Selective Amplification of Plasmonic Sensor Signal for Cortisol Detection Using Gold Nanoparticles

Nanoparticle-assisted plasmonic sensors: Recent developments in clinical applications

Nanotechnology is an important science that finds a wide range of applications from energy production to industrial production processes and biomedical applications. Nanoparti-cles, which are the most frequently preferred nanomaterials that form the basis of nanotechnolo-gy, are prepared with different composition, size, shape and surface chemistry to provide new techniques in applications in many different fields. The use of nanoparticles in the preparation of plasmonic sensors has increased the interest in plasmonic sensors such as surface plasmon resonance, electrochemical sensors, surface enhanced raman scattering and colorimetric sensors due to their increased sensing capacity on sensor surfaces. Plasmonic sensors are an important option in many different fields, such as medicine, environmental agriculture and food safety, thanks to their ability to solve a multitude of challenges. Because, plasmonic sensors are defined as sensing devices with important features such as sensitive and fast detection, no need for labels, real-time analysis, portability. In this review, the information about nanoparticles and their types and working principles of plasmonic sensors is given. Then, examples in clinical applications using different plasmonic sensors prepared with plasmonic nanoparticles are discussed in detail.

Tailoring Infrared Light-Molecule Coupling for Highly Sensitive Cortisol Detection Employing Aptamer-Conjugated Gold Nanonails

Chemically synthesized gold nanoantennas possess easy processability, low cost, and suitability for large-area fabrication, making them advantageous for surface-enhanced infrared (SEIRA) biosensing. Nevertheless, current gold nanoantennas face challenges with limited enhancement of biomolecular signals that hinder their practical applications. Here, we demonstrate that the coupling rate between antennas and molecules critically impacts the enhancement of molecular signals based on temporal coupled mode theory. To improve this coupling rate, we synthesized gold nanonails with sharp tips, significantly amplifying the localized electric fields of antenna resonance modes. Modulating the nanonail aspect ratio allows us to tailor antenna resonance frequencies to match molecular vibrational frequencies. Additionally, we introduced specific aptamers on antenna surfaces through solution exchange methods to control the antenna-molecule distances. These combined strategies enabled noninvasive, label-free detection with high sensitivity for the biomarker cortisol. Experiments revealed 3 orders of magnitude enhancement in cortisol detection levels upon increasing coupling efficiency, achieving a detection limit of 0.1 ng/mL, notably lower than the normal cortisol concentration in human saliva (0.398 ng/mL). In addition to demonstrating a novel strategy for cortisol detection, this study provides a viable approach to biomarker detection for future applications in disease diagnosis and human health monitoring.

Real-time monitoring of vancomycin using a split-aptamer surface plasmon resonance biosensor

Real-time monitoring of therapeutic drugs is crucial for treatment management and pharmacokinetic studies. We present the optimization and affinity tuning of split-aptamer sandwich assay for real-time monitoring of the narrow therapeutic window drug vancomycin, using surface plasmon resonance (SPR). To achieve reversible, label-free sensing of small molecules by SPR, we adapted a vancomycin binding aptamer in a sandwich assay format through the split-aptamer approach. By evaluating multiple split sites within the secondary structure of the original aptamer, we identified position 27 (P27) as optimal for preserving target affinity, ensuring reversibility, and maximizing sensitivity. The assay demonstrated robust performance under physiologically relevant ranges of pH and divalent cations, and the specific ternary complex formation of the aptamer split segments with the analyte was confirmed by circular dichroism spectroscopy. Subsequently, we engineered a series of split-aptamer pairs with increasing complementarity in the stem regions, improving both the affinity and limit of detection up to 10-fold, as compared to the primary P27 pair. The kinetics of the engineered split-aptamer pairs were evaluated, revealing fast association and dissociation rates, confirming improved affinity and detection limits across variants. Most importantly, the reversibility of the assay, essential for real-time monitoring, was maintained in all pairs. Finally, the assay was further validated in complex biological matrices, including the cerebrospinal fluid from dogs and diluted plasma from rats, demonstrating functionality in biological environments and stability exceeding 9 hours. Our study paves the way for applications of split-aptamers in real-time monitoring of small molecules, with potential implications for in vivo therapeutic drug monitoring and pharmacokinetic studies.

Cortisol: Biosensing and detection strategies

Cortisol, a crucial steroid hormone synthesized by the adrenal glands, has diverse impacts on multiple physiological processes, such as metabolism, immune function, and stress management. Disruption in cortisol levels can result in conditions like Cushing's syndrome and Addison's disease. This review provides an in-depth exploration of cortisol, covering its structure, various forms in the body, detection methodologies, and emerging trends in cancer treatment and detection. Various techniques for cortisol detection, including electrochemical, chromatographic, and immunoassay methods were discussed and highlighted for their merits and applications. Electrochemical immunosensing emerges as a promising approach, which offered high sensitivity and low detection limits. Moreover, the review delves into the intricate relationship between cortisol and cancer, emphasizing cortisol's role in cancer progression and treatment outcomes. Lastly, the utilization of biomarkers, in-silico modeling, and machine learning for electrochemical cortisol detection were explored, which showcased innovative strategies for stress monitoring and healthcare advancement.

Nanomaterial-Based Sensors for Coumarin Detection

Sensors are widely used owing to their advantages including excellent sensing performance, user-friendliness, portability, rapid response, high sensitivity, and specificity. Sensor technologies have been expanded rapidly in recent years to offer many applications in medicine, pharmaceuticals, the environment, food safety, and national security. Various nanomaterial-based sensors have been developed for their exciting features, such as a powerful absorption band in the visible region, excellent electrical conductivity, and good mechanical properties. Natural and synthetic coumarin derivatives are attracting attention in the development of functional polymers and polymeric networks for their unique biological, optical, and photochemical properties. They are the most abundant organic molecules in medicine because of their biological and pharmacological impacts. Furthermore, coumarin derivatives can modulate signaling pathways that affect various cellular processes. This review covers the discovery of coumarins and their derivatives, the integration of nanomaterial-based sensors, and recent advances in nanomaterial-based sensing for coumarins. This review also explains how sensors work, their types, their pros and cons, and sensor studies for coumarin detection in recent years.

Biosensing Platforms for Cardiac Biomarker Detection

Myocardial infarction (MI) is a cardiovascular disease that occurs when there is an elevated demand for myocardial oxygen as a result of the rupture or erosion of atherosclerotic plaques. Globally, the mortality rates associated with MI are steadily on the rise. Traditional diagnostic biomarkers employed in clinical settings for MI diagnosis have various drawbacks, prompting researchers to investigate fast, precise, and highly sensitive biosensor platforms and technologies. Biosensors are analytical devices that combine biological elements with physicochemical transducers to detect and quantify specific compounds or analytes. These devices play a crucial role in various fields including healthcare, environmental monitoring, food safety, and biotechnology. Biosensors developed for the detection of cardiac biomarkers are typically electrochemical, mass, and optical biosensors. Nanomaterials have emerged as revolutionary components in the field of biosensing, offering unique properties that significantly enhance the sensitivity and specificity of the detection systems. This review provides a comprehensive overview of the advancements and applications of nanomaterial-based biosensing systems. Beginning with an exploration of the fundamental principles governing nanomaterials, we delve into their diverse properties, including but not limited to electrical, optical, magnetic, and thermal characteristics. The integration of these nanomaterials as transducers in biosensors has paved the way for unprecedented developments in analytical techniques. Moreover, the principles and types of biosensors and their applications in cardiovascular disease diagnosis are explained in detail. The current biosensors for cardiac biomarker detection are also discussed, with an elaboration of the pros and cons of existing platforms and concluding with future perspectives.

Exploring the potential of molecularly imprinted polymers and metal/metal oxide nanoparticles in sensors: recent advancements and prospects

Metal/metal oxide nanoparticles have gained increasing attention in recent years due to their outstanding features, including optical and catalytic properties, as well as their excellent conductivity. The implementation of metal/metal oxide nanoparticles, combined with molecularly imprinted polymers (MIPs) has paved the way for a new generation of building blocks to engineer and enhance the fascinating features of advanced sensors. This review critically evaluates the impact of combining metal/metal oxide nanoparticles with MIPs in sensors. It covers synthesis strategies, advantages of coupling these materials with MIPs, and addresses questions about the selectivity of these hybrid materials. In the end, the current challenges and future perspectives of this field are discussed, with a particular focus on the potential applications of these hybrid composites in the sensor field. This review highlights the exciting opportunities of using metal/metal oxide nanoparticles along with MIPs for the development of next-generation sensors.

A Multi-Enzyme Cascade Response for the Colorimetric Recognition of Organophosphorus Pesticides Utilizing Core-Shell Pd@Pt Nanoparticles with High Peroxidase-like Activity

In modern agricultural practices, organophosphorus pesticides or insecticides (OPs) are regularly used to restrain pests. Their limits are closely monitored since their residual hinders the capability of acetylcholinesterase (AChE) and brings out a threatening accumulation of the neurotransmitter acetylcholine (ACh), which affects human well-being. Therefore, spotting OPs in food and the environment is compulsory to prevent human health. Several techniques are available to identify OPs but encounter shortcomings like time-consuming, operating costs, and slow results achievement, which calls for further solutions. Herein, we present a rapid colorimetric sensor for quantifying OPs in foods using TMB as a substrate, a multi-enzyme cascade system, and the synergistic property of core-shell Palladinum@Platinum (Pd@Pt) nanoparticles. The multi-enzyme cascade response framework is a straightforward and effective strategy for OPs recognition and can resolve the previously mentioned concerns. Numerous OPs, including Carbofuran, Malathion, Parathion, Phoxim, Rojor, and Phosmet, were successfully quantified at different concentrations. The cascade method established using Pd@Pt had a simple and easy operation, a lower detection limit range of (1-2.5 ng/mL), and a short detection time of about 50 min. With an R2 value of over 0.93, OPs showed a linear range of 10-200 ng/mL, portraying its achievement in quantifying pesticide residue. Lastly, the approach was utilized in food samples and recovered more than 80% of the residual OPs.

Voltammetric Sensing of Nifedipine Using a Glassy Carbon Electrode Modified with Carbon Nanofibers and Gold Nanoparticles

Nifedipine, a widely utilized medication, plays a crucial role in managing blood pressure in humans. Due to its global prevalence and extensive usage, close monitoring is necessary to address this widespread concern effectively. Therefore, the development of an electrochemical sensor based on a glassy carbon electrode modified with carbon nanofibers and gold nanoparticles in a Nafion® film was performed, resulting in an active electrode surface for oxidation of the nifedipine molecule. This was applied, together with a voltammetric methodology, for the analysis of nifedipine in biological and environmental samples, presenting a linear concentration range from 0.020 to 2.5 × 10-6 µmol L-1 with a limit of detection 2.8 nmol L-1. In addition, it presented a good recovery analysis in the complexity of the samples, a low deviation in the presence of interfering potentials, and good repeatability between measurements.

Electrochemical Detection of Cortisol by Silver Nanoparticle-Modified Molecularly Imprinted Polymer-Coated Pencil Graphite Electrodes

The sensitive cortisol detection by an electrochemical sensor based on silver nanoparticle-doped molecularly imprinted polymer was successfully improved. This study describes the method development for cortisol detection in both aqueous solution and biological samples using molecularly imprinted poly(hydroxyethyl methacrylate-N-methacryloyl-(l)-histidine methyl ester)-coated pencil graphite electrodes modified with silver nanoparticles (AgNPs) by differential pulse voltammetry (DPV). The cortisol-imprinted pencil graphite electrode (PGE) has a large surface area because of doped AgNPs with enhanced electroactivity. The prepared molecularly imprinted polymer was characterized by scanning electron microscopy. The DPV response of the synthesized electrode with outstanding electrical conductivity was clarified. Cortisol-imprinted polymer-coated PGEs (MIP), cortisol-imprinted polymer-coated PGEs with AgNPs (MIP@AgNPs), and nonimprinted polymer-coated PGEs with AgNPs (NIP@AgNPs) were evaluated for sensitive and selective detection of cortisol in aqueous solution. Five different cortisol concentrations (0.395, 0.791, 1.32, 2.64, and 3.96 nM) were applied to the MIP@AgNPs, and signal responses were detected by the DPV with a regression coefficient (R2) value of 0.9951. The modified electrode showed good electrocatalytic activity toward cortisol for the linear concentration range from 0.395 to 3.96 nM, and a low limit of detection was recorded as 0.214 nM. The results indicate that the MIP@AgNPs sensor has great potential for sensitive and selective cortisol determination in biological samples.

Aptamer-Based Point-of-Care Devices: Emerging Technologies and Integration of Computational Methods

Recent innovations in point-of-care (POC) diagnostic technologies have paved a critical road for the improved application of biomedicine through the deployment of accurate and affordable programs into resource-scarce settings. The utilization of antibodies as a bio-recognition element in POC devices is currently limited due to obstacles associated with cost and production, impeding its widespread adoption. One promising alternative, on the other hand, is aptamer integration, i.e., short sequences of single-stranded DNA and RNA structures. The advantageous properties of these molecules are as follows: small molecular size, amenability to chemical modification, low- or nonimmunogenic characteristics, and their reproducibility within a short generation time. The utilization of these aforementioned features is critical in developing sensitive and portable POC systems. Furthermore, the deficiencies related to past experimental efforts to improve biosensor schematics, including the design of biorecognition elements, can be tackled with the integration of computational tools. These complementary tools enable the prediction of the reliability and functionality of the molecular structure of aptamers. In this review, we have overviewed the usage of aptamers in the development of novel and portable POC devices, in addition to highlighting the insights that simulations and other computational methods can provide into the use of aptamer modeling for POC integration.

Novel hydrocortisone magnetic molecularly imprinted polymers: Preparation, characterization, and application

In this work, magnetic molecularly imprinted polymers (MMIPs) were prepared by a surface imprinting method using Fe₃O₄ nanoparticles as a support. The products were characterized by FT-IR spectroscopy, VSM, TGA, SEM, and TEM. Combined with HPLC, hydrocortisone in milk powder and milk were separated and purified, and their contents were monitored. The results showed that MMIPs with a particle size of approximately 1000 nm were successfully prepared. The adsorption mechanism of MMIPs was confirmed by kinetic adsorption and thermodynamic adsorption experiments; the maximum adsorption capacity was found to be 17.2 mg g^-1, and adsorption equilibrium could be reached within 40 min. In the actual sample application, the recovery rates of milk powder and milk were 93.88-99.15% and 95.80-98.10%, respectively. These results showed that MMIPs had good performance in selectively identifying hydrocortisone and were suitable for determining hydrocortisone in milk products.

A surface plasmon resonance sensor with synthetic receptors decorated on graphene oxide for selective detection of benzylpenicillin

Antibiotic residues in foods, water and the environment reveal antibiotic-resistant bacterial strains, disrupting the ecological balance and causing serious health problems. For these reasons, the detection of antibiotic residues is crucial for the protection of human health. Herein, the detection of benzylpenicillin antibiotic from aqueous and milk sample solutions was carried out by surface plasmon resonance (SPR) sensor using synthetic receptor-molecularly imprinted polymer. The benzylpenicillin-imprinted poly(hydroxyethyl methacrylate-graphene oxide-N-methacryloyl-l-phenylalanine) (MIP-GO) SPR sensor was prepared. Benzylpenicillin detection was performed by MIP-GO SPR sensor in a 1-100 ppb concentration range of benzylpenicillin with 0.9665 linear correlation and 0.021 ppb detection limit. Selectivity analysis showed that the MIP-GO SPR sensor detected the benzylpenicillin molecule 8.16 times more selectively than amoxicillin and 14.04 times more selectively than ampicillin. To examine the imprinting efficiency, non-imprinted poly(hydroxyethyl methacrylate-graphene oxide-N-methacryloyl-l-phenylalanine) (NIP-GO) SPR sensor was also prepared using the same procedure without benzylpenicillin addition. Since graphene oxide (GO) was added to enhance the sensor signal response by increasing sensitivity, the control analyses were performed by a poly(hydroxyethyl methacrylate-N-methacryloyl-l-phenylalanine) (MIP) SPR sensor without adding GO. Moreover, repeatability studies of MIP-GO SPR sensor were statistically evaluated and the RSD of intra-day assays less than 1% specified that there was no loss of performance for the benzylpenicillin detection ability even after four cycles. As a real food sample analysis, the benzylpenicillin spiked and unspiked milk samples were evaluated and high-performance liquid chromatography experiments were carried out for validation.

Development of a Plasmonic Sensor for a Chemotherapeutic Agent Cabazitaxel

Drug dosage is a crucial subject in both human and animal treatment. Administering less drug dosage may prevent treatment or make it less effective, and high drug dosage may cause a heightened risk of adverse effects, or in some cases, cost a patient's life. Also, even when the dosage is administered carefully, metabolic differences may cause different effects on different patients. Because of these considerations, monitoring drug dosage in the body is a critical and significant requirement in the health industry. Within the scope of this study, a reusable surface plasmon resonance (SPR) chip with fast response, high selectivity, and no pretreatment is produced for the chemotherapeutic agent cabazitaxel. A cabazitaxel-imprinted nanofilm was synthesized on the sensor chip surface and characterized by atomic force microscopy, ellipsometry, and contact angle measurements. Standard cabazitaxel solution and an artificial plasma sample were used for the kinetic analysis. Docetaxel, methylprednisolone, and dexamethasone were analyzed for their selectivity experiment. In addition, the repeatability and storage durability of the sensor were also evaluated. As a result of the adsorption studies, the limit of detection and limit of quantitation values were found to be 0.012 and 0.036 μg/mL, respectively. High-performance liquid chromatography analysis was used to validate the response of the cabazitaxel-imprinted sensor.

Nanomaterials for Cortisol Sensing

Space represents one of the most dangerous environments for humans, which can be affected by high stress levels. This can lead to severe physiological problems, such as headaches, gastrointestinal disorders, anxiety, hypertension, depression, and coronary heart diseases. During a stress condition, the human body produces specific hormones, such as dopamine, adrenaline, noradrenaline, and cortisol. In particular, the control of cortisol levels can be related to the stress level of an astronaut, particularly during a long-term space mission. The common analytical methods (HPLC, GC-MS) cannot be used in an extreme environment, such as a space station, due to the steric hindrance of the instruments and the absence of gravity. For these reasons, the development of smart sensing devices with a facile and fast analytical protocol can be extremely useful for space applications. This review summarizes the recent (from 2011) miniaturized sensoristic devices based on nanomaterials (gold and carbon nanoparticles, nanotubes, nanowires, nano-electrodes), which allow rapid and real-time analyses of cortisol levels in biological samples (such as saliva, urine, sweat, and plasma), to monitor the health conditions of humans under extreme stress conditions.