Magnetic colorimetric immunoassay for human interleukin-6 based on the oxidase activity of ceria spheres

Distance-based paper analytical device for multiplexed quantification of cytokine biomarkers using carbon dots integrated with molecularly imprinted polymer

This article introduces distance-based paper analytical devices (dPADs) integrated with molecularly imprinted polymers (MIPs) and carbon dots (CDs) for simultaneous quantification of cytokine biomarkers, namely C-reactive protein (CRP), tumor necrosis factor-alpha (TNF-α), and interleukin-6 (IL-6) in human biological samples for diagnosis of cytokine syndrome. Using fluorescent CDs and MIP technology, the dPAD exhibits high selectivity and sensitivity. Detection is based on fluorescence quenching of CDs achieved through the interaction of the target analytes with the MIP layer on the paper substrate. Quantitative analysis is easily accomplished by measuring the distance length of quenched fluorescence with a traditional ruler and naked eye readout enabling rapid diagnosis of cytokine syndrome and the underlying infection. Our sensor demonstrated linear ranges of 2.50-24.0 pg mL-1 (R2 = 0.9974), 0.25-3.20 pg mL-1 (R2 = 0.9985), and 1.50-16.0 pg mL-1 (R2 = 0.9966) with detection limits (LODs) of 2.50, 0.25, and 1.50 pg mL-1 for CRP, TNF-α, and IL-6, respectively. This sensor also demonstrated remarkable selectivity compared to a sensor employing a non-imprinted polymer (NIP), and precision with the highest relative standard deviation (RSD) of 5.14%. The sensor is more accessible compared to prior methods relying on expensive reagents and instruments and complex fabrication methods. Furthermore, the assay provided notable accuracy for monitoring these biomarkers in various human samples with recovery percentages ranging between 99.22% and 103.58%. By integrating microfluidic systems, nanosensing, and MIPs technology, our developed dPADs hold significant potential as a cost-effective and user-friendly analytical method for point-of-care diagnostics (POC) of cytokine-related disorders. This concept can be further extended to developing diagnostic devices for other biomarkers.

Ceria-Based Nanozymes in Point-of-Care Diagnosis: An Emerging Futuristic Approach for Biosensing

In recent years, there has been a notable increase in interest surrounding nanozymes due to their ability to imitate the functions and address the limitations of natural enzymes. The scientific community has been greatly intrigued by the study of nanoceria, primarily because of their distinctive physicochemical characteristics, which include a variety of enzyme-like activities, affordability, exceptional stability, and the ability to easily modify their surfaces. Consequently, nanoceria have found extensive use in various biosensing applications. However, the impact of its redox activity on the enzymatic catalytic mechanism remains a subject of debate, as conflicting findings in the literature have presented both pro-oxidant and antioxidant effects. Herein, we creatively propose a seesaw model to clarify the regulatory mechanism on redox balance and survey possible mechanisms of multienzyme mimetic properties of nanoceria. In addition, this review aims to showcase the latest advancements in this field by systematically discussing over 180 research articles elucidating the significance of ceria-based nanozymes in enhancing, downsizing, and enhancing the efficacy of point-of-care (POC) diagnostics. These advancements align with the ASSURED criteria established by the World Health Organization (WHO). Furthermore, this review also examines potential constraints in order to offer readers a concise overview of the emerging role of nanoceria in the advancement of POC diagnostic systems for future biosensing applications.

Recent Progresses in Optical Biosensors for Interleukin 6 Detection

Interleukin 6 (IL-6) is pleiotropic cytokine with pathological pro-inflammatory effects in various acute, chronic and infectious diseases. It is involved in a variety of biological processes including immune regulation, hematopoiesis, tissue repair, inflammation, oncogenesis, metabolic control, and sleep. Due to its important role as a biomarker of many types of diseases, its detection in small amounts and with high selectivity is of particular importance in medical and biological fields. Laboratory methods including enzyme-linked immunoassays (ELISAs) and chemiluminescent immunoassays (CLIAs) are the most common conventional methods for IL-6 detection. However, these techniques suffer from the complexity of the method, the expensiveness, and the time-consuming process of obtaining the results. In recent years, too many attempts have been conducted to provide simple, rapid, economical, and user-friendly analytical approaches to monitor IL-6. In this regard, biosensors are considered desirable tools for IL-6 detection because of their special features such as high sensitivity, rapid detection time, ease of use, and ease of miniaturization. In this review, current progresses in different types of optical biosensors as the most favorable types of biosensors for the detection of IL-6 are discussed, evaluated, and compared.

Highly Sensitive Photothermal Microfluidic Thread-Based Duplex Immunosensor for Point-of-Care Monitoring

Herein, we successfully developed a thread-based analytical device (μTAD) for simultaneous immunosensing of two biomolecules with attomolar sensitivity by using a photothermal effect. A photothermal effect exploits a strong light-to-heat energy conversion of plasmonic metallic nanoparticles at localized surface plasmon resonance. The key innovation is to utilize the cotton thread to realize this sensor and the use of chitosan modification for enhancing the microfluidic properties, for improving the efficiency of photothermal conversion, and for sensor stability. The developed μTAD sensor consists of (i) a sample zone, (ii) a conjugation zone coated with gold nanoparticles bound with an antibody (AuNPs-Ab2), and (iii) a test zone immobilized with a capture antibody (anti-Ab1). The prepared μTAD is assembled in a custom three-dimensional (3D) printed device which holds the laser for illumination and the thermometer for readout. The 3D-printed supportive device enhances signal response by focusing light and localizing the heat generated. For proof of concept, simultaneous sensing of two key stress and inflammation biomarkers, namely, cortisol and interleukin-6 (IL-6), are monitored using this technique. Under optimization, this device exhibited a detection linear range of 2.0-14.0 ag/mL (R2 = 0.9988) and 30.0-360.0 fg/mL (R2 = 0.9942) with a detection limit (LOD) of 1.40 ag/mL (∼3.86 amol/L) and 20.0 fg/mL (∼950.0 amol/L) for cortisol and IL-6, respectively. Furthermore, the analysis of both biomolecules in human samples indicated recoveries in the range of 98.8%-102.88% with the highest relative standard deviation being 3.49%, offering great accuracy and precision. These results are the highest reported sensitivity for these analytes using an immunoassay method. Our PT-μTAD strategy is therefore a promising approach for detecting biomolecules in resource-limited point-of-care settings.

An electrochemical paper-based hydrogel immunosensor to monitor serum cytokine for predicting the severity of COVID-19 patients

Analysis of cytokines levels in human serum is critical as it can be a "symptom diagnostic biomarker" in COVID-19, giving real-time information about human health status. Here, we present the construction and performance of a low-price immunosensor (∼US$0.428 per test) based on microfluidic paper-based system to detect cytokine for predicting the health status of COVID-19 patients. Interleukin-6 (IL-6) was selected as the detection model for the close relationship between IL-6 and COVID-19. The assay, which we integrated into foldable paper system, leverages the magnetic immunoassay, the streptavidin-horseradish peroxidase (HRP) associated with tetramethyl benzidine/hydrogen peroxide (TMB/H₂O₂) to amplify the signal for electrochemical readout. To improve the sensitivity of cytokine detection, a hybrid of gold nanoparticles (AuNPs) and polypyrrole (PPy) hydrogel was modified on the working electrode to increase the conductivity and improve the electron transfer rate. With our prototypic origami paper-based immunosensor operated in differential pulse voltammetry (DPV) mode, we achieved excellent results with a dynamic range from 5 to 1000 pg/mL and a lower detection limit (LOD) of 0.654 pg/mL. Furthermore, we evaluated the capability of the clinical application of the proposed immunosensor using human serum samples from a hospital. The results indicate that our proposed immunosensor has great potential in early diagnosing high-risk COVID-19 patients.

Distance-Based All-In-One Immunodevice for Point-of-Care Monitoring of Cytokine Interleukin-6

We report the development of a distance-based paper analytical device combined with a hydrophilic bridge valve (B-dPAD) as a quantitative immunoassay method to monitor human interleukin-6 (IL-6) in human samples. Our device design features (i) a circular sample inlet zone, (ii) a circular capture zone with immobilized anti-IL-6 (anti-Ab₁), and (iii) a detection zone channel coated with methylene blue (MB). Two hydrophilic valves are positioned between these three zones. IL-6 levels were determined quantitatively by measuring the extent of degradation of MB to a colorless product along the length of the detection zone channel. Following method optimization, we obtained a linear range from 0.05 to 25.0 pg/mL (R² = 0.9995) and a detection limit (LOD) of 0.05 pg/mL by the naked-eye readout. This is directly within the clinically relevant range. The system does not require any external instrumentation, and the bridge valves can be easily connected and disconnected by a minimally trained operator. The total analysis time is 35 min, significantly reduced from a typical ELISA assay, which takes around 1 h since the B-dPAD workflow circumvents washing steps. The device was tested for IL-6 quantification in human saliva and urine samples of volunteers, with no significant difference found between our method and the standard clinical laboratory method at 95% confidence levels. Recoveries ranged from 98 to 105% with the highest standard deviation at 3.9%. Our B-dPAD immunodevice is therefore a promising approach for rapid IL-6 monitoring in the context of point-of-care diagnostics and analysis in resource-limited settings.

Recent advances in nanomaterials-based optical sensors for detection of various biomarkers (inorganic species, organic and biomolecules)

This review briefly emphasizes the different detection approaches (electrochemical sensors, chemiluminescence, surface-enhanced Raman scattering), functional nanostructure materials (quantum dots, metal nanoparticles, metal nanoclusters, magnetic nanomaterials, metal oxide nanoparticles, polymer-based nanomaterials, and carbonaceous nanomaterials) and detection mechanisms. Further, this review emphasis on the integration of functional nanomaterials with optical spectroscopic techniques for the identification of various biomarkers (nucleic acids, glucose, uric acid, oxytocin, dopamine, ascorbic acid, bilirubin, spermine, serotonin, thiocyanate, Pb²⁺ , Cu²⁺ , Hg²⁺ , F^- , peptides, and cancer biomarkers (mucin 1, prostate specific antigen, carcinoembryonic antigen, CA15-3, human epidermal growth factor receptor 2, C-reactive protein, and interleukin-6). Analytical characteristics of nanomaterials-based optical sensors are summarized in Tables, providing the insights of nanomaterials-based optical sensors for biomarkers detection. Finally, the opportunities and challenges of nanomaterials-based optical analytical approaches for the detection of various biomarkers (inorganic, organic, biomolecules, peptides and proteins) are discussed.

Development of a new automated IL-6 immunoassay

OBJECTIVES

Quantitative detection of interleukin-6 (IL-6) in serum and plasma can help monitor immune responses and the development of acute inflammation to guide patient management. We developed an IL-6 immunoassay for use with the automated ARCHITECT system for detecting an increase in the inflammatory response.

METHODS

Immunized mouse sera were tested and selected B-cells were harvested for fusion with myeloma cells. A panel of monoclonal antibodies were produced, from which capture and detection monoclonal antibodies for the prototype IL-6 immunoassay were selected and screened on the ARCHITECT instrument. The antibody pair that most effectively captured and detected IL-6 was selected to develop a prototype IL-6 immunoassay. Calibrator and panel preparations using an internal recombinant IL-6 standard were compared to serum panels prepared with the IL-6 International Standard 89/548. Assay specificity and spike recovery were determined, and assay sensitivity was compared with the Roche EUA Elecsys IL-6 assay run on the cobas analyzer.

RESULTS

Twenty-one antibodies in 441 antibody pairs were screened. The prototype IL-6 assay showed high sensitivity with an estimated limit of detection of 0.317 pg/mL and limit of quantitation of <1.27. Spike recovery was 90%-110% in serum and plasma. The internal recombinant human IL-6 calibrator showed excellent stability for 63 days at 2-8 °C. The prototype IL-6 immunoassay was specific for IL-6, exhibited no cross reactivity to related cytokines and interleukins, and was 10-fold more sensitive than the Elecsys IL-6 assay.

CONCLUSIONS

The prototype ARCHITECT IL-6 automated immunoassay is a reliable and robust method for the quantitative determination of IL-6 in human serum and plasma.

Advances in Nanotechnology-Based Biosensing of Immunoregulatory Cytokines

Cytokines are a large group of small proteins secreted by immune and non-immune cells in response to external stimuli. Much attention has been given to the application of cytokines' detection in early disease diagnosis/monitoring and therapeutic response assessment. To date, a wide range of assays are available for cytokines detection. However, in specific applications, multiplexed or continuous measurements of cytokines with wearable biosensing devices are highly desirable. For such efforts, various nanomaterials have been extensively investigated due to their extraordinary properties, such as high surface area and controllable particle size and shape, which leads to their tunable optical emission, electrical, and magnetic properties. Different types of nanomaterials such as noble metal, metal oxide, and carbon nanoparticles have been explored for various biosensing applications. Advances in nanomaterial synthesis and device development have led to significant progress in pushing the limit of cytokine detection. This article reviews currently used methods for cytokines detection and new nanotechnology-based biosensors for ultrasensitive cytokine detection.

Development of quantum dot-based fluorescence lateral flow immunoassay strip for rapid and quantitative detection of serum interleukin-6

BACKGROUND

Interleukin-6 (IL-6) is an inflammatory factor that increases rapidly in response to infectious diseases including sepsis. The aim of this study is to develop a quantum dot (QD)-based fluorescence lateral flow immunoassay (LFIA) strip that can rapidly and accurately detect IL-6 levels.

METHODS

QD-based LFIA strips were fabricated by conjugating CdSe/ZnS QDs to the IL-6 antibody. Performance verification and clinical sample analysis were carried out to evaluate the newly developed strip.

RESULTS

QD-based LFIA strips were successfully fabricated. The test strip's linear range was 10-4000 pg/ml, with a linear correlation coefficient of R²  ≥ .959. The sensitivity of the test strip was 1.995 pg/ml. The recovery rate was 95.72%-102.63%, indicating satisfying accuracy. The coefficient of variation (CV) of the intra-assay was 2.148%-3.903%, while the inter-assay was 2.412%-5.293%, verifying the strip's high precision. The cross-reaction rates with various interleukins (IL-1α, IL-1β, IL-2, IL-4, and IL-8) and interferon-γ (IFN-γ) were all <0.1%. When the strip was placed in a 50°C oven for 1, 2, 3, and 4 weeks, the test results were not significantly altered compared to storage at room temperature. Furthermore, 200 clinical serum samples were analyzed to compare the strip with the Beckman chemiluminescence immunoassay (CLIA) kit, which revealed a high correlation (n = 200, R²  = .9971) for the detection of IL-6.

CONCLUSIONS

The QD-based test strip can rapidly and quantitatively detect IL-6 levels, thus meeting the requirement of point-of-care test (POCT) and showing excellent clinical prospects.

A highly sensitive and versatile transcription immunoassay using a DNA-encoding tandem repetitive light-up aptamer

Highly sensitive and accurate measurements of protein biomarkers are crucial for early diagnosis and disease monitoring. Here we report a versatile detection platform for sensitive detection of a protein biomarker using a tandem repeat Spinach aptamer DNA-based transcription immunoassay, which is a immunoassay combined with transcription-assisted Spinach RNA aptamer generation. We designed a DNA template encoding spa tandem repetitive Spinach sequence for enhanced generation of an RNA aptamer. The tandem repeated Spinach DNA template is consist of multiple monomeric units which is composed of T7 promoter, Spinach-2 and terminator. After in vitro transcription, the fluorescence signal from the 16R (nR, n = number of repeats) DNA template was enhanced up to ~ 15-fold compared to a single form (1R) DNA template. Using tandem repeat DNA, the proposed transcription immunoassay showed a limit of detection (LOD) of 37 aM, which is 10³-fold lower than that of the conventional enzyme-linked immunosorbent assay (ELISA). The results demonstrate substantial promise for the ultrasensitive detection of various biological analytes using simple ELISA techniques. The high sensitivity and reliability of the proposed transcription immunoassay offer great promise for clinical assays.

Biosensors: A novel approach to and recent discovery in detection of cytokines

Cytokines in tissues and physiological fluids can function as potentially suitable biomarkers. Cytokines are involved in stimulating different body responses including inflammatory response to external pathogens, regulating cell-to-cell communication, and maintaining tissue homeostasis. Consequently, cytokines are extensively used to monitor and predict disease progression and to track the outcome of patient treatment. The critical diagnosis of cytokine and chemokine biomarkers has been the focus of attention and it has been continuously directing the trajectory of related research to developing a novel sensing platform. Given the major challenges and constraints of the older identification methods including their high costs, low sensitivity, and high specificity, the development of biosensor technology as a simple and inexpensive tool with high sensitivity is quite attractive and interesting. The fundamental aim of this study is to present the state-of-the-art biosensor systems in order to detect different types of cytokines and to emphasize the role of these systems in the prevention, monitoring, and treatment of various cytokine-associated diseases.

Nanoparticle-based mobile biosensors for the rapid detection of sepsis biomarkers in whole blood

Detecting small variations in the levels of IL-6 is crucial for the early diagnosis of sepsis. To be useful in clinical decision-making, this requires detecting IL-6 rapidly in whole blood and with portable readers. Here we introduce immunosensors made of filter paper that use plasmonic nanoprobes to detect IL-6 rapidly in unprocessed blood with an unmodified smartphone. Key aspects of the biosensor fabrication were optimized in order to reduce the assay time without losing sensitivity. This included testing three bioconjugation routes for protein attachment to nanoprobes using gold nanoparticles covered with carboxylate or amine moieties, or polyvinylpyrrolidone (PVP), as starting materials, and using alternating layers of polyelectrolytes to bind the capture antibody to the paper substrate. Smartphone-based signal quantification was achieved with a custom-made app featuring a unique augmented reality guidance system that circumvents the need for smartphone attachments and automates all the steps involved in color quantification. The biosensors were able to detect IL-6 with a limit of detection of 0.1 pg mL-1 and a total assay time within 17 min. They could also detect an increase in IL-6 of only 12.5 pg mL-1 over basal levels in whole blood with 99% confidence. The high sensitivity and rapid turnaround time afforded by the optimized biosensors and the fully automated real-time densitometry app make our biosensors well suited for emergency healthcare situations such as the identification of potential sepsis cases.

Recent Advances in Electrochemical and Optical Biosensors Designed for Detection of Interleukin 6

Interleukin 6 (IL-6), being a major component of homeostasis, immunomodulation, and hematopoiesis, manifests multiple pathological conditions when upregulated in response to viral, microbial, carcinogenic, or autoimmune stimuli. High fidelity immunosensors offer real-time monitoring of IL-6 and facilitate early prognosis of life-threatening diseases. Different approaches to augment robustness and enhance overall performance of biosensors have been demonstrated over the past few years. Electrochemical- and fluorescence-based detection methods with integrated electronics have been subjects of intensive research due to their ability to offer a better signal-to-noise ratio, high specificity, ultra-sensitivity, and wide dynamic range. In this review, the pleiotropic role of IL-6 and its clinical significance is discussed in detail, followed by detection schemes devised so far for their quantitative analysis. A critical review on underlying signal amplification strategies and performance of electrochemical and optical biosensors is presented. In conclusion, we discuss the reliability and feasibility of the proposed detection technologies for commercial applications.

Implication of Magnetic Nanoparticles in Cancer Detection, Screening and Treatment

During the last few decades, magnetic nanoparticles have been evaluated as promising materials in the field of cancer detection, screening, and treatment. Early diagnosis and screening of cancer may be achieved using magnetic nanoparticles either within the magnetic resonance imaging technique and/or sensing systems. These sensors are designed to selectively detect specific biomarkers, compounds that can be related to the onset or evolution of cancer, during and after the treatment of this widespread disease. Some of the particular properties of magnetic nanoparticles are extensively exploited in cancer therapy as drug delivery agents to selectively target the envisaged location by tailored in vivo manipulation using an external magnetic field. Furthermore, individualized treatment with antineoplastic drugs may be combined with magnetic resonance imaging to achieve an efficient therapy. This review summarizes the studies about the implications of magnetic nanoparticles in cancer diagnosis, treatment and drug delivery as well as prospects for future development and challenges of magnetic nanoparticles in the field of oncology.

Rapid and sensitive detection of interleukin-6 in serum via time-resolved lateral flow immunoassay

Interleukin 6 (IL-6) is an interleukin that acts as both a proinflammatory and anti-inflammatory cytokine. It can be used as a potential diagnostic biomarker for sepsis. The aim of this study was to establish an easy-to-use detection kit for rapid, quantitative and on-site detection of IL-6. To develop the new IL-6 quantitative detecting kit, a double-antibody sandwich immunofluorescent assay was employed based on europium nanoparticles (Eu-np) combined with lateral flow immunoassay (LFIA). The performance of the new developed kit was evaluated in the aspects of parallel analysis, linearity, sensitivity, precision, accuracy, specificity and clinical sample analysis. Two-hundred and fourteen serum samples were used to carry out the clinical sample analysis. The new IL-6 quantitative detecting kit exhibited a wide linear range (2-500 pg/mL) and a good sensitivity (0.37 pg/mL). The intra-assay coefficient of variation (CV) and the inter-assay CV were 5.92%-8.87% and 7.59%-9.04%, respectively. The recovery rates ranged from 102% to 106%. Furthermore, a high correlation (n = 214, r = 0.9756, p < 0.01) was obtained when compared with SIEMENS CLIA IL-6 kit. Thus, the new quantitative method for detecting IL-6 has been successfully established. The results indicated that the newly-developed strip based on Eu-np combined with LFIA was a facile, fast, highly sensitive, low-cost, reliable biosensor and suitable for rapid and point-of-care test (POCT) for IL-6 in serum.

Nanomaterials-Based Colorimetric Immunoassays

Colorimetric immunoassays for tumor marker detection have attracted considerable attention due to their simplicity and high efficiency. With the achievements of nanotechnology and nanoscience, nanomaterials-based colorimetric immunoassays have been demonstrated to be promising alternatives to conventional colorimetric enzyme-linked immunoassays. This review is focused on the progress in colorimetric immunoassays with the signal amplification of nanomaterials, including nanomaterials-based artificial enzymes to catalyze the chromogenic reactions, analyte-induced aggregation or size/morphology change of nanomaterials, nanomaterials as the carriers for loading enzyme labels, and chromogenic reactions induced by the constituent elements released from nanomaterials.

Colorimetric and electrochemical (dual) thrombin assay based on the use of a platinum nanoparticle modified metal-organic framework (type Fe-MIL-88) acting as a peroxidase mimic

An electrochemical and colorimetric dual-readout method is described for the determination of thrombin. A platinum nanoparticle (Pt NP) modified metal organic framework (MOF) acts as a peroxidase (POx) mimic that causes the formation of a blue product from 3,3',5,5'-tetramethylbenzidine (TMB) and hydrogen peroxide, with an absorption maximum at 650 nm. In addition, gold nanoparticles enrich initiators that trigger the hybridization chain reaction for dual signal amplification to generate an electrochemical current typically measured at 0.31 V (from -0.5 to -0.1 V) and allow quantitation of thrombin with high sensitivity and over a wide detection range. The colorimetric and electrochemical (dual) thrombin assay produces two kinds of signals which warrants accuracy, diversity, and an option for visual inspection. The dual-channel sensor allows for the quantitative determination of thrombin with a low detection limit (0.33 fM) for the electrochemical method and 0.17 pM for the colorimetric method) and over a wide detection range (1 fM to 10 nM for electrochemical method and 0.5 pM to 1 nM for colorimetric method). The electrochemical detection limit is lower than that of colorimetry, and the linear range is wider, which is more suitable for further quantitative analysis of the target. Graphical abstract Schematic representation of a colorimetric and electrochemical (dual) thrombin assay based on the use of a platinum nanoparticle modified metal-organic framework for color development and hybridization chain reaction for electrochemical signal. C-TBA: complementary sequences of thrombin aptamer, TBA: thrombin aptamer, I-Au NPs: initiators enriched by gold nanoparticles, S-AuE: sensing gold electrode, RS-AuE: reacted sensing gold electrode, TB: thrombin, MB: Methylene Blue, HCR: hybridization chain reaction.

Combined electrochemiluminescent and electrochemical immunoassay for interleukin 6 based on the use of TiO2 mesocrystal nanoarchitectures

A dual-responsive sandwich-type immunosensor is described for the detection of interleukin 6 (IL-6) by combining electrochemiluminescent (ECL) and electrochemical (EC) detection based on the use of two kinds of TiO₂ mesocrystal nanoarchitectures. A composite was prepared from TiO₂ (anatase) mesocages (AMCs) and a carboxy-terminated ionic liquid (CTIL) and then placed on a glassy carbon electrode (GCE). In the next step, the ECL probe Ru(bpy)₃(II) and antibody against IL-6 (Ab₁) were immobilized on the GCE. Octahedral anatase TiO₂ mesocrystals (OAMs) served as the matrix for immobilizing acid phosphatase (ACP) and secondary antibody (Ab₂) labeled with horseradish peroxidase (HRP) to form a bioconjugate of type Ab₂-HRP/ACP/OAMs. It was self-assembled on the GCE by immunobinding. 1-Naphthol, which is produced in-situ on the surface of the GCE due to the hydrolysis of added 1-naphthyl phosphate by ACP, is oxidized by HRP in the presence of added H₂O₂. This results in an electrochemical signal (typically measured at 0.4 V vs. Ag/AgCl) that increases linearly in the 10 fg·mL^-1 to 90 ng·mL^-1 IL-6 concentration range with a detection limit of 0.32 fg·mL^-1. Secondly, the oxidation product of 1-naphthol quenches the ECL emission of Ru(bpy)₃²⁺. This leads to a decrease in ECL intensity which is linear in the 10 ag·mL^-1 to 90 ng·mL^-1 concentration range, with a detection limit of 3.5 ag·mL^-1. The method exhibits satisfying selectivity and good reproducibility which demonstrates its potential in clinical testing and diagnosis. Graphical abstract A dual-responsive sandwich-type immunosensor was fabricated for the detection of interleukin 6 by combining electrochemiluminescence and electrochemical detection based on the use of two kinds of TiO₂ mesocrystal nanoarchitectures.

A highly sensitive electrochemical immunosensor for hepatitis B virus surface antigen detection based on Hemin/G-quadruplex horseradish peroxidase-mimicking DNAzyme-signal amplification

Here we prepared an electrochemical immunosensor employing Au sheet as working electrode, Fe₃O₄ magnetic nanoparticles (MNPs) as supporting matrix and hemin/G-quadruplex DNAzyme as signal amplifier for determination of hepatitis B virus surface antigen (HBsAg). First, the primary antibody of HBs (Ab₁) was immobilized on the surface of the carboxyl-modified MNPs. Then, the assembly of antibody and alkylthiol/G-quadruplex DNA/hemin on gold nanoparticles was used as bio-bar-coded nanoparticle probe. Protein target was sandwiched between the primary antibody of HBs (Ab₁) immobilized on the MNPs and hemin bio-bar-coded AuNPs probe labeled antibody (Ab₂). Hemin/G-quadruplex structure as HRP mimicking-DNAzyme significantly improved the catalytic reduction of H₂O₂ by oxidation of methylene blue (MB). Square wave voltammetry signals of MB provided quantitative measurements of HBsAg with a linear concentration range of 0.3-1000 pgmL^-1 and detection limit of 0.19 pgmL^-1. Due to efficient catalytic activity of HRP mimicking-DNAzyme, the proposed immunosensor exhibited high sensitivity and it holds great promise for clinical application and provides a new platform for immunosensor development and fast disease diagnosis.

Emerging Cytokine Biosensors with Optical Detection Modalities and Nanomaterial-Enabled Signal Enhancement

Protein biomarkers, especially cytokines, play a pivotal role in the diagnosis and treatment of a wide spectrum of diseases. Therefore, a critical need for advanced cytokine sensors has been rapidly growing and will continue to expand to promote clinical testing, new biomarker development, and disease studies. In particular, sensors employing transduction principles of various optical modalities have emerged as the most common means of detection. In typical cytokine assays which are based on the binding affinities between the analytes of cytokines and their specific antibodies, optical schemes represent the most widely used mechanisms, with some serving as the gold standard against which all existing and new sensors are benchmarked. With recent advancements in nanoscience and nanotechnology, many of the recently emerging technologies for cytokine detection exploit various forms of nanomaterials for improved sensing capabilities. Nanomaterials have been demonstrated to exhibit exceptional optical properties unique to their reduced dimensionality. Novel sensing approaches based on the newly identified properties of nanomaterials have shown drastically improved performances in both the qualitative and quantitative analyses of cytokines. This article brings together the fundamentals in the literature that are central to different optical modalities developed for cytokine detection. Recent advancements in the applications of novel technologies are also discussed in terms of those that enable highly sensitive and multiplexed cytokine quantification spanning a wide dynamic range. For each highlighted optical technique, its current detection capabilities as well as associated challenges are discussed. Lastly, an outlook for nanomaterial-based cytokine sensors is provided from the perspective of optimizing the technologies for sensitivity and multiplexity as well as promoting widespread adaptations of the emerging optical techniques by lowering high thresholds currently present in the new approaches.

Dual-mode refractive index and charge sensing to investigate complex surface chemistry on nanostructures

This work presents a novel dual-mode charge and refractive index sensitive device integrated with nanoplasmonic islands, for the first time, on insulator-semiconductor junctions. The developed nano-metal-insulator semiconductor (nMIS) sensor facilitates simultaneous detection of charge and mass changes on the nanoislands due to the binding of biomolecules. The charging of the nanoislands is traced by using the capacitive field-effect electrolyte-metal-insulator-semiconductor structure and the refractive index changes are quantified by measuring the change in the localized surface plasmon resonances of the nanoislands. To demonstrate the performance of our dual-mode sensor we study the effect of oxygen plasma on immobilized biomolecules. As a case study biotinylated aptamers specific to interleukin 6 (IL-6) were chosen to conduct the immunoassay studies. We confirm that the adsorbed aptamers on the nanoislands do not lose their functionality after exposure to low energy oxygen plasma (<600 J). This finding is critical for the development of 'ready-to-use' microfluidic immunoassay platforms (glass-PDMS based) where immobilizing biomolecules on one of the substrates is often required prior to the bonding of glass and PDMS. Our results also open new opportunities for utilizing plasma to encapsulate biomolecules in polymers and hydrogels. More significantly, nMIS sensors can readily be adopted for multiplexed and high throughput label free immunoassay systems, further driving innovations in biomedical and healthcare research.

Rapid biosensing tools for cancer biomarkers

The present review critically discusses the latest developments in the field of smart diagnostic systems for cancer biomarkers. A wide coverage of recent biosensing approaches involving aptamers, enzymes, DNA probes, fluorescent probes, interacting proteins and antibodies in vicinity to transducers such as electrochemical, optical and piezoelectric is presented. Recent advanced developments in biosensing approaches for cancer biomarker owes much credit to functionalized nanomaterials due to their unique opto-electronic properties and enhanced surface to volume ratio. Biosensing methods for a plenty of cancer biomarkers has been summarized emphasizing the key principles involved.