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The immunostimulating factor (ISTF) plays an important role in immunopathologic changes associated with Actinobacillus actinomycetemcomitans where it is located in the outer cell membrane. We describe a novel method by which ISTF can be monitored using a protein chip system based on surface plasmon resonance (SPR). The affinity of ISTF to its monoclonal antibodies and other proteins was compared. In fabrication of an ISTF immunosensor, a calix[4]crown ether monolayer was anchored onto a gold surface for use as an artificial protein linker system, and then characterized by Fourier Transform infrared reflection absorption spectroscopy, atomic force microscopy, and cyclic voltammetry. Anti-ISTF was immobilized onto the monolayer, and the interaction between ISTF and its antibodies was investigated by SPR. The calix[4]crown ether was found to assemble as a monolayer on the gold surface. Orientation and accessibility of anti-ISTF were assessed by the selective binding of ISTF. Modification of the SPR chip with the calix[4]crown monolayer provides a reliable and simple experimental platform for investigation of isolated proteins under experimental conditions resembling those of their native environment. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Fluorescent silica nanoparticles deposited with highly monodisperse gold nanoparticles (1–2 nm) were synthesized viathe W/O method and intensive ultrasound irradiation. A large surface area of gold-doped fluorescent silica nanoparticle serves as a platform to immobilize a specific binding protein for biomolecules interaction in bioimaging applications. [ABSTRACT FROM AUTHOR]

Abstract: Attachment of proteins to a solid support is fundamental to development of advanced biosensors, biochips, implantable electronic devices, and many diagnostic techniques. Profound knowledge of the orientation and specificity of an intricate protein in a particular antibody and adsorption to solid surfaces are of great importance in fabrication of nanoscale interface with maximized biological performance. Here we investigate antibody surface coverage and antibody layer thickness utilizing surface plasmon resonance (SPR) on the ProLinker™, a well-known protein artificial receptor molecule. The immunoactivity of immobilized antibodies was compared using two different methods. SPR revealed that antibodies were vertically immobilized in a dense monolayer when directly immobilized on the ProLinker™ SAM in an orientation comparable to that of protein G immediate antibody immobilization. Considering that surface coverage and native activity of the immobilized antibody are affected by antibody orientation, it is clear that the antibody is mainly adsorbed on the ProLinker™ SAM in an end-on orientation, which was verified by atomic force microscope (AFM). Aside from its original function, i.e., analyte monitoring, we used simple SPR spectroscopic analysis to monitor differences in orientation and concentration of immobilized bio-moieties at the molecular level. [Copyright &y& Elsevier]

Abstract A glassy carbon electrode (GCE) is modified with a nanotriplex [ i.e., three nanolayers consisting of graphene quantum dot (GQD)-coated Fe 3 O 4 @Ag core-shell nanostructure (Fe 3 O 4 @Ag/GQD)]. The nanotriplex is a sensitive electrochemical biosensor platform for detecting Mycobacterium tuberculosis antigen (culture filtrate protein; CFP-10). Gold nanoparticles (AuNPs) conjugated to an anti-CFP-10 antibody are used as a label for signal amplification. The nanotriplex-based sensing platform attains synergetic electrochemical performance by the three different roles of three nanomaterials: Fe 3 O 4 increases the surface to volume ratio; Ag enhances electrical conductivity; and GQD for loading more of the anti-CFP-10 antibody onto the electrode. The electron transfer kinetics at the surface of the electrode is simulated by means of the Butler–Volmer model. A sandwich-type immunoassay results by immobilizing the first antibody on the Fe 3 O 4 @Ag/GQD-modified GCE and by incubating this system with the antigen and then with AuNPs conjugated with the second anti-CFP-10 antibody (Ab 2 −AuNPs). The AuNPs are quantified by exposing the immunocomplex to a potential of 1.3 V for 40 s and scanning by differential pulse voltammetry. The immunosensor shows a wide linear range (0.005–500 μg/mL) with a limit of detection (signal/noise = 3) reaching 0.33 ng/mL. The results suggest that the reliable and robust performance with high selectivity and simple operation may be extended to detection of other biomarkers of pathogenic bacteria. Highlights • The nanotriplex particles (Fe 3 O 4 @Ag/GQD) were prepared with different reagents by stepwise functionalization. • An electrochemical biosensor was developed for detection of a Mtb antigen CFP-10 using a GCE modified with a nanotriplex. • The nanotriplex-based sensing platform showed synergetic electrochemical performance by means of three nanomaterials. • The immunosensor showed high selectivity and a wide linear range with a LOD (S/N = 3) reaching 0.33 ng/mL. [ABSTRACT FROM AUTHOR]

Since amine compounds have been widespread pollutants in nature and they are extensively used in pharmaceutical industeries and dye manufacturing, it is highly desirable to develop simple, effective and naked-eye available analytical methods for such aliphatic diamines determination. Calixarenes as macrocycles have drawn intensive interests for fields such as biomedicine, supramolecular chemistry and smart materials. Here, instead of the normal complicated modification strategy, a facile and efficient method for one-pot synthesis of calix[4]arene crown ether (CCE4) capped gold nanoparticles (AuNPs) is proposed. The as-prepared CCE4–AuNPs are not only high water dispersity and stability even after storage for 3 months, but also capable of host–guest recognition of diamines in aqueous systems. Size-selective encapsulation of amine group between CCE4 and diamines carry out the aggregation of CCE4–AuNPs. The determination of diamines such as hexamethylenediamine or spermine can be realized by the UV–vis absorbance change and visual color difference. [ABSTRACT FROM AUTHOR]

Abstract: An antigen (Ag), CFP-10, found in tissue fluids of tuberculosis (TB) patients may be an ultimate candidate for use as a sensitive TB marker with a sensing method for early simplified diagnosis of TB. In this study, chemical and optical optimizations were carried out using novel immuno-materials for establishment of a self-assembled surface plasmon resonance (SPR) optical immunosensor system for detection of CFP-10, which is valuable for pre-clinical work, prior to conduct of massive clinical observations. For creation of a simple sensing interface, a monoclonal antibody (anti-CFP-10) was immobilized directly on a gold surface, followed by blocking with cystamine. Orientation and accessibility of anti-CFP-10 were assessed by the selective binding of CFP-10. Recent results indicate that the reusability of the sensor chip adopting the cystamine method was found to be preferable to other immobilization methods. A linear relationship was well correlated between SPR angle shift and CFP concentrations in the range from 100ngmL−1 to 1μgmL−1. Modification of the SPR chip with antibody provides a simple experimental platform for investigation of isolated proteins under experimental conditions resembling those of their native environment. [Copyright &y& Elsevier]

• A new biosensor for detecting CTCs with outstanding selectivity, sensitivity, and stability is fabricated. • Dual selectivity and multi-signal amplifications are achieved by FA-AuNPs and M-AuNPs. • The biosensor has a low detection limit of 1 cell, which is in accordance with clinical detection standards. Circulating tumor cells (CTCs) are an important biomarker of cancer and are valuable in evaluating the risk of metastatic progression and in facilitating precise therapeutic treatments. In this paper, a dual-selective strategy was constructed to achieve the sensitive detection of CTCs. Cell membrane fragment-functionalized AuNPs (M-AuNPs) and folic acid-functionalized AuNPs (FA-AuNPs) were fabricated and characterized. CTCs membrane containing the specific junction plakoglobin (JUP) could be captured onto Anti-JUP-modified gold chip selectively. FA-AuNPs can bind with M-AuNPs through the overexpressed FA receptors in the CTCs membrane. These double selective recognitions through the specific interaction between JUP and Anti-JUP, FA and FA receptor can ensure the sensor's accuracy and specificity. The ultra-sensitive CTCs detection was achieved through multi-signal amplifications, including cell membrane fragments, M-AuNPs and FA-AuNPs. The biosensor constructed here has a low detection limit of 1 cell within the linear range of 101–105 cell mL−1. The low detection limit is in accordance with clinical detection standards. Owing to its outstanding selectivity, sensitivity, and stability, this new biosensor strategy for detecting CTCs offers new possibilities for clinical testing. [ABSTRACT FROM AUTHOR]