Surface Plasmon Resonance: An Introduction to a Surface Spectroscopy Technique

Recent advances in the development of multiplexed nanophotonic biosensors

Over the years, the field of nanophotonics has advanced and can be utilized as a method to detect different infectious diseases. The introduction of multiplex nanophotonic diagnostics has enabled the speedy and simultaneous detection of viral infections and specific biomarkers. The quick reaction times, high sensitivity, and specificity of multiplex nanophotonic diagnostics enable real-time identification of viruses without the need for nucleic acid amplification. This review presents an overview of nanophotonic tools used to identify diseases and particular biomarkers. The paper also examines possible research areas for the development of unique, cutting-edge multiplex nanophotonic diagnostics capable of concurrently detecting various diseases or biomarkers/biomolecules. Furthermore, it discusses barriers to further advancement and offers insight into anticipated trends.

Generation and Characterization of Engineered Ubiquitin Variants to Modulate the Ubiquitin Signaling Cascade

The ubiquitin signaling cascade plays a crucial role in human cells. Consistent with this, malfunction of ubiquitination and deubiquitination is implicated in the initiation and progression of numerous human diseases, including cancer. Therefore, the development of potent and specific modulators of ubiquitin signal transduction has been at the forefront of drug development. In the past decade, a structure-based combinatorial protein-engineering approach has been used to generate ubiquitin variants (UbVs) as protein-based modulators of multiple components in the ubiquitin-proteasome system. Here, we review the design and generation of phage-displayed UbV libraries, including the processes of binder selection and library improvement. We also provide a comprehensive overview of the general in vitro and cellular methodologies involved in characterizing UbV binders. Finally, we describe two recent applications of UbVs for developing molecules with therapeutic potential.

Utilisation of molecularly imprinting technology for the detection of glucocorticoids for a point of care surface plasmon resonance (SPR) device

Herein, we describe the synthesis and characterisation of four synthetic recognition materials (nanoMIPs) selective for the glucocorticoid steroids - prednisolone, prednisone, dexamethasone, and cortisone. Using a solid-phase synthesis approach, these materials were then applied in the development of a surface plasmon resonance (SPR) sensor for the detection of these four targets in doped urine, to mimic the routine testing of agricultural waste for possible environmental exposure. The synthesised particles displayed a range of sizes between 104 and 160 nm. Affinity studies were performed, and these synthetic materials were shown to display nanomolar affinities (15.9-62.8 nM) towards their desired targets. Furthermore, we conducted cross-reactivity studies to assess the materials selectivity towards their desired target and the materials showed excellent selectivity when compared to the non-desired target, with selectivity factors calculated. Furthermore, through the use of 3D visualisation it can be seen that small changes between structures (such as a hydroxyl to ketone transformation) there is excellent selectivity between the compounds in the ranges of 100 fold plus. Using Surine™ doped samples the materials offered comparable nanomolar affinities (10.7-75.7 nM) towards their targets when compared to the standardised buffer preparation. Detection levels in urine for all compounds was in the nanomolar range. The developed sensor offers potential for these devices to be used in the prevention of these pharmaceutical compounds to enter the surrounding environment through agricultural waste through monitoring at source. Likewise, they can be used to monitor use in clinical samples.

Polychaeta-mediated synthesis of gold nanoparticles: A potential antibacterial agent against Acute Hepatopancreatic Necrosis Disease (AHPND)-causing bacteria, Vibrio parahaemolyticus

Gold nanoparticles (AuNPs) have emerged as a promising application in aquaculture. Their nano-sized dimensions, comparable to pathogens offer potential solutions for combating antibiotic resistance. In this study, AuNPs were synthesized by using polychaetes, Marphysa moribidii as the bio-reducing agent. Modifications were made to reduce agglomeration in green-synthesized AuNPs through ultrasonication. The antibacterial activities of AuNPs against V. parahaemolyticus were evaluated. The physicochemical characteristics of the green synthesized AuNPs were comprehensively investigated. The successful formation of AuNPs was confirmed by the appearance of a red ruby colour and the presence of surface Plasmon resonance (SPR) absorption peaks at 530 nm as observed from UV-vis spectroscopy. Scanning electron microscopy (SEM) revealed spherical-shaped AuNPs with some agglomerations. Transmission electron microscopy (TEM) showed particle size of AuNPs ranging from 10 nm to 60 nm, meanwhile dynamic light scattering (DLS) analysis indicated an average particle size of 24.36 nm. X-ray diffraction (XRD) analysis confirmed the high crystallinity of AuNPs, and no AuNPs were detected in the polychaetes extracts prior to synthesis. A brief ultrasonication significantly reduced the tendencies for AuNPs to coalesce. The green-synthesized AuNPs demonstrated a remarkable antibacterial efficacy against V. parahaemolyticus. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) tests revealed that a concentration of 0.3 g/ml of AuNPs effectively inhibited V. parahaemolyticus. These findings highlighted the potential of green-synthesized AuNPs as antibacterial agents for the prevention and management of AHPND in aquaculture.

Multifunctional lipid-based nanoparticles for wound healing and antibacterial applications: A review

Wound healing primarily involves preventing severe infections, accelerating healing, and reducing pain and scarring. Therefore, the multifunctional application of lipid-based nanoparticles (LBNs) has received considerable attention in drug discovery due to their solid or liquid lipid core, which increases their ability to provide prolonged drug release, reduce treatment costs, and improve patient compliance. LBNs have also been used in medical and cosmetic practices and formulated for various products based on skin type, disease conditions, administration product costs, efficiency, stability, and toxicity; therefore, understanding their interaction with biological systems is very important. Therefore, it is necessary to perform an in-depth analysis of the results from a comprehensive characterization process to produce lipid-based drug delivery systems with desired properties. This review will provide detailed information on the different types of LBNs, their formulation methods, characterisation, antimicrobial activity, and application in various wound models (both in vitro and in vivo studies). Also, the clinical and commercial applications of LBNs are summarized.

Recent Advances in Optical Sensing for the Detection of Microbial Contaminants

Microbial contaminants are responsible for several infectious diseases, and they have been introduced as important potential food- and water-borne risk factors. They become a global burden due to their health and safety threats. In addition, their tendency to undergo mutations that result in antimicrobial resistance makes them difficult to treat. In this respect, rapid and reliable detection of microbial contaminants carries great significance, and this research area is explored as a rich subject within a dynamic state. Optical sensing serving as analytical devices enables simple usage, low-cost, rapid, and sensitive detection with the advantage of their miniaturization. From the point of view of microbial contaminants, on-site detection plays a crucial role, and portable, easy-applicable, and effective point-of-care (POC) devices offer high specificity and sensitivity. They serve as advanced on-site detection tools and are pioneers in next-generation sensing platforms. In this review, recent trends and advances in optical sensing to detect microbial contaminants were mainly discussed. The most innovative and popular optical sensing approaches were highlighted, and different optical sensing methodologies were explained by emphasizing their advantages and limitations. Consequently, the challenges and future perspectives were considered.

Aptamers Targeting Membrane Proteins for Sensor and Diagnostic Applications

Many biological processes (physiological or pathological) are relevant to membrane proteins (MPs), which account for almost 30% of the total of human proteins. As such, MPs can serve as predictive molecular biomarkers for disease diagnosis and prognosis. Indeed, cell surface MPs are an important class of attractive targets of the currently prescribed therapeutic drugs and diagnostic molecules used in disease detection. The oligonucleotides known as aptamers can be selected against a particular target with high affinity and selectivity by iterative rounds of in vitro library evolution, known as Systematic Evolution of Ligands by EXponential Enrichment (SELEX). As an alternative to antibodies, aptamers offer unique features like thermal stability, low-cost, reuse, ease of chemical modification, and compatibility with various detection techniques. Particularly, immobilized-aptamer sensing platforms have been under investigation for diagnostics and have demonstrated significant value compared to other analytical techniques. These "aptasensors" can be classified into several types based on their working principle, which are commonly electrochemical, optical, or mass-sensitive. In this review, we review the studies on aptamer-based MP-sensing technologies for diagnostic applications and have included new methodological variations undertaken in recent years.

Toward waterborne protozoa detection using sensing technologies

Drought and limited sufficient water resources will be the main challenges for humankind during the coming years. The lack of water resources for washing, bathing, and drinking increases the use of contaminated water and the risk of waterborne diseases. A considerable number of waterborne outbreaks are due to protozoan parasites that may remain active/alive in harsh environmental conditions. Therefore, a regular monitoring program of water resources using sensitive techniques is needed to decrease the risk of waterborne outbreaks. Wellorganized point-of-care (POC) systems with enough sensitivity and specificity is the holy grail of research for monitoring platforms. In this review, we comprehensively gathered and discussed rapid, selective, and easy-to-use biosensor and nanobiosensor technologies, developed for the early detection of common waterborne protozoa.

Progress and Challenges of Point-of-Need Photonic Biosensors for the Diagnosis of COVID-19 Infections and Immunity

The new coronavirus disease, COVID-19, caused by SARS-CoV-2, continues to affect the world and after more than two years of the pandemic, approximately half a billion people are reported to have been infected. Due to its high contagiousness, our life has changed dramatically, with consequences that remain to be seen. To prevent the transmission of the virus, it is crucial to diagnose COVID-19 accurately, such that the infected cases can be rapidly identified and managed. Currently, the gold standard of testing is polymerase chain reaction (PCR), which provides the highest accuracy. However, the reliance on centralized rapid testing modalities throughout the COVID-19 pandemic has made access to timely diagnosis inconsistent and inefficient. Recent advancements in photonic biosensors with respect to cost-effectiveness, analytical performance, and portability have shown the potential for such platforms to enable the delivery of preventative and diagnostic care beyond clinics and into point-of-need (PON) settings. Herein, we review photonic technologies that have become commercially relevant throughout the COVID-19 pandemic, as well as emerging research in the field of photonic biosensors, shedding light on prospective technologies for responding to future health outbreaks. Therefore, in this article, we provide a review of recent progress and challenges of photonic biosensors that are developed for the testing of COVID-19, consisting of their working fundamentals and implementation for COVID-19 testing in practice with emphasis on the challenges that are faced in different development stages towards commercialization. In addition, we also present the characteristics of a biosensor both from technical and clinical perspectives. We present an estimate of the impact of testing on disease burden (in terms of Disability-Adjusted Life Years (DALYs), Quality Adjusted Life Years (QALYs), and Quality-Adjusted Life Days (QALDs)) and how improvements in cost can lower the economic impact and lead to reduced or averted DALYs. While COVID19 is the main focus of these technologies, similar concepts and approaches can be used and developed for future outbreaks of other infectious diseases.

Recent Advances of Optical Sensors for Copper Ion Detection

A trace element copper (Cu²⁺) ion is the third most plentiful metal ion that necessary for all living organisms and playing a critical role in several processes. Nonetheless, according to cellular needs, deficient or excess Cu²⁺ ion cause various diseases. For all these reasons, optical sensors have been focused rapid Cu²⁺ ion detection in real-time with high selectivity and sensitivity. Optical sensors can measure fluorescence in the refractive index-adsorption from the relationships between light and matter. They have gained great attention in recent years due to the excellent advantages of simple and naked eye recognition, real-time detection, low cost, high specificity against analytes, a quick response, and the need for less complex equipment in analysis. This review aims to show the significance of Cu²⁺ ion detection and electively current trends in optical sensors. The integration of optical sensors with different systems, such as microfluidic systems, is mentioned, and their latest studies in medical and environmental applications also are depicted. Conclusions and future perspectives on these advances is added at the end of the review.

Photonic Materials Cloud: An Online Interactive Open Tool for Creating, Comparing, and Testing Photonic Materials

Recent advances in nanoscale fabrication and characterization further accelerated research on photonics and plasmonics, which has already attracted long-standing interest. Alongside morphological constraints, phenomena in both fields highly depend on the materials’ optical properties, dimensions, and surroundings. Building up the required knowledge and experience to design next-generation photonic devices can be a complex task for novice and experienced researchers who intend to evaluate the impact of subtle material and morphology variations while setting up experiments or getting a general overview. Here, we introduce the Photonic Materials Cloud (PMCloud), a web-based, interactive open tool for designing and analyzing photonic materials. PMCloud allows identification of the subtle differences between optical material models generated from a database, experimental data input, and inline-generated materials from various analytical models. Furthermore, it provides a fully interactive interface to evaluate their performance in important fundamental (numerical) optical experiments. We demonstrate PMCloud’s applicability to state-of-the-art research questions, namely the comparison of the novel plasmonic materials aluminium-doped zinc oxide and zirconium nitride and the design of an optical, dielectric thin-film Bragg reflector. PMCloud opens a rapid, freely accessible path towards prototyping optical materials and simple fundamental devices and may serve as an educational platform for photonic materials research.

A Critical Analysis on the Sensitivity Enhancement of Surface Plasmon Resonance Sensors with Graphene

The use of graphene in surface plasmon resonance sensors, covering a metallic (plasmonic) film, has a number of demonstrated advantages, such as protecting the film against corrosion/oxidation and facilitating the introduction of functional groups for selective sensing. Recently, a number of works have claimed that few-layer graphene can also increase the sensitivity of the sensor. However, graphene was treated as an isotropic thin film, with an out-of-plane refractive index that is identical to the in-plane index. Here, we critically examine the role of single and few layers of graphene in the sensitivity enhancement of surface plasmon resonance sensors. Graphene is introduced over the metallic film via three different descriptions: as an atomic-thick two-dimensional sheet, as a thin effective isotropic material (same conductivity in the three coordinate directions), and as an non-isotropic layer (different conductivity in the perpendicular direction to the two-dimensional plane). We find that only the isotropic layer model, which is known to be incorrect for the optical modeling of graphene, provides sizable sensitivity increases, while the other, more accurate, models lead to a negligible contribution to the sensitivity.

Detection of selective androgen receptor modulators (SARMs) in serum using a molecularly imprinted nanoparticle surface plasmon resonance sensor

Selective Androgen Receptor Modulators (SARMs) are a fairly new class of therapeutic compounds that act upon the androgen receptor. They proffer similar anabolic properties to steroids, but with a much-reduced androgenic profile. They have become a popular substance of abuse in competitive sport. Being relatively new, detection systems are limited to chromatographic methods. Here we present a surface plasmon resonance sensor for three commonly-used SARMS, Andarine, Ligandrol and RAD-140, using high-affinity molecularly imprinted nanoparticles (nanoMIPs) as the recognition element. Synthesised nanoMIPS exhibited dissociation constant (K_D) values of 29.3 nM, 52.5 nM and 75.1 nM for Andarine, Ligandrol and RAD-140 nanoMIPs, respectively. Cross-reactivity of the particles was explored using the alternative SARMs, with the nanoMIPs demonstrating good specificity. Fetal Bovine Serum (FBS) was used to assess the ability of the SPR-based nanoMIP sensor to detect the target compounds in a comparable biological matrix, with observed K_D values of 12.3 nM, 31.9 nM and 28.1 nM for Andarine, Ligandrol and RAD-140 nanoMIPs, respectively. Theoretical limits of detection (LoD) were estimated from a calibration plot in FBS and show that the nanoMIP-based sensors have the potential to theoretically measure these SARMs in the low to sub nM range. Crucially these levels are below the minimum required performance limit (MRPL) set for these compounds by WADA. This study highlights the power of modern molecular imprinting to rapidly address required molecular recognition for new compounds of interest.

An SPR-based method for Hill coefficient measurements: the case of insulin-degrading enzyme

Insulin-degrading enzyme (IDE) is a highly conserved zinc metallopeptidase and is capable to catalytically cleave several substrates besides insulin, playing a pivotal role in several different biochemical pathways. Although its mechanism of action has been widely investigated, many conundrums still remain, hindering the possibility to rationally design specific modulators which could have important therapeutical applications in several diseases such as diabetes and Alzheimer's disease. In this scenario, we have developed a novel surface plasmon resonance (SPR) method which allows for directly measuring the enzyme cooperativity for the binding of insulin in the presence of different IDE activity modulators: carnosine, ATP, and EDTA. Results indicate that both positive and negative modulations of the IDE activity can be correlated to an increase and a decrease of the measured Hill coefficient, respectively, giving a new insight into the IDE activity mechanism. The use of the IDE R767A mutant for which oligomerization is hindered confirmed that the positive allosteric modulation of IDE by carnosine is due to a change in the enzyme oligomeric state occurring also for the enzyme immobilized on the gold SPR chip.

Exploiting a strong coupling regime of organic pentamer surface plasmon resonance based on the Otto configuration for creatinine detection

The sandwiched material-analyte layer in the surface plasmon resonance (SPR)-Otto configuration emulates an optical cavity and, coupled with large optical nonlinearity material, the rate of light escaping from the system is reduced, allowing the formation of a strong coupling regime. Here, we report an organic pentamer SPR sensor using the Otto configuration to induce a strong coupling regime for creatinine detection. Prior to that, the SPR sensor chip was modified with an organic pentamer, 1,4-bis[2-(5-thiophene-2-yl)-1-benzothiopene]-2,5-dioctyloxybenzene (BOBzBT₂). To improve the experimental calibration curve, a normalisation approach based on the strong coupling-induced second dip was also developed. By using this procedure, the performance of the sensor improved to 0.11 mg/dL and 0.36 mg/dL for the detection and quantification limits, respectively.

Nano-enabled sensing of per-/poly-fluoroalkyl substances (PFAS) from aqueous systems - A review

Per-/poly-fluoroalkyl substances (PFAS) are an emerging class of environmental contaminants used as an additive across various commodity and fire-retardant products, for their unique thermo-chemical stability, and to alter their surface properties towards selective liquid repellence. These properties also make PFAS highly persistent and mobile across various environmental compartments, leading to bioaccumulation, and causing acute ecotoxicity at all trophic levels particularly to human populations, thus increasing the need for monitoring at their repositories or usage sites. In this review, current nano-enabled methods towards PFAS sensing and its monitoring in wastewater are critically discussed and benchmarked against conventional detection methods. The discussion correlates the materials' properties to the sensitivity, responsiveness, and reproducibility of the sensing performance for nano-enabled sensors in currently explored electrochemical, spectrophotometric, colorimetric, optical, fluorometric, and biochemical with limits of detection of 1.02 × 10^-6 μg/L, 2.8 μg/L, 1 μg/L, 0.13 μg/L, 6.0 × 10^-5 μg/L, and 4.141 × 10^-7 μg/L respectively. The cost-effectiveness of sensing platforms plays an important role in the on-site analysis success and upscalability of nano-enabled sensors. Environmental monitoring of PFAS is a step closer to PFAS remediation. Electrochemical and biosensing methods have proven to be the most reliable tools for future PFAS sensing endeavors with very promising detection limits in an aqueous matrix, short detection times, and ease of fabrication.

A molecularly imprinted polymer nanoparticle-based surface plasmon resonance sensor platform for antibiotic detection in river water and milk

Using a solid-phase molecular imprinting technique, high-affinity nanoparticles (nanoMIPs) selective for the target antibiotics, ciprofloxacin, moxifloxacin, and ofloxacin have been synthesised. These have been applied in the development of a surface plasmon resonance (SPR) sensor for the detection of the three antibiotics in both river water and milk. The particles produced demonstrated good uniformity with approximate sizes of 65.8 ± 1.8 nm, 76.3 ± 4.1 nm, and 85.7 ± 2.5 nm, and were demonstrated to have affinities of 36.2 nM, 54.7 nM, and 34.6 nM for the ciprofloxacin, moxifloxacin, and ofloxacin nanoMIPs, respectively. Cross-reactivity studies highlighted good selectivity towards the target antibiotic compared with a non-target antibiotic. Using spiked milk and river water samples, the nanoMIP-based SPR sensor offered comparable affinity with 66.8 nM, 33.4 nM, and 55.0 nM (milk) and 39.3 nM, 26.1 nM, and 42.7 nM (river water) for ciprofloxacin, moxifloxacin, and ofloxacin nanoMIPs, respectively, to that seen within a buffer standard. Estimated LODs for the three antibiotic targets in both milk and river water were low nM or below. The developed SPR sensor showed good potential for using the technology for the capture and detection of antibiotics from food and environmental samples.

Recent advances in predicting protein-protein interactions with the aid of artificial intelligence algorithms

Protein-protein interactions (PPIs) are essential in the regulation of biological functions and cell events, therefore understanding PPIs have become a key issue to understanding the molecular mechanism and investigating the design of drugs. Here we highlight the major developments in computational methods developed for predicting PPIs by using types of artificial intelligence algorithms. The first part introduces the source of experimental PPI data. The second part is devoted to the PPI prediction methods based on sequential information. The third part covers representative methods using structural information as the input feature. The last part is methods designed by combining different types of features. For each part, the state-of-the-art computational PPI prediction methods are reviewed in an inclusive view. Finally, we discuss the flaws existing in this area and future directions of next-generation algorithms.

A CMOS Image Sensor Based Refractometer without Spectrometry

The refractive index (RI), an important optical property of a material, is measured by commercial refractometers in the food, agricultural, chemical, and manufacturing industries. Most of these refractometers must be equipped with a prism for light dispersion, which drastically limits the design and size of the refractometer. Recently, there have been several reports on the development of a surface plasmon resonance (SPR)-based RI detector, which is characterized by its high sensitivity and simplicity. However, regardless of the prism, an expensive spectrometer is required to analyze the resonance wavelength or angle of incidence. This paper proposes a method that eliminates the need for the prism and other conventional spectrometer components. For this purpose, total internal reflection SPR technology was used on an Ag thin film, and RI analysis was combined with a lens-free CMOS image sensor or a smartphone camera. A finite-difference time-domain (FDTD) numerical simulation was performed to evaluate the relationship between the output power intensity and Ag film thickness for different RIs at three wavelengths of commercial light-emitting diodes (LEDs). The maximum sensitivity of −824.54 RIU⁻¹ was achieved with AG20 at an incident wavelength of 559 nm. Due to its simple design and cost effectiveness, this prism-less, SPR-based refractometer combined with a lens-free CMOS image sensor or a smartphone could be a superior candidate for a point-of-care device that can determine the RIs of various analytes in the field of biological or chemical sensing.

The Effects of Three-Dimensional Ligand Immobilization on Kinetic Measurements in Biosensors

The field of biosensing is in constant evolution, propelled by the need for sensitive, reliable platforms that provide consistent results, especially in the drug development industry, where small molecule characterization is of uttermost relevance. Kinetic characterization of small biochemicals is particularly challenging, and has required sensor developers to find solutions to compensate for the lack of sensitivity of their instruments. In this regard, surface chemistry plays a crucial role. The ligands need to be efficiently immobilized on the sensor surface, and probe distribution, maintenance of their native structure and efficient diffusion of the analyte to the surface need to be optimized. In order to enhance the signal generated by low molecular weight targets, surface plasmon resonance sensors utilize a high density of probes on the surface by employing a thick dextran matrix, resulting in a three-dimensional, multilayer distribution of molecules. Despite increasing the binding signal, this method can generate artifacts, due to the diffusion dependence of surface binding, affecting the accuracy of measured affinity constants. On the other hand, when working with planar surface chemistries, an incredibly high sensitivity is required for low molecular weight analytes, and furthermore the standard method for immobilizing single layers of molecules based on self-assembled monolayers (SAM) of epoxysilane has been demonstrated to promote protein denaturation, thus being far from ideal. Here, we will give a concise overview of the impact of tridimensional immobilization of ligands on label-free biosensors, mostly focusing on the effect of diffusion on binding affinity constants measurements. We will comment on how multilayering of probes is certainly useful in terms of increasing the sensitivity of the sensor, but can cause steric hindrance, mass transport and other diffusion effects. On the other hand, probe monolayers on epoxysilane chemistries do not undergo diffusion effect but rather other artifacts can occur due to probe distortion. Finally, a combination of tridimensional polymeric chemistry and probe monolayer is presented and reviewed, showing advantages and disadvantages over the other two approaches.

Therapeutic potential of targeting LSD1/ KDM1A in cancers

LSD1 was the first histone demethylase identified by Professor Shi Yang and his team members in 2004. LSD1 employs FAD as its cofactor, which catalyzes the demethylation of H3K4 and H3K9. It is aberrantly overexpressed in different types of cancers and is associated with the growth, invasion, and metastasis of cancer cells. The knockout or inhibition of LSD1 could effectively suppress tumor development, and thus, it has become an attractive molecular target for cancer therapy. Moreover, many LSD1 inhibitors have been developed in preclinical and clinical trials to treat solid tumors and hematological malignancy. This study made an extensive review of the research obtained from the literature retrieval of electronic databases, such as PubMed, Web of Science, RCSB PDB, ClinicalTrials.gov, and EU clinical trials register. This review summarizes recent studies on the advances of LSD1 inhibitors in the literature, covering January 2015 to June 2021. It focuses on the function of LSD1 in tumor cells, summarizes the crystal structures of homo sapiens LSD1, reviews the structural characteristics of LSD1 inhibitors, compares the screening methods of LSD1 inhibitors, and proposes guidelines for the future exploitation of LSD1 inhibitors.

A Mechanistic Site-Of-Action Model: A Tool for Informing Right Target, Right Compound, And Right Dose for Therapeutic Antagonistic Antibody Programs

Quantitative modeling is increasingly utilized in the drug discovery and development process, from the initial stages of target selection, through clinical studies. The modeling can provide guidance on three major questions–is this the right target, what are the right compound properties, and what is the right dose for moving the best possible candidate forward. In this manuscript, we present a site-of-action modeling framework which we apply to monoclonal antibodies against soluble targets. We give a comprehensive overview of how we construct the model and how we parametrize it and include several examples of how to apply this framework for answering the questions postulated above. The utilities and limitations of this approach are discussed.

Fast, accurate, point-of-care COVID-19 pandemic diagnosis enabled through advanced lab-on-chip optical biosensors: Opportunities and challenges

The sudden rise of the worldwide severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic in early 2020 has called into drastic action measures to perform instant detection and reduce the rate of spread. Common clinical and nonclinical diagnostic testing methods have been partially effective in satisfying the increasing demand for fast detection point-of-care (POC) methods to slow down further spread. However, accurate point-of-risk diagnosis of this emerging viral infection is paramount as the need for simultaneous standard operating procedures and symptom management of SARS-CoV-2 will be the norm for years to come. A sensitive, cost-effective biosensor with mass production capability is crucial until a universal vaccination becomes available. Optical biosensors can provide a noninvasive, extremely sensitive rapid detection platform with sensitivity down to ∼67 fg/ml (1 fM) concentration in a few minutes. These biosensors can be manufactured on a mass scale (millions) to detect the COVID-19 viral load in nasal, saliva, urine, and serological samples, even if the infected person is asymptotic. Methods investigated here are the most advanced available platforms for biosensing optical devices that have resulted from the integration of state-of-the-art designs and materials. These approaches include, but are not limited to, integrated optical devices, plasmonic resonance, and emerging nanomaterial biosensors. The lab-on-chip platforms examined here are suitable not only for SARS-CoV-2 spike protein detection but also for other contagious virions such as influenza and Middle East respiratory syndrome (MERS).

PANDA: Predicting the change in proteins binding affinity upon mutations by finding a signal in primary structures

Accurately determining a change in protein binding affinity upon mutations is important to find novel therapeutics and to assist mutagenesis studies. Determination of change in binding affinity upon mutations requires sophisticated, expensive, and time-consuming wet-lab experiments that can be supported with computational methods. Most of the available computational prediction techniques depend upon protein structures that bound their applicability to only protein complexes with recognized 3D structures. In this work, we explore the sequence-based prediction of change in protein binding affinity upon mutation and question the effectiveness of [Formula: see text]-fold cross-validation (CV) across mutations adopted in previous studies to assess the generalization ability of such predictors with no known mutation during training. We have used protein sequence information instead of protein structures along with machine learning techniques to accurately predict the change in protein binding affinity upon mutation. Our proposed sequence-based novel change in protein binding affinity predictor called PANDA performs comparably to the existing methods gauged through an appropriate CV scheme and an external independent test dataset. On an external test dataset, our proposed method gives a maximum Pearson correlation coefficient of 0.52 in comparison to the state-of-the-art existing protein structure-based method called MutaBind which gives a maximum Pearson correlation coefficient of 0.59. Our proposed protein sequence-based method, to predict a change in binding affinity upon mutations, has wide applicability and comparable performance in comparison to existing protein structure-based methods. We made PANDA easily accessible through a cloud-based webserver and python code available at https://sites.google.com/view/wajidarshad/software and https://github.com/wajidarshad/panda, respectively.

Targeting NRF2 to treat cancer

NRF2 is a basic leucine zipper (bZip) transcription factor that is the master regulator of redox homeostasis. Under basal conditions, the cellular level of NRF2 is low due to a posttranslational regulation by the ubiquitin proteasome system (UPS). But, when an organism is challenged with oxidative or xenobiotic stress, the NRF2 pathway is activated by inhibition of the E3 ubiquitin ligase complex that normally marks NRF2 for destruction. For several decades, researchers have searched for molecules that can intentionally activate NRF2, as this was shown to be a means to prevent certain diseases, at least in animal models. In the present era, there are many compounds known to activate the NRF2 pathway including natural products and synthetic compounds, covalent and non-covalent compounds, and others. However, it was also revealed that like many protective pathways, the NRF2 pathway has a dark side. Just as NRF2 can protect normal cells from damage, it can protect malignant cells from damage. As cells transform, they are exposed to many stressors and aberrant upregulation of NRF2 can facilitate transformation and it can help cancer cells to grow, to spread, and to resist treatment. For this reason, researchers are also interested in the discovery and development of NRF2 inhibitors. In the present review, we will begin with a general discussion of NRF2 structure and function, we will discuss the latest in NRF2 non-covalent activators, and we will discuss the current state of NRF2 inhibitors.

Optical biosensors - Illuminating the path to personalized drug dosing

Optical biosensors are low-cost, sensitive and portable devices that are poised to revolutionize the medical industry. Healthcare monitoring has already been transformed by such devices, with notable recent applications including heart rate monitoring in smartwatches and COVID-19 lateral flow diagnostic test kits. The commercial success and impact of existing optical sensors has galvanized research in expanding its application in numerous disciplines. Drug detection and monitoring seeks to benefit from the fast-approaching wave of optical biosensors, with diverse applications ranging from illicit drug testing, clinical trials, monitoring in advanced drug delivery systems and personalized drug dosing. The latter has the potential to significantly improve patients' lives by minimizing toxicity and maximizing efficacy. To achieve this, the patient's serum drug levels must be frequently measured. Yet, the current method of obtaining such information, namely therapeutic drug monitoring (TDM), is not routinely practiced as it is invasive, expensive, time-consuming and skilled labor-intensive. Certainly, optical sensors possess the capabilities to challenge this convention. This review explores the current state of optical biosensors in personalized dosing with special emphasis on TDM, and provides an appraisal on recent strategies. The strengths and challenges of optical biosensors are critically evaluated, before concluding with perspectives on the future direction of these sensors.

Molecular Characterization of the Extracellular Domain of Human Junctional Adhesion Proteins

The junction adhesion molecule (JAM) family of proteins play central roles in the tight junction (TJ) structure and function. In contrast to claudins (CLDN) and occludin (OCLN), the other membrane proteins of the TJ, whose structure is that of a 4α-helix bundle, JAMs are members of the immunoglobulin superfamily. The JAM family is composed of four members: A, B, C and 4. The crystal structure of the extracellular domain of JAM-A continues to be used as a template to model the secondary and tertiary structure of the other members of the family. In this article, we have expressed the extracellular domains of JAMs fused with maltose-binding protein (MBP). This strategy enabled the work presented here, since JAM-B, JAM-C and JAM4 are more difficult targets due to their more hydrophobic nature. Our results indicate that each member of the JAM family has a unique tertiary structure in spite of having similar secondary structures. Surface plasmon resonance (SPR) revealed that heterotypic interactions among JAM family members can be greatly favored compared to homotypic interactions. We employ the well characterized epithelial cadherin (E-CAD) as a means to evaluate the adhesive properties of JAMs. We present strong evidence that suggests that homotypic or heterotypic interactions among JAMs are stronger than that of E-CADs.

Microfluidic devices for multiplexed detection of foodborne pathogens

The global burden of foodborne diseases is substantial and foodborne pathogens are the major cause for human illnesses. In order to prevent the spread of foodborne pathogens, detection methods are constantly being updated towards rapid, portable, inexpensive, and multiplexed on-site detection. Due to the nature of the small size and low volume, microfluidics has been applied to rapid, time-saving, sensitive, and portable devices to meet the requirements of on-site detection. Simultaneous detection of multiple pathogens is another key parameter to ensure food safety. Multiplexed detection technology, including microfluidic chip design, offers a new opportunity to achieve this goal. In this review, we introduced several sample preparation and corresponding detection methods on microfluidic devices for multiplexed detection of foodborne pathogens. In the sample preparation section, methods of cell capture and enrichment, as well as nucleic acid sample preparation, were described in detail, and in the section of detection methods, amplification, immunoassay, surface plasmon resonance and impedance spectroscopy were exhaustively illustrated. The limitations and advantages of all available experimental options were also summarized and discussed in order to form a comprehensive understanding of cutting-edge technologies and provide a comparative assessment for future investigation and in-field application.

Biosynthesis and characterization of gold nanoparticles using Brazilian red propolis and evaluation of its antimicrobial and anticancer activities

Gold nanoparticles (AuNPs) are highlighted due to their low toxicity, compatibility with the human body, high surface area to volume ratio, and surfaces that can be easily modified with ligands. Biosynthesis of AuNPs using plant extract is considered a simple, low-cost, and eco-friendly approach. Brazilian Red Propolis (BRP), a product of bees, exhibits anti-inflammatory, anti-tumor, antioxidant, and antimicrobial activities. Here, we described the biosynthesis of AuNPs using BRP extract (AuNPextract) and its fractions (AuNPhexane, AuNPdichloromethane, AuNPethyl acetate) and evaluated their structural properties and their potential against microorganisms and cancer cells. AuNPs showed a surface plasmon resonance (SPR) band at 535 nm. The sizes and morphologies were influenced by the BRP sample used in the reaction. FTIR and TGA revealed the involvement of bioactive compounds from BRP extract or its fractions in the synthesis and stabilization of AuNPs. AuNPdichloromethane and AuNPhexane exhibited antimicrobial activities against all strains tested, showing their efficacy as antimicrobial agents to treat infectious diseases. AuNPs showed dose-dependent cytotoxic activity both in T24 and PC-3 cells. AuNPdichloromethane and AuNPextract exhibited the highest in vitro cytotoxic effect. Also, the cytotoxicity of biogenic nanoparticles was induced by mechanisms associated with apoptosis. The results highlight a potential low-cost green method using Brazilian red propolis to synthesize AuNPs, which demonstrated significant biological properties.

Review of Integrated Optical Biosensors for Point-Of-Care Applications

This article reviews optical biosensors and their integration with microfluidic channels. The integrated biosensors have the advantages of higher accuracy and sensitivity because they can simultaneously monitor two or more parameters. They can further incorporate many functionalities such as electrical control and signal readout monolithically in a single semiconductor chip, making them ideal candidates for point-of-care testing. In this article, we discuss the applications by specifically looking into point-of-care testing (POCT) using integrated optical sensors. The requirement and future perspective of integrated optical biosensors for POC is addressed.

Recent progress on developing of plasmon biosensing of tumor biomarkers: Efficient method towards early stage recognition of cancer

Cancer is the second most extended disease with an improved death rate over the past several time. Due to the restrictions of cancer analysis methods, the patient's real survival rate is unknown. Therefore, early stage diagnosis of cancer is crucial for its strong detection. Bio-analysis based on biomarkers may help to overcome the problem Biosensors with high sensitivity and specificity, low-cost, high analysis speed and minimum limit of detection are practical alternatives for laboratory tests. Surface plasmon resonance (SPR) is reaching a maturity level sufficient for their application in detection and determination cancer biomarkers in clinical samples. This review discusses main concepts and performance characteristics of SPR biosensor. Mainly, it focuses on newly emerged enhanced SPR biosensors towards high-throughput and ultrasensitive screening of cancer biomarkers such as PSA, α-fetoprotein, CEA, CA125, CA 15-3, HER2, ctDNA, ALCAM, hCG, VEGF, TNF, Interleukin, IFN-γ, CD24, CD44, Ferritin, COLIV using labeling processes with focusing on the future application in biomedical research and clinical diagnosis. This article reviews current status of the field, showcasing a series of early successes in the application of SPR for clinical bioanalysis of cancer related biomolecules and detailing a series of considerations regarding sensing schemes, exposing issues with analysis in biofluids, while providing an outlook of the challenges currently associated with plasmonic materials, bioreceptor selection, microfluidics, and validation of a clinical bioassay for applying SPR biosensors to clinical samples. Research opportunities are proposed to further advance the field and transition SPR biosensors from research proof-of-concept stage to actual clinical usage.

Exploring Graphene and MoS2 Chips Based Surface Plasmon Resonance Biosensors for Diagnostic Applications

Until now, two-dimensional (2D) nanomaterials have been widely studied and applied in the biosensor field. Some of the advantages offered by these 2D materials include large specific surface area, high conductivity, and easy surface modification. This review discusses the use of 2D material in surface plasmon resonance (SPR) biosensor for diagnostic applications. Two-dimensional material reviewed includes graphene and molybdenum disulfide (MoS2). The discussion begins with a brief introduction to the general principles of the SPR biosensor. The discussion continues by explaining the properties and characteristics of each material and its effect on the performance of the SPR biosensor, in particular its sensitivity. This review concludes with some recent applications of graphene- and MoS2-based SPR biosensor in diagnostic applications.

G-quadruplex-based aptamers targeting human thrombin: Discovery, chemical modifications and antithrombotic effects

First studies on thrombin-inhibiting DNA aptamers were reported in 1992, and since then a large number of anticoagulant aptamers has been discovered. TBA - also named HD1, a 15-mer G-quadruplex (G4)-forming oligonucleotide - is the best characterized thrombin binding aptamer, able to specifically recognize the protein exosite I, thus inhibiting the conversion of soluble fibrinogen into insoluble fibrin strands. Unmodified nucleic acid-based aptamers, in general, and TBA in particular, exhibit limited pharmacokinetic properties and are rapidly degraded in vivo by nucleases. In order to improve the biological performance of aptamers, a widely investigated strategy is the introduction of chemical modifications in their backbone at the level of the nucleobases, sugar moieties or phosphodiester linkages. Besides TBA, also other thrombin binding aptamers, able to adopt a well-defined G4 structure, e.g. mixed duplex/quadruplex sequences, as well as homo- and hetero-bivalent constructs, have been identified and optimized. Considering the growing need of new efficient anticoagulant agents associated with the strong therapeutic potential of these thrombin inhibitors, the research on thrombin binding aptamers is still a very hot and intriguing field. Herein, we comprehensively described the state-of-the-art knowledge on the DNA-based aptamers targeting thrombin, especially focusing on the optimized analogues obtained by chemically modifying the oligonucleotide backbone, and their biological performances in therapeutic applications.

Polysaccharides as the Sensing Material for Metal Ion Detection-Based Optical Sensor Applications

The incorporation of a proper sensing material towards the construction of high selectivity optical sensing devices is vital. Polysaccharides, such as chitosan and carrageenan, are among the bio-based sensing materials that are extensively employed due to their remarkable physicochemical attributes. This paper highlights the critical aspects of the design of suitable polysaccharides for the recognition of specific analytes through physical and chemical modifications of polysaccharide structure. Such modifications lead to the enhancement of physicochemical properties of polysaccharides and optical sensor performance. Chitosan and carrageenan are two materials that possess excellent features which are capable of sensing target analytes via various interactions. The interaction between polysaccharides and analytes is dependent on the availability of functional groups in their structure. The integration of polysaccharides with various optical sensing techniques further improves optical sensor performance. The application of polysaccharides as sensing materials in various optical sensing techniques is also highlighted, particularly for metal ion sensing.

Insight into the Development of PET Radiopharmaceuticals for Oncology

While the development of positron emission tomography (PET) radiopharmaceuticals closely follows that of traditional drug development, there are several key considerations in the chemical and radiochemical synthesis, preclinical assessment, and clinical translation of PET radiotracers. As such, we outline the fundamentals of radiotracer design, with respect to the selection of an appropriate pharmacophore. These concepts will be reinforced by exemplary cases of PET radiotracer development, both with respect to their preclinical and clinical evaluation. We also provide a guideline for the proper selection of a radionuclide and the appropriate labeling strategy to access a tracer with optimal imaging qualities. Finally, we summarize the methodology of their evaluation in in vitro and animal models and the road to clinical translation. This review is intended to be a primer for newcomers to the field and give insight into the workflow of developing radiopharmaceuticals.

Antiviral Peptides: Identification and Validation

Despite rapid advances in the human healthcare, the infection caused by certain viruses results in high morbidity and mortality accentuate the importance for development of new antivirals. The existing antiviral drugs are limited, due to their inadequate response, increased rate of resistance and several adverse side effects. Therefore, one of the newly emerging field “peptide-based therapeutics” against viruses is being explored and seems promising. Over the last few years, a lot of scientific effort has been made for the identification of novel and potential peptide-based therapeutics using various advanced technologies. Consequently, there are more than 60 approved peptide drugs available for sale in the market of United States, Europe, Japan, and some Asian countries. Moreover, the number of peptide drugs undergoing the clinical trials is rising gradually year by year. The peptide-based antiviral therapeutics have been approved for the Human immunodeficiency virus (HIV), Influenza virus and Hepatitis virus (B and C). This review enlightens the various peptide sources and the different approaches that have contributed to the search of potential antiviral peptides. These include computational approaches, natural and biological sources (library based high throughput screening) for the identification of lead peptide molecules against their target. Further the applications of few advanced techniques based on combinatorial chemistry and molecular biology have been illustrated to measure the binding parameters such as affinity and kinetics of the screened interacting partners. The employment of these advanced techniques can contribute to investigate antiviral peptide therapeutics for emerging infections.

Pseurotin A as a novel suppressor of hormone dependent breast cancer progression and recurrence by inhibiting PCSK9 secretion and interaction with LDL receptor

Hypercholesterolemia has been documented to drive hormone-dependent breast cancer (BC) progression and resistance to hormonal therapy. Proprotein convertase subtilisin/kexin type-9 (PCSK9) regulates cholesterol metabolism through binding to LDL receptor (LDLR) and targeting the receptor for lysosomal degradation. Inhibition of PCSK9 is an established strategy to treat hypercholesterolemia. Pseurotin A (PS) is a unique spiro-heterocyclic γ-lactam alkaloid isolated from the fungus Aspergillus fumigatus. Preliminary studies indicated that PS lowered PCSK9 secretion in cultured HepG2 hepatocellular carcinoma cells, with an IC₅₀ value of 1.20 μM. Docking studies suggested the ability of PS to bind at the PCSK9 narrow interface pocket that accommodates LDLR. Surface plasmon resonance (SPR) showed PS ability to inhibit the PCSK9-LDLR interaction at a concentration range of 10-150 μM. PS showed in vitro dose-dependent reduction of PCSK9, along with increased LDLR levels in hormone-dependent BT-474 and T47D breast cancer (BC) cell lines. In vivo, daily oral 10 mg/kg PS suppressed the progression of the hormone-dependent BT-474 BC cells in orthotopic nude mouse xenograft model. Immunohistochemistry (IHC) investigation of BT-474 breast tumor tissue proved the PS ability to reduce PCSK9 expression. PS also effectively suppressed BT-474 BC cells locoregional recurrence after primary tumor surgical excision. Western blot analysis showed decreased PCSK9 expression in liver tissues of PS-treated mice compared to vehicle-treated control group. PS treatment significantly reduced PCSK9 expression and normalized LDLR levels in collected primary and recurrent breast tumors at the study end. PS-treated mice showed reduced plasma cholesterol and 17β-estradiol levels. Inhibition of tumor recurrence was associated with significant reductions in plasma level of the human BC recurrence marker CA 15-3 in treated mice at the study end. Histopathological examination of various PS-treated mice organs indicated lack of metastatic tumor cells and any pathological changes. The results of this study provide the first evidence for the suppression of the hormone-dependent breast tumor progression and recurrence by targeting the PCSK9-LDLR axis. PS is a novel first-in-class PCSK9-targeting lead appropriate for the use to control hormone-dependent BC progression and recurrence.

Current and Future Point-of-Care Tests for Emerging and New Respiratory Viruses and Future Perspectives

The availability of pathogen-specific treatment options for respiratory tract infections (RTIs) increased the need for rapid diagnostic tests. Besides, retrospective studies, improved lab-based detection methods and the intensified search for new viruses since the beginning of the twenty-first century led to the discovery of several novel respiratory viruses. Among them are human bocavirus (HBoV), human coronaviruses (HCoV-HKU1, -NL63), human metapneumovirus (HMPV), rhinovirus type C (RV-C), and human polyomaviruses (KIPyV, WUPyV). Additionally, new viruses like SARS coronavirus (SARS-CoV), MERS coronavirus (MERS-CoV), novel strains of influenza virus A and B, and (most recently) SARS coronavirus 2 (SARS-CoV-2) have emerged. Although clinical presentation may be similar among different viruses, associated symptoms may range from a mild cold to a severe respiratory illness, and thus require a fast and reliable diagnosis. The increasing number of commercially available rapid point-of-care tests (POCTs) for respiratory viruses illustrates both the need for this kind of tests but also the problem, i.e., that the majority of such assays has significant limitations. In this review, we summarize recently published characteristics of POCTs and discuss their implications for the treatment of RTIs. The second key aspect of this work is a description of new and innovative diagnostic techniques, ranging from biosensors to novel portable and current lab-based nucleic acid amplification methods with the potential future use in point-of-care settings. While prototypes for some methods already exist, other ideas are still experimental, but all of them give an outlook of what can be expected as the next generation of POCTs.

Are plasmonic optical biosensors ready for use in point-of-need applications?

Plasmonics has drawn significant attention in the area of biosensors for decades due to the unique optical properties of plasmonic resonant nanostructures. While the sensitivity and specificity of molecular detection relies significantly on the resonance conditions, significant attention has been dedicated to the design, fabrication, and optimization of plasmonic substrates. The adequate choice of materials, structures, and functionality goes hand in hand with a fundamental understanding of plasmonics to enable the development of practical biosensors that can be deployed in real life situations. Here we provide a brief review of plasmonic biosensors detailing most recent developments and applications. Besides metals, novel plasmonic materials such as graphene are highlighted. Sensors based on Surface Plasmon Resonance (SPR), Localized Surface Plasmon Resonance (LSPR), and Surface Enhanced Raman Spectroscopy (SERS) are presented and classified based on their materials and structure. In addition, most recent applications to environment monitoring, health diagnosis, and food safety are presented. Potential problems related to the implementation in such applications are discussed and an outlook is presented.

Antimicrobial Susceptibility Test for the Determination of Resistant and Susceptible S. aureus and Enterococcus spp. Using a Multi-Channel Surface Plasmon Resonance Device

The objective of this study was to investigate the development of a surface plasmon resonance (SPR) sensor platform equipped with multiple channels for the simultaneous determination of methicillin-resistant S. aureus (MRSA), methicillin-susceptible S. aureus (MSSA) and vancomycin-resistant Enterococcus (VRE), and vancomycin-susceptible Enterococcus (VSE). Drug resistance of S. aureus strains against cefoxitin and Enterococcus strains against vancomycin were investigated both using the minimum inhibitory concentration method (MIC) assay and the SPR system equipped with single and multiple channels. The MIC values of MRSA and MSSA ranged from 32 µg/mL to >128 µg/mL and from 1 µg/mL to 4 µg/mL, respectively. The MIC values of VRE and VSE were between 64 to >128 µg/mL and 2-4 µg/mL, respectively. With the multiple-channel system, the angle shifts of MRSA, MSSA, VRE and VSE were found to be -0.030° and -0.260°, -0.010° and -0.090° respectively. The antibiotic-resistant and susceptible strains were distinguished within 3 h for S. aureus strains and within 6 h for Enterococcus strains.

Structural features of methionine aminopeptidase2-active core peptide essential for binding with S100A4

Methionine aminopeptidase 2 (MetAP2) is one of the effector proteins of S100A4, a metastasis-associated calcium-binding protein. This interaction is involved in angiogenesis. The region of MetAP2 that interacts with S100A4 includes amino acids 170 to 208. A peptide corresponding to this region, named as NBD, has potent anti-angiogenic activity and suppresses tumor growth in a xenograft cancer model. However, the binding mode of NBD to S100A4 was totally unknown. Here we describe our analysis of the relationship between the inhibitory activity and the structure of NBD, which adopts a characteristic helix-turn-helix structure as shown by X-ray crystallographic analysis, and peptide fragments of NBD. We conducted physicochemical analyses of the interaction between S100A4 and the peptides, including surface plasmon resonance, microscale thermophoresis, and circular dichroism, and performed docking/molecular dynamics simulations. Active peptides had stable secondary structures, whereas inactive peptides had a little secondary structure. A computational analysis of the interaction mechanism led to the design of a peptide smaller than NBD, NBD-ΔN10, that possessed inhibitory activity. Our study provides a strategy for design for a specific peptide inhibitor against S100A4 that can be applied to the discovery of inhibitors of other protein-protein interactions.

Perylene Bisimide Aggregates as Probes for Subnanomolar Discrimination of Aromatic Biogenic Amines

Perylene bisimide derivatives show peculiar physical chemical features, such as a highly conjugated system, high extinction coefficients and elevated fluorescence quantum yields, making them suitable for the development of optical sensors of compounds of interest. In particular, they are characterized by the tendency to aggregate into π-π stacked supramolecular structures. In this contribution, the behavior of the PBI derivative N, N'-bis(2-(trimethylammonium)ethylene)perylene bisimide dichloride was investigated both in aqueous solution and on solid support. The electronic communication between PBI aggregates and biogenic amines was exploited in order to discriminate aromatic amines down to subnanomolar concentrations by observing PBI fluorescence variations in the presence of various amines and at different concentrations. The experimental findings were corroborated by density functional theory calculations. In particular, phenylethylamine and tyramine were demonstrated to be selectively detected down to 10^-10 M concentration. Then, in order to develop a surface plasmon resonance (SPR) device, PBI was deposited onto a SPR support by means of the layer-by-layer method. PBI was deposited in the aggregated form and was demonstrated to preserve the capability to discriminate, selectively and with an outstanding analytical sensitivity, tyramine in the vapor phase and even if mixed with other aromatic amines.

Fabrication of Miniature Surface Plasmon Resonance Sensor Chips by Using Confined Sessile Drop Technique

In this study, we demonstrate a simple and efficient method to fabricate miniature surface plasmon resonance (SPR) sensor chips by using confined sessile drop technique. A liquid optical adhesive (NOA 61) was dropped on the circular flat surface of cylindrical substrates made of poly(dimethylsiloxane) (PDMS). The formation of hemispherical optical prisms was accomplished by taking advantage of the sharp edges of cylindrical PDMS substrates that prevented the overflow of liquid NOA 61 at the edge of substrates. The size of the hemispherical optical prisms can be controlled by changing the diameter of the cylindrical PDMS substrates. After UV curing, the SPR sensor chips were obtained by the deposition of 3 nm thick chromium and 47 nm thick gold on the flat side of the prisms. The fabricated miniature SPR sensor chips were then mounted on a three-dimensional-printed flow cell to complete the microfluidic SPR sensor module. The miniature SPR sensor chips provided a comparable sensitivity to the conventional high-refractive-index glass SPR chips. To demonstrate the detection capability of nanometer-sized materials, we applied the miniature microfluidic SPR system for monitoring the deposition of layer-by-layer ultrathin films of poly(diallyldimethylammonium chloride)/poly(sodium 4-styrenesulfonate) and for detecting human immunoglobulin G.

A plasmonic refractive index sensor with an ultrabroad dynamic sensing range

Refractive index sensors based on surface plasmon resonance (SPR) promise to deliver high sensitivities. However, these sensitivities depend on the derivative of the monitored SPR parameters near resonance, so this dependency leads to a relatively narrow detection range for refractive index changes. Herein, we introduce an idea to improve the detection range refractive index through a high-contrast-index curved waveguide surrounded with an outer gold ring. The proposed detection technique, based on the output power measurement of the curved waveguide, offers a linear response over an ultrabroad range of the refractive index for a surrounding medium from n = 1 to 2.36. Meanwhile, an theoretically ultrahigh refractive index resolution (RIU) of 4.53 × 10⁻¹⁰ could be accessible for such a broad testing range, available for both gas and aqueous chemical sample refractive indices Furthermore, the power detection approach enables an integrated photodetector for a lab-on-chip sensor platform, revealing a high potential for a multifunctional, compact, and highly sensitive sensor-on-chip device.