Fiber-optic biosensor based on the laccase immobilization on silica-functionalized fluorescent carbon dots for the detection of dopamine and multi-color imaging applications in neuroblastoma cells

Fluorescent Reporter-Based Fiber Optic Probe for Continuous Detection of Antibodies

Measurement of antibody and antibody fusion protein concentration is vital for process development and manufacturing. Continuous, in-line monitoring of antibody concentration could be useful in a variety of applications, such as controlling the loading of protein A columns to prevent breakthrough, monitoring bioreactor titer, and detecting leaks past ultrafiltration/diafiltration membranes. Molecule-specific monitoring techniques are advantageous for antibody detection in cell culture fluid in the presence of complex process impurities. Here we report a continuous in-line, real-time IgG monitoring platform using a fiber-optic biosensor with a replaceable sensor tip covalently functionalized with a fluor-labeled protein consisting of a pentamer of the Z domain (a more stable form of the B domain) of protein A. The sensor demonstrates concentration-dependent fluorescence enhancement in the presence of human IgG (0.01-0.75 g/L), with consistent signals during five runs each with 1 and 0.1 g/L IgG, and maintains its specificity in the presence of Chinese hamster ovary (CHO) cell culture fluid. A 5% breakthrough of a typical 10 g/L load would be detected in less than 20 s in a flowing stream emerging from a protein A column without prior sample preparation. This sensor platform may be suitable for monitoring IgG and fragment, crystallizable (Fc) fusion proteins in diverse upstream and downstream bioprocess applications.

Reliability of Multi-Emissive Carbon Quantum Dots for Multiplexing; Assessing the Figures of Merit

Incredible properties of quantum dots (QDs) have once again been acclaimed with this year's (2023) Nobel prize in chemistry. On the other hand, the invention of multicolour molecular imaging of cell surface receptors for tumour diagnosis by Koyama and group has opened up a new era in diagnostics. Among them carbon quantum dots (CQDs) are interesting class of fluorescent nanomaterials, superior in terms of low toxicity, high solubility and biocompatibility along with simple and cost-effective synthesis processes unlike the traditional metal chalcogenide or perovskite quantum dots. Multi emissive fluorescence property of these carbon quantum dots are very useful in multiplex sensing. Their excellent biocompatibility and low toxicity have attracted researchers to use them extensively for biosensing and imaging of multiple analytes at a time. Core state emission from π-domains and surface state emissions of functional groups surrounding CQDs play a major role in achieving the multicolour emissions and this review discusses the various strategies used to achieve desired multi colour emissions, yet preserving their stability, non-interactive emissive states and quantum yields. Their fine tuning via variation in temperature, pH, time, and heteroatom doping has been comprehensively discussed. A thorough history compared to a list of characteristics for creating effective multicolour CQDs will point us in the proper route. This minireview also assesses the electronic band structure of these multicolour CQDs, their stability with respect to multi emissions, photoluminescence quantum yields, approaches employed for tunability of their optical band gaps, and also enhancement of carrier lifetimes, to arrive at conclusions on the reliability of these materials for multiplexing. The mechanisms namely chemical coupling, FRET, On-Off, Ab-antigen interactions involved in sensing mechanisms involving these materials are analysed in depth. Ultimately, the present obstacles and future directions for the use of these CQDs in sensing applications are discussed.

Advancements in Cerebrospinal Fluid Biosensors: Bridging the Gap from Early Diagnosis to the Detection of Rare Diseases

Cerebrospinal fluid (CSF) is a body fluid that can be used for the diagnosis of various diseases. However, CSF collection requires an invasive and painful procedure called a lumbar puncture (LP). This procedure is applied to any patient with a known risk of central nervous system (CNS) damage or neurodegenerative disease, regardless of their age range. Hence, this can be a very painful procedure, especially in infants and elderly patients. On the other hand, the detection of disease biomarkers in CSF makes diagnoses as accurate as possible. This review aims to explore novel electrochemical biosensing platforms that have impacted biomedical science. Biosensors have emerged as techniques to accelerate the detection of known biomarkers in body fluids such as CSF. Biosensors can be designed and modified in various ways and shapes according to their ultimate applications to detect and quantify biomarkers of interest. This process can also significantly influence the detection and diagnosis of CSF. Hence, it is important to understand the role of this technology in the rapidly progressing field of biomedical science.

Optical fiber biosensors toward in vivo detection

This review takes stock of the various optical fiber-based biosensors that could be used for in vivo applications. We discuss the characteristics that biosensors must have to be suitable for such applications and the corresponding transduction modes. In particular, we focus on optical fiber biosensors based on fluorescence, evanescent wave, plasmonics, interferometry, and Raman phenomenon. The operational principles, implemented solutions, and performances are described and debated. The different sensing configurations, such as the side- and tip-based fiber biosensors, are illustrated, and their adaptation for in vivo measurements is discussed. The required implementation of multiplexed biosensing on optical fibers is shown. In particular, the use of multi-fiber assemblies, one of the most optimal configurations for multiplexed detection, is discussed. Different possibilities for multiple localized functionalizations on optical fibers are presented. A final section is devoted to the practical in vivo use of fiber-based biosensors, covering regulatory, sterilization, and packaging aspects. Finally, the trends and required improvements in this promising and emerging field are analyzed and discussed.

An ultra-sensitive SARS-CoV-2 antigen optical biosensor based on angiotensin converting enzyme 2 (ACE-2) functionalized magnetic-fluorescent silica nanoparticles

This work reports on the design and synthesis of an angiotensin-converting enzyme 2 (ACE-2) functionalized magnetic fluorescent silica nanoparticles (Fe-FSNP) as a biosensing platform to detect severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antigen. Iron oxide (Fe3O4) nanoparticles were synthesized via ultrasonic-assisted coprecipitation and then coated with fluorescent silica nanoparticles (FSNP) through thesol-gelmethod forming the Fe-FSNP samples. Silica obtained from local geothermal powerplant was used in this work and Rhodamine B was chosen as the incorporated fluorescent dye, hence this reports for the first time ACE-2 was immobilized on the natural silica surface. The Fe-FSNP nanoparticle consists of a 18-25 nm magnetic core and a silica shell with a thickness of 30 nm as confirmed from the transmission electron microscopy image. Successful surface functionalization of the Fe-FSNP with ACE-2 as bioreceptor was conducted through hydrosylilation reaction and confirmed through the Fourier transform infrared spectroscopy. The detection of SARS-Cov-2 antigen by Fe-FSNP/ACE2 was measured through the change in its maximum fluorescence intensity at 588 nm where fluorescence- quenching had occurred. The biosensing platform showed a rapid response at 30 min with a linear range of 10-6to 10-2μg ml-1. The magnetic-fluorescent properties of the nanoparticle enables an ultra-sensitive detection of SARS-Cov-2 antigen with the limit of detection as low as 2 fg ml-1.

Breaking Barriers: Exploring Neurotransmitters through In Vivo vs. In Vitro Rivalry

Neurotransmitter analysis plays a pivotal role in diagnosing and managing neurodegenerative diseases, often characterized by disturbances in neurotransmitter systems. However, prevailing methods for quantifying neurotransmitters involve invasive procedures or require bulky imaging equipment, therefore restricting accessibility and posing potential risks to patients. The innovation of compact, in vivo instruments for neurotransmission analysis holds the potential to reshape disease management. This innovation can facilitate non-invasive and uninterrupted monitoring of neurotransmitter levels and their activity. Recent strides in microfabrication have led to the emergence of diminutive instruments that also find applicability in in vitro investigations. By harnessing the synergistic potential of microfluidics, micro-optics, and microelectronics, this nascent realm of research holds substantial promise. This review offers an overarching view of the current neurotransmitter sensing techniques, the advances towards in vitro microsensors tailored for monitoring neurotransmission, and the state-of-the-art fabrication techniques that can be used to fabricate those microsensors.

A review of the growing trend towards heteroatoms-doped carbon dots based on dopamine acting as a hybrid agent and detected analyte

Dopamine (DA) is a biomolecule that plays a critical part in the functioning of our brains by promoting motivation, maintaining focus, and altering mood. Excessive or low-level concentrations of DA in the human brain led to a dangerous neurological disorder. It is significantly important to trace the precise amount of DA to prevent such risky brain disease. Recently, heteroatoms-doped carbon dots (H-CDs) have attracted great attention for their capacity to detect biomolecules, metal ions, organic solvents, chemical dyes, etc. In this review, we have provided a comprehensive summary of the emerging trends in the heteroatom functional dopamine-doped carbon dots (DA-CDs), which are based on DA used as starting substances or functionalizing agents. Our analysis encompasses a detailed exploration of the synthetic methods, physical and chemical properties of carbon dots derived from dopamine, as well as their diverse range of applications. Additionally, we have also discussed the application of H-CDs in the dopmine detection by using various fluorescent, colorimetric, and electrochemical techniques.

Fluorescent-Based Neurotransmitter Sensors: Present and Future Perspectives

Neurotransmitters (NTs) are endogenous low-molecular-weight chemical compounds that transmit synaptic signals in the central nervous system. These NTs play a crucial role in facilitating signal communication, motor control, and processes related to memory and learning. Abnormalities in the levels of NTs lead to chronic mental health disorders and heart diseases. Therefore, detecting imbalances in the levels of NTs is important for diagnosing early stages of diseases associated with NTs. Sensing technologies detect NTs rapidly, specifically, and selectively, overcoming the limitations of conventional diagnostic methods. In this review, we focus on the fluorescence-based biosensors that use nanomaterials such as metal clusters, carbon dots, and quantum dots. Additionally, we review biomaterial-based, including aptamer- and enzyme-based, and genetically encoded biosensors. Furthermore, we elaborate on the fluorescence mechanisms, including fluorescence resonance energy transfer, photon-induced electron transfer, intramolecular charge transfer, and excited-state intramolecular proton transfer, in the context of their applications for the detection of NTs. We also discuss the significance of NTs in human physiological functions, address the current challenges in designing fluorescence-based biosensors for the detection of NTs, and explore their future development.

Enzymatic Electrochemical/Fluorescent Nanobiosensor for Detection of Small Chemicals

The detection of small molecules has attracted enormous interest in various fields, including the chemical, biological, and healthcare fields. In order to achieve such detection with high accuracy, up to now, various types of biosensors have been developed. Among those biosensors, enzymatic biosensors have shown excellent sensing performances via their highly specific enzymatic reactions with small chemical molecules. As techniques used to implement the sensing function of such enzymatic biosensors, electrochemical and fluorescence techniques have been mostly used for the detection of small molecules because of their advantages. In addition, through the incorporation of nanotechnologies, the detection property of each technique-based enzymatic nanobiosensors can be improved to measure harmful or important small molecules accurately. This review provides interdisciplinary information related to developing enzymatic nanobiosensors for small molecule detection, such as widely used enzymes, target small molecules, and electrochemical/fluorescence techniques. We expect that this review will provide a broad perspective and well-organized roadmap to develop novel electrochemical and fluorescent enzymatic nanobiosensors.

Bioremediation of multifarious pollutants using laccase immobilized on magnetized and carbonyldiimidazole-functionalized cellulose nanofibers

An easily recyclable biocatalyst (Lac@CDI-MCNFs) was synthesized by immobilizing laccase on rice straw-derived carbonyldiimidazole mediated magnetized cellulose nanofibers (MCNFs). Lac@CDI-MCNFs were utilized for bioremediation of cefixime antibiotic (CT), carbofuran pesticide (CF) and safranin O dye (SO) via oxidation-reduction reactions in wastewater. MCNFs provided enhanced pH, temperature and storage stability to laccase and allowed reusability for up to 25 cycles with mere 20 % decline in efficacy. The Lac@CDI-MCNFs effectively degraded 98.2 % CT and 96.8 % CF into benign metabolites within 20 h and completely degraded SO in just 7 h. Response surface modelling (RSM) was employed based on the Box Behnken Design to evaluate the effect of various parameters i.e. pH, catalyst dosage and the pollutants concentration which was further validated with experimental studies. The degradation products were identified using LCMS, which allowed the degradation pathway of the pollutants to be determined. The degradation of all pollutants followed first- order kinetics with rate constants of 0.1775, 0.0832 and 0.958 h^-1 and half-life of 3.9, 5.0 and 0.723 h for CT, CF and SO, respectively. Lac@CDI-MCNFs was demonstrated to be an effective catalyst for the degradation of multifarious pollutants.

Smart green CQD@SiO2 hybrid coated optical fiber manifesting dual versatile absorptive and MIP features towards epinephrine detection

For the first time, in this study, a novel optical fiber biosensor is proposed and developed via coating only one smart functional layer of silica-supported carbon dots realizing the concepts of both lossy mode resonance (LMR) and molecularly imprinted polymer (MIP) for epinephrine detection. The carbon quantum dots (CQDs) are prepared using a green synthesis method and then treated with a molecularly imprinted polymer (MIP) strategy. Under ultrasonic irradiation, a SiO2 shell was stabilized on the surface of the CQDs to graft and to provide the LMR/MIP functional layer onto the curved optical fiber surface. Accurate structural and morphological characterization confirmed the carbon quantum dot agents and also the SiO2 supporting shells on the optical fiber, while spectroscopic analysis confirms the formation of the imprinted polymer and desirable absorbance characteristics. The experimental and numerical sensing studies revealed that the proposed sensing probe allows the rapid adsorption/desorption of epinephrine to the sensing films and highly permeable coating for studying the influence of effective parameters. Under the optimal experimental conditions, the sensitivity of the proposed LMR-based optical fiber sensor is reported to be 0.37 nm μM-1 with a correlation coefficient of 0.99. So, sensitive detection of epinephrine at a low concentration can be guaranteed with a 0.72 mM LOD.

Optically Active Nanomaterials and Its Biosensing Applications-A Review

This article discusses optically active nanomaterials and their optical biosensing applications. In addition to enhancing their sensitivity, these nanomaterials also increase their biocompatibility. For this reason, nanomaterials, particularly those based on their chemical compositions, such as carbon-based nanomaterials, inorganic-based nanomaterials, organic-based nanomaterials, and composite-based nanomaterials for biosensing applications are investigated thoroughly. These nanomaterials are used extensively in the field of fiber optic biosensing to improve response time, detection limit, and nature of specificity. Consequently, this article describes contemporary and application-based research that will be of great use to researchers in the nanomaterial-based optical sensing field. The difficulties encountered during the synthesis, characterization, and application of nanomaterials are also enumerated, and their future prospects are outlined for the reader's benefit.

Vinyl-functionalized polyphenolic-carbon dot-based fluorometric turn-off-on biosensor for the dual detection of mercury and cysteine and their in vivo sensing in zebrafish larvae

The fluorometric turn-off-on biosensor was developed for the ultra-sensitive detection of mercury (Hg²⁺) and cysteine (Cys) utilizing the highly fluorescent carbon dots (CDs). Herein, the sophisticated low-temperature reflux-mediated reaction was adopted using precursors namely citric acid (CA) and polyphenolic kaempferol (KMP) by using dimethylformamide (DMF) as a solvent. The resulting CDs (i.e., CKCDs) were in the highly negative charged groups (-OH) presented with a bright-orange fluorescence. These CKCDs were functionalized with 4-vinylaniline (4-VA) by employing EDC/NHS coupling reaction, which switched its photoluminescence (PL) towards the strong-blue colored emission and termed as V-CKCDs. The functionalized V-CKCDs can be capable enough to detect mercury via the strong electrostatic interactions between positively charged Hg²⁺ cations and negatively charged anions (-OH groups). Hence, an adequate fluorescence quenching was observed in V-CKCDs with the lowest concentrations of Hg²⁺ around 0.5 μM. Significantly, after adding the complex of V-CKCDs-Hg²⁺ to the Cys, the fluorescence enhancement was observed. This might be attributed from the strong interactions between Hg²⁺ in the fluorescence sensing system and thiol (-SH) moieties from the Cys. The developed V-CKCDs are highly sensitive for detecting Hg²⁺ and Cys, which showed detection limits of 10.6 and 42. 48 nM, respectively. Also, the in vivo studies were investigated in zebrafish larvae using V-CKCDs for the detection of Hg²⁺ and Cys. The V-CKCDs were investigated in the real water samples and human serum to detect Hg²⁺ and Cys, respectively.

Advances in Novel Nanomaterial-Based Optical Fiber Biosensors-A Review

This article presents a concise summary of current advancements in novel nanomaterial-based optical fiber biosensors. The beneficial optical and biological properties of nanomaterials, such as nanoparticle size-dependent signal amplification, plasmon resonance, and charge-transfer capabilities, are widely used in biosensing applications. Due to the biocompatibility and bioreceptor combination, the nanomaterials enhance the sensitivity, limit of detection, specificity, and response time of sensing probes, as well as the signal-to-noise ratio of fiber optic biosensing platforms. This has established a practical method for improving the performance of fiber optic biosensors. With the aforementioned outstanding nanomaterial properties, the development of fiber optic biosensors has been efficiently promoted. This paper reviews the application of numerous novel nanomaterials in the field of optical fiber biosensing and provides a brief explanation of the fiber sensing mechanism.

Recent Advances in the Development of Laccase-Based Biosensors via Nano-Immobilization Techniques

Monitoring phenolic compounds is critical in the environmental, food, and medical sectors. Among many recent advanced detection platforms, laccase-based biosensing platforms gave very rapid, effective, online, and in situ sensing of phenolic compounds. In laccase-based biosensors, laccase immobilization techniques have a vital role. However, a detailing of the advancements in laccase immobilization techniques employed in laccase-based biosensors is lacking in the literature. Thus, in this review, we assessed how the nano-immobilization techniques shaped the laccase biosensing platforms. We discussed novel developments in laccase immobilization techniques such as entrapment, adsorption, cross-linking, and covalent over new nanocomposites in laccase biosensors. We made a comprehensive assessment based on the current literature for future perspectives of nano-immobilized laccase biosensors. We found the important key areas toward which future laccase biosensor research seems to be heading. These include 1. A focus on the development of multi-layer laccase over electrode surface, 2. The need to utilize more covalent immobilization routes, as they change the laccase specificity toward phenolic compounds, 3. The advancement in polymeric matrices with electroconductive properties, and 4. novel entrapment techniques like biomineralization using laccase molecules. Thus, in this review, we provided a detailed account of immobilization in laccase biosensors and their feasibility in the future for the development of highly specific laccase biosensors in industrial, medicinal, food, and environmental applications.

Overview and emerging trends in optical fiber aptasensing

Optical fiber biosensors have attracted growing interest over the last decade and quickly became a key enabling technology, especially for the detection of biomarkers at extremely low concentrations and in small volumes. Among the many and recent fiber-optic sensing amenities, aptamers-based sensors have shown unequalled performances in terms of ease of production, specificity, and sensitivity. The immobilization of small and highly stable bioreceptors such as DNA has bolstered their use for the most varied applications e.g., medical diagnosis, food safety and environmental monitoring. This review highlights the recent advances in aptamer-based optical fiber biosensors. An in-depth analysis of the literature summarizes different fiber-optic structures and biochemical strategies for molecular detection and immobilization of receptors over diverse surfaces. In this review, we analyze the features offered by those sensors and discuss about the next challenges to be addressed. This overview investigates both biochemical and optical parameters, drawing the guiding lines for forthcoming innovations and prospects in this ever-growing field of research.

Coconut Carbon Dots: Progressive Large-Scale Synthesis, Detailed Biological Activities and Smart Sensing Aptitudes towards Tyrosine

In the recent era, carbon dots (C-dots) have been extensively considered as a potential tool in drug delivery analysis. However, there have been fewer reports in the literature on their application in the sensing of amino acids. As part of our ongoing research on coconut-husk-derived C-dots, we synthesized C-dots under different temperature conditions and utilized them in the field of amino acid sensing and found them to be highly selective and sensitive towards tyrosine. The detailed characterization of the prepared C-dots was carried out. The developed C-dots exhibit good values of quantum yield. BSA, HSA and glutamic acid were utilized to explore the binding efficiency of C-dots with biologically active components. Hemolysis, blood clotting index activity and cell viability assays using the prepared C-dots were evaluated and they were found to be biocompatible. Therefore, the C-dots described in this work have high potential to be utilized in the field of amino acid sensing, especially L-tyrosine. The limit of detection and the binding constant for the developed C-dots in the presence of tyrosine were found to be 0.96 nM and 296.38 nM-1, respectively. The efficiency of the developed C-dots was also investigated in the presence of various other amino acids and different water mediums in order to enhance the working scope of the developed sensors.

Highly effective enzymes immobilization on ceramics: Requirements for supports and enzymes

Enzyme immobilization is a well-known method for the improvement of enzyme reusability and stability. To achieve very high effectiveness of the enzyme immobilization, not only does the method of attachment need to be optimized, but the appropriate support must be chosen. The essential necessities addressed to the support applied for enzyme immobilization can be focused on the material features as well as on the stability and resistances in certain conditions. Ceramic membranes and nanoparticles are the most widespread supports for enzyme immobilization. Hence, the immobilization of enzymes on ceramic membrane and nanoparticles are summarized and discussed. The important properties of the supports are particle size, pore structure, active surface area, volume to surface ratio, type and number of reactive available groups, as well as thermal, mechanical, and chemical stability. The modifiers and the crosslinkers are crucial to the enzyme loading amount, the chemical and physical stability, and the reusability and catalytical activity of the immobilized enzymes. Therefore, the chemical and physical methods of modification of ceramic materials are presented. The most popular and used modifiers (e.g. APTES, CPTES, VTES) as well as activating agents (GA, gelatin, EDC and/or NHS) applied to the grafting process are discussed. Moreover, functional groups of enzymes are presented and discussed since they play important roles in the enzyme immobilization via covalent bonding. The enhanced physical, chemical, and catalytical properties of immobilized enzymes are discussed revealing the positive balance between the effectiveness of the immobilization process, preservation of high enzyme activity, its good stability, and relatively low cost.

Enzyme-free fluorescence determination of uric acid and trace Hg(II) in serum using Si/N doped carbon dots

A new fluorescence probe method for the detection of Hg(II) in serum was established, which has the detection limit of 3.57 nM and quantification limit of 5 nM, based on the electrostatic induced agglomeration quenching and complexation between Hg(II) and silicon-nitrogen-doped carbon nanodots (Si/N-CDs). Furthermore, the fluorescence probe also showed the satisfactory results in the determination of Hg(II) in human serum. Subsequently, take advantage of the uric acid (UA) to recover the fluorescence of the Si/N-CDs-Hg(II) complex probe, another enzyme-free ways to determine UA was developed. The complex probe can selectively detect the UA content in the 0.5-30 μM range, and its detection limit can reach 0.14 μM, which has successfully detected the UA in total serum, and the results were no significant difference comparing with the controls.

Enzyme (Single and Multiple) and Nanozyme Biosensors: Recent Developments and Their Novel Applications in the Water-Food-Health Nexus

The use of sensors in critical areas for human development such as water, food, and health has increased in recent decades. When the sensor uses biological recognition, it is known as a biosensor. Nowadays, the development of biosensors has been increased due to the need for reliable, fast, and sensitive techniques for the detection of multiple analytes. In recent years, with the advancement in nanotechnology within biocatalysis, enzyme-based biosensors have been emerging as reliable, sensitive, and selectively tools. A wide variety of enzyme biosensors has been developed by detecting multiple analytes. In this way, together with technological advances in areas such as biotechnology and materials sciences, different modalities of biosensors have been developed, such as bi-enzymatic biosensors and nanozyme biosensors. Furthermore, the use of more than one enzyme within the same detection system leads to bi-enzymatic biosensors or multi-enzyme sensors. The development and synthesis of new materials with enzyme-like properties have been growing, giving rise to nanozymes, considered a promising tool in the biosensor field due to their multiple advantages. In this review, general views and a comparison describing the advantages and disadvantages of each enzyme-based biosensor modality, their possible trends and the principal reported applications will be presented.