Layered material platform for surface plasmon resonance biosensing

Plasmonic biosensing has emerged as the most sensitive label-free technique to detect various molecular species in solutions and has already proved crucial in drug discovery, food safety and studies of bio-reactions. This technique relies on surface plasmon resonances in ~50 nm metallic films and the possibility to functionalize the surface of the metal in order to achieve selectivity. At the same time, most metals corrode in bio-solutions, which reduces the quality factor and darkness of plasmonic resonances and thus the sensitivity. Furthermore, functionalization itself might have a detrimental effect on the quality of the surface, also reducing sensitivity. Here we demonstrate that the use of graphene and other layered materials for passivation and functionalization broadens the range of metals which can be used for plasmonic biosensing and increases the sensitivity by 3-4 orders of magnitude, as it guarantees stability of a metal in liquid and preserves the plasmonic resonances under biofunctionalization. We use this approach to detect low molecular weight HT-2 toxins (crucial for food safety), achieving phase sensitivity~0.5 fg/mL, three orders of magnitude higher than previously reported. This proves that layered materials provide a new platform for surface plasmon resonance biosensing, paving the way for compact biosensors for point of care testing

New analytical applications of gold nanoparticles

The work includes improvements of surface technology, new analytical applications of metallic nanoparticles and optimization of technological steps for production of different types of metallic nanoparticles in discrete and continuous modes. The technology of LbL deposition was optimized and applied for immobilization of metallic nanoparticles. SPR detection was used for the determination of optimal deposition conditions and on-line monitoring of the deposition process. Simple approach for automation of LbL deposition allowing one to deposit up to hundreds of layers was developed. The technology was proved by electrochemical analysis for deposition of electrochemically active polymers. A new diffusion based semi-quantitative assay for detection of sugars was suggested. Electrochemical oxidation of glucose and dopamine on electrodes modified with gold nanoparticles was studied. Conditions for electrochemical analysis of these substances in the presence of typical natural interferents were evaluated. A combination of voltammetry and impedance spectroscopy was used to demonstrate a formation of insulating layer on gold surface, this resulted in explanation of anomalous shape of voltammetric curves. A combination of electrochemical and SPR measurements demonstrated directly a formation of an insulating layer on the electrode surface and was used for optimization of the assay conditions. The results indicate a possibility to develop an enzyme free sensors for glucose and dopamine. It was discovered that gold nanoparticles are effective nucleating agents for protein crystallization. Nanoparticles induce protein crystallization at lower supersaturation and increase the number of protein crystals formed at higher supersaturation. The fact that this technology works with so different proteins as lysozyme and ferritin allows one to suggest that it may be also applied for many other proteins including the ones which are reluctant to crystallization by known technologies. Irreversible freezing indicators based on gold nanoparticles were developed. The filling suspension containing nanoparticles, nucleation and stabilization agents were optimized in sense of stability and irreversibility of color changes. A large scale production of this indicator will be started in spring 2008

Towards label-free biosensors based on localized surface plasmon resonance

Medical diagnostics is in constant search of new tools and devices able to provide in short time, accurate and versatile tests performed on patients. Nanotechnology has contributed largely in developing biosensors of smaller size at a lower cost by using a minimal amount of sample. Biosensors aim to monitor and diagnosticate “in situ” the patient status and the diseases caused by alteration of the body metabolism by, for example, the detection of gene mutations, alteration of gene expression or alteration of proteins. The aim of this work is the development of biosensors that satisfy the requirements which are critical for applications. A biosensor must be i) easy to use, ii) economically convenient, and therefore preferentially label free, iii) highly sensitive, iv) reversible, v) and suitable for Point of Care Testing, that is to be used ”in situ” on the patient. We have focused on biosensors based on the optical properties of nanostructured metals as Au or Ag, in particular by using on Localized Surface Plasmon Resonance (LSPR) spectroscopy. Nanostructured metals under irradiation of electromagnetic wave (as light) exhibit intense absorption bands as results of the localized electronic charges of the metal surface coming into resonance with the incident energy. According to the Mie’s theory, the LSPR absorption band feature changes when the refractive index of the media surrounding the metal nanostructures is varied. Of particular interest for our purpose are the possible changes of the LSPR band features taking place under molecular interactions occurring at the nanostructures surfaces: the shift of LSPR bands is the “transducer” of molecular interactions. These changes can be easily detected by conventional UV-Vis spectroscopy, in transmittance mode. While a large number of studies have been carried out on monodisperse nanoparticles suspended in solution, gold nanoparticles (NPs) deposited on a transparent surface open the possibility to fabricate biosensor based on multiplex array platforms. Nonetheless, one of the major problems in using these plasmonic materials for biosensing purpose is related to the stability of the metal NPs in different solvents and in particular in aqueous solutions. In this study we demonstrate i) the possibility to achieve highly stable NPs by simple thermal evaporation of Au on a substrate commercially available, the Fluorine Tin Oxide (FTO) (Chapter 2); ii) a reproducible variation of the LSPR bands under formation of organic selfassembled monolayers (SAMs), iii) reversible changes in the features of the LSPR bands, (Chapter 3), iv) a specific and reproducible LSPR band changes under molecular interactions occurring at NPs surfaces, as DNA hybridization (Chapter 4). This work demonstrates that the plasmonic material based on Au NPs deposited on FTO surfaces represents a convenient platform for biosensors because of i) inexpensive fabrication, ii) stability of this material in various solvent, including water, of, iii) the easy way to detect the molecular interaction, and iv) the good sensitivity to molecular interactions

Recent advances in the field of bionanotechnology: An insight into optoelectric bacteriorhodopsin, quantum dots, and noble metal nanoclusters

Molecular sensors and molecular electronics are a major component of a recent research area known as bionanotechnology, which merges biology with nanotechnology. This new class of biosensors and bioelectronics has been a subject of intense research over the past decade and has found application in a wide variety of fields. The unique characteristics of these biomolecular transduction systems has been utilized in applications ranging from solar cells and single-electron transistors (SETs) to fluorescent sensors capable of sensitive and selective detection of a wide variety of targets, both organic and inorganic. This review will discuss three major systems in the area of molecular sensors and electronics and their application in unique technological innovations. Firstly, the synthesis of optoelectric bacteriorhodopsin (bR) and its application in the field of molecular sensors and electronics will be discussed. Next, this article will discuss recent advances in the synthesis and application of semiconductor quantum dots (QDs). Finally, this article will conclude with a review of the new and exciting field of noble metal nanoclusters and their application in the creation of a new class of fluorescent sensors

Single- and Multi-Transducer Arrays Employing Nanoparticle Interface Layers as Vapor Detectors for a Microfabricated Gas Chromatograph.

This body of research focuses on improving microsensor arrays used as detectors in Si-microfabricated gas chromatographs (µGC) for the determination of volatile organic compounds (VOCs). By means of such improvements, µGC technology should find wider application in homeland security, disease diagnosis, and environmental monitoring. The microsensors considered here all employ thiolate-monolayer-protected gold nanoparticles (MPN) as vapor sorptive interface layers. The central hypothesis is that by altering the MPN ligand, core size, and/or the underlying transducer, the diversity of responses to VOCs provided by microsensor arrays with MPN interfaces can be improved. The first study evaluated a single transducer (ST) array of MPN-coated chemiresistors (CR) as a µGC detector for three semi-volatile markers of the explosive 2,4,6-trinitrotoluene in the presence of alkane interferences of similar volatility. The effects of flow rate and temperature on chromatographic resolution, sensitivity, and limits of detection (LOD) were assessed. Under optimized conditions, a complete analysis required 95%). These types of sensor arrays can enhance the vapor discrimination of sorption-based detectors utilized in µGC technology, making the analysis of complex VOC mixtures possible.PHDChemistryUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/111430/1/lkamos_1.pd

Chemically bound gold nanoparticle arrays on silicon: assembly, properties and SERS study of protein interactions

A highly reproducible and facile method for formation of ordered 2 dimensional arrays of CTAB protected 50 nm gold nanoparticles bonded to silicon wafers is described. The silicon wafers have been chemically modified with long-chain silanes terminated with thiol that penetrate the CTAB bilayer and chemically bind to the underlying gold nanoparticle. The silicon wafer provides a reproducibly smooth, chemically functionalizable and non-fluorescent substrate with a silicon phonon mode which may provide a convenient internal frequency and intensity calibration for vibrational spectroscopy. The CTAB bilayer provides a potentially biomimetic environment for analyte, yet allows a sufficiently small nanoparticle separation to achieve a significant electric field enhancement. The arrays have been characterized using SEM and Raman spectroscopy. These studies reveal that the reproducibility of the arrays is excellent both between batches (< 10% RSD) and across a single batch (< 5% RSD). The arrays also exhibit good stability, and the effect of temperature on the arrays was also investigated. The interaction of protein and amino acid with the nanoparticle arrays was investigated using Raman microscopy to investigate their potential in bio-SERS spectroscopy. Raman of phenylalanine and the protein bovine pancreatic trypsin inhibitor, BPTI were studied using 785 nm excitation, coincident with the surface plasmon absorbance of the array. The arrays exhibit SERS enhancements of the order of 2.6 x 104 for phenylalanine, the standard deviation on the relative intensity of the 1555 cm-1 mode of phenylalanine is less than 10% for 100 randomly distributed locations across a single substrate and less than 20% between different substrates. Significantly, comparisons of the Raman spectra of the protein and phenlyalanine in solution and immobilized on the nanoparticle arrays indicates that the protein is non-randomly orientated on the arrays. Selective SERS enhancements suggest that aromatic residues penetrate through the bilayer inducing conformational changes in the protein

Self‐Assembled Monolayers of Carbohydrate Derivatives on Gold Surfaces

Self‐assembled monolayers (SAMs) presenting carbohydrates (glycans) have been widely prepared on gold surfaces to mimic the carbohydrate surfaces that are involved in molecular recognition phenomena in living cells. The binding affinity of carbohydrate immbolized on SAM surfaces to various carbohydrate‐binding proteins (such as lectins) can be studied by optical, electrochemical, piezoelectrical and thermal sensing techniques. The lectins present on the surface of pathogens (e.g., bacteria or viruses) can be used as targets for capturing onto carbohydrates immobilized on SAM surfaces. The immobilized carbohydrates can also be used for detecting different types of disease biomarkers present in bodily fluids. Synergistic properties of carbohydrate SAMs and gold nanoparticles can be used for vaccine preparation and drug delivery. By studying different types of glycans, their properties, and the behavior toward recognition of specific pathogens and biomarkers, we can develop not only new therapeutics but also enhance the diagnostic strategies of various diseases. In this chapter, we discuss carbohydrate‐terminated SAMs and their common preparation strategies. Next, we focus on roles of different components of SAMs, characterization techniques, and applications

Harnessing the plasmonic properties of gold nanoparticles: functionalization strategies coupled with novel spectroscopic tools

Metallic plasmonic substrates such as gold nanoparticles (AuNPs) have fascinated researchers due to their usefulness in verious interdisciplinary studies at the interface between applied physics, biochemistry, engineering, and medicine. A good understanding of the physics of these noble nanostructures, particularly the plasmonic and optical properties, can be employed to improve a wide range of sensors and electronic devices. The relevance of molecular recognition and the binding of biological and chemical entities to diagnostics, biosensors, and drug delivery has attracted significant research interest. By addressing material functionalization design and advanced characterization methods, this doctoral work aims to highlight efforts to exploit the surface modification strategies to enhance the responsiveness of nanoparticle substrates for improved detection of health-relevant biomolecules. The self-assembly of small ligands, such as alkanethiols, and oligonucleotides on the surface of AuNPs provided a possible starting route for the preparation of bio-nanomaterials with precise physicochemical properties. The versatile AuNPs were optimized and thoroughly characterized by employing electron microscopy techniques such as transmission electron microscope (TEM), atomic force microscopy (AFM), and scanning electron microscopy (SEM), spectroscopic techniques, including ultraviolet/visible (UV/Vis), dynamic light scattering (DLS), and thermal lens spectrometry (TLS), and biochemical assays (gel electrophoresis, Dot plot, Western plot, and the Enzyme Linked Immunosorbent Assay (ELISA)). Subsequently, the molecular recognition capabilities of functionalized AuNPs were investigated using multiple techniques, including novel detection routes such as the electrophoresis approach coupled with online TLS. This work establishes a versatile platform for AuNP engineering with controlled size and surface functionality. The strategies presented in this thesis aim to improve medical diagnostics to make them affordable for point-of-care scenarios to enhance the quality of human health.wide range of sensors and electronic devices. The relevance of molecular recognition and the binding of biological and chemical entities to diagnostics, biosensors, and drug delivery has attracted significant research interest. By addressing material functionalization design and advanced characterization methods, this doctoral work aims to highlight efforts to exploit the surface modification strategies to enhance the responsiveness of nanoparticle substrates for improved detection of health-relevant biomolecules. The self-assembly of small ligands, such as alkanethiols and oligonucleotides on the surface of AuNPs provided a possible starting route for the preparation of bio-nanomaterials with precise physicochemical properties. The versatile AuNPs were optimized and thoroughly characterized by employing electron microscopy techniques such as transmission electron microscope (TEM), atomic force microscopy (AFM), and scanning electron microscopy (SEM), spectroscopic techniques, including ultraviolet/visible (UV/Vis), dynamic light scattering (DLS), and thermal lens spectrometry (TLS), and biochemical assays (gel electrophoresis, Dot plot, Western plot, and the Enzyme Linked Immunosorbent Assay (ELISA)). Subsequently, the molecular recognition capabilities of functionalized AuNPs were investigated using multiple techniques, including novel detection routes such as the electrophoresis approach coupled with online TLS. This work establishes a versatile platform for AuNP engineering with controlled size and surface functionality. The strategies presented in this thesis aim to improve medical diagnostics to make them affordable for point-of-care scenarios to enhance the quality of human health