Fluorescence-based biosensors

Vertasile ferritin nanocages: Applications in detection and bioimaging

Food safety and human health remain significant concerns in the food industry. Detecting food contaminants and diagnosing diseases are critical aspects. Ferritin, an iron storage protein widely found in nature, offers unique advantages. Its hollow protein nanocage structure, distinct interfaces, hydrophobic or hydrophilic channels, and B-C loop regions recognized by transferrin receptor 1 make ferritin versatile for detecting heavy metals, free radicals, and bioimaging both in vitro and in vivo. This review summarizes ferritin's general characteristics, its specific properties as biosensors, and its applications in food safety and in vivo imaging. It emphasizes not only ferritin's role in detecting heavy metals like mercury and chemical hazards but also its potential in early diagnosing chronic diseases such as tumors, macrophages, and kidney diseases. Further research into ferritin promises advancements in enhancing food safety and improving human health diagnostics.

Integration of secreted signaling molecule sensing on cell monitoring platforms: a critical review

Monitoring cell secretion in complex microenvironments is crucial for understanding cellular behavior and advancing physiological and pathological research. While traditional cell culture methods, including organoids and spheroids, provide valuable models, real-time monitoring of cell secretion of signaling molecules remains challenging. Integrating advanced monitoring technologies into these systems often disrupts the delicate balance of the microenvironment, making it difficult to achieve sensitivity and specificity. This review explored recent strategies for integrating the monitoring of cell secretion of signaling molecules, crucial for understanding and replicating cell microenvironments, within cell culture platforms, addressing challenges such as non-adherent cell models and the focus on single-cell methodologies. We highlight advancements in biosensors, microfluidics, and three-dimensional culture methods, and discuss their potential to enhance real-time, multiplexed cell monitoring. By examining the advantages, limitations, and future prospects of these technologies, we aim to contribute to the development of integrated systems that facilitate comprehensive cell monitoring, ultimately advancing biological research and pharmaceutical development.

Fabrication of a low-cost benchtop optical imager for quantum dot microarray-based stress biomarker detection

We report on a simplified optical imager to detect the presence of a stress biomarker protein, namely the Heat shock protein 90 (Hsp90). The imager consists of two elements the optical unit and the sensor, which is a custom-made biochip. Measurement is based on the masking of the streptavidin conjugated quantum dot's (Sav-QDs) fluorescence when Hsp90 attaches to it via biotinylated antibodies (Ab). The masking effect was directly proportional to the Hsp90 concentration. The cost-efficient benchtop imager developed comprises a CMOS sensor, standard optical lenses, and a narrow bandpass filter for optically eliminating background fluorescence. This approach is promising for the realization of cheap, robust, and reliable point-of-care detection systems for various biomarker analyses.

Advances in electrochemical-optical dual-mode biosensors for detection of environmental pathogens

Electrochemical techniques are commonly used to analyze and screen various environmental pathogens. When used in conjunction with other optical recognition methods, it can extend the sensing range, lower the detection limit, and offer mutual validation. Nowadays, electrochemical-optical dual-mode biosensors have ensured the accuracy of test results by integrating two signals into one, indicating their potential use in primary food safety quantitative assays and screening tests. Particularly, visible optical signals from electrochemical/colorimetric dual-mode biosensors could meet the demand for real-time screening of microbial pathogens. While electrochemical-optical dual-mode probes have been receiving increasing attention, there is limited emphasis on the design approaches for sensors intended for microbial pathogens. Here, we review the recent progress in the merging of optical and electrochemical techniques, including fluorescence, colorimetry, surface plasmon resonance (SPR), and surface enhanced Raman spectroscopy (SERS). This study particularly emphasizes the reporting of various sensing performances, including sensing principles, types, cutting-edge design approaches, and applications. Finally, some concerns and upcoming advancements in dual-mode probes are briefly outlined.

Sensors for in situ monitoring of oral and dental health parameters in saliva

OBJECTIVES

The oral cavity is an easily accessible unique environment and open system which is influenced by the oral fluids, microbiota, and nutrition. Little is known about the kinetics and dynamics of metabolic processes at the intraoral surfaces. Real-time monitoring of salivary biomarkers, e.g., glucose, lactate, fluoride, calcium, phosphate, and pH with intraoral sensors is therefore of major interest. The aim of this review is to overview the existing literature for intraoral saliva sensors.

MATERIALS AND METHODS

A comprehensive literature search was performed to review the most relevant studies on intraoral saliva sensor technology.

RESULTS

There is limited literature about the in situ saliva monitoring of salivary biomarkers. Bioadhesion and biofouling processes at the intraoral surfaces limit the performances of the sensors. Real-time, long-term, and continuous intraoral measurement of salivary metabolites remains challenging and needs further investigation as only few well-functioning sensors have been developed until today. Until now, there is no sensor that measures reliably beyond hours for any analyte other than glucose.

CONCLUSIONS

Saliva's complex and dynamic structure as well as bioadhesion are key challenges and should be addressed in the future developments. Consequently, more studies that focus particularly on biofouling processes and interferential effects of the salivary matrix components on sensor surfaces are required.

CLINICAL RELEVANCE

By monitoring fluids in the oral cavity, as the entrance to the digestive system, extensive information can be obtained regarding the effects of foods and preventive agents on the oral microbiota and the tooth surfaces. This may lead to a better understanding of strategies to modulate oral and general health.

Quantification of Polymer Surface Degradation Using Fluorescence Spectroscopy

One solution to minimizing plastic pollution is to improve reuse and recycling strategies. Recycling, however, is limited by the overall degradation of plastics being used, and current techniques for monitoring this plastic degradation fail to observe this in its early stages, which is key for optimizing reusability. This research seeks to develop an inexpensive, reproducible, and nondestructive technique for monitoring degradation of polyethylene (PE) and polypropylene (PP) materials using Nile red as a fluorescent probe. Changes in Nile red's fluorescence spectra were observed upon exposure to stained, aged PE and PP samples. As the surface hydrophobicity of the plastic decreases, Nile red's fluorescence signal undergoes a corresponding signal shift to longer wavelengths (lower energy). The trends seen in the fluorescent profile were related to more commonly used measurements of plastic degradation, namely, the carbonyl index from infrared spectroscopy and bulk crystallinity from calorimetry. Results demonstrate clear trends in fluorescence spectra shifts as related to the chemical and physical changes to the plastics, with trends dependent on the polymer type but independent of polymer film thickness. The strength of this technique is divided into two defined fits of the fluorescence signal; one fit characterizes the degradation throughout the whole range of degradative oxidation and the other is tailored to provide insight into the early stages of degradation. Overall, this work establishes a characterization tool that assesses the extent of plastics' degradation, which may ultimately impact our ability to recover plastics and minimize plastic waste.

Fluorescence-Based Portable Assays for Detection of Biological and Chemical Analytes

Fluorescence-based detection techniques are part of an ever-expanding field and are widely used in biomedical and environmental research as a biosensing tool. These techniques have high sensitivity, selectivity, and a short response time, making them a valuable tool for developing bio-chemical assays. The endpoint of these assays is defined by changes in fluorescence signal, in terms of its intensity, lifetime, and/or shift in spectrum, which is monitored using readout devices such as microscopes, fluorometers, and cytometers. However, these devices are often bulky, expensive, and require supervision to operate, which makes them inaccessible in resource-limited settings. To address these issues, significant effort has been directed towards integrating fluorescence-based assays into miniature platforms based on papers, hydrogels, and microfluidic devices, and to couple these assays with portable readout devices like smartphones and wearable optical sensors, thereby enabling point-of-care detection of bio-chemical analytes. This review highlights some of the recently developed portable fluorescence-based assays by discussing the design of fluorescent sensor molecules, their sensing strategy, and the fabrication of point-of-care devices.

Label-free laser spectroscopy for respiratory virus detection: A review

Infectious diseases are among the most severe threats to modern society. Current methods of virus infection detection based on genome tests need reagents and specialized laboratories. The desired characteristics of new virus detection methods are noninvasiveness, simplicity of implementation, real-time, low cost and label-free detection. There are two groups of methods for molecular biomarkers' detection and analysis: (i) a sample physical separation into individual molecular components and their identification, and (ii) sample content analysis by laser spectroscopy. Variations in the spectral data are typically minor. It requires the use of sophisticated analytical methods like machine learning. This review examines the current technological level of laser spectroscopy and machine learning methods in applications for virus infection detection.

Graphene quantum dots: synthesis, properties, and applications to the development of optical and electrochemical sensors for chemical sensing

GQDs exhibits exceptional electrochemical activity owing to their active edge sites that make them very attractive for biosensing applications. However, their use in the design of new biosensing devices for application to the detection and quantification of toxins, pathogens, and clinical biomarkers has so far not investigated in detail. In this regard, herein we provide a detailed review on various methodologies employed for the synthesis of GQDs, including bottom-up and top-down approaches, with a special focus on their applications in biosensing via fluorescence, photoluminescence, chemiluminescence, electrochemiluminescence, fluorescence resonance energy transfer, and electrochemical techniques. We believe that this review will shed light on the critical issues and widen the applications of GQDs for the design of biosensors with improved analytical response for future applications. HIGHLIGHTS: • Properties of GQDs play a critical role in biosensing applications. • Synthesis of GQDs using top-down and bottom-up approaches is discussed comprehensively. • Overview of advancements in GQD-based sensors over the last decade. • Methods for the design of selective and sensitive GQD-based sensors. • Challenges and opportunities for future GQD-based sensors.

Interfacing DNA nanotechnology and biomimetic photonic complexes: advances and prospects in energy and biomedicine

Self-assembled photonic systems with well-organized spatial arrangement and engineered optical properties can be used as efficient energy materials and as effective biomedical agents. The lessons learned from natural light-harvesting antennas have inspired the design and synthesis of a series of biomimetic photonic complexes, including those containing strongly coupled dye aggregates with dense molecular packing and unique spectroscopic features. These photoactive components provide excellent features that could be coupled to multiple applications including light-harvesting, energy transfer, biosensing, bioimaging, and cancer therapy. Meanwhile, nanoscale DNA assemblies have been employed as programmable and addressable templates to guide the formation of DNA-directed multi-pigment complexes, which can be used to enhance the complexity and precision of artificial photonic systems and show the potential for energy and biomedical applications. This review focuses on the interface of DNA nanotechnology and biomimetic photonic systems. We summarized the recent progress in the design, synthesis, and applications of bioinspired photonic systems, highlighted the advantages of the utilization of DNA nanostructures, and discussed the challenges and opportunities they provide.

Recent developments on nanomaterial-based optical biosensor as potential Point-of-Care Testing (PoCT) probe in carcinoembryonic antigen detection: A review

For the past decades, several cancer biomarkers have been exploited for rapid and accurate prognosis or diagnosis purposes. In this review, the optical biosensor is targeted for carcinoembryonic antigen (CEA) detection. The CEA level is a prominent parameter currently used in clinical cases for the prognosis of cancer-related diseases. Many nanomaterial-based biosensors are invented as alternatives for the commonly used enzyme-linked immunosorbent assays (ELISA) immunoassay method in CEA detection as the traditional approach but they possess certain drawbacks such as tedious procedure, high technical demand, and costly. Nevertheless, the effort appears to be wasted as none of them are being actualised. Generally, the sensor function was carried out by converting bio-signals generated upon the interface of the receptor into light signals. These sensors were popular due to specific advantages such as sensitivity, being free from chemical and electromagnetic interferences, wide dynamic range, and being easy to be monitored. The features of PoC diagnostics are discussed and associated with the various applications of colorimetric-based and chemiluminescent-based biosensors. The roles of nanomaterials in each application were also summarised by comparing the modification, incubation period, lowest detection limit (LOD) and linear range of detection amount. The challenges and future perspectives were highlighted at the end of the review.

New Insights for Biosensing: Lessons from Microbial Defense Systems

Microorganisms have gained defense systems during the lengthy process of evolution over millions of years. Such defense systems can protect them from being attacked by invading species (e.g., CRISPR-Cas for establishing adaptive immune systems and nanopore-forming toxins as virulence factors) or enable them to adapt to different conditions (e.g., gas vesicles for achieving buoyancy control). These microorganism defense systems (MDS) have inspired the development of biosensors that have received much attention in a wide range of fields including life science research, food safety, and medical diagnosis. This Review comprehensively analyzes biosensing platforms originating from MDS for sensing and imaging biological analytes. We first describe a basic overview of MDS and MDS-inspired biosensing platforms (e.g., CRISPR-Cas systems, nanopore-forming proteins, and gas vesicles), followed by a critical discussion of their functions and properties. We then discuss several transduction mechanisms (optical, acoustic, magnetic, and electrical) involved in MDS-inspired biosensing. We further detail the applications of the MDS-inspired biosensors to detect a variety of analytes (nucleic acids, peptides, proteins, pathogens, cells, small molecules, and metal ions). In the end, we propose the key challenges and future perspectives in seeking new and improved MDS tools that can potentially lead to breakthrough discoveries in developing a new generation of biosensors with a combination of low cost; high sensitivity, accuracy, and precision; and fast detection. Overall, this Review gives a historical review of MDS, elucidates the principles of emulating MDS to develop biosensors, and analyzes the recent advancements, current challenges, and future trends in this field. It provides a unique critical analysis of emulating MDS to develop robust biosensors and discusses the design of such biosensors using elements found in MDS, showing that emulating MDS is a promising approach to conceptually advancing the design of biosensors.

Nanostructured Carbons: towards Soft-Bioelectronics, Biosensing and Theraputic Applications

Recently, nanostructured carbon-based soft bioelectronics and biosensors have received tremendous attention due to their outstanding physical and chemical properties. The ultrahigh specific surface area, high flexibility, lightweight, high electrical conductivity, and biocompatibility of 1D and 2D nanocarbons, such as carbon nanotubes (CNT) and graphene, are advantageous for bioelectronics applications. These materials improve human life by delivering therapeutic advancements in gene, tumor, chemo, photothermal, immune, radio, and precision therapies. They are also utilized in biosensing platforms, including optical and electrochemical biosensors to detect cholesterol, glucose, pathogenic bacteria (e. g., coronavirus), and avian leucosis virus. This review summarizes the most recent advancements in bioelectronics and biosensors by exploiting the outstanding characteristics of nanocarbon materials. The synthesis and biocompatibility of nanocarbon materials are briefly discussed. In the following sections, applications of graphene and CNTs for different therapies and biosensing are elaborated. Finally, the key challenges and future perspectives of nanocarbon materials for biomedical applications are highlighted.

A Photosensitized Singlet Oxygen (1O2) Toolbox for Bio-Organic Applications: Tailoring 1O2 Generation for DNA and Protein Labelling, Targeting and Biosensing

Singlet oxygen (¹O₂) is the excited state of ground, triplet state, molecular oxygen (O₂). Photosensitized ¹O₂ has been extensively studied as one of the reactive oxygen species (ROS), responsible for damage of cellular components (protein, DNA, lipids). On the other hand, its generation has been exploited in organic synthesis, as well as in photodynamic therapy for the treatment of various forms of cancer. The aim of this review is to highlight the versatility of ¹O_2, discussing the main bioorganic applications reported over the past decades, which rely on its production. After a brief introduction on the photosensitized production of ¹O₂, we will describe the main aspects involving the biologically relevant damage that can accompany an uncontrolled, aspecific generation of this ROS. We then discuss in more detail a series of biological applications featuring ¹O₂ generation, including protein and DNA labelling, cross-linking and biosensing. Finally, we will highlight the methodologies available to tailor ¹O₂ generation, in order to accomplish the proposed bioorganic transformations while avoiding, at the same time, collateral damage related to an untamed production of this reactive species.

Imidazo-pyridine-based zinc(II) complexes as fluorescent hydrogen sulfide probes

In this work we explore the interaction of HS^- with a family of fluorescent zinc complexes. In particular we selected a family of complexes with N,O-bidentate ligands aiming at assessing whether the zinc-chelating ligand plays a role in influencing the reactivity of HS^- with the complexes under investigation. Different experiments, performed by diverse spectroscopic techniques, provide evidence that HS^- binds the zinc center of all the complexes included in this study. The results highlight the potential of the devised systems to be used as HS^-/H₂S fluorescent sensors via a coordinative-based approach. To shed light on the species formed in solution when HS^-/H₂S interacts with the title complexes and aiming to rationalize the photophysical properties of the sensing constructs, we performed a computational analysis based on the time dependent density functional theory (TD-DFT). Preliminary bio-imaging experiments were also performed and the results indicate the potential of this class of compounds as probes for the detection of H₂S in living cells.

Liquid Biopsy-Based Biosensors for MRD Detection and Treatment Monitoring in Non-Small Cell Lung Cancer (NSCLC)

Globally, non-small cell lung cancer (NSCLC) is the leading cause of cancer deaths. Despite advancements in chemotherapy and targeted therapies, the 5-year survival rate has remained at 16% for the past forty years. Minimal residual disease (MRD) is described as the existence of either isolated tumour cells or circulating tumour cells in biological liquid of patients after removal of the primary tumour without any clinical signs of cancer. Recently, liquid biopsy has been promising as a non-invasive method of disease monitoring and treatment guidelines as an MRD marker. Liquid biopsy could be used to detect and assess earlier stages of NSCLC, post-treatment MRD, resistance to targeted therapies, immune checkpoint inhibitors (ICIs) and tumour mutational burden. MRD surveillance has been proposed as a potential marker for lung cancer relapse. Principally, biosensors provide the quantitative analysis of various materials by converting biological functions into quantifiable signals. Biosensors are usually operated to detect antibodies, enzymes, DNA, RNA, extracellular vesicles (EVs) and whole cells. Here, we present a category of biosensors based on the signal transduction method for identifying biosensor-based biomarkers in liquid biopsy specimens to monitor lung cancer treatment.

Ultrasensitive fluorescence detection of antitumor drug methotrexate based on a terbium-doped silica dendritic probe

A novel strategy was developed for the detection of methotrexate (MTX) via the quenching effect of MTX on the fluorescence intensity of terbium-doped dendritic silica particles (Tb@KCC-1). The fluorescence intensity of Tb@KCC-1 can be effectively quenched by MTX at 546 nm under an excitation wavelength of 233 nm. The quenched fluorescence is proportional to the amount of MTX in both plasma and exhaled breath condensate (EBC) samples. Under the optimal conditions, the linear dynamic ranges of the developed method were 44 nM to 2.2 μM for EBC, 44 nM to 0.22 μM and 0.22-2.2 μM for plasma samples. The limit of detection (LOD) and limit of quantification (LOQ) in both plasma and EBC media are 35 and 116 nM, respectively. The developed method has the benefits of fast analysis time, simple approach, high specificity, and sensitivity for the detection of MTX in both media. This nanoprobe has been successfully utilized for the quantification of MTX in patients' plasma and spiked EBC samples, proving the applicability of the nanoprobe for MTX detection in real samples.

Characterization of Two NMN Deamidase Mutants as Possible Probes for an NMN Biosensor

Nicotinamide mononucleotide (NMN) is a key intermediate in the nicotinamide adenine dinucleotide (NAD+) biosynthesis. Its supplementation has demonstrated beneficial effects on several diseases. The aim of this study was to characterize NMN deamidase (PncC) inactive mutants to use as possible molecular recognition elements (MREs) for an NMN-specific biosensor. Thermal stability assays and steady-state fluorescence spectroscopy measurements were used to study the binding of NMN and related metabolites (NaMN, Na, Nam, NR, NAD, NADP, and NaAD) to the PncC mutated variants. In particular, the S29A PncC and K61Q PncC variant forms were selected since they still preserve the ability to bind NMN in the micromolar range, but they are not able to catalyze the enzymatic reaction. While S29A PncC shows a similar affinity also for NaMN (the product of the PncC catalyzed reaction), K61Q PncC does not interact significantly with it. Thus, PncC K61Q mutant seems to be a promising candidate to use as specific probe for an NMN biosensor.

Recent Advances in Nanotechnology-Based Biosensors Development for Detection of Arsenic, Lead, Mercury, and Cadmium

Heavy metals cause considerable environmental pollution due to their extent and non-degradability in the environment. Analysis and trace levels of arsenic, lead, mercury, and cadmium as the most toxic heavy metals show that they can cause various hazards in humans' health. To achieve rapid, high-sensitivity methods for analyzing ultra-trace amounts of heavy metals in different environmental and biological samples, novel biosensors have been designed with the participation of strategies applied in nanotechnology. This review attempted to investigate the novel, sensitive, efficient, cost-benefit, point of care, and user-friendly biosensors designed to detect these heavy metals based on functional mechanisms. The study's search strategies included examining the primary databases from 2015 onwards and various keywords focusing on heavy metal biosensors' performance and toxicity mechanisms. The use of aptamers and whole cells as two important bio-functional nanomaterials is remarkable in heavy metal diagnostic biosensors' bioreceptor design. The application of hybridized nanomaterials containing a specific physicochemical function in the presence of a suitable transducer can improve the sensing performance to achieve an integrated detection system. Our study showed that in addition to both labeled and label-free detection strategies, a wide range of nanoparticles and nanocomposites were used to modify the biosensor surface platform in the detection of heavy metals. The detection limit and linear dynamic range as an essential characteristic of superior biosensors for the primary toxic metals are studied. Furthermore, the perspectives and challenges facing the design of heavy metal biosensors are outlined. The development of novel biosensors and the application of nanotechnology, especially in real samples, face challenges such as the capability to simultaneously detect multiple heavy metals, the interference process in complex matrices, the efficiency and stability of nanomaterials implemented in various laboratory conditions.

Cocrystal engineering of pharmaceutical solids: therapeutic potential and challenges

This highlight presents an overview of pharmaceutical cocrystal production and its potential in reviving problematic properties of drugs in different dosage forms. The challenges and future outlook of its translational development are discussed.

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.

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

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

Fluorescent salen-type Zn(II) Complexes As Probes for Detecting Hydrogen Sulfide and Its Anion: Bioimaging Applications

In this work, we investigate the mode of interaction of a family of fluorescent zinc complexes with HS- and H2S. Different experiments, performed by diverse spectroscopic techniques, provide evidence that HS- binds the zinc center of all the complexes under investigation. Treatment with neutral H2S exhibits a markedly different reactivity which indicates selectivity for HS- over H2S of the systems under investigation. Striking color changes, visible to the naked eye, occur when treating the systems with HS- or by an H2S flow. Accordingly, also the fluorescence is modulated by the presence of HS-, with the possible formation of multiple adducts. The results highlight the potential of the devised systems to be implemented as HS-/H2S colorimetric and fluorescent sensors. Bioimaging experiments indicate the potential of using this class of compounds as probes for the detection of H2S in living cells.

Structural features of the glutamate-binding protein from Corynebacterium glutamicum

L-glutamate (Glu) is the major excitatory transmitter in mammalian brain. Inadequate concentration of Glu in the brain correlates to mood disorder. In industry, Glu is used as a flavour enhancer in food and in foodstuff processing. A high concentration of Glu has several effects on human health such as hypersensitive effects, headache and stomach pain. The presence of Glu in food can be detected by different analytical methods based on chromatography, or capillary electrophoresis or amperometric techniques. We have isolated and characterized a glutamate-binding protein (GluB) from the Gram-positive bacteria Corynebacterium glutamicum. Together with GluC protein, GluD protein and the cytoplasmic protein GluA, GluB permits the transport of Glu in/out of cell. In this study, we have investigated the binding features of GluB as well as the effect of temperature on its structure both in the absence and in the presence of Glu. The results have showed that GluB has a high affinity and selectivity versus Glu (nanomolar range) and the presence of the ligand induces a higher thermal stability of the protein structure.

Nanoscale Technologies in Highly Sensitive Diagnosis of Cardiovascular Diseases

Cardiovascular diseases (CVD) are the leading cause of death and morbidity in the world and are a major contributor to healthcare costs. Although enormous progress has been made in diagnosing CVD, there is an urgent need for more efficient early detection and the development of novel diagnostic tools. Currently, CVD diagnosis relies primarily on clinical symptoms based on molecular imaging (MOI) or biomarkers associated with CVDs. However, sensitivity, specificity, and accuracy of the assay are still challenging for early-stage CVDs. Nanomaterial platform has been identified as a promising candidate for improving the practical usage of diagnostic tools because of their unique physicochemical properties. In this review article, we introduced cardiac biomarkers and imaging techniques that are currently used for CVD diagnosis. We presented the applications of various nanotechnologies on diagnosis within cardiac immunoassays (CIAs) and molecular imaging. We also summarized and compared different cardiac immunoassays based on their sensitivities and working ranges of biomarkers.

The origin of the longer wavelength emission in 2-(4-fluorophenylamino)-5-(2,4-dihydroxybenzeno)-1,3,4-thiadiazole and its analogue 2-phenylamino-5-(2-hydroxybenzono)-1,3,4-thiadiazole† ‡

In aqueous solution, 2-(4-fluorophenylamino)-5-(2,4-dihydroxybenzeno)-1,3,4-thiadiazole (FABT) was found to emit dual emission and the longer wavelength emission was assigned to the combination of aggregation and conformational change. In a number of molecules that possess an intramolecular hydrogen bond between the proton donor and the acceptor, the longer wavelength emission is often observed due to the emission from the tautomer formed by excited state intramolecular proton transfer (ESIPT). Therefore, an analogue of FABT, 2-phenylamino-5-(2-hydroxybenzono)-1,3,4-thiadiazole (PHBT), was synthesized to determine the origin of the longer wavelength emission. The luminescence of PHBT and its methoxy derivatives was studied and compared with that of FABT. Theoretical calculations were also performed on both FABT and PHBT. Based on the experimental and theoretical investigations, the nonexistence of the keto tautomer in the ground state and the origin of the longer wavelength emission are divulged.

Towards Portable Nanophotonic Sensors

A range of nanophotonic sensors composed of different materials and device configurations have been developed over the past two decades. These sensors have achieved high performance in terms of sensitivity and detection limit. The size of onchip nanophotonic sensors is also small and they are regarded as a strong candidate to provide the next generation sensors for a range of applications including chemical and biosensing for point-of-care diagnostics. However, the apparatus used to perform measurements of nanophotonic sensor chips is bulky, expensive and requires experts to operate them. Thus, although integrated nanophotonic sensors have shown high performance and are compact themselves their practical applications are limited by the lack of a compact readout system required for their measurements. To achieve the aim of using nanophotonic sensors in daily life it is important to develop nanophotonic sensors which are not only themselves small, but their readout system is also portable, compact and easy to operate. Recognizing the need to develop compact readout systems for onchip nanophotonic sensors, different groups around the globe have started to put efforts in this direction. This review article discusses different works carried out to develop integrated nanophotonic sensors with compact readout systems, which are divided into two categories; onchip nanophotonic sensors with monolithically integrated readout and onchip nanophotonic sensors with separate but compact readout systems.

Design and Manufacturing of a Disposable, Cyclo-Olefin Copolymer, Microfluidic Device for a Biosensor †

This contribution outlines the design and manufacturing of a microfluidic device implemented as a biosensor for retrieval and detection of bacteria RNA. The device is fully made of Cyclo-Olefin Copolymer (COC), which features low auto-fluorescence, biocompatibility and manufacturability by hot-embossing. The RNA retrieval was carried on after bacteria heat-lysis by an on-chip micro-heater, whose function was characterized at different working parameters. Carbon resistive temperature sensors were tested, characterized and printed on the biochip sealing film to monitor the heating process. Off-chip and on-chip processed RNA were hybridized with capture probes on the reaction chamber surface and identification was achieved by detection of fluorescence tags. The application of the mentioned techniques and materials proved to allow the development of low-cost, disposable albeit multi-functional microfluidic system, performing heating, temperature sensing and chemical reaction processes in the same device. By proving its effectiveness, this device contributes a reference to show the integration potential of fully thermoplastic devices in biosensor systems.

Development of novel metabolite-responsive transcription factors via transposon-mediated protein fusion

Naturally evolved metabolite-responsive biosensors enable applications in metabolic engineering, ranging from screening large genetic libraries to dynamically regulating biosynthetic pathways. However, there are many metabolites for which a natural biosensor does not exist. To address this need, we developed a general method for converting metabolite-binding proteins into metabolite-responsive transcription factors-Biosensor Engineering by Random Domain Insertion (BERDI). This approach takes advantage of an in vitro transposon insertion reaction to generate all possible insertions of a DNA-binding domain into a metabolite-binding protein, followed by fluorescence activated cell sorting to isolate functional biosensors. To develop and evaluate the BERDI method, we generated a library of candidate biosensors in which a zinc finger DNA-binding domain was inserted into maltose binding protein, which served as a model well-studied metabolite-binding protein. Library diversity was characterized by several methods, a selection scheme was deployed, and ultimately several distinct and functional maltose-responsive transcriptional biosensors were identified. We hypothesize that the BERDI method comprises a generalizable strategy that may ultimately be applied to convert a wide range of metabolite-binding proteins into novel biosensors for applications in metabolic engineering and synthetic biology.

DNA methylation detection: recent developments in bisulfite free electrochemical and optical approaches

DNA methylation is one of the significant epigenetic modifications involved in mammalian development as well as in the initiation and progression of various diseases like cancer. Over the past few decades, an enormous amount of research has been carried out for the quantification of DNA methylation in the mammalian genome. Earlier, most of these methodologies used bisulfite treatment. However, the low conversion, false reading, longer assay time and complex chemical reaction are the common limitations of this method that hinder their application in routine clinical screening. Thus, as an alternative to bisulfite conversion-based DNA methylation detection, numerous bisulfite-free methods have been proposed. In this regard, electrochemical biosensors have gained much attention in recent years for being highly sensitive yet cost-effective, portable, and simple to operate. On the other hand, biosensors with optical readouts enable direct real time detection of biological molecules and are easily adaptable to multiplexing. Incorporation of electrochemical and optical readouts into bisulfite free DNA methylation analysis is paving the way for the translation of this important biomarker into standard patient care. In this review, we provide a critical overview of recent advances in the development of electrochemical and optical readout based bisulfite free DNA methylation assays.

Fundamentals and commercial aspects of nanobiosensors in point-of-care clinical diagnostics

Among various problems faced by mankind, health-related concerns are prevailing since long which are commonly found in the form of infectious diseases and different metabolic disorders. The clinical cure and management of such abnormalities are greatly dependent on the availability of their diagnoses. The conventional diagnostics used for such purposes are extremely powerful; however, most of these are limited by time-consuming protocols and require higher volume of test sample, etc. A new evolving technology called "biosensor" in this context shows an enormous potential for an alternative diagnostic device, which constantly compliments the conventional diagnoses. In this review, we have summarized different kinds of biosensors and their fundamental understanding with various state-of-the-art examples. A critical examination of different types of biosensing mechanisms is also reported highlighting the advantages of electrochemical biosensors for its great potentials in next-generation commercially viable modules. In recent years, a number of nanomaterials are extensively used to enhance not only the performance of biosensing mechanism, but also obtain robust, cheap, and fabrication-friendly durable mechanism. Herein, we have summarized the importance of nanomaterials in biosensing mechanism, their syntheses as well as characterization techniques. Subsequently, we have discussed the probe fabrication processes along with various techniques for assessing its analytical performances and potentials for commercial viability.

Engineering Modular Biosensors to Confer Metabolite-Responsive Regulation of Transcription

Efforts to engineer microbial factories have benefitted from mining biological diversity and high throughput synthesis of novel enzymatic pathways, yet screening and optimizing metabolic pathways remain rate-limiting steps. Metabolite-responsive biosensors may help to address these persistent challenges by enabling the monitoring of metabolite levels in individual cells and metabolite-responsive feedback control. We are currently limited to naturally evolved biosensors, which are insufficient for monitoring many metabolites of interest. Thus, a method for engineering novel biosensors would be powerful, yet we lack a generalizable approach that enables the construction of a wide range of biosensors. As a step toward this goal, we here explore several strategies for converting a metabolite-binding protein into a metabolite-responsive transcriptional regulator. By pairing a modular protein design approach with a library of synthetic promoters and applying robust statistical analyses, we identified strategies for engineering biosensor-regulated bacterial promoters and for achieving design-driven improvements of biosensor performance. We demonstrated the feasibility of this strategy by fusing a programmable DNA binding motif (zinc finger module) with a model ligand binding protein (maltose binding protein), to generate a novel biosensor conferring maltose-regulated gene expression. This systematic investigation provides insights that may guide the development of additional novel biosensors for diverse synthetic biology applications.

Alizarin red S–zinc(ii) fluorescent ensemble for selective detection of hydrogen sulphide and assay with an H2S donor

A new Alizarin Red S based fluorescent ensemble ARS–Zn(ii) for the selective detection of H₂S is reported. It exhibited H₂S selectivity and also detected H₂S in serum under physiological conditions. The calculated detection limit of H₂S was 92 nM.

Amino acid transport in thermophiles: characterization of an arginine-binding protein from Thermotoga maritima. 3. Conformational dynamics and stability

Arginine-binding protein from Thermotoga maritima (TmArgBP) is a 27.7 kDa protein possessing the typical two domain structure of the periplasmic binding protein family. The protein is characterized by high specificity and affinity for binding a single molecule of l-arginine. In this work, the effect of temperature and/or guanidine hydrochloride on structure and stability of the protein in the absence and in the presence of l-arginine has been investigated by differential scanning calorimetry, far-UV circular dichroism and intrinsic tryptophan phosphorescence and fluorescence. The results revealed that TmArgBP undergoes an irreversible one-step thermal unfolding process in a cooperative mode. The TmArgBP melting temperature was recorded at 115 °C. The presence of l-arginine did not change the protein secondary structure content as well as the intrinsic phosphorescence and fluorescence protein properties, even if it increases the structural stability of the protein. The obtained results are discussed in combination with a detailed inspection of the three-dimensional structure of the protein.