A contemporary approach for design and characterization of fiber-optic-cortisol sensor tailoring LMR and ZnO/PPY molecularly imprinted film

Enhancement of lossy mode resonance sensing properties by the introduction of an intermediate low-refractive-index layer

Devices based on the lossy mode resonance (LMR) effect have found numerous sensing applications. Herein, the enhancement of the sensing properties by the introduction of an intermediate layer between the substrate and the LMR-supporting film is discussed. Experimental results for a silicon oxide (SiO₂) layer of tuned thickness between a glass slide substrate and a thin film of titanium oxide (TiO₂) prove the possibility of significantly increasing the LMR depth and the figure of merit (FoM) for refractive index sensing applications, which is supported by a numerical analysis using the plane wave method for a one-dimensional multilayer waveguide. The application of the intermediate layer allows the introduction of a new, to the best of our knowledge, degree of freedom into the design of LMR-based sensors, resulting in improved performance for demanding fields such as chemical sensing or biosensing.

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.

Rational In Silico Design of Molecularly Imprinted Polymers: Current Challenges and Future Potential

The rational design of molecularly imprinted polymers has evolved along with state-of-the-art experimental imprinting strategies taking advantage of sophisticated computational tools. In silico methods enable the screening and simulation of innovative polymerization components and conditions superseding conventional formulations. The combined use of quantum mechanics, molecular mechanics, and molecular dynamics strategies allows for macromolecular modelling to study the systematic translation from the pre- to the post-polymerization stage. However, predictive design and high-performance computing to advance MIP development are neither fully explored nor practiced comprehensively on a routine basis to date. In this review, we focus on different steps along the molecular imprinting process and discuss appropriate computational methods that may assist in optimizing the associated experimental strategies. We discuss the potential, challenges, and limitations of computational approaches including ML/AI and present perspectives that may guide next-generation rational MIP design for accelerating the discovery of innovative molecularly templated materials.

Cortisol Monitoring Devices toward Implementation for Clinically Relevant Biosensing In Vivo

Cortisol is a steroid hormone that regulates energy metabolism, stress reactions, and immune response. Cortisol is produced in the kidneys' adrenal cortex. Its levels in the circulatory system are regulated by the neuroendocrine system with a negative feedback loop of the hypothalamic-pituitary-adrenal axis (HPA-axis) following circadian rhythm. Conditions associated with HPA-axis disruption cause deteriorative effects on human life quality in numerous ways. Psychiatric, cardiovascular, and metabolic disorders as well as a variety of inflammatory processes accompanying age-related, orphan, and many other conditions are associated with altered cortisol secretion rates and inadequate responses. Laboratory measurements of cortisol are well-developed and based mainly on the enzyme linked immunosorbent assay (ELISA). There is a great demand for a continuous real-time cortisol sensor that is yet to be developed. Recent advances in approaches that will eventually culminate in such sensors have been summarized in several reviews. This review compares different platforms for direct cortisol measurements in biological fluids. The ways to achieve continuous cortisol measurements are discussed. A cortisol monitoring device will be essential for personified pharmacological correction of the HPA-axis toward normal cortisol levels through a 24-h cycle.

Cortisol Immunosensors: A Literature Review

Cortisol is a steroid hormone that is involved in a broad range of physiological processes in human/animal organisms. Cortisol levels in biological samples are a valuable biomarker, e.g., of stress and stress-related diseases; thus, cortisol determination in biological fluids, such as serum, saliva and urine, is of great clinical value. Although cortisol analysis can be performed with chromatography-based analytical techniques, such as liquid chromatography-tandem mass spectrometry (LC-MS/MS), conventional immunoassays (radioimmunoassays (RIAs), enzyme-linked immunosorbent assays (ELISAs), etc.) are considered the "gold standard" analytical methodology for cortisol, due to their high sensitivity along with a series of practical advantages, such as low-cost instrumentation, an assay protocol that is fast and easy to perform, and high sample throughput. Especially in recent decades, research efforts have focused on the replacement of conventional immunoassays by cortisol immunosensors, which may offer further improvements in the field, such as real-time analysis at the point of care (e.g., continuous cortisol monitoring in sweat through wearable electrochemical sensors). In this review, most of the reported cortisol immunosensors, mainly electrochemical and also optical ones, are presented, focusing on their immunosensing/detection principles. Future prospects are also briefly discussed.

Influence of Post Processing on Thermal Conductivity of ITO Thin Films

This work presents the influence of post processing on morphology, thermal and electrical properties of indium tin oxide (ITO) thin films annealed at 400 °C in different atmospheres. The commercially available 170 nm thick ITO layers deposited on glass were used as a starting material. The X-ray diffraction measurements revealed polycrystalline structure with dominant signal from (222) plane for all samples. The annealing reduces the intensity of this peak and causes increase of (221) and (440) peaks. Atomic force microscopy images showed that the surface morphology is typical for polycrystalline layers with roughness not exceeding few nm. Annealing in the oxygen and the nitrogen-hydrogen mixture (NHM) changes shapes of grains. The electrical conductivity decreases after annealing except the one of layer annealed in NHM. Thermal conductivities of annealed ITO thin films were in range from 6.4 to 10.6 W·m^-1·K^-1, and they were higher than the one for starting material-5.1 W·m^-1·K^-1. Present work showed that annealing can be used to modify properties of ITO layers to make them useful for specific applications e.g., in ITO based solar cells.

Molecularly Imprinted Polymer-Based Sensor for Electrochemical Detection of Cortisol

As a steroid hormone, cortisol has a close relationship with the stress response, and therefore, can be used as a biomarker for early detection of stress. An electrochemical immunosensor is one of the most widely used methods to detect cortisol, with antibodies as its bioreceptor. Apart from conventional laboratory-based methods, the trend for cortisol detection has seemed to be exploiting antibodies and aptamers. Both can provide satisfactory performance with high selectivity and sensitivity, but they still face issues with their short shelf life. Molecularly imprinted polymers (MIPs) have been widely used to detect macro- and micro-molecules by forming artificial antibodies as bioreceptors. MIPs are an alternative to natural antibodies, which despite demonstrating high selectivity and a low degree of cross-reactivity, often also show a high sensitivity to the environment, leading to their denaturation. MIPs can be prepared with convenient and relatively affordable fabrication processes. They also have high durability in ambient conditions, a long shelf life, and the ability to detect cortisol molecules at a concentration as low as 2 ag/mL. By collecting data from the past five years, this review summarizes the antibody and aptamer-based amperometric sensors as well as the latest developments exploiting MIPs rather than antibodies. Lastly, factors that can improve MIPs performance and are expected to be developed in the future are also explained.

New Trends in Fluorescent Nanomaterials-Based Bio/Chemical Sensors for Neurohormones Detection-A Review

The study of neurotransmitters and stress hormones allows the determination of indicators of the current stress load in the body. These species also create a proper strategy of stress protection. Nowadays, stress is a general factor that affects the population, and it may cause a wide range of serious disorders. Abnormalities in the level of neurohormones, caused by chronic psychological stress, can occur in, for instance, corporate employees, health care workers, shift workers, policemen, or firefighters. Here we present a new nanomaterials-based sensors technology development for the determination of neurohormones. We focus on fluorescent sensors/biosensors that utilize nanomaterials, such as quantum dots or carbon nanomaterials. Nanomaterials, owing to their diversity in size and shape, have been attracting increasing attention in sensing or bioimaging. They possess unique properties, such as fluorescent, electronic, or photoluminescent features. In this Review, we summarize new trends in adopting nanomaterials for applications in fluorescent sensors for neurohormone monitoring.

Development of a Redox-Label-Doped Molecularly Imprinted Polymer on β-Cyclodextrin/Reduced Graphene Oxide for Electrochemical Detection of a Stress Biomarker

Cortisol is a major stress biomarker involved in the regulation of metabolic and immune responses. Readily accessible assays with sufficient quantitative and temporal resolution can assist in prevention, early diagnosis, and management of chronic diseases. Whereas conventional assays are costly in terms of time, labor, and capital, an electrochemical approach offers the possibility of miniaturization and detection at the point-of-care. Here, we investigate the biosensor application of molecularly imprinted polypyrrole (PPy) doped with hexacyanoferrate (HCF) and coupled to reduced graphene oxide functionalized with β-cyclodextrin (β-CD). β-CD provides an inclusion site for lipophilic cortisol and was electrochemically grafted simultaneous with reduction of GO. Next, PPy was electrochemically deposited in presence of cortisol template with HCF dopant ions serving as intrinsic redox probe. Thus, the sensor response was evaluated via changes of redox peak current in cyclic voltammetry and demonstrated a broad logarithmic detection range (5 pg/mL to 5000 ng/mL, R ² = 0.995), with a sensitivity of 8.809 μA log^-1 (ng/mL) cm^-2 and LOD of 19.3 pM. The sensor was shown to be specific toward cortisol in reference to salivary cortisol concentration in saliva over structural analogues. The sensor was exhibited to determine cortisol in artificial saliva at normal and elevated levels. The good performance and facile electrochemical fabrication of this antibody- and external label-free interface are promising for the development of affordable point-of-care biosensors.

Cost-Effective Fiber Optic Solutions for Biosensing

In the last years, optical fiber sensors have proven to be a reliable and versatile biosensing tool. Optical fiber biosensors (OFBs) are analytical devices that use optical fibers as transducers, with the advantages of being easily coated and biofunctionalized, allowing the monitorization of all functionalization and detection in real-time, as well as being small in size and geometrically flexible, thus allowing device miniaturization and portability for point-of-care (POC) testing. Knowing the potential of such biosensing tools, this paper reviews the reported OFBs which are, at the moment, the most cost-effective. Different fiber configurations are highlighted, namely, end-face reflected, unclad, D- and U-shaped, tips, ball resonators, tapered, light-diffusing, and specialty fibers. Packaging techniques to enhance OFBs' application in the medical field, namely for implementing in subcutaneous, percutaneous, and endoscopic operations as well as in wearable structures, are presented and discussed. Interrogation approaches of OFBs using smartphones' hardware are a great way to obtain cost-effective sensing approaches. In this review paper, different architectures of such interrogation methods and their respective applications are presented. Finally, the application of OFBs in monitoring three crucial fields of human life and wellbeing are reported: detection of cancer biomarkers, detection of cardiovascular biomarkers, and environmental monitoring.

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

Herein, gold nanoparticles (AuNP)-modified cortisol-imprinted (AuNP-MIP) plasmonic sensor was developed for signal amplification and real-time cortisol determination in both aqueous and complex solutions. Firstly, the sensor surfaces were modified with 3-(trimethoxylyl)propyl methacrylate and then pre-complex was prepared using the functional monomer N-methacryloyl-L-histidine methyl ester. The monomer solution was made ready for polymerization by adding 2-hydroxyethyl methacrylate to ethylene glycol dimethacrylate. In order to confirm the signal enhancing effect of AuNP, only cortisol-imprinted (MIP) plasmonic sensor was prepared without AuNP. To determine the selectivity efficiency of the imprinting process, the non-imprinted (AuNP-NIP) plasmonic sensor was also prepared without cortisol. The characterization studies of the sensors were performed with atomic force microscopy and contact angle measurements. The kinetic analysis of the AuNP-MIP plasmonic sensor exhibited a high correlation coefficient (R² = 0.97) for a wide range (0.01–100 ppb) with a low detection limit (0.0087 ppb) for cortisol detection. Moreover, the high imprinting efficiency (k′ = 9.67) of the AuNP-MIP plasmonic sensor was determined by comparison with the AuNP-NIP plasmonic sensor. All kinetic results were validated and confirmed by HPLC.

Label-free plasmonic immunosensor for cortisol detection in a D-shaped optical fiber

Measuring cortisol levels as a stress biomarker is essential in many medical conditions associated with a high risk of metabolic syndromes such as anxiety and cardiovascular diseases, among others. One technology that has a growing interest in recent years is fiber optic biosensors that enable ultrasensitive cortisol detection. Such interest is allied with progress being achieved in basic interrogation, accuracy improvements, and novel applications. The development of improved cortisol monitoring, with a simplified manufacturing process, high reproducibility, and low cost, are challenges that these sensing mechanisms still face, and for which solutions are still needed. In this paper, a comprehensive characterization of a D-shaped fiber optic immunosensor for cortisol detection based on surface plasmon resonance (SPR) enabled by gold coating is reported. Specifically, the sensor instrumentation and fabrication processes are discussed in detail, and a simulation with its complete mathematical formalism is also presented. Moreover, experimental cortisol detection tests were performed for a detection range of 0.01 to 100 ng/mL, attaining a logarithmic sensitivity of 0.65 ± 0.02 nm/log(ng/mL) with a limit of detection (LOD) of 1.46 ng/mL. Additionally, an investigation of signal processing is also discussed, with the main issues addressed in order to highlight the best way to extract the sensing information from the spectra measured with a D-shaped sensor.

Tunable and Sensitive Detection of Cortisol Using Anisotropic Phosphorene with a Surface Plasmon Resonance Technique: Numerical Investigation

Tunable and ultrasensitive surface plasmon resonance (SPR) sensors are highly desirable for monitoring stress hormones such as cortisol, a steroid hormone formed in the human body’s adrenal glands. This paper describes the detection of cortisol using a bimetallic SPR sensor based on a highly anisotropic two-dimensional material, i.e., phosphorene. Thicknesses of bi-metal layers, such as copper (Cu) and nickel (Ni), are optimized to achieve strong SPR excitation. The proposed sensor is rotated in-plane with a rotation angle (φ) around the z-axis to obtain the phosphorene anisotropic behavior. The performance parameters of the sensor are demonstrated in terms of higher sensitivity (347.78 °/RIU), maximum angular figure of merit (FOM* = 1780.3), and finer limit of detection (0.026 ng/mL). Furthermore, a significant penetration depth (203 nm) is achieved for the proposed sensor. The obtained results of the above parameters indicate that the proposed sensor outperforms the previously reported papers in the literature on cortisol detection using the SPR technique.

Optical Biomedical Diagnostics Using Lab-on-Fiber Technology: A Review

Point-of-care and in-vivo bio-diagnostic tools are the current need for the present critical scenarios in the healthcare industry. The past few decades have seen a surge in research activities related to solving the challenges associated with precise on-site bio-sensing. Cutting-edge fiber optic technology enables the interaction of light with functionalized fiber surfaces at remote locations to develop a novel, miniaturized and cost-effective lab on fiber technology for bio-sensing applications. The recent remarkable developments in the field of nanotechnology provide innumerable functionalization methodologies to develop selective bio-recognition elements for label free biosensors. These exceptional methods may be easily integrated with fiber surfaces to provide highly selective light-matter interaction depending on various transduction mechanisms. In the present review, an overview of optical fiber-based biosensors has been provided with focus on physical principles used, along with the functionalization protocols for the detection of various biological analytes to diagnose the disease. The design and performance of these biosensors in terms of operating range, selectivity, response time and limit of detection have been discussed. In the concluding remarks, the challenges associated with these biosensors and the improvement required to develop handheld devices to enable direct target detection have been highlighted.

Molecularly Imprinted Polymers in Diagnostics: Accessing Analytes in Biofluids

Bio-applied molecularly imprinted polymers (MIPs) are biomimetic materials with tailor-made synthetic recognition sites, mimicking biological counterparts known for their sensitive and selective analyte detection. MIPs, specifically designed for biomarker analysis...

Immunosensing Based on Optical Fiber Technology: Recent Advances

The evolution of optical fiber technology has revolutionized a variety of fields, from optical transmission to environmental monitoring and biomedicine, given their unique properties and versatility. For biosensing purposes, the light guided in the fiber core is exposed to the surrounding media where the analytes of interest are detected by different techniques, according to the optical fiber configuration and biofunctionalization strategy employed. These configurations differ in manufacturing complexity, cost and overall performance. The biofunctionalization strategies can be carried out directly on bare fibers or on coated fibers. The former relies on interactions between the evanescent wave (EW) of the fiber and the analyte of interest, whereas the latter can comprise plasmonic methods such as surface plasmon resonance (SPR) and localized SPR (LSPR), both originating from the interaction between light and metal surface electrons. This review presents the basics of optical fiber immunosensors for a broad audience as well as the more recent research trends on the topic. Several optical fiber configurations used for biosensing applications are highlighted, namely uncladded, U-shape, D-shape, tapered, end-face reflected, fiber gratings and special optical fibers, alongside practical application examples. Furthermore, EW, SPR, LSPR and biofunctionalization strategies, as well as the most recent advances and applications of immunosensors, are also covered. Finally, the main challenges and an outlook over the future direction of the field is presented.

A Disposable Printed Liquid Gate Graphene Field Effect Transistor for a Salivary Cortisol Test

Circadian rhythm of salivary cortisol is of clinical significance, tracking salivary cortisol in domicile is welcomed by both doctor and patient, due to its merits of noninvasion, ease of sampling, and free-of-stress response. Here, we present a portable salivary cortisol test setup based on a liquid gate graphene field effect transistor (Lg-GFET) for the first time. In this work, the Lg-GFET was prepared by the printing technology and exploited as a sensitive material. In the procedures of device preparation, the modified liquid exfoliation method and direct-ink-write technology were utilized for synthesizing the graphene ink and printing Lg-GFETs; then, the as-prepared Lg-GFETs were decorated and functionalized by tetrakis(4-carboxyphenyl) porphyrin and the cortisol aptamer, successively. Their sensitivity, selectivity, and robustness are seriously examined. The test results indicate that the sensors have good linear sensitivities over a seven-log analyte concentration range (0.01 to 10⁴ nM) and the anti-interference ability to distinguish from the substancess with similar chemical structures. Moreover, the conceptual application for tracking circadian rhythm was carried out successfully. Conclusively, the proposed flexible Lg-GFET-based salivary cortisol detection platform can satisfy the requirements of the salivary cortisol's assay for instant detection. Additionally, it also provides an alternative solution for developing similar household medical appliances.

Non-Invasive Electrochemical Biosensors Operating in Human Physiological Fluids

Non-invasive healthcare technologies are an important part of research and development nowadays due to the low cost and convenience offered to both healthcare receivers and providers. This work overviews the recent advances in the field of non-invasive electrochemical biosensors operating in secreted human physiological fluids, viz. tears, sweat, saliva, and urine. Described electrochemical devices are based on different electrochemical techniques, viz. amperometry, coulometry, cyclic voltammetry, and impedance spectroscopy. Challenges that confront researchers in this exciting area and key requirements for biodevices are discussed. It is concluded that the field of non-invasive sensing of biomarkers in bodily fluid is highly convoluted. Nonetheless, if the drawbacks are appropriately addressed, and the pitfalls are adroitly circumvented, the approach will most certainly disrupt current clinical and self-monitoring practices.

Current methods for stress marker detection in saliva

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Introduction of relevant biomarkers in stress conditions.

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Reference ranges of biomarkers in normal conditions.

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Saliva as easy-accessible specimen.

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Review of analytical methods for biomarker determination in saliva.

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Possibilities for design of point-of-care devices.

Stress and stress-related diseases are leading to drastic consequences in private and professional life. Therefore, the need for stress prevention strategies is of personal and economic interest. Especially during the recent period related to covid-19 outbreak and lock-down, an ongoing discussion of increasing stress etiology is reported. Biomarker analysis may help to assist diagnosis and classification of stress-related diseases and therefore support therapeutical decisions. Due to its non-invasive sampling, the analysis of saliva has become highly attractive compared to the detection methods in other specimen. This review article summarizes the status of research, innovative approaches, and trends. Scientific literature published since 2011 was excerpted with concentration on the detection of up to seven promising marker substances. Most often reported cortisol represents the currently best evaluated stress marker, while norepinephrine (noradrenaline) or its metabolite 3-methoxy-4-hydroxyphenylglycol is also a quite commonly considered stress marker. Other complementary stress marker candidates are testosterone, dehydroepiandrosterone (DHEA) and its sulfonated analogue DHEA-S, alpha-amylase, secretory immunoglobulin A, and chromogranin A. Several working groups are researching in the field of stress marker detection to develop reliable, fast, and affordable methods. Analytical methods reported mainly focused on immunological and electrochemical as well as chromatographic methods hyphenated to mass spectrometric detection to yield the required detection limits.

Improving the width of lossy mode resonances in a reflection configuration D-shaped fiber by nanocoating laser ablation

The full width at half maximum (FWHM) of lossy mode resonances (LMRs) in the optical spectrum depends on the homogeneity of the thin film deposited. In this Letter, a method for improving the FWHM is applied for an LMR generated by a D-shaped optical fiber in reflection configuration. For this purpose, three samples with different attenuation were deposited with DC sputtering thin films of SnO_2-x, and a further controlled immersion of the samples in water was performed. A laser-cleaner method was used to improve the FWHM characteristics of one of the samples from 106 to 53 nm. This improvement can be applied to thin-film-based sensors where there is a problem with the inhomogeneity of the coating thickness. Moreover, with this technique, it was proved that a coated length of just 3-4 mm permits the generation of an LMR, with implications for the miniaturization of the final device.

On The Application of SiO2/SiC Grating on Ag for High-Performance Fiber Optic Plasmonic Sensing of Cortisol Concentration

This paper reports on high-accuracy simulation of a grating structure based fiber optic plasmonic sensor for salivary cortisol sensing. Gratings of SiO2 and SiC (one at a time) in combination with a thin Ag layer are considered to be in direct contact with analyte medium (solutions containing different concentrations of cortisol) considering that the groove regions are also filled with analyte. The optimization of Ag layer thickness is carried out to achieve maximum power loss (PL) corresponding to cortisol concentration variation. The variation of PL (in dB) spectra with the angle of incidence (α) is the sensing mechanism of the proposed scheme. Sensing performance is extensively analyzed in terms of sensitivity, limit-of-detection (LOD) and figure-of-merit (FOM) that incorporates both the sensitivity and the width of the corresponding PL curves. While the sensitivity and FOM values are significantly large, the results also reveal that in angular interrogation mode (AIM), an average LOD of 9.9 pg/mL and 9.8 pg/mL is obtained for SiO2 and SiC-based sensor designs, respectively. When the intensity interrogation method (IIM) in place of AIM is considered, an average LOD of 22.6 fg/mL and 68.17 fg/mL is obtained for SiO2 and SiC-based sensor designs, respectively. LOD (with IIM, in particular) is considerably better than the present-state-of-art related to cortisol monitoring. Pragmatic model for possible practical implementation of sensor scheme is also discussed. The involvement of optical fiber in the proposed sensor design makes it possible to implement it as a flexible sensor or for wearable solution for cortisol detection via sweat monitoring as well as for measuring cortisol level in aquaculture tanks where concentration levels are much lower than 10 ng/mL.

A Comprehensive Review: Materials for the Fabrication of Optical Fiber Refractometers Based on Lossy Mode Resonance

Lossy mode resonance based sensors have been extensively studied in recent years. The versatility of the lossy mode resonance phenomenon has led to the development of sensors based on different configurations that make use of a wide range of materials. The coating material is one of the key elements in the performance of a refractometer. This review paper intends to provide a global view of the wide range of coating materials available for the development of lossy mode resonance based refractometers.

A multichannel system integrating molecularly imprinted conductive polymers for ultrasensitive voltammetric determination of four steroid hormones in urine

This work reports on a modularized electrochemical method for the determination of the hormones cortisol, progesterone, testosterone and 17β-estradiol in urine. These hormones were employed as templates when generating molecular imprints from aniline and metanilic acid by electropolymerization on the surface of screen-printed electrodes. The electrically conductive imprint was characterized by SEM, AFM and cyclic voltammetry. A four-channel system was then established to enable simultaneous determination of the hormones by cyclic voltammetry. The detection limits for cortisol, progesterone, testosterone and 17β-estradiol are as low as 2, 2.5, 10 and 9 ag·mL^-1 (for S/N = 3). Graphical abstract A four-channel system was established to enable simultaneous determination of 4 steroid hormones by cyclic voltammetry and by using moleculalry imprinted polymers.

Saliva, a Magic Biofluid Available for Multilevel Assessment and a Mirror of General Health-A Systematic Review

Background: Saliva has been recently proposed as an alternative to classic biofluid analyses due to both availability and reliability regarding the evaluation of various biomarkers. Biosensors have been designed for the assessment of a wide spectrum of compounds, aiding in the screening, diagnosis, and monitoring of pathologies and treatment efficiency. This literature review aims to present the development in the biosensors research and their utility using salivary assessment. Methods: a comprehensive literature search has been conducted in the PubMed database, using the keywords “saliva” and “sensor”. A two-step paper selection algorithm was devised and applied. Results: The 49 papers selected for the present review focused on assessing the salivary biomarkers used in general diseases, oral pathologies, and pharmacology. The biosensors proved to be reliable tools for measuring the salivary levels of biochemical metabolic compounds such as glucose, proteinases and proteins, heavy metals and various chemical compounds, microorganisms, oncology markers, drugs, and neurotransmitters. Conclusions: Saliva is a biofluid with a significant clinical applicability for the evaluation and monitoring of a patient’s general health. Biosensors designed for assessing a wide range of salivary biomarkers are emerging as promising diagnostic or screening tools for improving the patients’ quality of life.

Molecularly Imprinted Polymers in Electrochemical and Optical Sensors

Molecular imprinting is the process of template-induced formation of specific recognition sites in a polymer. Synthetic receptors prepared using molecular imprinting possess a unique combination of properties such as robustness, high affinity, specificity, and low-cost production, which makes them attractive alternatives to natural receptors. Improvements in polymer science and nanotechnology have contributed to enhanced performance of molecularly imprinted polymer (MIP) sensors. Encouragingly, recent years have seen an increase in high-quality publications describing MIP sensors for the determination of biomolecules, drugs of abuse, and explosives, driving toward applications of this technology in medical and forensic diagnostics. This review aims to provide a focused overview of the latest achievements made in MIP-based sensor technology, with emphasis on research toward real-life applications.

Imprinted Oxide and MIP/Oxide Hybrid Nanomaterials for Chemical Sensors †

The oxides of transition, post-transition and rare-earth metals have a long history of robust and fast responsive recognition elements for electronic, optical, and gravimetric devices. A wide range of applications successfully utilized pristine or doped metal oxides and polymer-oxide hybrids as nanostructured recognition elements for the detection of biologically relevant molecules, harmful organic substances, and drugs as well as for the investigative process control applications. An overview of the selected recognition applications of molecularly imprinted sol-gel phases, metal oxides and hybrid nanomaterials composed of molecularly imprinted polymers (MIP) and metal oxides is presented herein. The formation and fabrication processes for imprinted sol-gel layers, metal oxides, MIP-coated oxide nanoparticles and other MIP/oxide nanohybrids are discussed along with their applications in monitoring bioorganic analytes and processes. The sensor characteristics such as dynamic detection range and limit of detection are compared as the performance criterion and the miniaturization and commercialization possibilities are critically discussed.

Performance analysis of zinc oxide-implemented lossy mode resonance-based optical fiber refractive index sensor utilizing thin film/nanostructure

A detailed primeval study on the lossy mode resonance (LMR) behavior of zinc oxide (ZnO)-coated optical fiber as a refractive index sensor is carried out. Theoretical evaluation predicts ZnO as a good choice for the LMR-based chemical and gas sensor operating in the visible region of the electromagnetic spectrum. To confirm, the optical fiber probe has been fabricated with an optimized film thickness of ZnO over an unclad core of fiber and characterized. Additionally, an LMR-based nanosensor platform utilizing ZnO has also been investigated to find the compatibility of a nanotechnological LMR sensor. The nanostructured LMR sensors have shown enhanced sensitivity in comparison to a bulk layered probe.

High Sensitivity Refractometer Based on Reflective Smf-Small Diameter No Core Fiber Structure

A high sensitivity refractive index sensor based on a single mode-small diameter no core fiber structure is proposed. In this structure, a small diameter no core fiber (SDNCF) used as a sensor probe, was fusion spliced to the end face of a traditional single mode fiber (SMF) and the end face of the SDNCF was coated with a thin film of gold to provide reflective light. The influence of SDNCF diameter and length on the refractive index sensitivity of the sensor has been investigated by both simulations and experiments, where results show that the diameter of SDNCF has significant influence. However, SDNCF length has limited influence on the sensitivity. Experimental results show that a sensitivity of 327 nm/RIU (refractive index unit) has been achieved for refractive indices ranging from 1.33 to 1.38, which agrees well with the simulated results with a sensitivity of 349.5 nm/RIU at refractive indices ranging from 1.33 to 1.38.

Highly sensitive and selective erythromycin nanosensor employing fiber optic SPR/ERY imprinted nanostructure: Application in milk and honey

An erythromycin (ERY) detection method is proposed using the fiber optic core decorated with the coatings of silver and an over layer of ERY imprinted nanoparticles. Synthesis of ERY imprinted nanoparticles is carried out using miniemulsion method. The operating range of the sensor is observed to be from 1.62×10^-3 to 100µM while the sensor possesses the linear response for ERY concentration range from 0.1 to 5µM. The sensing method shows a maximum sensitivity of 205nm/µM near ERY concentration of 0.01µM. The detection limit and the quantification limit of the sensor are found to be 1.62×10^-3µM and 6.14×10^-3µM, respectively. The sensor's applicability in real samples is also examined and is found to be in good agreement for the industrial application. The sensor possesses numerous advantages like fast response time (<15s), simple, low cost, highly selective along with abilities towards online monitoring and remote sensing of analyte.