Surface Reaction of Electroosmotic Flow-Driven Free Antigens With Immobilized Magnetic-Microbeads-Tagged-Antibodies in Microchannels

Immunoassays based on reactions between target pathogen (antigen; Ag) and antibody (Ab) are frequently used for Ag detection. An external magnetic field was used to immobilize magnetic microbeads-tagged-antibodies (mMB-Ab) on the surface of a microchannel in the capture zone. The mMB-Ab was subsequently used for Ag detection. The objective of this numerical study, with experimental validation, is to assess the surface reaction between mMB-Ab and Ag in the presence of electro-osmotic flow (EOF). First, immobilization of mMB-Ab complex in the wall of the capture zone was achieved. Subsequently, the Ag was transported by EOF toward the capture zone to bind with the immobilized mMB-Ab. Lastly, mMB-Ab:Ag complex was formed and immobilized in the capture zone. A finite volume solver was used to implement the above steps. The surface reaction between the mMB-Ab and Ag was investigated in the presence of electric fields (E): 150 V/cm-450 V/cm and Ag concentrations: 0.001 M-1000 M. The depletion of mMB-Ab increases with time as the E decreases. Furthermore, as the concentration of Ag decreases, the depletion of mMB-Ab increases with time. These results quantify the detection of Ag using the EOF device; thus, signifying its potential for rapid throughput screening of Ag. This platform technology can lead to the development of portable devices for the detection of target cells, pathogens, and biomolecules for testing water systems, biological fluids, and biochemicals.

Influence of different conjugation methods for activating antibodies on polymeric nanoparticles: Effects for polyclonal expansion of human CD8+ T cells

Particle-based systems have become a state-of-the-art method for in vitro expanding cytotoxic T cells by tailoring their surface with activating molecules. However, commonly used methods utilize facile carbodiimide chemistry leading to uncontrolled orientation of the immobilized antibodies on the particle surface that can lead to poor binding to target cells. To address this, selective coupling strategies utilizing regioselective chemical groups such as disulfide bridges offer a simple approach. In this work we present a set of methods to investigate the effect of polymeric nanoparticles, conjugated with either regioselective- or randomly-immobilized antiCD3 and antiCD28 antibodies, on the activation potential, expansion and expression of activation markers in T cells. We show that nanoparticles with well-oriented monovalent antibodies conjugated via maleimide require fewer ligands on the surface to efficiently expand T cells compared to bivalent antibodies randomly-immobilized via carbodiimide conjugation. Analysis of the T cell expression markers reveal that the T cell phenotype can be fine-tuned by adjusting the surface density of well-oriented antibodies, while randomly immobilized antibodies showed no differences despite their ligand density. Both conjugation techniques induced cytotoxic T cells, evidenced by analyzing their Granzyme B secretion. Furthermore, antibody orientation affects the immunological synapse and T cell activation by changing the calcium influx profile upon activation. Nanoparticles with well-oriented antibodies showed lower calcium influx compared to their bivalent randomly-immobilized counterparts. These results highlight the importance of controlling the antibody density and orientation on the nanoparticle surface via controlled coupling chemistries, helping to develop improved particle-based expansion protocols to enhance T cell therapies.

An integrated electrochemical immunosensor based on Pd-Ir cubic nanozyme and Ketjen black for ultrasensitive detection of circulating tumor cells

Ultrasensitive detection of circulating tumor cells (CTCs) holds significant clinical importance in monitoring metastasis and therapeutic outcomes. In this study, we have developed a novel electrochemical sensing model based on nanomaterials for highly sensitive and specific determination of CTCs. A gold electrode co-modified with Ketjin black (KB) and Au nanoparticles (AuNPs) exhibits exceptional conductivity. By conjugating palladium-iridium cubic nanozyme (Pd-Ir CNE) with antibodies, we have created a detection probe capable of catalyzing hydrogen peroxide (H2O2), thereby amplifying the output signal and resulting in significantly enhanced current on the electrode for detecting CTCs. The constructed immunosensor has achieved a detection limit of 2 cell mL-1 for model MCF-7 cells. Furthermore, the as-constructed electrochemical immunosensor can accurately detect whole blood-spiked target CTCs, showing great promise for clinical applications in early cancer diagnosis and prognosis.

Ultrasensitive and Rapid Detection of Procalcitonin via Waveguide-Enhanced Nanogold-Linked Immunosorbent Assay for Early Sepsis Diagnosis

Sepsis, a life-threatening inflammatory response, demands economical, accurate, and rapid detection of biomarkers during the critical "golden hour" to reduce the patient mortality rate. Here, we demonstrate a cost-effective waveguide-enhanced nanogold-linked immunosorbent assay (WENLISA) based on nanoplasmonic waveguide biosensors for the rapid and sensitive detection of procalcitonin (PCT), a sepsis-related inflammatory biomarker. To enhance the limit of detection (LOD), we employed sandwich assays using immobilized capture antibodies and detection antibodies conjugated to gold nanoparticles to bind the target analyte, leading to a significant evanescent wave redistribution and strong nanoplasmonic absorption near the waveguide surface. Experimentally, we detected PCT for a wide linear response range of 0.1 pg/mL to 1 ng/mL with a record-low LOD of 48.7 fg/mL (3.74 fM) in 8 min. Furthermore, WENLISA has successfully identified PCT levels in the blood plasma of patients with sepsis and healthy individuals, offering a promising technology for early sepsis diagnosis.

Au/PANI@PtCu-based electrochemical immunosensor for ultrasensitive determination of pro-gastrin-releasing peptide

An ultrasensitive sandwich-type electrochemical immunosensor for pro-gastrin-releasing peptide (ProGRP) detection was constructed based on PtCu nanodendrites functionalized Au/polyaniline nanospheres (Au/PANI@PtCu). The prepared Au/PANI@PtCu nanocomposites not only possessed excellent electro-catalytic activity of H2O2 reduction due to the synergistic effect between the Au/PANI and PtCu NDs but also provided large specific surface area for detection of antibodies (Ab2) immobilization. In addition, Au nanoparticles encapsulated multi-wall carbon nanotubes (AuNPs@MWCNTs) were also applied to modify the glassy carbon electrode interface for loading numerous capture antibodies (Ab1). In the presence of target ProGRP, a sandwich-type electrochemical immunosensor showed a strong current response from the electro-catalysis of Au/PANI@PtCu toward H2O2 reduction. Benefiting from the exceptional electro-catalytic performance of Au/PANI@PtCu and the high conductivity of AuNPs@MWCNTs, the sandwich-type immunoassay exhibited remarkable sensitivity in detection. The linear range extended from 100 fg/mL to 10 ng/mL, while achieving an impressively low limit of detection of 77.62 fg/mL.

A liquid crystal-based biosensor for sensitive detection of tumor necrosis factor-alpha

Tumor necrosis factor-alpha (TNF-α) is a cytokine secreted by the macrophages and Th1 cells of the immune system in response to inflammation. Given its significance as a biomarker with elevated levels in physiological fluids in various conditions, there is an increasing demand for a simple and accurate TNF-α detection strategy. In this article, we present a liquid crystal (LC)-based biosensor developed for sensitive TNF-α detection. The biosensor operates as follows: TNF-α and detection antibodies (DAbs) form complexes during preincubation. These complexes then bind with the surface-immobilized capture antibodies (CAbs), facilitating the antigen-antibody reaction between the CAbs and the TNF-α/DAb complexes. This target recognition interaction alters the surface topography, disrupting the vertical orientation of LCs produced by dimethyloctadecyl[3-(trimethoxysilyl)-propyl]ammonium chloride. The orientational change in the LCs can be easily visualized with a polarized optical microscope, resulting in brighter images as TNF-α levels rise. Our results demonstrated a linear range of 5.00-500 pg/mL, with a limit of detection and limit of quantification being 1.08 and 3.56 pg/mL, respectively. Recovery experiments on diluted saliva samples produced reasonable results, with TNF-α recoveries ranging from 97.1% ± 2.58% to 107% ± 5.95%.

Extending the Shelf-Life of Immunoassay-Based Microfluidic Chips through Freeze-Drying Sublimation Techniques

Point-of-care testing (POCT) platforms utilizing immunoassay-based microfluidic chips offer a robust and specific method for detecting target antibodies, demonstrating a wide range of applications in various medical and research settings. Despite their versatility and specificity, the adoption of these immunoassay chips in POCT has been limited by their short shelf-life in liquid environments, attributed to the degradation of immobilized antibodies. This technical limitation presents a barrier, particularly for resource-limited settings where long-term storage and functionality are critical. To address this challenge, we introduce a novel freeze-dry sublimation process aimed at extending the shelf-life of these microfluidic chips without compromising their functional integrity. This study elaborates on the mechanisms by which freeze-drying preserves the bioactivity of the immobilized antibodies, thereby maintaining the chip's performance over an extended period. Our findings reveal significant shelf-life extension, making it possible for these POCT platforms to be more widely adopted and practically applied, especially in settings with limited resources. This research paves the way for more accessible, long-lasting, and effective POCT solutions, breaking down previous barriers to adoption and application.

CRISPR/Cas12a-Powered Competitive Immunosorbent Assay for Small Molecules

CRISPR/Cas systems are powerful tools for sensitive nucleic acid molecular diagnosis due to their specific nucleic acid recognition and high trans-cleavage activity and have also allowed for quantification of non-nucleic acid targets, relying on a strategy to convert the target detection to analysis of nucleic acids. Here, we describe a CRISPR/Cas12a-powered immunosorbent assay for sensitive small-molecule detection by using the antibody coated on the microplate to recognize the target and the small molecule-labeled active DNA (acDNA) to trigger the activity of CRISPR/Cas12a. In the absence of small-molecule targets, acDNA probes are captured by the antibody on the microplate and then activate Cas12a in catalytic trans-cleavage of fluorescent DNA reporters, generating strong fluorescence. The presence of small-molecule targets displaces the acDNA probes from the antibody, causing a decrease of acDNA probes on the microplate and reduction of activated Cas12a, so the fluorescence signal decreases, and small molecules can be detected by monitoring the fluorescence change. After systematically optimizing experimental conditions (e.g., Cas12a reaction), the proposed method achieved the detection of three model small molecules, biotin, digoxin, and folic acid, with low detection limits, and a flexible detection concentration range was obtained by simply changing the amount of acDNA probes and immobilized antibodies. The assay showed high selectivity and good applicability in complex media. The integration of the CRISPR/Cas12a system improves the analytical performance of immunoassay, broadening and facilitating its applications in rapid, simple, and sensitive small molecule analysis.

Immunoaffinity Chromatography for Protein Purification and Analysis

Immunoaffinity chromatography (IAC) is a type of liquid chromatography that uses immobilized antibodies or related binding agents as selective stationary phases for sample separation or analysis. The strong binding and high selectivity of antibodies have made IAC a popular tool for the purification and analysis of many chemicals and biochemicals, including proteins. The basic principles of IAC are described as related to the use of this method for protein purification and analysis. The main factors to consider in this technique are also presented under a discussion of the general strategy to follow during the development of a new IAC method. Protocols, as illustrated using human serum albumin (HSA) as a model protein, are provided for the use of IAC in several formats. This includes both the use of IAC with traditional low-performance supports such as agarose for off-line immunoextraction and supports used in high-performance IAC for on-line immunoextraction. The use of IAC for protein analysis as a flow-based or chromatographic immunoassay is also discussed and described using HSA and a competitive binding assay format as an example. © 2023 Wiley Periodicals LLC. Basic Protocol 1: Off-line immunoextraction by traditional immunoaffinity chromatography Basic Protocol 2: On-line immunoextraction by high-performance immunoaffinity chromatography Basic Protocol 3: Competitive binding chromatographic immunoassay.

Release from persistent T cell receptor engagement and blockade of aryl hydrocarbon receptor activity enhance IL-6-dependent mouse follicular helper T-like cell differentiation in vitro

Follicular helper T (Tfh) cells are crucial for humoral immunity. Dysregulation of Tfh cell differentiation can cause infectious, allergic, and autoimmune diseases. To elucidate the molecular mechanisms underlying Tfh cell differentiation, we attempted to establish an in vitro mouse model of Tfh cell differentiation in the absence of other cell types. Various cytokines and cell surface molecules are suggested to contribute to the differentiation. We found that stimulating naïve CD4+ T cells with immobilized antibodies to CD3, ICOS, and LFA-1 in the presence of soluble anti-CD28 antibody, IL-6, and antibodies that block IL-2 signaling for 3 days induced the expression of Bcl6 and Rorc(γt), master regulator genes of Tfh and Th17 cells, respectively. TGF-β significantly enhanced cell proliferation and Bcl6 and Rorc(γt) expression. An additional 2 days of culture without immobilized antibodies selectively downregulated Rorc(γt) expression. These cells produced IL-21 and promoted B cells to produce IgG antibodies. Adding the aryl hydrocarbon receptor (AhR) antagonist CH-223191 to the T cell culture further downregulated Rorc(γt) expression without significantly affecting Bcl6 expression, and upregulated expression of a key Tfh marker, CXCR5. Although their CXCR5 expression levels were still not high, the CH-223191-treated cells showed chemotactic activity towards the CXCR5 ligand CXCL13. On the other hand, AhR agonists upregulated Rorc(γt) expression and downregulated CXCR5 expression. These findings suggest that AhR activity and the duration of T cell receptor stimulation contribute to regulating the balance between Tfh and Th17 cell differentiation. Although this in vitro system needs to be further improved, it may be useful for elucidating the mechanisms of Tfh cell differentiation as well as for screening physiological or pharmacological factors that affect Tfh cell differentiation including CXCR5 expression.

3D-printed capillaric ELISA-on-a-chip with aliquoting

Sandwich immunoassays such as the enzyme-linked immunosorbent assay (ELISA) have been miniaturized and performed in a lab-on-a-chip format, but the execution of the multiple assay steps typically requires a computer or complex peripherals. Recently, an ELISA for detecting antibodies was encoded structurally in a chip thanks to the microfluidic chain reaction (Yafia et al. Nature, 2022, 605, 464-469), but the need for precise pipetting and intolerance to commonly used surfactant concentrations limit the potential for broader adoption. Here, we introduce the ELISA-on-a-chip with aliquoting functionality that simplifies chip loading and pipetting, accommodates higher surfactant concentrations, includes barrier channels that delay the contact between solutions and prevent undesired mixing, and that executed a quantitative, high-sensitivity assay for the SARS-CoV-2 nucleocapsid protein in 4×-diluted saliva. Upon loading the chip using disposable pipettes, capillary flow draws each reagent and the sample into a separate volumetric measuring reservoir for detection antibody (70 μL), enzyme conjugate (50 μL), substrate (80 μL), and sample (210 μL), and splits washing buffer into 4 different reservoirs of 40, 40, 60, and 20 μL. The excess volume is autonomously drained via a structurally encoded capillaric aliquoting circuit, creating aliquots with an accuracy of >93%. Next, the user click-connects the assay module, comprising a nitrocellulose membrane with immobilized capture antibodies and a capillary pump, to the chip which triggers the step-by-step, timed flow of all aliquoted solutions to complete the assay in 1.5 h. A colored precipitate forming a line on a nitrocellulose strip serves as an assay readout, and upon digitization, yielded a binding curve with a limit of detection of 54 and 91 pg mL^-1 for buffer and diluted saliva respectively, vastly outperforming rapid tests. The ELISA chip is 3D-printed, modular, adaptable to other targets and assays, and could be used to automate ELISA in the lab; or as a diagnostic test at the point of care with the convenience and form factor of rapid tests while preserving the protocol and performance of central laboratory ELISA.

Characterization of FcγRIa (CD64) as a Ligand Molecule for Site-Specific IgG1 Capture: A Side-By-Side Comparison with Protein A

Fc γ receptors (FcγRs) are one of the structures that can initiate effector function for monoclonal antibodies. FcγRIa has the highest affinity toward IgG1-type monoclonal antibodies among all FcγRs. In this study, a comprehensive characterization was performed for FcγRIa as a potential affinity ligand for IgG1-type monoclonal antibody binding. The binding interactions were assessed with the SPR technique using different immobilization techniques such as EDC-NHS coupling, streptavidin-biotin interaction, and His-tagged FcγRIa capture. The His-tagged FcγRIa capture was the most convenient method based on assay repeatability. Next, a crude IgG1 sample and its fractions with different monomer contents obtained from protein A affinity chromatography were used to evaluate FcγRIa protein in terms of monoclonal antibody binding capacity. The samples were also compared with a protein A-immobilized chip (a frequently used affinity ligand) for IgG1 binding responses. The antibody binding capacity of the protein A-immobilized chip surface was significantly better than that of the FcγRIa-immobilized chip surface due to its 5 Ig binding domains. The antibody binding responses changed similarly with protein A depending on the monomer content of the sample. Finally, a different configuration was used to assess the binding affinity of free FcγRs (FcγRIa, FcγRIIa, and FcγRIIIa) to three different immobilized IgGs by immobilizing protein L to the chip surface. Unlike previous immobilization techniques tested where the FcγRIa was utilized as a ligand, nonimmobilized or free FcγRIa resulted in a significantly higher antibody binding response than free protein A. In this configuration, kinetics data of FcγRI revealed that the association rate (k_a 50-80 × 10⁵ M^-1 s^-1) increased in comparison to His capture method (1.9-2.4 × 10⁵ M^-1 s^-1). In addition, the dissociation rate (k_d 10^-5 s^-1) seemed slower over the His capture method (10^-4 s^-1) and provided stability on the chip surface during the dissociation phase. The K_D values for FcγRIa were found in the picomolar range (2.1-10.33 pM from steady-state affinity analysis and 37.5-46.2 pM from kinetic analysis) for IgG1-type antibodies. FcγRIa possesses comparable ligand potential as well as protein A. Even though the protein A-immobilized surface bound more antibodies than the FcγRIa-captured surface, FcγRIa presented a significant antibody binding capacity in protein L configuration. The results suggest FcγRIa protein as a potential ligand for site-oriented immobilization of IgG1-type monoclonal antibodies, and it needs further performance investigation on different surfaces and interfaces for applications such as sensing and antibody purification.

Label-Free Immunosensor Based on Polyaniline-Loaded MXene and Gold-Decorated β-Cyclodextrin for Efficient Detection of Carcinoembryonic Antigen

Multiple strategies have been employed to improve the performance of label-free immunosensors, among which building highly conductive interfaces and introducing suitable biocompatible carriers for immobilizing antibodies or antigens are believed to be efficient in most cases. Inspired by this, a label-free immunosensor for carcinoembryonic antigen (CEA) detection was constructed by assembling AuNPs and β-CD (Au-β-CD) on the surface of FTO modified with PANI-decorated f-MXene (MXene@PANI). Driven by the high electron conductivity of MXene@PANI and the excellent capability of Au-β-CD for antibody immobilization, the BSA/anti-CEA/Au-β-CD/MXene@PANI/FTO immunosensor exhibits balanced performance towards CEA detection, with a practical linear range of 0.5–350 ng/mL and a low detection limit of 0.0429 ng/mL. Meanwhile, the proposed sensor presents satisfying selectivity, repeatability, and stability, as well as feasibility in clinic serum samples. This work would enlighten the prospective research on the alternative strategies in constructing advanced immunosensors.

A label-free electrochemical immunosensor based on a gold-vertical graphene/TiO2 nanotube electrode for CA125 detection in oxidation/reduction dual channels

A label-free immunosensor was constructed in oxidation and reduction dual channel mode for the trace detection of cancer antigen 125 (CA125) in serum. The gold-vertical graphene/titanium dioxide (Au-VG/TiO₂) electrode was used as the signal-amplification platform, and cytosine and dopamine were used as probes in the oxidation and reduction channels, respectively. VG nanosheets were synthesized on a TiO₂ nanotube array via chemical vapor deposition (CVD), and Au nanoparticles were deeply embedded on the surface and in the root of the VG nanosheets via electrodeposition. The CA125 antibody was then directly immobilized onto the electrode surface, benefitting from its natural affinity for Au nanoparticles. In the oxidation and reduction channels the CA125 antibody-Au-VG/TiO₂ immune electrode had the same response concentration range (0.01-1000 mU∙mL^-1) for the determination of the CA125 antigen. However, the oxidation channel had a higher sensitivity (14.82 μA•(log(mU•mL^-1))^-1 at a working potential of ~ 1.25 V vs. SCE), lower detection limit (0.0001 mU∙mL^-1), higher stability, and lower performance deviation than the reduction channel. This immunosensor was successfully used for CA125 detection in human serum. The recoveries of spiked serum samples ranged from 99.8 ± 0.5 to 100 ± 0.4%. The study on the difference in the sensing performance between oxidation and reduction channels provides a preliminary experimental reference for exploring dual-channel synchronous detection immunosensors and verifying the accuracy of the assay based on dual-channel data, which will promote the development of reliable electrochemical immunosensor technology.

A Novel Prototype Biosensor Array Electrode System for Detecting the Bacterial Pathogen Salmonella typhimurium

Salmonellosis caused by Salmonella sp. has long been reported all over the world. Despite the availability of various diagnostic methods, easy and effective detection systems are still required. This report describes a dialysis membrane electrode interface disc with immobilized specific antibodies to capture antigenic Salmonella cells. The interaction of a specific Salmonella antigen with a mouse anti-Salmonella monoclonal antibody complexed to rabbit anti-mouse secondary antibody conjugated with HRP and the substrate o-aminophenol resulted in a response signal output current measured using two electrode systems (cadmium reference electrode and glassy carbon working electrode) and an agilent HP34401A 6.5 digital multimeter without a potentiostat or applied potential input. A maximum response signal output current was recorded for various concentrations of Salmonella viz., 3, 30, 300, 3000, 30,000 and 300,000 cells. The biosensor has a detection limit of three cells, which is very sensitive when compared with other detection sensors. Little non-specific response was observed using Streptococcus, Vibrio, and Pseudomonas sp. The maximum response signal output current for a dialysis membrane electrode interface disc was greater than that for gelatin, collagen, and agarose. The device and technique have a range of biological applications. This novel detection system has great potential for future development and application in surveillance for microbial pathogens.

A Tri-Channel Oxide Transistor Concept for the Rapid Detection of Biomolecules Including the SARS-CoV-2 Spike Protein

Solid-state transistor sensors that can detect biomolecules in real time are highly attractive for emerging bioanalytical applications. However, combining upscalable manufacturing with the required performance remains challenging. Here, an alternative biosensor transistor concept is developed, which relies on a solution-processed In₂ O₃ /ZnO semiconducting heterojunction featuring a geometrically engineered tri-channel architecture for the rapid, real-time detection of important biomolecules. The sensor combines a high electron mobility channel, attributed to the electronic properties of the In₂ O₃ /ZnO heterointerface, in close proximity to a sensing surface featuring tethered analyte receptors. The unusual tri-channel design enables strong coupling between the buried electron channel and electrostatic perturbations occurring during receptor-analyte interactions allowing for robust, real-time detection of biomolecules down to attomolar (am) concentrations. The experimental findings are corroborated by extensive device simulations, highlighting the unique advantages of the heterojunction tri-channel design. By functionalizing the surface of the geometrically engineered channel with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibody receptors, real-time detection of the SARS-CoV-2 spike S1 protein down to am concentrations is demonstrated in under 2 min in physiological relevant conditions.

Impedimetric and Plasmonic Sensing of Collagen I Using a Half-Antibody-Supported, Au-Modified, Self-Assembled Monolayer System

This research presents an electrochemical immunosensor for collagen I detection using a self-assembled monolayer (SAM) of gold nanoparticles (AuNPs) and covalently immobilized half-reduced monoclonal antibody as a receptor; this allowed for the validation of the collagen I concentration through two different independent methods: electrochemically by Electrochemical Impedance Spectroscopy (EIS), and optically by Surface Plasmon Resonance (SPR). The high unique advantage of the proposed sensor is based on the performance of the stable covalent immobilization of the AuNPs and enzymatically reduced half-IgG collagen I antibodies, which ensured their appropriate orientation onto the sensor's surface, good stability, and sensitivity properties. The detection of collagen type I was performed in a concentration range from 1 to 5 pg/mL. Moreover, SPR was utilized to confirm the immobilization of the monoclonal half-antibodies and sensing of collagen I versus time. Furthermore, EIS experiments revealed a limit of detection (LOD) of 0.38 pg/mL. The selectivity of the performed immunosensor was confirmed by negligible responses for BSA. The performed approach of the immunosensor is a novel, innovative attempt that enables the detection of collagen I with very high sensitivity in the range of pg/mL, which is significantly lower than the commonly used enzyme-linked immunosorbent assay (ELISA).

NS1 glycoprotein detection in serum and urine as an electrochemical screening immunosensor for dengue and Zika virus

The incidence of infection by the dengue virus (DENV) has grown dramatically, reaching 128 countries in tropical and subtropical regions worldwide, with a pattern of hyper-endemicity. DENV is a mosquito-borne disease having four serotypes, one or two circulating in epidemic outbreaks. The diagnosis of DENV is challenging mainly due to the circulation of new viruses with remarkable similarities, such as Zika (ZIKV) that may cause fetal microcephaly. DENV affects 390 million people per year, but these numbers may be higher due to the underreported and misclassified cases. Recently, the NS1 nonstructural protein has been described in serum and urine of DENV and ZIKV patients, suggesting its use as a biomarker for screening since a negative NS1 sample confirms the absence of these infections. Herein, a label-free immunosensor comprising an assembled nanostructured thin film of carbon nanotube-ethylenediamine is described. The advantage of in situ electrosynthesis of polymer film is to allow major control of thickness and conductivity, in addition to designing the reactive groups for functionalization. A quartz crystal microbalance system was used to estimate the thickness of the polymeric film obtained. The anti-NS1 monoclonal antibodies were immobilized to carbon nanotubes by covalent linkage, permitting a high stability during measurements. Analytical responses to NS1 were obtained by differential pulse voltammetry (DPV), showing a linear range from 20 to 800 ng mL^-1 and reproducibility of 3.0%, with a limit of detection (LOD) of 6.8 ng mL^{- 1}. This immunosensor was capable of detecting ZIKV and DENV NS1 in spiked urine and real serum in a clinical range.Graphical abstract.

Fenton reaction-mediated dual-attenuation of signal for ultrasensitive amperometric immunoassay

In order to alter the complexion of immunoprobe with large impedance as negative factor in sensitivity of amperometric immunosensor, a strategy of Fenton reaction-mediated dual-attenuation of signal was proposed. Herein, metal-polydopamine-Fe³⁺ composite with the ability of Fenton reaction was initially prepared as immunoprobe for an ultrasensitive immunoassay. The polymerization of dopamine occurred on the surface of ZIF-67 to gain the metal-polydopamine shell, which possessed rich functional groups, negative charge and high specific surface. Then the prepared functional shell was further used to absorb Fe³⁺ and immobilize labeling antibody as immunoprobe, which was used to construct a sandwich type immunosensor. With addition of H₂O₂ and aniline, Fenton reaction was triggered to produce hydroxyl radicals, which can not only decrease the current value by degrading methylene blue molecules, but also further initiate aniline to polymerize into non-conductive polyaniline for successive abatement of signal intensity. Therefore, the dual-attenuation of signal model rendered the immunoprobe into a favorable factor and synchronously enhance sensitivity. Expectedly, the detection performance with a linear range from 1.0 × 10^-4-100 ng mL^-1 and ultralow detection limit of 9.07 × 10^-5 ng mL^-1 toward neuron-specific enolase was obtained under optimal conditions. This work offered a novel tactic for enhancing sensitivity of immunosensor through the preparation of functional immunoprobe and its rational utilization as signal enhancer.

Immobilized Antibodies on Mercaptophenylboronic Acid Monolayers for Dual-Strategy Detection of 20S Proteasome

A dual strategy for the electrochemical detection for 20S proteasome (20S) is proposed, based on the oriented immobilization of a capture monoclonal antibody (Abβ) on a self-assembled monolayer of 4-mercaptophenylboronic acid (4-MPBA) on gold electrodes, which led to the Au/4-MPBA/Abβ immunosensor. The methodology comprises the correlation of 20S concentration with (i) its proteolytic activity toward the Z-LLE-AMC substrate, using the Au/4-MPBA/Abβ/20S, and (ii) the enzymatic activity of an alkaline phosphatase (AlkP) from the AlkP-labeled secondary antibody (Abcore-AlkP), which involves the conversion of aminophenylphosphate to the electroactive aminophenol using Au/4-MPBA/Abβ/20S/Abcore-AlkP. The step-by-step construction of the immunosensor and the interactions at its surface were evaluated by surface plasmon resonance and gravimetric analysis with quartz crystal microbalance, showing a high affinity between both antibodies and 20S. Morphological analysis by scanning electron microscopy demonstrated a pattern of parallel lines upon immobilization of Abβ on 4-MPBA and morphological changes to a well-organized granular structure upon binding of 20S. A voltametric and impedimetric characterization was performed after each step in the immunosensor construction. The two detection strategies were evaluated. It was shown that the immunosensor responds linearly with 20S concentration in the range between 5 and 100 µg mL-1, which corresponds to proteasome levels in serum in the case of diverse pathological situations, and LoD values of 1.4 and 0.2 µg mL-1 were calculated for the detection strategies. The immunosensor was applied to the detection of 20S in serum samples with recovery values ranging from 101 to 103%.

Highly Sensitive Detection of CA 125 Protein with the Use of an n-Type Nanowire Biosensor

The detection of CA 125 protein in a solution using a silicon-on-insulator (SOI)-nanowire biosensor with n-type chip has been experimentally demonstrated. The surface of nanowires was modified by covalent immobilization of antibodies against CA 125 in order to provide the biospecificity of the target protein detection. We have demonstrated that the biosensor signal, which results from the biospecific interaction between CA 125 and the covalently immobilized antibodies, increases with the increase in the protein concentration. At that, the minimum concentration, at which the target protein was detectable with the SOI-nanowire biosensor, amounted to 1.5 × 10⁻¹⁶ M.

Periodic concentration-polarization-based formation of a biomolecule preconcentrate for enhanced biosensing

Ionic concentration-polarization (CP)-based biomolecule preconcentration is an established method for enhancing the detection sensitivity of target biomolecules. However, the formed preconcentrated biomolecule plug rapidly sweeps over the surface-immobilized antibodies, resulting in a short-term overlap between the capture agent and the analyte, and subsequently suboptimal binding. To overcome this, we designed a setup allowing for the periodic formation of a preconcentrated biomolecule plug by activating the CP for predetermined on/off intervals. This work demonstrated the feasibility of cyclic CP actuation and optimized the sweeping conditions required to obtain the maximum retention time of a preconcentrated plug over a desired sensing region and enhanced detection sensitivity. The ability of this method to efficiently preconcentrate different analytes and to successfully increase immunoassay sensitivity underscore its potential in immunoassays serving the clinical and food testing industries.

A label-free immunosensor for sensitive detection of RACK 1 cancer biomarker based on conjugated polymer modified ITO electrode

A new flexible biosensor based on conjugated polymer functionalized indium tin oxide (ITO) sheet was fabricated for Receptor for Activated C Kinase 1 (RACK 1) determination. Poly(3-thiophene acetic acid) (P(Thi-Ac)) was used as an immobilization matrix for construction of RACK 1 immunosensor. This polymer had a great number of carboxyl groups on its end site and these carboxyl ends provided anchoring points to the anti-RACK 1 antibodies. Anti-RACK 1 antibodies were covalently attached on the ITO electrode and recognized the RACK 1 antigens. Electrochemical characterizations were made by employing electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques. Additionally, single frequency impedance method (SFI) was applied to follow the specific biointeraction between antibody and antigen. As a result of specific biointeraction, the designed immunosensor exhibited a wide linear detection range between 0.01 pg/mL and 2 pg/mL RACK 1 with a detection limit of 3.1 fg/mL. Scanning electron microscopy and atomic force microscopy analyses were employed for electrode surface morphology investigation. The designed RACK 1 biosensor had good repeatability (5.73 %, RSD), excellent reproducibility (2.5 %, RSD), long storage-stability and reusable property. In addition, the fabricated RACK 1 biosensor was applied to determine RACK 1 concentration in human serums and the recovery was ranging from 98.79%-100.22%. This work illustrated a new tool to construct a sensitive and low-cost disposable biosensor for applications in clinical monitoring.

Checkpoint enrichment for sensitive detection of target bacteria from large volume of food matrices

A gap in biosensor development is the ability to enrich and detect targets in large sample volumes in a complex matrix. To bridge this gap, our goal in this work is to propose a practical strategy, termed as checkpoint-style enrichment, for rapid enrichment of the target bacteria from large volume of food samples with particulates and evaluate its enrichment and improvement in detection. The checkpoint-style enrichment was conducted with antibody modified polyethylene terephthalate (PET) pads as capture substrates. In our approach, blended lettuce sample cocktail was circulated through antibody modified PET pads such as a checkpoint in the sample solution pathway, where target pathogens were selectively captured with immobilized antibodies. The obtained PET pads with the captured target pathogens were then used for enhanced detection by colorimetry. To render the checkpoint-style enrichment approach practical and applicable for on-site rapid screening tests, only a simple syringe-based setup with antibody modified PET pad was required. The developed method could process up to 50 ml of lettuce cocktail blended from 5g samples and purposefully inoculated with E. coli O157:H7. Overall, the enrichment method developed required only 40 min of sample processing time. After enrichment, as low as 100 CFU/ml of E. coli O157:H7 could be detected by a simple colorimetric procedure due to the enhancement from the proposed checkpoint-style enrichment in the presence of ∼3000 CFU/ml of non-target bacteria. A linear response was obtained from blank to 100000 CFU/ml of E. coli O157:H7 in blended lettuce samples. The conceptualized approach demonstrates a promising means to improve the detection of target bacteria with a high degree of sensitivity and specificity and could be used in low resourse settings.

3D carbon nanosphere and gold nanoparticle-based voltammetric cytosensor for cell line A549 and for early diagnosis of non-small cell lung cancer cells

An electrochemical cytosensor for the detection of the non-small-cell lung cancer cell line A549 (NSCLC) had been developed. A microwave-hydrothermal method was employed to prepare monodisperse colloidal carbon nanospheres (CNSs). Gold nanoparticles (AuNPs) were placed on the surface of the colloidal CNSs by self-assembly to obtain 3D-structured microspheres of the type CNS@AuNP. The results of an MTT assay show the microspheres to possess good biocompatibility. The CNS@AuNP nanocomposite was then placed, in a chitosan film, on a glassy carbon electrode (GCE). The voltammetric signals and detection sensitivity are significantly enhanced owing to the synergistic effect of CNSs and AuNPs. A cytosensor was then obtained by immobilization of antibody against the carcinoembryonic antigen (which is a biomarker for NSCLC) on the GCE via crosslinking with glutaraldehyde. Hexacyanoferrate is used as an electrochemical probe, and the typical working voltage is 0.2 V (vs. SCE). If exposed to A549 cells, the differential pulse voltammetric signal decreases in the 4.2 × 10^-1 to 4.2 × 10^-6 cells mL^-1 concentration range, and the detection limit is 14 cells mL^-1 (at S/N = 3). Graphical abstract Schematic presentation of design strategy and fabrication process of the electrochemical cytosensor for A549 cells. (CNS: carbon nanospheres; GA: glutaraldehyde; PEI: polyethyleneimine; AuNPs: gold nanoparticles; BSA: Bovine serum albumin).

Two-dimensional gold trisoctahedron nanoparticle superlattice sheets: self-assembly, characterization and immunosensing applications

Nanoparticles were called "artificial atoms" about two decades ago due to their ability to organize into regular lattices or supracrystals. Their self-assembly into free-standing, two-dimensional (2D) nanoparticle arrays enables the generation of 2D metamaterials for novel applications in sensing, nanophotonics and energy fields. However, their controlled fabrication is nontrivial due to the complex nanoscale forces among nanoparticle building blocks. Here, we report a new type of 2D plasmonic superlattice from high-index gold trisoctahedron (TOH) nanoparticles. TOH is an anisotropic polyhedron with 24 facets and 14 vertices. By using polymer ligands in conjunction with drying-mediated self-assembly, we obtained highly ordered 2D superlattices as quantified by synchrotron based grazing-incidence small-angle X-ray scattering (GISAXS). The plasmonic properties were optimized by adjusting the ligand length and particle size. The excellent surface-enhanced Raman scattering (SERS) performance enables us to demonstrate TOH superlattices as uniform SERS immunosubstrates with a detection limit down to 1 pg ml^-1 and a dynamic range from 1 pg ml^-1 to 100 ng ml^-1.

A non-competitive surface plasmon resonance immunosensor for rapid detection of triazophos residue in environmental and agricultural samples

The wide application of an organophosphate pesticide triazophos raises concern on the environmental pollution and the potential risk to human health. Thus, it is crucial to regularly monitor triazophos residue in the environment and agro-products. Herein we described a non-competitive immunoassay for trace detection of triazophos using a direct surface plasmon resonance (SPR) biosensor. Two anti-triazophos monoclonal antibodies (mAbs) were immobilized on the sensor chip and characterized by SPR-based kinetic analysis. The mAb with relatively slow dissociation rate was used for direct immunosensing of triazophos. The biosensor assay showed a high specificity and a low detection limit of 0.096ngmL^-1 to triazophos, with the linear detection range of 0.98-8.29ngmL^-1. Under the optimal condition, the sensor chip could be regenerated for 160cycles at least. Moreover, the sensitive method was applied to determine triazophos in the spiked environmental water and agricultural products, as well as in unknown real-life samples (including Chinese cabbage, cucumber, and apple). Desirable results demonstrated that the newly-developed immunosensor could be used as a rapid, convenient, and reliable tool to regularly monitor triazophos and meet the detection requirement of its maximum residue limits.

Development of a phage chemiluminescent enzyme immunoassay with high sensitivity for the determination of imidaclothiz in agricultural and environmental samples

In this study, we isolated six phage-displayed peptides by biopanning phage-displayed peptide libraries on an immobilized anti-imidaclothiz monoclonal antibody. After analyzing the relative sensitivity of the individual phage-displayed peptides, we subsequently developed and optimized both a phage enzyme immunoassay (P-ELISA) and a phage chemiluminescent enzyme immunoassay (P-CLEIA) to improve the sensitivity and linear range of imidaclothiz assays. The P-CLEIA (50% inhibition concentration (IC₅₀) of 0.86ngmL^-1, linear range of 0.13-5.84ngmL^-1) was more sensitive and had a wider linear range compared to the P-ELISA (IC₅₀ of 1.45ngmL^-1, linear range of 0.55-3.82ngmL^-1). Besides, the sensitivities of the P-ELISA and P-CLEIA were increased by >4-fold and 8-fold, respectively as compared to homologous immunoassays developed using the same monoclonal antibody. Neither method had significant cross-reactivity with the analogues of imidaclothiz except for imidacloprid. Recoveries of the P-ELISA and P-CLEIA for imidaclothiz in paddy water, soil, cabbage, rice, apple, pakchoi, pear and tomato samples were 72.3-101.3% and 73.9-102.6%, respectively. The P-ELISA and P-CLEIA detected imidaclothiz in the authentic samples, and showed good correlation with results obtained from high-performance liquid chromatography (HPLC).

Electrokinetically operated microfluidic devices for integrated immunoaffinity monolith extraction and electrophoretic separation of preterm birth biomarkers

Biomarkers are often present in complex biological fluids like blood, requiring multiple, slow sample preparation steps that pose limitations in simplifying analysis. Here we report integrated immunoaffinity extraction and separation devices for analysis of preterm birth biomarkers in a human blood serum matrix. A reactive polymer monolith was used for immobilization of antibodies for selective extraction of target preterm birth biomarkers. Microfluidic immunoaffinity extraction protocols were optimized and then integrated with microchip electrophoresis for separation. Using these integrated devices, a ∼30 min analysis was carried out on low nanomolar concentrations of two preterm birth biomarkers spiked in a human serum matrix. This work is a promising step towards the development of an automated, integrated platform for determination of preterm birth risk.

Cost-Effective and Handmade Paper-Based Immunosensing Device for Electrochemical Detection of Influenza Virus

Although many studies concerning the detection of influenza virus have been published, a paper-based, label-free electrochemical immunosensor has never been reported. Here, we present a cost-effective, handmade paper-based immunosensor for label-free electrochemical detection of influenza virus H1N1. This immunosensor was prepared by modifying paper with a spray of hydrophobic silica nanoparticles, and using stencil-printed electrodes. We used a glass vaporizer to spray the hydrophobic silica nanoparticles onto the paper, rendering it super-hydrophobic. The super-hydrophobicity, which is essential for this paper-based biosensor, was achieved via 30-40 spray coatings, corresponding to a 0.39-0.41 mg cm-2 coating of nanoparticles on the paper and yielding a water contact angle of 150° ± 1°. Stencil-printed carbon electrodes modified with single-walled carbon nanotubes and chitosan were employed to increase the sensitivity of the sensor, and the antibodies were immobilized via glutaraldehyde cross-linking. Differential pulse voltammetry was used to assess the sensitivity of the sensors at various virus concentrations, ranging from 10 to 10⁴ PFU mL-1, and the selectivity was assessed against MS2 bacteriophages and the influenza B viruses. These immunosensors showed good linear behaviors, improved detection times (30 min), and selectivity for the H1N1 virus with a limit of detection of 113 PFU mL-1, which is sufficiently sensitive for rapid on-site diagnosis. The simple and inexpensive methodologies developed in this study have great potential to be used for the development of a low-cost and disposable immunosensor for detection of pathogenic microorganisms, especially in developing countries.

Polymethacrylate Coated Electrospun PHB Fibers as a Functionalized Platform for Bio-Diagnostics: Confirmation Analysis on the Presence of Immobilized IgG Antibodies against Dengue Virus

In this article, a combination of far field electrospinning (FFES) and free-radical polymerization has been used to create a unique platform for protein immobilization via the physical attachment of biomolecules to the surface of the fiber mats. The large specific surface area of the fibers with its tailored chemistry provides a desirable platform for effective analyte-surface interaction. The detailed analysis of protein immobilization on a newly developed bio-receptive surface plays a vital role to gauge its advantages in bio-diagnostic applications. We relied on scanning electron microscopy (SEM), diameter range analysis, and X-ray photoelectron spectroscopy (XPS), along with thermal gravimetric analysis (TGA), water-in-air contact angle analysis (WCA), Fourier transform infrared spectroscopy (FTIR), and atomic force microscopy (AFM) to study our developed platforms and to provide valuable information regarding the presence of biomolecular entities on the surface. Detailed analyses of the fiber mats before and after antibody immobilization have shown obvious changes on the surface of the bioreceptive surface including: (i) an additional peak corresponding to the presence of an antibody in TGA analysis; (ii) extra FTIR peaks corresponding to the presence of antibodies on the coated fiber platforms; and (iii) a clear alteration in surface roughness recorded by AFM analysis. Confirmation analyses on protein immobilization are of great importance as they underlay substantial grounds for various biosensing applications.

Electrochemical Flow-ELISA for Rapid and Sensitive Determination of Microcystin-LR Using Automated Sequential Injection System

An amperometric immunoanalysis system based on monoclonal antibodies immobilized on Sepharose beads and packed into a micro-immunocolumn was developed for the quantification of microcystin-LR. Microcystin-LR (MCLR) was used as a reference microcystin variant. Inside the immunocolumn, free microcystins and microcystin-horseradish peroxidase (tracer) were sequentially captured by the immobilized antibodies, and the detection was performed electrochemically using Super AquaBlue ELISA substrate 2,2'-azinobis(3-ethylbenzothiazoline-sulfonic acid) (ABTS). The ABTS^●+ generated by enzymatic oxidation of ABTS was electrochemically determined at a carbon working electrode by applying a reduction potential set at 0.4 V versus Ag/AgCl reference electrode. The peak current intensity was inversely proportional to the amount of analyte bound to the immunocolumn. The amperometric flow-ELISA system, which was automatically controlled through the CapSenze^TM (Lund, Sweden) computer software, enabled determination of MCLR as low as 0.01 µg/L. The assay time was very short (20 min for one assay cycle). In addition, the electrochemical signals were not significantly affected by possible interferences which could be present in the real samples. Along with the simplicity of automation, this makes the developed method a promising tool for use in water quality assessment.

A Portable Immunosensor with Differential Pressure Gauges Readout for Alpha Fetoprotein Detection

A portable, affordable and simple detector is requested in a "Point-of-Care-Testing" (POCT) system. In this study, we exploited the potentialities of Differential Pressure Gauge (DPG) to the orientation of POCT technology. Alpha fetoprotein (AFP) was chosen as a model analyte that could specifically recognized by its antigen, and a tiny outfits equipped with a DPG was employed as the signal readout. Pt/SiO2 nanospheres were synthesized and modified with the detection antibody. In the presence of target, a sandwich of immunocomplex specifically formed and the Pt/SiO2 had been modified on the capture antibody. Which then can be dissolved to release plenty of Pt and the suspensions were transferred into a closed vial filled with appropriated amount of hydrogen peroxide. Subsequently, hydrogen peroxide was decomposed to produce oxygen, resulting in the enhancement of pressure in the closed vial and which can be detected by DPG easily. Under the optimized conditions, the read out signal from DPG had a direct relationship with AFP concentrations in the range of 10~200 ng/mL, and the detection limit was as low as 3.4 ng/mL. The proposed portable sensor had been successfully applied to detect AFP in serum samples with satisfactory results. This strategy holds a great promising in biological analysis as its convenient operations, reliable results and flexible apparatus.

Bioinspired Hierarchically Structured Surfaces for Efficient Capture and Release of Circulating Tumor Cells

The development of novel bioinspired surfaces with hierarchical micro- and nanoscale topographic structures for efficient capture and release of circulating tumor cells (CTCs) is reported. The capture of CTCs, facilitated by surface-immobilized epithelial cell adhesion molecule antibodies (anti-EpCAM), was shown to be significantly enhanced in novel three-dimensional hierarchically structured surfaces that were fabricated by replicating the natural micro- and nanostructures of rose petals. Under static conditions, these hierarchical capture substrates exhibited up to 6 times higher cell capture ability at concentrations of 100 cells mL^-1 in contrast to flat anti-EpCAM-functionalized polydimethylsiloxane (PDMS) surfaces. As indicated by scanning electron microscopy (SEM) and immunofluorescent images, this enhancement can be in large part attributed to the topographical interaction between nanoscale cell surface components and nanostructures on the substrate. Similarly, the increased surface area affords a higher nominal coverage of anti-EpCAM, which increases the number of available binding sites for cell capture. By treating the substrates with the biocompatible reductant glutathione (GSH), up to 85% of the captured cells were released, which displayed over 98% cell viability after culturing on tissue culture polystyrene (TCP) for 24 h. Therefore, these bioinspired hierarchically structured and functionalized substrates can be successfully applied to capture CTCs, as well as release CTCs for subsequent analysis. These findings provide new prospects for designing cell-material interfaces for advanced cell-based biomedical studies in the future.

DNA-Directed Antibody Immobilization for Robust Protein Microarrays: Application to Single Particle Detection 'DNA-Directed Antibody Immobilization

Protein microarrays are emerging tools which have become very powerful in multiplexed detection technologies. A variety of proteins can be immobilized on a sensor chip allowing for multiplexed diagnostics. Therefore, various types of analyte in a small volume of sample can be detected simultaneously. Protein immobilization is a crucial step for creating a robust and sensitive protein microarray-based detection system. In order to achieve a successful protein immobilization and preserve the activity of the proteins after immobilization, DNA-directed immobilization is a promising technique. Here, we present the design and the use of DNA-directed immobilized (DDI) antibodies in fabrication of robust protein microarrays. We focus on application of protein microarrays for capturing and detecting nanoparticles such as intact viruses. Experimental results on Single-particle interferometric reflectance imaging sensor (SP-IRIS) are used to validate the advantages of the DDI method.

Sorption of his-tagged Protein G and Protein G onto chitosan/divalent metal ion sorbent used for detection of microcystin-LR

A highly sensitive, specific, simple, and rapid chemiluminescence enzyme immunoassay (CLEIA) was developed for the determination of microcystin-LR (MC-LR) by using strategies for oriented immobilization of functionally intact polyclonal antibodies on chitosan surface. Several physicochemical parameters such as metal ion adsorption, hexahistidine-tagged Protein G sorption, the dilution ratio polyclonal antibody concentration, and peroxidase-labeled MC-LR concentration were studied and optimized. The sorption in batch system of G-histidine and G-proteins was studied on a novel sorbent consisting of chitosan/divalent metal ions. Transition metals as Ni⁺⁺ and Zn⁺⁺ were immobilized through interaction with -NH₂ groups of chitosan in order to supply a material capable to efficiently remove the proteins from aqueous solutions. The maximum uptake of divalent metals onto the chitosan material was found to be 230 mg g^-1 for Zn⁺⁺ and 62 mg g^-1 for Ni⁺⁺. Experimental data were evaluated using the Langmuir and Freundlich models; the results were well fitted with the Langmuir model; chitosan/Ni⁺⁺ foam was found to be the best sorbent for G-protein, maximum sorption capacity obtained was 17 mg g^-1, and chitosan/Zn⁺⁺ was found to be the best for G-histidine with a maximum sorption capacity of 44 mg g^-1. Kinetic data was evaluated with pseudo-first- and pseudo-second-order models; the sorption kinetics were in all cases better represented by a pseudo-second-order model. Under optimum conditions, the calibration curve obtained for MC-LR gave detection limits of 0.5 ± 0.06 μg L^-1, the 50 % inhibition concentration (IC50) was 2.75 ± 0.03 μg L^-1, and the quantitative detection range was 0.5-25 μg L^-1. The limit of detection (LOD) attained from the calibration curves and the results obtained demonstrate the potential use of CLEIA with chitosan support as a screening tool for the analysis of pollutants in environmental samples.

Advancing the global proteome survey platform by using an oriented single chain antibody fragment immobilization approach

Increasing the understanding of a proteome and how its protein composition is affected by for example different diseases, such as cancer, has the potential to improve strategies for early diagnosis and therapeutics. The Global Proteome Survey or GPS is a method that combines mass spectrometry and affinity enrichment with the use of antibodies. The technology enables profiling of complex proteomes in a species independent manner. The sensitivity of GPS, and other methods relying on affinity enrichment, is largely affected by the activity of the exploited affinity reagent. We here present an improvement of the GPS platform by utilizing an antibody immobilization approach which ensures a controlled immobilization process of the antibody to the magnetic bead support. More specifically, we make use of an antibody format that enables site-directed biotinylation and use this in combination with streptavidin coated magnetic beads. The performance of the expanded GPS platform was evaluated by profiling yeast proteome samples. We demonstrate that the oriented antibody immobilization strategy increases the ability of the GPS platform and results in larger fraction of functional antibodies. Additionally, we show that this new antibody format enabled in-solution capture, i.e. immobilization of the antibodies after sample incubation. A workflow has been established that permit the use of an oriented immobilization strategy for the GPS platform.

Surface functionalization allowing repetitive use of optical sensors for real-time detection of antibody-bacteria interaction

In this study, sensor surface functionalization allowing the repetitive use of a sensing device was evaluated for antibody-based detection of living bacteria using an optical planar Bragg grating sensor. To achieve regenerable immobilization of bacteria specific antibodies, the heterobifunctional cross-linker N-succinimidyl 3-(2-pyridyldithio) propionate (SPDP) was linked to an aminosilanized sensor surface and subsequently reduced to expose sulfhydryl groups enabling the covalent conjugation of SPDP-activated antibodies via disulfide bonds. The immobilization of a capture antibody specific for Staphylococcus aureus on the sensor surface as well as specific binding of S. aureus could be monitored, highlighting the applicability of optical sensors for the specific detection of large biological structures. Reusability of bacteria saturated sensors was successfully demonstrated by cleaving the antibody along with bound bacteria through reduction of disulfide bonds and subsequent re-functionalization with activated antibody, resulting in comparable sensitivity towards S. aureus.

Efficient capture and simple quantification of circulating tumor cells using quantum dots and magnetic beads

Circulating tumor cells (CTCs) are valuable biomarkers for monitoring the status of cancer patients and drug efficacy. However, the number of CTCs in the blood is extremely low, and the isolation and detection of CTCs with high efficiency and sensitivity remain a challenge. Here, we present an approach to the efficient capturing and simple quantification of CTCs using quantum dots and magnetic beads. Anti-EpCAM antibody-conjugated quantum dots are used for the targeting and quantification of CTCs, and quantum-dot-attached CTCs are isolated using anti-IgG-modified magnetic beads. Our approach is shown to result in a capture efficiency of about 70%-80%, enabling the simple quantification of captured CTCs based on the fluorescence intensity of the quantum dots. The present method can be used effectively in the capturing and simple quantification of CTCs with high efficiency for cancer diagnosis and monitoring.

Extended nanofluidic immunochemical reaction with femtoliter sample volumes

The growing need to optimize immunoassay performance driven by interest in analyzing individual cells has resulted in a decrease in the amount of sample required. Miniaturized immunoassays that use ultra-small femtoliter to attoliter sample volumes, a range known as the extended nanospace, can satisfy this analytical need; however, capturing every targeted molecule without loss in extended nanochannels for subsequent detection remains challenging. This is the first report of a successful extended nanofluidics-based quantitative immunochemical reaction capable of high capture efficiency using a femtoliter-scale sample volume. A novel patterning method using a photolithographic technique with vacuum ultraviolet light and low-temperature (100 °C) bonding enables patterning of functional groups for antibody immobilization before bonding, resulting in an immunochemical reaction space of only 86 fL. Reaction rate analyses indicate a decrease in the required sample volume to 810 fL and improvement in the limit of detection to 3 zmol, 5-6 orders of magnitude better than possible with the microfluidic immunoassay format. Highly efficient (near 100%) immunochemical reactions on a seconds time scale are possible due to the nm-scale diffusion length, which should be advantageous for the analysis of ultra-low-volume samples.

A sandwich-type immunosensor using Pd-Pt nanocrystals as labels for sensitive detection of human tissue polypeptide antigen

A sandwich-type immunosensor was developed for the detection of human tissue polypeptide antigen (hTPA). In this work, a graphene sheet (GS) was synthesized to modify the surface of a glassy carbon electrode (GCE), and Pd-Pt bimetallic nanocrystals were used as secondary-antibody (Ab2) labels for the fabrication of the immunosensor. The amperometric response of the immunosensor for catalyzing hydrogen peroxide (H2O2) was recorded. And electrochemical impedance spectroscopy was used to characterize the fabrication process of the immunosensor. The anti-human tissue polypeptide antigen primary antibody (Ab1) was immobilized onto the GS modified GCE via cross-linking with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide (EDC/NHS). With Ab1 immobilized onto the GS modified GCE and Ab2 linked on Pd-Pt bimetallic nanocrystals, the immunosensor demonstrated a wide linear range (0.0050-15 ng ml(-1)), a low detection limit (1.2 pg ml(-1)), good reproducibility, good selectivity and acceptable stability. This design strategy may provide many potential applications in the detection of other cancer biomarkers.

Array-based immunoassays with rolling-circle amplification detection

This chapter describes methods for the use of antibody microarrays with rolling-circle amplification (RCA). The methods are divided into three sections. The first section covers antibody preparation and microarray production, the second describes the method for using biological samples on antibody microarrays, and the third describes the method for RCA use on antibody microarrays. RCA can be used on antibody microarrays to increase the signal from each antibody spot and lower the detection limits of the assays. We also describe a practical method for running multiple, low-volume microarrays on a single microscope slide. These methods should be useful for researchers interested in rapidly developing and optimizing custom immunoassays for the analysis of low-abundance analytes using low sample volumes.

Application of carbon nanotubes layered on silicon wafer for the detection of breast cancer marker carbohydrate antigen 15-3 by immuno-polymerase chain reaction

A highly sensitive detection of breast cancer marker, carbohydrate antigen 15-3 (CA 15-3) by carbon nanotube (CNT) based immuno-polymerase chain reaction was reported. The study was aimed to develop a precise and sensitive method to diagnose breast cancer and its recurrence. The hydrofluoric acid (HF) treated silicon wafer layered with bundled CNT was used as the substrate. The surface was treated with HNO3/H2SO4 to graft carboxyl groups on the tips of CNT. Subsequently, polyoxyethylene bis-amine was grafted to conjugate anti human CA 15-3 antibodies. Water contact angle measurement, scanning electron microscope, Fourier transform infrared spectrometer, Raman spectrometer and sodium dodecyl sulfate polyacrylamide gel electrophoresis were employed to confirm the surface modification. The captured antibodies on the CNT were used to capture the target antigen CA 15-3 and the biotinylated secondary antibodies were subsequently bound with the target antigen. A bi-functional streptavidin was used to link biotinylated DNA to the biotinylated detection antibodies. The biotinylated target DNA was amplified by PCR, and then analyzed by agarose gel electrophoresis. The lower limit of detection of CA 15-3 by the proposed immuno-PCR system was 0.001 U/mL, which is extremely sensitive than the other bioanalytical techniques.

Atrazine-based self-assembled monolayers and their interaction with anti-atrazine antibody: building of an immunosensor

As a part of our objective to build an immunosensor for the detection of the pesticide atrazine (ATZ) in environmental samples, we studied the self-assembling process of the disulfide derivative of the pesticide atrazine on a gold substrate. Atrazine-based self-assembled monolayers were characterized by ellipsometry, scanning tunneling microscopy, polarization-modulation infrared reflection-absorption spectroscopy (PM IRRAS), X-ray photoelectron spectroscopy and quartz crystal microbalance (QCM) measurements. Two different time constants for the adsorption process were observed, depending on the experimental method used. The QCM data reflect adsorption kinetics of the original disulfide compound, whereas ellipsometry and ex situ PM IRRAS refer to the formation of thiolate (ATZS) monolayers. In situ QCM data demonstrated the suitability of such monolayers for the detection of atrazine in aqueous samples. Exposure of the ATZS sensing surface to an anti-atrazine antibody (anti-ATZ IgG) resulted in complete coverage of the surface by antibody, whereas approximately half of the antibody molecules were displaced from the QCM sensor surface by further addition of atrazine into the solution.

Design and fabrication of low-cost 1536-chamber microfluidic microarrays for mood-disorders-related serological studies

Mood disorders are common mental diseases, but physiological diagnostic methods are still lacking. Since much evidence has implied a relationship between mood disorders and the protein composition of blood sera, it is conceivable to develop a serological criterion for assisting diagnosis of mood disorders, based on a correlative database with enough capacity and high quality. In this pilot study, a low-cost microfluidic microarray device for quantifying at most 384 serological biomarkers at the same time was designed for the data acquisition of the serological study. The 1,536-chamber microfluidic device was modeled on a 1,536-well microtiter plate in order to employ a common microplate reader as the detection module for measuring the chemiluminescent immunoassay tests on the chips. The microfluidic microarrays were rapidly fabricated on polymethylmethacrylate slides using carbon dioxide laser ablation, followed by effective surface treatment processing. Sixteen types of different capture antibodies were immobilized on the chips to test the corresponding hormones and cytokines. The preliminary tests indicated that the signal-to-noise ratio and the limit of detection of microfluidic microarrays have reached the level of standard ELISA tests, whereas the operation time of microfluidic microarrays was sharply reduced.

Reduction of nanoparticle avidity enhances the selectivity of vascular targeting and PET detection of pulmonary inflammation

Targeting nanoparticles (NPs) loaded with drugs and probes to precise locations in the body may improve the treatment and detection of many diseases. Generally, to achieve targeting, affinity ligands are introduced on the surface of NPs that can bind to molecules present on the cell of interest. Optimization of ligand density is a critical parameter in controlling NP binding to target cells, and a higher ligand density is not always the most effective. In this study, we investigated how NP avidity affects targeting to the pulmonary vasculature, using NPs targeted to ICAM-1. This cell adhesion molecule is expressed by quiescent endothelium at modest levels and is upregulated in a variety of pathological settings. NP avidity was controlled by ligand density, with the expected result that higher avidity NPs demonstrated greater pulmonary uptake than lower avidity NPs in both naive and pathological mice. However, in comparison with high-avidity NPs, low-avidity NPs exhibited several-fold higher selectivity of targeting to pathological endothelium. This finding was translated into a PET imaging platform that was more effective in detecting pulmonary vascular inflammation using low-avidity NPs. Furthermore, computational modeling revealed that elevated expression of ICAM-1 on the endothelium is critical for multivalent anchoring of NPs with low avidity, while high-avidity NPs anchor effectively to both quiescent and activated endothelium. These results provide a paradigm that can be used to optimize NP targeting by manipulating ligand density and may find biomedical utility for increasing detection of pathological vasculature.

A fast universal immobilization of immunoglobulin G at 4 °C for the development of array-based immunoassays

To maintain the antibody activity and enhance performance of array-based immunoassays, protein G was used to allow a shorter duration of immunoglobulin G immobilization at 4 °C, with the antibody placed in the appropriate orientation. The multiplexed detection of six pain-related message molecules (PRMMs) was used as examples for the development of array-based immunoassays: substance P, calcitonin gene-related peptide, nerve growth factor, brain-derived neurotrophic factor, tumor necrosis factor-α, and β-endorphin. Protein G- and non-protein G-coated slides were tested. Compared to non-protein G immunoassays, protein G shortened the antibody immobilization time at 4 °C from overnight to 2 hours. Only protein G-facilitated immunoassays succeeded in simultaneously detecting all six PRMMs with high specificity. Dose-response curves showed that the limits of detection of the protein G-multiplexed immunoassays for the PRMMs was approximately 164, 167, 120, 60, 80, and 92 pg/ml, respectively. Thus, protein G effectively shortens the duration of antibody immobilization at 4 °C, allowing the use of sensitive array-based immunoassays for the simultaneous detection of PRMMs.

Biorecognition layer engineering: overcoming screening limitations of nanowire-based FET devices

Detection of biological species is of great importance to numerous areas of medical and life sciences from the diagnosis of diseases to the discovery of new drugs. Essential to the detection mechanism is the transduction of a signal associated with the specific recognition of biomolecules of interest. Nanowire-based electrical devices have been demonstrated as a powerful sensing platform for the highly sensitive detection of a wide-range of biological and chemical species. Yet, detecting biomolecules in complex biosamples of high ionic strength (>100 mM) is severely hampered by ionic screening effects. As a consequence, most of existing nanowire sensors operate under low ionic strength conditions, requiring ex situ biosample manipulation steps, that is, desalting processes. Here, we demonstrate an effective approach for the direct detection of biomolecules in untreated serum, based on the fragmentation of antibody-capturing units. Size-reduced antibody fragments permit the biorecognition event to occur in closer proximity to the nanowire surface, falling within the charge-sensitive Debye screening length. Furthermore, we explored the effect of antibody surface coverage on the resulting detection sensitivity limit under the high ionic strength conditions tested and found that lower antibody surface densities, in contrary to high antibody surface coverage, leads to devices of greater sensitivities. Thus, the direct and sensitive detection of proteins in untreated serum and blood samples was effectively performed down to the sub-pM concentration range without the requirement of biosamples manipulation.

MRl of prostate cancer antigen expression for diagnosis and immunotherapy

Background

Tumor antigen (TA)–targeted monoclonal antibody (mAb) immunotherapy can be effective for the treatment of a broad range of cancer etiologies; however, these approaches have demonstrated variable clinical efficacy for the treatment of patients with prostate cancer (PCa). An obstacle currently impeding translational progress has been the inability to quantify the mAb dose that reaches the tumor site and binds to the targeted TAs. The coupling of mAb to nanoparticle-based magnetic resonance imaging (MRI) probes should permit in vivo measurement of patient-specific biodistributions; these measurements could facilitate future development of novel dosimetry paradigms wherein mAb dose is titrated to optimize outcomes for individual patients.

Methods

The prostate stem cell antigen (PSCA) is broadly expressed on the surface of prostate cancer (PCa) cells. Anti-human PSCA monoclonal antibodies (mAb 7F5) were bound to Au/Fe₃O₄ (GoldMag) nanoparticles (mAb 7F5@GoldMag) to serve as PSCA-specific theragnostic MRI probe permitting visualization of mAb biodistribution in vivo. First, the antibody immobilization efficiency of the GoldMag particles and the efficacy for PSCA-specific binding was assessed. Next, PC-3 (prostate cancer with PSCA over-expression) and SMMC-7721 (hepatoma cells without PSCA expression) tumor-bearing mice were injected with mAb 7F5@GoldMag for MRI. MRI probe biodistributions were assessed at increasing time intervals post-infusion; therapy response was evaluated with serial tumor volume measurements.

Results

Targeted binding of the mAb 7F5@GoldMag probes to PC-3 cells was verified using optical images and MRI; selective binding was not observed for SMMC-7721 tumors. The immunotherapeutic efficacy of the mAb 7F5@GoldMag in PC-3 tumor-bearing mice was verified with significant inhibition of tumor growth compared to untreated control animals.

Conclusion

Our promising results suggest the feasibility of using mAb 7F5@GoldMag probes as a novel paradigm for the detection and immunotherapeutic treatment of PCa. We optimistically anticipate that the approaches have the potential to be translated into the clinical settings.

Signal amplification by magnetic force on polydiacetylene supramolecules for detection of prostate cancer

A method in which a permanent magnet is introduced onto polydiacetylene (PDA) vesicle chips is introduced for enhancement of the fluorescence of PDA vesicles. This strategy can be applied to general antibody-based PDA vesicle chips to detect clinically important biomarkers for disease diagnosis.