Site-directed immobilization of antibody using EDC-NHS-activated protein A on a bimetallic-based surface plasmon resonance chip

Signal amplification of a quartz crystal microbalance immunosensor by gold nanoparticles-polyethyleneimine for hepatitis B biomarker detection

The procedures currently used for hepatitis B (HB) detection are not suitable for screening, clinical diagnosis, and point-of-care testing (POCT). Therefore, we developed and tested a QCM-based immunosensor by surface modification with AuNP-PEIs to amplify the signal and provide an oriented-immobilization surface. The AuNP-PEIs were characterized by ICP-Mass, UV/Vis, DLS, FE-SEM, and ATR-FTIR. After coating AuNP-PEIs on the gold electrode surface, anti-HBsAg antibodies were immobilized using NHS/EDC chemistry based on response surface methodology (RSM) optimization. The efficiency of the immunosensor was assessed by human sera and data were compared to gold-standard ELISA using receiver-operating-characteristic (ROC) analysis. FE-SEM, AFM, EDS, and EDS mapping confirmed AuNP-PEIs are homogeneously distributed on the surface with a high density and purity. After antibody immobilization, the immunosensor exhibited good recognition of HBsAg with a calibration curve of ∆F =  - 6.910e-7x + 10(R2 = 0.9905), a LOD of 1.49 ng/mL, and a LOQ of 4.52 ng/mL. The immunosensor yielded reliable and accurate results with a specificity of 100% (95% CI 47.8-100.0) and sensitivity of 100% (95% CI 96.2-100.0). In conclusion, the fabricated immunosensor has the potential as an analytic tool with high sensitivity and specificity. However, further investigations are needed to convert it to a tiny lab-on-chip for HB diagnosis in clinical samples.

Semi-Synthetic Click-Gelatin Hydrogels as Tunable Platforms for 3D Cancer Cell Culture

Basement membrane extracts (BME) derived from Engelbreth-Holm-Swarm (EHS) mouse sarcomas such as Matrigel^® remain the gold standard extracellular matrix (ECM) for three-dimensional (3D) cell culture in cancer research. Yet, BMEs suffer from substantial batch-to-batch variation, ill-defined composition, and lack the ability for physichochemical manipulation. Here, we developed a novel 3D cell culture system based on thiolated gelatin (Gel-SH), an inexpensive and highly controlled raw material capable of forming hydrogels with a high level of biophysical control and cell-instructive bioactivity. We demonstrate the successful thiolation of gelatin raw materials to enable rapid covalent crosslinking upon mixing with a synthetic poly(ethylene glycol) (PEG)-based crosslinker. The mechanical properties of the resulting gelatin-based hydrogels were readily tuned by varying precursor material concentrations, with Young's moduli ranging from ~2.5 to 5.8 kPa. All hydrogels of varying stiffnesses supported the viability and proliferation of MDA-MB-231 and MCF-7 breast cancer cell lines for 14 and 21 days of cell culture, respectively. Additionally, the gelatin-based hydrogels supported the growth, viability, and osteogenic differentiation of patient-derived preosteoblasts over 28 days of culture. Collectively, our data demonstrate that gelatin-based biomaterials provide an inexpensive and tunable 3D cell culture platform that may overcome the limitations of traditional BMEs.

Microfluidic synthesis of Janus-structured QD-encoded magnetic microbeads for multiplex immunoassay

Uniform and monodisperse quantum dot (QD)-encoded magnetic microbeads with Janus structure were produced in a microfluidic device via photopolymerization. UV light through a microscope objective was used to solidify the microbeads which showed sharp interfaces and excellent magnetic responses. QDs with different emission peaks (450 nm for blue and 640 nm for red) were mixed at different ratios to provide three spectral codes. The QD-encoded microbeads can be distinguished by analyzing their fluorescent images in HSV color space. After hydrolysis of the anhydride group in alkaline solution, protein was immobilized on microbeads via activation of carboxyl groups using (1-ethyl-3(3-dimethylaminoprophyl) carbodiimide/N-hydroxysuccinimide (EDC/NHS). A microhole array in polydimethylsiloxane (PDMS) substrates with a specific size was fabricated to trap individual microbeads in a single microhole. The combination of Janus-structured QD-encoded magnetic microbeads and microhole arrays facilitates both flexibility, binding kinetics, sensitivity for suspension assay, and fluorescence mapping analysis for conventional biochips, thus providing a novel platform for multiplex bioanalysis. The capability of this integration for multiplex immunoassays was verified using three kinds of IgG and their corresponding anti-IgG. A detection limit of 0.07 ng/mL was achieved for human IgG, indicating practical applications in various fields.

Recent Advancements in Receptor Layer Engineering for Applications in SPR-Based Immunodiagnostics

The rapid progress in the development of surface plasmon resonance-based immunosensing platforms offers wide application possibilities in medical diagnostics as a label-free alternative to enzyme immunoassays. The early diagnosis of diseases or metabolic changes through the detection of biomarkers in body fluids requires methods characterized by a very good sensitivity and selectivity. In the case of the SPR technique, as well as other surface-sensitive detection strategies, the quality of the transducer-immunoreceptor interphase is crucial for maintaining the analytical reliability of an assay. In this work, an overview of general approaches to the design of functional SPR-immunoassays is presented. It covers both immunosensors, the design of which utilizes well-known and often commercially available substrates, as well as the latest solutions developed in-house. Various approaches employing chemical and passive binding, affinity-based antibody immobilization, and the introduction of nanomaterial-based surfaces are discussed. The essence of their influence on the improvement of the main analytical parameters of a given immunosensor is explained. Particular attention is paid to solutions compatible with the latest trends in the development of label-free immunosensors, such as platforms dedicated to real-time monitoring in a quasi-continuous mode, the use of in situ-generated receptor layers (elimination of the regeneration step), and biosensors using recombinant and labelled protein receptors.

A Reliable, Label Free Quality Control Method for the Production of DNA Microarrays with Clinical Applications

The manufacture of a very high-quality microarray support is essential for the adoption of this assay format in clinical routine. In fact, poorly surface-bound probes can affect the diagnostic sensitivity or, in worst cases, lead to false negative results. Here we report on a reliable and easy quality control method for the evaluation of spotted probe properties in a microarray test, based on the Interferometric Reflectance Imaging Sensor (IRIS) system, a high-resolution label free technique able to evaluate the variation of the mass bound to a surface. In particular, we demonstrated that the IRIS analysis of microarray chips immediately after probe immobilization can detect the absence of probes, which recognizably causes a lack of signal when performing a test, with clinical relevance, using fluorescence detection. Moreover, the use of the IRIS technique allowed also to determine the optimal concentration of the probe, that has to be immobilized on the surface, to maximize the target recognition, thus the signal, but to avoid crowding effects. Finally, through this preliminary quality inspection it is possible to highlight differences in the immobilization chemistries. In particular, we have compared NHS ester versus click chemistry reactions using two different surface coatings, demonstrating that, in the diagnostic case used as an example (colorectal cancer) a higher probe density does not reflect a higher binding signal, probably because of a crowding effect.

Anti-Tumor Efficacy of an Adjuvant Built-In Nanovaccine Based on Ubiquitinated Proteins from Tumor Cells

Background and Aim

We have previously identified ubiquitinated proteins (UPs) from tumor cell lysates as a promising vaccine for cancer immunotherapy in different mouse tumor models. In this study, we aimed at developing a highly efficient therapeutic adjuvant built-in nanovaccine (α-Al₂O₃-UPs) by a simple method, in which UPs from tumor cells could be efficiently and conveniently enriched by α-Al₂O₃ nanoparticles covalently coupled with Vx3 proteins (α-Al₂O₃-CONH-Vx3).

Methods

The α-Al₂O₃ nanoparticles were modified with 4-hydroxybenzoic acid followed by coupling with ubiquitin-binding protein Vx3. It was then used to enrich UPs from 4T1 cell lysate. The stability and the efficiency for the UPs enrichment of α-Al₂O₃-CONH-Vx3 were examined. The ability of α-Al₂O₃-UPs to activate DCs was examined in vitro subsequently. The splenocytes from the vaccinated mice were re-stimulated with inactivated tumor cells, and the IFN-γ secretion was detected by ELISA and flow cytometry. Moreover, the therapeutic efficacy of α-Al₂O₃-UPs, alone and in combination with chemotherapy, was examined in 4T1 tumor-bearing mice.

Results

Our results showed that α-Al₂O₃-UPs were successfully synthesized and abundant UPs from tumor cell lysate were enriched by the new method. In vitro study showed that compared to the physical mixture of α-Al₂O₃ nanoparticles and UPs (α-Al₂O₃+UPs), α-Al₂O₃-UPs stimulation resulted in higher upregulations of CD80, CD86, MHC class I, and MHC class II on DCs, indicating the higher ability of DC activation. Moreover, α-Al₂O₃-UPs elicited a more effective immune response in mice, demonstrated by higher IFN-γ secretion than α-Al₂O₃+UPs. Furthermore, α-Al₂O₃-UPs also exhibited a more potent effect on tumor growth inhibition and survival prolongation in 4T1 tumor-bearing mice. Notably, when in combination with low dose chemotherapy, the anti-tumor effect was further enhanced, rather than using α-Al₂O₃-UPs alone.

Conclusion

This study presents an adjuvant built-in nanovaccine generated by a new simple method that can be potentially applied to cancer immunotherapy and lays the experimental foundation for future clinical application.

Preparation and characterization of DNA array slides via surface Michael addition

The reliability and stability of array slides are a big concern for array vendors and end users. Herein, we report on a new type of array slide with high reactivity toward DNA probes and low side reaction. A one-step surface reaction via the Michael addition involved in preparing array slides was developed and characterized by x-ray photoelectron spectroscopy, contact angle, and fluorescence labeling. The effects of array fabrication and storage conditions, i.e., spotting solution pH, high humidity, and long-term storage on the reactivity of the slides were examined. The fabricated DNA arrays could realize good hybridization efficiency (38.2% for slides with 0.88 pmol/cm²), low limit of detection (4 × 10^-14M), as well as high mismatch selectivity.

Methodologies for "Wiring" Redox Proteins/Enzymes to Electrode Surfaces

The immobilization of redox proteins or enzymes onto conductive surfaces has application in the analysis of biological processes, the fabrication of biosensors, and in the development of green technologies and biochemical synthetic approaches. This review evaluates the methods through which redox proteins can be attached to electrode surfaces in a "wired" configuration, that is, one that facilitates direct electron transfer. The feasibility of simple electroactive adsorption onto a range of electrode surfaces is illustrated, with a highlight on the recent advances that have been achieved in biotechnological device construction using carbon materials and metal oxides. The covalent crosslinking strategies commonly used for the modification and biofunctionalization of electrode surfaces are also evaluated. Recent innovations in harnessing chemical biology methods for electrically wiring redox biology to surfaces are emphasized.

Development of Escherichia coli Asparaginase II for Immunosensing: A Trade-Off between Receptor Density and Sensing Efficiency

The clinical success of Escherichia colil-asparaginase II (EcAII) as a front line chemotherapeutic agent for acute lymphoblastic leukemia (ALL) is often compromised because of its silent inactivation by neutralizing antibodies. Timely detection of silent immune response can rely on immobilizing EcAII, to capture and detect anti-EcAII antibodies. Having recently reported the use of a portable surface plasmon resonance (SPR) sensing device to detect anti-EcAII antibodies in undiluted serum from children undergoing therapy for ALL (Aubé et al., ACS Sensors2016, 1 (11), 1358-1365), here we investigate the impact of the quaternary structure and the mode of immobilization of EcAII onto low-fouling SPR sensor chips on the sensitivity and reproducibility of immunosensing. We show that the native tetrameric structure of EcAII, while being essential for activity, is not required for antibody recognition because monomeric EcAII is equally antigenic. By modulating the mode of immobilization, we observed that low-density surface coverage obtained upon covalent immobilization allowed each tetrameric EcAII to bind up to two antibody molecules, whereas high-density surface coverage arising from metal chelation by N- or C-terminal histidine-tag reduced the sensing efficiency to less than one antibody molecule per tetramer. Nonetheless, immobilization of EcAII by metal chelation procured up to 10-fold greater surface coverage, thus resulting in increased SPR sensitivity and allowing reliable detection of lower analyte concentrations. Importantly, only metal chelation achieved highly reproducible immobilization of EcAII, providing the sensing reproducibility that is required for plasmonic sensing in clinical samples. This report sheds light on the impact of multiple factors that need to be considered to optimize the practical applications of plasmonic sensors.

A strategy to minimize the sensing voltage drift error in a transistor biosensor with a nanoscale sensing gate

An ion-sensitive field-effect transistor (ISFET) biosensor is thought to be the center of the next era of health diagnosis. However, questions are raised about its functions and reliability in liquid samples. Consequently, real-life clinical applications are few in number. In this study, we report a strategy to minimize the sensing signal drift error during bioanalyte detection in an ISFET biosensor. A nanoscale SnO₂ thin film is used as a gate oxide layer (GOL), and the surface of the GOL is chemically modified for improving bioanalyte-specific binding and for reducing undesirable ion reactions in sample solutions. The ISFET biosensor with surface-modified GOL shows significantly reduced sensing signal error compared with an ISFET with bare GOL in both diluted and undiluted phosphate buffered saline solutions.

Surface Coating of Polytetrafluoroethylene with Extracellular Matrix and Anti-CD34 Antibodies Facilitates Endothelialization and Inhibits Platelet Adhesion Under Sheer Stress

Expanded polytetrafluoroethylene (ePTFE) polymers do not support endothelialization because of nonconductive characteristics towards cellular attachment. Inner surface modification of the grafts can improve endothelialization and increase the long-term patency rate of the ePTFE vascular grafts. Here we reported a method of inner-surface modification of ePTFE vascular graft with extracellular matrix (ECM) and CD34 monoclonal antibodies (CD34 mAb) to stimulate the adhesion and proliferation of circulating endothelial progenitor cells on ePTFE graft to enhance graft endothelialization. The inner surface of ECM-coated ePTFE grafts were linked with CD34 mAb in the presence of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide/N-hydroxysuccinimide (EDC/NHS) solution and the physicochemical properties, surface morphology, biocompatibility, and hemocompatibility of the grafts were studied. The hydrophilicity of CD34 mAb-coated graft inner surface was significantly improved. Fourier transform infrared spectroscopy analysis confirmed ECM and CD34 mAb cross-linking in the ePTFE vascular grafts with our method. Scanning electron microscopy analysis showed protein layer covering uniformly on the inner surface of the modified grafts. The cell-counting kit-8 (CCK-8) assay confirmed that the modified graft has no obvious cytotoxicity. The modified graft showed a low hemolytic rate (0.9%) in the direct contact hemolysis test, suggesting the modification improved hemocompatibility of biopolymers. The modification also decreased adhesion of platelets, while significantly increased the adhesion of endothelial cells on the grafts. We conclude that our method enables ePTFE polymers modification with ECM and CD34 mAb, facilitates endothelialization, and inhibits platelet adhesion on the grafts, thus may increase the long-term patency rate of the prosthetic bypass grafts.

Synthesis of Clickable Coating Polymers by Postpolymerization Modification: Applications in Microarray Technology

In this paper, we report on the postpolymerization modification (PPM) of a polymer to introduce new functionalities that enable click chemistry reactions for microarray applications. The parent polymer, named copoly(DMA-NAS-MAPS), is composed of N,N-dimethylacrylamide (DMA), a monomer that self-adsorbs onto different materials through weak interactions such as hydrogen bonding or van der Waals forces, 3-(trimethoxysilyl)propyl methacrylate (MAPS) that strengthens the stability of the coating through the formation of covalent bonds with siloxane groups on the surface to be coated, and N-acryloyloxysuccinimide (NAS), an active ester group, highly reactive toward nucleophiles, which enables bioprobe immobilization. This copolymer has been widely exploited to coat surfaces for microarray applications but exhibits some limitations because of the potential hydrolysis of the active ester (NHS ester). The degradation of the NHS ester hampers the use of this coating in some situations, for example, when probe immobilization cannot be accomplished through a microspotting situation, but in large volumes, for example, in microchannel derivatization or micro-/nanoparticle functionalization. To overcome the limitations of NHS esters, we have developed a family of polymers that originate from the common copolymer precursor, by reacting the active ester contained in the polymer chain with a bifunctional amine. In particular, the functional groups introduced in the polymer using PPM enable click chemistry reactions such as azide/alkyne or thiol/maleimide "click" reactions, with suitably modified biomolecules. The advantages of such reactions are quantitative yields, orthogonality of functional groups, and insensitivity of the reaction to pH. The new click functionalities, inserted with quantitative yields, improve the stability of the coating, enabling the attachment of biomolecules directly from a solution and avoiding the spotting of reduced volumes (pL) of probes. Finally, we have demonstrated the applicability of the click surfaces in a highly effective solid-phase PCR for the genotyping of the G12D KRAS mutation.

Single nanoparticle plasmonic sensors

The adoption of plasmonic nanomaterials in optical sensors, coupled with the advances in detection techniques, has opened the way for biosensing with single plasmonic particles. Single nanoparticle sensors offer the potential to analyse biochemical interactions at a single-molecule level, thereby allowing us to capture even more information than ensemble measurements. We introduce the concepts behind single nanoparticle sensing and how the localised surface plasmon resonances of these nanoparticles are dependent upon their materials, shape and size. Then we outline the different synthetic approaches, like citrate reduction, seed-mediated and seedless growth, that enable the synthesis of gold and silver nanospheres, nanorods, nanostars, nanoprisms and other nanostructures with tunable sizes. Further, we go into the aspects related to purification and functionalisation of nanoparticles, prior to the fabrication of sensing surfaces. Finally, the recent developments in single nanoparticle detection, spectroscopy and sensing applications are discussed.

Novel synthesizing method of pH-dependent doxorubicin-loaded anti-CD22-labelled drug delivery nanosystem

The objective of this study was to investigate the anticancer efficacy of dimercaptosuccinic acid-modified iron oxide magnetic nanoparticles coloaded with anti-CD22 antibodies and doxorubicin (anti-CD22-MNPs-DOX) on non-Hodgkin’s lymphoma cells. The physical properties of anti-CD22-MNPs-DOX were studied and its antitumor effect on Raji cells in vitro was evaluated using the Cell Counting Kit-8 assay. Furthermore, cell apoptosis and intracellular accumulation of doxorubicin were determined by flow cytometry. The results revealed that anti-CD22-MNPs-DOX inhibited the proliferation of Raji cells, significantly increased the uptake of doxorubicin, and induced apoptosis. Therefore, it was concluded that a coloaded antibody and chemotherapeutic drug with magnetic nanoparticles might be an efficient targeted treatment strategy for non-Hodgkin’s lymphoma.

Real-time selective monitoring of allergenic Aspergillus molds using pentameric antibody-immobilized single-walled carbon nanotube-field effect transistors

A SWNT-FET directly functionalized with immunoglobulin M shows a wide detection range from sub-picomolar to micromolar with an excellent sensitivity due to chemical gating in selective monitoring of fungal allergens.

A simple and sensitive label-free fluorescent approach for protein detection based on a Perylene probe and aptamer

Highly sensitive detection of proteins is of great importance for effective clinical diagnosis and biomedical research. However, so far most detection methods rely on antibody-based immunoassays and are usually laborious and time-consuming with poor sensitivity. Here, we developed a simple and ultra-sensitive method to detect a biomarker protein-thrombin by taking advantage of the fluorescent probe Perylene tetracarboxylic acid diimide (PTCDI) derivatives and thrombin aptamer. The water-soluble dye PTCDI shows strong fluorescence in buffer solution for the existence of free dye monomer, but becomes weak after aggregation through self-assembly on nucleic acid aptamer. In the presence of thrombin, it specifically binds to thrombin aptamer which causes the conformational transition between aptamer and PTCDI and results in a significant fluorescence recovery. The results showed that as low as 40 pM of thrombin could be detected by this method. The high sensitivity of the developed sensing system mainly attributes to the ultra-sensitivity of the fluorescence intensity changes of PTCDI. With the specificity of aptamer, the assay exhibited high selectivity for thrombin against three other proteins (bovine serum albumin, lysozyme, mouse IgG) and 1% diluted fetal bovine serum. The detection method might be extended to sensitive detection of a variety of proteins for its advantages of isothermal conditions required, simple and rapid without multiple separation and washing steps.