Localized surface plasmon resonance as a biosensing platform for developing countries

Advances in Nanoplasmonic Biosensors: Optimizing Performance for Exosome Detection Applications

The development of sensitive and specific exosome detection tools is essential because they are believed to provide specific information that is important for early detection, screening, diagnosis, and monitoring of cancer. Among the many detection tools, surface-plasmon resonance (SPR) biosensors are analytical devices that offer advantages in sensitivity and detection speed, thereby making the sample-analysis process faster and more accurate. In addition, the penetration depth of the SPR biosensor, which is <300 nm, is comparable to the size of the exosome, making the SPR biosensor ideal for use in exosome research. On the other hand, another type of nanoplasmonic sensor, namely a localized surface-plasmon resonance (LSPR) biosensor, has a shorter penetration depth of around 6 nm. Structural optimization through the addition of supporting layers and gap control between particles is needed to strengthen the surface-plasmon field. This paper summarizes the progress of the development of SPR and LSPR biosensors for detecting exosomes. Techniques in signal amplification from two sensors will be discussed. There are three main parts to this paper. The first two parts will focus on reviewing the working principles of each sensor and introducing several methods that can be used to isolate exosomes. This article will close by explaining the various sensor systems that have been developed and the optimizations carried out to obtain sensors with better performance. To illustrate the performance improvements in each sensor system discussed, the parameters highlighted include the detection limit, dynamic range, and sensitivity.

Applications of Surface Plasmon Resonance (SPR) to the Study of Diverse Protein-Ligand Interactions

Functional characterization of enzymes/proteins requires determination of the binding affinity of small molecules or other biomolecules with the target proteins. Several available techniques, such as proteomics and drug discovery strategies, require a precise and high-throughput assay for rapid and reliable screening of potential candidates for further testing. Surface plasmon resonance (SPR), a well-established label-free technique, directly measures biomolecular affinities. SPR assays require immobilization of one interacting component (ligand) on a conductive metal (mostly gold or silver) and a continuous flow of solution containing potential binding partner (analyte) across the surface. The SPR phenomenon occurs when polarized light excites the electrons at the interface of the metal and the dielectric medium to generate electromagnetic waves that propagate parallel to the surface. Changes in the refractive index due to interaction between the ligand and analyte are measured by detecting the reflected light, providing real-time data on kinetics and specificity. A prominent use of SPR is identifying compounds in crude plant extracts that bind to specific molecules. Procedures that utilize SPR are becoming increasingly applicable outside the laboratory setting, and SPR imaging and localized SPR (LSPR) are cheaper and more portable alternative for in situ detection of plant or mammalian pathogens and drug discovery studies. LSPR, in particular, has the advantage of direct attachment to test tissues in live-plant studies. Here, we describe three protocols utilizing SPR-based assays for precise analysis of protein-ligand interactions. © 2024 Wiley Periodicals LLC. Basic Protocol 1: SPR comparison of binding affinities of viral reverse transcriptase polymorphisms Basic Protocol 2: SPR screening of crude plant extract for protein-binding agents Basic Protocol 3: Localized SPR-based antigen detection using antibody-conjugated gold nanoparticles.

Localized Surface Plasmon Resonance Sensing and its Interplay with Fluidics

In this Feature Article, we discuss the interplay between fluidics and the localized surface plasmon resonance (LSPR) sensing technique, primarily focusing on its applications in the realm of bio/chemical sensing within fluidic environments. Commencing with a foundational overview of LSPR principles from a sensing perspective, we subsequently showcase the development of a streamlined LSPR chip integrated with microfluidic structures. This integration opens the doors to advanced experiments involving fluid dynamics, greatly expanding the scope of LSPR-based research. Our discussions then turn to the practical implementation of LSPR and microfluidics in real-time biosensing, with a specific emphasis on monitoring DNA polymerase activity. Additionally, we illustrate the direct sensing of biological fluids, exemplified by the analysis of urine, while also shedding light on a unique particle assembly process that occurs on LSPR chips. We not only discuss the significance of LSPR sensing but also explore its potential to investigate a plethora of phenomena at liquid-liquid and solid-liquid interfaces. This is particularly noteworthy, as existing transduction methods and sensors fall short in fully comprehending these interfacial phenomena. Concluding our discussion, we present a futuristic perspective that provides insights into potential opportunities emerging at the intersection of fluidics and LSPR sensing.

CA19-9 and CEA biosensors in pancreatic cancer

Cancer is a complex pathophysiological condition causing millions of deaths each year. Early diagnosis is essential especially for pancreatic cancer. Existing diagnostic tools rely on circulating biomarkers such as Carbohydrate Antigen 19-9 (CA19-9) and Carcinoembryonic Antigen (CEA). Unfortunately, these markers are nonspecific and may be increased in a variety of disorders. Accordingly, diagnosis of pancreatic cancer generally involves more invasive approaches such as biopsy as well as imaging studies. Recent advances in biosensor technology have allowed the development of precise diagnostic tools having enhanced analytical sensitivity and specificity. Herein we examine these advances in the detection of cancer in general and in pancreatic cancer specifically. Furthermore, we highlight novel technologies in the measurement of CA19-9 and CEA and explore their future application in the early detection of pancreatic cancer.

Biogenic synthesis of gold nanoparticles using dual extract of tulsi-Vinca for breast cancer tumor regression in mice

Aim: This work aims to synthesize the gold nanoparticles (GNPs) using a dual extract of tulsi and Vinca (T+V-Gold) for breast cancer tumor regression. Methods: The GNPs were synthesized and characterized for their microscopic, spectroscopic and crystalline properties. Further, the GNPs were investigated for in vitro and in vivo studies for the treatment of the 4T1-induced triple-negative breast cancer murine model. Results: The GNPs for 4T1 tumor-challenged mice resulted in delayed tumor development and lower tumor burden, with T+V-Gold demonstrating the highest prevention of tumor spread. The antitumor effect of T+V-Gold is highly significant in the glutathione family antioxidants glutathione S-transferase and glutathione in tumor tissue samples. Conclusion: The bioefficacy and anticancer outcomes of T+V-Gold nanoformulation can be used as therapeutic agents and drug-delivery vehicles.

Micro- and nanosystems for the detection of hemorrhagic fever viruses

Hemorrhagic fever viruses (HFVs) are virulent pathogens that can cause severe and often fatal illnesses in humans. Timely and accurate detection of HFVs is critical for effective disease management and prevention. In recent years, micro- and nano-technologies have emerged as promising approaches for the detection of HFVs. This paper provides an overview of the current state-of-the-art systems for micro- and nano-scale approaches to detect HFVs. It covers various aspects of these technologies, including the principles behind their sensing assays, as well as the different types of diagnostic strategies that have been developed. This paper also explores future possibilities of employing micro- and nano-systems for the development of HFV diagnostic tools that meet the practical demands of clinical settings.

Sonocatalytic Optimization of Titanium-Based Therapeutic Nanomedicine

Recent considerable technological advances in ultrasound-based treatment modality provides a magnificent prospect for scientific communities to conquer the related diseases, which is featured with remarkable tissue penetration, non-invasive and non-thermal characteristics. As one of the critical elements that influences treatment outcomes, titanium (Ti)-based sonosensitizers with distinct physicochemical properties and exceptional sonodynamic efficiency have been applied extensively in the field of nanomedical applications. To date, a myriad of methodologies has been designed to manipulate the sonodynamic performance of titanium-involved nanomedicine and further enhance the productivity of reactive oxygen species for disease treatments. In this comprehensive review, the sonocatalytic optimization of diversified Ti-based nanoplatforms, including defect engineering, plasmon resonance modulation, heterojunction, modulating tumor microenvironment, as well as the development of synergistic therapeutic modalities is mainly focused. The state-of-the-art Ti-based nanoplatforms ranging from preparation process to the extensive medical applications are summarized and highlighted, with the goal of elaborating on future research prospects and providing a perspective on the bench-to-beside translation of these sonocatalytic optimization tactics. Furthermore, to spur further technological advancements in nanomedicine, the difficulties currently faced and the direction of sonocatalytic optimization of Ti-based therapeutic nanomedicine are proposed and outlooked.

Signal amplification strategies in biosensing of extracellular vesicles (EVs)

Extracellular vesicles (EVs) are membrane-enclosed vesicles secreted from mammalian cells. EVs act as multicomponent delivery vehicles to carry a wide variety of biological molecular information and participate in intercellular communications. Since elevated levels of EVs are associated with some pathological states such as inflammatory diseases and cancers, probing circulating EVs holds a great potential for early diagnostics. To this end, several detection methods have been developed in which biosensors have attracted great attentions in identification of EVs due to their simple instrumentation, versatile design and portability for point-of-care applications. The concentrations of EVs in bodily fluids are extremely low (i.e. 1-100 per μl) at early stages of a disease, which necessitates the use of signal amplification strategies for EVs detection. In this way, this review presents and discusses various amplification strategies for EVs biosensors based on detection modalities including surface plasmon resonance (SPR), calorimetry, fluorescence, electrochemical and electrochemiluminescence (ECL). In addition, microfluidic systems employed for signal amplification are reviewed and discussed in terms of their design and integration with the detection methods.

Cancer Treatment Using Different Shapes of Gold-Based Nanomaterials in Combination with Conventional Physical Techniques

The conventional methods of cancer treatment and diagnosis, such as radiotherapy, chemotherapy, and computed tomography, have developed a great deal. However, the effectiveness of such methods is limited to the possible failure or collateral effects on the patients. In recent years, nanoscale materials have been studied in the field of medical physics to develop increasingly efficient methods to treat diseases. Gold nanoparticles (AuNPs), thanks to their unique physicochemical and optical properties, were introduced to medicine to promote highly effective treatments. Several studies have confirmed the advantages of AuNPs such as their biocompatibility and the possibility to tune their shapes and sizes or modify their surfaces using different chemical compounds. In this review, the main properties of AuNPs are analyzed, with particular focus on star-shaped AuNPs. In addition, the main methods of tumor treatment and diagnosis involving AuNPs are reviewed.

Novel insight on chemo-specific detection of toxic environmental chromium residues existing as recalcitrant Cr(III)-carboxyl complexes using plasmonic silver nanoplatform bi-functionalized with citrate and PVP

Chromium (Cr) is a toxic environmental pollutant that majorly exists in trivalent and hexavalent forms. Though Cr(VI) is more dangerous than Cr(III), the trivalent Cr forms complexes with environmentally-available organic molecules. This makes them potentially harmful and difficult to detect. In this study, we have designed an ultrasensitive plasmonic nanosensor using citrate and PVP functionalized Ag nanoparticles (Ag-citrate-PVPNPs) for the detection of trivalent chromium organic complexes such as Cr(III)-EDTA (Cr-E), Cr(III)-acetate (Cr-A), Cr(III)-citrate (Cr-C) and Cr(III)-tartrate (Cr-T). The nanoparticles (NPs) were structurally characterized by XRD, SEM, HRTEM, SAED, EDX and elemental mapping. The citrate and PVP molecules played a vital role in the detection mechanism and stability of the sensor. Upon detection, the yellow-colored Ag-citrate-PVP NPs turned into different shades of brown depending on the type of the Cr complex and concentration. It was accompanied by diminishing and/or shifting UV-Visible absorbance peaks due to the aggregation of Ag-citrate-PVP NPs. Further, a linear relationship was observed between absorbance reduction and analyte concentration. The selectivity tests showed that the sensor was non-functional to other metal ions and inorganic anions. The sensor was optimized using pH and temperature studies. The mechanism of detection was elucidated with the help of characterization techniques such as Raman spectroscopy, FTIR, XPS and UV-visible spectrophotometer. The limit of detection (LOD) was found to be 3.29, 4.87, 1.76 and 1.79 nM for Cr-E, Cr-A, Cr-C and Cr-T complexes respectively. This study provides a rapid and sensitive approach for the detection of multiple Cr(III)-organic complexes present in an aqueous solution.

Zinc- and magnesium-doped hydroxyapatite-urea nanohybrids enhance wheat growth and nitrogen uptake

The ongoing and unrestrained application of nitrogen fertilizer to agricultural lands has been directly linked to climate change and reductions in biodiversity. The agricultural sector needs a technological upgrade to adopt sustainable methods for maintaining high yield. We report synthesis of zinc and magnesium doped and undoped hydroxyapatite nanoparticles, and their urea nanohybrids, to sustainably deliver nitrogen to wheat. The urea nanohybrids loaded with up to 42% nitrogen were used as a new source of nitrogen and compared with a conventional urea-based fertilizer for efficient and sufficient nitrogen delivery to pot-grown wheat. Doping with zinc and magnesium manipulated the hydroxyapatite crystallinity for smaller size and higher nitrogen loading capacity. Interestingly, 50% and 25% doses of urea nanohybrids significantly boosted the wheat growth and yield compared with 100% doses of urea fertilizer. In addition, the nutritional elements uptake and grain protein and phospholipid levels were significantly enhanced in wheat treated with nanohybrids. These results demonstrate the potential of the multi-nutrient complexes, the zinc and magnesium doped and undoped hydroxyapatite-urea nanoparticles, as nitrogen delivery agents that reduce nitrogen inputs by at least 50% while maintaining wheat plant growth and nitrogen uptake to the same level as full-dose urea treatments.

Materials Perspectives of Integrated Plasmonic Biosensors

With the growing need for portable, compact, low-cost, and efficient biosensors, plasmonic materials hold the promise to meet this need owing to their label-free sensitivity and deep light-matter interaction that can go beyond the diffraction limit of light. In this review, we shed light on the main physical aspects of plasmonic interactions, highlight mainstream and future plasmonic materials including their merits and shortcomings, describe the backbone substrates for building plasmonic biosensors, and conclude with a brief discussion of the factors affecting plasmonic biosensing mechanisms. To do so, we first observe that 2D materials such as graphene and transition metal dichalcogenides play a major role in enhancing the sensitivity of nanoparticle-based plasmonic biosensors. Then, we identify that titanium nitride is a promising candidate for integrated applications with performance comparable to that of gold. Our study highlights the emerging role of polymer substrates in the design of future wearable and point-of-care devices. Finally, we summarize some technical and economic challenges that should be addressed for the mass adoption of plasmonic biosensors. We believe this review will be a guide in advancing the implementation of plasmonics-based integrated biosensors.

Endorsing a Hidden Plasmonic Mode for Enhancement of LSPR Sensing Performance in Evolved Metal-insulator Geometry Using an Unsupervised Machine Learning Algorithm

Large-area nanoplasmonic structures with pillared metal-insulator geometry, also called nanomushrooms (NM), consist of an active spherical-shaped plasmonic material such as gold as its cap and silicon dioxide as its stem. NM is a geometry which evolves from its precursor, nanoislands (NI) consisting of aforementioned spherical structures on flat silicon dioxide substrates, via selective physical or chemical etching of the silicon dioxide. The NM geometry is well-known to provide enhanced localized surface plasmon resonance (LSPR) sensitivity in biosensing applications as compared to NI. However, precise optical phenomenon behind this enhancement is unknown and often associated with the existence of electric fields in the large fraction of the spatial region between the pillars of NM, usually accessible by the biomolecules. Here, we uncover the association of LSPR enhancement in such geometries with a hidden plasmonic mode by conducting magneto-optics measurements and by deconvoluting the absorbance spectra obtained during the local refractive index change of the NM and NI geometries. By the virtue of principal component analysis, an unsupervised machine learning technique, we observe an explicit relationship between the deconvoluted modes of LSPR, the differential absorption of left and right circular polarized light, and the refractive index sensitivity of the LSPR sensor. Our findings may lead to the development of new approaches to extract unknown properties of plasmonic materials or establish new fundamental relationships between less understood photonic properties of nanomaterials.

Elucidating Sensitivity and Stability Relationship of Gold-Carbon Hybrid LSPR Sensors Using Principal Component Analysis

Sensitive localized surface plasmon resonance (LSPR) sensing is achieved using nanostructured geometries of noble metals which typically have dimensions less than 100 nm. Among the plethora of geometries and materials, the spherical geometries of gold (Au) are widely used to develop sensitive bio/chemical sensors due to ease of manufacturing and biofunctionlization. One major limitation of spherical-shaped geometries of Au, used for LSPR sensing, is their low refractive index (RI) sensitivity which is commonly addressed by adding another material to the Au nanostructures. However, the process of addition of new material on Au nanostructures, while retaining the LSPR of Au, often comes with a trade-off which is associated with the instability of the developed composite, especially in harsh chemical environments. Addressing this challenge, we develop a Au-graphene-layered hybrid (Au-G) with high stability (studied up to 2 weeks here) and enhanced RI sensitivity (a maximum of 180.1 nm/RIU) for generic LSPR sensing applications using spherical Au nanostructures in harsh chemical environments, involving organic solvents. Additionally, by virtue of principal component analysis, we correlate stability and sensitivity of the developed system. The relationship suggests that the shelf life of the material is proportional to its sensitivity, while the stability of the sensor during the measurement in liquid environment decreases when the sensitivity of the material is increased. Though we uncover this relationship for the LSPR sensor, it remains evasive to explore similar relationships within other optical and electrochemical transduction techniques. Therefore, our work serves as a benchmark report in understanding/establishing new correlations between sensing parameters.

Plasmonic Nanosensors: Design, Fabrication, and Applications in Biomedicine

Current advances in the fabrication of smart nanomaterials and nanostructured surfaces find wide usage in the biomedical field. In this context, nanosensors based on localized surface plasmon resonance exhibit unprecedented optical features that can be exploited to reduce the costs, analytic times, and need for expensive lab equipment. Moreover, they are promising for the design of nanoplatforms with multiple functionalities (e.g., multiplexed detection) with large integration within microelectronics and microfluidics. In this review, we summarize the most recent design strategies, fabrication approaches, and bio-applications of plasmonic nanoparticles (NPs) arranged in colloids, nanoarrays, and nanocomposites. After a brief introduction on the physical principles behind plasmonic nanostructures both as inherent optical detection and as nanoantennas for external signal amplification, we classify the proposed examples in colloid-based devices when plasmonic NPs operate in solution, nanoarrays when they are assembled or fabricated on rigid substrates, and nanocomposites when they are assembled within flexible/polymeric substrates. We highlight the main biomedical applications of the proposed devices and offer a general overview of the main strengths and limitations of the currently available plasmonic nanodevices.

Recent advancements in optical biosensors for cancer detection

Optical biosensors are rapid, real-time, and portable, have a low detection limit and a high sensitivity, and have a great potential for diagnosing various types of cancer. Optical biosensors can detect cancer in a few million malignant cells, in comparison to conventional diagnosis techniques that use 1 billion cells in tumor tissue with a diameter of 7 nm-10 nm. Current cancer detection methods are also costly, inconvenient, complex, time consuming, and require technical specialists. This review focuses on recent advances in optical biosensors for early detection of cancer. It is primarily concerned with advancements in the design of various biosensors using resonance, scattering, chemiluminescence, luminescence, interference, fluorescence, absorbance or reflectance, and various fiber types. The development of various two-dimensional materials with optical properties such as biocompatibility, field enhancement, and a higher surface-to-volume ratio, as well as advancements in microfabrication technologies, have accelerated the development of optical sensors for early detection of cancer and other diseases. Surface enhanced Raman spectroscopy technology has the potential to detect a single molecule with high specificity, and terahertz waves are a recently explored technology for cancer detection. Due to the low electromagnetic interference, small size, multiplexing, and remote sensing capabilities of optical fiber-based platforms, they may be a driving force behind the rapid development of biosensors. The advantages and disadvantages of existing and future optical biosensor designs for cancer detection are discussed in detail. Additionally, a prospect for future advancements in the development of optical biosensors for point-of-care and clinical applications is highlighted.

Cancer and Disease Diagnosis - Biosensor as Potential Diagnostic Tool for Biomarker Detection

Analysis of cancer biomarkers has enormous promise for advancing our molecular understanding of illness and facilitating more precise and timely diagnosis and follow-up care. MicroRNA, exosomes, ctDNA, CTCs, and proteins are only some of the circulating biomarkers that can be detected by liquid biopsy instead of the more intrusive and time-consuming process of doing a tissue biopsy. As the cancer diagnosis bio-markers reveal ultra-low levels in the early stages of the disease, highly sensitive approaches are urgently required. Researchers have taken an interest in a optical biosensor for detecting cancer biomarkers as a potential tool for early disease diagnosis. These techniques have the potential to aid in the development of effective treatments, ultimately leading to a higher rate of patient survival. This review briefly discuss the i) understanding of cancer and biomarkers for early diagonosis purpose ii) Molecular methods and ii) biosensor-based diagnostics. The reseach primary focus on advancement in biosensor design using various concepts ie., Electrochemical, Chemiluminescence and Colorimetric, Surface plasmons (SP), Surface plasmon resonance (SPR), localized surface plasmon resonance (LSPR), Fluorescence, Fiber-based sensors, Terahertz based biosensors, and Surface enhanced Raman spectroscopy (SERS). As a result of the local electric field amplification around plasmonic (usually gold and silver) nanostructures, surface-enhanced Raman spectroscopy (SERS) has emerged as a rapid, selective, and sensitive alternative to conventional laboratory analytical methods, making significant strides in a number of biosensing applications but still under developing stage to be used as diagnostic tool in clinical research.

LSPR immuno-sensing based on iso-Y nanopillars for highly sensitive and specific imidacloprid detection

Imidacloprid is the most widely used insecticide in agriculture and its intensive use over the last 30 years has caused a global concern due to its potentially toxic effects on the ecosystem. Considering the recent scientific interest in novel simple methods for imidacloprid analysis, we propose a label-free sensitive and specific localised surface plasmon resonance system for the detection of the insecticide based on 2D nanostructured metasurfaces with highly performing plasmonic properties. The specificity of the sensor proposed was achieved by covalent bio-functionalization of the metasurface using a smart and easy one-step procedure mediated by carbon disulphide. The biosensor produced was tested using a set of imidacloprid standard solutions showing a competitive limit of detection, lower than 1 ng mL^-1. Our novel nanosensing configuration represents a valid and reliable solution to realize low-cost portable POC tests as an alternative to the laborious and expensive methods traditionally used for insecticide detection.

Recent Advancements in Biosensing Approaches for Screening and Diagnostic Applications

Recent advancements in molecular recognition have provided additional diagnostic and treatment approaches for multiple diseases, including autoimmune disorders and cancers. Research investigating how the composition of biological fluids is altered during disease progression, including differences in the expression of the small molecules, proteins, RNAs, and other components present in patient tears, saliva, blood, urine, or other fluids, has provided a wealth of potential candidates for early disease screening; however, adoption of biomarker screening into clinical settings has been challenged by the need for more robust, low-cost, and high-throughput assays. This review examines current approaches in molecular recognition and biosensing for the quantification of biomarkers for disease screening and diagnostic outcomes.

Advanced Nanoporous Anodic Alumina-Based Optical Sensors for Biomedical Applications

Close-packed hexagonal array nanopores are widely used both in research and industry. A self-ordered nanoporous structure makes anodic aluminum oxide (AAO) one of the most popular nanomaterials. This paper describes the main formation mechanisms for AAO, the AAO fabrication process, and optical sensor applications. The paper is focused on four types of AAO-based optical biosensor technology: surface-Enhanced Raman Scattering (SERS), surface Plasmon Resonance (SPR), reflectometric Interference Spectroscopy (RIfS), and photoluminescence Spectroscopy (PL). AAO-based optical biosensors feature very good selectivity, specificity, and reusability.

Molecularly Imprinted Polymers for Chemical Sensing: A Tutorial Review

The field of molecularly imprinted polymer (MIP)-based chemosensors has been experiencing constant growth for several decades. Since the beginning, their continuous development has been driven by the need for simple devices with optimum selectivity for the detection of various compounds in fields such as medical diagnosis, environmental and industrial monitoring, food and toxicological analysis, and, more recently, the detection of traces of explosives or their precursors. This review presents an overview of the main research efforts made so far for the development of MIP-based chemosensors, critically discusses the pros and cons, and gives perspectives for further developments in this field.

Review of optical sensing and manipulation of chiral molecules and nanostructures with the focus on plasmonic enhancements [Invited]

Chiral molecules are ubiquitous in nature; many important synthetic chemicals and drugs are chiral. Detecting chiral molecules and separating the enantiomers is difficult because their physiochemical properties can be very similar. Here we review the optical approaches that are emerging for detecting and manipulating chiral molecules and chiral nanostructures. Our review focuses on the methods that have used plasmonics to enhance the chiroptical response. We also review the fabrication and assembly of (dynamic) chiral plasmonic nanosystems in this context.

Pesticide Aptasensors-State of the Art and Perspectives

Contamination by pesticides in the food chain and the environment is a worldwide problem that needs to be actively monitored to ensure safety. Unfortunately, standard pesticide analysis based on mass spectrometry takes a lot of time, money and effort. Thus, simple, reliable, cost-effective and field applicable methods for pesticide detection have been actively developed. One of the most promising technologies is an aptamer-based biosensor or so-called aptasensor. It utilizes aptamers, short single-stranded DNAs or RNAs, as pesticide recognition elements to integrate with various innovative biosensing technologies for specific and sensitive detection of pesticide residues. Several platforms for aptasensors have been dynamically established, such as colorimetry, fluorometry, electrochemistry, electrochemiluminescence (ECL) and so forth. Each platform has both advantages and disadvantages depending on the purpose of use and readiness of technology. For example, colorimetric-based aptasensors are more affordable than others because of the simplicity of fabrication and resource requirements. Electrochemical-based aptasensors have mainly shown better sensitivity than others with exceedingly low detection limits. This paper critically reviews the progression of pesticide aptasensors throughout the development process, including the selection, characterization and modification of aptamers, the conceptual frameworks of integrating aptamers and biosensors, the ASSURED (affordable, sensitive, specific, user-friendly, rapid and robust, equipment-free and deliverable to end users) criteria of different platforms and the future outlook.

Optical Biosensors for the Detection of Rheumatoid Arthritis (RA) Biomarkers: A Comprehensive Review

A comprehensive review of optical biosensors for the detection of biomarkers associated with rheumatoid arthritis (RA) is presented here, including microRNAs (miRNAs), C-reactive protein (CRP), rheumatoid factor (RF), anti-citrullinated protein antibodies (ACPA), interleukin-6 (IL-6) and histidine, which are biomarkers that enable RA detection and/or monitoring. An overview of the different optical biosensors (based on fluorescence, plasmon resonances, interferometry, surface-enhanced Raman spectroscopy (SERS) among other optical techniques) used to detect these biomarkers is given, describing their performance and main characteristics (limit of detection (LOD) and dynamic range), as well as the connection between the respective biomarker and rheumatoid arthritis. It has been observed that the relationship between the corresponding biomarker and rheumatoid arthritis tends to be obviated most of the time when explaining the mechanism of the optical biosensor, which forces the researcher to look for further information about the biomarker. This review work attempts to establish a clear association between optical sensors and rheumatoid arthritis biomarkers as well as to be an easy-to-use tool for the researchers working in this field.

Nanophotonic-Carbohydrate Lab-on-a-Microneedle for Rapid Detection of Human Cystatin C in Finger-Prick Blood

Miniaturized total analysis systems, for the rapid detection of disease biomarkers, with features including high biomarker sensitivity, selectivity, biocompatibility, and disposability, all at low cost are of profound importance in the healthcare sector. Within this frame of reference, we developed a lab-on-a-carbohydrate-microneedle biodevice by integrating localized surface plasmon resonance (LSPR) paper-based substrates with biocompatible microneedles of high aspect ratio (>60:1 length:width). These microneedles are completely fabricated with carbohydrate (maltose) and further coated with poly lactic-co-glycolic acid (PLGA), which together serves the purpose of fluid channels. The porous nature of PLGA, in addition to drawing blood by capillary action, filters out the whole blood, allowing only the blood plasma to reach the biorecognition layer of the developed biodevice. While the use of maltose provides biocompatibility to the microneedle, the axial compression and transverse load analysis revealed desired mechanical strength of the microneedle, with mechanical failure occurring at 11N and 9 N respectively for the compressive and transverse load. For a proof-of-principle demonstration, the developed biodevice is validated for its operational features by direct detection of cystatin C in finger-prick blood and up to a concentration of 0.01 μg/mL in buffered conditions using the LSPR technique. Furthermore, by changing the biorecognition layer, the use of the developed needle can be extended to other disease biomarkers, and therefore the innovation presented in this work represents a hallmark in the state of the art of lab-on-a-chip biodevices.

Utilizing molecular resonance-localized surface plasmon resonance coupling for copper ion detection in plasma

The rapid, point-of-care detection of copper in plasma can greatly aid in a large number of diseases where copper has been implicated to be an important factor, such as cancer, Alzheimer's and Diabetes mellitus. Localized surface plasmon resonance (LSPR) technologies show promise in the inexpensive detection of copper, whereas previous platforms are plagued with selectivity and sensitivity issues. Herein, we have created a sensitive and selective on-chip copper sensor which can produce a colorimetric reading in 60 minutes. The selectivity of the assay is based on 'Click' chemistry and is shown to have little interference with other metal ions present in plasma. The sensitivity of the assay is generated from the coupling of the molecular resonance of a dye and the LSPR of the gold nanoparticles. The assay is capable of measuring copper concentrations in human plasma as low as 4 μM and the linear range of sensitivity, 4 to 20 μM, is in the physiologically relevant range. This robust, colorimetric assay should prove useful in a point-of-care setting.

Biosensors for detection of Tau protein as an Alzheimer's disease marker

Known as a main neural MAP (microtubule associated protein), tau protein contributes to stabilizing microtubules involved in cellular transmission. Tau dysfunction is mainly associated with neurodegenerative diseases, particularly Alzheimer's disease (AD). In these patients, all the six tau isoforms, which are in hyperphosphorylated form, are first aggregated and then polymerized into neurofibrillary tangles inside the brain. Tau protein detected in cerebrospinal fluid (CSF) is significantly correlated with AD and is well recognized as a hallmark of the disease. Served for detection of analytes of interest, biosensor device comprises a physical transducer and a keen biological recognition component. Qualitative and quantitative evaluations may be performed through analyzation of the data, which is gathered by measurable signals converted from biological reaction. Antibodies, receptors, microorganisms, nucleic acids, enzymes, cells and tissues, as well as some biomimetic structures, normally constitute the biosensor biological recognition part. Production of nanobiosensor, which was made possible through several accomplishments in nano- and fabrication technology, opens up new biotechnological horizons in diagnosis of multiple diseases. In recent years, many researches have been focused on developing novel and effective tau protein biosensors for rapid and accurate detection of AD. In this review, tau protein function and correlation with AD as well as the eminent research on developing nanobiosensor based on optical, electrochemical and piezoelectric approaches will be highlighted.

Optical Detection of Denatured Ferritin Protein via Plasmonic Gold Nanoparticles Exposure through Aminosilane Solution

The presence of denatured proteins within a therapeutic drug product can create a series of serious adverse effects, such as mild irritation, immunogenicity, anaphylaxis, or instant death to a patient. The detection of protein degradation is complicated and expensive due to current methods associated with expensive instrumentation, reagents, and processing time. We have demonstrated here a platform for visual biosensing of denatured proteins that is fast, low cost, sensitive, and user friendly by exploiting the plasmonic properties of noble metal nanoparticles. In this study we have exposed artificially heat stressed ferritin and gold nanoparticles to 3-aminopropyl triethoxysilane, which degrades the protein by showing a systematic blue shift in the absorbance spectra of the gold nanoparticle/ferritin and aminosilane solution. This blue shift in absorbance produces a detectable visual color transition from a blue color to a purple hue. By studying the Raman spectroscopy of the gold nanoparticle/ferritin and aminosilane solution, the extent of ferritin degradation was quantified. The degradation of ferritin was again confirmed using dynamic light scattering and was attributed to the aggregation of the ferritin due to accelerated heat stress. We have successfully demonstrated a proof of concept for visually detecting ferritin from horse spleen that has experienced various levels of degradation, including due to heat stress.

Plasmonic fiber optic hydrogen sensor using oxygen defects in nanostructured molybdenum trioxide film

Hydrogen is one of the most promising candidates for fulfilling the next energy demands in transportation, aerospace, heating, and power generation. Due to its highly explosive nature, hydrogen leakage sensors are considered a critical industrial need. We propose a room-temperature, high-sensitivity hydrogen sensor using oxygen defect-induced plasmonic features. The proposed sensing probe utilizes nanostructured α-MoO₃ thin film as the sensing material in which free carriers and plasmonic properties are induced in response to hydrogen exposure. A notable blue spectral shift of 70.6 nm is observed in response to hydrogen gas exposure from 150 ppm to 2000 ppm, which confirms the sensor's capability for efficient detection of low hydrogen concentrations. The sensor's sensitivity, linearity, and reversibility are experimentally investigated through a simple optical setup.

Supersensitive Detection of the Norovirus Immunoplasmon by 3D Total Internal Reflection Scattering Defocus Microscopy with Wavelength-Dependent Transmission Grating

Norovirus (NoV) is a major foodborne pathogen, and even low levels of virus can cause infection and gastroenteritis. We developed a supersensitive NoV sensor that detects NoV group-I capsid protein (NoVP) via three-dimensional (3D) total internal reflection scattering defocus microscopy (TIRSDM) with wavelength-dependent transmission grating (TG). The combination of evanescent wave scattering and TG significantly enhanced the detection sensitivity and selectivity of NoVP in first-order spectral images (n = +1) by minimizing spectroscopic interference and background noise. In particular, wavelength-dependent 3D defocused TG imaging (3D TG-TIRSDM) separated silver nanotag and gold nanoplate signals on a NoVP immunoplasmon chip along the x, y, and z coordinates simultaneously. Additionally, the use of wavelength-dependent TG increased the spectral resolution by 5-fold along the xy-axis and 1.4-fold along the z-axis compared to conventional 3D TIRSDM at the subdiffraction limit. The NoVP sensor exhibited a lower limit of detection of 820 yM, which is 29 000 times better than the previous potentiometer method, and a wide dynamic detection range of 820 yM to 92.45 pM (R = 0.9801). This new method could be applied to detect various pathogenic viruses during the initial stage of infection.

Ultra-sensitive plasmonic sensing based on gold nanostrip arrays

The extra-narrow reflection feature in angular dependence of reflectivity of periodic gold nanostrip arrays presents interest for sensing application. We explore its behavior in a modified dielectric environment and characterize the capability for sensing small changes in the dielectric permittivity of the environment.

Real-time monitoring of DNA immobilization and detection of DNA polymerase activity by a microfluidic nanoplasmonic platform

DNA polymerase catalyzes the replication of DNA, one of the key steps in cell division. The control and understanding of this reaction owns great potential for the fundamental study of DNA-enzyme interactions. In this context, we developed a label-free microfluidic biosensor platform based on the principle of localized surface plasmon resonance (LSPR) to detect the DNA-polymerase reaction in real-time. Our microfluidic LSPR chip integrates a polydimethylsiloxane (PDMS) channel bonded with a nanoplasmonic substrate, which consists of densely packed mushroom-like nanostructures with silicon dioxide stems (~40 nm) and gold caps (~22 nm), with an average spacing of 19 nm. The LSPR chip was functionalized with single-stranded DNA (ssDNA) template (T30), spaced with hexanedithiol (HDT) in a molar ratio of 1:1. The DNA primer (P8) was then attached to T30, and the second strand was subsequently elongated by DNA polymerase assembling nucleotides from the surrounding fluid. All reaction steps were detected in-situ inside the microfluidic LSPR chip, at room temperature, in real-time, and label-free. In addition, the sensor response was successfully correlated with the amount of DNA and HDT molecules immobilized on the LSPR sensor surface. Our platform represents a benchmark in developing microfluidic LSPR chips for DNA-enzyme interactions, further driving innovations in biosensing technologies.

Plasmonic nanobiosensor based on Au nanorods with improved sensitivity: A comparative study for two different configurations

Biosensors presenting high sensitivity for the detection of biomolecules are very promising for diseases diagnosis. Nowadays, there is a need for the development of biosensors with fast, trustworthy diagnosis and mostly with low cost, mainly for applications in developing countries. Label-free plasmonic biosensors are good candidates to reach out all these characteristics due to the possibility of spectral tunability, fast sensor response, real-time detection, strong enhancement of the local electric field and excellent adaptability to assemble different nanobiotechnology architectures. In this paper, two different configurations for LSPR based biosensor were developed by using solution-phase gold nanorods (S-P-AuNRs) and AuNRs-chip. The LSPR sensitivities were evaluated by monitoring shifts in the longitudinal plasmon band with changes in the refractive index of the medium surrounding the nanoparticles. AuNRs-chip presented higher sensitivity of 297 nm RIU^-1 (refractive index unit) against 196 nm RIU^-1 for S-P-AuNRs. Figure of merit (FOM) for AuNRs-chip and S-P-AuNRs were 3.0 and 2.2 RIU^-1, respectively. This result was assigned to the coupling of the lower energy longitudinal LSPR mode of propagation for AuNRs-chip among nearby nanoparticles in the film. In addition, an improvement of at least 18% in sensitivity was obtained comparing to others AuNRs based assay with similar aspect ratio. FOM is more appropriate to compare different approaches, in this case, the proposed biosensor reached improvements of at least 114%, presenting higher values even when compared to AuNRs of higher aspect ratio. As a proof of concept, AuNRs surface was chemically modified using mercaptoundecanoic acid followed activation with ethylcarbodiimide and N-hidroxysuccinimide to allow the interaction between Bovine Serum Albumin (BSA) antibody and correspondent antigen. Both configurations studied resulted in efficient plasmonic biosensors, presenting high sensitivity for changes in the refractive index and for surface binding with anti-BSA.

Irreversible photo-Fenton-like triggered agglomeration of ultra-small gold nanoparticles capped with crosslinkable materials

A photo-Fenton-like process can promote the agglomeration and LSPR red-shifting of ultra-small gold nanoparticles by triggering a crosslink-degradation pathway that involves the surface coating, Fe(iii)-citrate and hydrogen peroxide. Applications may range from controlled photo-deposition of active materials to asynchronous sensing technologies to light-focused microfabrication.

Nanoplasmonic response of porous Au-TiO2 thin films prepared by oblique angle deposition

In this work, a versatile method is proposed to increase the sensitivity of optical sensors based on the localized surface plasmon resonance (LSPR) phenomenon. It combines a physical deposition method with the oblique angle deposition technique, allowing the preparation of plasmonic thin films with tailored porosity. Thin films of Au-TiO₂ were deposited by reactive magnetron sputtering in a 3D nanostructure (zigzag growth), at different incidence angles (0° ≤ α ≤ 80°), followed by in-air thermal annealing at 400 °C to induce the growth of the Au nanoparticles. The roughness and surface porosity suffered a gradual increment by increasing the incidence angle. The resulting porous zigzag nanostructures that were obtained also decreased the principal refractive indexes (RIs) of the matrix and favoured the diffusion of Au through grain boundaries, originating broader nanoparticle size distributions. The transmittance minimum of the LSPR band appeared at around 600 nm, leading to a red-shift to about 626 nm for the highest incidence angle α = 80°, due to the presence of larger (scattering) nanoparticles. It is demonstrated that zigzag nanostructures can enhance adsorption sites for LSPR sensing by tailoring the porosity of the thin films. Atmosphere controlled transmittance-LSPR measurements showed that the RI sensitivity of the films is improved for higher incidence angles.

Gas Sensing with Nanoplasmonic Thin Films Composed of Nanoparticles (Au, Ag) Dispersed in a CuO Matrix

Magnetron sputtered nanocomposite thin films composed of monometallic Au and Ag, and bimetallic Au-Ag nanoparticles, dispersed in a CuO matrix, were prepared, characterized, and tested, which aimed to find suitable nano-plasmonic platforms capable of detecting the presence of gas molecules. The Localized Surface Plasmon Resonance phenomenon, LSPR, induced by the morphological changes of the nanoparticles (size, shape, and distribution), and promoted by the thermal annealing of the films, was used to tailor the sensitivity to the gas molecules. Results showed that the monometallic films, Au:CuO and Ag:CuO, present LSPR bands at ~719 and ~393 nm, respectively, while the bimetallic Au-Ag:CuO film has two LSPR bands, which suggests the presence of two noble metal phases. Through transmittance-LSPR measurements, the bimetallic films revealed to have the highest sensitivity to the refractive index changes, as well as high signal-to-noise ratios, respond consistently to the presence of a test gas.

Unravelling the Role of Electric and Magnetic Dipoles in Biosensing with Si Nanoresonators

High refractive index dielectric nanoresonators are attracting much attention due to their ability to control both electric and magnetic components of light. Due to the combination of confined modes with reduced absorption losses, they have recently been proposed as an alternative to nanoplasmonic biosensors. In this context, we study the use of semirandom silicon nanocylinder arrays, fabricated with simple and scalable colloidal lithography for the efficient and reliable detection of biomolecules in biological samples. Interestingly, electric and magnetic dipole resonances are associated with two different transduction mechanisms: extinction decrease and resonance red shift. By contrasting both observables, we identify clear advantages in tracking changes in the extinction magnitude. Our data demonstrate that, despite its simplicity, the proposed platform is able to detect prostate-specific antigen in human serum with limits of detection meeting clinical needs.

Hybrid Nanodisk Film for Ultra-Narrowband Filtering, Near-Perfect Absorption and Wide Range Sensing

The miniaturization and integration of photonic devices are new requirements in the novel optics field due to the development of photonic information technology. In this paper, we report that a multifunctional layered structure of Au, SiO₂ and hexagonal nanodisk film is advantageous for ultra-narrowband filtering, near-perfect absorption and sensing in a wide refractive index (RI) region. This hexagonal nanostructure presented two remarkable polarization independent plasmon resonances with near-zero reflectivity and near-perfect absorptivity under normal incidence in the visible and near-infrared spectral ranges. The narrowest full width at half maximum (FWHM) of these resonances was predicted to be excellent at 5 nm. More notably, the double plasmon resonances showed extremely obvious differences in RI responses. For the first plasmon resonance, an evident linear redshift was observed in a wide RI range from 1.00 to 1.40, and a high RI sensitivity of 600 nm/RIU was obtained compared to other plasmonic nanostructures, such as square and honeycomb-like nanostructures. For the second plasmon resonance with excellent FWHM at 946 nm, its wavelength position almost remained unmovable in the case of changing RI surrounding nanodisks in the same regime. Most unusually, its resonant wavelength was insensitive to nearly all structural parameters except the structural period. The underlying physical mechanism was analyzed in detail for double plasmon resonances. This work was significant in developing high-performance integrated optical devices for filtering, absorbing and biomedical sensing.

A Short Review on the Role of the Metal-Graphene Hybrid Nanostructure in Promoting the Localized Surface Plasmon Resonance Sensor Performance

Localized Surface Plasmon Resonance (LSPR) sensors have potential applications in essential and important areas such as bio-sensor technology, especially in medical applications and gas sensors in environmental monitoring applications. Figure of Merit (FOM) and Sensitivity (S) measurements are two ways to assess the performance of an LSPR sensor. However, LSPR sensors suffer low FOM compared to the conventional Surface Plasmon Resonance (SPR) sensor due to high losses resulting from radiative damping of LSPs waves. Different methodologies have been utilized to enhance the performance of LSPR sensors, including various geometrical and material parameters, plasmonic wave coupling from different structures, and integration of noble metals with graphene, which is the focus of this report. Recent studies of metal-graphene hybrid plasmonic systems have shown its capability of promoting the performance of the LSPR sensor to a level that enhances its chance for commercialization. In this review, fundamental physics, the operation principle, and performance assessment of the LSPR sensor are presented followed by a discussion of plasmonic materials and a summary of methods used to optimize the sensor’s performance. A focused review on metal-graphene hybrid nanostructure and a discussion of its role in promoting the performance of the LSPR sensor follow.

Dynamically Tunable Light Absorbers as Color Filters Based on Electrowetting Technology

A device that uses the electrowetting fluid manipulation technology to realize the reversible and dynamical modulation of the local surface plasmon resonance is invented. By varying the electrowetting voltage, the distribution of fluids media surrounding the grating structure get changed accordingly, causing the modulation of the plasmonic resonance peak. The simulation results indicated that three primary colors, that are cyan, magenta and yellow (CMY) can be respectively reflected through selecting suitable structural parameters. More importantly, for the first time, the invented fluid-based devices have exhibited fine-tuning characteristics for each primary color. Finally, the device has been proved to have a large color gamut range in the Commission International De L’E’clairage (CIE) 1931 color space.

Chiral Plasmonic Biosensors

Biosensing requires fast, selective, and highly sensitive real-time detection of biomolecules using efficient simple-to-use techniques. Due to a unique capability to focus light at nanoscale, plasmonic nanostructures provide an excellent platform for label-free detection of molecular adsorption by sensing tiny changes in the local refractive index or by enhancing the light-induced processes in adjacent biomolecules. This review discusses the opportunities provided by surface plasmon resonance in probing the chirality of biomolecules as well as their conformations and orientations. Various types of chiral plasmonic nanostructures and the most recent developments in the field of chiral plasmonics related to biosensing are considered.

Tunable Au-Ag nanobowl arrays for size-selective plasmonic biosensing

Selectivity is often a major obstacle for localized surface plasmon resonance-based biosensing in complex biological solutions. An additional degree of selectivity can be achieved through the incorporation of shape complementarity on the nanoparticle surface. Here, we report the versatile fabrication of substrate-bound Au-Ag nanobowl arrays through the galvanic ion replacement of silver nanodisk arrays. Both localized surface plasmon resonance (LSPR) and surface enhanced Raman spectroscopy (SERS) were carried out to detect the binding of analytes of varying size to the nanobowl arrays. Large increases in the LSPR and SERS response were measured for analytes that were small enough to enter the nanobowls, compared to those too large to come into contact with the interior of the nanobowls. This size-selective sensing should prove useful in both size determination and differentiation of large analytes in biological solutions, such as viruses, fungi, and bacterial cells.

Microfluidic Devices for Label-Free DNA Detection

Sensitive and specific DNA biomarker detection is critical for accurately diagnosing a broad range of clinical conditions. However, the incorporation of such biosensing structures in integrated microfluidic devices is often complicated by the need for an additional labelling step to be implemented on the device. In this review we focused on presenting recent advances in label-free DNA biosensor technology, with a particular focus on microfluidic integrated devices. The key biosensing approaches miniaturized in flow-cell structures were presented, followed by more sophisticated microfluidic devices and higher integration examples in the literature. The option of full DNA sequencing on microfluidic chips via nanopore technology was highlighted, along with current developments in the commercialization of microfluidic, label-free DNA detection devices.