Gold nanorods functionalized with DNA oligonucleotide probes for biosensing and plasmon-enhanced fluorescence detection

Gold nanorods display plasmon resonances that are very sensitive to the refraction index close to the particle’s surface. The site-selective functionalization of Plasmon hot-spots with bioreceptors is crucial to develop plasmonic sensors with improved response bycapturing the target species at the most sensitive regions of the particle. Firstly, we used surface immobilized biotin-functionalized gold nanorods for streptavidin sensing.The selective functionalization of the nanorods’ tips was achieved with a CTAB bilayer and using a thiol linker to attach the desired biotin functionality. The sensor performance was characterized by measuring binding kinetic assays. In the recent years, Dengue virus DENV-2 has been reported as the largest dengue epidemic type and early stage detection of this virus would save the life of many patients. Thus, a plasmonic model biosensor was designed for the detection of RNA sequences proposed as disease biomarkers for Dengue virus.For this purpose, we have functionalized gold nanorods with thiolated DNA oligonucleotide probes complementary to a RNA sequence of Dengue virus.As a signal amplification strategy, we have used biotin-labeled oligonucleotide target sequences, in order to bind streptavidin or anti-biotin antibody to increase the surface plasmon response. Plasmon-enhanced fluorescence (PEF) microscopy provides fast, high-contrast, and lowbackground detection of single molecules. The interaction between the localized surface plasmon of gold nanorods and a fluorophore in their vicinity can induce the acceleration of excitation and decay rates thus leading to substantial fluorescence enhancements. In the third part of this Thesis, it was studied the interaction between gold nanorod antennas and a weakly fluorescence dye, TMPyP porphyrin. This interaction was mediated by electrostatic attraction between the tetracationic TMPyP and the DNA oligonucleotide coating on the nanorods’ surface. Preliminary measurements of optical spectroscopy were carried out to characterize the interaction in solution of TMPyP and single or double-stranded DNA oligonucleotides complementary to a RNA sequence of Dengue virus.The apparent equilibrium constants for the complex of TMPyP with single and double-stranded DNA were determined to be Ka= 3.9×107 M-1and 4.5×107 M-1respectively. The spectral changes show a strong specific intercalation of TMPyP with ds-DNA and ss-DNA because of GC-rich sites in the selected sequences. Next, the plasmon-enhanced fluorescence of TMPyP induced by gold nanorods was investigated using confocal fluorescence lifetime microscopy to perform measurements of nanoparticle emission intensity and spectrum, fluorescence correlation spectroscopy, emission intensity time trace and fluorescence decay. The gold nanorods were immobilized on glass and functionalized with a thiolated oligonucleotide coating, while TMPyP molecules are diffusing in solution and stochastically interact with the rod’s surface. The emission intensity traces measured on single particles show strong fluorescence bursts when TMPyP molecules come into close proximity of the nanorod. We have calculated the emission enhancement factors from a comparison with the non-enhanced emission of TMPyP in the same experimental conditions and found surprisingly large enhancement factors of around 60000-fold for TMPyP’s emission.These values of enhancement are two orders of magnitude larger than our calculated highest enhanced fluorescence expected for TMPyP molecule.Os nano-bastonetes de ouro são caracterizados por plasmões de superfície com frequências de ressonância bastante sensíveis ao índice de refração na proximidade da sua superfície. A funcionalização seletiva da superfície destas nanopartículas com bio-receptores é crucial para o desenvolvimento de sensores plasmónicos com resposta melhorada, pois permite a captura de analitos nas regiões mais sensíveis da nanopartícula. Em primeiro lugar foram preparadas superfícies com nano-bastonetes de ouro que depois foram funcionalizados com recetores biotina para ensaios modelo de deteção de estreptavidina. A funcionalização seletiva das extremidades dos nano-bastonetes foi conseguida através da proteção das suas paredes laterais com uma bicamada de tensioativo CTAB e usando uma biotina derivatizada com uma função tiól. O desempenho do sensor foi caracterizado por medidas da cinética de associação biotina-estreptavidina monitorizada por espectroscopia ótica de absorção. Em anos recentes, a infeção pelo vírus do Dengue DENV-2 tem sido relatada como a maior epidemia por este tipo de vírus, e a deteção precoce desta infeção poderia salvar a vida de muitos pacientes. Deste modo, foi desenhado um sensor plasmónico modelo para a deteção de sequências de ARN propostas como bio-marcadores para a infeção pelo vírus do Dengue. Para o efeito, foram funcionalizados nano-bastonetes de ouro com cadeias de oligonucleotídos de ADN complementares a uma sequência do ARN do vírus do Dengue. Como estratégia de amplificação de sinal foram usadas cadeias de oligonucleotídos alvo marcadas com biotina, de modo a ser possível num segundo passo ligar estreptavidina ou anticorpo anti-biotina com o objetivo de aumentar a resposta do plasmão de superfície dos nano-bastonetes de ouro. A fluorescência intensificada por efeito plasmónico permite a deteção rápida e com elevado contraste de molécula única em microscopia de fluorescência. A interação entre os modos localizados de plasmão de superfície de nano-bastonetes de ouro e moléculas fluorescentes na sua proximidade pode induzir a aceleração das taxas de excitação, decaimento radiativo e não-radiativo, e conduzir a uma intensificação de fluorescência.Na terceira parte desta Dissertação, foram investigadas as interações entre nano-antenas de ouro e um cromóforo pouco fluorescente, a porfirina TMPyP. Esta interação foi mediada pela atração eletrostática entre a porfirina tetra-catiónica e o revestimento de ADN na superfície dos nano-bastonetes de ouro. Ensaios preliminares de espectroscopia ótica foram realizados para caracterizar a interação em solução da TMPyP com sequências de ADN de cadeia simples ou duplacomplementares a uma sequência do ARN do vírus do Dengue. A constante aparente de equilíbrio para o complexo da TMPyP com as sequências de ADN de cadeia simples e dupla foram determinadas como sendo Ka= 3.9×107 M-1and 4.5×107 M-1, respetivamente. As alterações dos espectros de absorção e emissão mostram uma forte interação, provavelmente intercalação, daTMPyPcom ods-DNA,etambém com o ss-DNA, devido ao elevado conteúdo em pares GC nas sequências escolhidas. Em seguida, a fluorescência intensificada por efeito plasmónico na TMPyP induzida por nano-bastonetes de ouro foi investigada por microscopia confocal de tempos-de-vida, tendo sido realizadas medidas de intensidade e espectro de emissão de nanopartículas, espectroscopia de correlação de fluorescência, traços temporais de intensidade de emissão e de decaimento de fluorescência.Os nano-bastonetes de ouro foram imobilizados em vidro e funcionalizados com um revestimento de oligonucleotídostiolados, enquanto que as moléculas de TMPyP difundem-se em solução e podem interatuar estocasticamente com a superfície da nanopartícula. Os traços de intensidade de emissão medidos em nanopartículas individuais mostram picos de fluorescência intensos quando as moléculas de TMPyP se aproximam do nano-bastonete de ouro em resultado do efeito de nano-antena.Foram calculados os fatores de emissão intensificada por comparação com a emissão não-intensificada da TMPyP nas mesmas condições experimentais e obtiveram-se valores surpreendentemente elevados de cerca de 60000 vezes para a emissão intensificada da TMPyP. Estes fatores de intensificação são duas ordens de grandeza mais elevados do que as estimativas teóricas calculadas para a intensificação da emissão da TMPyP pelos nanobastonetes de ouro

Recent Progress in Optical Sensors for Biomedical Diagnostics

In recent years, several types of optical sensors have been probed for their aptitude in healthcare biosensing, making their applications in biomedical diagnostics a rapidly evolving subject. Optical sensors show versatility amongst different receptor types and even permit the integration of different detection mechanisms. Such conjugated sensing platforms facilitate the exploitation of their neoteric synergistic characteristics for sensor fabrication. This paper covers nearly 250 research articles since 2016 representing the emerging interest in rapid, reproducible and ultrasensitive assays in clinical analysis. Therefore, we present an elaborate review of biomedical diagnostics with the help of optical sensors working on varied principles such as surface plasmon resonance, localised surface plasmon resonance, evanescent wave fluorescence, bioluminescence and several others. These sensors are capable of investigating toxins, proteins, pathogens, disease biomarkers and whole cells in varied sensing media ranging from water to buffer to more complex environments such as serum, blood or urine. Hence, the recent trends discussed in this review hold enormous potential for the widespread use of optical sensors in early-stage disease prediction and point-of-care testing devices.DFG, 428780268, Biomimetische Rezeptoren auf NanoMIP-Basis zur Virenerkennung und -entfernung mittels integrierter Ansätz

Design and optimization of a nanoprobe comprising amphiphilic chitosan colloids and Au-nanorods: Sensitive detection of human serum albumin in simulated urine

Metallic nanoparticles have been utilized as analytical tools to detect a wide range of organic analytes. In most reports, gold (Au)-based nanosensors have been modified with ligands to introduce selectivity towards a specific target molecule. However, in a recent study a new concept was presented where bare Au-nanorods on self-assembled carboxymethyl-hexanoyl chitosan (CHC) nanocarriers achieved sensitive and selective detection of human serum albumin (HSA) after manipulation of the solution pH. Here this concept was further advanced through optimization of the ratio between Au-nanorods and CHC nanocarriers to create a nanotechnology-based sensor (termed CHC-AuNR nanoprobe) with an outstanding lower detection limit (LDL) for HSA. The CHC-AuNR nanoprobe was evaluated in simulated urine solution and a LDL as low as 1.5 pM was achieved at an estimated AuNR/CHC ratio of 2. Elemental mapping and protein adsorption kinetics over three orders of magnitude in HSA concentration confirmed accumulation of HSA on the nanorods and revealed the adsorption to be completed within 15 min for all investigated concentrations. The results suggest that the CHC-AuNR nanoprobe has potential to be utilized for cost-effective detection of analytes in complex liquids

Gold nanorod-based localized surface plasmon resonance biosensors: A review

Noble metal nanoparticle-based localized surface plasmon resonance (LSPR) is an advanced and powerful label-free biosensing technique which is well-known for its high sensitivity to the surrounding refractive index change in the local environment caused by the biomolecular interactions around the sensing area. The characteristics of the LSPR effect in such sensors are highly dependent on the size, shape and nature of the material properties of the metallic nanoparticles considered. Among the various types of metallic nanoparticles used in studies employing the LSPR technique, the use of gold nanorods (GNRs) has attracted particular attention for the development of sensitive LSPR biosensors, this arising from the unique and intriguing optical properties of the material. This paper provides a detailed review of the key underpinning science for such systems and of recent progress in the development of a number of LSPR-based biosensors which use GNR as the active element, including an overview of the sensing principle, the synthesis of GNRs, the fabrication of a number of biosensors, techniques for surface modification of GNRs and finally their performance in several biosensing applications. The review ends with a consideration of key advances in GNR-based LSPR sensing and prospects for future research and advances for the development of the GNR-based LSPR biosensors

Gold nanonetwork film on the ITO surface exhibiting one-dimensional optical properties

A network of gold nanostructures exhibiting one-dimensional gold nanostructure properties may become a prospective novel structure for optical, electrical and catalytic applications benefited by its unusual characteristics resulting from the collective properties of individual nanostructures in the network. In this paper, we demonstrate a facile method for the formation of high-density gold nanonetwork film on the substrate surface composed of quasi-1D nanoparticles (typically fusiform) with length ca. 10 nm - via reduction of gold ions in the presence of nanoseeds attached surface, binary surfactants of cetyltrimethylammonium bromide and hexamethyleneteramine and Ag(+) ions. The length of the nanonetworks can be up to ca. 100 nm, which corresponds to the aspect ratio of ca. 10. The quasi-1D gold nanostructures as well as the nanonetworks were found to be sensitive to the binary surfactants system and the Ag(+) ions as they can only be formed if all the chemicals are available in the reaction. The nanonetworks exhibit unique 1D optical properties with the presence of transverse and longitudinal surface plasmon resonance absorption. Owing to their peculiar structures that are composed of small quasi-1D nanoparticles, the nanonetworks may produce unusual optical and catalytic properties, which are potentially used in surface-enhanced Raman scattering, catalysis and optical and non-linear optical applications

Highly sensitive surface enhanced Raman scattering (SERS) detection platforms formed by large area self-assembled Au nanorod arrays

This thesis explores a new method to fabricate SERS detection platforms formed by large area self-assembled Au nanorod arrays. For the fabrication of these new SERS platforms a new droplet deposition method for the self-assembly of Au nanorods was developed. The method, based in the controlled evaporation of organic suspensions of Au nanorods, was used for the fabrication of horizontal and vertical arrays of Au nanorods over large areas (100μm2). The fabricated nanorods arrays showed a high degree of order measured by SEM and optical microscopy over mm2 areas, but unfortunately they detached from the support when immersed in any analyte solutions. In order to improve adhesion of arrays to the support and clean off residual organic matter, we introduced an additional stamping process. The stamping process allows the immobilization of the arrays on different flexible and rigid substrates, whose feasibility as SERS platforms were tested satisfactory with the model molecule 4ABT. Following the feasibility study, the substrates were used for the detection of the food contaminant Crystal Violet and the drug analogue Benzocaine as examples of recognition of health menaces in real field applications

Gold and Silver Nanowires for Fluorescence Enhancement

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