 2% baking soda and 2% corn starch were found to be the most effective baking soda concentration and starch granule respectively. 2% corn starch was the most effective removal method overall, with 99% of pesticide with/without adjuvant removed in just 5 minutes of wash time. Overall, this study demonstrated that although adjuvant Surf-Ac 910 could affect the surface persistence of pesticides, washing with common household materials such as 2% corn starch can be used as an effective, safe, and economic way to reduce pesticide exposure through fresh produce.

In the search for the conformation of extant or extinct life in an extraterrestrial setting the detection of organic molecular species which may be considered diagnostic of life is a key objective. These molecular targets comprise a range of distinct chemical species, with recognisable spectroscopic features. This project aims to use these features to develop an in-situ molecular specific Raman spectroscopic methodology which can provide structural information about the organic–inorganic interface. The development of this methodology identified a surface enhanced Raman spectroscopic technique, that required minimal sample preparation, allowed for the detection of selected organic species immobilised on an inorganic matrix and was effective for quantities below those which conventional dispersive Raman spectroscopy would detect. For the first time spectral information was gained which allowed analysis of the organic–inorganic interface to be carried out, this gave an insight into the orientation with which molecules arrange on the surfaces of the matrices. Additionally a method for the detection of organic residues intercalated into the interlamellar space of smectite type clays was developed. An evaluation of the effectiveness of uni and multivariate methods for the analysis of large datasets containing a small number of organic features was also carried out, with a view to develop an unsupervised methodology capable of performing with minimal user interaction. It has been shown that a novel use of the Hotellings T2 test when applied to the principal component analysis of the datasets combined with SERS allows identification of a small number of organic features in an otherwise inorganic dominated dataset. Both the SERS and PCA methods hold relevance for the detection of organic residues within interplanetary exploration but may also be applied to terrestrial environmental chemistry.