An enhanced LSPR fiber-optic nanoprobe for ultrasensitive detection of protein biomarkers

A miniaturized, localized surface plasmon resonance (LSPR)-coupled fiber-optic (FO) nanoprobe is reported as a biosensor that is capable of label-free, sensitive detection of a cancer protein biomarker, free prostate specific antigen (f-PSA). The biosensor is based on the LSPR at the reusable dielectric-metallic hybrid interface with a robust, gold nano-disk array at the fiber end facet that is directly fabricated using EBL and metal lift-off process. The f-PSA has been detected with a mouse anti-human PSA monoclonal antibody (mAb) as a specific receptor linked with a self-assembled monolayer at the LSPR-FO facet surfaces. Experimental investigation and data analysis found near field refractive index (RI) sensitivity at ~226 nm/RIU with current LSPR-FO nanoprobe, and demonstrated the lowest limit of detection (LOD) at 100 fg/mL (~3 fM) of f-PSA in PBS solutions. The control experimentation using 5 mg/mL bovine serum albumin in PBS and nonspecific surface test shows the excellent specificity and selectivity in the detection of f-PSA in PBS. These results present important progress towards a miniaturized, multifunctional fiber-optic technology that integrates informational communication and sensing function for developing a high performance, label-free, point-of-care (POC) device

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

Creation of novel gold-nanorod-based localized surface plasmon resonance biosensors

Starting with a comprehensive review of both surface plasmon resonance (SPR) based and localized surface plasmon resonance (LSPR) based sensors, this thesis reports the studies on the development of a novel sensitive gold nanorod (GNR) based label-free LSPR optical fibre biosensor, and the development of a novel robust method for effectively modifying the surface of cetyl-trimethyl ammonium bromide (CTAB) capped GNRs and their LSPR biosensing applications. A novel GNR-based LSPR optical fibre sensor was fabricated and evaluated in this work. The sensor probe was prepared by covalently immobilizing GNRs, synthesized using a seed-mediated growth method, on the decladed surface of a piece of multimode optical fibre. In order to operate the LSPR sensor as a reflective sensor, a silver mirror was also coated at one distal end of the sensor probe by a dip coating method. In the refractive index sensitivity test, it was found that the longitudinal plasmon band (LPB) of GNRs is highly sensitive to the refractive index change close to the GNRs surface, and the sensitivity of the LSPR optical fibre sensor increases with the increase of the aspect ratio of GNRs. The results showed that the GNR-based LSPR optical fibre sensors prepared in this work have linear and high refract index sensitivities. For sensors based on GNRs with aspect ratios of 2.6, 3.1, 3.7 and 4.3, their refractive index sensitivities were found to be 269, 401, 506 and 766 nm/RIU (RIU = refractive index unit), respectively, in the refractive index range from 1.34 to 1.41. In order to evaluate the biosensing performance, the GNR-based LSPR optical fibre sensor with aspect ratio of 4.1 and a 2 cm sensing length was further functionalized with human IgG to detect the specific target — anti-human IgG, and a detection limit of 1.6 nM was observed using a wavelength-based interrogation approach. In another study, in order to overcome the drawbacks of the CTAB-capped GNRs found in biosensing and biomedical applications, a simple yet robust pH-mediated method for effectively modifying the surface of CTAB-capped GNRs synthesized by the seed-mediated growth method was developed. This method allows the complete replacement of the CTAB molecules attached on the GNRs surface with the 11-mercaptoundecaonic acid (MUA) molecules to take place in a total aqueous environment by controlling the pH of the MUA aqueous solution, thus avoiding the irreversible aggregation of GNRs during the complex surface modification process observed in the previous reported methods. The success of the complete replacement of CTAB with MUA was confirmed by the surface elemental analysis using an X-ray photoelectron spectroscopy (XPS), and the MUA-modified GNRs created in this work demonstrated a high stability up to 4 months at least when stored in a buffer solution at pH 9 at 4°C. The MUA-modified GNRs with an aspect ratio of 3.9 were furthered developed as a solution-phase-based label-free LSPR biosensor by functionalizing the GNRs with human IgG. A detection limit as low as 0.4 nM for detecting anti-human IgG was achieved by this sensor. The achievements of this work are concluded and the directions of future work are also pointed out

Localized Surface Plasmon Resonance for Optical Fiber-Sensing Applications

It is well known that optical fiber sensors have attracted the attention of scientific community due to its intrinsic advantages, such as lightweight, small size, portability, remote sensing, immunity to electromagnetic interferences and the possibility of multiplexing several signals. This field has shown a dramatic growth thanks to the creation of sensitive thin films onto diverse optical fiber configurations. In this sense, a wide range of optical fiber devices have been successfully fabricated for monitoring biological, chemical, medical or physical parameters. In addition, the use of nanoparticles into the sensitive thin films has resulted in an enhancement in the response time, robustness or sensitivity in the optical devices, which is associated to the inherent properties of nanoparticles (high surface area ratio or porosity). Among all of them, the metallic nanoparticles are of great interest for sensing applications due to the presence of strong absorption bands in the visible and near-infrared regions, due to their localized surface plasmon resonances (LSPR). These optical resonances are due to the coupling of certain modes of the incident light to the collective oscillation of the conduction electrons of the metallic nanoparticles. The LSPR extinction bands are very useful for sensing applications as far as they can be affected by refractive index variations of the surrounding medium of the nanoparticles, and therefore, it is possible to create optical sensors with outstanding properties such as high sensitivity and optical self-reference. In this chapter, the attractive optical properties of metal nanostructures and their implementation into different optical fiber configuration for sensing or biosensing applications will be studied

Novel highly sensitive protein sensors based on tapered optical fibres modified with Au-based nanocoatings

Novel protein sensors based on tapered optical fibres modified with Au coatings deposited using two different procedures are proposed. Au-based coatings are deposited onto a nonadiabatic tapered optical fibre using (i) a novel facile method composed of layer-by-layer deposition consisting of polycation (poly(allylamine hydrochloride), PAH) and negatively charged SiO₂ nanoparticles (NPs) followed by the deposition of the charged Au NPs and (ii) the sputtering technique.The Au NPs and Au thin film surfaces are then modified with biotin in order to bind streptavidin (SV) molecules and detect them. The sensing principle is based on the sensitivity of the transmission spectrum of the device to changes in the refractive index of the coatings induced by the SV binding to the biotin. Both sensors showed high sensitivity to SV, with the lowest measured concentration levels below 2.5 nM. The calculated binding constant for the biotin-SV pair was 2.2×10‾¹¹ M‾¹ when a tapered fibre modified with the LbL method was used, with a limit of detection (LoD) of 271 pM. The sensor formed using sputtering had a binding constant of 1.01 × 10‾¹⁰ M‾¹ with a LoD of 806 pM. These new structures and their simple fabrication technique could be used to develop other biosensors

Optical Microfibre Based Photonic Components and Their Applications in Label-Free Biosensing

Optical microfibre photonic components offer a variety of enabling properties, including large evanescent fields, flexibility, configurability, high confinement, robustness and compactness. These unique features have been exploited in a range of applications such as telecommunication, sensing, optical manipulation and high Q resonators. Optical microfibre biosensors, as a class of fibre optic biosensors which rely on small geometries to expose the evanescent field to interact with samples, have been widely investigated. Due to their unique properties, such as fast response, functionalization, strong confinement, configurability, flexibility, compact size, low cost, robustness, ease of miniaturization, large evanescent field and label-free operation, optical microfibres based biosensors seem a promising alternative to traditional immunological methods for biomolecule measurements. Unlabeled DNA and protein targets can be detected by monitoring the changes of various optical transduction mechanisms, such as refractive index, absorption and surface plasmon resonance, since a target molecule is capable of binding to an immobilized optical microfibre. In this review, we critically summarize accomplishments of past optical microfibre label-free biosensors, identify areas for future research and provide a detailed account of the studies conducted to date for biomolecules detection using optical microfibres

Mini Review of Glucose Detection Using Plasmonic Sensor

Glucose is a crucial compound in human life. Glucose has important roles in energy source production and overall brain health. In addition, it can be converted into other compounds essential for the growth, repair, and maintaining tissues throughout the body. Also, glucose becomes an indicator of diabetes, i.e., ill when the body can not produce insulin hormone properly. The poor management of diabetes can affect long-term complications that can significantly impact a person's quality of life and may lead to disability or even premature death if not properly addressed. Thus, it is important to do glucose detection to stay within a healthy range. The common methods patients use are glucose meters and urine testing on the laboratory scale. This method has several areas for improvement, such as being invasive, needing experts, and requiring a long-time detection. Thus, researchers come into various alternative glucose detection such as chromatography, mass spectrometry, electrochemical, and plasmonic sensor. Chromatography for glucose detection is rarely used in recent years because of its complexity. Then, for mass spectrometry, it is also complicated for the result and maintenance. As for electrochemical methods, the disadvantage is that other electroactive components on the sample can be interfered with. Plasmonic sensors that utilize the Localized Surface Plasmon Resonance (LSPR) phenomenon are considered due to their advantage, i.e., non-invasive, real-time monitoring, and highly sensitive to surrounding medium change. Plasmonic sensors usually use components of light absorption, luminescence, fluorescence, Raman scattering, reflectance, and refractive index based on the nanoparticles used as sensing materials. Still, transmission and reflection are popular and widely applied. Furthermore, plasmonic sensors generally consist of instruments such as a light source, fiber optic, chamber to place substrate/analyte, spectrometer/detector, and computer. Besides, plasmonic sensors can produce different analytical characteristics suitable for different cases and tuned for the need because of the various sensing materials used. Hence, plasmonic sensors become a promising alternative method for glucose detection

Creation of novel gold-nanorod-based localized surface plasmon resonance biosensors

Starting with a comprehensive review of both surface plasmon resonance (SPR) based and localized surface plasmon resonance (LSPR) based sensors, this thesis reports the studies on the development of a novel sensitive gold nanorod (GNR) based label-free LSPR optical fibre biosensor, and the development of a novel robust method for effectively modifying the surface of cetyl-trimethyl ammonium bromide (CTAB) capped GNRs and their LSPR biosensing applications. A novel GNR-based LSPR optical fibre sensor was fabricated and evaluated in this work. The sensor probe was prepared by covalently immobilizing GNRs, synthesized using a seed-mediated growth method, on the decladed surface of a piece of multimode optical fibre. In order to operate the LSPR sensor as a reflective sensor, a silver mirror was also coated at one distal end of the sensor probe by a dip coating method. In the refractive index sensitivity test, it was found that the longitudinal plasmon band (LPB) of GNRs is highly sensitive to the refractive index change close to the GNRs surface, and the sensitivity of the LSPR optical fibre sensor increases with the increase of the aspect ratio of GNRs. The results showed that the GNR-based LSPR optical fibre sensors prepared in this work have linear and high refract index sensitivities. For sensors based on GNRs with aspect ratios of 2.6, 3.1, 3.7 and 4.3, their refractive index sensitivities were found to be 269, 401, 506 and 766 nm/RIU (RIU = refractive index unit), respectively, in the refractive index range from 1.34 to 1.41. In order to evaluate the biosensing performance, the GNR-based LSPR optical fibre sensor with aspect ratio of 4.1 and a 2 cm sensing length was further functionalized with human IgG to detect the specific target — anti-human IgG, and a detection limit of 1.6 nM was observed using a wavelength-based interrogation approach. In another study, in order to overcome the drawbacks of the CTAB-capped GNRs found in biosensing and biomedical applications, a simple yet robust pH-mediated method for effectively modifying the surface of CTAB-capped GNRs synthesized by the seed-mediated growth method was developed. This method allows the complete replacement of the CTAB molecules attached on the GNRs surface with the 11-mercaptoundecaonic acid (MUA) molecules to take place in a total aqueous environment by controlling the pH of the MUA aqueous solution, thus avoiding the irreversible aggregation of GNRs during the complex surface modification process observed in the previous reported methods. The success of the complete replacement of CTAB with MUA was confirmed by the surface elemental analysis using an X-ray photoelectron spectroscopy (XPS), and the MUA-modified GNRs created in this work demonstrated a high stability up to 4 months at least when stored in a buffer solution at pH 9 at 4°C. The MUA-modified GNRs with an aspect ratio of 3.9 were furthered developed as a solution-phase-based label-free LSPR biosensor by functionalizing the GNRs with human IgG. A detection limit as low as 0.4 nM for detecting anti-human IgG was achieved by this sensor. The achievements of this work are concluded and the directions of future work are also pointed out.EThOS - Electronic Theses Online ServiceGBUnited Kingdo