Line-Monitoring, Hyperspectral Fluorescence Setup for Simultaneous Multi-Analyte Biosensing

Conventional fluorescence scanners utilize multiple filters to distinguish different fluorescent labels, and problems arise because of this filter-based mechanism. In this work we propose a line-monitoring, hyperspectral fluorescence technique which is designed and optimized for applications in multi-channel microfluidic systems. In contrast to the filter-based mechanism, which only records fluorescent intensities, the hyperspectral technique records the full spectrum for every point on the sample plane. Multivariate data exploitation is then applied to spectra analysis to determine ratios of different fluorescent labels and eliminate unwanted artifacts. This sensor is designed to monitor multiple fluidic channels simultaneously, providing the potential for multi-analyte biosensing. The detection sensitivity is approximately 0.81 fluors/μm2, and this sensor is proved to act with a good homogeneity. Finally, a model experiment of detecting short oligonucleotides has demonstrated the biomedical application of this hyperspectral fluorescence biosensor

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

Sensors and biosensors for pathogen and pest detection in agricultural systems : recent trends and oportunities

Pathogen and pest-linked diseases across agriculture and ecosystems are a major issue towards enhancing current thresholds in terms of farming yields and food security. Recent developments in nanotechnology allowed the designing of new generation sensors and biosensors in order to detect and mitigate these biological hazards. However, there are still important challenges concerning its respective applications in agricultural systems, typically related to point-of-care testing, cost reduction and real-time analysis. Thus, an important question arises: what are the current state-of-the-art trends and relationships among sensors and biosensors for pathogen and pest detection in agricultural systems? Targeted to meet this gap, a comparative study is performed by a literature review of the past decade and further data mining analysis. With the majority of the results coming from recent studies, leading trends towards new technologies were reviewed and identified, along with its respective agricultural application and target pathogens, such as bacteria, viruses, fungi, as well as pests like insects and parasites. Results have indicated lateral flow assay, lab-on-a-chip technologies and infrared thermography (both fixed and aerial) as the most promising categories related to sensors and biosensors driven to the detection of several different pathogenic varieties. The main existing interrelations between the results are especially associated to cereals, fruits and nuts, meat and dairy along with vegetables and legumes, mostly caused by bacterial and fungal infections. Additional results also presented and discussed, providing a fertile groundwork for decision-making and further developments in modern smart farming and IoT-based agriculture

Novel Low Dimensional Sensors for Rapid Disease Diagnosis and Efficient Biomolecular Detection

Nanomaterials have been used in diverse biosensing applications over the years for their unique properties compared to their ‘bulk’ counterparts. The quantum effects observed in nanomaterials of different dimensions have been exploited, in particular, for fluorescence sensing using surface plasmons. The present work is directed towards the understanding of these effects and the physics behind such plasmons and its application. In the first chapter (Chapter 1), a succinct introduction to quantum confinement and fluorescence biosensors has been presented, followed by a brief overview of the applications of nanomaterials in biosensing. Chapter 2 focuses on the various analytical and characterization techniques used in this work. Chapter 3 describes the effects of shape on the plasmonic enhancement in silver nanoparticles. In chapter 4, the work on the development of a novel bio-sensing platform (AIDLuQ) has been outlined along with its use in the ultrasensitive detection of biomolecules. Building on chapter 4, the AIDLuQ platform was used for a real-life application in the detection of a cancer biomarker. This was supported with DFT simulations providing an insight into the electronic interactions between graphene and the quantum dots at the nano-scale. This has been described in chapter 5. These findings lay the groundwork for further in-depth research to study the linear as well as non-linear optical interactions in nanoparticles in the vicinity of other nanoparticles, as elucidated in chapter 6

Plasmon-exciton coupling for signal amplification and biosensing : fundamentals and application

Surface plasmon resonance (SPR) is the collective oscillation of frequency-matched free-space photons and surface electrons at a metal/dielectric interface. Their inherent sensitivity to refractive index changes and ability to couple with exciton species and enhance light-matter interaction make them ideal candidates for low-concentration analyte detection compared to conventional biosensors. The use of metal nanostructures and nanomaterials to excite SPR represents the current state-of-the-art. However, the challenges associated with repeatable synthesis of uniform nanomaterials, complex nanostructure fabrication, low SPR generation efficiency and limited understanding of the mechanism of plasmon-exciton coupling for signal amplification have motivated the search for alternative architectures and procedures. The uniform and repeatable gold nanoslit (NS) and nanoledge (NL) array architectures offers a promising route towards addressing the above issues, and hence this research attempts to take advantage of these platforms to achieve efficient SPR generation and exciton coupling for biosensing applications. The overarching scope of this dissertation extends to the design, fabrication, and optimization of metal NS and NL structures for SPR generation and sensing applications. Emphasis is placed on investigating the mechanism of optical signal enhancement arising from plasmon-exciton coupling (PEC) with particular focus on (a) exploring the role of geometry and size of the nanostructures (b) examining the influence of SPR spectral mode overlap with exciton’s absorption and/or emission energies on the overall optical signal in a NS or NL system, and (c) investigating the analytical sensitivity and signal transduction of the PEC system to biomolecular interactions. The nanoimprinting technique based on soft lithography for NS fabrication, which is used in this work for NS array fabrication, required addressing a critical issue, namely PDMS diffusion into nanoscale patterns for high aspect ratio realization. This was mitigated by curing temperature variation and incubation time to achieve 50 nm-130 nm width NS arrays with an intense, broad spectral response that red-shifts and diminishes with increasing NS width. The 50 nm width structure exhibited ~57× optical enhancement when coupled with acridine orange, a fluorescence dye, whose absorption and emission spectra closely overlaps with plasmonic spectra. A sensitive assay for detecting DNA hybridization was generated using the interaction of the selected SARS-CoV-2 ssDNA and dsDNA with AO to trigger the metachromatic behaviour of the dye to produce a strong optical signal amplification on the formation of AO-ssDNA complex and a quenched signal upon hybridization to the complementary target DNA along with a blue shift in the fluorescence of AO-dsDNA. The SARS-CoV-2 DNA hybridization assay, based on the PEC exhibited 0.21 nM sensitivity to complementary strand target, distinguished 1-, 2-, and 3-base mismatched DNA targets, reusability of ~6 x with 96% signal recovery, stable for up to 10 days at room temperature. Regarding the NL sensing platform, the principle of the sensing mechanism is based on plasmon-mediated extraordinary optical transmission (EOT) whose wavelength red-shifts with increase in refractive index (RI) at near-metal surface. The NL plasmonic-based biosensor fabricated using a patented E-beam writing method exhibited ~ 384.08 nm/RIU sensitivity, limit of detection to cardiac troponin I (TnI) at 0.079 ng/mL, 0.084 ng/mL and 0.097 ng/mL in PBS buffer, human serum, and human blood, respectively. The direct measurement of TnI in whole human blood without any purification or sample preparation step highlights the significance of the sensing platform for point-of-care detection. Thus, this work innovates (a) a tunable SPR to meet the requirement for plasmon-exciton spectral overlap for optical signal amplification, (b) the mechanism of optical enhancements due to PEC in NS arrays, and (c) a new application of PEC in NS and EOT in NL for the sensitive detection of SARS-CoV-2 DNA hybridization and cardiovascular biomarker TnI in human blood, respectively. The enhanced light-matter interactions have a broader impact beyond healthcare to light harvesting for solar cells, heat generation for cancer therapy, and photocatalysis for nanoscale reactions like water splitting

Nanophotonics for bacterial detection and antimicrobial susceptibility testing

Photonic biosensors are a major topic of research that continues to make exciting advances. Technology has now improved sufficiently for photonics to enter the realm of microbiology and to allow for the detection of individual bacteria. Here, we discuss the different nanophotonic modalities used in this context and highlight the opportunities they offer for studying bacteria. We critically review examples from the recent literature, starting with an overview of photonic devices for the detection of bacteria, followed by a specific analysis of photonic antimicrobial susceptibility tests. We show that the intrinsic advantage of matching the optical probed volume to that of a single, or a few, bacterial cell, affords improved sensitivity while providing additional insight into single-cell properties. We illustrate our argument by comparing traditional culture-based methods, which we term macroscopic, to microscopic free-space optics and nanoscopic guided-wave optics techniques. Particular attention is devoted to this last class by discussing structures such as photonic crystal cavities, plasmonic nanostructures and interferometric configurations. These structures and associated measurement modalities are assessed in terms of limit of detection, response time and ease of implementation. Existing challenges and issues yet to be addressed will be examined and critically discussed